WO2025198044A1 - Adhesive sheet, method for manufacturing same, and method for peeling object from adhesive sheet - Google Patents

Abstract

The present invention makes it possible for an object held on an adhesive sheet provided with protrusions and recesses on the surface thereof to be picked up by means of a milder operation.　This adhesive sheet comprises a base material, and an adhesive layer that has protrusions and recesses on the surface thereof. The adhesive layer contains an acrylic acid ester copolymer, and the copolymerization ratio of an energy ray-curable group-containing monomer in the acrylic acid ester copolymer is 20%-50%.

Description

Adhesive sheet, manufacturing method thereof, and method for peeling an object from an adhesive sheet

The present invention relates to an adhesive sheet, a method for manufacturing the same, and a method for peeling an object from the adhesive sheet, and particularly to the manufacture of semiconductor chips.

Adhesive sheets can be used to temporarily hold an object in place. For example, such adhesive sheets can be used to transfer an object to a desired location.

On the other hand, to improve production efficiency, there is also a demand for easier peeling of objects from adhesive sheets. For example, Patent Document 1 discloses a configuration in which an electronic component is attached to a smooth first adhesive film and then irradiated with ultraviolet light, thereby reducing the adhesive strength of the film. In the method described in Patent Document 1, the electronic component is further pressed onto a second adhesive film, and then the first adhesive film is peeled off, thereby transferring the electronic component from the first adhesive film to the second adhesive film. Furthermore, Patent Document 2 discloses an adhesive sheet that is expandable in the plane direction and has an adhesive layer with an uneven surface, configured to facilitate easier peeling of objects.

Japanese Patent Application Laid-Open No. 2020-61529 International Publication No. 2024/063124

Adhesive sheets such as those disclosed in Patent Documents 1 and 2 are desired to have both the ability to hold an object in place and the ease with which the object can be removed from the adhesive sheet. In particular, when handling fragile objects such as thin semiconductor chips, it is necessary to reduce the force required to pick up the object. The adhesive sheets disclosed in Patent Documents 1 and 2 leave room for improvement in terms of ease of removal.

One embodiment of the present invention makes it possible to pick up objects held on an adhesive sheet with an adhesive layer having an uneven surface with a gentler operation.

After extensive research, the inventor discovered that by appropriately designing the adhesive layer of the adhesive sheet, it becomes easier to pick up objects from the adhesive sheet, thereby solving the above-mentioned problem. After further research, the inventors have completed the present invention.

That is, embodiments of the present invention relate to the following [1] to [14].
[1] An adhesive sheet comprising a substrate and an adhesive layer having an uneven surface, wherein the adhesive layer contains an acrylic acid ester copolymer, and the copolymerization rate of an energy ray-curable group-containing monomer in the acrylic acid ester copolymer is 20% or more and 50% or less.
[2] The pressure-sensitive adhesive sheet described in [1], wherein the acrylic acid ester copolymer has the energy ray-curable group-containing monomer which is a (meth)acrylic acid ester monomer, and a (meth)acrylic acid ester monomer crosslinked with another (meth)acrylic acid ester monomer.
[3] The pressure-sensitive adhesive sheet according to [2], wherein the energy ray-curable group-containing monomer is a (meth)acrylic acid ester monomer having a carbon-carbon double bond-containing group in a side chain via a hydroxy group.
[4] The pressure-sensitive adhesive sheet according to any one of [2] to [3], wherein the (meth)acrylic acid ester monomer crosslinked with the other (meth)acrylic acid ester monomer is crosslinked with the other (meth)acrylic acid ester monomer via a hydroxy group.
[5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the content of the acrylic ester copolymer relative to the total amount of components constituting the pressure-sensitive adhesive layer is 70 to 100 mass%.
[6] The pressure-sensitive adhesive sheet according to any one of [1] to [5], wherein the acrylic acid ester copolymer has a mass average molecular weight of 10,000 or more.
[7] The pressure-sensitive adhesive sheet according to any one of [1] to [6], wherein the pressure-sensitive adhesive sheet is expandable in the planar direction.
[8] The pressure-sensitive adhesive sheet according to any one of [1] to [7], wherein the height of the convex portions of the pressure-sensitive adhesive layer is 1 μm or more.
[9] The adhesive sheet according to any one of [1] to [8], wherein the adhesive layer has a plurality of convex portions spaced apart from each other and bounded by concave portions, and the pitch of the plurality of convex portions is 1 μm or more and 100 μm or less.
[10] The pressure-sensitive adhesive sheet according to any one of [1] to [9], wherein the pressure-sensitive adhesive layer has a plurality of convex portions, and the height of the plurality of convex portions is uniform.
[11] The pressure-sensitive adhesive sheet according to any one of [1] to [10], further comprising a release layer having an uneven surface complementary to the uneven surface of the pressure-sensitive adhesive layer.
[12] A method for producing a pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer having an uneven surface, the method comprising: a preparation step of preparing a pressure-sensitive adhesive composition, the pressure-sensitive adhesive composition comprising a step of introducing an energy ray-curable group into an acrylic acid ester copolymer having a monomer capable of introducing an energy ray-curable group by reacting the monomer with an energy ray-curable group-introducing agent, and a formation step of forming the pressure-sensitive adhesive layer on the substrate using the pressure-sensitive adhesive composition, wherein the copolymerization rate of the monomer capable of introducing an energy ray-curable group in the acrylic acid ester copolymer is ^RA %, and in the preparation step, the energy ray-curable group-introducing agent is reacted in an amount equivalent to ^RB % with the monomer capable of introducing an energy ray-curable group, and the product of ^RA % and ^RB % is 23.0% or more and 50.0% or less.
[13] The production method according to [12], wherein the (meth)acrylic acid ester monomer capable of introducing an energy ray-curable group is a (meth)acrylic acid ester monomer having a hydroxy group, and the energy ray-curable group introducing agent is an isocyanate compound having a carbon-carbon double bond-containing group.
[14] A method for peeling an object from an adhesive sheet according to any one of [1] to [11], in which the object is held on an adhesive layer, the peeling method comprising an irradiation step of irradiating the adhesive layer with energy rays, an expansion step of expanding the adhesive sheet in the planar direction, and a peeling step of peeling the object from the adhesive layer of the adhesive sheet.

One embodiment of the present invention makes it possible to pick up objects held on an adhesive sheet with an adhesive layer having an uneven surface with a gentler operation.

Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals.

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 4 is a cross-sectional view showing an example of the unevenness of the adhesive layer before expansion. FIG. 10 is a cross-sectional view showing an example of the unevenness of the adhesive layer after expansion. FIG. 10 is a top view showing an example of the unevenness of the adhesive layer before expansion. FIG. 10 is a top view showing an example of the unevenness of the adhesive layer after expansion. FIG. 10 is a top view showing another example of the unevenness of the adhesive layer. FIG. 3 is a cross-sectional view showing an example of the unevenness of the adhesive layer. FIG. 3 is a cross-sectional view showing an example of the unevenness of the adhesive layer. FIG. 3 is a cross-sectional view showing an example of the unevenness of the adhesive layer. 10A to 10C are diagrams illustrating a method for expanding an adhesive sheet. 10A to 10C are diagrams illustrating a method for expanding an adhesive sheet. 3 is a flowchart of a method for manufacturing a pressure-sensitive adhesive sheet according to an embodiment. 1 is a flowchart of a peeling method according to an embodiment.

The following embodiments are described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the multiple features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numbers are used for identical or similar components, and duplicate descriptions will be omitted.

(definition)
In this specification, the mass average molecular weight (Mw) and number average molecular weight (Mn) are values calculated as standard polystyrene as measured by size exclusion chromatography, specifically, values measured in accordance with JIS K7252-1: 2016. Furthermore, in this specification, "(meth)acrylic acid" is a term that refers to both "acrylic acid" and "methacrylic acid," and the same applies to other similar terms.

In this specification, when one or more lower limits and one or more upper limits of a numerical range (e.g., a range of content, etc.) are described, it can be understood that any combination of lower and upper limits therein is described. For example, a description such as "preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and preferably 9 or less, more preferably 8 or less, even more preferably 7 or less" clearly means that the numerical range may be any of 1 or more and 9 or less, 1 or more and 8 or less, 1 or more and 7 or less, 2 or more and 9 or less, 2 or more and 8 or less, 2 or more and 7 or less, 3 or more and 9 or less, 3 or more and 8 or less, and 3 or more and 7 or less. Furthermore, in this specification, parts by mass and % by mass indicate proportions based on the mass of the solid content, unless otherwise specified.

(Configuration of adhesive sheet)
An adhesive sheet according to one embodiment of the present invention comprises a substrate 120 and an adhesive layer 110 having an uneven surface. The adhesive sheet can be used as a transfer sheet for temporarily holding an object and transferring it to a destination. For example, the adhesive sheet can be used to receive an object held on another holding substrate, temporarily hold the object, and transfer the object to a desired position on the destination. The substrate 120 can support the adhesive layer 110. The configuration of such an adhesive sheet will be described below with reference to FIG. 1, which is a schematic diagram of an adhesive sheet according to one embodiment.

(Base material)
The substrate 120 functions as a support for supporting the adhesive layer 110. The substrate 120 is located on the surface of the adhesive layer 110 opposite to the surface having the irregularities.

In one embodiment, the adhesive sheet is expandable in the planar direction. From this perspective, a flexible substrate can be used as the substrate 120. Furthermore, using a flexible substrate as the substrate 120 can improve cushioning when holding an object, facilitate stacking of the adhesive sheet, or allow the adhesive sheet to be in a roll form. For example, a resin film can be used as the substrate 120. A resin film is a film that uses a resin-based material as its main material, and may be made of a resin material, or may contain additives in addition to the resin material. The resin film may be laser light transparent.

Specific examples of resin films include polyethylene films such as low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, and high-density polyethylene (HDPE) film; polyolefin films such as polypropylene film, polybutene film, polybutadiene film, poly(4-methyl-1-pentene) film, ethylene-norbornene copolymer film, and norbornene resin film; ethylene copolymer films such as ethylene-vinyl acetate copolymer film, ethylene-(meth)acrylic acid copolymer film, and ethylene-(meth)acrylic acid ester copolymer film; polyvinyl chloride films such as polyvinyl chloride film and vinyl chloride copolymer film; polyester films such as polyethylene terephthalate film and polybutylene terephthalate film; polyurethane film; polyimide film; polystyrene film; polycarbonate film; and fluororesin films. Films containing a mixture of two or more materials, crosslinked films in which the resins forming these films are crosslinked, and modified films such as ionomer films may also be used. Furthermore, the substrate 120 may be a laminate film in which two or more resin films are laminated.

In order to facilitate expansion of the adhesive sheet, the substrate 120 is preferably a polyolefin film or a vinyl chloride copolymer film. Examples of polyolefin films include polyethylene film, polypropylene film, and copolymers containing unsubstituted olefins such as ethylene or propylene as structural units, such as ethylene copolymers containing ethylene-methacrylic acid copolymer (EMAA). Examples of vinyl chloride copolymer films include vinyl chloride-vinylidene chloride copolymer film, vinyl chloride-vinyl acetate copolymer film, and vinyl chloride-ethylene copolymer film. The form of such copolymers is not particularly limited and may be any of block copolymers, random copolymers, alternating copolymers, and graft copolymers. These films may also contain other resin components or additives.

The thickness of the substrate 120 is not particularly limited, but from the viewpoint of achieving both supportability and roll winding properties, it is preferably 10 μm or more, more preferably 25 μm or more, and even more preferably 40 μm or more, while it is preferably 500 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, even more preferably 150 μm or less, even more preferably 120 μm or less, and particularly preferably 90 μm or less.

To facilitate uniform expansion of the adhesive sheet, the tensile modulus of the substrate 120 is preferably 50 MPa or more, more preferably 80 MPa or more, even more preferably 120 MPa or more, and preferably 2500 MPa or less, more preferably 1000 MPa or less, even more preferably 500 MPa or less. In this specification, the tensile modulus is measured in accordance with JIS K7161-1:2014.

Similarly, to facilitate expansion of the adhesive sheet, the breaking elongation of the substrate 120 is preferably 105% or more, more preferably 110% or more, and even more preferably 115% or more. In this specification, breaking elongation is measured in accordance with JIS K 7127:1999.

(adhesive layer)
The adhesive layer 110 is a layer having adhesive properties. As described above, the adhesive layer 110 has an uneven surface. The adhesive sheet may have two or more adhesive layers 110. For example, the adhesive sheet may have a laminate of one type or two or more types of adhesive layers 110.

The following describes example compositions of the adhesive layer 110. However, the composition of the adhesive layer 110 is not limited to those shown below.

(resin)
The adhesive layer 110 may contain a resin. The adhesive layer 110 may contain one type of resin, or two or more types of resins. Examples of resins contained in the adhesive layer 110 include rubber-based resins such as polyisobutylene-based resins, polybutadiene-based resins, and styrene-butadiene-based resins, acrylic-based resins, urethane-based resins, polyester-based resins, olefin-based resins, silicone-based resins, and polyvinyl ether-based resins. The adhesive layer may be heat-resistant, and examples of materials for the adhesive layer 110 that have such heat resistance include polyimide-based resins and silicone-based resins. The adhesive layer 110 may contain a copolymer having two or more types of structural units. The form of such a copolymer is not particularly limited, and may be any of a block copolymer, a random copolymer, an alternating copolymer, and a graft copolymer.

The resin contained in the adhesive layer 110 is preferably an adhesive resin that exhibits adhesive properties by itself. In one embodiment, the resin is a polymer having a mass average molecular weight (Mw) of 10,000 or more. From the viewpoint of improving holding power, the mass average molecular weight (Mw) of the resin is preferably 10,000 or more, more preferably 70,000 or more, and even more preferably 140,000 or more. From the viewpoint of maintaining the storage modulus at a predetermined value or less, it is preferably 2,000,000 or less, and more preferably 1,200,000 or less. From the viewpoint of improving holding power, the number average molecular weight (Mn) of the resin is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more. From the viewpoint of maintaining the storage modulus at a predetermined value or less, it is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,200,000 or less. In this specification, the mass average molecular weight (Mw) and number average molecular weight (Mn) of the adhesive layer 110 containing an energy ray-reactive resin refer to the mass average molecular weight (Mw) and number average molecular weight (Mn) before the crosslinking reaction due to energy ray irradiation, unless otherwise specified.

Furthermore, from the viewpoint of improving the holding power of the adhesive layer 110, the glass transition temperature (Tg) of the resin is preferably -75°C or higher, more preferably -70°C or higher, and preferably 5°C or lower, more preferably -20°C or lower. If the resin has two or more types of structural units, the glass transition temperature (Tg) of the resin can be calculated using the Fox formula. The Tg of the monomer from which the structural units are derived can be calculated using the value listed in the Polymer Data Handbook or the Adhesive Handbook.

The amount of resin contained in adhesive layer 110 relative to the total amount of components constituting adhesive layer 110 can be set appropriately depending on the desired adhesive strength of adhesive layer 110, but is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and is preferably 99.99% by mass or less, more preferably 99.95% by mass or less, even more preferably 99.90% by mass or less, even more preferably 99.80% by mass or less, even more preferably 99.50% by mass or less.

In one embodiment, the resin contained in the adhesive layer 110 may include a thermoplastic resin. When a thermoplastic resin is used, it becomes easy to form irregularities in the adhesive layer 110 by heating and softening the resin, and it also becomes easy to maintain the irregular shape formed by cooling. Examples of thermoplastic resins include rubber-based resins, acrylic-based resins, urethane-based resins, and olefin-based resins. Examples include polybutadiene-based thermoplastic elastomers that use butadiene as a monomer, styrene-based thermoplastic elastomers that use styrene as a monomer, and acrylic-based thermoplastic elastomers that use (meth)acrylic acid or a (meth)acrylic acid ester as a monomer.

In one embodiment, the adhesive layer 110 is energy ray reactive. For example, the adhesive layer 110 may contain an energy ray reactive component in addition to a resin. Alternatively, the adhesive layer 110 may contain an energy ray reactive resin. In this specification, the adhesive layer 110 being energy ray reactive means that the storage modulus of the adhesive layer 110 is improved by irradiating it with energy rays. The type of energy ray is not particularly limited, and examples include ultraviolet rays, electron beams, and ionizing radiation. Ultraviolet rays are preferred as the energy ray, and therefore the adhesive layer 110 is preferably ultraviolet ray reactive.

The energy ray-reactive component can be a compound into which a polymerizable functional group has been introduced. A polymerizable functional group is a functional group that crosslinks upon irradiation with energy rays. Examples of such polymerizable functional groups include multiple bond-containing groups, oxetanyl groups, and epoxy groups. Examples of multiple bond-containing groups include alkenyl groups such as vinyl groups and allyl groups, and double bond-containing groups such as (meth)acryloyl groups. Crosslinking of such polymerizable functional groups proceeds in the presence of an appropriate polymerization initiator or crosslinking agent.

The energy ray-reactive component may be a difunctional or polyfunctional monomer into which a polymerizable functional group such as those described above has been introduced. Examples of such monomers include polyfunctional (meth)acrylates such as difunctional (meth)acrylates. Specific examples of polyfunctional (meth)acrylates include cycloalkyl di(meth)acrylates such as tricyclodecane dimethanol diacrylate.

An energy ray reactive resin refers to a resin whose storage modulus improves when irradiated with energy rays. An energy ray reactive resin may be an energy ray curable resin. Note that in this specification, resins whose storage modulus has already improved through irradiation with energy rays and whose storage modulus does not improve even when further irradiated with energy rays (for example, ultraviolet curable resins after curing has been completed) are not included in the term energy ray reactive resin.

The energy ray reactive resin is, for example, a polymer having an energy ray curable group. This polymer may be a copolymer. Furthermore, this polymer may have a side chain having an energy ray curable group. Examples of the energy ray curable group include the above-mentioned multiple bond-containing groups, oxetanyl groups, and epoxy groups. Preferred examples of the energy ray curable group include alkenyl groups such as vinyl groups and allyl groups, and carbon-carbon double bond-containing groups such as (meth)acryloyl groups. By irradiating such an energy ray reactive resin with energy rays, the energy ray curable groups of the polymer can be crosslinked to each other. In one embodiment, the energy ray curable group is an ultraviolet ray curable group.

In this way, when the adhesive layer 110 contains an energy ray reactive resin, the storage modulus of the adhesive layer 110 is more likely to improve when irradiated with energy rays, compared to when the adhesive layer 110 contains a combination of a resin and an energy ray reactive component. It also becomes easier to achieve both the adhesive layer 110's ability to hold an object before energy ray irradiation and the adhesive layer 110's ability to easily peel an object after energy ray irradiation. Furthermore, by having the adhesive layer 110 contain an energy ray reactive resin, it becomes easier to maintain high adhesive strength before energy ray irradiation while improving the ability of the adhesive layer 110 to retain the uneven shape.

In one embodiment, the main component of the adhesive layer 110 is an energy ray reactive resin. From the viewpoint of reducing adhesive strength after curing, the content of the polymer having an energy ray curable group relative to the total amount of components constituting the adhesive layer 110 is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and is 100% by mass or less, more preferably 99% by mass or more, and even more preferably 98% by mass or less.

(Energy ray reactive acrylate copolymer)
In one embodiment, the adhesive layer 110 includes an acrylic acid ester copolymer. The acrylic acid ester copolymer is a copolymer having a (meth)acrylic acid ester as a structural unit. This acrylic acid ester copolymer may have energy ray reactivity.

(Meth)acrylic acid esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n- (Meth)acrylic acid acrylates in which the alkyl group constituting the alkyl ester has a chain structure having 1 to 18 carbon atoms, such as octyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, myristyl (meth)acrylate, pentadecyl (meth)acrylate, palmityl (meth)acrylate, heptadecyl (meth)acrylate, and stearyl (meth)acrylate. (meth)acrylic acid cycloalkenyl esters such as dicyclopentenyl (meth)acrylate; (meth)acrylic acid cycloalkenyloxyalkyl esters such as dicyclopentenyloxyethyl (meth)acrylate; imide (meth)acrylate; glycidyl group-containing (meth)acrylic acid esters such as glycidyl (meth)acrylate; hydroxy group-containing (meth)acrylic acid esters such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate; and substituted amino group-containing (meth)acrylic acid esters such as N-methylaminoethyl (meth)acrylate. Here, "substituted amino group" refers to a group having a structure in which one or two hydrogen atoms of an amino group have been substituted with a group other than a hydrogen atom. The acrylic acid ester copolymer may be a copolymer of an acrylic acid ester and a methacrylic acid ester.

An acrylic acid ester copolymer having energy ray reactivity can have an energy ray-curable group-containing monomer as a constituent unit. For example, the acrylic acid ester copolymer may have a side chain having an energy ray-curable group as described above. An example of an energy ray-curable group-containing monomer is a (meth)acrylic acid ester monomer having an energy ray-curable group. An example of a (meth)acrylic acid ester monomer having an energy ray-curable group is a (meth)acrylic acid ester monomer having an energy ray-curable group, such as a carbon-carbon double bond-containing group, in the side chain via a hydroxy group. For example, the acrylic acid ester copolymer may be a copolymer of an acrylic acid ester having an energy ray-curable group, an acrylic acid ester not having an energy ray-curable group, and a methacrylic acid ester not having an energy ray-curable group.

The acrylic acid ester copolymer may be a cross-linked polymer. As described above, the adhesive layer 110 has an uneven surface. For this reason, it is desirable that the adhesive layer 110 has a storage modulus that is sufficient to maintain the uneven surface even before energy beam irradiation. By using a cross-linked polymer as the acrylic acid ester copolymer, it becomes easier to maintain the uneven surface of the adhesive layer 110.

For example, an acrylic acid ester copolymer may have, as a structural unit, a monomer crosslinked with another monomer. Specifically, a (meth)acrylic acid ester monomer may be crosslinked with another (meth)acrylic acid ester monomer via a hydroxy group. Furthermore, two (meth)acrylic acid ester monomers contained in an acrylic acid ester copolymer may be urethane-crosslinked with each other. Thus, an acrylic acid ester copolymer may contain, in addition to an energy ray-curable group-containing (meth)acrylic acid ester monomer, a (meth)acrylic acid ester monomer crosslinked with another (meth)acrylic acid ester monomer. A preferred example of an acrylic acid ester copolymer is a copolymer of an acrylic acid ester having an energy ray-curable group, an acrylic acid ester crosslinked with another acrylic acid ester monomer, and an alkyl (meth)acrylate ester.

The acrylic acid ester copolymer may contain (meth)acrylic acid ester monomers other than the energy ray-curable group-containing monomer and the monomer crosslinked with other monomers. The acrylic acid ester copolymer may also contain monomers other than (meth)acrylic acid ester. For example, the acrylic acid ester copolymer may have, in addition to (meth)acrylic acid ester, one or more monomers selected from itaconic acid, vinyl acetate, acrylonitrile, styrene, N-methylolacrylamide, etc. as structural units. The combination and ratio of monomers constituting the acrylic acid ester copolymer can be selected depending on the desired properties of the adhesive layer 110.

An acrylic ester copolymer having reactivity to energy rays can be prepared by a polymerization reaction using a monomer containing an energy ray-curable group. Alternatively, an acrylic ester copolymer having reactivity to energy rays can be prepared by modifying the acrylic ester copolymer to introduce an energy ray-curable group.

For example, the material to be modified can be an acrylic acid ester copolymer having a monomer into which an energy ray-curable group can be introduced. The (meth)acrylic acid ester monomer into which an energy ray-curable group can be introduced can be, for example, a (meth)acrylic acid ester monomer having a specific functional group such as a hydroxy group. In one embodiment, the acrylic acid ester copolymer to be modified contains a hydroxy group-containing acrylic acid ester as a constituent unit.

By reacting such an acrylic acid ester copolymer with an energy ray-curable group-introducing agent, it is possible to introduce an energy ray-curable group into the (meth)acrylic acid ester monomer. The energy ray-curable group-introducing agent can be a compound having an energy ray-curable group and a functional group that forms a bond with a specific functional group. For example, the energy ray-curable group-introducing agent can be a compound having an isocyanate group and an energy ray-curable group, such as 2-isocyanatoethyl methacrylate. By using such a compound, it is possible to introduce an energy ray-curable group into the (meth)acrylic acid ester monomer via the hydroxy group possessed by the (meth)acrylic acid ester monomer.

Here, the copolymerization rate of the monomer capable of introducing an energy ray-curable group in the acrylic ester copolymer is defined as ^RA %. Here, the copolymerization rate indicates the molar ratio of the monomer capable of introducing an energy ray-curable group to all monomers contained in the acrylic ester copolymer. Furthermore, the equivalent of the energy ray-curable group-introducing agent relative to the monomer capable of introducing an energy ray-curable group is defined as ^RB %. Here, the equivalent indicates the molar ratio of the energy ray-curable group-introducing agent to be added relative to the substituent contained in the acrylic ester copolymer that reacts with the energy ray-curable group-introducing agent. When the monomer capable of introducing an energy ray-curable group has one hydroxy group that reacts with the energy ray-curable group-introducing agent, ^RB % indicates the molar ratio of the energy ray-curable group-introducing agent to be added relative to the monomer having a hydroxy group contained in the acrylic ester copolymer. However, in this specification, the upper limit of ^RB is 100%. That is, when an excess amount of the energy ray-curable group-introducing agent is used relative to the amount of the monomer capable of introducing an energy ray-curable group, R 2 ^B is defined as 100%.

The product of ^RA % and ^RB % indicates the copolymerization rate of the monomer into which the energy ray curable group has been introduced in the acrylic acid ester copolymer when the monomer capable of introducing an energy ray curable group and the energy ray curable group introducing agent have completely reacted. In one embodiment, from the viewpoint of sufficiently reducing the object retention force in the adhesive layer 110 after energy ray irradiation, the product of RA% and ^{RB %} is 23.0% or more, more preferably 24.0% or more, and even more preferably 25.0% or more. On the other hand, in one embodiment, from the viewpoint of suppressing the positional displacement of the object in the adhesive layer 110 after energy ray irradiation, the product of ^RA % and ^RB % is 50.0% or less, more preferably 40.0% or less, even more preferably 30.0% or less, and particularly preferably 27.0% or less.

Here, from the viewpoint of sufficiently reducing the object retention force of the adhesive layer 110 after energy ray irradiation, ^RA % is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more. On the other hand, from the viewpoint of sufficiently increasing the object retention force of the adhesive layer 110 before energy ray irradiation, ^RA % is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less.

Furthermore, from the viewpoint of sufficiently reducing the object-retaining force of the adhesive layer 110 after energy ray irradiation, R ^B % is preferably 50% or more, more preferably 65% or more, and even more preferably 75% or more. On the other hand, R ^B % is 100% or less.

Furthermore, cross-linked acrylic acid ester copolymers can be obtained by modifying the acrylic acid ester copolymer to cross-link its monomers. For example, the material to be modified can be an acrylic acid ester copolymer having a monomer capable of reacting with a cross-linking agent. The monomer capable of reacting with the cross-linking agent can be, for example, a (meth)acrylic acid ester monomer having a specific functional group such as a hydroxy group. By reacting such an acrylic acid ester copolymer with a cross-linking agent, the (meth)acrylic acid ester monomers can be cross-linked to each other.

As a crosslinking agent, a compound having two or more functional groups that form bonds with specific functional groups can be used. Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, and metal chelate-based crosslinking agents. A thermal crosslinking agent that induces a crosslinking reaction by heat treatment may also be used as a crosslinking agent. These crosslinking agents may be used alone or in combination of two or more types.

Among these crosslinking agents, isocyanate-based crosslinking agents are preferred from the viewpoints of increasing cohesive strength and maintaining the uneven shape, as well as ease of availability. By using an isocyanate-based crosslinking agent, it is possible to crosslink the hydroxy groups in the (meth)acrylic acid ester monomers. Examples of the isocyanate crosslinking agent include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate; alicyclic polyisocyanates such as dicyclohexylmethane-4,4'-diisocyanate, bicycloheptane triisocyanate, cyclopentylene diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, methylenebis(cyclohexyl isocyanate), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, and hydrogenated xylylene diisocyanate; and polyvalent isocyanate compounds such as acyclic aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. Further examples of isocyanate-based crosslinking agents include trimethylolpropane adduct-type modified products of the polyisocyanate compounds, biuret-type modified products obtained by reacting them with water, and isocyanurate-type modified products containing an isocyanurate ring, such as isocyanurate-type hexamethylene diisocyanate.

The amount of crosslinking agent used in this case is not particularly limited, and may be, for example, an excess amount relative to the monomer capable of reacting with the crosslinking agent contained in the copolymer before modification. In one embodiment, the amount of isocyanate-based crosslinking agent per 100 parts by mass of the copolymer before modification is preferably 1.5 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 2.5 parts by mass or more, from the viewpoint of maintaining the uneven shape of the surface of the adhesive layer 110. Furthermore, from the viewpoint of increasing the object retention force of the adhesive layer 110, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

Furthermore, an energy ray-reactive and crosslinked acrylic ester copolymer can be prepared by modifying an acrylic ester copolymer having a monomer into which an energy ray-curable group can be introduced and a monomer capable of reacting with a crosslinking agent. Also, an energy ray-reactive and crosslinked acrylic ester copolymer can be prepared by modifying an acrylic ester copolymer having a monomer into which an energy ray-curable group can be introduced and a monomer capable of reacting with a crosslinking agent. In this case, first, an acrylic ester copolymer having a monomer into which an energy ray-curable group has been introduced and a monomer capable of reacting with a crosslinking agent can be prepared by first modifying the acrylic ester copolymer to introduce an energy ray-curable group into some of the monomers contained in the unmodified copolymer. Furthermore, an energy ray-reactive and crosslinked acrylic ester copolymer can be prepared by further modifying the acrylic ester copolymer to crosslink the other part of the monomers.

For example, such an acrylic ester copolymer can be prepared by modifying an acrylic ester copolymer having a monomer with a hydroxy group. First, some of the hydroxy groups can be modified using an isocyanate compound having a carbon-carbon double bond-containing group in an equivalent amount less than the hydroxy groups in the copolymer before modification. Furthermore, another portion of the hydroxy groups can be urethane-crosslinked using an isocyanate-based crosslinking agent such as a polyisocyanate compound. In this case, in the modified copolymer, the hydroxy groups in some of the monomers have been modified to have a carbon-carbon double bond-containing group via a urethane bond. Furthermore, in the modified copolymer, the hydroxy groups in the other portion of the monomers have been modified to form urethane crosslinks.

In this case, the equivalent R ^B % of the energy ray-curable group introducing agent relative to the monomer capable of introducing an energy ray-curable group is preferably 50% or more, more preferably 65% or more, and even more preferably 75% or more from the viewpoint of sufficiently reducing the object retention force of the adhesive layer 110 after energy ray irradiation. On the other hand, from the viewpoint of easily maintaining the uneven shape of the adhesive layer 110 before energy ray irradiation, it is preferably 99% or less, more preferably 96% or less, and even more preferably 93% or less.

As described above, in one embodiment, the adhesive layer 110 includes an acrylic ester copolymer. In the acrylic ester copolymer according to one embodiment, the copolymerization rate of the energy ray-curable group-containing monomer is 23.0% or more and 50.0% or less. In this specification, the copolymerization rate of the energy ray-curable group-containing monomer in the acrylic ester copolymer is defined based on the raw material composition, and is specifically represented by the product of the above-mentioned ^RA % and ^RB %. The preferred range of the copolymerization rate of the energy ray-curable group-containing monomer in the acrylic ester copolymer is the same as the preferred range of the product of ^RA % and ^RB % described above.

It is possible that the reaction between the monomer capable of introducing an energy ray-curable group and the energy ray-curable group-introducing agent may not proceed completely, resulting in unreacted energy ray-curable group-introducing agent being contained in the adhesive layer 110. In one embodiment, the actual copolymerization rate of the energy ray-curable group-containing monomer in the acrylic ester copolymer is 23.0% or more and 50.0% or less. In one embodiment, from the viewpoint of sufficiently reducing the object-retaining force of the adhesive layer 110 after energy ray irradiation, the actual copolymerization rate is more preferably 24.0% or more, and even more preferably 25.0% or more. On the other hand, from the viewpoint of suppressing object displacement in the adhesive layer 110 after energy ray irradiation, the actual copolymerization rate is more preferably 40.0% or less, even more preferably 30.0% or less, and particularly preferably 27.0% or less. Here, the actual copolymerization rate of the energy ray-curable group-containing monomer in the acrylic ester copolymer refers to the molar ratio of the monomer having an energy ray-curable group to all the monomers contained in the acrylic ester copolymer. Such actual copolymerization ratio can be measured, for example, by NMR or pyrolysis GC/MS.

From the viewpoint of improving holding power, the mass average molecular weight (Mw) of the acrylic acid ester copolymer is preferably 10,000 or more, more preferably 70,000 or more, and even more preferably 140,000 or more. Furthermore, from the viewpoint of keeping the storage modulus below a predetermined value, it is preferably 2,000,000 or less, and even more preferably 1,200,000 or less. Furthermore, from the viewpoint of improving holding power, the number average molecular weight (Mn) of the resin is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more. Furthermore, from the viewpoint of keeping the storage modulus below a predetermined value, it is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,200,000 or less.

The content of the acrylic acid ester copolymer relative to the total amount of components constituting the adhesive layer 110 is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of sufficiently reducing the object retention force of the adhesive layer 110 after energy ray irradiation. On the other hand, the content of the acrylic acid ester copolymer relative to the total amount of components constituting the adhesive layer 110 is 100% by mass or less, and may be 99% by mass or more, or 98% by mass or less.

(Other components of the adhesive layer)
The adhesive layer 110 may contain components other than resin, for example, the adhesive layer 110 may contain one or more of a crosslinking agent, a photopolymerization initiator, an antioxidant, and other additives.

Examples of crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, and metal chelate-based crosslinking agents. These crosslinking agents may be used alone or in combination of two or more. The crosslinking agent can be selected according to the resin contained in the adhesive layer 110. The crosslinking agent may be a crosslinking agent for the resin contained in the adhesive layer 110. For example, the crosslinking agent may be a crosslinking agent for an acrylic resin. Note that the crosslinking agent referred to here refers to unreacted crosslinking agent contained in the adhesive layer 110. Examples of crosslinking agents that can be used include those described above.

The adhesive layer 110 may contain one type of crosslinking agent, or may contain two or more types of crosslinking agents. From the viewpoint of properly carrying out the crosslinking reaction, the content of the crosslinking agent in the adhesive layer 110 is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

The photopolymerization initiator initiates a crosslinking reaction in response to irradiation with energy rays. If the adhesive layer 110 contains an energy reactive resin, the adhesive layer 110 can further contain a photopolymerization initiator, allowing the crosslinking reaction to proceed even with the application of relatively low energy.

Examples of photopolymerization initiators include 1-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzyl phenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, 8-chloroanthraquinone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

The adhesive layer 110 may contain one type of polymerization initiator, or may contain two or more types of polymerization initiators. The content of the photopolymerization initiator in the adhesive layer 110 is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less.

Examples of antioxidants include phenol-based compounds such as hindered phenol-based compounds, aromatic amine-based compounds, sulfur-based compounds, and phosphorus-based compounds such as phosphate ester compounds.

Other additives that may be contained in the adhesive layer 110 include, but are not limited to, ultraviolet absorbers such as benzotriazole-based compounds, oxazolic acid amide compounds, or benzophenone-based compounds; light stabilizers such as hindered amine-based, benzophenone-based, or benzotriazole-based; resin stabilizers such as imidazole-based resin stabilizers, dithiocarbamate-based resin stabilizers, phosphorus-based resin stabilizers, or sulfur ester-based resin stabilizers; fillers, pigments, extenders, and softeners.

When the adhesive layer 110 contains these additives, the content of the additives in the adhesive layer 110 is preferably 0.0001% by mass or more, more preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, even more preferably 1% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

(Shape of adhesive layer)
The surface of the adhesive layer 110 according to this embodiment has projections and depressions. In one embodiment, the adhesive layer 110 has a plurality of projections on its surface that are spaced apart and bounded by depressions. Each of the projections may be spaced apart by a depression that is continuous across the entire adhesive layer 110.

Figures 2A and 2B are side views showing the shape of adhesive layer 110, and Figures 3A to 3C are top views showing the shape of adhesive layer 110. Figures 2A and 3A show an example of adhesive layer 110 before expansion, and Figures 2B and 3B show an example of adhesive layer 110' after expansion. Also, while Figures 2A and 2B depict object 140 held by convex portions 111 of adhesive layer 110, Figures 3A to 3C omit the object 140 held by convex portions 111.

As shown in Figures 2A and 3A, the convex portions 111 may be regularly arranged on the surface of the adhesive layer 110. Regularly arranged convex portions means that the convex portions are lined up in a straight line at regular intervals. On the other hand, the convex portions 111 may be arranged so that the intervals between them vary regularly. For example, the intervals between convex portions may be short in the center of the adhesive sheet and long in the periphery of the adhesive sheet. Furthermore, the convex portions may be arranged irregularly.

Figure 3C is a top view showing another shape of the adhesive layer 110. As shown in Figure 3C, stripe-shaped protrusions 111 may be provided on the surface of the adhesive layer 110. In Figure 3C, line-shaped protrusions 111 having a constant width are arranged at regular intervals. The width or interval of these line-shaped protrusions 111 may vary regularly, or the line-shaped protrusions 111 may be arranged irregularly.

The pitch P of the convex portions 111 before expansion is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 15 μm or more, from the viewpoint of adjusting the holding force. On the other hand, from the viewpoint of increasing the contact area between the adhesive layer 110 and the object and thereby increasing the holding force, this pitch P is preferably 100 μm or less, more preferably 75 μm or less, even more preferably 50 μm or less, even more preferably 35 μm or less, and even more preferably 25 μm or less. Here, the pitch P of the convex portions 111 refers to the distance between the center point of one arbitrarily selected convex portion 111 and the center point of another convex portion 111 closest to that convex portion 111. For example, in the case of Figure 2A, the pitch P of the convex portions 111 represents the distance between the center point of the convex portion 111 on a straight line on which the convex portions 111 are arranged at regular intervals and the center point of another convex portion 111 closest to that convex portion 111. When the convex portions 111 are arranged on multiple straight lines, the pitch P represents the distance between the center points of the convex portions on the line on which the convex portions 111 are arranged at the shortest pitch. In this specification, the spacing between the convex portions 111 means the spacing between the centers of the convex portions.

The specific shape of the convex portion 111 is not particularly limited. For example, the convex portion 111 may have a pillar shape. Specific examples include a cylindrical, prismatic, conical, pyramidal, spherical, or hemispherical shape. As described above, the convex portion 111 may extend in a line shape, or may extend in a curved shape such as a wave shape. Furthermore, these convex portions 111 may be tapered or inverted tapered.

Figure 4A shows a cross-sectional view of an adhesive layer 110 according to one embodiment, taken perpendicular to the surface of the adhesive layer 110 and passing through a convex portion 111. The convex portion 111 shown in Figure 4A is tapered, i.e., the convex portion 111 is tapered. Furthermore, as shown in Figure 4B, the tip of the convex portion 111 may be curved. With this configuration, the impact when an object is held by the adhesive layer 110 is further alleviated, making it easier for the adhesive layer 110 to hold the object without it slipping. On the other hand, the tip of the convex portion may be flat.

As shown in FIG. 4A, the surface of the adhesive layer 110 may have flat recesses and protruding portions 111 protruding from the recesses. In this manner, the adhesive layer 110 has multiple protruding portions 111 that are spaced apart from one another and may be bounded by the recesses.

As another example, the convex portion may be hemispherical or part of a sphere, as shown in FIG. 4B. Furthermore, the convex portion 111 may be T-shaped, as shown in FIG. 4C. As yet another example, the convex portion 111 may be in the shape of a collection of particles, mushroom-shaped, the surface of a lotus leaf, or needle-shaped. As yet another example, the surface of the adhesive layer 110 may be rough or fibrous, and such a surface may also be said to have unevenness.

From the viewpoint of maintaining the holding power of the object, the width or diameter of each protrusion 111 is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 5 μm or more, and even more preferably 10 μm or more. On the other hand, from the viewpoint of increasing the ease with which the object can be peeled off, it is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less. Here, the width and diameter of the protrusion 111 refer to the minimum and maximum distances, respectively, between two parallel lines that contact the protrusion 111 from both sides on the surface of the recess (represented by W in Figure 4A).

Furthermore, from the viewpoint of maintaining the holding force of the object, the area of each protrusion 111 is preferably ¹⁰ μm2 or more, more preferably ²⁰ μm2 or more, and even more preferably ³⁰ μm2 or more. On the other hand, from the viewpoint of increasing the ease with which the object can be peeled off, the area is preferably 2000 ^μm2 or less, more preferably 1000 ^μm2 or less, and even more preferably 500 ^μm2 or less. Here, the area of the protrusion 111 means the area of the portion protruding from the surface of the recess (the area of a circle with a diameter W in the case of FIG. 4A ).

In one embodiment, the height of each protrusion 111 is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more, from the viewpoint of increasing the ease of peeling an object. On the other hand, from the viewpoint of increasing the holding power of an object, the height of each protrusion 111 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. This makes it possible to change the holding power of an object. Here, the height of the protrusion 111 is represented by H in FIG. 4A. Also, in one embodiment, the height of the multiple protrusions in the adhesive layer 110 is uniform. In another embodiment, the adhesive layer 110 may have a first multiple protrusions having a first uniform height and a second multiple protrusions having a different height. Here, the second multiple protrusions may have a second uniform height. For example, the protrusions 111 may be composed of such first protrusions and second protrusions. In a further embodiment, the adhesive layer 110 may have multiple protrusions of random heights.

Furthermore, from the viewpoint of maintaining the holding power of the object, the total area of the convex portions 111 relative to the area of the adhesive layer 110 is preferably 1% or more, more preferably 5% or more, even more preferably 10% or more, even more preferably 18% or more, and even more preferably 40% or more. On the other hand, from the viewpoint of increasing the ease with which the object can be peeled off, the total area of the convex portions relative to the area of the adhesive layer 110 is preferably 95% or less, more preferably 75% or less, and even more preferably 60% or less.

(Characteristics of adhesive layer)
As described above, in one embodiment, the adhesive layer 110 is energy ray reactive. Therefore, by irradiating the adhesive layer 110 with energy rays, the storage modulus of the adhesive layer 110 increases. Furthermore, by irradiating the adhesive layer 110 with energy rays, the adhesive strength of the adhesive layer 110 decreases.

In one embodiment, the temperature at which tan δ stops increasing when the adhesive layer 110 is heated from 0°C after energy beam irradiation is greater than 55°C. The temperature at which tan δ stops increasing is preferably greater than 57°C, and more preferably greater than 59°C. tan δ is also called the loss tangent and is expressed as tan δ = G"/G'. Here, G' is the storage modulus. G" is also the loss modulus. The storage modulus and loss modulus of the adhesive layer 110 are measured using a torsional vibration method in accordance with JIS K7244-7:2007. Specifically, a cylindrical sample of the same material as the adhesive layer 110, 1 mm thick and 8 mm in diameter, is prepared, and a dynamic viscoelasticity measuring device is used to apply a 10 Hz vibration and measure the sample while raising the sample's temperature from -30°C to 120°C. This allows the storage modulus and loss modulus of the adhesive layer 110 to be measured. In this specification, the adhesive layer 110 after irradiation with energy rays refers to the adhesive layer 110 after irradiation with an amount of energy rays that completes the crosslinking reaction. In consideration of the possibility that noise may be present in the measured value of tan δ, in this specification, when tan δ is measured at measurement intervals of 0.2°C or more, the minimum X (X is a positive integer) at which the average value of tan δ at temperatures between X - 2.5°C and X + 2.5°C is equal to or greater than the average value of tan δ at temperatures between (X + 1) - 2.5°C and (X + 1) + 2.5°C is defined as the temperature at which the increase in tan δ stops.

The present inventors have discovered that using an adhesive layer 110 in which the temperature at which tan δ stops increasing is greater than 55°C makes it easier to pick up an object (especially a thin object) from the adhesive sheet. While not intending to limit the present invention, the present inventors believe the reason for this is as follows: Generally, an increase in tan δ with increasing temperature reflects a decrease in the storage modulus. Therefore, by setting the temperature at which tan δ stops increasing to greater than 55°C, it is expected that the storage modulus will be maintained at a stable high level in a normal environment, near room temperature. This is thought to make it more difficult for the convex portions of the adhesive layer 110 to follow the object when picking up the object, making it easier to pick up the object from the adhesive sheet. Furthermore, when the adhesive sheet is expanded after energy beam irradiation and then the object is picked up, the shear stress acting between the convex portions of the adhesive layer 110 and the object when the adhesive sheet is expanded is greater, making it more likely that the object will peel off from the adhesive layer 110. This is also thought to contribute to the effect of making it easier to pick up an object from the adhesive sheet. Furthermore, by maintaining a stable high storage modulus near room temperature, it is expected that objects will be easier to pick up from the adhesive sheet even if the temperature of the adhesive layer 110 rises due to energy ray irradiation. Alternatively, when the temperature of the adhesive layer 110 rises significantly due to energy ray irradiation, the cooling time of the adhesive layer 110 can be shortened, which is expected to improve productivity.

In one embodiment, the adhesive layer 110 after energy ray irradiation has a value of (tan δ at 50°C)/(tan δ at 30°C) of 1.30 or greater. The value of (tan δ at 50°C)/(tan δ at 30°C) is preferably 1.40 or greater, more preferably 1.50 or greater, and even more preferably 1.60 or greater.

The present inventors have discovered that using an adhesive layer 110 in which the value of (tan δ at 50°C)/(tan δ at 30°C) is 1.30 or greater makes it easier to pick up an object (particularly a thin object) from the adhesive sheet. While not intending to limit the present invention, the present inventors believe the reason for this is as follows: Generally, an increase in tan δ with increasing temperature reflects a decrease in the storage modulus. Therefore, if tan δ increases sharply with increasing temperature, it is expected that the storage modulus will be maintained stably at a high level in a normal environment near room temperature. For this reason, as described above, the holding force of the adhesive layer 110 on an object after irradiation with energy rays is reduced, making it easier to pick up an object from the adhesive sheet.

In one embodiment, the adhesive layer 110 after irradiation with energy rays has a tan δ value of 0.25 or less at 23°C. The tan δ value at 23°C is preferably 0.22 or less, and more preferably 0.18 or less.

The present inventors have discovered that using an adhesive layer 110 with a tan δ value of 0.25 or less at 23°C makes it easier to pick up an object (particularly a thin object) from the adhesive sheet. While not intending to limit the present invention, the present inventors believe the reason for this is as follows: if the tan δ value is sufficiently low near room temperature, which is a normal environment, it is expected that the storage modulus will be maintained stably high near this temperature. For this reason, as described above, the adhesive layer 110's ability to hold an object after irradiation with energy rays is reduced, making it easier to pick up an object from the adhesive sheet.

From the viewpoint of making it easier to pick up an object (especially a thin object) from the adhesive sheet, the storage modulus value at 23°C of the adhesive layer 110 after energy ray irradiation is preferably 0.80 GPa or more, more preferably 1.0 GPa or more, even more preferably 1.2 GPa or more, and even more preferably 1.5 GPa or more. On the other hand, from the viewpoint of suppressing displacement of an object after energy ray irradiation, the storage modulus value at 23°C of the adhesive layer 110 after energy ray irradiation is preferably 10 GPa or less, more preferably 7.0 GPa or more, even more preferably 5.0 GPa or less, and even more preferably 3.0 GPa or more.

Furthermore, from the viewpoint of increasing the object retention force, the storage modulus of the adhesive layer 110 at 23°C before irradiation with energy rays is preferably 100 MPa or less, more preferably 50 MPa or less, even more preferably 20 MPa or less, and particularly preferably 5.0 MPa or less.

Furthermore, the adhesive sheet according to one embodiment is expandable in the planar direction. The adhesive layer 110 shown in FIGS. 2A and 3A is transformed into the adhesive layer 110' shown in FIGS. 2B and 3B by expanding the adhesive sheet. Comparing the adhesive layer 110 and the adhesive layer 110', the pitch P of the convex portions 111 in the adhesive layer 110' is increased due to expansion, and the number of convex portions 111 that hold one object 140 is reduced. As a result, the adhesive layer 110' has a lower holding force for the object 140 via the convex portions 111 than the adhesive layer 110. Furthermore, shear stress acts between the convex portions 111 and the object 140 due to expansion of the adhesive sheet. The inventors of the present application believe that this also leads to a decrease in the holding force of the convex portions 111 to the object 140. The adhesive sheet according to one embodiment may be expandable by 1% or more in the planar direction (e.g., one direction or two orthogonal directions) or by 5% or more, from the viewpoint of sufficiently reducing the holding force for the object.

(Release layer)
The pressure-sensitive adhesive sheet according to the present embodiment may also have a release sheet 150 in contact with the pressure-sensitive adhesive layer 110, as shown in Fig. 1. For the sake of explanation, Fig. 1 shows a state in which the pressure-sensitive adhesive layer 110 and the release sheet 150 are separated. As shown in Fig. 1, the release sheet 150 has an uneven surface that is complementary to the uneven surface of the pressure-sensitive adhesive layer 110.

The release sheet 150 has a release layer 160. The release layer 160 is a layer that is easily peelable from the adhesive layer 110. The release layer 160 may have an uneven surface that is complementary to the uneven surface of the adhesive layer 110. That is, the release layer 160 has recesses 161, and the recesses 161 have a shape that is complementary to the protrusions 111. However, it is not essential that the recesses 161 have a shape that is complementary to the protrusions 111.

The release sheet 150 may have a substrate 170 on the side that does not contact the adhesive layer 110. This substrate 170 may be designed similarly to the substrate 120, but does not need to have the same composition or structure as the substrate 120. In addition, the release sheet 150 may have an undercoat layer (not shown) between the release layer 160 and the substrate 170.

(Other layers)
The above-mentioned sheet may have layers other than the substrate 120 and the adhesive layer 110. For example, an additional adhesive layer may be provided on the surface of the substrate 120 opposite the adhesive layer 110. The sheet can be attached to another object via such an adhesive layer. The type of the additional adhesive layer is not particularly limited, and the additional adhesive layer can be formed using, for example, a general adhesive.

(Method for manufacturing pressure-sensitive adhesive sheet)
There are no particular limitations on the method for manufacturing the adhesive sheet and adhesive layer 110. An example of a method for manufacturing the adhesive sheet will be described below with reference to FIG.

In S610, a pressure-sensitive adhesive composition serving as a material for the pressure-sensitive adhesive layer 110 is prepared. The pressure-sensitive adhesive composition can be prepared by adding an organic solvent to a raw material composition containing the above-described components of the pressure-sensitive adhesive layer 110. The pressure-sensitive adhesive composition can contain, for example, the above-described energy ray-reactive acrylic acid ester copolymer. As already described, an energy ray-curable group can be introduced into the energy ray-curable group-introducing monomer by reacting an energy ray-curable group-introducing agent with an acrylic acid ester copolymer having the energy ray-curable group-introducing monomer. The process of preparing the pressure-sensitive adhesive composition may include a process of preparing an energy ray-reactive acrylic acid ester copolymer. In this case, the copolymerization rate ^RA % of the energy ray-curable group-introducing monomer in the acrylic acid ester copolymer and the equivalent ^RB % of the energy ray-curable group-introducing agent to be reacted are as already described.

The adhesive composition may also contain the above-mentioned acrylic ester copolymer having a monomer into which an energy ray-curable group has been introduced and a monomer capable of reacting with a crosslinking agent. The adhesive composition may also contain a crosslinking agent for crosslinking the monomers contained in the acrylic ester copolymer.

Examples of organic solvents used to prepare the pressure-sensitive adhesive composition include toluene, ethyl acetate, and methyl ethyl ketone. Examples of methods for applying the solution include spin coating, spray coating, bar coating, knife coating, roll coating, roll knife coating, blade coating, die coating, gravure coating, and printing methods (e.g., screen printing and inkjet printing).

In S620 and S630, the adhesive composition prepared in S610 is used to form an adhesive layer having an uneven surface on substrate 120. First, in S620, a layer of the adhesive composition is formed on substrate 120. For example, the adhesive composition is applied to substrate 120 to form a coating film, which is then dried, thereby providing a layer of the adhesive composition on substrate 120.

In S630, irregularities are formed on the surface of the adhesive composition layer thus formed. There are no particular limitations on the process for forming the irregularities. For example, irregularities can be formed on the surface of the layer using an imprinting method. In the imprinting method, a mold with an irregular surface complementary to the irregularities to be formed can be used. In this way, an adhesive layer 110 with an irregular surface is formed. Specifically, the adhesive composition layer is pressed with the mold, the layer is heated and maintained for a predetermined period of time, and then the material layer is cooled and the mold is removed. During heating, for example, the material layer can be heated to a temperature higher than the softening point of the adhesive composition layer. A specific method for heating the material layer while pressing the layer with the mold is to vacuum laminate the adhesive composition layer provided on the substrate 120 and the mold. Alternatively, a release sheet 150 having a release layer 160 with irregularities as described above may be used as the mold.

On the other hand, to improve the retention of the uneven shape, a crosslinking reaction of the resin contained in the adhesive composition may be carried out when forming the unevenness on the surface of the adhesive composition layer or after forming the unevenness. As already explained, in one embodiment in which the adhesive composition contains an acrylic acid ester copolymer having a monomer capable of reacting with a crosslinking agent, the monomers can be crosslinked with each other by reacting the acrylic acid ester copolymer with a crosslinking agent. By promoting the curing reaction in the adhesive composition layer in this way, the storage modulus of the adhesive layer 110 can be increased and the retention of the uneven shape can be improved. As a specific example, an adhesive layer 110 having an uneven surface can be formed by curing the adhesive composition layer while bringing the adhesive composition layer into contact with a mold having an uneven surface complementary to the unevenness. When the adhesive composition layer contains a copolymer before crosslinking and a thermal crosslinking agent, the crosslinking reaction proceeds by heating the material layer while pressing it with the mold, and an adhesive layer 110 containing a crosslinked copolymer is formed. By using a crosslinking reaction due to heating in this way, unreacted energy ray-curable groups can be left in the adhesive layer 110.

As an alternative method, an adhesive layer 110 having a rough surface can be provided by spray-coating an adhesive composition. Furthermore, an adhesive layer 110 having a rough or fibrous surface can be provided by adding a filler to the adhesive composition and coating such a solution. As yet another alternative method, an adhesive layer 110 having a textured shape can be provided directly on the substrate 120 by applying the adhesive composition according to the desired pattern using a printing method such as an inkjet method.

As yet another alternative method, an adhesive layer 110 having an uneven surface may be formed on a release sheet 150. As described above, the surface of the release sheet 150 may have an uneven surface that is complementary to the uneven surface of the adhesive layer 110. In this case, by providing a layer of an adhesive composition on the uneven surface of the release sheet 150, an adhesive layer having an uneven surface (i.e., the interface between the adhesive layer 110 and the release sheet 150) can be provided. Furthermore, a substrate 120 can be attached to the surface of the adhesive layer 110 opposite the uneven surface. The adhesive layer 110 may be formed on the substrate 120 by such a method.

(How to use the adhesive sheet)
The adhesive sheet according to this embodiment can be used to handle an object. For example, the adhesive sheet according to this embodiment can be used to temporarily hold an object. The adhesive sheet according to this embodiment can also be used to transfer an object. As a specific example, the adhesive sheet according to this embodiment can be used to transfer a semiconductor chip obtained by dicing to a desired position.

The method for handling an object using the adhesive sheet according to this embodiment will be described with reference to the flowchart in Figure 7.

(S710: Holding an object)
In S710, an object is held on the adhesive layer of the adhesive sheet according to this embodiment. The type of object is not particularly limited. The object may be, for example, an element. Examples of elements include semiconductor chips such as LED chips, semiconductor chips with protective films, and semiconductor chips with die attach films (DAFs). The element may also be a micro light-emitting diode, a mini light-emitting diode, a power device, a MEMS (Micro Electro Mechanical Systems), or a controller chip, or a component thereof. The element may also be a singulated object such as a wafer, panel, or substrate. The element may have a circuit surface on which an integrated circuit having circuit elements such as transistors, resistors, and capacitors is formed. The element is not necessarily limited to a singulated object, but may also be various unsingulated wafers or substrates.

The size of the object is not particularly limited. For example, the size of the object is preferably 100 μm ² or more, more preferably 500 μm ² or more, and even more preferably 1000 μm ² or more. On the other hand, the size of the object is preferably 100 mm ² or less, more preferably 25 mm ² or less, and even more preferably 1 mm ² or less.

Examples of wafers include semiconductor wafers such as silicon wafers, silicon carbide (SiC) wafers, and compound semiconductor wafers (e.g., gallium phosphide (GaP) wafers, gallium arsenide (GaAs) wafers, indium phosphide (InP) wafers, and gallium nitride (GaN) wafers). The size of the wafer is not particularly limited, but is preferably 6 inches (diameter approximately 150 mm) or larger, and more preferably 12 inches (diameter approximately 300 mm) or larger. The shape of the wafer is not limited to circular, and may be angular, such as square or rectangular.

An example of a panel is a fan-out type semiconductor package (e.g., FOWLP or FOPLP). In other words, the workpiece may be a semiconductor package before or after singulation in fan-out type semiconductor package manufacturing technology. The size of the panel is not particularly limited, but may be, for example, a rectangular substrate of approximately 300 to 700 mm.

Examples of substrates include glass substrates, sapphire substrates, and compound semiconductor substrates.

In one embodiment, elements are transferred from a holding substrate to an adhesive sheet, and the adhesive sheet holds the transferred elements. For example, a semiconductor wafer can be attached to a wafer substrate, and the semiconductor wafer can then be diced. The elements on the wafer substrate obtained by dicing can then be brought into close contact with adhesive layer 110 of the adhesive sheet. Thereafter, an external stimulus such as laser light can be applied to reduce the adhesion between the wafer substrate and the elements. This process allows the elements to be transferred from the wafer substrate to the adhesive sheet. As an alternative method, elements obtained by dicing a semiconductor wafer can be transferred to a holding substrate, thereby obtaining a holding substrate with elements attached thereto. The elements attached to the holding substrate can then be transferred to adhesive layer 110 of the adhesive sheet in a similar manner.

In another embodiment, an external stimulus may be used to separate an element attached to a holding substrate from the holding substrate. Specifically, the element moves away from the holding substrate. Alternatively, the element moves closer to the adhesive sheet. Then, when the element comes into contact with the adhesive layer 110 of the adhesive sheet, the element is separated from the holding substrate and captured by the adhesive sheet. The type of external stimulus is not particularly limited, but examples include application of energy, cooling, expansion of the holding substrate, and physical stimulation (e.g., pressing the back surface of the holding substrate with a pin, etc.). By using one or more of these external stimuli, the bonding force between the holding substrate and the element can be reduced, and the element can be separated from the holding substrate. For example, the element can be separated from the holding substrate by irradiation with laser light (laser lift-off method). In such an embodiment, when the separated element approaches the adhesive layer 110, pressure is generated between the element and the adhesive layer 110. However, the uneven surface of the adhesive layer 110 reduces the pressure generated between the element and the adhesive layer 110, making it easier to capture the element at the desired position on the adhesive sheet.

In a further embodiment, an object held on the adhesive layer 110 of the adhesive sheet can be processed. The processing method is not particularly limited. For example, processing such as wiring formation, back metal formation, cleaning, plating, singulation, thinning, and sealing can be performed. For example, a semiconductor wafer can be attached to the adhesive layer 110 of the adhesive sheet. Then, elements can be formed by dicing the semiconductor wafer on the adhesive layer 110. This method also allows the adhesive sheet to hold elements.

(S720: Adhesion reduction process)
In S720, the adhesive strength of the adhesive layer 110 holding the object is reduced. To reduce the adhesive strength, a treatment step of irradiating the adhesive layer 110 with energy rays and an expansion step of expanding the adhesive sheet in the planar direction can be performed. By irradiating the energy ray-reactive adhesive layer 110 with energy rays, the storage modulus of the adhesive layer 110 increases and the adhesive strength is reduced. Furthermore, by expanding the adhesive sheet in the planar direction, the holding strength of the adhesive layer 110 to the object is reduced as described above.

The amount of energy rays applied in the treatment step can be set depending on the type of adhesive layer 110 and the desired adhesive strength. For example, when irradiating with ultraviolet light, the amount of ultraviolet light is preferably 20 mJ/ ^cm2 or more, and more preferably 100 mJ/ ^cm2 or more, from the viewpoint of sufficiently reducing the adhesive strength. Furthermore, the amount of ultraviolet light is preferably 1000 mJ/ ^cm2 or less, and more preferably 500 mJ/ ^cm2 or less, from the viewpoint of shortening the treatment time.

In the expansion process, the adhesive sheet is expanded in the planar direction. The method for expanding the adhesive sheet is not particularly limited. For example, the adhesive sheet may be expanded in one direction, two directions, or multiple other directions. The expansion rate of the adhesive sheet is also not particularly limited. For example, from the perspective of sufficiently reducing the holding force of the object, the expansion rate of the adhesive sheet in one direction may be 1% or more, or 5% or more. Furthermore, from the perspective of preventing the adhesive sheet from breaking, the expansion rate of the adhesive sheet in one direction may be 50% or less, or 20% or less. From a similar perspective, the expansion rate of the adhesive sheet in two mutually perpendicular directions may be 1% or more, or 5% or more, or may be 50% or less, or 20% or less.

As a specific example, the adhesive sheet can be expanded by fixing the adhesive sheet to a frame and pressing a base against the adhesive sheet inside the frame. Such an example will be described with reference to Figures 5A and 5B. Figure 5A shows a state in which the adhesive sheet holds objects 140a to 140d. As shown in Figure 5A, the outer periphery of the adhesive sheet can be fixed to frame 320. The shape of frame 320 is not particularly limited. For example, frame 320 may be a circular or rectangular frame-shaped member with an opening. In one embodiment, a circular ring frame is used as the frame. Using a ring frame allows the adhesive sheet to expand in all directions.

The adhesive sheet fixed to frame 320 can then be expanded by contacting the base 310 with the base, and then displacing (pulling down) frame 320 toward base 310 as shown in FIG. 5B. The configuration of base 310 is not particularly limited, and may be, for example, cylindrical or rectangular. Base 310 may also be mesh-shaped or ring-shaped. Frame 320 may be displaced relative to base 310 at a speed of, for example, 0.1 mm/sec or more, or 1 mm/sec or more. In this case, the displacement amount of frame 320, i.e., the pull-down amount, may be, for example, 1 mm or more, or 5 mm or more, from the viewpoint of sufficiently reducing the object holding force. On the other hand, the displacement amount of frame 320 may be 30 mm or less, or 20 mm or less, from the viewpoint of preventing damage to the adhesive sheet.

(S730: Peeling off the object)
After reducing the adhesive force of the adhesive layer 110, in S730, the object is peeled from the adhesive layer 110 of the adhesive sheet. For example, the object can be peeled from the adhesive layer 110 of the adhesive sheet after the treatment process and the expansion process have been performed. The method for peeling the object is not particularly limited. For example, the method described above can be used to transfer an object attached to a holding substrate to an adhesive sheet. As an example, the object can be peeled from the adhesive layer 110 of the adhesive sheet using an adsorption member such as a vacuum collet. The adsorbed object can then be moved to a desired transfer location. By reducing the holding force of the adhesive layer 110 as in this embodiment, the object can be peeled from the adhesive layer 110 of the adhesive sheet without applying a physical stimulus, such as pressure from the opposite side of the adhesive layer 110 using a pin or the like. However, the object may also be peeled from the adhesive layer 110 of the adhesive sheet while applying a physical stimulus from the opposite side of the adhesive layer 110 of the adhesive sheet.

According to the inventors' investigations, when attempting to peel an object from the adhesive layer 110, increasing the suction force in accordance with the holding power of the adhesive layer 110 makes the object, such as a device, more susceptible to damage. In particular, when peeling a thin object such as a device, increasing the suction force makes the object more susceptible to damage. On the other hand, decreasing the adhesive power of the adhesive layer 110 reduces the holding power of the object in the adhesive layer 110. For example, when transferring devices obtained by dicing from a wafer substrate to an adhesive sheet, if the adhesive power of the adhesive layer 110 is low, part of the device may remain on the wafer substrate. In this embodiment, by using a process that reduces the adhesive power, it is possible to achieve both high holding power of the adhesive layer 110 when holding an object on the adhesive sheet and low holding power of the adhesive layer 110 when peeling the object from the adhesive sheet. From this perspective, the handling method and adhesive sheet of this embodiment are suitable for handling thin objects. For example, the thickness of the object held by the adhesive sheet is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less.

By using the above-described procedure, an object can be transferred to any desired destination using an adhesive sheet. One embodiment of the present invention relates to a method for peeling an object from an adhesive sheet holding the object on the adhesive layer. Such a peeling method can include a step of reducing adhesive strength as in S720, and a step of peeling the object as in S730.

Furthermore, such a peeling method can be used to manufacture electronic components or semiconductor devices having elements. For example, a method for manufacturing an article according to one embodiment of the present invention can include, in addition to the step of peeling an object from an adhesive sheet according to the above-described peeling method, a step of manufacturing the article by performing post-processing on the object. In the example of Figure 7, in S740, a post-processing step is performed on the object. The type of post-processing is not particularly limited. For example, processes such as wiring formation, backmetal formation, cleaning, plating, singulation, thinning, and sealing can be performed.

The present invention will be explained in more detail below using examples. However, the present invention is not limited to the following examples in any way.

The following compounds were used in the examples and comparative examples.
<Component (A): Acrylic Ester Copolymer>
The following acrylic acid ester copolymers were used.
(A1) A butyl acrylate resin (monomer mass ratio: butyl acrylate/methyl methacrylate/2-hydroxyethyl acrylate=52/20/28) was reacted with 2-isocyanatoethyl methacrylate in an amount of 90% equivalent to the 2-hydroxyethyl acrylate, thereby introducing an energy ray-curable group into the polymer side chain via the hydroxy group (copolymerization rate of energy ray-curable group-containing monomer: 25.6%, mass average molecular weight (Mw): 520,000, number average molecular weight (Mn): 155,000).
(A2) A butyl acrylate resin (monomer mass ratio: butyl acrylate/methyl methacrylate/2-hydroxyethyl acrylate=62/10/28) was reacted with 2-isocyanatoethyl methacrylate in an amount of 80% equivalent to the 2-hydroxyethyl acrylate, thereby introducing an energy ray-curable group into the polymer side chain via the hydroxy group (copolymerization rate of energy ray-curable group-containing monomer: 23.4%, mass average molecular weight (Mw): 715,000, number average molecular weight (Mn): 139,000).
(A3) A 2-ethylhexyl acrylate resin (monomer mass ratio: 2-ethylhexyl acrylate/2-hydroxyethyl acrylate=80/20) was reacted with 2-isocyanatoethyl methacrylate in an amount of 80% equivalent to the 2-hydroxyethyl acrylate, thereby introducing an energy ray-curable group into the polymer side chain via the hydroxy group (copolymerization rate of energy ray-curable group-containing monomer: 22.7%, number average molecular weight (Mn): 86,400).

<Component (B): Thermal Crosslinking Agent>
As the crosslinking agent, an isocyanurate type polyisocyanate derived from hexamethylene diisocyanate was used.

Examples 1 to 5
A pressure-sensitive adhesive composition was prepared by dissolving the acrylic acid ester copolymer (A1) or (A2) and the crosslinking agent (B) in toluene in the amounts shown in Table 1. Table 1 shows the solid content parts by mass of each material.

This adhesive composition was applied to the release-treated surface of a release substrate (fine-embossed release sheet) with a concave pattern, and the resulting coating was dried at 100°C for 2 minutes to form an adhesive layer with a thickness of 25 μm. The concave-convex pattern on the surface of the formed adhesive layer was a grid-like arrangement of pillars, similar to Figure 2A. The pitch P between pillars on the adhesive sheet was 20 μm. Furthermore, as shown in Figure 4A, each pillar had a height (H) of 8 μm, a tip diameter (T) of 8 μm, and a base diameter (W) of 16 μm. The release sheet used above had a concave pattern on its surface that was complementary to the concave-convex pattern.

An adhesive sheet was produced by laminating a substrate (ethylene methacrylic acid copolymer (EMAA) film, acid content 9% by mass, one surface embossed to give it a matte finish, thickness 80 μm, tensile modulus 160 MPa) onto the adhesive layer thus obtained.

(Comparative Examples 1 and 2)
A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, except that the amounts of acrylic acid ester copolymer (A3) and crosslinking agent (B) shown in Table 1 were dissolved in toluene to prepare the pressure-sensitive adhesive composition, and a pressure-sensitive adhesive sheet was produced.

(Method for measuring elastic modulus of adhesive layer)
The storage modulus and tan δ of the adhesive layers in each Example and Comparative Example were measured as follows. Specifically, the adhesive composition used in each Example was applied, and the resulting coating was dried at 100°C for 2 minutes to form an adhesive layer with a thickness of 25 μm. The adhesive layers thus formed were laminated to a thickness of 1 mm. Then, using an ultraviolet irradiator (manufactured by Heraeus), the laminate was irradiated with ultraviolet light at an illuminance of 130 mW/ ^cm2 and a light dose of 210 mJ/ ^cm2 , thereby crosslinking the energy beam-curable groups in the adhesive layer. The resulting adhesive layer was punched into a cylindrical shape with a diameter of 8 mm to prepare a sample for dynamic viscoelasticity measurement.

Dynamic viscoelasticity measurements were performed on the obtained samples using the torsional vibration method in accordance with JIS K7244-7:2007. Specifically, a viscoelasticity measuring device (Rheometrics, device name "DYNAMIC ANALYZER RDAII") was used to apply a 10 Hz vibration and measure the sample while raising its temperature from -30°C to 120°C, thereby measuring the storage modulus E' and loss modulus E'' at each temperature. The loss tangent tanδ at each temperature is expressed as E''/E'.

(Pickup property evaluation)
The pickup properties of the objects held by the pressure-sensitive adhesive sheets obtained in each of the Examples and Comparative Examples were evaluated as follows: As shown below, the objects used were silicon chips having a thickness of 150 μm and silicon chips having a thickness of 50 μm.

First, the adhesive sheet obtained in each example and comparative example was attached to a ring frame (stainless steel, inner diameter 194 mm), and the adhesive sheet was cut to fit the outer diameter of the ring frame. Next, a wafer substrate (ground silicon wafer, 6 inches, 150 μm or 50 μm thick) was fixed to separately prepared dicing tape. The wafer substrate was then diced into 8 mm x 8 mm squares to obtain multiple elements (silicon chips, element size 8 mm x 8 mm x 50 μm or 150 μm). The resulting multiple elements were attached to the adhesive layer of the adhesive sheet in the center of the inner side of the ring frame, with the ground surface attached to the uneven surface of the adhesive layer. Attachment was performed by lamination at room temperature (23°C). The dicing tape was then peeled off, transferring the multiple elements from the dicing tape to the adhesive sheet. In this way, an adhesive sheet with multiple elements mounted thereon and supported by a ring frame was obtained as an evaluation sample.

The obtained evaluation sample was irradiated with ultraviolet light at an illuminance of 130 mW/cm ² and a light quantity of 210 mJ/cm ² using an ultraviolet irradiator (manufactured by Heraeus).

After UV irradiation, the evaluation sample was placed in a pickup device (Canon Machinery Inc., product name "BESTEM-D510"). After expanding the adhesive sheet, an attempt was made to pick up the element using a vacuum suction collet. The adhesive sheet was expanded as shown in Figures 5A and 5B. That is, with the element supported by base 310 over the adhesive sheet, ring frame 320 was pulled down 10 mm relative to base 310, expanding the adhesive sheet. This evaluation also assessed whether the element could be picked up without poking the surface (substrate) of the adhesive sheet opposite the element to be picked up with a needle. If the element could be picked up without damage, it was evaluated as "pickup possible" (A). If the element was damaged during pickup, could not be picked up, or transfer of the element from the wafer substrate to the adhesive sheet failed, it was evaluated as "pickup impossible" (F).

The evaluation results are shown in Table 1.

As shown in Table 1, thin, easily breakable elements, such as those 50 μm thick, could be picked up from the adhesive sheets of Examples 1 to 5 without using a needle. Meanwhile, all elements were transferred from the dicing tape to the adhesive sheets of Examples 1 to 5, confirming that the adhesive sheets of Examples 1 to 5 have sufficient adhesive strength. Furthermore, elements could not be picked up from the adhesive sheets of Comparative Examples 1 and 2 without damaging them. This is thought to be because the adhesive sheets of Comparative Examples 1 and 2 have high adhesive strength even after UV irradiation, necessitating the use of a large adsorption force for pickup. Thus, it was confirmed that by setting the copolymerization rate of the energy beam-curable group-containing monomer in the acrylic acid ester copolymer contained in the adhesive layer to 23.0% or more, the decrease in adhesive strength due to UV irradiation is promoted, making it easier to pick up objects from the adhesive sheet.

The invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the invention.

This application claims priority based on Japanese Patent Application No. 2024-046979 filed on March 22, 2024, Japanese Patent Application No. 2024-046980 filed on March 22, 2024, Japanese Patent Application No. 2024-046981 filed on March 22, 2024, Japanese Patent Application No. 2024-046982 filed on March 22, 2024, Japanese Patent Application No. 2024-170363 filed on September 30, 2024, and Japanese Patent Application No. 2024-170369 filed on September 30, 2024, the entire contents of which are incorporated herein by reference.

Claims (14)

A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer having an uneven surface,
The pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer contains an acrylic ester copolymer, and the copolymerization rate of the energy ray-curable group-containing monomer in the acrylic ester copolymer is 20% or more and 50% or less. The pressure-sensitive adhesive sheet of claim 1, wherein the acrylic ester copolymer comprises the energy ray-curable group-containing monomer, which is a (meth)acrylic ester monomer, and a (meth)acrylic ester monomer crosslinked with another (meth)acrylic ester monomer. The pressure-sensitive adhesive sheet according to claim 2, wherein the energy ray-curable group-containing monomer is a (meth)acrylic acid ester monomer having a carbon-carbon double bond-containing group in the side chain via a hydroxy group. The pressure-sensitive adhesive sheet according to claim 2, wherein the (meth)acrylic acid ester monomer crosslinked with the other (meth)acrylic acid ester monomer is crosslinked with the other (meth)acrylic acid ester monomer via a hydroxy group. The adhesive sheet according to claim 1, wherein the content of the acrylic ester copolymer relative to the total amount of components constituting the adhesive layer is 70 to 100 mass%. The pressure-sensitive adhesive sheet according to claim 1, wherein the acrylic ester copolymer has a mass average molecular weight of 10,000 or more. The adhesive sheet according to claim 1, wherein the adhesive sheet is expandable in the planar direction. The adhesive sheet of claim 1, wherein the height of the convex portions of the adhesive layer is 1 μm or more. The adhesive sheet of claim 1, wherein the adhesive layer has a plurality of protrusions spaced apart from one another and bounded by recesses, and the pitch of the plurality of protrusions is 1 μm or more and 100 μm or less. The adhesive sheet of claim 1, wherein the adhesive layer has multiple convex portions, and the heights of the multiple convex portions are uniform. The adhesive sheet of claim 1, further comprising a release layer having an uneven surface complementary to the uneven surface of the adhesive layer. A method for producing a pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer having an uneven surface, comprising:
a preparation step of preparing a pressure-sensitive adhesive composition, the step including a step of reacting an energy ray-curable group-introducing agent with an acrylic acid ester copolymer having a monomer capable of introducing an energy ray-curable group, thereby introducing an energy ray-curable group into the monomer capable of introducing an energy ray-curable group;
a forming step of forming the adhesive layer on the substrate using the adhesive composition;
Including,
the copolymerization rate of the monomer capable of introducing an energy ray-curable group in the acrylic acid ester copolymer is R ^A %,
In the preparation step, the monomer capable of introducing an energy ray-curable group is reacted with an energy ray-curable group-introducing agent in an amount equivalent to ^RB %;
The production method, wherein the product of R ^A % and R ^B % is 23.0% or more and 50.0% or less. The (meth)acrylic acid ester monomer into which an energy ray-curable group can be introduced is a (meth)acrylic acid ester monomer having a hydroxy group,
The method according to claim 12, wherein the energy ray-curable group-introducing agent is an isocyanate compound having a carbon-carbon double bond-containing group. A method for peeling an object from the adhesive sheet according to any one of claims 1 to 11, wherein the adhesive layer holds the object, comprising:
an irradiation step of irradiating the adhesive layer with energy rays;
an expanding step of expanding the pressure-sensitive adhesive sheet in a surface direction;
a peeling step of peeling the object from the adhesive layer of the adhesive sheet;
A peeling method comprising: