WO2025169707A1 - Protective sheet and production method for semiconductor device - Google Patents

Abstract

A protective sheet according to the present invention includes a base material and, in order on one principal surface of the base material, an intermediate layer and a photocurable adhesive layer. The intermediate layer is a thermoset product of a resin composition that contains: a (meth)acrylic resin (A1) that does not contain an ethylenically unsaturated group; and a crosslinking agent (B1). The photocurable adhesive layer is a thermoset product of an adhesive composition that contains: a (meth)acrylic resin (A2) that contains an ethylenically unsaturated group; a crosslinking agent (B2); and a photopolymerization initiator (C). The (meth)acrylic resin (A2) that contains an ethylenically unsaturated group is at least a product of adding an ethylenically unsaturated compound (a2-3) that contains an epoxy group to a (meth)acrylic resin (A2-0) for which an alkyl (meth)acrylate (a2-1) and an ethylenically unsaturated compound (a2-2) that contains a carboxyl group are used as starting material monomers. The photocurable adhesive layer contains 1000–100000 mass ppm of silicon atoms.

Description

PROTECTIVE SHEET AND METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE

The present disclosure relates to a method for manufacturing a protective sheet and a semiconductor device.

A variety of protective sheets are used in the manufacturing process of semiconductor devices. Specific examples include backgrinding tape and dicing tape. Backgrinding tape is a sheet used to protect semiconductor wafers during the backgrinding process, while dicing tape is a fixing sheet used in the dicing process, where the semiconductor wafer is cut into small element pieces. These protective sheets are removable, being affixed to the semiconductor wafer as an adherend and then peeled off from the adherend after the specified processing steps are completed.

In recent years, as electronic devices have become smaller and denser, flip-chip mounting has become the mainstream method for mounting semiconductor elements in the smallest possible space. In flip-chip mounting, semiconductor chips with solder-tipped bump electrodes (e.g., Through Silicon Via (TSV) chips) are used to bond chips together. These bumped semiconductor chips are electrically bonded to other semiconductor chips or substrates through a reflow process, in which the chip is heated to a temperature above the solder's melting point, typically 200°C or higher, for mounting. However, when semiconductor chips are mounted in electronic devices for communications, electromagnetic waves generated inside the chip can sometimes cause communication problems. To prevent this, a sputtering process is sometimes performed, in which a metal film is vapor-deposited around the periphery of the semiconductor chip as an electromagnetic wave shield. The sputtering process is typically performed at 150°C or higher. A removable protective sheet is used to protect the bump surface during the reflow and sputtering processes.

For example, Patent Document 1 describes a method for manufacturing an electronic device using an electronic component having a circuit-forming surface and an adhesive laminate film having, in that order, a base layer, an irregularity-absorbing resin layer, and an adhesive resin layer.

Japanese Patent Application Laid-Open No. 2021-163785

Semiconductor devices such as bumped semiconductor chips and bumped printed wiring boards (PCBs) have large irregularities on their surfaces. Therefore, while fulfilling their surface protection function during processing, etc., protective sheets must accurately conform to these irregularities and adhere tightly. In addition, protective sheets must have high heat resistance. If heat resistance is insufficient, problems such as outgassing from the protective sheet during high-temperature treatments such as reflow and sputtering, causing the sheet to lift from the substrate, or leaving adhesive residue on the substrate when peeled off, can occur. The sputtering process coats the periphery of semiconductor devices with a metal film. As a result, gaps exist between the semiconductor devices, and the metal film is also deposited on the protective sheet during sputtering. From the perspective of preventing contamination in the semiconductor manufacturing process, it is desirable for the metal film attached to the protective sheet to remain on the protective sheet even after the semiconductor device is peeled off from the protective sheet.

However, conventional protective sheets did not satisfy all of the above requirements. For example, in Patent Document 1, due to insufficient heat resistance, adhesive residue could remain on the semiconductor device when the protective sheet was peeled off. Furthermore, when the semiconductor device was picked up and peeled off from the protective sheet after the sputtering process was completed, the adhesion between the protective sheet and the metal film was insufficient, causing the metal film to detach from the protective sheet, contaminating the semiconductor device or becoming a source of contamination in the semiconductor manufacturing process.

The present disclosure provides a protective sheet that, through various processing steps, accurately conforms to the unevenness of the surface of semiconductor devices with uneven surfaces, such as semiconductor chips with bumps and PCBs with bumps, and adheres tightly to the surfaces. It can be peeled off from the semiconductor devices after UV irradiation without leaving any adhesive residue, while maintaining excellent adhesion to coated metal films even after UV irradiation. In particular, the disclosure provides a protective sheet that accurately conforms to the unevenness of the surface and adheres tightly to the surfaces, even when the unevenness of the adherend surface is large, or even after undergoing a high-temperature treatment process at 200°C or higher. It can be peeled off from the semiconductor devices after UV irradiation without leaving any adhesive residue, while maintaining excellent adhesion to coated metal films even after UV irradiation. Furthermore, a method for manufacturing semiconductor devices using the protective sheet is provided.

The present disclosure includes the following aspects.
[1]
A protective sheet having a substrate, and an intermediate layer and a photocurable pressure-sensitive adhesive layer in this order on one main surface of the substrate,
the intermediate layer is a thermosetting product of a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1), the ethylenically unsaturated group-free (meth)acrylic resin (A1) having a plurality of functional groups reactive with functional groups possessed by the crosslinking agent (B1);
the photocurable pressure-sensitive adhesive layer is a thermosetting product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C);
the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a plurality of functional groups reactive with functional groups contained in the crosslinking agent (B2),
the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) having, as raw material monomers, at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2);
The photocurable pressure-sensitive adhesive layer contains 1,000 to 100,000 ppm by mass of silicon atoms.
[2]
The protective sheet according to [1], wherein a silicon-containing ethylenically unsaturated compound (a2-4) is further used as a raw material monomer for the (meth)acrylic resin (A2-0).
[3]
The protective sheet according to [1] or [2], wherein the pressure-sensitive adhesive composition further contains a silicon-containing photocurable compound (D).
[4]
The protective sheet according to any one of [1] to [3], wherein the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a glass transition temperature (Tg) of −80 to 0° C.
[5]
the ethylenically unsaturated group-free (meth)acrylic resin (A1) is a copolymer containing, as raw material monomers, at least an alkyl (meth)acrylate (a1-1) and a hydroxy group-containing (meth)acrylate (a1-2);
The protective sheet according to any one of [1] to [4], wherein the crosslinking agent (B1) is an isocyanate crosslinking agent.
[6]
The protective sheet according to [5], wherein a carboxyl group-containing ethylenically unsaturated compound (a1-3) is further used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1).
[7]
The protective sheet according to [5] or [6], wherein a (meth)acrylamide compound (a1-4) is further used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1).
[8]
The protective sheet according to any one of [1] to [7], wherein the acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is 1 to 100 mgKOH/g.
[9]
The protective sheet according to any one of [1] to [8], wherein the ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is 500 to 5000 g/mol.
[10]
The protective sheet according to any one of [1] to [9], wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a glass transition temperature (Tg) of −80 to 0° C.
[11]
The protective sheet according to any one of [1] to [10], wherein the crosslinking agent (B2) is at least one selected from the group consisting of epoxy crosslinking agents and aziridine crosslinking agents.
[12]
The protective sheet according to any one of [1] to [11], wherein the substrate is a resin sheet, and the raw material resin of the resin sheet is at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), polyamide (PA), and polyimide (PI).
[13]
The protective sheet according to any one of [1] to [12], wherein the thickness of the substrate is 5 μm to 300 μm.
[14]
The thickness of the intermediate layer is 30 to 600 μm,
The photocurable pressure-sensitive adhesive layer has a thickness of 1 to 100 μm,
The protective sheet according to any one of [1] to [13], wherein the thickness ratio of the intermediate layer to the photocurable pressure-sensitive adhesive layer (intermediate layer/photocurable pressure-sensitive adhesive layer) is 1 to 50.
[15]
a protection step of attaching the photocurable adhesive layer surface of the protective sheet according to any one of [1] to [14] to a bump electrode-bearing surface of an unprocessed semiconductor device;
an active energy ray irradiation step of irradiating the protective sheet with active energy rays to photocure the photocurable pressure-sensitive adhesive layer;
A method for manufacturing a semiconductor device having bump electrodes, comprising: a heating step of the unprocessed semiconductor device to which the protective sheet is attached; and a peeling step of peeling the protective sheet from the surface with the bump electrodes.
[16]
[16] The method for manufacturing a semiconductor device according to [15], wherein d/H is 1.00 to 100, where H [μm] is the height of the bump electrode and d [μm] is the total thickness of the intermediate layer and the photocurable adhesive layer.
[17]
The method for manufacturing a semiconductor device according to [15] or [16], wherein the maximum temperature reached in the heating step is 80 to 300°C.

According to the present disclosure, a protective sheet can be provided that, through various processing steps, accurately conforms to the unevenness of the surface of semiconductor devices with uneven surfaces, such as semiconductor chips with bumps and PCBs with bumps, and adheres tightly to the semiconductor devices after UV irradiation without leaving any adhesive residue. It also has excellent adhesion to coated metal films, even after UV irradiation. In particular, even when the unevenness of the adherend surface is large, or even after undergoing a high-temperature treatment process at 200°C or higher, a protective sheet can be provided that accurately conforms to the unevenness of the surface and adheres tightly to the semiconductor devices after UV irradiation without leaving any adhesive residue. It also has excellent adhesion to coated metal films, even after UV irradiation. Furthermore, a method for manufacturing semiconductor devices using the protective sheet can be provided.

The adhesive strength of the photocurable adhesive layer of the protective sheet is reduced by irradiation with active energy rays. Specifically, the photocurable adhesive layer exhibits sufficient adhesive strength to the adherend before irradiation with active energy rays, but after irradiation with active energy rays, the unsaturated bonds in the resin form a three-dimensional crosslinked structure and harden, reducing the adhesive strength and exhibiting excellent removability while also fully preventing adhesive residue on the adherend after peeling. Meanwhile, even when the adhesive strength of the photocurable adhesive layer of the protective sheet is reduced by irradiation with active energy rays, the adhesive layer still maintains a certain degree of adhesion to the metal film. Therefore, the amount of metal film coated on the photocurable adhesive layer that detaches after irradiation with active energy rays can be reduced, thereby reducing metal contamination in the semiconductor manufacturing process.

FIG. 1 is a schematic cross-sectional view of a protective sheet in one embodiment.

The following describes in detail an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

In this specification, when "~" is used to describe a numerical range, the numerical values at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created using all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

In this disclosure, (meth)acrylic means "acrylic" or "methacrylic". (meth)acrylate means "acrylate" or "methacrylate", and (meth)acryloyloxy means "acryloyloxy" or "methacryloyloxy".

In this disclosure, "ethylenically unsaturated bond" means a double bond formed between carbon atoms excluding carbon atoms forming an aromatic ring, "ethylenically unsaturated group" means a group having an ethylenically unsaturated bond, and "ethylenically unsaturated compound" means a compound having an ethylenically unsaturated bond.

In the present disclosure, the "weight average molecular weight (Mw)" and the "number average molecular weight (Mn)" are values measured at room temperature (23°C) using gel permeation chromatography (GPC) under the following conditions and calculated using a standard polystyrene calibration curve.
Apparatus: Shodex (trademark) GPC-101 (Resonac Co., Ltd.)
Column: Shodex (trademark) LF-804 (Resonac Inc.)
Column temperature: 40°C
Sample: 0.2% by mass solution of sample in tetrahydrofuran Flow rate: 1 mL/min Eluent: tetrahydrofuran Detector: RI detector

In the present disclosure, the glass transition temperature (Tg) of a (meth)acrylic resin means a value obtained by converting the glass transition temperature Tga in absolute temperature, which is obtained using the FOX equation (Fox, T. G., Bull. Am. Phys. Soc., 1 (1956), p. 123) of the following formula (1), into Celsius temperature:
1/Tga=Σi(Wi/Tgi)...(1)
(In formula (1), Tga is the glass transition temperature (unit: absolute temperature) of the (meth)acrylic resin. Wi is the mass proportion of each monomer i in the (meth)acrylic resin. Tgi is the glass transition temperature (unit: absolute temperature) of a homopolymer formed only from each monomer i.)

In this disclosure, "acid value (mgKOH/g)" refers to the value measured in accordance with JIS K 0070:1992.

In this disclosure, "hydroxyl value (mgKOH/g)" refers to the value measured in accordance with JIS K 0070:1992.

In this disclosure, "ethylenically unsaturated group equivalent (g/mol)" refers to a value calculated from the iodine value measured in accordance with JIS K 0070:1992.

<Protective sheet>
A protective sheet according to one embodiment comprises a substrate, an intermediate layer, and a photocurable adhesive layer, in that order, on one main surface of the substrate. Because the protective sheet comprises the intermediate layer and the photocurable adhesive layer, it adheres accurately to the irregularities on the adherend even after high-temperature treatment, such as at 200°C, and can be peeled off without leaving any adhesive residue after irradiation with active energy rays. Furthermore, by incorporating silicon into the adhesive layer, the adhesion between the adhesive layer and metal can be improved. As a result, even after forming a metal film by a coating process such as sputtering and then irradiating it with active energy rays, the coated metal film is prevented from detaching from the protective sheet and contaminating the adherend or becoming a source of contamination in the semiconductor manufacturing process. Figure 1 is a schematic cross-sectional view of a protective sheet according to one embodiment. The protective sheet 10 comprises a substrate 12, an intermediate layer 14 disposed on one main surface of the substrate 12, and a photocurable adhesive layer 16 disposed on the intermediate layer 14. In Figure 1, the intermediate layer 14 is disposed on the upper main surface of the substrate 12. The protective sheet 10 may further include a release sheet 18 disposed on the photocurable pressure-sensitive adhesive layer 16, as needed. The release sheet 18 is attached to the outside of the photocurable pressure-sensitive adhesive layer for the purpose of protecting the surface of the photocurable pressure-sensitive adhesive layer, i.e., the surface to be attached to an adherend, until the protective sheet is put into use. The protective sheet can be suitably used, for example, as a backgrinding tape or a dicing tape.

The protective sheet may be cut into a shape that matches the shape of the adherend by a punching method or the like. The protective sheet may also be wound up and cut into a roll for use.

The thickness of the protective sheet depends on the unevenness of the adherend surface, such as the bump height, but is preferably 36 μm to 1000 μm, more preferably 50 μm to 800 μm, and even more preferably 75 μm to 600 μm. From the perspective of more reliably following the unevenness of the adherend surface and ensuring the processing accuracy of the adherend during the processing step, it is preferable for the protective sheet thickness to be approximately 1.00 to 100 times the unevenness of the adherend surface.

The peel strength of the protective sheet will vary depending on the thickness of the protective sheet, the type of adherend, and the type and order of processing steps, but for example, the peel strength before active energy ray irradiation is preferably 2.0 to 25 N/25 mm, more preferably 3.0 to 20 N/25 mm, and even more preferably 5.0 to 15 N/25 mm. If the peel strength before active energy ray irradiation is 2.0 N/25 mm or higher, the adhesive strength to the adherend before active energy ray irradiation is good. If the peel strength before active energy ray irradiation is 25 N/25 mm or less, it is possible to sufficiently reduce the peel strength during peeling, thereby reducing adhesive residue on the adherend.

The peel strength of the protective sheet decreases when irradiated with active energy rays, allowing it to be easily peeled from the adherend without leaving any adhesive residue during the peeling process. The peel strength of the protective sheet after irradiating with active energy rays varies depending on the thickness of the protective sheet, the type of adherend, and the type and order of processing steps, but is preferably 0.001 to 1.0 N/25 mm, more preferably 0.005 to 0.75 N/25 mm, and even more preferably 0.01 to 0.5 N/25 mm.

In this disclosure, peel strength refers to the peel strength (N/25 mm) of the protective sheet against the substrate measured in a 180° tensile test conducted in accordance with JIS Z 0237:2009 at a temperature of 23°C and humidity of 50% at a peel rate of 300 mm/min.

[Base material]
The substrate can be appropriately selected from known sheet-shaped materials, and is preferably a resin sheet made of a transparent resin material.

The raw resins for the resin sheet include, for example, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyether ether ketone (PEEK); polyamide (PA); polyimide (PI); polyphenylene sulfide (PPS); and polytetrafluoroethylene (PTFE). Among these raw resins, it is preferable to use at least one selected from the group consisting of PET, PEN, PEEK, PA, and PI as the raw resin, as this will result in a sheet with appropriate flexibility and heat resistance. The raw resins may be used alone or in a mixture of two or more.

When a resin sheet is used as the substrate, the resin sheet may be a single layer, or may have a multi-layer structure of two or more layers, for example a three-layer structure. In a resin sheet with a multi-layer structure, the resin material constituting each layer may be one type, or two or more types.

The thickness of the substrate can be selected appropriately depending on the type of semiconductor processing, the substrate material, etc., but may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more, and 300 μm or less, 100 μm or less, or 60 μm or less. When the protective sheet protects a bumped semiconductor chip or bumped flexible printed circuit board (FPC) during a reflow process or sputtering process and the substrate is a resin sheet, the thickness of the substrate is preferably 5 to 300 μm, more preferably 10 to 300 μm. A substrate thickness of 5 μm or more provides high rigidity for the protective sheet. Therefore, the protective sheet tends to be less likely to wrinkle or lift when attached to an adherend such as a semiconductor chip or peeled from the adherend. In addition, the protective sheet is easy to peel from the adherend, providing good workability. A substrate thickness of 5 μm or more reduces wrinkles in the protective sheet, thereby reducing the detachment of the coated metal film during a sputtering process or other process. When the thickness of the substrate is 300 μm or less, the rigidity of the protective sheet is appropriate and workability is good.

When a resin sheet is used as the substrate, the substrate can be manufactured using the above-mentioned raw resin material and a conventional, well-known sheet molding method. Examples of sheet molding methods include extrusion molding, T-die molding, inflation molding, and uniaxial or biaxial stretching molding.

The surface of the substrate that comes into contact with the intermediate layer may be subjected to a surface treatment to improve adhesion between the substrate and the intermediate layer. Examples of surface treatments include corona discharge treatment, acid treatment, ultraviolet irradiation treatment, plasma treatment, and primer coating.

[Middle class]
The intermediate layer is a thermoset product of a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1). The thermoset product is a reaction product, i.e., a crosslinked product, between a functional group possessed by the ethylenically unsaturated group-free (meth)acrylic resin (A1) that is reactive with a functional group possessed by the crosslinking agent (B1) and a functional group possessed by the crosslinking agent (B1). By including the intermediate layer, the protective sheet has good step-conforming properties even when steps on the surface of an adherend, such as large bump heights, are present.

The thickness of the intermediate layer is preferably 30 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more. The thickness of the intermediate layer is preferably 600 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. When the thickness of the intermediate layer is 30 μm or more, the protective sheet can conform well to unevenness on the surface of the adherend. When the thickness of the intermediate layer is 600 μm or less, the processing precision of the adherend during the processing step is good.

(Ethylenically Unsaturated Group-Free (Meth)acrylic Resin (A1))
The ethylenically unsaturated group-free (meth)acrylic resin (A1) is not particularly limited as long as it contains a (meth)acrylic acid ester as an essential raw material monomer, has an ethylenically unsaturated group equivalent of more than 5000 g/mol, does not contain an ethylenically unsaturated group, and has multiple functional groups reactive with the functional groups contained in the crosslinking agent (B1). In one embodiment, the ethylenically unsaturated group-free (meth)acrylic resin (A1) does not contain an ethylenically unsaturated group. Examples of functional groups reactive with the functional groups contained in the crosslinking agent (B1) include a hydroxy group, a carboxy group, an isocyanato group, a glycidyl group, an amino group, and an amide group. The ethylenically unsaturated group-free (meth)acrylic resin (A1) may be used alone or in combination of two or more. By forming the intermediate layer using the (meth)acrylic resin (A1) that does not contain an ethylenically unsaturated group, the protective sheet has high heat resistance and exhibits high conformability to the irregularities of the adherend even when exposed to high temperature conditions from the step of attaching the sheet to the adherend to the processing step and the peeling step. In addition, it exhibits good conformability to the irregularities even when the irregularities on the adherend surface become large.

Specific examples of raw material monomers for the ethylenically unsaturated group-free (meth)acrylic resin (A1) include the alkyl (meth)acrylate (a1-1), hydroxy group-containing (meth)acrylate (a1-2), carboxy group-containing ethylenically unsaturated compound (a1-3), (meth)acrylamide compound (a1-4), and other monomers (a1-5) described below. The ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably a copolymer having alkyl (meth)acrylate (a1-1) and hydroxy group-containing (meth)acrylate (a1-2) as essential raw material monomers, and more preferably a copolymer having alkyl (meth)acrylate (a1-1), hydroxy group-containing (meth)acrylate (a1-2), and carboxy group-containing ethylenically unsaturated compound (a1-3) as essential raw material monomers. As the alkyl (meth)acrylate (a1-1), which is a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), it is preferable to use at least one selected from 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate. The total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers for the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 50 mol% or more, more preferably 60 mol% or more. The upper limit of the total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers for the ethylenically unsaturated group-free (meth)acrylic resin (A1) is not particularly limited, but may be, for example, 99 mol%, 95 mol%, or 80 mol%.

The glass transition temperature (Tg) of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -60°C or higher. The glass transition temperature (Tg) of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. When the glass transition temperature is -80°C or higher, an intermediate layer with high cohesive strength is obtained, thereby preventing resin elution during sheet molding. When the glass transition temperature is 0°C or lower, the adhesion between the intermediate layer and the photocurable pressure-sensitive adhesive layer is even better.

The weight-average molecular weight of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 100,000 to 2,000,000, more preferably 150,000 to 1,500,000, and even more preferably 200,000 to 1,000,000. A weight-average molecular weight of 100,000 or more results in an intermediate layer with high cohesive strength, preventing resin elution during sheet formation. A weight-average molecular weight of 2,000,000 or less facilitates molding and processing.

As described below, examples of crosslinking agents that can be used as the crosslinking agent (B1) include isocyanate crosslinking agents and epoxy crosslinking agents. Isocyanate crosslinking agents are compounds that have multiple isocyanato groups, and epoxy crosslinking agents are compounds that have multiple epoxy groups.

In an embodiment in which the crosslinking agent (B1) is an isocyanate crosslinking agent, the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably a copolymer whose raw material monomers are at least an alkyl (meth)acrylate (a1-1) and a hydroxy group-containing (meth)acrylate (a1-2). If necessary, at least one selected from the group consisting of a carboxy group-containing ethylenically unsaturated compound (a1-3), a (meth)acrylamide compound (a1-4), and other monomers (a1-5) may also be used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1). As raw material monomers for the ethylenically unsaturated group-free (meth)acrylic resin (A1), preferably, at least one selected from the group consisting of an alkyl (meth)acrylate (a1-1), a hydroxy group-containing (meth)acrylate (a1-2), a carboxy group-containing ethylenically unsaturated compound (a1-3), and a (meth)acrylamide compound (a1-4) is used, and more preferably, an alkyl (meth)acrylate (a1-1), a hydroxy group-containing (meth)acrylate (a1-2), a carboxy group-containing ethylenically unsaturated compound (a1-3), and a (meth)acrylamide compound (a1-4) is used.

In this embodiment, the hydroxyl value of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0.5 to 100 mgKOH/g, more preferably 1 to 50 mgKOH/g, and even more preferably 5 to 30 mgKOH/g. A hydroxyl value of 0.5 mgKOH/g or higher allows for sufficient reaction with the isocyanate crosslinking agent, resulting in an intermediate layer with high cohesive strength. A hydroxyl value of 100 mgKOH/g or lower results in the resulting resin being soluble in commonly used organic solvents such as ethyl acetate and toluene, providing excellent handleability.

In this embodiment, the content of alkyl (meth)acrylate (a1-1) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 50 to 99.5 mol%, more preferably 60 to 95 mol%, and even more preferably 70 to 90 mol%. When the content of alkyl (meth)acrylate (a1-1) is 50 mol% or more, the intermediate layer has good adhesion to the substrate and the photocurable pressure-sensitive adhesive layer. When the content of alkyl (meth)acrylate (a1-1) is 99.5 mol% or less, a sufficient content of hydroxy group-containing (meth)acrylate (a1-2) can be ensured, thereby ensuring a sufficient amount of crosslinking with the crosslinking agent (B1) and improving the cohesive strength of the intermediate layer.

In this embodiment, the content of the hydroxy group-containing (meth)acrylate (a1-2) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0.5 to 30 mol %, more preferably 1 to 20 mol %, and even more preferably 1.5 to 10 mol %. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 0.5 mol % or more, a sufficient amount of crosslinking with the crosslinking agent (B1) is ensured, improving the cohesive strength of the intermediate layer. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 30 mol % or less, the resulting resin is soluble in commonly used organic solvents such as ethyl acetate and toluene, resulting in excellent handleability.

In this embodiment, when a carboxy group-containing ethylenically unsaturated compound (a1-3) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), its content is preferably 0.01 to 10 mol %, more preferably 0.05 to 5 mol %, and even more preferably 0.1 to 3 mol %, based on the total amount of raw material monomers. When the content of the carboxy group-containing ethylenically unsaturated compound (a1-3) is 0.01 mol % or more, the cohesive strength of the intermediate layer is good. When the content of the carboxy group-containing ethylenically unsaturated compound (a1-3) is 10 mol % or less, the cohesive strength of the resulting resin is not too high, resulting in excellent handleability.

In this embodiment, when the (meth)acrylamide compound (a1-4) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), its content is preferably 0.5 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount of raw material monomers.

In this embodiment, when the other monomer (a1-5) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.5 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount of the raw material monomers.

The alkyl (meth)acrylate (a1-1) is not particularly limited as long as it is a compound that does not have a functional group such as a hydroxy group or a carboxy group, and has an alkyl group and a (meth)acryloyloxy group. Specific examples include linear or branched alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, n-hexyl (meth)acrylate, isooctyl (meth)acrylate, and lauryl (meth)acrylate; and cyclic alkyl group-containing (meth)acrylates such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and dicyclopentanyloxyethyl (meth)acrylate. Among these, at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate is preferred, and at least one selected from n-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is more preferred. From the viewpoint of step-conforming ability, it is preferred to use a linear or branched alkyl (meth)acrylate in which the alkyl group has 4 to 20 carbon atoms, more preferred to use a linear or branched alkyl (meth)acrylate in which the alkyl group has 4 to 12 carbon atoms, and even more preferred to use at least one selected from n-butyl (meth)acrylate, tert-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate. The alkyl (meth)acrylate (a1-1) may be used alone or in combination of two or more types.

The hydroxy group-containing (meth)acrylate (a1-2) is not particularly limited as long as it is a compound having a hydroxy group and a (meth)acryloyloxy group. Specific examples include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 1,3-butanediol (meth)acrylate, 1,4-butanediol (meth)acrylate, 1,6-hexanediol (meth)acrylate, and 3-methylpentanediol (meth)acrylate. From the standpoint of conformability to uneven surfaces, hydroxyalkyl (meth)acrylates having a hydroxy group at the end of a linear alkyl group are preferred, and at least one selected from 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are more preferred. The hydroxy group-containing (meth)acrylate (a1-2) may be used alone or in combination of two or more types.

The carboxy group-containing ethylenically unsaturated compound (a1-3) is not particularly limited, as long as it does not contain a hydroxy group and contains a carboxy group and an ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. By using the carboxy group-containing ethylenically unsaturated compound (a1-3) as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the carboxy group derived from the carboxy group-containing ethylenically unsaturated compound (a1-3) crosslinks with the hydroxy group derived from the hydroxy group-containing (meth)acrylate (a1-2) during the formation of the intermediate layer, thereby improving cohesive strength. When the photocurable pressure-sensitive adhesive layer contains a carboxy group, the interlayer adhesion between the photocurable pressure-sensitive adhesive layer and the intermediate layer is improved. Furthermore, if the crosslinking agent (B2) in the photocurable pressure-sensitive adhesive layer is an epoxy crosslinking agent, crosslinking of the carboxy groups derived from the carboxy group-containing ethylenically unsaturated compound (a1-3) by the epoxy crosslinking agent in the photocurable pressure-sensitive adhesive layer proceeds at the interface between the photocurable pressure-sensitive adhesive layer and the intermediate layer, resulting in stronger interlayer adhesion, which is preferable.

Specific examples of the carboxyl group-containing ethylenically unsaturated compound (a1-3) include (meth)acrylic acid, carboxymethyl (meth)acrylate, and β-carboxyethyl (meth)acrylate. From the viewpoint of ease of polymerization, (meth)acrylic acid is preferred. The carboxyl group-containing ethylenically unsaturated compound (a1-3) may be used alone or in combination of two or more types.

Examples of the (meth)acrylamide compound (a1-4) include (meth)acrylamide; N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropylacrylamide, and N-hexyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; (meth)acryloylmorpholine; and diacetone acrylamide.

Among these, N,N-dialkyl(meth)acrylamides are more preferred, and N,N-dimethyl(meth)acrylamide is even more preferred, from the viewpoint of improving adhesion to the adherend.

The other monomer (a1-5) is not particularly limited, as long as it is a compound other than (a1-1) to (a1-4) and has an ethylenically unsaturated group copolymerizable therewith. Examples include alkoxyalkyl (meth)acrylate, alkoxy(poly)alkylene glycol (meth)acrylate, aromatic group-containing (meth)acrylate, fluorinated alkyl (meth)acrylate, and dialkylaminoalkyl (meth)acrylate. The other monomer (a1-5) may be used alone or in combination of two or more.

Examples of alkoxyalkyl (meth)acrylates include ethoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, and butoxyethyl (meth)acrylate.

Examples of alkoxy(poly)alkylene glycol (meth)acrylates include methoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, and methoxydipropylene glycol (meth)acrylate. (Poly)alkylene means "alkylene" or "polyalkylene."

Examples of aromatic group-containing (meth)acrylates include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, 3-phenoxyphenyl acrylate, 4-phenoxyphenyl acrylate, 2-biphenyl acrylate, 4-biphenyl acrylate, phenoxypolyethylene glycol (meth)acrylate, phenoxypropyl (meth)acrylate, and phenoxypolypropylene glycol (meth)acrylate.

An example of a fluorinated alkyl (meth)acrylate is octafluoropentyl (meth)acrylate.

Examples of dialkylaminoalkyl (meth)acrylates include N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate.

Other specific examples of the other monomer (a1-5) include acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl stearate, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyl toluene, N-vinylpyridine, N-vinylpyrrolidone, itaconic acid dialkyl esters, fumaric acid dialkyl esters, allyl alcohol, hydroxybutyl vinyl ether, hydroxyethyl vinyl ether, 4-hydroxymethylcyclohexylmethyl vinyl ether, triethylene glycol monovinyl ether, diethylene glycol monovinyl ether, methyl vinyl ketone, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone.

In an embodiment in which the crosslinking agent (B1) is an epoxy crosslinking agent, the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably a copolymer whose raw material monomers are at least an alkyl (meth)acrylate (a1-1) and a carboxy group-containing ethylenically unsaturated compound (a1-3). If necessary, at least one raw material monomer selected from the group consisting of a hydroxy group-containing (meth)acrylate (a1-2), a (meth)acrylamide compound (a1-4), and other monomers (a1-5) may also be used for the ethylenically unsaturated group-free (meth)acrylic resin (A1).

In this embodiment, (a1-1) to (a1-5) can be the same as those described above.

In this embodiment, the content of alkyl (meth)acrylate (a1-1) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 50 to 99.5 mol%, more preferably 60 to 99 mol%, and even more preferably 70 to 98 mol%. When the content of alkyl (meth)acrylate (a1-1) is 50 mol% or more, the intermediate layer has good adhesion to the substrate and the photocurable pressure-sensitive adhesive layer. When the content of alkyl (meth)acrylate (a1-1) is 99.5 mol% or less, a sufficient content of carboxyl group-containing ethylenically unsaturated compound (a1-3) can be ensured, thereby ensuring a sufficient amount of crosslinking with the crosslinking agent (B1) and improving the cohesive strength of the intermediate layer.

In this embodiment, the content of the carboxy group-containing ethylenically unsaturated compound (a1-3) relative to the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is preferably 0.01 to 30 mol %, more preferably 0.1 to 20 mol %, and even more preferably 1 to 10 mol %. When the content of the carboxy group-containing ethylenically unsaturated compound (a1-3) is 0.01 mol % or more, an intermediate layer with high cohesion strength is obtained. When the content of the carboxy group-containing ethylenically unsaturated compound (a1-3) is 30 mol % or less, the cohesion strength of the obtained intermediate layer is not too high, and handleability is good.

In this embodiment, the acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A1) is preferably 1 mgKOH/g or more, more preferably 3 mgKOH/g or more, and even more preferably 5 mgKOH/g or more. The acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A1) is preferably 30 mgKOH/g or less, more preferably 20 mgKOH/g or less, and even more preferably 10 mgKOH/g or less. When the acid value is 1 mgKOH/g or more, sufficient reaction with the crosslinking agent (B1) can be achieved, resulting in an intermediate layer with high cohesive strength. When the acid value is 30 mgKOH/g or less, the cohesive strength of the resulting intermediate layer is not too high, and handling is favorable.

In this embodiment, when a hydroxy group-containing (meth)acrylate (a1-2) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), its content is preferably 0.01 to 30 mol %, more preferably 0.1 to 20 mol %, and even more preferably 0.1 to 10 mol %, based on the total amount of raw material monomers. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 0.01 mol % or more, a sufficient amount of crosslinking with the crosslinking agent (B1) can be ensured. When the content of the hydroxy group-containing (meth)acrylate (a1-2) is 30 mol % or less, the resulting resin is soluble in commonly used organic solvents such as ethyl acetate and toluene, resulting in excellent handleability.

In this embodiment, when the (meth)acrylamide compound (a1-4) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), its content is preferably 0.5 to 30 mol %, more preferably 1 to 25 mol %, and even more preferably 5 to 20 mol %, based on the total amount of raw material monomers.

In this embodiment, when the other monomer (a1-5) is used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1), the content thereof is preferably 0.1 to 45 mol%, more preferably 0.1 to 35 mol%, and even more preferably 0.1 to 25 mol%, based on the total amount of the raw material monomers.

(Crosslinking agent (B1))
The crosslinking agent (B1) is not particularly limited as long as it is a compound having multiple functional groups capable of reacting with any of the multiple functional groups possessed by the ethylenically unsaturated group-free (meth)acrylic resin (A1), and can be selected according to the functional groups possessed by the ethylenically unsaturated group-free (meth)acrylic resin (A1). For example, when the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a hydroxy group, it is preferable to use at least one selected from the group consisting of an isocyanate crosslinking agent and an epoxy crosslinking agent as the crosslinking agent (B1), and it is more preferable to use an isocyanate crosslinking agent. When the ethylenically unsaturated group-free (meth)acrylic resin (A1) has a carboxy group, it is preferable to use at least one selected from the group consisting of an isocyanate crosslinking agent, an epoxy crosslinking agent, and an aziridine crosslinking agent as the crosslinking agent (B1), and it is more preferable to use an epoxy crosslinking agent. When the intermediate layer contains the crosslinking agent (B1), the cohesive strength of the intermediate layer is improved, thereby preventing cohesive failure of the intermediate layer when the protective sheet is peeled from the adherend. The crosslinking agent (B1) may be used alone or in combination of two or more kinds.

Preferred combinations of the ethylenically unsaturated group-free (meth)acrylic resin (A1) and the crosslinking agent (B1) include a combination of a hydroxyl group-containing ethylenically unsaturated group-free (meth)acrylic resin (A1) and an isocyanate crosslinking agent, a combination of a carboxyl group-containing ethylenically unsaturated group-free (meth)acrylic resin (A1) and an epoxy crosslinking agent, and a combination of a carboxyl group-containing ethylenically unsaturated group-free (meth)acrylic resin (A1) and an aziridine crosslinking agent, and more preferably a hydroxyl group-containing ethylenically unsaturated group-free (meth)acrylic resin (A1) and an isocyanate crosslinking agent.

An isocyanate crosslinker is a compound that has two or more isocyanato groups. Here, "isocyanato group" includes compounds that generate isocyanato groups upon deblocking. Specific examples of the isocyanate crosslinking agent include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, diphenylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, an isocyanurate of hexamethylene diisocyanate, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, a tolylene diisocyanate adduct of trimethylolpropane, a xylylene diisocyanate adduct of trimethylolpropane, triphenylmethane triisocyanate, methylenebis(4-phenylmethane)triisocyanate, etc. Among these, an isocyanurate of hexamethylene diisocyanate and a tolylene diisocyanate adduct of trimethylolpropane are preferred. Isocyanate crosslinking agents may be used alone or in combination of two or more.

Epoxy crosslinkers are compounds containing two or more epoxy groups. Examples include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, bisphenol A epoxy resin, N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine], ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, and epoxy-terminated polydimethylsiloxane. Epoxy crosslinkers may be used alone or in combination of two or more.

Aziridine crosslinkers are compounds that contain two or more aziridinyl groups. Examples include ethylene glycol-bis-[3-(2-aziridinyl)propionate], trimethylolpropane-tris[3-(2-aziridinyl)propionate], trimethylolpropane-tris[3-(1-aziridinyl)propionate], trimethylolpropane-tris[3-(2-methyl-1-aziridinyl)propionate], tetramethylolmethane-tris[3-(2-aziridinyl)propionate], pentaerythritol-tris[ 3-(1-aziridinyl)propionate], N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxamide), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, tris(1-aziridinyl)phosphine oxide, 2,2-bis(hydroxymethyl)butanol-tris[3-(1-aziridinyl)propionate], etc. Aziridine crosslinking agents may be used alone or in combination of two or more.

The content of crosslinking agent (B1) is preferably 0.05 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-free (meth)acrylic resin (A1). When the content of crosslinking agent (B1) is 0.05 parts by mass or more, a sufficient three-dimensional crosslinked structure is formed in the intermediate layer, resulting in an intermediate layer with high heat resistance. When the content of crosslinking agent (B1) is 30 parts by mass or less, an appropriate gelation time can be ensured during sheet molding.

(Other ingredients)
The resin composition may contain other components in addition to the ethylenically unsaturated group-free (meth)acrylic resin (A1) and the crosslinking agent (B1), as necessary, such as a tackifier, a solvent, and various additives.

<Tackifier>
Any conventionally known tackifier can be used without any particular limitation. Examples of tackifiers include terpene-based tackifier resins, phenol-based tackifier resins, rosin-based tackifier resins, aliphatic petroleum resins, aromatic petroleum resins, copolymer-based petroleum resins, alicyclic petroleum resins, xylene resins, epoxy-based tackifier resins, polyamide-based tackifier resins, ketone-based tackifier resins, and elastomer-based tackifier resins. The tackifiers may be used alone or in combination of two or more.

If the resin composition contains a tackifier, the content thereof is preferably 30 parts by mass or less, and more preferably 5 to 20 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-free (meth)acrylic resin (A1).

<Solvent>
The solvent can be used to dilute the resin composition to adjust its viscosity. For example, when applying the resin composition, the solvent can be used to adjust the viscosity of the resin composition to an appropriate level. The solvent is removed when the intermediate layer is formed.

The solvent may be, for example, an organic solvent such as methyl ethyl ketone, methyl isobutyl ketone, acetone, ethyl acetate, propyl acetate, tetrahydrofuran, dioxane, cyclohexanone, hexane, toluene, xylene, n-propanol, or isopropyl alcohol. The solvent may be used alone or in a mixture of two or more.

Additives
Examples of additives include plasticizers, surface lubricants, leveling agents, softeners, antioxidants, antiaging agents, ultraviolet absorbers, polymerization inhibitors, light stabilizers such as benzotriazole-based ones, phosphate ester-based and other flame retardants, surfactants, and antistatic agents.

[Method for producing ethylenically unsaturated group-free (meth)acrylic resin (A1)]
The method for producing the ethylenically unsaturated group-free (meth)acrylic resin (A1) is not particularly limited. For example, the ethylenically unsaturated group-free (meth)acrylic resin (A1) can be obtained by copolymerizing raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1) by a known polymerization method. Specifically, the polymerization method may be a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, an alternating copolymerization method, or the like. Among these polymerization methods, the solution polymerization method is preferred in terms of ease of reaction.

When producing the ethylenically unsaturated group-free (meth)acrylic resin (A1) by solution polymerization, a radical polymerization initiator is used as needed.

The radical polymerization initiator is not particularly limited and can be appropriately selected from known initiators. Examples of the radical polymerization initiator include azo-based polymerization initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), and dimethyl-2,2'-azobis(2-methylpropionate); and oil-soluble polymerization initiators such as peroxide-based polymerization initiators such as benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane.

The radical polymerization initiators may be used alone or in combination of two or more.

The amount of radical polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 4 parts by mass, and even more preferably 0.03 to 3 parts by mass, per 100 parts by mass of the total raw material monomers of the ethylenically unsaturated group-free (meth)acrylic resin (A1).

When producing the ethylenically unsaturated group-free (meth)acrylic resin (A1) by solution polymerization, a common solvent can be used. Examples of solvents include esters such as ethyl acetate, propyl acetate, and butyl acetate; aromatic hydrocarbons such as toluene, xylene, and benzene; aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; ketones such as methyl ethyl ketone and methyl isobutyl ketone; glycols such as ethylene glycol, propylene glycol, and dipropylene glycol; glycol ethers such as methyl cellosolve, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether; and glycol esters such as ethylene glycol diacetate and propylene glycol monomethyl ether acetate.

The solvents may be used alone or in combination of two or more.

[Method of producing resin composition]
The resin composition can be produced by a conventionally known method, for example, by mixing and stirring the ethylenically unsaturated group-free (meth)acrylic resin (A1), the crosslinking agent (B1), and other components, such as a tackifier, a solvent, and various additives, which may be contained as needed, by a conventionally known method.

There are no particular limitations on the method for mixing and stirring the components contained in the resin composition. Mixing and stirring can be carried out using, for example, a stirring device equipped with stirring blades such as a homodisper or paddle blade.

[Method of manufacturing intermediate layer]
The intermediate layer can be produced, for example, by the method described below. First, a resin composition is applied to a substrate, and if a solvent is contained, the composition is heated and dried to remove the solvent, thereby forming a pre-cured intermediate layer. Thereafter, a release sheet is attached to the pre-cured intermediate layer as needed, until immediately before laminating the photocurable pressure-sensitive adhesive layer or the pre-thermocurable photocurable pressure-sensitive adhesive layer. The pre-cured intermediate layer may undergo a curing reaction and form a crosslinked structure by heat-curing the obtained sheet in an oven or the like for a certain period of time. The curing reaction may be carried out after laminating the pre-cured intermediate layer and the photocurable pressure-sensitive adhesive layer or the pre-thermocurable photocurable pressure-sensitive adhesive layer.

The intermediate layer can also be manufactured by the following method. A resin composition is applied to a release sheet, and if a solvent is contained, the composition is heated and dried to remove the solvent, forming a pre-cured intermediate layer. The release sheet with the pre-cured intermediate layer is then placed on a substrate, with the surface of the pre-cured intermediate layer facing the substrate, and the intermediate layer is transferred onto the substrate. The resulting sheet may be subjected to the process described above to form a crosslinked structure.

Known methods can be used to apply the resin composition to the substrate or release sheet. Specific examples include coating methods using conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, and direct coaters.

The conditions for heat-drying the applied resin composition are not particularly limited, but are typically 25 to 180°C, preferably 60 to 150°C, for 1 to 20 minutes, preferably 1 to 10 minutes. Heat-drying under these conditions allows the solvent contained in the resin composition to be removed. The reaction conditions for curing the uncured intermediate layer after heat-drying are not particularly limited, but are typically 25 to 100°C, preferably 30 to 80°C, for 1 to 14 days, preferably 1 to 7 days. By carrying out the curing reaction under these conditions, the ethylenically unsaturated group-free (meth)acrylic resin (A1) and the crosslinking agent (B1) are crosslinked, allowing the gelation rate of the intermediate layer to be adjusted within the desired range.

(Release sheet)
As the release sheet, a known sheet-like material can be appropriately selected and used. The release sheet is sometimes called a separator. As the release sheet, the same material as the resin sheet used as the substrate can be used.

The thickness of the release sheet can be selected appropriately depending on the material of the release sheet, etc. When a resin sheet is used as the release sheet, the thickness of the release sheet is preferably 5 to 300 μm, more preferably 10 to 200 μm, and even more preferably 25 to 100 μm.

The release surface of the release sheet, i.e., the surface that comes into contact with the intermediate layer, may be subjected to a release treatment using a conventional release agent such as a silicone-based, long-chain alkyl-based, or fluorine-based release agent, as needed.

[Photocurable adhesive layer]
The photocurable pressure-sensitive adhesive layer is a thermosetting adhesive composition containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C), and contains 1,000 to 100,000 ppm by mass of silicon atoms. The thermosetting adhesive is a reaction product between a functional group contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2) that is reactive with a functional group contained in the crosslinking agent (B2) and a functional group contained in the crosslinking agent (B2), i.e., a crosslinked product, and is not a photocured product formed by the photopolymerization initiator (C). In the photocurable pressure-sensitive adhesive layer, irradiation with active energy rays such as ultraviolet rays decomposes the photopolymerization initiator (C), causing the ethylenically unsaturated groups contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2) to initiate radical polymerization, forming a further crosslinked structure, i.e., photocuring. By having a photocurable pressure-sensitive adhesive layer, the protective sheet does not lift off and has good adhesion to the adherend even when it undergoes various processing steps while attached to the adherend. Furthermore, after the processing steps are completed, the peel strength of the photocurable pressure-sensitive adhesive layer can be reduced by irradiation with active energy rays, allowing the pressure-sensitive adhesive layer to be peeled off from the adherend without leaving any adhesive residue. Furthermore, by incorporating silicon into the photocurable pressure-sensitive adhesive layer, the adhesion between the pressure-sensitive adhesive layer and metal can be improved. As a result, even after forming a metal film by a coating process such as sputtering and then irradiating it with active energy rays, the coated metal film can be prevented from detaching from the protective sheet and contaminating the adherend or becoming a source of contamination in the semiconductor manufacturing process.

The silicon atom content of the photocurable adhesive layer is 1,000 ppm by mass or more, preferably 2,000 ppm by mass or more, and more preferably 3,000 ppm by mass or more. The silicon atom content of the photocurable adhesive layer is 100,000 ppm by mass or less, preferably 80,000 ppm by mass or less, and more preferably 50,000 ppm by mass or less. A silicon atom content of 1,000 ppm by mass or more improves adhesion between the photocurable adhesive layer and the metal film coated thereon, reducing contamination sources from the metal film in the semiconductor manufacturing process and reducing metal contamination of electronic components. A silicon atom content of 100,000 ppm by mass or less ensures sufficient adhesive strength for the protective sheet. The silicon atom content of the photocurable adhesive layer is preferably 2,000 to 80,000 ppm by mass, and more preferably 3,000 to 50,000 ppm by mass.

The silicon atom content (mass) of the photocurable adhesive layer is a calculated value calculated from the amount of raw materials charged.

Silicon can be introduced into the photocurable adhesive layer by, for example, using a silicon-containing ethylenically unsaturated compound (a2-4) as a raw material monomer for the ethylenically unsaturated group-containing (meth)acrylic resin (A2), by adding a silicon-containing photocurable compound (D) to the adhesive composition, or by both.

The thickness of the photocurable adhesive layer is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more. The thickness of the photocurable adhesive layer is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. When the thickness of the photocurable adhesive layer is 1 μm or more, good adhesion to the adherend is achieved. When the thickness of the photocurable adhesive layer is 100 μm or less, the occurrence of adhesive residue is further reduced.

The thickness ratio of the intermediate layer to the photocurable adhesive layer (intermediate layer/photocurable adhesive layer) is preferably 1 to 50, more preferably 1 to 40, and even more preferably 1 to 30. When the thickness ratio is within the above range, both the ability to conform to irregularities and heat resistance can be achieved. The thickness ratio of the intermediate layer to the photocurable adhesive layer (intermediate layer/photocurable adhesive layer) may be 3 to 20, or 5 to 15.

(Ethylenically Unsaturated Group-Containing (Meth)acrylic Resin (A2))
The ethylenically unsaturated group-containing (meth)acrylic resin (A2) is not particularly limited, as long as it is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) with a (meth)acrylic resin (A2-0) containing at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2) as raw material monomers. The present inventors have discovered that the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is less likely to leave adhesive residue on an adherend than a resin in which an ethylenically unsaturated group is introduced into the side chain of the (meth)acrylic resin using a compound having an isocyanato group. This is thought to be because, when an ethylenically unsaturated group is introduced into the side chain of the (meth)acrylic resin using a compound having an isocyanato group, the urethane bond formed during the reaction between the compound having an isocyanato group and the (meth)acrylic resin is cleaved during the heating process, resulting in the compound separating from the (meth)acrylic resin and leaving adhesive residue. On the other hand, by forming a photocurable pressure-sensitive adhesive layer using an ethylenically unsaturated group-containing (meth)acrylic resin (A2), which is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic copolymer having a carboxy group, the protective sheet has high heat resistance and maintains high conformability to the irregularities of the adherend even when exposed to high temperature conditions from the step of attaching to the adherend, to the processing step, and the peeling step. In addition, when peeling the protective sheet from the adherend after the processing step, good peelability can be obtained by irradiating with active energy rays.

The raw material monomers for the (meth)acrylic resin (A2-0) include at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2). It is preferable to use at least one alkyl (meth)acrylate selected from 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate as the alkyl (meth)acrylate (a2-1). The total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers for the (meth)acrylic resin (A2-0) is preferably 30 mol% or more, more preferably 40 mol% or more, and even more preferably 55 mol% or more. There is no particular upper limit on the total content of 2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate relative to the total raw material monomers of the (meth)acrylic resin (A2-0), but it may be, for example, 99 mol%, 90 mol%, or 80 mol%.

The functional group possessed by the ethylenically unsaturated group-containing (meth)acrylic resin (A2) that can react with the functional group possessed by the crosslinking agent (B2) can be, for example, a carboxy group when the functional group possessed by the crosslinking agent (B2) is at least one selected from the group consisting of an epoxy group, an aziridinyl group, and a hydroxy group. For example, when the functional group possessed by the crosslinking agent (B2) is a hydroxy group, examples of the functional group that can react with the functional group possessed by the crosslinking agent (B2) include an isocyanato group and a carboxy group.

In one embodiment, a silicon-containing ethylenically unsaturated compound (a2-4) may also be used as a raw material monomer for the (meth)acrylic resin (A2-0). By adjusting the content of the silicon-containing ethylenically unsaturated compound (a2-4), the silicon atom content of the photocurable pressure-sensitive adhesive layer can be adjusted, thereby achieving a balance between adhesive strength to the adherend and adhesion to the metal film, resulting in a protective sheet with reduced metal film detachment.

The ethylenically unsaturated group-containing (meth)acrylic resin (A2) may be used alone or in combination of two or more types.

The glass transition temperature (Tg) of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -60°C or higher. The glass transition temperature (Tg) of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. A glass transition temperature of -80°C or higher results in a photocurable pressure-sensitive adhesive layer with high cohesive strength, thereby preventing resin elution during sheet molding. A glass transition temperature of 0°C or lower results in even better adhesion between the intermediate layer and the photocurable pressure-sensitive adhesive layer.

The weight-average molecular weight of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 100,000 to 2,000,000, more preferably 150,000 to 1,500,000, and even more preferably 200,000 to 1,000,000. A weight-average molecular weight of 100,000 or more results in a photocurable pressure-sensitive adhesive layer with high cohesive strength, and prevents resin elution during sheet formation. A weight-average molecular weight of 2,000,000 or less facilitates molding and processing.

The ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 500 g/mol or more, more preferably 550 g/mol or more, and even more preferably 600 g/mol or more. The ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 5000 g/mol or less, more preferably 4000 g/mol or less, and even more preferably 2000 g/mol or less. The ethylenically unsaturated group equivalent of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) may be 1500 g/mol or less, or may be 1000 g/mol or less. When the ethylenically unsaturated group equivalent is within the above range, sufficient curability can be imparted.

The acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 1 mgKOH/g or more, more preferably 5 mgKOH/g or more, and even more preferably 10 mgKOH/g or more. The acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is preferably 100 mgKOH/g or less, more preferably 50 mgKOH/g or less, and even more preferably 35 mgKOH/g or less. When the acid value is 1 mgKOH/g or more, the resin can react sufficiently with a crosslinking agent having a functional group reactive with an acid group, resulting in a photocurable pressure-sensitive adhesive layer with high cohesive strength. When the acid value is 100 mgKOH/g or less, the cohesive strength of the resulting resin is not too high, resulting in good handleability.

The content of alkyl (meth)acrylate (a2-1) relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is preferably 30 to 99 mol%, more preferably 40 to 90 mol%, and even more preferably 55 to 85 mol%. When the content of alkyl (meth)acrylate (a2-1) is 30 mol% or more, adhesion to the intermediate layer is good. When the content of alkyl (meth)acrylate (a2-1) is 99 mol% or less, a sufficient content of carboxy group-containing ethylenically unsaturated compound (a2-2) can be ensured, thereby ensuring a sufficient amount of crosslinking with the crosslinking agent (B2) and improving the cohesive strength of the photocurable pressure-sensitive adhesive layer. In addition, a sufficient amount of ethylenically unsaturated groups can be introduced, thereby sufficiently reducing the peel strength of the protective sheet when irradiated with active energy rays.

The content of the carboxyl group-containing ethylenically unsaturated compound (a2-2) relative to the total raw material monomers of the (meth)acrylic resin (A2-0) is preferably 1 to 60 mol%, more preferably 5 to 50 mol%, and even more preferably 10 to 40 mol%. When the content of the carboxyl group-containing ethylenically unsaturated compound (a2-2) is 1 mol% or more, a sufficient amount of crosslinking with the crosslinking agent (B2) is ensured, improving the cohesive strength of the photocurable pressure-sensitive adhesive layer. In addition, a sufficient amount of ethylenically unsaturated groups can be introduced by the addition reaction of the epoxy group-containing ethylenically unsaturated compound (a2-3), thereby enabling a sufficient reduction in the peel strength of the protective sheet when irradiated with active energy rays.

The amount of epoxy group-containing ethylenically unsaturated compound (a2-3) is preferably 0.5 to 55 mol, more preferably 3 to 45 mol, and even more preferably 5 to 35 mol, relative to a total of 100 mol of the raw material monomers of (meth)acrylic resin (A2-0). The addition rate of epoxy group-containing ethylenically unsaturated compound (a2-3) relative to the carboxy groups derived from carboxy group-containing ethylenically unsaturated compound (a2-2) is preferably 10 to 99%, more preferably 20 to 95%, and even more preferably 40 to 90%. By ensuring the amount within the above range, it is possible to ensure a sufficient amount of ethylenically unsaturated groups introduced while also ensuring the amount of crosslinking with crosslinking agent (B2).

If necessary, at least one selected from the group consisting of silicon-containing ethylenically unsaturated compounds (a2-4) and other monomers (a2-5) may be used as a raw material monomer for the (meth)acrylic resin (A2-0).

When a silicon-containing ethylenically unsaturated compound (a2-4) is used as a raw material monomer for the (meth)acrylic resin (A2-0), its content is preferably 0.01 to 10 mol %, more preferably 0.02 to 5 mol %, and even more preferably 0.1 to 1 mol %, based on the total amount of raw material monomers. When the content of the silicon-containing ethylenically unsaturated compound (a2-4) is 0.01 mol % or more, adhesion between the photocurable pressure-sensitive adhesive layer and the metal film formed by a coating process such as sputtering is improved. When the content of the silicon-containing ethylenically unsaturated compound (a2-4) is 10 mol % or less, sufficient adhesion between the photocurable pressure-sensitive adhesive layer and the intermediate layer can be ensured.

When other monomer (a2-5) is used as a raw material monomer for (meth)acrylic resin (A2-0), its content is preferably 0.1 to 30 mol %, more preferably 0.1 to 20 mol %, and even more preferably 0.1 to 10 mol %, based on the total amount of raw material monomers.

The alkyl (meth)acrylate (a2-1) is not particularly limited as long as it is a compound that does not have a functional group such as a hydroxy group or a carboxy group, nor a silicon atom, but has an alkyl group and a (meth)acryloyloxy group. Specific examples and preferred examples of the alkyl (meth)acrylate (a2-1) are the same as those of the alkyl (meth)acrylate (a1-1). The alkyl (meth)acrylate (a2-1) may be used alone or in combination of two or more. The carboxy group-containing ethylenically unsaturated compound (a2-2) is not particularly limited as long as it is a compound that has a carboxy group and an ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. Specific examples and preferred examples of the carboxy group-containing ethylenically unsaturated compound (a2-2) are the same as those of the carboxy group-containing ethylenically unsaturated compound (a1-3). The carboxy group-containing ethylenically unsaturated compound (a2-2) may be used alone or in combination of two or more.

The epoxy group-containing ethylenically unsaturated compound (a2-3) is not particularly limited as long as it does not have a carboxy group and has an epoxy group and an ethylenically unsaturated group. In the present disclosure, the term "epoxy group-containing ethylenically unsaturated compound" also encompasses ethylenically unsaturated compounds containing an oxetane ring instead of an epoxy group. Specific examples include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexane-1-allyl carboxylate, 3,4-epoxytricyclo[5.2.1.0 ^2,6 ]decaneoxyethyl acrylate, and (3-ethyloxetan-3-yl)methyl (meth)acrylate. Among these, glycidyl (meth)acrylate is preferred from the viewpoint of ease of synthesis, and 3,4-epoxycyclohexylmethyl (meth)acrylate is preferred from the viewpoint of heat resistance. The epoxy group-containing ethylenically unsaturated compounds (a2-3) may be used alone or in combination of two or more kinds.

The silicon-containing ethylenically unsaturated compound (a2-4) is not particularly limited as long as it does not have a carboxy group and has a silicon atom and an ethylenically unsaturated group. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. The silicon-containing ethylenically unsaturated compound (a2-4) is preferably at least one selected from the group consisting of [(meth)acryloyloxy]alkyltrialkoxysilane, [[(meth)acryloyloxy]alkyl]alkyldialkoxysilane, and a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and a methacryloyloxy group at one end, and more preferably a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and a methacryloyloxy group at one end. Specific examples of the silicon-containing ethylenically unsaturated compound (a2-4) include [(meth)acryloyloxy]alkyltrialkoxysilanes and [(meth)acryloyloxy]propylsilanes such as [(meth)acryloyloxy]methyltriethoxysilane, [(meth)acryloyloxy]ethyltriethoxysilane, [(meth)acryloyloxy]propyltrimethoxysilane, [(meth)acryloyloxy]propyltriethoxysilane, [(meth)acryloyloxy]octyltrimethoxysilane, and [(meth)acryloyloxy]octyltriethoxysilane. Examples include [(meth)acryloyloxy]alkyl]alkyldialkoxysilanes such as [(meth)acryloyloxy]propylmethyldimethoxysilane, [(meth)acryloyloxy]propylmethyldiethoxysilane, [(meth)acryloyloxy]ethylmethyldiethoxysilane, and [(meth)acryloyloxy]nonylmethyldiethoxysilane; p-styryltrimethoxysilane; methacryloyloxypropyltris(trimethylsilyloxy)silane; and silicone compounds having a polydimethylsiloxane skeleton in their molecular structure and a methacryloyloxy group at one end.

Commercially available silicon-containing ethylenically unsaturated compounds (a2-4) can also be used. For example, commercially available products include "X-22-174ASX," "X-22-174BX," "X-22-2404," and "KF-2012" (all of which are single-terminated methacrylic-modified silicone oils, Shin-Etsu Chemical Co., Ltd.), and "FM-0711," "FM-0721," and "FM-0725" (all of which are Silaplane, JNC Corporation), which have a polydimethylsiloxane skeleton in their molecular structure. Examples of suitable silane coupling agents include silicone compounds having a methacryloyloxy group at one end; "TM-0701T" (Silaplane, JNC Corporation); silane coupling agents having a trialkoxysilyl group in their molecular structure, such as "KBE-503," "KBM-503," "KBM-5103," "KBM-5803," and "KBM-1403"; and silane coupling agents having an alkyldialkoxysilyl group in their molecular structure, such as "KBE-502" and "KBM-502." Among these, from the perspective of reactivity, it is preferable to use at least one selected from "X-22-174ASX," "KF-2012," "FM-0711," "FM-0721," and "FM-0725." In this disclosure, a silane coupling agent is a compound having a hydrolyzable silyl group and a reactive organic functional group. The silicon-containing ethylenically unsaturated compound (a2-4) may be used alone or in combination of two or more.

Other monomers (a2-5) other than (a2-1), (a2-2), and (a2-4) can be compounds similar to the hydroxy group-containing (meth)acrylate (a1-2), (meth)acrylamide compound (a1-4), and other monomers (a1-5). The other monomers (a2-5) can be used alone or in combination of two or more.

(Crosslinking agent (B2))
The crosslinking agent (B2) is not particularly limited as long as it is a compound that does not contain silicon atoms and has multiple functional groups capable of reacting with any of the multiple functional groups contained in the ethylenically unsaturated group-containing (meth)acrylic resin (A2). Since the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has a carboxy group, examples of crosslinking agents that can be used as the crosslinking agent (B2) include epoxy crosslinking agents and aziridine crosslinking agents. By including the crosslinking agent (B2) in the photocurable pressure-sensitive adhesive layer, the cohesive strength of the photocurable pressure-sensitive adhesive layer is improved, and adhesive residue when the protective sheet is peeled from the adherend can be reduced. The crosslinking agent (B2) may be used alone or in combination of two or more types.

As the epoxy crosslinking agent and aziridine crosslinking agent, any of the epoxy crosslinking agents and aziridine crosslinking agents used as crosslinking agent (B1) that does not contain a silicon atom can be used. Epoxy crosslinking agents can be used alone, or two or more types can be used in combination. Aziridine crosslinking agents can be used alone, or two or more types can be used in combination.

The content of crosslinking agent (B2) is preferably 0.05 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2). When the content of crosslinking agent (B2) is 0.05 parts by mass or more, a sufficient three-dimensional crosslinked structure is formed in the photocurable pressure-sensitive adhesive layer, resulting in a photocurable pressure-sensitive adhesive layer with sufficiently high cohesive strength. When the content of crosslinking agent (B2) is 30 parts by mass or less, an appropriate gelation time can be ensured during sheet molding.

(Photopolymerization initiator (C))
Examples of the photopolymerization initiator (C) include benzophenone, benzil, benzoin, ω-bromoacetophenone, chloroacetone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, 2-chlorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-bisdiethylaminobenzophenone, Michler's ketone, benzoin methyl ether, benzoin isobutyl ether, benzoin-n-butyl ether, benzyl methyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, Examples of the photopolymerization initiator include carbonyl-based photopolymerization initiators such as methyl benzoyl formate, 4'-dimethylaminoacetophenone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one; sulfide-based photopolymerization initiators such as diphenyl disulfide, dibenzyl disulfide, tetraethyl thiuram disulfide, and tetramethylammonium monosulfide; acyl phosphine oxide-based photopolymerization initiators such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide; quinone-based photopolymerization initiators such as benzoquinone and anthraquinone; sulfochloride-based photopolymerization initiators; and thioxanthone-based photopolymerization initiators such as thioxanthone, 2-chlorothioxanthone, and 2-methylthioxanthone.

Among these, it is preferable to use at least one selected from the group consisting of carbonyl-based photopolymerization initiators and acylphosphine oxide-based photopolymerization initiators, from the standpoint of high sensitivity to ultraviolet light and heat resistance.

The photopolymerization initiator (C) may be used alone or in combination of two or more types.

The content of the photopolymerization initiator (C) is preferably 0.1 to 10.0 parts by mass, and more preferably 0.5 to 5.0 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2). When the content of the photopolymerization initiator (C) is 0.1 parts by mass or more, the photocurable pressure-sensitive adhesive layer can be cured at a sufficiently fast curing rate by irradiation with active energy rays, thereby sufficiently reducing the peel strength of the pressure-sensitive adhesive layer after irradiation with active energy rays. When the content of the photopolymerization initiator (C) is 10.0 parts by mass or less, the pressure-sensitive adhesive layer is less likely to remain on the adherend when the protective sheet is peeled from the adherend. Even if the content of the photopolymerization initiator (C) exceeds 10.0 parts by mass, no effect commensurate with the content of the photopolymerization initiator (C) is observed. Therefore, by setting the content to 10.0 parts by mass or less, the pressure-sensitive adhesive composition can be produced economically.

(Silicon-containing photocurable compound (D))
The photocurable pressure-sensitive adhesive layer may contain a silicon-containing photocurable compound (D) as needed. The silicon-containing photocurable compound (D) is not particularly limited as long as it contains a silicon atom and two or more ethylenically unsaturated groups in the molecule. The ethylenically unsaturated group is preferably a (meth)acryloyloxy group. Examples of the silicon-containing photocurable compound (D) include silicone compounds having a polydimethylsiloxane skeleton in the molecular structure and methacryloyloxy groups at both ends, silicone compounds having a polydimethylsiloxane skeleton in the molecular structure and vinyl groups at both ends, bis(divinyl)-terminated polydimethylsiloxane; silicone compounds having two or more acryloyloxy groups such as silicone diacrylate, silicone hexaacrylate, and silicone hexaurethaneacrylate; and silane coupling agents whose reactive organic functional groups have an allyl isocyanurate structure. Among these, from the viewpoint of solubility in the (meth)acrylic resin (A2), at least one selected from the group consisting of a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and methacryloyloxy groups at both ends, a silicone diacrylate, and a silicone hexaacrylate is preferred.

Commercially available silicon-containing photocurable compounds (D) can also be used, such as "X-22-164," "X-22-164AS," "X-22-164A," "X-22-164B," "X-22-164C," "X-22-164E," and "X-12-1290" (all from Shin-Etsu Chemical Co., Ltd.), "FM-7711," "FM-7721," and "FM-7725" (all from Silaplane, JNC Corporation), "EBECRYL 350," "EBECRYL 1360," "EBECRYL 1365," and "KRM8479" (all from Daicel Allnex Corporation), and "DMS-V34," "DMS-R11," and "DMS-VD11" (all from AZMAX Corporation). Among these, from the viewpoint of solubility in the (meth)acrylic resin (A2), at least one selected from "X-22-164A," "X-22-164B," "X-22-164C," "X-22-164E," "FM-7721," "FM-7725," "EBECRYL 350," and "EBECRYL 1360" is preferred. The silicon-containing photocurable compound (D) may be used alone or in combination of two or more types.

By adjusting the content of the silicon-containing photocurable compound (D), the silicon atom content of the photocurable pressure-sensitive adhesive layer can be adjusted, thereby achieving a balance between adhesive strength to the adherend and adhesion to the metal film, resulting in a protective sheet with a reduced amount of metal film detachment. The content of the silicon-containing photocurable compound (D) is preferably 0.1 to 20.0 parts by mass, more preferably 0.5 to 10.0 parts by mass, and even more preferably 1.0 to 5.0 parts by mass, per 100 parts by mass of the ethylenically unsaturated group-containing (meth)acrylic resin (A2). When the content of the silicon-containing photocurable compound (D) is 0.1 part by mass or more, the adhesion between the photocurable pressure-sensitive adhesive layer and the metal film coated thereon is improved. When the content of the silicon-containing photocurable compound (D) is 20.0 parts by mass or less, sufficient adhesive strength of the protective sheet can be obtained.

(Other ingredients)
The pressure-sensitive adhesive composition may optionally contain other components in addition to the above-described ethylenically unsaturated group-containing (meth)acrylic resin (A2), crosslinking agent (B2), photopolymerization initiator (C), and optional silicon-containing photocurable compound (D). Examples of other components include tackifiers, solvents, and various additives. The tackifiers, solvents, and various additives may be the same as those described for the resin composition.

[Method for producing ethylenically unsaturated group-containing (meth)acrylic resin (A2)]
The method for producing the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is not particularly limited. The ethylenically unsaturated group-containing (meth)acrylic resin (A2) can be obtained, for example, by copolymerizing raw material monomers for the (meth)acrylic resin (A2-0) by a known polymerization method, and then adding an epoxy group-containing ethylenically unsaturated compound (a2-3) to at least a portion of the carboxy groups in the (meth)acrylic resin (A2-0).

The (meth)acrylic resin (A2-0) used in producing the ethylenically unsaturated group-containing (meth)acrylic resin (A2) can be obtained by the same method as the production method for the ethylenically unsaturated group-free (meth)acrylic resin (A1). Among these, solution polymerization is preferred, and the type and amount of radical polymerization initiator and solvent used are the same as those described for the production method for the ethylenically unsaturated group-free (meth)acrylic resin (A1).

When the epoxy group-containing ethylenically unsaturated compound (a2-3) is added to at least a portion of the carboxy groups of the (meth)acrylic resin (A2-0), the temperature of the addition reaction is preferably 80 to 150°C, and particularly preferably 90 to 130°C. An addition reaction temperature of 80°C or higher ensures a sufficient reaction rate. An addition reaction temperature of 150°C or lower prevents crosslinking of double bonds due to thermal radical polymerization, which would otherwise cause gelation. The solvent used in the addition reaction is the same as that described for the solution polymerization method.

In the addition reaction, known catalysts can be used as needed. Examples of catalysts include primary amines such as n-butylamine, n-hexylamine, benzylamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine; tertiary amines such as triethylamine, tributylamine, dimethylbenzylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 1,4-diazabicyclo[2.2.2]octane; and aromatic amines such as aniline, toluidine, phenylenediamine, diaminodiphenylmethane, and 1,8-diaminonaphthalene. Pyridine compounds such as pyridine, 2,6-lutidine, and 4-dimethylaminopyridine; imidazole compounds such as imidazole, 2-methylimidazole, 2-ethylimidazole, and 2-ethyl-4-methylimidazole; ammonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, and tetrabutylammonium hydroxide; alkyl ureas such as tetramethylurea; alkyl guanidines such as tetramethylguanidine; phosphine compounds such as triphenylphosphine, dimethylphenylphosphine, tricyclohexylphosphine, tributylphosphine, tris(4-methylphenyl)phosphine, tris(4-methoxyphenyl)phosphine, tris(2,6-dimethylphenyl)phosphine, tris(2,6-dimethoxyphenyl)phosphine, tris(2,4,6-trimethylphenyl)phosphine, and tris(2,4,6-trimethoxyphenyl)phosphine; and tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium Examples of suitable phosphonium salts include phosphonium iodide, tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium tetrakispentafluorophenylborate, 4-hydroxyphenyl-2-(triphenylphosphonium)phenolate, 4-hydroxyphenyl-2-{tris-(4-methylphenyl)phosphonium}phenolate, benzyltriphenylphosphonium chloride, methyltriphenylphosphonium bromide, ethyltriphenylphosphonium bromide, and butyltriphenylphosphonium bromide. Among these, pyridine compounds, imidazole compounds, ammonium salts, phosphine compounds, and phosphonium salts are preferred from the standpoint of reactivity.

The amount of catalyst used in the addition reaction is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, and even more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the total of the (meth)acrylic resin (A2-0) and the epoxy group-containing ethylenically unsaturated compound (a2-3).

Furthermore, during the addition reaction, a gas with a polymerization-inhibiting effect may be introduced into the reaction system, or a polymerization inhibitor may be added. By introducing a gas with a polymerization-inhibiting effect into the reaction system, or by adding a polymerization inhibitor, gelation during the addition reaction can be prevented.

Gases that have the effect of inhibiting polymerization include gases that contain oxygen to a degree that does not fall within the explosive range of the substances in the system, such as air.

The polymerization inhibitor may be any known one, and is not particularly limited. Examples include 4-methoxyphenol, hydroquinone, methoquinone, 2,6-di-t-butylphenol, 2,2'-methylenebis(4-methyl-6-t-butylphenol), and phenothiazine. The polymerization inhibitor may be used alone or in combination of two or more.

The amount of polymerization inhibitor used is preferably 0.005 to 5 parts by mass, more preferably 0.03 to 3 parts by mass, and even more preferably 0.05 to 1.5 parts by mass, per 100 parts by mass of the total of the (meth)acrylic resin (A2-0) and the epoxy group-containing ethylenically unsaturated compound (a2-3). If the amount of polymerization inhibitor used is 0.005 parts by mass or more, gelation during the addition reaction can be prevented. On the other hand, if the amount of polymerization inhibitor used is 5 parts by mass or less, sufficient exposure sensitivity of the photocurable pressure-sensitive adhesive layer can be obtained when irradiated with active energy rays.

Using a gas with polymerization inhibitor effects in combination with a polymerization inhibitor is preferable, as it reduces the amount of polymerization inhibitor used and increases the polymerization inhibitor effect.

[Method of manufacturing pressure-sensitive adhesive composition]
The pressure-sensitive adhesive composition can be produced by a conventionally known method, for example, by mixing and stirring the ethylenically unsaturated group-containing (meth)acrylic resin (A2), the crosslinking agent (B2), the photopolymerization initiator (C), and optionally the silicon-containing photocurable compound (D), and other components such as a tackifier, a solvent, and various additives, using a conventionally known method.

There are no particular limitations on the method for mixing and stirring the components contained in the pressure-sensitive adhesive composition. Mixing and stirring can be carried out using, for example, a stirring device equipped with stirring blades such as a homodisper or paddle blade.

[Method of manufacturing a photocurable pressure-sensitive adhesive layer]
The photocurable pressure-sensitive adhesive layer can be produced, for example, by the method described below. First, a pressure-sensitive adhesive composition is applied onto a release sheet, and if a solvent is contained, the composition is heated and dried to remove the solvent, thereby forming a pre-thermally cured photocurable pressure-sensitive adhesive layer. Thereafter, if necessary, a release sheet may be attached to the surface of the pre-thermally cured photocurable pressure-sensitive adhesive layer to be attached to the intermediate layer or pre-cured intermediate layer until immediately before lamination with the intermediate layer or pre-cured intermediate layer. The pre-thermally cured photocurable pressure-sensitive adhesive layer may undergo a curing reaction by heat curing the obtained sheet in an oven or the like for a certain period of time, thereby forming a crosslinked structure. The curing reaction may be carried out after laminating the intermediate layer or pre-cured intermediate layer and the pre-thermally cured photocurable pressure-sensitive adhesive layer.

The photocurable adhesive layer can also be produced by the following method. A sheet having an intermediate layer on one main surface of a substrate is coated with an adhesive composition directly onto the intermediate layer. If a solvent is contained, the composition is heated and dried to remove the solvent, forming a pre-thermally cured photocurable adhesive layer. A release sheet is then laminated, if necessary, onto the pre-thermally cured photocurable adhesive layer. A crosslinked structure is then formed on the resulting sheet as described above. Alternatively, a sheet having a pre-thermally cured intermediate layer on one main surface of a substrate is coated with an adhesive composition directly onto the pre-cured intermediate layer. If a solvent is contained, the composition is heated and dried to remove the solvent, forming a pre-thermally cured photocurable adhesive layer. A release sheet is then laminated, if necessary, onto the pre-thermally cured photocurable adhesive layer. The pre-cured intermediate layer and the pre-thermally cured photocurable adhesive layer are then simultaneously cured. These methods eliminate the need for the step of laminating an intermediate layer and a photocurable adhesive layer to obtain a protective sheet.

The method for applying the adhesive composition onto the release sheet or onto the intermediate layer or pre-cured intermediate layer, the conditions and preferred ranges for heating and drying the applied adhesive composition, and the conditions and preferred ranges for curing the pre-thermosetting photocurable adhesive layer in an oven for a certain period of time after heating and drying are the same as those described for the method for manufacturing the intermediate layer.

(Release sheet)
The release sheet can be selected from known sheet-shaped materials as appropriate and can be the same as the above-mentioned resin sheet used as the substrate.

The thickness of the release sheet can be selected appropriately depending on the application of the protective sheet, the material of the release sheet, etc. When a resin sheet is used as the release sheet, the thickness of the release sheet is preferably 5 to 300 μm, more preferably 10 to 200 μm, and even more preferably 25 to 100 μm.

The release surface of the release sheet, i.e., the surface that comes into contact with the photocurable adhesive layer, may be subjected to a release treatment using a conventional release agent such as a silicone-based, long-chain alkyl-based, or fluorine-based release agent, if necessary.

[Protective sheet manufacturing method]
The protective sheet may be produced, for example, by first curing either the pre-curing intermediate layer or the pre-thermosetting light-curable pressure-sensitive adhesive layer, and then laminating the other pre-curing layer and curing the pre-curing layer, or by laminating the pre-curing intermediate layer and the pre-thermosetting light-curable pressure-sensitive adhesive layer and curing both layers simultaneously. The protective sheet may be produced by laminating an intermediate layer that is a thermosetting product and a photo-curable pressure-sensitive adhesive layer that is also a thermosetting product.

A specific example of a method for manufacturing a protective sheet is shown below. A sheet having a pre-curing intermediate layer on one main surface of a substrate, and a sheet having a pre-thermosetting light-curing adhesive layer on a release sheet are prepared. If a release sheet is laminated on the bonding surfaces of the two sheets, this is peeled off, and the sheets are bonded together so that the bonding surface of the pre-curing intermediate layer, i.e., the surface opposite the substrate, faces the bonding surface of the pre-thermosetting light-curing adhesive layer, i.e., the surface opposite the release sheet.

The pre-curing intermediate layer and the pre-thermosetting light-curable adhesive layer are then laminated together and heated in an oven for a certain period of time for a curing process. This thermally cures the pre-curing intermediate layer and the pre-thermosetting light-curable adhesive layer, yielding a cured product of both layers. The conditions for the curing process are not particularly limited, but curing is typically performed at 30 to 100°C, preferably 40 to 80°C, for 1 to 14 days, preferably 1 to 7 days. Curing under these conditions allows the gel fraction of each layer to be adjusted to the desired range. Depending on the combination of components, crosslinking at the interface between the intermediate layer and the photo-curable adhesive layer, i.e., crosslinking between the ethylenically unsaturated group-free (meth)acrylic resin (A1) and the crosslinking agent (B2), and crosslinking between the ethylenically unsaturated group-containing (meth)acrylic resin (A2) and the crosslinking agent (B1), can also occur. Therefore, the curing process is expected to improve the interlayer adhesion between the intermediate layer and the photo-curable adhesive layer.

[Method for manufacturing a semiconductor device having bump electrodes]
A method for manufacturing a semiconductor device having a bump electrode according to one embodiment includes the steps of:
a protection step of attaching the photocurable adhesive layer surface of the protection sheet to the bump electrode-bearing surface of the unprocessed semiconductor device;
an active energy ray irradiation step of irradiating the protective sheet with active energy rays to photocure the photocurable pressure-sensitive adhesive layer;
The method includes a heating step of the unprocessed semiconductor device to which the protective sheet is attached, and a peeling step of peeling the protective sheet from the surface with the bump electrodes. Note that a processing step of the unprocessed semiconductor device may be performed between the protection step and the peeling step, and the order of the other steps may be reversed as long as the protection step is performed first and the peeling step is performed last.

(Protection process)
In the protection step, the photocurable adhesive layer surface of the protective sheet is attached to the bump electrode-bearing surface of the pre-processed semiconductor device having bump electrodes. This protects the bump electrode-bearing surface of the pre-processed semiconductor device. Specific examples of pre-processed semiconductor devices include semiconductor devices with uneven surfaces, such as bumped semiconductor chips, bumped printed wiring boards (PCBs), and bumped flexible printed circuit boards (FPCs). These semiconductor devices are subjected to various processing steps in the manufacturing process up to the mounting step in which the bump electrodes are connected to other electronic devices. Protecting the bump electrode-bearing surface during the processing steps can prevent scratches, damage, contamination, etc., on the bump electrode-bearing surface. The protective sheet can also serve as a temporary fixation function for the pre-processed semiconductor device for subsequent processing steps.

When the height of the bump electrode is H [μm] and the total thickness of the intermediate layer and photocurable adhesive layer is d [μm], d/H is preferably 1.00 or greater, more preferably 1.05 or greater, and even more preferably 1.10 or greater. d/H is preferably 100 or less, more preferably 20 or less, and even more preferably 10 or less.

If a release sheet is provided on the photo-curable adhesive layer, the release sheet can protect the photo-curable adhesive layer until it is ready for use. If a release sheet is provided on the photo-curable adhesive layer, the release sheet can be peeled off to expose the photo-curable adhesive layer, and the surface of the photo-curable adhesive layer can be efficiently pressed against the surface of the semiconductor device with bump electrodes before processing.

If a semiconductor device has multiple surfaces with bump electrodes, protective sheets are attached to some or all of the surfaces with bump electrodes during the protection process. For example, when stacking semiconductor chips as disclosed in JP 2014-225546 A, etc., protective sheets can be attached to non-mounting surfaces excluding the mounting surfaces of the surfaces with bump electrodes.

(Processing process)
The method for manufacturing a semiconductor device may include a processing step between the protection step and the peeling step described below.

The processing step can be any processing step used in the manufacture of conventionally known semiconductor devices, without any particular restrictions. For example, when using a protective sheet as a wafer dicing tape, the protective sheet is attached to a wafer on which multiple components are formed in the protection step, and then the processing step involves a dicing step in which the wafer is cut into individual components to obtain small element pieces (also called chips). When a semiconductor chip stacking process is performed as a processing step, only the non-mounting surfaces of the surfaces with bump electrodes are protected in the protection step, and the mounting surfaces not covered by the protective sheet are brought into contact with each other and electrically connected while being stacked.

(Heating process)
The method for manufacturing a semiconductor device includes a heating step between the protection step and the peeling step described below. When the method for manufacturing a semiconductor device includes a processing step after the protection step, the order of the processing step and the heating step is not limited. From the viewpoint of maximizing the protective function and temporary fixing function of the protective sheet, i.e., the adhesion performance, it is preferable that the processing step and the heating step be performed simultaneously, or that the processing step be performed before the heating step.

The heating process can be any heating process used in the manufacture of conventional semiconductor devices, without any particular restrictions. Examples of heating processes include the after-cure process for PCBs with bumps, the sputtering process for semiconductor chips, and the reflow process for connecting semiconductor chips.

The conditions for the heating step are not particularly limited. By performing the protection step before the heating step, the surface with the bump electrodes can be well protected even when high-temperature treatment is performed at, for example, 150°C or higher, 180°C or higher, or 200°C or higher. The maximum temperature reached in the heating step is not particularly limited, but may be, for example, 80°C or higher or 100°C or higher, and 260°C or lower or 230°C or lower. The maximum temperature reached in the heating step is not particularly limited, but from the perspective of the heat resistance of the protective sheet, it is preferably 300°C or lower, more preferably 270°C or lower. The heating time is not particularly limited, but is, for example, 1 to 180 minutes, preferably 1 to 120 minutes, and more preferably 1 to 60 minutes.

The conditions for the sputtering process are not particularly limited. For example, a metal such as Cr, Cu, Ti, Ag, Pt, or Au, an alloy such as Ni—Cr, SUS, or Cu—Zn, or a metal oxide such as ITO, SiO ₂ , TiO ₂ , Nb ₂ O ₅ , or ZnO may be used as a target, and film formation may be performed using an inert gas such as Ar. Examples of sputtering methods include magnetron sputtering, bipolar sputtering, DC (direct current) sputtering, RF (radio frequency) sputtering, reactive sputtering, and ion beam sputtering. The film formation temperature in the sputtering process is not particularly limited, but even when performed under high-temperature conditions such as 100° C. or higher, 130° C. or higher, or 150° C. or higher, the surface with the bump electrode can be well protected.

If gaps exist between semiconductor chips before the sputtering process, for example, if a semiconductor device is diced into small pieces and gaps exist between the semiconductor chips, the photo-curable adhesive layer of the protective sheet will be exposed in the gaps between the semiconductor chips. As a result, a metal film is formed during the sputtering process not only on the surface of the semiconductor chip, but also on the exposed areas of the photo-curable adhesive layer. The protective sheet maintains its adhesion to the metal film even after the active energy ray irradiation process, all the way up to the peeling process, and is able to reduce detachment of the metal film. This reduces metal contamination of the equipment and semiconductor chips used in each process.

(Active energy ray irradiation step)
In the active energy ray irradiation step, active energy rays are usually irradiated from the substrate side of the protective sheet. If the adherend is light-transmitting, active energy rays may be irradiated from the adherend side toward the protective sheet. Irradiation with active energy rays can crosslink and cure the photocurable pressure-sensitive adhesive layer, thereby increasing the heat resistance of the protective sheet or improving the releasability of the protective sheet. The active energy ray irradiation step may be performed between the protection step and the peeling step described below, and the order of the processing step and the heating step is not limited.

The active energy ray irradiation step may be carried out in two separate steps. For example, by carrying out the active energy ray irradiation step between the protection step and the processing step and crosslinking and curing some of the ethylenically unsaturated groups contained in the photocurable pressure-sensitive adhesive layer, the heat resistance of the protective sheet can be improved. Furthermore, by carrying out a second active energy ray irradiation step immediately before the peeling step described below and crosslinking the remaining ethylenically unsaturated groups, the peel strength of the protective sheet can be reduced and its releasability from the adherend can be improved.

Examples of active energy rays include gamma rays, ultraviolet (UV), visible light, infrared, radio waves, alpha rays, beta rays, electron beams, plasma flow, ionizing rays, and particle beams, with ultraviolet (UV) rays being preferred. Examples of light sources used to irradiate UV rays on a protective sheet attached to an adherend before removal include LED lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, xenon lamps, metal halide lamps, chemical lamps, and black lights. It is preferable to use an LED lamp, high-pressure mercury lamp, or metal halide lamp for active energy ray irradiation.

The active energy ray irradiation dose applied to the protective sheet is preferably 50 to 3000 mJ/ ^cm2 , and more preferably 100 to 1500 mJ/ ^cm2 . When the active energy ray irradiation dose applied to the protective sheet is 50 mJ/ ^cm2 or more, the photocurable pressure-sensitive adhesive layer can be cured at a sufficiently fast curing rate by the active energy ray irradiation, and the adhesive strength of the photocurable pressure-sensitive adhesive layer after the active energy ray irradiation can be sufficiently reduced. Even if the active energy ray irradiation dose applied to the protective sheet exceeds 3000 mJ/ ^cm2 , a corresponding effect cannot be obtained. Therefore, by setting the active energy ray irradiation dose applied to the protective sheet to 3000 mJ/cm2 or ^less , the ethylenically unsaturated groups contained in the photocurable pressure-sensitive adhesive layer can be crosslinked economically while reducing the impact of the active energy ray irradiation on the adherend.

(Peeling process)
In the peeling process, the protective sheet is peeled and removed from the surface with the bump electrodes. The peeling process is performed after the photocurable pressure-sensitive adhesive layer is cured by irradiating it with active energy rays. By irradiating it with active energy rays, the ethylenically unsaturated bonds contained in the photocurable pressure-sensitive adhesive layer form a three-dimensional crosslinked structure and are cured. As a result, the peel strength of the photocurable pressure-sensitive adhesive layer is reduced. Then, the protective sheet is peeled off from the semiconductor device.

In one embodiment of the method for manufacturing a semiconductor device having bump electrodes, even when a heating process is performed, no outgassing occurs and semiconductor devices can be obtained without adhesive residue on the surface of the bumped substrate, allowing the subsequent mounting process to be carried out without any problems. Furthermore, even when a metal film is formed on a partially exposed photocurable adhesive layer by coating in a sputtering process or the like, the photocurable adhesive layer maintains adhesion to the metal film up until the peeling process, reducing the amount of metal film detachment. This reduces metal contamination of the equipment and semiconductor devices used in each process.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

The raw materials used are shown below.
Alkyl (meth)acrylate (a1-1) or (a2-1):
Methyl methacrylate, Nippon Shokubai Co., Ltd.,
n-Butyl acrylate, Osaka Organic Chemical Industry Ltd.
2-Ethylhexyl acrylate, Osaka Organic Chemical Industry Co., Ltd. hydroxy group-containing (meth)acrylate (a1-2) or other monomer (a2-5):
2-Hydroxyethyl acrylate, Nippon Shokubai Co., Ltd. Carboxy group-containing ethylenically unsaturated compound (a1-3) or (a2-2):
Acrylic acid, Nippon Shokubai Co., Ltd. (meth)acrylamide compound (a1-4):
N,N-dimethylacrylamide radical polymerization initiator:
2,2'-Azobis(isobutyronitrile), Fujifilm Wako Pure Chemical Industries, Ltd. Epoxy group-containing ethylenically unsaturated compound (a2-3):
Glycidyl methacrylate, NOF Corporation,
3,4-epoxycyclohexylmethyl methacrylate, Daicel Corporation;
4HBAGE (4-hydroxybutyl acrylate glycidyl ether), Mitsubishi Chemical Corporation. Silicon-containing ethylenically unsaturated compound (a2-4):
FM-0711 (a compound represented by the following formula, number average molecular weight (Mn): 1000), JNC Corporation;
FM-0721 (a compound represented by the following formula, number average molecular weight (Mn): 5000), JNC Corporation;
(In the formula, m represents the number of repetitions.)
KF-2012 (a silicone compound having a polydimethylsiloxane skeleton in its molecular structure and a methacryloyloxy group at one end), Shin-Etsu Chemical Co., Ltd. Isocyanato group-containing ethylenically unsaturated compound:
Karenz™ MOI (2-isocyanatoethyl methacrylate), Resonac Co., Ltd.
Crosslinking agent (B1):
L-45E (trimethylolpropane tolylene diisocyanate adduct), Tosoh Corporation, product name: Coronate L-45E,
Crosslinker (B2):
L-45E (trimethylolpropane tolylene diisocyanate adduct), Tosoh Corporation, product name: Coronate L-45E,
Tetrad X (N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine]), Mitsubishi Gas Chemical Company, Inc., trade name: TETRAD-X
Photopolymerization initiator (C):
TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), BASF, trade name: L-TPO
Silicon-containing photocurable compound (D):
EBECRYL 1360 (silicone hexaacrylate), Daicel Allnex Co., Ltd.
FM-7725 (compound represented by the following formula, number average molecular weight (Mn): 10,000), JNC Corporation
(In the formula, n represents the number of repeats.)

Synthesis Example 1: Production of Ethylenically Unsaturated Group-Free (Meth)acrylic Resin (A1-1)
A mixed solution containing raw material monomers, namely, 6.7 parts by mass of methyl methacrylate, 48.1 parts by mass of n-butyl acrylate, 33.7 parts by mass of 2-ethylhexyl acrylate, 9.6 parts by mass of N,N-dimethylacrylamide, 1.4 parts by mass of 2-hydroxyethyl acrylate, and 0.5 parts by mass of acrylic acid, and 0.10 parts by mass of 2,2′-azobis(isobutyronitrile) as a polymerization initiator per 100 parts by mass of the raw material monomers, was prepared.

122.2 parts by mass of ethyl acetate per 100 parts by mass of raw monomers was charged into a four-neck flask equipped with a stirrer, dropping funnel, condenser, and nitrogen inlet tube as a solvent, and the temperature was raised to 80°C under a nitrogen gas atmosphere. While maintaining the reaction temperature at 80°C ± 2°C, the above mixed solution was added dropwise to the four-neck flask at a uniform rate over a period of 4 hours. After the addition was completed, stirring was continued at 80°C ± 2°C for an additional 6 hours to allow polymerization. The mixture was then diluted with 27.8 parts by mass of ethyl acetate to obtain a reaction solution (solids content: 40% by mass) containing an ethylenically unsaturated group-free (meth)acrylic resin (A1-1) (weight average molecular weight (Mw): 300,000, glass transition temperature (Tg): -42°C, acid value: 3.74 mg KOH/g, hydroxyl value: 6.97 mg KOH/g).

Synthesis Example 2: Production of Ethylenically Unsaturated Group-Containing (Meth)acrylic Resin (A2-1)
A first mixed solution was prepared containing raw material monomers, 81.0 parts by mass of 2-ethylhexyl acrylate, 1.5 parts by mass of FM-0711, and 17.5 parts by mass of acrylic acid, and 0.10 parts by mass of 2,2′-azobis(isobutyronitrile) as a radical polymerization initiator per 100 parts by mass of the raw material monomers.

Next, a second mixed solution was prepared containing 31.0 parts by mass of glycidyl methacrylate as the epoxy group-containing ethylenically unsaturated compound (a2-3), 1.5 parts by mass of tris(4-methylphenyl)phosphine (TPTP) as a catalyst, and 98.8 parts by mass of butyl acetate as a solvent, relative to a total of 100 parts by mass of the raw material monomers and epoxy group-containing ethylenically unsaturated compound (a2-3) used in the first mixed solution.

100 parts by mass of butyl acetate per 100 parts by mass of raw material monomer was charged into a four-neck flask equipped with a stirrer, dropping funnel, condenser, and nitrogen inlet tube, and the temperature was raised to 80°C under a nitrogen gas atmosphere. While maintaining the reaction temperature at 80°C ± 2°C, the first mixed solution was added dropwise to the four-neck flask at a uniform rate over a period of four hours. After the addition was complete, the mixture was stirred for an additional six hours at 80°C ± 2°C to carry out polymerization, yielding a carboxy group-containing copolymer ((meth)acrylic resin (A2-0)). Subsequently, 0.15 parts by mass of 4-methoxyphenol was added as a polymerization inhibitor to the reaction system per 100 parts by mass of the raw material monomer and epoxy group-containing ethylenically unsaturated compound (a2-3).

The reaction system to which 4-methoxyphenol had been added was heated to 100°C, and the second mixed solution described above was added dropwise over 0.5 hours. Stirring was then continued at 100°C for 8 hours, and the mixture was then cooled to room temperature (23°C), yielding a reaction solution (solids content: 40% by mass) containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2-1) (weight average molecular weight (Mw): 510,000, glass transition temperature (Tg): -41°C, acid value: 10.6 mg KOH/g, hydroxyl value: 93.3 mg KOH/g, ethylenically unsaturated group equivalent: 602 g/mol).

Synthesis Examples 3 to 5: Production of Ethylenically Unsaturated Group-Containing (Meth)acrylic Resins (A2-2) to (A2-4)
Reaction solutions containing ethylenically unsaturated group-containing (meth)acrylic resins (A2-2) to (A2-4) were obtained in the same manner as in Synthesis Example 2, except that the raw material monomers and the epoxy group-containing ethylenically unsaturated compound (a2-3) shown in Table 2 were used in the blending amounts shown in Table 2 and the amount of butyl acetate was adjusted so that the solid content was 40 mass%.

Comparative Synthesis Example 1: Production of Ethylenically Unsaturated Group-Containing (Meth)acrylic Resin (cA2-1)
A mixed solution containing 50 parts by mass of ethyl acetate, 86.5 parts by mass of 2-ethylhexyl acrylate, 13.4 parts by mass of 2-hydroxyethyl acrylate, and 0.1 part by mass of acrylic acid as raw material monomers, and 0.10 parts by mass of 2,2′-azobis(isobutyronitrile) as a radical polymerization initiator per 100 parts by mass of the raw material monomers was prepared.

A four-neck flask equipped with a stirrer, dropping funnel, condenser, and nitrogen inlet tube was charged with 50.0 parts by mass of ethyl acetate per 100 parts by mass of raw monomer as a solvent, and the temperature was raised to 80°C under a nitrogen gas atmosphere. While maintaining the reaction temperature at 80°C ± 2°C, the above mixed solution was added dropwise to the four-neck flask at a uniform rate over a period of four hours. After the addition was complete, polymerization was carried out with continued stirring at a temperature of 80°C ± 2°C for an additional six hours. The temperature of the reactants was then lowered to 60°C, and a mixture of 16.0 parts by mass of 2-isocyanatoethyl methacrylate, 0.05 parts by mass of dibutyltin dilaurate (a urethane catalyst), and 74 parts by mass of ethyl acetate was added dropwise through the dropping funnel. After the dropwise addition was completed, the reaction system was maintained at 70°C for 4 hours to eliminate the isocyanate groups, yielding a reaction solution (solids content: 40% by mass) containing an ethylenically unsaturated group-containing (meth)acrylic resin (cA2-1) (weight average molecular weight (Mw): 600,000, glass transition temperature (Tg): -44°C, acid value: 0.8 mg KOH/g, hydroxyl value: 5.9 mg KOH/g, ethylenically unsaturated group equivalent: 1125 g/mol).

(Production of Pre-Cured Intermediate Layer (X1-1))
A resin (A1-1) solution containing 30 mass % of resin (A1-1) was obtained by adding ethyl acetate as a diluent solvent to a reaction solution containing the ethylenically unsaturated group-free (meth)acrylic resin (A1-1) (also simply referred to as resin (A1-1)) obtained in Synthesis Example 1. Using the resin (A1-1) solution, a resin composition (X1) for an intermediate layer was obtained by the method described below.

In a room shielded from active energy rays, the resin (A1-1) solution and L-45E as crosslinking agent (B1) were added to a plastic container in the amounts (parts by mass) shown in Table 3 and stirred to obtain resin composition (X1) for the intermediate layer. The values in Table 3 for the resin (A1) solution, i.e., the (meth)acrylic resin (A1) solution not containing ethylenically unsaturated groups, are the amounts (parts by mass) used for the resin (A1) solution containing 30% by mass of resin (A1). The values for the crosslinking agent (B1) are the amounts (parts by mass) added per 100 parts by mass of the resin (A1) solution.

The resin composition (X1) was applied directly to a substrate so that the film thickness after heat curing would be 125 μm, and the resulting film was dried by heating at 100°C for 5 minutes to form a pre-cured intermediate layer (X1-1). A release sheet was then attached to the pre-cured intermediate layer (X1-1). A 25 μm-thick polyethylene terephthalate (PET) film (E5100, Toyobo Co., Ltd.) was used as the substrate. A 25 μm-thick polyethylene terephthalate (PET) film (E7006, Toyobo Co., Ltd.) was used as the release sheet. The film thickness after heat curing was measured on the intermediate layer (X1-1) obtained by curing the pre-cured intermediate layer (X1-1) in an oven at 40°C for 3 days.

(Production of Pre-Cured Intermediate Layer (X1-2))
A pre-cured intermediate layer (X1-2) with a release sheet attached was obtained in the same manner as the pre-cured intermediate layer (X1-1), except that a 25 μm thick polyamide (PA) film (EX-25, Unitika Ltd.) was used as the substrate, and the film thickness after thermal curing was measured.

(Production of Pre-Cured Intermediate Layer (X1-3))
A pre-cured intermediate layer (X1-3) with a release sheet attached was obtained in the same manner as the pre-cured intermediate layer (X1-1), except that a 50 μm thick polyethylene naphthalate (PEN) film (Q83, Toyobo Co., Ltd.) was used as the substrate, and the film thickness after thermal curing was measured.

(Production of intermediate layer (X2))
An ethylene vinyl acetate copolymer (product name: Evaflex EV150, melting point: 70°C, Mitsui Dow Polychemicals Co., Ltd.) was extruded onto a 25 μm thick polyethylene terephthalate (PET) film (E5100, Toyobo Co., Ltd.) using a single-screw extruder (single-screw extruder, Technovel Co., Ltd.) to a thickness of 125 μm to form an intermediate layer (X2). A release sheet (25 μm thick polyethylene terephthalate (PET) film (E7006, Higashiyama Film Co., Ltd.)) was attached to the formed intermediate layer (X2). Furthermore, the film thickness of the intermediate layer (X2) was measured.

(Production of Pre-thermal Curing Photocurable Pressure-Sensitive Adhesive Layer (Y1-1))
A resin (A2-1) solution containing 30 mass % of resin (A2-1) was obtained by adding ethyl acetate as a dilution solvent to a reaction solution containing the ethylenically unsaturated group-containing (meth)acrylic resin (A2-1) (also simply referred to as resin (A2-1)) obtained in Synthesis Example 2. A pressure-sensitive adhesive composition (Y1) for a photocurable pressure-sensitive adhesive layer was obtained using the resin (A2-1) solution by the method described below.

In a room shielded from active energy rays, the resin (A2-1) solution, Tetrad X as the crosslinking agent (B2), and TPO as the photopolymerization initiator (C) were added to a plastic container in the amounts (parts by mass) shown in Table 4 and stirred to obtain a pressure-sensitive adhesive composition (Y1) for the photocurable pressure-sensitive adhesive layer.

The values for resin (A2) solution in Table 4, i.e., ethylenically unsaturated group-containing (meth)acrylic resin (A2) solution, are the amounts (parts by mass) used for resin (A2) solution containing 30% by mass of resin (A2). The values for resin (cA2) solution in Table 4, i.e., ethylenically unsaturated group-containing (meth)acrylic resin (cA2) solution, are the amounts (parts by mass) used for resin (cA2) solution containing 30% by mass of resin (cA2). The values for crosslinker (B2) and photopolymerization initiator (C) are the amounts (parts by mass) blended per 100 parts by mass of resin (A2) solution or resin (cA2) solution. However, the values for silicon-containing photocurable compound (D) are the amounts (parts by mass) blended per 100 parts by mass of resin (A2).

The adhesive composition (Y1) was coated directly onto a release sheet so that the film thickness after heat curing would be 25 μm, and then heated and dried at 100°C for 2 minutes to form a pre-heat-curing photocurable adhesive layer (Y1-1). A release sheet was then laminated onto the pre-heat-curing photocurable adhesive layer (Y1-1). A 25 μm-thick polyethylene terephthalate (PET) film (E7006, Toyobo Co., Ltd.) was used as the release sheet. The film thickness after heat curing was measured on the photocurable adhesive layer (Y1-1) obtained by curing the pre-heat-curing photocurable adhesive layer (Y1-1) in an oven at 40°C for 3 days.

(Production of Pre-thermal Curing Photocurable Pressure-Sensitive Adhesive Layers (Y2-1) to (Y7-1))
Pressure-sensitive adhesive compositions (Y2) to (Y7) were obtained in the same manner as in the production of pressure-sensitive adhesive composition (Y1), except for using the raw materials and blending amounts shown in Table 4. Pre-heat-cure photo-curable pressure-sensitive adhesive layers (Y2-1) to (Y7-1) with release sheets attached were obtained in the same manner as in the production of pre-heat-cure photo-curable pressure-sensitive adhesive layer (Y1-1), except for using pressure-sensitive adhesive compositions (Y2) to (Y7) instead of pressure-sensitive adhesive composition (Y1), and the film thicknesses after thermal curing were measured.

(Production of Pre-thermal Curing Photocurable Pressure-Sensitive Adhesive Layer (Y1-2))
A pre-thermo-curing photocurable pressure-sensitive adhesive layer (Y1-2) with a release sheet attached was obtained in the same manner as in the production of the pre-thermo-curing photocurable pressure-sensitive adhesive layer (Y1-1), except that the film thickness after thermal curing was 150 μm, and the film thickness after thermal curing was measured.

[Example 1] (Production of protective sheet)
The release sheet was peeled from the pre-curing intermediate layer (X1-1) to which it had been attached, and the release sheet was peeled from one side of the pre-thermo-cure light-curable pressure-sensitive adhesive layer (Y1-1) to which the release sheet had been attached, and the two layers were attached with the exposed surfaces facing each other. Thereafter, the layers were cured in an oven at 40°C for 3 days to crosslink and cure the pre-curing intermediate layer (X1-1) and the pre-thermo-cure light-curable pressure-sensitive adhesive layer (Y1-1), thereby obtaining the protective sheet of Example 1.

[Examples 2 to 4, Comparative Examples 1 to 5]
A protective sheet was obtained in the same manner as in Example 1, except that the pre-curing intermediate layer (X) or the intermediate layer (X) and the pre-thermo-curing photocurable pressure-sensitive adhesive layer (Y) shown in Table 5 was used.

The obtained protective sheets were evaluated for the following items using the methods described below. The results are shown in Table 5.

[Peel strength before UV irradiation]
The protective sheet was cut into a size of 25 mm long and 100 mm wide, and the release sheet on the photocurable pressure-sensitive adhesive layer side was peeled off to expose the photocurable pressure-sensitive adhesive layer. The protective sheet was then attached to a glass plate so that the exposed photocurable pressure-sensitive adhesive layer, i.e., the measurement surface, was in contact with the glass plate, and a 2 kg rubber roller (width: approximately 50 mm) was rolled back and forth once to obtain a sample for measuring peel strength before UV irradiation.

The resulting measurement sample was left for 24 hours in an environment with a temperature of 23°C and humidity of 50%. Then, in accordance with JIS Z 0237:2009, a tensile test was conducted in the 180° direction at a peel rate of 300 mm/min in an environment with a temperature of 23°C and humidity of 50% using a tensile tester (Texture Analyzer, Eiko Seiki Co., Ltd.), and the peel strength (N/25 mm) of the adhesive sheet against the glass plate was measured.

[Peel strength after UV irradiation]
A sample identical to that used to measure peel strength before UV irradiation was prepared and irradiated with ultraviolet (UV) light from the protective sheet side at an irradiation dose of 1000 mJ/ ^cm2 to obtain a sample for measuring peel strength after UV irradiation. For UV irradiation, a conveyor-type ultraviolet irradiation device (Eye Graphics Co., Ltd., 2 kW lamp, 80 W/cm) was used.

The peel strength (N/25 mm) of the adhesive sheet against the glass plate was measured for the obtained measurement sample in the same manner as for "Peel strength before UV irradiation."

[Glue residue]
The sample for measuring peel strength before UV irradiation was heated at 200°C for 2 hours, and then irradiated with ultraviolet (UV) rays from the surface on the protective sheet side at an irradiation dose of 1000 mJ/ ^cm2 , and the protective sheet was peeled off from the glass plate. Adhesive residue was evaluated as "good" if no adhesive residue remained on the glass surface, and "poor" if residue remained.

[Gap filling: protection process]
The release sheet of the protective sheet was peeled off to expose the photocurable adhesive layer. Next, the exposed photocurable adhesive layer and a PCB with bumps (bump diameter φ=20 μm, bump spacing 30 μm, bump height 45, 80, or 100 μm) were attached using a mounter (Hugle Electronics, HS7800) at 40° C. for 5 minutes to obtain a sample for process testing. This sample was observed with an optical microscope from the protective sheet side, and the step filling ability in the protection process was evaluated as "excellent" when the area containing air bubbles was 1% or less of the entire PCB with bumps, "good" when it was more than 1% but less than 10%, and "poor" when it was 10% or more.

[Step filling: dicing process]
The process test sample obtained in the protection process was diced using a blade (SDC200 R100NMR, kerf width: 0.3 mm, blade rotation speed: 28,000 rpm, cutting speed: 30 mm/sec, cut depth: 100 μm, Tokyo Seimitsu Co., Ltd.) to obtain small pieces of process test samples. These were irradiated with UV from the protective sheet side at 50 mJ/ ^cm² to partially cure the photocurable adhesive layer. For UV irradiation, a conveyor-type ultraviolet irradiation device (Eye Graphics Co., Ltd., 2 kW lamp, 80 W/cm²) was used. After UV irradiation, the sample was observed with an optical microscope from the protective sheet side, and the step filling ability in the dicing process was evaluated as "excellent" if the area containing air bubbles was 1% or less of the entire PCB with bumps, "good" if it was greater than 1% but less than 10%, and "poor" if it was 10% or more.

[Gap filling: heating process]
The small process test samples obtained in the dicing process were subjected to a heat treatment for 2 hours at 200° C. After cooling, the samples were observed under an optical microscope from the protective sheet side, and the step filling ability in the heating process was evaluated as "excellent" if the area where air bubbles were mixed in was 1% or less of the entire PCB with bumps, "good" if it was more than 1% but less than 10%, and "poor" if it was 10% or more.

[Metal film adhesion]
A sputtering device SDH Series (product name, ULVAC, Inc.) was used to form a copper film approximately 1.8 μm thick on the small process test samples obtained in the dicing process at a temperature of 60 to 150°C and a pressure of 7 × 10 ^-1 Pa, forming an electromagnetic shield. UV was irradiated from the protective sheet side at 500 mJ/cm ² to cure the photocurable adhesive layer. Then, a die bonder BESTEM-02 (product name, Canon Machinery Inc.) was used to pick up the bumped PCB under conditions of a collet size of 9 mm, 13 pins, and a thrust speed of 20 mm/sec, resulting in a protective sheet having a copper film on a portion of its surface. When the protective sheet was oriented so that the surface having the copper film was facing downwards, the metal film adhesion was evaluated as "excellent" if the area ratio of the copper powder peeled off from the protective sheet was 1% or less, "good" if it was more than 1% but less than 10%, and "poor" if it was 10% or more. The area evaluation was performed using an optical microscope.

In Examples 1 to 4, the step-filling ability, adhesive residue, and metal film adhesion were all "excellent" or "good." In contrast, in Comparative Example 1, which did not have an intermediate layer, the step-filling ability was all "poor." In Comparative Example 2, which did not use an acrylic resin in the intermediate layer, cracks occurred in the intermediate layer and the adhesive residue was "poor." In Comparative Examples 4 and 5, in which the ethylenically unsaturated group was introduced by a compound having an isocyanato group, the adhesive residue was "poor." In Comparative Examples 3 and 5, which did not contain silicon, the metal adhesion was "poor."

12 Base material 14 Intermediate layer 16 Photocurable adhesive layer 18 Release sheet 10 Protective sheet

Claims (17)

A protective sheet having a substrate, and an intermediate layer and a photocurable pressure-sensitive adhesive layer in this order on one main surface of the substrate,
the intermediate layer is a thermosetting product of a resin composition containing an ethylenically unsaturated group-free (meth)acrylic resin (A1) and a crosslinking agent (B1), the ethylenically unsaturated group-free (meth)acrylic resin (A1) having a plurality of functional groups reactive with functional groups possessed by the crosslinking agent (B1);
the photocurable pressure-sensitive adhesive layer is a thermoset product of a pressure-sensitive adhesive composition containing an ethylenically unsaturated group-containing (meth)acrylic resin (A2), a crosslinking agent (B2), and a photopolymerization initiator (C), the ethylenically unsaturated group-containing (meth)acrylic resin (A2) having a plurality of functional groups reactive with functional groups contained in the crosslinking agent (B2);
the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is an adduct of an epoxy group-containing ethylenically unsaturated compound (a2-3) to a (meth)acrylic resin (A2-0) having, as raw material monomers, at least an alkyl (meth)acrylate (a2-1) and a carboxy group-containing ethylenically unsaturated compound (a2-2);
The photocurable pressure-sensitive adhesive layer contains 1,000 to 100,000 ppm by mass of silicon atoms. The protective sheet according to claim 1, wherein a silicon-containing ethylenically unsaturated compound (a2-4) is further used as a raw material monomer for the (meth)acrylic resin (A2-0). The protective sheet according to claim 1, wherein the pressure-sensitive adhesive composition further contains a silicon-containing photocurable compound (D). The protective sheet according to any one of claims 1 to 3, wherein the glass transition temperature (Tg) of the ethylenically unsaturated group-free (meth)acrylic resin (A1) is -80 to 0°C. the ethylenically unsaturated group-free (meth)acrylic resin (A1) is a copolymer containing, as raw material monomers, at least an alkyl (meth)acrylate (a1-1) and a hydroxy group-containing (meth)acrylate (a1-2);
The protective sheet according to any one of claims 1 to 3, wherein the crosslinking agent (B1) is an isocyanate crosslinking agent. The protective sheet according to claim 5, wherein a carboxyl group-containing ethylenically unsaturated compound (a1-3) is further used as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1). The protective sheet according to claim 5, further comprising a (meth)acrylamide compound (a1-4) as a raw material monomer for the ethylenically unsaturated group-free (meth)acrylic resin (A1). The protective sheet according to any one of claims 1 to 3, wherein the acid value of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is 1 to 100 mgKOH/g. The protective sheet according to any one of claims 1 to 3, wherein the ethylenically unsaturated group-containing (meth)acrylic resin (A2) has an ethylenically unsaturated group equivalent of 500 to 5,000 g/mol. The protective sheet according to any one of claims 1 to 3, wherein the glass transition temperature (Tg) of the ethylenically unsaturated group-containing (meth)acrylic resin (A2) is -80 to 0°C. The protective sheet according to any one of claims 1 to 3, wherein the crosslinking agent (B2) is at least one selected from the group consisting of epoxy crosslinking agents and aziridine crosslinking agents. The protective sheet according to any one of claims 1 to 3, wherein the substrate is a resin sheet, and the raw material resin of the resin sheet is at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), polyamide (PA), and polyimide (PI). The protective sheet according to any one of claims 1 to 3, wherein the thickness of the substrate is 5 μm to 300 μm. The thickness of the intermediate layer is 30 to 600 μm,
The photocurable pressure-sensitive adhesive layer has a thickness of 1 to 100 μm,
The protective sheet according to any one of claims 1 to 3, wherein the thickness ratio of the intermediate layer to the photocurable pressure-sensitive adhesive layer (intermediate layer/photocurable pressure-sensitive adhesive layer) is 1 to 50. A protection step of attaching the photocurable pressure-sensitive adhesive layer surface of the protective sheet according to any one of claims 1 to 3 to a surface of the semiconductor device having bump electrodes before processing;
an active energy ray irradiation step of irradiating the protective sheet with active energy rays to photocure the photocurable pressure-sensitive adhesive layer;
A method for manufacturing a semiconductor device having bump electrodes, comprising: a heating step of the unprocessed semiconductor device to which the protective sheet is attached; and a peeling step of peeling the protective sheet from the surface with the bump electrodes. The method for manufacturing a semiconductor device according to claim 15, wherein d/H is 1.00 to 100, where H [μm] is the height of the bump electrode and d [μm] is the total thickness of the intermediate layer and the photocurable adhesive layer. The method for manufacturing a semiconductor device according to claim 15, wherein the maximum temperature reached in the heating step is 80 to 300°C.