HK1237715B - Nonporous molded article for polishing layer, polishing pad, and polishing method - Google Patents

Description

Non-porous molded body for polishing layer, polishing pad and polishing method

Technical Field

The present invention relates to a polishing pad, and more particularly to a polishing pad for polishing semiconductor wafers, semiconductor devices, silicon wafers, hard disks, glass substrates, optical products, various metals, and the like.

Background Art

Chemical mechanical polishing (CMP) is a well-known polishing method used to mirror-finish semiconductor wafers and flatten the surfaces of insulating films and conductive films in semiconductor devices. CMP is a method of polishing the surface of a material to be polished, such as a wafer, using a polishing slurry (hereinafter referred to as "slurry") containing an abrasive and a reaction liquid with a polishing pad.

In the past, non-woven polishing pads were widely used as polishing pads for CMP. Non-woven polishing pads are soft polishing pads made of non-woven fabric impregnated with polyurethane. Because non-woven polishing pads are soft, they have the advantage of good contact with the material being polished. In addition, because there are gaps in the non-woven fabric, they also have the advantage of good slurry retention. On the other hand, because non-woven polishing pads are soft, they have the disadvantage of poor flatness (called flatness) of the performance of flattening the polished surface. In addition, non-woven polishing pads have the disadvantage of easily causing scratches on the polished surface when the gaps in the non-woven fabric are clogged with abrasives or polishing shavings. In addition, when abrasives or polishing shavings penetrate deep into the gaps in the non-woven fabric, they cannot be fully removed by cleaning, which also shortens their service life.

In addition, as a different type from non-woven polishing pads, polishing pads based on polymer foam with a closed-cell bubble structure are known. Compared to non-woven polishing pads, polishing pads based on polymer foam have higher rigidity and therefore superior flatness. In addition, because polishing pads based on polymer foam have a closed-cell bubble structure, abrasives and polishing shavings are less likely to penetrate deep into the pores as they do in non-woven polishing pads. Therefore, the removal of abrasives and polishing shavings through cleaning is relatively easy, resulting in a longer lifespan. As polishing pads based on polymer foam, for example, the following patent documents 1 to 6 disclose polishing pads having a polishing layer made from a foamed polyurethane molded by injection foaming of a two-component curable polyurethane. From the perspective of excellent wear resistance, it is preferred to use a foamed polyurethane molded body as the polishing layer.

Integrated circuits in semiconductor devices are becoming increasingly highly integrated and feature multi-layer wiring. Polishing pads used in the planarization of semiconductor devices are required to exhibit even higher levels of flatness. A polishing pad with high flatness has a high polishing speed for the areas to be polished and a slow polishing speed for the areas not to be polished. Highly flat polishing pads require high hardness. Polishing pads with a polishing layer made of a foamed polyurethane molded body have a high hardness, resulting in high flatness.

In recent years, with the increasing integration and multi-layer wiring of semiconductor devices, polishing pads with higher flatness have been required. However, when using polishing pads with a foamed polyurethane polishing layer, achieving the high flatness achieved by increasing the hardness of the polishing layer is difficult. Furthermore, in order to provide polishing pads with even higher flatness, Patent Documents 7 and 8 below, for example, disclose high-hardness polishing pads primarily composed of non-foamed resin.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2000-178374

Patent Document 2: Japanese Patent Application Laid-Open No. 2000-248034

Patent Document 3: Japanese Patent Application Laid-Open No. 2001-89548

Patent Document 4: Japanese Patent Application Laid-Open No. 11-322878

Patent Document 5: Japanese Patent Application Laid-Open No. 2002-371154

Patent Document 6: International Publication No. 2007/034980

Patent Document 7: Japanese Patent Application Laid-Open No. 2014-038916

Patent Document 8: Japanese Patent Application Laid-Open No. 2009-101487

Summary of the Invention

Problems to be solved by the invention

Polishing pads used for CMP typically have grooves and holes (hereinafter collectively referred to as recesses) formed in them. These grooves and holes ensure that slurry is evenly and sufficiently supplied to the polishing surface of the material being polished. These recesses also help remove polishing debris that causes scratches and prevent wafer damage caused by adsorption on the polishing pad.

When concave portions are formed on the polishing surface of a high-hardness polishing layer primarily made of a non-porous resin (non-foamed resin), burrs gradually form at the corners (ends and shoulders) of the concave portions due to repeated contact between the polished material or the conditioner over time. Furthermore, these burrs gradually clog the concave portions, reducing the slurry supply. This results in a decrease in polishing speed and uniformity.

An object of the present invention is to provide a polishing layer of a polishing pad capable of suppressing the generation of burrs at corners of recessed portions formed on a polishing surface.

Technical solutions to problems

The present inventors have noted that when a molded article of a thermoplastic polyurethane with low resilience and high toughness is used as a polishing layer, repeated application of force to the corners of the recessed portion can easily cause the thermoplastic polyurethane to stretch, resulting in burrs. Furthermore, they have discovered that using a thermoplastic polyurethane with well-compatible soft and hard segments is less likely to produce burrs. Based on this insight, the present inventors have discovered a specific thermoplastic polyurethane that is less likely to produce burrs and exhibits moderate resilience and toughness, leading to the present invention.

That is, one aspect of the present invention is a non-porous molded body for a polishing layer (hereinafter, also referred to as a non-porous molded body), which is a non-porous molded body of thermoplastic polyurethane, wherein the maximum value of the loss tangent (tanδ) of the thermoplastic polyurethane in the range of -70 to -50°C is 4.00× ^10-2 or less. When such a non-porous molded body is used as a polishing layer, burrs are not easily generated at the corners of the concave portion formed on the polishing surface even if CMP polishing is performed for a long time. The inventors of the present invention speculate that the mechanism by which the generation of burrs can be suppressed for a polishing pad using such a non-porous molded body as a polishing layer is as follows. Thermoplastic polyurethane with a high tanδ value in the low temperature region is easily deformed and has high toughness. The polishing surface is subjected to high-frequency impacts, for example, due to contact with diamond particles of a regulator. The attenuation characteristics of the polishing pad to high-frequency impacts are related to tanδ in the low temperature region. Thermoplastic polyurethane with a low tanδ value in the low temperature region has low impact resistance, low toughness, and is brittle. Therefore, by abrading the thermoplastic polyurethane at the corners of the recess before burrs form, burr formation can be suppressed. Furthermore, the use of a polishing layer that suppresses burr formation allows for a consistent and long-term supply of slurry to the entire polishing surface. This results in a uniform polishing rate across the polished surface of a material such as a wafer. The result is polishing with excellent polishing uniformity.

Furthermore, thermoplastic polyurethane can be obtained by polymerizing a polymer diol having a number average molecular weight of 650 to 1400, an organic diisocyanate, and a chain extender, and the nitrogen content of the isocyanate groups of the organic diisocyanate is preferably 5.7 to 6.5% by mass. This is preferred because it is easy to obtain a thermoplastic polyurethane having a maximum loss tangent of 4.00 × 10 ^-2 or less in the range of -70 to -50°C and high compatibility between the soft and hard segments.

In addition, a thermoplastic polyurethane sheet with a thickness of 0.5 mm preferably has a laser transmittance of 70% or more for a laser with a wavelength of 660 nm. Such thermoplastic polyurethanes have high compatibility between the soft and hard segments. Using such thermoplastic polyurethanes, it is easy to obtain a non-porous molded body of thermoplastic polyurethane having a maximum loss tangent of 4.00 × 10 ^-2 or less in the range of -70 to -50°C. Furthermore, since the laser transmittance is 70% or more, the above-mentioned thermoplastic polyurethane is preferred from the perspective of being suitable for inspection using optical methods, which are optical methods for polishing the polished surface of a material such as a wafer while determining the polishing endpoint and inspecting the material being polished.

Furthermore, from the perspective of obtaining a polishing layer with a high hardness that is less likely to cause scratches during polishing, the tensile modulus of the thermoplastic polyurethane after saturation swelling in warm water at 50°C is preferably 130 to 800 MPa. If the hardness of the polishing pad decreases over time, flatness tends to decrease, leading to reduced polishing efficiency.

Furthermore, from the viewpoint of being less likely to be scratched, the contact angle of the thermoplastic polyurethane sheet with water is preferably 80 degrees or less.

In addition, for thermoplastic polyurethane, from the viewpoint of preventing the polishing characteristics from changing over time during polishing, it is preferred that the retention rate of the tensile elastic modulus when saturated with water is 55% or more. The retention rate of the tensile elastic modulus when saturated with water is calculated by the following formula: A/B×100 (A is the tensile elastic modulus when saturated with warm water at 50°C, and B is the tensile elastic modulus when not saturated).

Another aspect of the present invention is a polishing pad comprising any of the above-described non-porous molded articles for a polishing layer as a polishing layer. With such a polishing pad, polishing with excellent polishing uniformity can be achieved.

In addition, from the perspective of being able to form a polished surface with an excellent balance between global flatness (overall flatness) and local flatness (local flatness), the polishing pad preferably includes the above-mentioned polishing layer and a buffer layer, wherein the buffer layer is stacked on the polishing layer and has a hardness lower than that of the polishing layer.

Another aspect of the present invention is a chemical mechanical polishing method using the polishing pad.

Effects of the Invention

According to the present invention, even by long-term CMP polishing, a polished layer can be obtained in which burrs are less likely to be generated at the corners of recessed portions formed on the polished surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram illustrating CMP using a polishing pad.

2 is a scanning electron microscope (SEM) photograph of a cross section of a polishing layer after an 8-hour accelerated dressing test was performed using the polishing pad produced in Example 1.

3 is a SEM photograph of a cross section of a polishing layer after an 8-hour accelerated dressing test was performed using the polishing pad produced in Comparative Example 3. FIG.

4 is a graph showing the measurement results of the loss tangent (tan δ) of the thermoplastic polyurethanes used in Example 1 and Comparative Example 3, covering the range of 70 to -50°C.

Explanation of symbols

10 polishing pads

11 Rotating Platform

12 Slurry supply nozzle

13 Pallet

14 Pad Adjuster

15. Polished material

16 Polishing slurry

20 CMP device

DETAILED DESCRIPTION

Hereinafter, a non-porous molded body for a polishing layer, a polishing pad, and a polishing method according to one embodiment of the present invention will be described in detail.

The non-porous molded article for a polishing layer of this embodiment is a non-porous molded article (non-foamed molded article) of thermoplastic polyurethane, and has a maximum loss tangent (tanδ) of 4.00×10 ⁻² or less in the range of -70 to -50°C.

For the thermoplastic polyurethane of this embodiment, the maximum value of the loss tangent in the range of -70 to -50°C is 4.00× ^10-2 or less, preferably 3.50× ^10-2 or less, and more preferably 3.00× ^10-2 or less. Such a thermoplastic polyurethane is a thermoplastic polyurethane with high compatibility between the soft segment and the hard segment, high resilience, and low toughness. When the upper limit of the maximum value of the loss tangent in the range of -70 to -50°C of the thermoplastic polyurethane exceeds 4.00× ^10-2 , it becomes a thermoplastic polyurethane with low resilience and high toughness. In this case, burrs are easily generated at the corners (ends, shoulders) of the concave portion formed on the polishing surface during polishing. As a result, the polishing efficiency is reduced. In addition, the loss tangent in the range of -70 to -50°C of the thermoplastic polyurethane is preferably 2.00× ^10-2 or more. In this case, a thermoplastic polyurethane with moderate resilience, toughness, and hardness can be obtained. As a result, there is a tendency for improved polishing uniformity.

The thermoplastic polyurethane having a maximum loss tangent of 4.00×10 ^-2 or less in the range of -70 to -50°C can be obtained using, for example, a thermoplastic polyurethane obtained by polymerizing a polymer diol having a number average molecular weight of 650 to 1400, an organic diisocyanate, and a chain extender, wherein the content of nitrogen derived from urethane bonds is 5.7 to 6.5% by mass.

The number average molecular weight of the polymer diol used for the polymerization of thermoplastic polyurethane is preferably 650 to 1400, more preferably 800 to 1200, and particularly preferably 800 to 1000. When the number average molecular weight of the polymer diol is too low, there is a tendency for the hardness and tensile modulus to decrease, and the flatness of the polished layer to decrease. On the other hand, when the number average molecular weight of the polymer diol is too high, the soft segment and the hard segment phase separate, and the maximum value of the loss tangent exceeds 4.00× ^10-2 , which easily produces a thermoplastic polyurethane with low resilience and high toughness. As a result, burrs are easily generated at the corners of the recessed portion during polishing. It should be noted that the number average molecular weight of the polymer diol is the number average molecular weight calculated based on the hydroxyl value measured in accordance with JIS K 1557.

Examples of the polymer diol include polyether diol, polyester diol, and polycarbonate diol.

Examples of the polyether glycol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polymethyltetramethylene glycol, polyoxypropylene glycol, and glycerol-based polyalkylene ether glycols. These glycols may be used alone or in combination of two or more. Among these, polyethylene glycol and polytetramethylene glycol are particularly preferred.

Examples of the polyester diol include polyester diols obtained by directly subjecting a dicarboxylic acid or an ester-forming derivative thereof such as an ester or an acid anhydride to an esterification reaction or an ester exchange reaction with a low-molecular-weight diol.

Examples of dicarboxylic acids include aliphatic dicarboxylic acids having 2 to 12 carbon atoms, such as oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylglutaric acid, 2-methylsuberic acid, 3,8-dimethyldecanedioic acid, and 3,7-dimethyldecanedioic acid; aliphatic dicarboxylic acids such as dimerized aliphatic dicarboxylic acids having 14 to 48 carbon atoms (dimer acids) obtained by dimerizing unsaturated fatty acids obtained by fractionation of triglycerides, and their hydrogenates (hydrogenated dimer acids); alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and phthalic acid. Examples of dimer acids and hydrogenated dimer acids include "Pripol 1004," "Pripol 1006," "Pripol 1009," and "Pripol 1013," manufactured by Uniqema. These dicarboxylic acids may be used alone or in combination of two or more.

Specific examples of low-molecular-weight diols include aliphatic diols such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 2-methyl-1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; and alicyclic diols such as cyclohexanedimethanol and cyclohexanediol. These diols may be used alone or in combination of two or more. Among these, diols having 6 to 12 carbon atoms are preferred, those having 8 to 10 carbon atoms are more preferred, and those having 9 carbon atoms are particularly preferred.

Examples of the polycarbonate diol include polycarbonate diols obtained by reacting a carbonate compound with a low-molecular-weight diol.

As the object lesson of carbonate compounds, for example, can enumerate: diaryl carbonates such as dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, alkylene carbonate, diphenyl carbonate etc. In addition, as low molecular glycol, can enumerate the low molecular glycol identical with above-mentioned low molecular glycol.These materials can be used alone respectively, also can combine 2 or more and use.

The polymer diol may be used alone or in combination of two or more. Among these, from the viewpoint of excellent hydrophilicity, it is particularly preferred to include: a polyether diol selected from polyethylene glycol and polytetramethylene glycol; a polyester diol selected from poly(nonamethylene adipate), poly(2-methyl-1,8-octamethylene adipate), poly(2-methyl-1,8-octamethylene-co-nonamethylene adipate), and poly(methylpentane adipate); or at least one selected from their derivatives.

As the organic diisocyanate used for the polymerization of thermoplastic polyurethane, any organic diisocyanate currently used for the polymerization of thermoplastic polyurethane can be used without particular limitation. Specific examples thereof include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, isophorone diisocyanate, isopropylidenebis(4-cyclohexylisocyanate), cyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethylhexanoate, bis(2-isocyanatoethyl)fumarate, bis(2-isocyanatoethyl)carbonate, 2-isocyanatoethyl-2,6-diisocyanate Aliphatic or alicyclic diisocyanates such as 2,4'- or 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-toluene diisocyanate, m- or p-phenylene diisocyanate, m- or p-xylylene diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane, chlorophenylene-2,4-diisocyanate, and tetramethylxylylene diisocyanate may be used. These diisocyanates may be used alone or in combination of two or more. Among them, from the viewpoint of obtaining a polishing layer excellent in wear resistance, at least one selected from 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and isophorone diisocyanate is preferred, and 4,4'-diphenylmethane diisocyanate is particularly preferred.

Examples of chain extenders used in the polymerization of thermoplastic polyurethane include low molecular weight compounds that are currently used in the polymerization of thermoplastic polyurethane and have two or more active hydrogen atoms reactive with isocyanate groups in the molecule, preferably having a molecular weight of 300 or less. Specific examples thereof include: glycols such as ethylene glycol, diethylene glycol, propylene glycol, 2,2'-diethyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4-bis(β-hydroxyethoxy)benzene, 1,4-cyclohexanediol, bis-(β-hydroxyethyl)terephthalate, 1,9-nonanediol, m-xylene glycol, and p-xylene glycol; and glycols such as ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, and nonamethylenediamine. diamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2',4-trimethylhexamethylenediamine, 2,4,4'-trimethylhexamethylenediamine, 3-methylpentamethylenediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,2-diaminopropane, 1,3-diaminopropane, hydrazine, xylenediamine, isophoronediamine, piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, toluenediamine, xylenediamine, adipic acid dihydrazide, isophthalic acid dihydrazide, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-bis(4-aminophenoxy) Biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 1,4'-bis(4-aminophenoxy)benzene, 1,3'-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 3,4-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-methylene-bis(2-chloroaniline), 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl sulfide, 2,6-diaminotoluene, 2,4-diaminochlorobenzene, 1,2-diaminoanthraquinone, 1,4-diaminoanthraquinone, 3,3'-diamino Benzophenone, 3,4-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminobibenzyl, R(+)-2,2'-diamino-1,1'-binaphthyl, S(+)-2,2'-diamino-1,1'-binaphthyl, 1,3-bis(4-aminophenoxy)alkane, 1,4-bis(4-aminophenoxy)alkane, 1,5-bis(4-aminophenoxy)alkane, 1,n-bis(4-aminophenoxy)alkane (n is 3 to 10), 1,2-bis[2-(4-aminophenoxy)ethoxy]ethane, 9,9'-bis(4-aminophenyl)fluorene, diamines such as 4,4'-diaminobenzanilide, etc. These compounds may be used alone or in combination of two or more. Among them, at least one selected from 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, and cyclohexanedimethanol is preferred.

The ratio of each component of the monomers used in the polymerization of thermoplastic polyurethane (TPU), including the polymer diol, chain extender, and organic diisocyanate, can be appropriately selected based on the desired physical properties, such as wear resistance. Specifically, from the perspective of achieving excellent mechanical strength, wear resistance, productivity, and storage stability of the TPU, for example, the ratio of isocyanate groups contained in the organic diisocyanate is preferably 0.95 to 1.3 moles, more preferably 0.96 to 1.10 moles, and particularly preferably 0.97 to 1.05 moles, per 1 mole of active hydrogen atoms contained in the polymer diol and chain extender. If the ratio of isocyanate groups is too low, the mechanical strength and wear resistance of the non-porous molded article tend to decrease. If the ratio of isocyanate groups is too high, the productivity and storage stability of the TPU tend to decrease.

The mass ratio of the polymer diol, the organic diisocyanate and the chain extender is preferably polymer diol amount/(organic diisocyanate and chain extender amount) = 15/85 to 45/55, more preferably 20/80 to 40/60, and particularly preferably 25/75 to 35/65.

The thermoplastic polyurethane of this embodiment can be obtained by, for example, polymerizing monomers comprising a polymer diol having a number average molecular weight of 650 to 1400, an organic diisocyanate, and a chain extender through a urethanization reaction using a known prepolymer method or a one-step method. Preferably, a method is employed in which the monomers are melt-mixed and continuously melt-polymerized in the substantial absence of a solvent using a single-screw or multi-screw extruder.

The content of nitrogen derived from isocyanate groups of the organic diisocyanate in the thermoplastic polyurethane is preferably 5.7 to 6.5% by mass, more preferably 5.7 to 6.1% by mass. If the content of nitrogen derived from isocyanate groups of the organic diisocyanate is too low, the non-porous thermoplastic polyurethane molded article used as a polishing layer tends to be too soft, resulting in reduced flatness and polishing efficiency. Furthermore, if the content of nitrogen derived from isocyanate groups of the organic diisocyanate is too high, the maximum loss tangent at -70 to -50°C tends to exceed 4.00 × 10 ^-2 .

In addition, for thermoplastic polyurethane, in a sheet with a thickness of 0.5 mm, the laser transmittance for a laser wavelength of 660 nm is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. It should be noted that the laser transmittance for a laser wavelength of 660 nm is the value measured under the conditions of laser wavelength (660 nm), laser output power (310 μW), distance between the detection head and the output head (100 mm), and sample position (midpoint between the detection head and the output head). When the laser transmittance is too low, the soft segment and the hard segment of the thermoplastic polyurethane are prone to phase separation, and thus, the maximum value of the loss tangent at -70 to -50 ° C is likely to be higher than 4.00 × 10 ^-2 . Therefore, it is easy to form a thermoplastic polyurethane with low resilience and high toughness, and there is a tendency to easily produce burrs that will clog the concave portion formed on the polished surface over time. In addition, when the laser transmittance is too low, there is a tendency to be difficult to use for inspection of the polished material and detection of the polishing end point.

The tensile modulus of the thermoplastic polyurethane after saturation swelling with water at 50°C is preferably 130 to 800 MPa, more preferably 180 to 750 MPa, particularly preferably 230 to 700 MPa, and even more preferably 280 to 650 MPa. If the tensile modulus after saturation swelling with water at 50°C is too low, the polishing layer tends to become soft, resulting in reduced flatness and polishing efficiency. Furthermore, if the tensile modulus after saturation swelling with water at 50°C is too high, scratches tend to form on the polished surface.

Furthermore, for the thermoplastic polyurethane of this embodiment, the water-saturated swell retention rate of the tensile modulus, calculated according to the following formula (1), is preferably 55% or greater, more preferably 60% or greater, and particularly preferably 75% or greater. If the water-saturated swell retention rate of the tensile modulus is too low, the properties of the polishing layer may change significantly due to moisture. For example, if the pad is left wet for several hours to several days after polishing, the polishing rate may tend to decrease.

A/B×100

(A is the tensile modulus when the sample is saturated and swollen with 50°C hot water, and B is the tensile modulus when the sample is not saturated and swollen with 50°C hot water)···(1)

The non-porous molded body of the present embodiment is preferably manufactured in the form of a sheet by extrusion molding or injection molding the thermoplastic polyurethane without a foaming agent using a T-die. In particular, from the viewpoint of obtaining a sheet of uniform thickness, the sheet obtained by extrusion molding using a T-die is preferred.

The thickness of the sheet is not particularly limited and can be appropriately adjusted according to the layer structure and application of the polishing pad. Specifically, it is preferably 1.5 to 3.0 mm, more preferably 1.7 to 2.8 mm, and particularly preferably 2.0 to 2.5 mm.

The contact angle of the sheet with water is preferably 80 degrees or less, more preferably 75 degrees or less, and particularly preferably 70 degrees or less. If the contact angle with water is too high, scratches tend to be easily generated on the polished surface.

The hardness of the sheet is preferably 55 or higher in JIS-D hardness, more preferably 60 to 80, and particularly preferably 65 to 75. If the JIS-D hardness is too low, the flatness tends to be locally reduced, while if the JIS-D hardness is too high, scratches tend to be easily generated.

The polishing pad of this embodiment includes a polishing layer formed by cutting a circular or other shaped piece from a sheet of the aforementioned non-porous molded body. The polishing pad may be a single-layer polishing pad made of a sheet of the non-porous molded body, or a multi-layer polishing pad made by laminating a cushioning layer on a sheet of the non-porous molded body.

The buffer layer is preferably a layer having a lower hardness than the polishing layer. When the hardness of the buffer layer is lower than that of the polishing layer, the hard polishing layer can easily follow the local unevenness of the polished surface. Because the buffer layer follows all the warping and undulations of the polished material, polishing with an excellent balance between global and local flatness can be achieved.

Specific examples of materials used for the cushioning layer include: known composites of non-woven fabrics impregnated with polyurethane; rubbers such as natural rubber, nitrile rubber, polybutadiene rubber, and silicone rubber; thermoplastic elastomers such as polyester thermoplastic elastomers, polyamide thermoplastic elastomers, and fluorine-containing thermoplastic elastomers; foamed plastics; and polyurethanes. Among these, polyurethanes having a foamed structure are particularly preferred due to their moderate flexibility.

The thickness of the buffer layer is not particularly limited, but is preferably 0.3 to 1.2 mm, more preferably 0.5 to 1.0 mm. If the buffer layer is too thin, the ability to adapt to the overall warping and undulation of the polishing material may be reduced, and the overall flatness of the polishing pad may be reduced. On the other hand, if the buffer layer is too thick, the polishing pad may become soft as a whole, making stable polishing difficult.

The polishing layer of the polishing pad of this embodiment is generally formed with concentric grooves or holes to ensure that the slurry is evenly and sufficiently supplied to the polishing surface. Such concave portions also help to remove polishing debris that causes scratches and prevent wafer damage caused by adsorption of the polishing pad.

The method for forming the concave portions on the polished surface is not particularly limited. Specifically, examples include methods of forming a predetermined concave pattern on the polished surface of the polishing layer by cutting the surface of a non-porous molded body, forming concave portions by transfer molding using a mold during injection molding, and imprinting using a heated mold.

For example, when the grooves are formed concentrically, the spacing between the grooves is preferably 2.0 to 50 mm, more preferably 5.5 to 30 mm, and particularly preferably 6.0 to 15 mm. Furthermore, the groove width is preferably 0.1 to 3.0 mm, more preferably 0.4 to 2.0 mm. Furthermore, the groove depth is preferably 0.2 to 1.8 mm, more preferably 0.4 to 1.5 mm. Furthermore, the cross-sectional shape of the grooves can be appropriately selected, for example, rectangular, trapezoidal, triangular, or semicircular, depending on the intended purpose.

When a concave portion is formed on the polishing surface, burrs may sometimes form at the corners (shoulders and ends) of the concave portion due to prolonged and repeated contact between the polished material, the regulator, and the concave portion. Furthermore, such burrs gradually clog the concave portion, gradually reducing the slurry supply. This results in a gradual decrease in polishing speed and polishing uniformity. The polishing layer using the non-porous molded body of thermoplastic polyurethane of this embodiment can suppress the formation of burrs that clog such concave portions.

An embodiment of CMP using the polishing pad of this embodiment will be described.

In CMP, for example, a CMP apparatus 20 including a circular rotating platform 11, a slurry supply nozzle 12, a support plate 13, and a pad conditioner 14, as shown in FIG1 , can be used. A polishing pad 10 is attached to the surface of the rotating platform 11 using double-sided tape or the like. Furthermore, the support plate 13 supports a material to be polished 15.

In the CMP apparatus 20, the rotating platform 11 is rotated by a motor (not shown) in the direction indicated by the arrow. Furthermore, the support plate 13 is rotated within the plane of the rotating platform 11 by a motor (not shown), for example, in the direction indicated by the arrow. The pad conditioner 14 is also rotated within the plane of the rotating platform 11 by a motor (not shown), for example, in the direction indicated by the arrow.

First, distilled water is flowed onto the polishing surface of the rotating polishing pad 10, which is fixed to a rotating platform 11. The rotating pad conditioner 14 is pressed to condition the polishing surface of the polishing pad 10. For example, a pad conditioner can be used in which diamond particles are fixed to the surface of a carrier by nickel plating. This adjusts the surface roughness of the polishing layer of the polishing pad 10 to a level appropriate for the polishing of the surface being polished. Next, polishing slurry 16 is supplied from a slurry supply nozzle 12 to the polishing surface of the rotating polishing pad 10. Polishing slurry 16 contains a liquid medium such as water or oil; a polishing agent such as silica, alumina, cerium oxide, zirconium oxide, or silicon carbide; and an alkali, acid, surfactant, oxidizing agent, reducing agent, or chelating agent. Lubricating oil, coolant, or the like can also be used in combination with the polishing slurry during CMP, as needed. Then, the material being polished 15, which is fixed to a rotating support plate 13, is pressed against the polishing pad 10, which is completely wetted with the polishing slurry 16. Then, the polishing process is continued until a given flatness is obtained. The quality of the finished product can be influenced by adjusting the pressing force and the relative movement speed of the rotating platform 11 and the support plate 13 during the polishing process.

Polishing conditions are not particularly limited. To efficiently perform polishing, the platform and substrate are preferably rotated at a low speed of 300 rpm or less. In addition, to suppress the generation of scratches, the pressure applied to the substrate is preferably 150 kPa or less. In addition, polishing slurry is preferably continuously supplied to the polishing surface during polishing. The supply amount of polishing slurry is preferably an amount that constantly wets the entire polishing surface.

Then, the polished material after polishing is fully cleaned with running water, and then preferably a rotary dryer is used to remove water droplets attached to the polished material and dry it. Thus, by polishing the polished surface with the polishing slurry, a flat surface can be obtained on the entire polished surface.

The CMP method of this embodiment can be preferably used for polishing in the manufacturing process of various semiconductor devices, MEMS (Micro Electro Mechanical Systems), etc. Examples of materials to be polished include: semiconductor wafers such as silicon wafers, silicon oxide, and fluorinated silicon oxide; inorganic insulating films such as silicon oxide films, glass films, and silicon nitride films formed on wiring boards having predetermined wiring; films mainly containing polycrystalline silicon, aluminum, copper, titanium, titanium nitride, tungsten, tantalum, and tantalum nitride; optical glass such as that used for photomasks, lenses, and prisms; inorganic conductive films such as tin-doped indium oxide (ITO); optical single crystals made of glass and crystalline materials for optical integrated circuits, optical switching elements, optical waveguides, optical fiber end faces, scintillators, etc.; solid-state laser single crystals; sapphire substrates for blue laser LEDs; semiconductor single crystals such as silicon carbide, gallium phosphide, and gallium arsenide; glass substrates for magnetic disks; magnetic heads; and synthetic resins such as methacrylic resin and polycarbonate resin.

Example

The present invention will be further described in detail below by way of examples. It should be noted that the scope of the present invention is not limited by these examples.

[Example 1]

A prepolymer was prepared by mixing polytetramethylene glycol (PTMG850) with a number average molecular weight of 850, 1,4-butanediol (BD), and 4,4'-diphenylmethane diisocyanate (MDI) at a mass ratio of PTMG850:BD:MDI = 32.5:15.6:51.9. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane A. Thermoplastic polyurethane A was then evaluated using the following evaluation method.

Maximum value of loss tangent (tanδ) in the range of -70 to -50°C

Thermoplastic polyurethane A was sandwiched between two metal plates and hot-pressed using a hot press molding machine (a table-type test press manufactured by Shinto Industries Co., Ltd.). In the hot press molding, after preheating at a heating temperature of 230°C for 2 minutes, the sheet was pressed for 1 minute at a pressing pressure of 300 μm in thickness. Then, the two metal plates sandwiching thermoplastic polyurethane A were taken out from the hot press molding machine and cooled, and then the pressed sheet was demoulded. The obtained pressed sheet was dried at 60°C for 16 hours in a reduced pressure dryer. Then, a 5.0×25 (mm) test piece was cut out from the pressed sheet. The temperature dependence of the dynamic viscoelastic modulus was measured at a frequency of 1.59 Hz on the cut test piece using a dynamic viscoelasticity measuring device (DVE Rheospectoler, manufactured by Rheology) in the range of -120 to 250°C. Then, the maximum value of the loss tangent (tan δ) in the range of -70 to -50°C was determined from the obtained temperature dependency graph of the dynamic viscoelastic modulus. The temperature dependency graph of the dynamic viscoelastic modulus is shown in FIG4 .

Light transmittance of thermoplastic polyurethane sheets

A press-molded sheet was obtained by the same method as in the loss tangent measurement except that the thickness was changed to 0.5 mm (500 μm). The press-molded sheet was then cut into a predetermined size and the light transmittance at a wavelength of 660 nm was measured under the following conditions.

Spectral transmittance measuring device: "U-4000 Spectrometer" manufactured by Hitachi, Ltd.

Laser wavelength: 660nm

Laser output power: 310μW

Distance between detection heads and output heads: 10cm

·Test piece measurement position: the middle position between the detection head and the output head

<Tensile elastic modulus during water swelling and retention rate of tensile elastic modulus during water swelling>

A No. 2 type test piece (JIS K7113) was punched out from the same press-molded sheet as used for the loss tangent measurement, and then allowed to stand for 3 days under conditions of 20° C. and 65% RH for conditioning.

Separately, another Type 2 test piece was immersed in 50°C warm water for 48 hours to saturate with water. The Type 2 test piece was then removed from the warm water, its surface moisture wiped off, and then left at 20°C, 65% RH for 3 days for conditioning.

The tensile modulus was then measured using each of the conditioned Type 2 test pieces. The tensile modulus was measured using an Instron 3367 under the following environmental conditions: 20°C, 65% RH, a chuck distance of 40 mm, a tensile speed of 500 mm/min, and a tensile strength of 6 pieces.

Then, the tensile modulus after saturation swelling with water was defined as A, and the tensile modulus in the dry state without saturation swelling with water was defined as B. The retention rate of the tensile modulus during water swelling was calculated by the following formula (1).

A/B×100···(1)

(A is the tensile modulus at 20°C and 65% RH after saturation swelling with 50°C hot water, and B is the tensile modulus at 20°C and 65% RH before saturation swelling).

Contact angle with water

The contact angle of water with the same press-molded sheet as that used in the loss tangent measurement was measured using DropMaster 500 manufactured by Kyowa Interface Science Co., Ltd.

<Determination of the Nitrogen Content Ratio of Isocyanate Groups Derived from Organic Diisocyanates>

First, the total nitrogen content was calculated by elemental analysis under the following conditions.

· Apparatus: Fully automatic elemental analyzer 2400 Series II (with automatic sampler as standard) manufactured by PerkinElmer Co., Ltd. C·H·N·S/O analyzer

Electric furnace temperature: 975℃

Sample size: 2 mg

Combustion aid: None

Sample container: Tin foil (has combustion-supporting effect, use 1)

Standard substance for preparing standard curve: p-aminobenzenesulfonamide

Next, nitrogen atoms derived from the organic diisocyanate and nitrogen atoms derived from the chain extender were detected by NMR measurement under the following conditions.

Device: Lambda500 nuclear magnetic resonance device manufactured by JEOL Ltd.

Measurement conditions: Resonance frequency; 1H 500MHz/probe; TH5FG2

Solvent: DMSO-d6 concentration: 5wt%/vol

·Measurement temperature: 80℃

Number of points: 64s

Then, the nitrogen content ratio derived from the isocyanate group of the organic diisocyanate was calculated based on the results of elemental analysis and NMR.

Accelerated dressing test

Except changing to a thickness of 2.0 mm, the same operation as the preparation method in the loss tangent determination was performed to obtain a press-formed sheet. Then, a 20 mm × 50 mm test piece was cut out from the press-formed sheet. A groove with a width of 1.0 mm and a depth of 1.0 mm was formed on the obtained test piece to make a sheet for the polishing layer. Then, a hole with the same shape as the test piece was opened on the polyurethane pad of the substrate, and the test piece was embedded to obtain a polishing pad. The polishing pad was installed in an electric rotary polisher (RK-3D type) manufactured by NIDEC-SHIMPO. Then, a diamond dresser (#100) manufactured by Allied Material was used. While the slurry was flowed at a speed of 150 mL/min, the polishing pad surface was ground for 8 hours under the conditions of a dresser speed of 61 rpm, a polishing pad speed of 60 rpm, and a dresser load of 2.75 psi. By visually observing the polishing layer after grinding, it was judged to be good in the case of no burr generation at all, and it was judged to be poor even if a little burr generation was also judged to be poor.

The above evaluation results are summarized in Table 1.

[Example 2]

A prepolymer was prepared by mixing polytetramethylene glycol (PTMG1000) with a number-average molecular weight of 1000, BD, and MDI at a mass ratio of PTMG1000:BD:MDI = 32.0:16.2:51.8. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane B.

The evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane B was used instead of thermoplastic polyurethane A. The results are shown in Table 1.

[Example 3]

A prepolymer was prepared by mixing polytetramethylene glycol (PTMG850) with a number-average molecular weight of 850, BD, and MDI at a mass ratio of PTMG850:BD:MDI = 28.9:16.6:54.5. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane C.

The evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane C was used instead of thermoplastic polyurethane A. The results are shown in Table 1.

[Comparative Example 1]

A prepolymer was prepared by mixing PTMG850, BD, 3-methylpentanediol (MPD), and MDI in a mass ratio of PTMG850:BD:MPD:MDI = 18.5:15.0:6.6:59.9. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane D.

The evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane D was used instead of thermoplastic polyurethane A. The results are shown in Table 1.

[Comparative Example 2]

A prepolymer was prepared by mixing polytetramethylene glycol (PTMG1400) with a number average molecular weight of 1400, BD, MPD, and MDI at a mass ratio of PTMG1400:BD:MPD:MDI = 32.4:12.2:5.4:50.0. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane E.

The evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane E was used instead of thermoplastic polyurethane A. The results are shown in Table 1.

[Comparative Example 3]

A prepolymer was prepared by mixing polytetramethylene glycol (PTMG2000) with a number average molecular weight of 2000, BD, MPD, and MDI in a mass ratio of PTMG2000:BD:MPD:MDI = 31.7:12.7:5.6:50.0. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane F.

Evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane F was used instead of thermoplastic polyurethane A. The results are shown in Table 1. FIG3 shows a scanning electron microscope (SEM) photograph of a cross-section of a polishing pad produced in Comparative Example 3 after an accelerated dressing test. FIG4 shows a graph of the temperature dependence of the dynamic viscoelastic modulus.

[Comparative Example 4]

A prepolymer was prepared by mixing PTMG2000, poly(2-methyl-1,8-octamethylene-co-nonamethylene adipate) diol (PNOA2000) with a number average molecular weight of 2000; the molar ratio of nonamethylene units to 2-methyl-1,8-octamethylene units was 7:3, 1,4-cyclohexanedimethanol (CHDM), BD, and MDI in a mass ratio of PTMG2000:PNOA2000:BD:CHDM:MDI = 21.7:9.3:13.6:5.4:50.0. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane G.

The evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane G was used instead of thermoplastic polyurethane A. The results are shown in Table 1.

[Comparative Example 5]

A prepolymer was prepared by mixing PTMG2000, PNOA2000, CHDM, BD, and MDI in a mass ratio of PTMG2000:PNOA2000:BD:CHDM:MDI = 17.0:7.3:15.2:6.1:54.4. The resulting prepolymer was then kneaded in a small kneader at 240°C and a screw speed of 100 rpm for 5 minutes to produce thermoplastic polyurethane H.

The evaluation was performed in the same manner as in Example 1, except that thermoplastic polyurethane H was used instead of thermoplastic polyurethane A. The results are shown in Table 1.

According to Table 1, the polishing pads of Examples 1 to 3, which used a non-porous thermoplastic polyurethane molded article having a maximum tan δ value of 4.00 × 10 ^-2 or less in the range of -70 to -50°C as the polishing layer, did not produce burrs during the accelerated dressing test. Furthermore, the thermoplastic polyurethane sheet had high laser transmittance. On the other hand, according to Table 1, the polishing pads of Comparative Examples 1 to 5, which used a non-porous thermoplastic polyurethane molded article having a maximum tan δ value of more than 4.00 × 10 ^-2 in the range of -70 to -50°C as the polishing layer, produced burrs during the accelerated dressing test. Furthermore, the thermoplastic polyurethane sheet had low laser transmittance.

Claims (8)

1. A non-porous molded body for a polishing layer, which is a non-porous molded body of thermoplastic polyurethane, wherein, The thermoplastic polyurethane is obtained by polymerizing a high molecular weight diol with a number average molecular weight of 650-1400, an organic diisocyanate, and a chain extender, wherein the nitrogen content of the isocyanate groups derived from the organic diisocyanate is 5.7-6.5% by mass. The maximum loss tangent (tanδ) of the thermoplastic polyurethane in the range of -70 to -50°C is less than 4.00 × ^10⁻² . 2. The non-porous molded body for polishing layer according to claim 1, wherein the 0.5 mm thick sheet of the thermoplastic polyurethane has a laser transmittance of 70% or more for a 660 nm wavelength laser. 3. The non-porous molded body for polishing layer according to claim 1, wherein the tensile elastic modulus after the thermoplastic polyurethane is saturated and swollen with warm water at 50°C is 130-800 MPa. 4. The non-porous molded body for polishing layer according to claim 1, wherein the retention rate of the tensile modulus of elasticity of the thermoplastic polyurethane during water saturation swelling is 55% or more, and the retention rate of the tensile modulus of elasticity during water saturation swelling is calculated by the following formula. A/B×100 A represents the tensile modulus of elasticity when the water at 50°C is used to saturate and swell it, while B represents the tensile modulus of elasticity when the water is not used to saturate and swell it. 5. The non-porous molded body for polishing layer according to claim 1, wherein the contact angle between the thermoplastic polyurethane sheet and water is less than 80 degrees. 6. A polishing pad comprising a polishing layer according to any one of claims 1 to 5, wherein the polishing layer is a non-porous molded body. 7. The polishing pad according to claim 6, comprising the polishing layer and a buffer layer, the buffer layer being stacked on the polishing layer and having a lower hardness than the polishing layer. 8. A chemical mechanical polishing method, the method comprising using the polishing pad as described in claim 6 or 7.