Polyurethane, polishing layer, polishing pad, and polishing method

Abstract

Provided are: a polyurethane for forming a polishing layer in which clogging can be suppressed, and polishing can be performed stably and with long service life with suppressed occurrence of damage; a polishing layer and polishing pad which use the polyurethane; and a polishing method.　A polyurethane having at least one structural unit derived from a compound having a carboxy group. A polishing layer and polishing pad which use the polyurethane, and a polishing method.

Description

[Technical Field]

[0001] The present invention relates to a novel polyurethane, an abrasive layer using the same, an abrasive pad, and a polishing method. [Background technology]

[0002] In recent years, with the increasing demand for higher integration and multi-layer wiring in semiconductor wafers and semiconductor devices, there has been a growing need for improvements in the fundamental quality of these materials, such as surface flatness. Chemical Mechanical Polishing (CMP) is a polishing method used to planarize the surface of semiconductor wafers. CMP is a method of polishing an object with high precision by supplying a slurry containing abrasive particles and a reaction solution to the surface of the object to be polished using a polishing pad. Examples of materials that make up the polishing layer of the polishing pad used in this method include polyurethane having a closed-cell structure. Polyurethane having a closed-cell structure is generally manufactured by casting and foaming a two-component curable polyurethane (for example, Patent Documents 1-4). However, this method makes it difficult to achieve uniformity in the reaction and foaming, and there are limitations to increasing the hardness of the resulting polyurethane, which makes the polishing properties such as the flatness and flattening efficiency of the polished surface prone to fluctuations. In addition, because the foam structure has independent pores, polishing slurry and polishing debris used in the polishing process tend to enter these pores and clog, leading to problems such as a decrease in polishing speed and a shortened pad life.

[0003] On the other hand, as a polyurethane constituting the polishing layer, there are also those in which polyurethane resin is impregnated into a nonwoven fabric and solidified (for example, Patent Documents 5-7). Such nonwoven fabric type polishing pads have an uneven structure, voids, and interconnected pores due to the structure of the nonwoven fabric, which makes it easy to improve the polishing rate because the slurry can be easily accumulated during polishing, and also has good contact with the wafer due to its high flexibility. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-178374 [Patent Document 2] Japanese Patent Publication No. 2000-248034 [Patent Document 3] Japanese Patent Publication No. 2001-89548 [Patent Document 4] Japanese Patent Application Publication No. 11-322878 [Patent Document 5] Japanese Patent Application Publication No. 11-99479 [Patent Document 6] Japanese Patent Publication No. 2005-212055 [Patent Document 7] Japanese Patent Application Publication No. 3-234475 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, while nonwoven fabric polishing pads have good slurry retention due to the uneven structure of the nonwoven fabric, they also have the problem that abrasive particles can clog these irregularities, altering the hardness and elastic modulus of the polyurethane, which in turn makes wafers more susceptible to scratching. Furthermore, the changes in hardness due to clogging reduce the stability of polishing and shorten the lifespan of the polishing pad.

[0006] The present invention has been made in view of the above-mentioned conventional problems, and aims to provide a polyurethane that constitutes an abrasive layer that can polish stably and for a long time while suppressing the occurrence of scratches by suppressing clogging of the abrasive layer, an abrasive layer using the same, a polishing pad, and a polishing method. [Means for solving the problem]

[0007] In order to solve the aforementioned problems, the inventors conducted extensive research and found that by using polyurethane containing carboxyl groups in its molecular structure as the polishing layer, the carboxyl groups dissociate during polishing, causing the entire polishing layer to change to a negative potential. As a result, they discovered that the repulsive force between the negatively potential polishing layer and the negatively potential abrasive grains prevents clogging of the abrasive grains, allowing for stable and long-lasting polishing while suppressing damage, thus completing the present invention.

[0008] The present invention is summarized in the following [1] to

[10] . [1] A polyurethane having at least one structural unit derived from a compound having a carboxyl group. [2] The polyurethane according to [1], comprising at least a structural unit derived from the compound having a carboxyl group, a structural unit derived from a chain extender, a structural unit derived from a polymer diol, and a structural unit derived from an organic diisocyanate. [3] The polyurethane according to [1] or [2], wherein the amount of structural units derived from the compound having the carboxyl group is 3 to 30 mol% of the total structural units constituting the polyurethane. [4] An abrasive layer using polyurethane as described in any of [1] to [3] above. [5] The polishing layer according to [4], wherein the polishing layer is obtained by impregnating a nonwoven fabric with polyurethane and then solidifying it. [6] The polishing layer according to [4] or [5], wherein the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is -10.0 mV or less. [7] The polishing layer according to any one of [4] to [6], wherein the polyurethane is non-foamed. [8] The polishing layer according to any one of [4] to [7], wherein the polyurethane is saturated and swollen with water at 50°C, and the storage modulus measured at 50°C is 50 to 1,200 MPa, and the contact angle with water is 80 degrees or less. [9] A polishing pad using the polishing layer described in any of the above [4] to [8].

[10] A polishing method using the polishing layer described in any of [4] to [8] above, A step of fixing a polishing pad provided with the polishing layer on a surface plate of a polishing apparatus; A step of holding an object to be polished by a holder of a polishing apparatus so as to face the polishing surface of the polishing layer; A step of polishing the object to be polished by relatively sliding the polishing pad and the object to be polished while supplying a neutral or alkaline polishing slurry between the polishing surface and the object to be polished; A polishing method comprising the above steps.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a polyurethane that constitutes a polishing layer capable of stably polishing with a long life while suppressing the generation of scratches by suppressing clogging of the polishing layer, a polishing layer using the same, a polishing pad, and a polishing method.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic diagram for explaining a carboxy group present in the molecular structure of the polyurethane of the present invention having a structural unit derived from dimethylolpropionic acid. [Figure 2] FIG. 2 is a schematic diagram for explaining a state in which the carboxy group is dissociated in FIG. 1. [Figure 3] FIG. 3 is a schematic diagram for explaining the polishing method of the present invention. [Figure 4] FIG. 4 is a photograph showing the types (evaluation criteria) of scratches on the object to be polished in Examples and Comparative Examples.

Embodiments for Carrying Out the Invention

[0011] [Polyurethane] The polyurethane of the present invention has at least one or more structural units derived from a compound having a carboxy group. According to the present invention, since the polyurethane has at least one structural unit derived from a compound having a carboxyl group, a carboxyl group is present within the molecular structure of the polyurethane. When this is used as the material for the polishing layer of a polishing pad, the repulsive force between the negative potential generated by the dissociation of the carboxyl group and the negative potential of the abrasive grains makes it difficult for the abrasive grains to clog the uneven parts of the polishing layer. Therefore, scratches caused by clogging can be suppressed, and polishing can be performed stably for a long time. Furthermore, in this invention, by adjusting the amount of carboxyl groups present in the molecular structure of the polyurethane, it is possible to impart not only a negative potential to the surface of the polyurethane but also properties such as hydrophilicity.

[0012] The polyurethane of the present invention can be produced, for example, by using a compound having a carboxyl group in addition to the raw materials used in the production of general polyurethanes. Specifically, examples of compounds having a carboxyl group include dimethylolpropionic acid, and by reacting this with raw materials such as polymer diols and isocyanates, a polyurethane having a carboxyl group in its molecular structure, as shown in the schematic diagram of Figure 1, can be obtained. As mentioned above, this carboxyl group can improve the hydrophilicity of the polyurethane surface and improve the wettability of the polyurethane surface.

[0013] Figure 2 is a diagram illustrating the state in which the carboxyl group of the polyurethane has dissociated in Figure 1. By setting the pH conditions to ionize the carboxyl group of the polyurethane in Figure 1, the carboxyl group becomes -COO as shown in Figure 2. - and H + Because it dissociates, -COO is formed on the surface of the polyurethane. - A negative potential can be imparted due to this. Therefore, when the polyurethane of the present invention is used as an abrasive layer, if an alkaline slurry is used, the carboxyl group dissociates, and -COO -This causes the zeta potential of the polishing layer to become negative. As a result, the abrasive grains in the alkaline slurry and the polyurethane repel each other, making it less likely for the abrasive grains to clog the uneven parts of the polishing layer, and consequently improving polishing efficiency.

[0014] The polyurethane of the present invention is not particularly limited as long as it has at least one structural unit derived from a compound having a carboxyl group, and may be a thermoplastic polyurethane or a thermosetting polyurethane, but it is preferably a thermoplastic polyurethane because it can be produced continuously by melt polymerization and can be easily processed into a sheet when used as an abrasive layer for an abrasive pad. Furthermore, the polyurethane of the present invention can be suitably used not only for the abrasive layer of polishing pads, but also for applications that impart hydrophilicity to the polyurethane surface or for applications that require modification of electrical properties, etc.

[0015] Below, thermoplastic polyurethane will be described in detail as an example of the polyurethane of the present invention. The thermoplastic polyurethane according to the present invention is preferably one that contains, for example, structural units derived from a compound having a carboxyl group, structural units derived from a chain extender, structural units derived from a polymer diol, and structural units derived from an organic diisocyanate, from the viewpoint of ease of manufacture.

[0016] [Compounds containing a carboxyl group] Specific examples of compounds having a carboxyl group include, for example, diols having a carboxyl group, diamines having a carboxyl group, polymeric diols having a carboxyl group, and derivatives thereof. Specifically, for example, compounds represented by the following general formulas (1) to (3) can be cited.

[0017] [ka] (In formulas (1) to (3), R 1 ~R 6Each of the following independently represents a hydroxyl group or an amino group. Furthermore, each of the following independently represents a trivalent hydrocarbon group or aromatic hydrocarbon group having 1 to 10 carbon atoms, which may have substituents, and each of the following independently represents a divalent hydrocarbon group having 1 to 10 carbon atoms. l, m, and n represent integers from 1 to 10.

[0018] Examples of compounds having such a carboxyl group include dimethylolpropionic acid, dimethylolbutanoic acid, tartaric acid, 2-hydroxypropionic acid, malic acid, and 4-hydroxymethylbenzoic acid, from the viewpoint of excellent reactivity and availability. Among these, the compound represented by formula (1) is preferred, and in the compound represented by formula (1), the compound in which R is a trivalent hydrocarbon group having 1 to 6 carbon atoms is more preferred, and from the viewpoint of ensuring the rigidity of the polished layer while exhibiting zeta potential characteristics, dimethylolpropionic acid and dimethylolbutanoic acid are even more preferred.

[0019] [Chain extender] Examples of chain extenders include compounds commonly used in the manufacture of polyurethanes (excluding compounds having the aforementioned carboxyl group). Specifically, examples include low-molecular-weight compounds with a molecular weight of 300 or less, having two or more active hydrogen atoms in the molecule that can react with an isocyanate group, and not containing a dienophile or diene. Examples of chain extenders include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 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, and cyclohexanedimethanol (1,4-bis(β-hydroxyethoxy)benzene). Diols such as chlorohexanedimethanol, bis(β-hydroxyethyl) terephthalate, 1,9-nonanediol, m-xylylene glycol, p-xylylene glycol, diethylene glycol, triethylene glycol, etc.; ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, 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, Hydrazine, Xylylenediamine, Isophoronediamine, Piperazine, o-Phenylenediamine, m-Phenylenediamine, p-Phenylenediamine, Tolylenediamine, Xylylenemine, Dihydrazide adipate, Dihydrazide isophthalate, 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'-diaminodiphenylsulfone, 3,4-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-methylene-bis(2-chloroaniline), 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,Examples of diamines include 4'-diaminodiphenyl sulfide, 2,6-diaminotoluene, 2,4-diaminochlorobenzene, 1,2-diaminoanthraquinone, 1,4-diaminoanthraquinone, 3,3'-diaminobenzophenone, 3,4-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminobibenzyl, 2,2'-diamino-1,1'-binaphthalene, 1,3-bis(4-aminophenoxy)alkane, 1,4-bis(4-aminophenoxy)alkane, 1,5-bis(4-aminophenoxy)alkane, and other 1,n-bis(4-aminophenoxy)alkanes (where n is 3 to 10), 1,2-bis[2-(4-aminophenoxy)ethoxy]ethane, 9,9-bis(4-aminophenyl)fluorene, and 4,4'-diaminobenzanilide. These can be used individually or in combination of two or more types. Among these, diols such as 1,4-butanediol and 1,5-pentanediol, and diamines such as hydrazine are preferred from the viewpoint of improving the rigidity of the polishing layer.

[0020] When using a chain extender, the ratio (mol%) of the compound having a carboxyl group to the total amount of the compound having a carboxyl group and the chain extender is appropriately selected depending on the purpose, but for example, it is preferably 5 to 90 mol%, more preferably 10 to 70 mol%, and even more preferably 15 to 60 mol%. By having the content of the compound having a carboxyl group within the above range, a negative potential that sufficiently repels the negative potential of the abrasive grains can be imparted to the polyurethane.

[0021] [High molecular weight diol] Specific examples of polymeric diols include, for example, polyether diols, polyester diols, and polycarbonate diols. These may be used individually or in combination of two or more. Among these, polyether diols and polycarbonate diols are preferred from the viewpoint of availability and reactivity, with polyether diols being more preferred.

[0022] The number-average molecular weight of the polymer diol is preferably 450 to 3,000, more preferably 500 to 2,700, and even more preferably 550 to 2,400. When the number-average molecular weight of the polymer diol is within the above range, it is easier to obtain a polished layer that maintains the required properties such as rigidity, hardness, and hydrophilicity. Note that the number-average molecular weight of the polymer diol refers to the number-average molecular weight calculated based on the hydroxyl value measured in accordance with JIS K 1557-1:2007.

[0023] (Polyetherdiol) Specific examples of polyetherdiols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(methyltetramethylene glycol), and glycerin-based polyalkylene ether glycol. These may be used individually or in combination of two or more. Among these, polyethylene glycol and polytetramethylene glycol are preferred.

[0024] (Polyester Diol) In the present invention, polyester diols can be used. Polyester diols can be obtained, for example, by directly esterifying or transesterifying a low molecular weight diol with an ester-forming derivative such as a dicarboxylic acid or its ester or anhydride.

[0025] Specific examples of dicarboxylic acids, their esters, and their anhydrides for producing polyester diols include, for example, 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, dodecanedicarboxylic acid, 2-methylsuccinic acid, 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanediic acid, and 3,7-dimethyldecanediic acid; aliphatic dicarboxylic acids having 14 to 48 carbon atoms obtained by dimerizing unsaturated fatty acids obtained by fractional distillation of triglycerides, and their hydrogenated products (hydrogenated dimer acids); alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and orthophthalic acid. Furthermore, specific examples of dimer acids and hydrogenated dimer acids include, for example, Unikema's trade names "Prepol 1004," "Prepol 1006," "Prepol 1009," and "Prepol 1013." These may be used individually or in combination of two or more types.

[0026] Furthermore, specific examples of low molecular weight diols for producing polyester diols include, for example, aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 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 may be used individually or in combination of two or more. Among these, diols having 6 to 12 carbon atoms are preferred, and diols having 8 to 10 carbon atoms are more preferred.

[0027] (Polycarbonate diol) Examples of polycarbonate diols include those obtained by the reaction of a low molecular weight diol with a carbonate compound such as a dialkyl carbonate, alkylene carbonate, or diaryl carbonate. Examples of low molecular weight diols for producing polycarbonate diols include those exemplified above. Examples of dialkyl carbonates include dimethyl carbonate and diethyl carbonate. Examples of alkylene carbonates include ethylene carbonate. Examples of diaryl carbonates include diphenyl carbonate.

[0028] [Organic diisocyanates] There are no particular restrictions on the organic diisocyanate used, as long as it is an organic diisocyanate commonly used in the manufacture of polyurethane. For example, ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, isophorone diisocyanate, isopropylidene bis(4-cyclohexyl isocyanate), cyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis(2-isocyanatoethyl) fumarate, bis(2-isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, cyclohexylene diisocyanate, Examples include aliphatic or alicyclic diisocyanates such as methylcyclohexylene diisocyanate and bis(2-isocyanatoethyl)-4-cyclohexene; and aromatic diisocyanates such as 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tollylene diisocyanate, 2,6-tollylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, 1,5-naphthylene diisocyanate, 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane, chlorophenylene-2,4-diisocyanate, and tetramethylxylylene diisocyanate. These can be used individually or in combination of two or more types.Among these, alicyclic diisocyanates and aromatic diisocyanates are preferred from the viewpoint of improving the wear resistance of the resulting polished layer, 4,4'-dicyclohexylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate are more preferred, and 4,4'-diphenylmethane diisocyanate is even more preferred from the viewpoint of improving the rigidity of the polished layer.

[0029] [Additives] The polyurethane of the present invention may optionally contain additives such as crosslinking agents, fillers, crosslinking accelerators, crosslinking aids, softeners, tackifiers, anti-aging agents, foaming agents, processing aids, adhesion enhancers, inorganic fillers, organic fillers, nucleating agents, heat stabilizers, weather stabilizers, antistatic agents, colorants, lubricants, flame retardants, flame retardant aids (such as antimony oxide), blooming inhibitors, mold release agents, thickeners, antioxidants, and conductive agents. The proportion of additives in the polyurethane is not particularly limited, but is preferably 50% by mass or less, more preferably 20% by mass or less, and even more preferably 5% by mass or less.

[0030] [Composition ratio] The proportions of each component can be adjusted as appropriate according to the desired properties. In the present invention, the amount of structural units derived from compounds having carboxyl groups in the total structural units constituting the polyurethane is preferably 3 to 30 mol%, more preferably 4 to 20 mol%, even more preferably 6 to 15 mol%, and even more preferably 6 to 12 mol%. When the amount of structural units of compounds having carboxyl groups is above the lower limit, the effects derived from carboxyl groups can be sufficiently imparted to the resulting polyurethane. That is, a sufficient negative potential derived from carboxyl groups can be imparted to the polyurethane, and by using this in the polishing layer, it is possible to repel the negatively potentialed abrasive grains and suppress clogging of the polishing layer. Furthermore, when the amount of structural units derived from compounds having carboxyl groups is below the upper limit, it becomes easier to adjust the physical properties of the polyurethane, such as hardness, to the range described later.

[0031] The amount of isocyanate groups in the organic diisocyanate relative to 1 mole of active hydroxyl groups in the carboxyl group-containing compound, polymer diol, and chain extender is preferably 0.80 to 1.3 moles, and more preferably 0.90 to 1.2 moles. When the ratio of isocyanate groups to 1 mole of active hydroxyl groups is above the lower limit, the mechanical strength and wear resistance of the thermoplastic polyurethane tend to improve, and the lifespan of the polishing layer also tends to be extended. On the other hand, when the ratio of isocyanate groups to 1 mole of active hydrogen atoms is below the upper limit, the productivity and storage stability of the thermoplastic polyurethane tend to improve, and the polishing layer tends to be easier to manufacture.

[0032] <Method for manufacturing thermoplastic polyurethane> Thermoplastic polyurethanes are obtained by polymerization using the aforementioned raw materials through a known prepolymerization method or a one-shot urethaneization reaction. More specifically, methods include producing them by melt polymerization while mixing the above-mentioned components in predetermined ratios using a single-screw or multi-screw extruder in substantially the absence of solvents, or by polymerization using a prepolymerization method in the presence of solvents. The melt polymerization may be carried out continuously. In the present invention, it is preferable to use solution polymerization from the viewpoint of stably producing the polyurethane of the present invention. The reaction solution concentration is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, and even more preferably 20 to 50% by mass, from the viewpoint of reactivity and operability due to viscosity.

[0033] The obtained thermoplastic polyurethane is then, for example, pelletized and then molded into a sheet-like molded body by various molding methods such as extrusion molding, injection molding, blow molding, and calendering. In particular, extrusion molding using a T-die yields a sheet-like molded body of uniform thickness.

[0034] [Polishing layer] The polishing layer of the present invention uses the polyurethane of the present invention. As described above, the polyurethane of the present invention has a carboxyl group in its molecular structure, and by using this in the polishing layer, clogging of the abrasive grains is less likely to occur due to the repulsive force between the negative potential of the carboxyl group and the negative potential of the abrasive grains, thereby enabling stable and long-lasting polishing while suppressing damage. More specifically, the slurries used in CMP include alkaline slurries, and the abrasive grains contained in alkaline slurries usually have a negative zeta potential. In contrast, since the polishing layer of the present invention uses polyurethane having a carboxyl group, when it comes into contact with an alkaline slurry, the carboxyl group on the surface becomes -COO - By dissociating, the zeta potential of the surface of the polishing layer is reduced to, for example, -10mV or less. In this case, the abrasive grains, which exhibit a negative zeta potential in alkaline conditions, and the polishing layer exhibit electrostatic repulsion. As a result, adhesion of abrasive grains to the polishing layer is prevented, and clogging can be suppressed, especially in nonwoven fabric-based polishing layers, which is presumed to reduce the occurrence of scratches and defects. The abrasive layer may be either a polyurethane foam or a non-foamed polyurethane, but a non-foamed polyurethane is preferred. When the abrasive layer is a non-foamed polyurethane, the abrasive properties are less likely to fluctuate, and stable abrasives can be achieved.

[0035] <Composition of the polished layer> The polishing layer of the present invention may be formed from polyurethane in a sheet shape, or it may be formed by impregnating a nonwoven fabric with the polyurethane of the present invention and then solidifying it. However, by using the polyurethane of the present invention, it becomes difficult for abrasive particles to get stuck in the irregularities caused by the nonwoven fabric, enabling long-lasting and stable polishing. Therefore, a polishing layer formed by impregnating a nonwoven fabric with the polyurethane of the present invention and then solidifying it is preferred.

[0036] As a method for impregnating a nonwoven fabric with polyurethane, first, an organic solution such as an N,N-dimethylformamide solution (DMF solution) with a polyurethane concentration of preferably 10-50% by mass, more preferably 20-40% by mass, is prepared. Next, this is preferably heated to about 27-40°C, and the nonwoven fabric is preferably left to stand on it for about 5-20 minutes to allow the organic solvent to penetrate. Then, the nonwoven fabric is preferably submerged in the polyurethane organic solution for 2-15 minutes, and any excess organic solution adhering to the removed nonwoven fabric is removed. After that, the polyurethane is solidified by immersing the nonwoven fabric in an aqueous solution with an organic solvent concentration of 5-30% by mass and a temperature of about 27-40°C. Next, if necessary, the nonwoven fabric is washed with an organic solvent, water, etc., and dried to obtain a nonwoven fabric impregnated with polyurethane. In this invention, the polyurethane solution used to impregnate the nonwoven fabric includes water-based polyurethane and solvent-based polyurethane. Here, water-based polyurethane refers to polyurethane that can be dispersed in water or an aqueous solution, and solvent-based polyurethane refers to polyurethane that can be dissolved in an organic solvent. Among these, solvent-based polyurethane is more preferred because it improves the freedom of selection of chain extenders that contribute to the expression of the zeta potential.

[0037] <Nonwoven fabric> There are no particular limitations on the nonwoven fabrics that can be used in the present invention, and examples include nonwoven fabrics made of polyester fibers such as nylon, polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). Among these, polyester fibers are less likely to absorb water during polishing, so the storage modulus does not fluctuate easily and the polishing efficiency remains stable. For example, in the case of highly absorbent fibers such as nylon fibers, the storage modulus fluctuates as the water absorption rate increases during polishing, making the polishing pad more prone to deformation and thus reducing the polishing efficiency.

[0038] When polyester fibers are used, the average single fiber fineness is preferably 0.01 to 5.0 dtex, and more preferably 0.03 to 1.0 dtex. If the average single fiber fineness is above the lower limit, the fibers are less likely to break during dressing, thus preventing scratches due to shedding. On the other hand, if the average single fiber fineness is below the upper limit, the load on the object to be polished does not become too great, thus preventing scratches.

[0039] <Zeta potential> From the viewpoint of suppressing clogging of the polishing layer and effectively suppressing scratches, the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is preferably -10.0 mV or less, more preferably -50.0 to -12.0 mV, even more preferably -40.0 to -15.0 mV, even more preferably -30.0 to -17.0 mV, and even more preferably -27.0 to -20.0 mV. When the zeta potential of the polyurethane constituting the polishing layer at pH 7.0 is below the upper limit, the polishing layer and the abrasive grains repel each other electrically, improving the clogging suppression effect. On the other hand, when the zeta potential at pH 7.0 is above the lower limit, the amount of slurry held on the polishing surface does not become too small, and a good polishing speed can be maintained. In this specification, zeta potential refers to the potential generated on the electric double layer surface (slip surface) by counterions depending on the surface charge of a substance when it comes into contact with a liquid. Specifically, it can be measured using an electrophoretic light scattering spectrometer (ELS-Z, manufactured by Otsuka Electronics Co., Ltd.) and monitor latex (manufactured by Otsuka Electronics Co., Ltd.) dispersed in a 10 mM NaCl aqueous solution adjusted to pH 7.0 with an NaCl aqueous solution.

[0040] Furthermore, the zeta potential of the polyurethane forming the polishing layer at pH 5.0 is preferably -5.0 mV or less, more preferably -40.0 to -12.0 mV, even more preferably -35.0 to -15.0 mV, and even more preferably -30.0 to -17.0 mV, from the same viewpoint as described above. Furthermore, the zeta potential of the polyurethane forming the polishing layer at pH 8.0 is preferably -15.0 mV or less, more preferably -60.0 to -20.0 mV, even more preferably -50.0 to -25.0 mV, and even more preferably -40.0 to -30.0 mV, from the same viewpoint as described above.

[0041] <Storage modulus> After saturating and swelling the polyurethane constituting the polishing layer with water at 50°C, the storage modulus measured at 50°C is preferably 50 to 1,200 MPa, more preferably 100 to 1,100 MPa, even more preferably 200 to 1,000 MPa, and even more preferably 400 to 1,000 MPa. When the storage modulus at 50°C is above the lower limit, the polishing layer has an appropriate softness, resulting in a good polishing speed. On the other hand, when the storage modulus is below the upper limit, there is a tendency for scratches on the polished surface of the workpiece to decrease. The storage modulus can be measured by the method described in the examples. A polyurethane that satisfies the aforementioned storage modulus can be obtained, for example, by adjusting the content of nitrogen atoms derived from isocyanate groups in the polyurethane. Specifically, the content of nitrogen atoms derived from isocyanate groups in the polyurethane is preferably 4.5 to 7.6% by mass, more preferably 5.0 to 7.4% by mass, and even more preferably 5.2 to 7.3% by mass.

[0042] <Contact angle with water> The contact angle of the polyurethane constituting the polishing layer with water is preferably 80 degrees or less, more preferably 70 degrees or less, even more preferably 60 degrees or less, and even more preferably 49 degrees or less. When the contact angle of the polyurethane with water is below the above upper limit, the hydrophilicity of the polishing surface is improved, which reduces scratches during polishing. The contact angle of polyurethane with water can be measured according to the method described in the examples.

[0043] The polyurethane constituting the polishing layer of the present invention preferably has a storage elastic modulus within the above range and a contact angle with water within the above range. Specifically, after the polyurethane constituting the polishing layer is saturated and swollen with water at 50°C, the storage elastic modulus measured at 50°C is preferably 50 to 1,200 MPa, more preferably 100 to 1,100 MPa, still more preferably 200 to 1,000 MPa, and the contact angle of the polyurethane constituting the polishing layer with water is preferably 80 degrees or less, more preferably 70 degrees or less, still more preferably 60 degrees or less, and even more preferably 50 degrees or less. When both the storage elastic modulus and the contact angle with water are within the above ranges, the polishing uniformity and polishing stability are further improved.

[0044] <Density> In the present invention, it may be an impregnated and coagulated non-woven fabric with polyurethane, or it may be made of a formed sheet of polyurethane. However, the density of the polyurethane in the case of being made of a formed sheet is preferably 1.0 g / cm 3 or more, more preferably 1.1 g / cm 3 or more, still more preferably 1.2 g / cm 3 or more. When the density of the formed body of the thermoplastic polyurethane is not less than the above lower limit value, it has appropriate flexibility as a polishing layer. Also, as the thermoplastic polyurethane, non-foamed thermoplastic polyurethane is particularly preferable because of its excellent polishing stability due to high rigidity and material homogeneity.

[0045] <Thickness of the polishing layer> The shape of the polishing layer of the present invention can be appropriately adjusted by cutting, slicing, punching, etc. of a sheet-shaped formed body of thermoplastic polyurethane, for example. The thickness of the polishing layer is not particularly limited, but is preferably 0.5 to 5.0 mm, more preferably 1.0 to 3.0 mm, still more preferably 1.2 to 2.0 mm. When the thickness of the polishing layer is within the above range, the productivity and handling property are improved, and the stability of the polishing performance is also improved.

[0046] <Hardness of the polishing layer> The hardness of the polishing layer, as measured according to JIS K 6253-3:2012, is preferably 60 or higher, more preferably 65 or higher, and preferably 95 or lower, and more preferably 90 or lower. If the hardness is above the lower limit, the conformability of the polishing pad to the polished surface decreases, improving flatness. On the other hand, if the hardness is below the upper limit, scratches are less likely to occur, which is preferable.

[0047] <Shape of the polished layer> Preferably, grooves or holes are formed on the polished surface of the polishing layer in predetermined patterns such as concentric circles, grids, spirals, or radials by grinding or laser processing. Such grooves help to uniformly and sufficiently supply slurry to the polishing surface, as well as to discharge polishing debris that causes scratches and prevent wafer damage due to the adsorption of the polishing layer. For example, when forming grooves in a concentric circle pattern, the spacing between grooves is preferably 1.0 to 50 mm, more preferably 1.5 to 30 mm, and even more preferably 2.0 to 15 mm. The width of the grooves is preferably 0.1 to 3.0 mm, and more preferably 0.2 to 2.0 mm. The depth of the grooves is less than the thickness of the polishing layer, preferably 0.2 to 1.8 mm, and more preferably 0.4 to 1.5 mm. The cross-sectional shape of the grooves can be appropriately selected according to the purpose, for example, a rectangle, trapezoid, triangle, or semicircle.

[0048] [Polishing pad] The polishing pad of the present invention utilizes the polishing layer of the present invention. The polishing pad of the present invention may consist only of the polishing layer of the present invention, or it may be a laminate in which a cushion layer is laminated on the side of the polishing layer that is not the polishing surface. The cushion layer is preferably a layer with a hardness lower than that of the polishing layer. When the hardness of the cushion layer is lower than that of the polishing layer, the hard polishing layer follows local irregularities on the surface to be polished, while the cushion layer follows warping and undulation of the entire substrate to be polished. This allows for polishing with an excellent balance between global flatness (a state in which large periodic irregularities on the wafer substrate are reduced) and local flatness (a state in which local irregularities are reduced).

[0049] Specific examples of materials used as cushioning layers include composites made by impregnating nonwoven fabric with polyurethane (for example, "Suba400" manufactured by Nitta Haas Co., Ltd.); rubbers such as natural rubber, nitrile rubber, polybutadiene rubber, and silicone rubber; thermoplastic elastomers such as polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and fluorine-based thermoplastic elastomers; foamed plastics; and polyurethane. Among these, polyurethane with a foamed structure is particularly preferred because it easily provides the desired flexibility for use as a cushioning layer.

[0050] The thickness of the cushion layer is not particularly limited, but it is preferably about 0.5 to 5 mm. If the cushion layer is too thin, the effect of following the overall warping and undulation of the surface to be polished decreases, and global flatness tends to decrease. On the other hand, if the cushion layer is too thick, the entire polishing pad becomes soft, and stable polishing tends to become difficult. When laminating a cushion layer on the polishing layer, the thickness of the polishing pad is preferably about 0.3 to 5 mm.

[0051] [Polishing method] The polishing method of the present invention uses the polishing layer of the present invention, and comprises the steps of fixing a polishing pad equipped with the polishing layer onto a surface plate of a polishing apparatus, A step of holding the object to be polished in a holder of the polishing apparatus so that it faces the polished surface of the polishing layer, A step of polishing the workpiece by supplying a neutral or alkaline polishing slurry between the polishing surface and the workpiece, and sliding the polishing pad and the workpiece relative to each other. This is a polishing method that has the following properties. According to the polishing method of the present invention, when performing CMP using an alkaline slurry, the repulsive force between the abrasive grains in the slurry and the polishing pad can be improved, thereby suppressing clogging of the abrasive grains and extending the lifespan of the polishing pad.

[0052] An embodiment of the present invention, in which the polishing method is performed by CMP, will be explained with reference to Figure 3. In CMP (Chemical Polishing), a CMP apparatus 10 is used, which includes a circular rotating platen 2, a slurry supply nozzle 3, a holder 4, and a pad conditioner 6, as shown in Figure 3. The polishing pad 1, which has the aforementioned polishing layer, is attached to the surface of the rotating platen 2 using double-sided tape or the like. The holder 4 supports the workpiece 5 to be polished.

[0053] In the CMP apparatus 10, the rotary platen 2 rotates in the direction indicated by the arrow by a motor (not shown). The holder 4 also rotates within the plane of the rotary platen 2 by a motor (not shown) in the direction indicated by the arrow, for example. The pad conditioner 6 also rotates within the plane of the rotary platen 2 by a motor (not shown) in the direction indicated by the arrow, for example.

[0054] First, while distilled water is flowed over the polishing surface of the polishing pad 1, which is fixed to the rotary platen 2 and rotates, a pad conditioner 6 for CMP, which has diamond particles fixed to the carrier surface by nickel electrodeposition or the like, is pressed against it to condition the polishing surface of the polishing pad 1. Conditioning adjusts the polishing surface to a surface roughness suitable for polishing the surface to be polished. Next, slurry 7 is supplied to the polishing surface of the rotating polishing pad 1 from the slurry supply nozzle 3. When performing CMP, lubricating oil, coolant, etc. may also be used in combination with the slurry as needed.

[0055] Here, the slurry can be acidic, alkaline, or near-neutral. However, a slurry used in CMP is preferably used, which contains a liquid medium such as water or oil; abrasive particles such as silica, alumina, cerium oxide, zirconium oxide, or silicon carbide; and oxidizing agents, reducing agents, chelating agents, etc., such as bases, acids, surfactants, and hydrogen peroxide. When using the polishing layer of the present invention, it is preferable to adjust the pH to alkaline using a neutral or alkaline slurry, preferably with a pH of 5.0 to 12.0, more preferably 6.0 to 10.0, when performing CMP, in order to maintain the repulsive force between the abrasive grains and the polishing layer.

[0056] Then, the workpiece 5, which is fixed to the holder 4 and rotates, is pressed against the polishing pad 1, on which the slurry 7 has been evenly distributed over the polishing surface of the polishing layer. The polishing process is continued until a predetermined degree of flatness is achieved. The finished quality is affected by adjusting the pressing force applied during polishing and the relative speed of motion between the rotating platen 2 and the holder 4.

[0057] While the polishing conditions are not particularly limited, for efficient polishing, it is preferable that the rotational speed of both the rotary platen and the holder be low, at 300 rpm or less, and that the pressure applied to the workpiece be polished be 150 kPa or less to prevent scratches from occurring after polishing. During polishing, it is preferable to continuously supply slurry to the polishing surface using a pump or the like. While the amount of slurry supplied is not particularly limited, it is preferable to supply it so that the polishing surface is always covered with slurry.

[0058] After polishing, it is preferable to thoroughly wash the workpiece with running water and then use a spin dryer or the like to remove any water droplets adhering to the workpiece and dry it. By polishing the workpiece surface with a slurry in this way, a smooth surface can be obtained over the entire surface. The above-described CMP can be suitably used for polishing various semiconductor materials such as silicon wafers. [Examples]

[0059] An example of the present invention will be described below with reference to the following examples. However, the scope of the present invention is not limited to the following examples.

[0060] [Example 1] A thermoplastic polyurethane containing a carboxyl group was produced by solution polymerization using polytetramethylene glycol (PTG850) with a number-average molecular weight of 850, dimethylolpropionic acid (DMP), 1,4-butanediol (BD), and 4,4'-diphenylmethane diisocyanate (MDI), which are compounds containing a carboxyl group, in a mass ratio of PTG850:DMP:BD:MDI of 19.9:6.0:16.0:58.1 (molar ratio of DMP to BD of 20 / 80). After forming a cast film from the solution of the produced thermoplastic polyurethane, the thermoplastic polyurethane was obtained by dehumidifying and drying at 80°C for 20 hours. The obtained thermoplastic polyurethane was evaluated as described below. The results are shown in Table 1.

[0061] [Examples 2-10, Comparative Examples 1-3] Except for the formulations shown in Table 1, polyurethanes for Examples 2-10 and Comparative Examples 1-3 were manufactured in the same manner as in Example 1. The obtained thermoplastic polyurethanes were evaluated as described below. The results are shown in Table 1.

[0062] The raw materials listed in Table 1 are as follows: BD:1,4-butanediol PD:1,5-pentanediol DMP: Dimethylolpropionic acid (2,2-bis(hydroxymethyl)propionic acid) DMB: Dimethylolbutanoic acid (2,2-bis(hydroxymethyl)butyrate) MPD: 3-methyl-1,5-pentanediol PTG850: Polytetramethylene glycol with a number-average molecular weight of 850 PEG600: Polyethylene glycol with a number-average molecular weight of 600 PD1000: Polycarbonate diol with a number-average molecular weight of 1000. MDI: 4,4'-diphenylmethane diisocyanate

[0063] [Evaluation Method] The thermoplastic polyurethanes obtained in the examples and comparative examples were evaluated according to the methods described later.

[0064] <Measuring Zeta Potential> The pellets (5-14g) of each thermoplastic polyurethane produced in the examples and comparative examples were sandwiched between Teflon® sheets, and then molded by pressing them at 200-230°C using a hot press to obtain molded thermoplastic polyurethane sheets with a thickness of 0.3-0.5 mm. Next, the resulting molded sheet was cut to 30 mm x 60 mm and its surface was washed. Then, using an electrophoretic light scattering spectrometer (ELS-Z, manufactured by Otsuka Electronics Co., Ltd.), the sample was mounted in a plate measurement cell. Subsequently, the zeta potential was measured using monitor latex (manufactured by Otsuka Electronics Co., Ltd.) dispersed in 10 mM NaCl aqueous solutions adjusted to pH 5.0, pH 7.0, and pH 8.0, respectively, with NaOH aqueous solution.

[0065] <Contact angle with water> For each thermoplastic polyurethane produced in the examples and comparative examples, a 300 μm thick film was prepared by hot pressing. The obtained films were then left for 3 days under conditions of 20°C and 65% RH. After dropping water onto the surface and waiting 15 minutes, the contact angle with water was measured using a DropMaster 500 manufactured by Kyowa Interface Science Co., Ltd.

[0066] <Storage modulus at 50°C after saturated swelling with 50°C water> For each thermoplastic polyurethane produced in the examples and comparative examples, injection-molded sheets with a width of 5 mm, a length of 30 mm, and a thickness of 2 mm were prepared. The injection-molded sheets were then immersed in water at 50°C for 3 days. After removing the injection-molded sheets from the water and wiping off the water from the surface, the storage modulus was determined by measuring the dynamic viscoelastic modulus at 50°C at a frequency of 11 Hz using a dynamic viscoelasticity measuring device ("DVE Rheospectr," manufactured by Rheology Co., Ltd.).

[0067] <Evaluation of polishing pads> Polishing pads were manufactured and evaluated using the polyurethane obtained in the examples and comparative examples.

[0068] [Manufacturing of raw material containing PET nonwoven fabric and non-porous polyurethane] A sea-island type composite fiber with 25 islands, containing polyethylene terephthalate (PET) as the island component and water-soluble thermoplastic PVA as the sea component, with a mass ratio of sea component to island component of 25 / 75, was extruded from a spinning die at 265°C, and the sea-island type composite fiber was spun by stretching and thinning it while cooling. Then, the fibers were continuously collected and pressed to obtain a long fiber web. Next, the long fiber webs were stacked and alternately subjected to needle punching on both sides to entangle the long fiber webs and obtain a three-dimensional entangled body. Next, as a non-porous polymeric elastic material, an aqueous emulsion of polyurethane for the base material was impregnated into a three-dimensional entangled material by dipping and nipping, followed by drying. Then, the three-dimensional entangled material was dipped and nipped in hot water to dissolve and remove the water-soluble thermoplastic PVA island component from the sea-island type composite fiber, and by drying, a base material was obtained containing a nonwoven fabric (thickness 1.8 mm) of PET fibers (average single fiber fineness 0.05 dtex) having 25 bundles of single fibers and non-porous polyurethane.

[0069] [Impregnation of thermoplastic polyurethane in examples and comparative examples] The obtained raw material was cut into 380 mm x 380 mm pieces. Next, the cut pieces of raw material were impregnated with the thermoplastic polyurethane obtained in the examples and comparative examples, respectively. The impregnation process was carried out as follows: A DMF solution containing 25% by mass of each thermoplastic polyurethane was heated to 30°C, and the raw material was left on top of it for 10 minutes to allow the DMF solution to penetrate. Next, the raw material was submerged in the DMF solution for 5 minutes, after which it was removed and placed on a glass plate, and the adhering DMF solution was removed by tracing the surface of the raw material with a doctor's knife. The same procedure was performed on the reverse side.

[0070] Next, an aqueous solution with a DMF concentration of 10% by mass was maintained at 30°C, and the raw material was immersed in it. After letting it stand for 30 minutes to solidify the thermoplastic polyurethane of the examples and comparative examples, the raw material impregnated with thermoplastic polyurethane was immersed in hot water at 70-95°C. Then, the raw material impregnated with thermoplastic polyurethane was sandwiched between metal rollers to squeeze out the water, and then immersed again in hot water for washing. This operation was repeated until the DMF concentration of the squeezed water was 0.3% by mass or less. The DMF concentration was measured using an Abbe refractometer 1T (ATAGO Corporation). Next, the washed raw material was placed in a hot air dryer (device name: Safety Oven SPH-202 / ESPEC Corporation) and dried at 100°C for 40 minutes. In this way, the raw material for the polishing pad was obtained.

[0071] [Flattening and grooving of the raw material for polishing pads] The surface of the raw material for the polishing pad was buffed with sandpaper (grit #180) to eliminate thickness variations and make it flat. Then, a flattening groove processing machine was used to form a grid groove on the polishing surface of the polishing pad with a groove width of 2.0 mm, a groove depth of 0.5 mm, and a pitch of 15 mm. The polishing pad with the grid grooves was then cut into a circle with a diameter of 370 mm to obtain a grooved polishing pad with a thickness of 1.5 mm (a polishing pad consisting only of the polishing layer).

[0072] Next, the obtained polishing pad was polished according to the polishing method of the present invention. Specifically, the obtained polishing pad was mounted on a polishing device "MAT-BC15" manufactured by M.A.T. Corporation. Then, using a diamond dresser (#100 - 80% coverage, 19 cm in diameter, 1 kg in mass) manufactured by Allied Material Corporation, the pad surface was conditioned for 15 minutes at a dresser rotation speed of 140 rpm and a platen rotation speed of 100 rpm while distilled water was flowed at a rate of 150 mL / min. Next, a slurry with a pH of 7.0 to 11 was prepared by diluting a slurry (colloidal silica, slurry concentration 1%) 20 times. Then, under conditions of a platen rotation speed of 100 rpm, a head rotation speed of 99 rpm, and a polishing pressure of 55.1 kPa, a 4-inch diameter silicon wafer having a silicon oxide film with a thickness of 1000 nm on its surface was polished for 60 seconds while supplying the slurry to the polishing surface of the polishing pad at a rate of 200 mL / min. After polishing for 60 seconds, the polishing pad was conditioned for 30 seconds. Then, another silicon wafer was polished again, followed by another 30 seconds of conditioning. Ten silicon wafers were polished in this manner. Then, the polishing speed was calculated from the weight change of the 10th silicon wafer before and after polishing, and the average value was taken as the polishing speed.

[0073] <Change in polishing speed (nm / min), polishing speed stability (%)> A 6-hour long-run test was conducted using each polishing layer. The change in polishing speed in the later stages of polishing (after 5 hours of polishing) was defined as "polishing speed change (nm / min)," using the polishing speed value at the point when the polishing speed stabilized (after 1 hour of polishing) as the baseline. The percentage change after 5 hours of polishing compared to after 1 hour of polishing was defined as "polishing speed stability (%)."

[0074] <Visual inspection (amount of scratches)> The polished workpieces were observed for their appearance using a high-intensity halogen lighting device. The presence and number of scratches, scuffs, dirt, and unpolished areas were evaluated according to the evaluation criteria below. Figure 4 shows the condition with scratches, the condition with scuffs, and the condition with dirt and unpolished areas, corresponding to evaluations "3" to "4" below. <Evaluation Criteria> [1: Very good] Over 90% of the evaluated silicon wafers were free of scratches, blemishes, and polishing residue. [2: Good] Between 70% and 90% of the evaluated silicon wafers were free of scratches, blemishes, dirt, and polishing residue. [3: Bad] Between 50% and 70% of the evaluated silicon wafers contained scratches, blemishes, dirt, and unpolished areas. [4: Very bad] More than 70% of the evaluated silicon wafers had scratches, blemishes, dirt, or unpolished areas, or large scratches occurred.

[0075] <Clogging (%)> After polishing for 6 hours, a photograph of the cross-section of the polishing pad was taken, and the percentage of the area where the abrasive grains were clogged (colored brown) was defined as the amount of clogging.

[0076] [Table 1]

[0077] As is clear from the results in Table 1, the present invention can suppress clogging and provide a polishing pad that can polish stably and for a long time while suppressing the occurrence of scratches. Furthermore, as is clear from the comparison of Examples 1-9 and Example 10 in Table 1, it is more preferable to use a polyether diol as the polymer diol from the viewpoint of superior stability and clogging suppression.

[0078] [Example 11] [Manufacturing of raw material containing PET nonwoven fabric and non-porous polyurethane] A sea-island type composite fiber with 25 islands, containing polyethylene terephthalate (PET) as the island component and water-soluble thermoplastic PVA as the sea component, with a mass ratio of sea component to island component of 25 / 75, was extruded from a spinning die at 265°C, and the sea-island type composite fiber was spun by stretching and thinning it while cooling. Then, the fibers were continuously collected and pressed to obtain a long fiber web. Next, the long fiber webs were stacked and alternately subjected to needle punching on both sides to entangle the long fiber webs and obtain a three-dimensional entangled body. Next, as a non-porous polymeric elastic material, an aqueous emulsion of polyurethane for the base material was impregnated into a three-dimensional entangled material by dipping and nipping, followed by drying. Then, the three-dimensional entangled material was dipped and nipped in hot water to dissolve and remove the water-soluble thermoplastic PVA island component from the sea-island type composite fiber, and by drying, a base material was obtained containing a nonwoven fabric (thickness 1.8 mm) of PET fibers (average single fiber fineness 0.05 dtex) having 25 bundles of single fibers and non-porous polyurethane.

[0079] [Impregnation of thermoplastic polyurethane in examples and comparative examples] Next, the obtained nonwoven fabric was impregnated with an aqueous dispersion of crosslinked polyurethane elastic material A, which was adjusted to a solid content concentration of 25% by mass. The aqueous dispersion of crosslinked polyurethane elastic material A is prepared by adding 3 parts by mass of a carbodiimide-based crosslinking agent to 100 parts by mass of an aqueous dispersion of polyurethane obtained by polymerizing a polyol component consisting of 95% by mass of an amorphous polycarbonate-based polyol, which is a copolymer polyol of hexamethylene carbonate and pentamethylene carbonate, and 5% by mass of 2,2-bis(hydroxymethyl)propionic acid, a chain extender (diol having a carboxyl group) consisting of dimethylolpropionic acid, a polyisocyanate compound consisting of 4,4'-dicyclohexylmethane diisocyanate, and an amine-based chain extender consisting of hydrazine. The ratio of polyol component, polyisocyanate component, and chain extender that form the polyurethane was set to polyol component:polyisocyanate component:chain extender = 55:40:5.

[0080] Furthermore, during impregnation, the amount of solid content of the aqueous dispersion relative to the mass of the nonwoven fabric was 15% by mass. The polyurethane was then solidified by heat treatment of the nonwoven fabric impregnated with the aqueous dispersion at 90°C in a 50% RH atmosphere. Subsequently, a cross-linked structure was formed by further heat treatment at 150°C. Finally, a raw material for the polishing pad was obtained by heat pressing at 150°C.

[0081] [Flattening and grooving of the raw material for polishing pads] The surface of the raw material for the polishing pad was buffed with sandpaper (grit #180) to eliminate thickness variations and make it flat. Then, a flattening groove processing machine was used to form a grid groove on the polishing surface of the polishing pad with a groove width of 2.0 mm, a groove depth of 0.5 mm, and a pitch of 15 mm. The polishing pad with the grid grooves was then cut into a circle with a diameter of 370 mm to obtain a grooved polishing pad with a thickness of 1.5 mm (a polishing pad consisting only of the polishing layer). The obtained polishing pads were evaluated in the same manner as in Examples 1 to 10. The results are shown in Table 2.

[0082] [Table 2]

[0083] As is clear from the results in Table 2, according to the present invention, even water-based polyurethanes can be obtained that can be polished stably and for a long time while suppressing the occurrence of scratches, similar to solvent-based polyurethanes.

Claims

1. An abrasive layer comprising a nonwoven fabric and a solvent-based polyurethane that is at least soluble in N,N-dimethylformamide impregnated into the nonwoven fabric, wherein the polyurethane has at least one structural unit derived from a compound having a carboxyl group, Among the structural units constituting the polyurethane, the compound having the carboxyl group is derived from A polished layer having a structural unit content of 3 to 30 mol%, Among the structural units constituting the polyurethane, in addition to structural units derived from a compound having a carboxyl group that imparts a carboxyl group to the polyurethane, the polyurethane further consists of structural units derived from a chain extender, structural units derived from a polymer diol, and structural units derived from an organic diisocyanate. The structural units derived from the compound having a carboxyl group are residues obtained by removing two hydrogen atoms from the two hydroxyl groups of the compound having a carboxyl group, and the compound having a carboxyl group is dimethylolpropionic acid or dimethylolbutanoic acid. The chain extender is ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 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, cyclohexanedimethanol, bis(β-hydroxyethoxy)benzene Droxyethyl terephthalate, 1,9-nonanediol, m-xylylene glycol, p-xylylene glycol, diethylene glycol, triethylene glycol, ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 3-methylpentamine Tameethylenediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 1,2-diaminopropane, hydrazine, xylylenediamine, isophoronediamine, piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, tolylenediamine, 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'-diaminodiphenylsulfone, 3,4-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 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'-diaminobenzophenone, 3,4-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-diaminobibenzyl, 2,2'-diamino-1,1'-binaphthalene, 1 The polishing layer is at least one compound selected from the group consisting of 3-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 and 4,4'-diaminobenzanilide; the polymer diol is at least one compound selected from the group consisting of polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(methyltetramethylene glycol), polyester diol and polycarbonate diol; and the organic diisocyanate is at least one compound selected from the group consisting of 4,4'-dicyclohexylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and 4,4'-diphenylmethane diisocyanate.

2. The zeta potential of the polyurethane constituting the abrasive layer at pH 7.0 is -10.0 The polishing layer according to claim 1, wherein the value is less than or equal to mV.

3. The polishing layer according to any one of claims 1 to 2, wherein the polyurethane is a non-foaming material.

4. The polyurethane was subjected to saturation swelling with water at 50°C, and then measured at 50°C. The storage modulus is 50 to 1,200 MPa, and the contact angle with water is 80 degrees or less. The polished layer described in any one of the requirements 1 to 3.

5. A polishing pad using the polishing layer described in any one of claims 1 to 4.

6. A polishing method using the polishing layer described in any one of claims 1 to 4, A step of fixing the polishing pad having the polishing layer onto the base plate of the polishing apparatus, A step of holding the object to be polished in a holder of the polishing apparatus so that it faces the polished surface of the polishing layer, While supplying a neutral or alkaline polishing slurry between the polishing surface and the workpiece, The workpiece is polished by sliding the polishing pad and the workpiece relative to each other. The process of doing so, A polishing method having

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