Polishing pad and method for manufacturing same

Abstract

The purpose of the present invention is to provide a polishing pad to which abrasive particles in slurry, particularly the silicon (Si) component, hardly adhere, and a method for manufacturing the same. Disclosed is a polishing pad comprising a polishing layer, the polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles. The polyurethane sheet comprises a polyurethane resin, and the polyurethane resin comprises an ionic polyurethane resin.

Description

Polishing pad and method for manufacturing the same

[0001] This invention relates to a polishing pad used for polishing semiconductor devices and the like.

[0002] Because flatness is required on the surfaces of materials such as silicon, hard disk substrates, mother glass for thin liquid crystal displays, semiconductor wafers, and semiconductor devices, polishing is performed using a free abrasive method with polishing pads. The free abrasive method is a method of polishing the processed surface of a workpiece while supplying a slurry (polishing liquid, polishing slurry) containing abrasive particles between the polishing pad and the workpiece.

[0003] Chemical mechanical polishing (CMP) is generally used as a method for planarizing the surfaces of semiconductor devices. Polishing pads for semiconductor devices require the following properties: openings to hold the polishing slurry, rigidity to maintain the flatness of the semiconductor device surface, and elasticity to prevent scratches on the semiconductor device surface. Polishing pads that meet these requirements and have a polishing layer manufactured from polyurethane resin foam are used.

[0004] Polyurethane resin foams are usually cured and molded by the reaction of a prepolymer containing a urethane bond-containing polyisocyanate compound with a curing agent (dry molding method). Then, a polishing pad is formed by slicing the foam into sheets. A polishing pad having a hard polishing layer manufactured by such a dry molding method (hereinafter sometimes abbreviated as a hard polishing pad) has relatively small substantially spherical bubbles formed inside the foam by means such as the addition of hollow fine particles, mechanical foaming by mixing an inert gas, or a chemical foaming agent typified by water. Therefore, open pores (openings) capable of holding slurry during polishing are formed on the polishing surface of the polishing pad formed by slicing. When a hard polishing pad is used, the flatness and polishing rate of the substrate can be improved. However, due to its hardness, there is a risk of generating defects such as scratches. In recent years, with the miniaturization of wiring widths, higher-precision polishing has been increasingly required, and there are more situations where it is difficult to cope with hard polishing pads. Therefore, especially in the finishing process, a polishing pad having a soft polishing layer manufactured by a wet film-forming method (hereinafter sometimes abbreviated as a soft polishing pad) is used.

[0005] As described above, chemical mechanical polishing technology is used for polishing semiconductor devices and the like, and polishing is performed by flowing a polishing slurry between the object to be polished and the polishing pad. The polishing slurry contains polishing particles, and the polishing particles have a zeta potential that varies depending on pH. For example, unmodified colloidal silica shows a zeta potential close to zero in the region of pH 4 or less, and cationic silica shows a strong positive zeta potential in the region of pH 6 or less. Anionic silica shows a strong negative zeta potential regardless of the pH region. On the other hand, since dielectric films (silicon nitride (SiN), silicon oxide (SiO2 or TEOS), polysilicon (Poly-Si)) also have charges respectively, Patent Document 1 describes adjusting the charge of the polishing particles according to the dielectric film to be polished and achieving selective polishing that polishes only a specific film type by electrostatic attraction and electrostatic repulsion forces.

[0006] Furthermore, Patent Document 2 describes that by setting the zeta potential of the polishing surface of a nonwoven fabric type polishing pad to -10.0 mV or less during polishing, the abrasive grains exhibiting a negative zeta potential and the polishing layer exhibit electrostatic repulsion, making it difficult for the abrasive grains to penetrate into the uneven areas caused by the nonwoven fabric, and suppressing clogging that can be observed from the cross-section. Furthermore, Patent Document 3 describes that by using a polishing pad in which the zeta potential of the polishing surface at pH 10.0 is +0.1 mV or higher, a high polishing speed can be obtained even when performing CMP with an alkaline slurry at pH 12.

[0007] Japanese Patent No. 7074635, International Publication No. 2021 / 117834, International Publication No. 2018 / 021428

[0008] However, the polishing pad described in Patent Document 2 is a polishing pad made by impregnating a nonwoven fabric with polyurethane resin, and is not a polishing pad comprising a polyurethane sheet containing multiple teardrop-shaped bubbles, manufactured by a so-called wet film formation method. Nonwoven fabric type polishing pads are hard pads in which the nonwoven fabric forms the framework, and polyurethane resin enters the gaps between the fibers and solidifies while adhering to the fibers. Because nonwoven fabric type polishing pads have irregularities on the polishing surface due to the nonwoven fabric fibers and are hard, they have high polishing efficiency and are used for polishing silicon wafers before metal wiring is formed, etc., in relatively early stages of polishing. Furthermore, the polishing pad used in Patent Document 3 is obtained by pelletizing thermoplastic polyurethane obtained by continuous melt polymerization and then forming it into a sheet-like molded body by a molding method such as extrusion molding, and is a non-foaming type hard polishing pad with (almost) no bubbles inside. Such hard polishing pads are used for polishing silicon wafers before metal wiring is formed, etc., in relatively early stages of polishing. In contrast, polishing pads (wet-formed polishing pads) that are manufactured by a so-called wet-formation method and consist of a polyurethane sheet containing multiple teardrop-shaped bubbles have multiple large teardrop-shaped bubbles and are soft, so they are used for wafers after metal wiring has been formed or for the final finishing polishing stage. Thus, polishing pads obtained by impregnating a nonwoven fabric with polyurethane resin, as in Patent Document 2, and non-foaming polishing pads, as in Patent Document 3, are used in different stages and have different characteristics from wet-formed polishing pads. Furthermore, Patent Document 3 aims to obtain a high polishing speed when polishing with an alkaline slurry of pH 12, and does not recognize the adhesion of abrasive particles and the problems caused by it (such as scratches) when using an acidic slurry. When using wet-formed polishing pads for finishing polishing, if a large amount of abrasive particles adhere to and accumulate on the polishing surface, they can aggregate and cause scratches and particles. Since finishing polishing is the final polishing process, the occurrence of scratches and particles on the workpiece, such as wafers, at that stage is a major problem.Therefore, there is a great demand for polishing pads of the so-called wet film-forming type used for finish polishing, which are polishing pads that do not easily allow abrasive particles in the slurry to adhere to them.

[0009] The present invention has been made in view of the above points, and aims to provide a wet-film-forming type polishing pad, that is, a polishing pad containing a plurality of teardrop-shaped bubbles, in which abrasive particles in the slurry, particularly silicon (Si) components, are less likely to adhere to the workpiece during polishing, and a method for manufacturing the same.

[0010] As a result of diligent research, the inventors have discovered that by including an ionic polyurethane resin in the polyurethane sheet constituting the polishing pad containing multiple teardrop-shaped bubbles, a polishing pad can be obtained that is less prone to adhesion of abrasive particles, particularly silicon (Si) components, in the slurry. The present invention includes the following embodiments.

[0011] [1] A polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, and the polyurethane resin contains an ionic polyurethane resin. [2] The polishing pad according to [1], wherein the polyurethane resin contains an anionic polyurethane resin, and the proportion of the anionic polyurethane resin to the polyurethane resin is 1 to 50% by mass. [3] The polishing pad according to [2], wherein the anionic polyurethane resin is a polyurethane resin containing an anionic ionic group in the polyol compound constituting the polyurethane resin. [4] The polishing pad according to [3], wherein the anionic ionic group contains a carboxyl group. [5] The polishing pad according to any one of [2] to [4], wherein the polyurethane resin comprises the anionic polyurethane resin and a polyurethane resin other than the anionic polyurethane resin, the mass ratio of the anionic polyurethane resin to the polyurethane resin other than the anionic polyurethane resin in the polyurethane resin is 1:99 to 50:50, and the polyurethane resin other than the anionic polyurethane resin is a polyurethane resin that does not contain anionic ionic groups selected from the group consisting of carboxyl groups, sulfo groups, phosphoric acid groups, and phenolic hydroxyl groups, nor cationic ionic groups selected from groups containing a nitrogen atom derived from at least one amine selected from the group consisting of primary amines to tertiary amines. [6] The polishing pad according to any one of [2] to [5], wherein the porosity of the polishing surface of the polyurethane sheet is 15 to 20%. [7] The polishing pad according to any one of [2] to [6], wherein the polyurethane sheet further comprises a paraffinic hydrocarbon. [8] A polishing pad according to any one of [2] to [7] for polishing an object to be polished using an alkaline slurry containing silicon atom-containing abrasive particles. [9] A polishing pad according to [1], wherein the polyurethane resin comprises a cationic polyurethane resin.

[10] A polishing pad according to [9], wherein the proportion of cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

[11] The polishing pad according to [9] or

[10] for polishing an object to be polished using an acidic slurry containing silicon atom-containing abrasive grains.

[12] The polishing pad according to any one of [9] to

[11] , wherein the cationic polyurethane resin is a polyurethane resin containing nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines.

[13] The polishing pad according to

[12] , wherein the cationic polyurethane resin contains nitrogen atoms derived from a tertiary amine in the polyol compound constituting the polyurethane resin.

[14] The polishing pad according to any one of [9] to

[13] , wherein the polyurethane resin comprises the cationic polyurethane resin and a polyurethane resin other than the cationic polyurethane resin, the mass ratio of the cationic polyurethane resin to the polyurethane resin other than the cationic polyurethane resin in the polyurethane resin is 1:99 to 50:50, and the polyurethane resin other than the cationic polyurethane resin is a polyurethane resin that does not contain nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, nor an anionic ionic group selected from the group consisting of carboxyl groups, sulfo groups, phosphoric acid groups, and phenolic hydroxyl groups.

[15] The polishing pad according to any one of [9] to

[14] , wherein the porosity of the polishing surface of the polyurethane sheet is 16 to 50%.

[16] The polishing pad according to any one of [9] to

[15] , wherein the polyurethane sheet further comprises a paraffinic hydrocarbon.

[17] A method for producing an abrasive pad according to any one of [1] to

[16] , comprising the steps of: applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate; and immersing the film-forming substrate coated with the resin solution composition in a solidifying solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin comprises an ionic polyurethane resin.

[18] The method according to

[17] , wherein the polyurethane resin comprises an anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

[19] The method according to

[17] , wherein the polyurethane resin comprises a cationic polyurethane resin.

[20] The manufacturing method according to

[19] , wherein the proportion of cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

[0012] According to the present invention, it is possible to suppress the adhesion of abrasive particles, particularly silicon (Si) components, in the slurry to the surface of the polishing pad. Therefore, by using the polishing pad of the present invention, it is expected that problems caused by the adhesion of abrasive particles to the polishing pad (such as scratches) can be reduced.

[0013] Figure 1 is a surface SEM image of the polishing pad of Comparative Example 1 after buffing. Figure 2 is a surface SEM image of the polishing pad of Comparative Example 2 after buffing. Figure 3 is a surface SEM image of the polishing pad of Example 1 after buffing. Figure 4 is a surface SEM image of the polishing pad of Example 2 after buffing. Figure 5 is a surface SEM image of the polishing pad of Comparative Example 3 after buffing. Figure 6 is a surface SEM image of the polishing pad of Comparative Example A1 after buffing. Figure 7 is a surface SEM image of the polishing pad of Comparative Example A2 after buffing. Figure 8 is a surface SEM image of the polishing pad of Example A1 after buffing. Figure 9 is a surface SEM image of the polishing pad of Example A2 after buffing. Figure 10 is a surface SEM image of the polishing pad of Example A3 after buffing.

[0014] The following describes embodiments for carrying out the present invention. <<First Embodiment (Polishing Pad)>> The polishing pad of the first embodiment is a polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, and the polyurethane resin contains an ionic polyurethane resin. In this specification and in the claims, the ionic polyurethane resin is a polyurethane resin having ionic properties. The ionic polyurethane resin is preferably a polyurethane resin that contains an ionic group (also called an ionic functional group) in its structure. Examples of ionic functional groups include anionic groups (e.g., carboxyl groups, sulfo groups, phosphate groups, phenolic hydroxyl groups, etc., preferably carboxyl groups) and cationic groups (e.g., a group containing a nitrogen atom derived from at least one amine selected from the group consisting of primary amines to tertiary amines). The proportion of the ionic polyurethane resin in the polyurethane resin is preferably 1 to 50% by mass.

[0015] <Aspect 1-1> The polishing pad of the first aspect preferably contains an anionic polyurethane resin (as an ionic polyurethane resin), and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass. That is, preferred aspect 1-1 of the polishing pad of the first aspect is a polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, the polyurethane resin contains an anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass. The following description will focus on this preferred aspect 1-1 of the polishing pad.

[0016] Polyurethane sheets have multiple teardrop-shaped bubbles. The term "teardrop-shaped bubbles" refers to bubbles formed inside the polyurethane sheet by the wet deposition method (anisotropic bubbles with a structure where the diameter increases from the top (the side in contact with the workpiece) to the bottom of the resin sheet), and is used to distinguish them from the roughly spherical bubbles found in dry molding. Therefore, a polyurethane sheet with multiple teardrop-shaped bubbles can be described as a polyurethane sheet formed by the wet deposition method. The wet deposition method involves dissolving the resin to be deposited in an organic solvent, applying the resin-containing solution to a sheet-like substrate, then passing it through a coagulation solution that dissolves the organic solvent but not the resin to replace the organic solvent, allowing it to coagulate, and finally drying it to form a foamed layer. Typically, when a polyurethane sheet is manufactured by the wet deposition method, multiple roughly teardrop-shaped macrobubbles (teardrop-shaped bubbles) are generated inside the polyurethane sheet. Furthermore, when polyurethane sheets are manufactured by a wet film deposition method, a large number of bubbles (microbubbles, minute bubbles) that are much finer than macrobubbles are usually formed in addition to macrobubbles. In this specification and the claims, a polyurethane sheet means a sheet whose main component is polyurethane resin (50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more of the total resin constituting the polyurethane sheet is polyurethane resin, and the polyurethane resin may be 100% by mass), and is clearly distinguished from sheets whose main component is other resins (such as silicone resin). In this specification and the claims, a polishing layer is a layer having a surface (polishing surface) that comes into contact with the object to be polished when polishing an object to be polished, such as a semiconductor device. A polishing pad may have other layers, such as a cushion layer, on the opposite side from the polishing layer. In this specification and the claims, a polyurethane sheet does not contain nonwoven fabric.

[0017] <Polyurethane Resin> Polyurethane sheets contain polyurethane resin. There are no particular restrictions on the type of polyurethane resin; it can be selected from various polyurethane resins according to the intended use. For example, polyester-based, polyether-based, or polycarbonate-based polyurethane resins can be used. Examples of polyester-based resins include polymers of polyester polyols, such as ethylene glycol or butanediol, and adipic acid, and diisocyanates such as diphenylmethane-4,4'-diisocyanate. Examples of polyether-based resins include polymers of polyether polyols, such as polytetramethylene ether glycol or polypropylene glycol, and isocyanates such as diphenylmethane-4,4'-diisocyanate. Examples of polycarbonate-based resins include polymers of polycarbonate polyols and isocyanates such as diphenylmethane-4,4'-diisocyanate. These resins may be commercially available resins such as "Crisbon" manufactured by DIC Corporation, "Samplen" manufactured by Sanyo Chemical Industries, Ltd., or "Rezamin" manufactured by Dainichi Seika Kogyo Co., Ltd., or a resin with the desired properties may be manufactured in-house.

[0018] In this specification and in the claims, an anionic polyurethane resin is a polyurethane resin having anionic properties. Preferably, an anionic polyurethane resin is a polyurethane resin containing an anionic ionic group in its structure (for example, a polyurethane resin into which anionic ionic groups have been introduced). Anionic ionic group (with anionic property) may also be referred to as an anionic functional group. Examples of anionic ionic groups include carboxyl groups, sulfol groups, phosphate groups, phenolic hydroxyl groups, etc., with carboxyl groups being preferred. In this specification and in the claims, a cationic polyurethane resin is a polyurethane resin having cationic properties. Preferably, a cationic polyurethane resin is a polyurethane resin containing a cationic ionic group in its structure (a polyurethane resin into which cationic ionic groups have been introduced). Cationic ionic group (with cationic property) may also be referred to as a cationic functional group. Examples of cationic ionic groups include groups containing a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines (hereinafter sometimes referred to as primary to tertiary amino groups), and preferably tertiary amino groups. Cationic polyurethane resins are preferably polyurethane resins that contain a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines in their structure (or contain a group containing such nitrogen atom as a cationic ionic group). In this specification and in the claims, nonionic polyurethane resins are polyurethane resins having nonionic properties, and preferably polyurethane resins that do not contain (have not introduced) anionic or cationic ionic groups. Nonionic polyurethane resins are preferably polyurethane resins that do not have a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines, nor anionic ionic groups, in their structure. There are no particular restrictions on the method for producing polyurethane resins containing the above-mentioned ionic groups in their structure, and known methods may be used as appropriate.For example, the above-mentioned ionic groups can be introduced into a prepolymer and / or chain extender that serves as a raw material for polyurethane resin, or a prepolymer and / or chain extender containing the above-mentioned ionic groups can be prepared, and then these raw materials can be reacted to produce polyurethane resin.

[0019] <Anionic Polyurethane Resin> The polyurethane resin in Embodiment 1-1 includes an anionic polyurethane resin. The proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass, preferably 2 to 45% by mass, more preferably 3 to 40% by mass, even more preferably 3 to 35% by mass, even more preferably 3 to 30% by mass, even more preferably 3 to 20% by mass, even more preferably 3 to 10% by mass, even more preferably 3 to 8% by mass, and even more preferably 4 to 6% by mass. When the proportion of the anionic polyurethane resin in the polyurethane resin is within the above range, a polishing pad can be obtained in which abrasive particles in the slurry, especially silicon (Si) components, do not easily adhere. Such a polishing pad can be preferably used to polish an object to be polished using a slurry containing silicon atom-containing abrasive particles, especially an alkaline slurry. The anionic polyurethane resin is preferably a polyurethane resin containing anionic ionic groups. Examples of anionic ionic groups include carboxyl groups, sulfo groups, phosphate groups, phenolic hydroxyl groups, etc. Among these, the anionic ionic group preferably includes at least one selected from the group consisting of a carboxyl group, a sulfo group, and a phosphate group, and more preferably includes a carboxyl group. Furthermore, the anionic ionic group preferably includes at least one selected from the group consisting of a carboxyl group, a sulfo group, and a phosphate group, and more preferably includes a carboxyl group. It is preferable that the anionic polyurethane resin contains an anionic ionic group in the polyol compound constituting the polyurethane resin. The polyol compound may be a polyol compound (A) constituting the prepolymer, or a polyol compound (A') used as a chain extender (C).

[0020] Anionic ionic groups may be contained in any structural unit constituting the polyurethane resin. Generally, polyurethane resin is obtained by reacting a polyol compound (A) (hereinafter sometimes referred to as component (A)), a polyisocyanate compound (B) (hereinafter sometimes referred to as component (B)), and a chain extender (C) (hereinafter sometimes referred to as component (C)). The anionic ionic groups may be contained in the polyol compound (A) or in the chain extender (C) (for example, the polyol compound (A') in the chain extender (C)). Preferably, the anionic ionic groups are contained in the chain extender (C). When producing polyurethane resin, the polyol compound (A), polyisocyanate compound (B), and chain extender (C) may be mixed and reacted at once, or the polyol compound (A) and the polyisocyanate compound may be reacted to produce a urethane bond-containing isocyanate compound (prepolymer), and then the prepolymer and chain extender (C) may be mixed and reacted. The following explains each of the ingredients.

[0021] (Polyol Compound (A)) In this specification and the claims, polyol compound (A) means a compound having two or more alcoholic hydroxyl groups in its molecule. Examples of polyol compound (A) include polyester polyols, polyether polyols, polycarbonate polyols, polyacrylic polyols, polybutadiene polyols, hydrogenated polybutadiene polyols, dimer ols, and the like. Diol compounds are preferred as polyol compound (A), with polyester diols, polyether diols, and polycarbonate diols being more preferred, and polyester diols being particularly preferred. These polyol compounds may be used individually or in combination of multiple polyol compounds.

[0022] (Polyisocyanate compound (B)) In this specification and the claims, polyisocyanate compound (B) means a compound having two or more isocyanate groups in its molecule. Polyisocyanate compound (B) is not particularly limited as long as it has two or more isocyanate groups in its molecule. For example, diisocyanate compounds having two isocyanate groups in their molecule include m-phenylenediisocyanate, p-phenylenediisocyanate, 2,6-tolylenediisocyanate (2,6-TDI), 2,4-tolylenediisocyanate (2,4-TDI), naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), 4,4'-methylene-bis(cyclohexyl isocyanate) (hydrogenated MDI), 3,3'-dimethoxy-4,4'-biphenyldiisocyanate, 3,3'-dimeth Examples of polyisocyanate compounds include diphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1,4-diisocyanate, p-phenylene diisothiocyanate, xylylene-1,4-diisothiocyanate, and ethyridine diisothiocyanate. Diisocyanate compounds are preferred as polyisocyanate compounds, with MDI, 2,4-TDI, and 2,6-TDI being more preferred, and MDI being particularly preferred. These polyisocyanate compounds may be used individually or in combination of multiple polyisocyanate compounds.

[0023] (Chain extender (C)) As the chain extender (C), for example, a polyol compound (A') and / or a polyamine compound (D) with a lower molecular weight than the polyol compound (A) can be used. Specific examples of low molecular weight polyol compounds (A') include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol. In this specification and in the claims, polyamine compound (D) means a compound having two or more amino groups in its molecule. Specific examples of low molecular weight polyamine compounds (D) include ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, and hydrazine.

[0024] <Anionic Ionic Groups> Anionic ionic groups may be contained in, for example, a polyol compound (component (A) and / or component (A')). That is, structural units derived from the polyol compound of the anionic polyurethane resin may have anionic ionic groups. By using a polyol compound having anionic ionic groups, anionic ionic groups can be included (introduced) into the polyurethane resin. Examples of polyols having anionic ionic groups include 2,2'-dimethylolpropionic acid, 2,2'-dimethylolbutanoic acid, 2,2'-dimethylolbutyric acid, and 2,2'-dimethylolvaleric acid. Compounds containing anionic ionic groups may be used as a chain extender (C) (component (A')) or as a polyol compound (component (A)), but it is preferable to use them as a chain extender (C).

[0025] There are no particular restrictions on the ratio of structural units derived from compounds containing anionic ionic groups to the total structural units constituting the anionic polyurethane resin. However, among the total structural units constituting the anionic polyurethane resin (structural units derived from polyol compounds, structural units derived from polyisocyanate compounds, structural units derived from chain extenders, and compounds derived from compounds having anionic ionic groups), the ratio of structural units derived from compounds having anionic ionic groups (preferably polyol compounds) is preferably in the range of 0.1 to 30 mol%, more preferably in the range of 0.5 to 20 mol%, even more preferably in the range of 1 to 15 mol%, even more preferably in the range of 1 to 10 mol%, and even more preferably in the range of 3 to 8 mol%. Furthermore, the ratio is particularly preferably 4 to 6 mol%, and most preferably 5 mol%. Furthermore, when a compound containing an anionic ionic group is used as a chain extender, the proportion of structural units derived from the compound having an anionic ionic group among the total structural units derived from the chain extender of the anionic polyurethane resin is preferably 1 to 50 mol%, more preferably 3 to 40 mol%, and even more preferably 5 to 30 mol%. Furthermore, when a compound containing anionic ionic group is used as a chain extender, the proportion of structural units derived from the compound having an anionic ionic group among the total structural units derived from the chain extender of the anionic polyurethane resin is preferably 5 to 65% by mass, more preferably 10 to 60% by mass, even more preferably 15 to 55% by mass, even more preferably 15 to 45% by mass, even more preferably 15 to 35% by mass, and particularly preferably 15 to 25% by mass.Furthermore, when using a compound containing anionic ionic groups as a chain extender, the mass ratio of structural units derived from a compound having anionic ionic groups to structural units derived from a compound not having anionic ionic groups (preferably also not having cationic ionic groups) is preferably 100:10 to 70, more preferably 100:15 to 65, even more preferably 100:15 to 60, even more preferably 100:15 to 50, even more preferably 100:15 to 40, and particularly preferably 100:20 to 30 (structural units derived from a compound not having anionic ionic groups: structural units derived from a compound having anionic ionic groups). The ratio of 100:25 is most preferred. The structural units derived from the chain extender of the anionic polyurethane resin are preferably composed of structural units derived from a compound having anionic ionic groups and structural units derived from a compound not having anionic ionic groups (preferably also not having cationic ionic groups). Furthermore, the compound having an anionic ionic group in the chain extender may have the same structure as the chain extender without an anionic ionic group, except for the presence of an anionic ionic group, or it may have a different structure.

[0026] <Polyurethane resins other than anionic polyurethane resins> The polyurethane resin in Embodiment 1-1 preferably contains an anionic polyurethane resin and a polyurethane resin other than anionic polyurethane resin. The mass ratio of the anionic polyurethane resin to the polyurethane resin other than anionic polyurethane resin in the polyurethane resin is preferably 1:99 to 50:50, more preferably 2:98 to 45:55, even more preferably 3:97 to 40:60, even more preferably 4:96 to 35:65, even more preferably 5:95 to 30:70, even more preferably 3:97 to 20:80, even more preferably 3:97 to 10:90, even more preferably 3:97 to 8:92, and even more preferably 4:96 to 6:94. When the mass ratio of the anionic polyurethane resin to the polyurethane resin other than anionic polyurethane resin in the polyurethane resin is within the above range, it is possible to reduce the adhesion of abrasive particles in the slurry to the polishing surface of the polishing pad.

[0027] There are no particular restrictions on polyurethane resins other than anionic polyurethane resins; any known polyurethane resin may be used. Examples of polyurethane resins other than anionic polyurethane resins include polyurethane resins that do not contain (have not introduced) anionic ionic groups selected from the group consisting of carboxyl groups, sulfo groups, phosphate groups, and phenolic hydroxyl groups, nor cationic ionic groups selected from the group consisting of groups containing a nitrogen atom derived from at least one amine selected from the group consisting of primary amines to tertiary amines. Cationic polyurethane resins and nonionic polyurethane resins are also examples of polyurethane resins other than anionic polyurethane resins. Among these, polyurethane resins other than anionic polyurethane resins are preferably polyurethane resins that do not contain anionic ionic groups selected from the group consisting of carboxyl groups, sulfol groups, phosphate groups, and phenolic hydroxyl groups; more preferably polyurethane resins that do not contain anionic ionic groups selected from the group consisting of carboxyl groups, sulfol groups, phosphate groups, and phenolic hydroxyl groups, nor cationic ionic groups selected from the group consisting of groups containing a nitrogen atom derived from at least one amine selected from the group consisting of primary amines to tertiary amines; even more preferably polyurethane resins that do not contain anionic ionic groups or cationic ionic groups selected from the group consisting of carboxyl groups, sulfol groups, phosphate groups, and phenolic hydroxyl groups; and even more preferably polyurethane resins that do not contain anionic ionic groups or cationic ionic groups. Furthermore, among polyurethane resins other than anionic polyurethane resins, it is preferable to have the same structural units as anionic polyurethane resins, except that structural units derived from compounds containing anionic ionic groups are replaced with structural units derived from compounds that do not contain anionic ionic groups. More preferable are polyurethane resins that have the same structural units as anionic polyurethane resins in the same proportions, except that structural units derived from compounds containing anionic ionic groups are replaced with structural units derived from compounds that do not contain anionic ionic groups.

[0028] <Zeta Potential> The zeta potential can be measured by the flow potential method, which measures the potential difference caused by the pressure difference, or by the electrophoresis method, which measures the mobility of tracer particles. Measurement by the flow potential method is preferred. In addition, the zeta potential of polyurethane resin is measured by preparing a dry film with a thickness of about 200 μm obtained by thinly spreading and drying the polyurethane resin (solution), and measuring the zeta potential of this dry film. In embodiment 1-1, the zeta potential of the polyurethane resin is preferably in the range of -60 to -75 mV at a pH of 8.8 to 8.9 (preferably pH 8.8), more preferably -63 to -74 mV, and even more preferably -64 to -73 mV.

[0029] (Modulus) Modulus is an index that represents the hardness of a resin, and is the value obtained by dividing the load applied when a non-foamed resin sheet is stretched to 100% (stretched to twice its original length) by the cross-sectional area (hereinafter sometimes referred to as 100% modulus). The higher this value, the harder the resin is. The polyurethane resin in Embodiment 1-1 preferably has a 100% modulus of 1 to 10 MPa, more preferably 3 to 8 MPa, and even more preferably 3 to 5 MPa. When the 100% modulus is within the above range, it tends to be easier to balance the polishing rate and polishing scratches.

[0030] <Hydrophobic Additives> It is preferable that polyurethane sheets contain hydrophobic additives. Hydrophobic additives act as film-forming aids and can improve the film-forming properties of polyurethane sheets. Various conventional hydrophobic additives can be used as hydrophobic additives. Examples of hydrophobic additives include paraffinic hydrocarbons and nonionic hydrocarbons. Among these, it is preferable to include paraffinic hydrocarbons. Examples of paraffinic hydrocarbons include straight-chain hydrocarbons with 5 to 30 carbon atoms, normal paraffinic hydrocarbons such as liquid paraffin, kerosene, and light oil, branched hydrocarbons with 5 to 40 carbon atoms, and isoparaffinic hydrocarbons such as liquid isoparaffin. There are no particular restrictions on the amount of hydrophobic additives contained in the polyurethane sheet as long as a film can be formed on the polyurethane sheet, and any amount can be used as appropriate according to the properties of the polyurethane resin. In general, as the proportion of anionic polyurethane resin in the polyurethane resin increases, the film-forming properties worsen, so the amount of hydrophobic additives may be adjusted to facilitate film formation. Among these, the amount of hydrophobic additive is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 18 parts by mass or less, and even more preferably 16 parts by mass or less, per 100 parts by mass of polyurethane resin. On the other hand, there is no particular lower limit on the amount of hydrophobic additive. For example, it may be 0.01 parts by mass or more, 0.1 parts by mass or more, 0.5 parts by mass or more, 1 part by mass or more, 2 parts by mass or more, 4 parts by mass or more, 6 parts by mass or more, 8 parts by mass or more, 10 parts by mass or more, or 12 parts by mass or more, per 100 parts by mass of polyurethane resin. The amount of hydrophobic additive is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, preferably 1 to 20 parts by mass, and even more preferably 10 to 20 parts by mass, per 100 parts by mass of polyurethane resin.

[0031] <Cellulose Derivatives> The resin sheet preferably contains a cellulose derivative. By including a cellulose derivative, a microcell structure can be sufficiently formed when a polyurethane resin-containing solution applied to a film-forming substrate is wet-coated. In addition, the brittleness of the polishing pad is less likely to increase, and physical properties such as elongation are less likely to decrease. Examples of cellulose derivatives include ester-based cellulose derivatives, ether-based cellulose derivatives, ether-ester-based cellulose derivatives, and aromatic-containing cellulose conductors. Among these, ester-based cellulose derivatives are more preferred. Examples of ester-based cellulose derivatives include acetylcellulose, triacetylcellulose, acetylbutylcellulose, diacetylcellulose, acetylpropylcellulose, ethylcellulose, cellulose propionate, cellulose butyrate, nitrocellulose, cellulose sulfate, cellulose phosphate, cellulose acetate butyrate, cellulose nitrate acetate, and cellulose acetate propionate. Among these, acetylcellulose, triacetylcellulose, acetylbutylcellulose, diacetylcellulose, and acetylpropylcellulose are preferred, and those in which some or all of the OH groups of cellulose, such as acetylcellulose and triacetylcellulose, are esterified with acetate (particularly acetylcellulose with a substitution degree of 2.41) are more preferred. There are no particular restrictions on the amount of cellulose derivative contained in the polyurethane sheet, but it is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, and even more preferably 0.5 to 5 parts by mass per 100 parts by mass of polyurethane resin.

[0032] <Other Components> In the first embodiment, preferably embodiment 1-1, the polishing pad may contain components other than those mentioned above in the polyurethane sheet, to the extent that it does not impair the effects of the present invention. Examples of components other than those mentioned above include fillers such as carbon black.

[0033] (Thickness) There are no particular restrictions on the thickness of the polyurethane sheet in the polishing pad of the first embodiment, preferably embodiment 1-1, but it can be used in the range of 0.3 to 3.0 mm, preferably 0.5 to 2.0 mm, and more preferably 0.7 to 1.5 mm.

[0034] (Other layers) The polishing pad of the first embodiment, preferably embodiment 1-1, is based on the premise that the surface of the polyurethane sheet (polishing surface) is in contact with the workpiece to be polished, and therefore no other resin layers exist on the polishing surface of the polyurethane sheet. On the other hand, in the polishing pad of the first embodiment, preferably embodiment 1-1, other resin layers (underlayer, support layer) may or may not be bonded to the surface of the polyurethane sheet opposite to the surface that polishes the workpiece to be polished (polishing surface). The characteristics of the other resin layer are not particularly limited, but it is preferable that a layer harder than the polyurethane sheet (a layer with high hardness such as Shore A hardness or Shore D hardness) is bonded. By providing a layer harder than the polyurethane sheet, it is possible to avoid the fine irregularities of the polishing platen affecting the shape of the polishing surface, and the polishing flatness is further improved. In addition, the overall rigidity of the polishing pad is increased, which suppresses the occurrence of wrinkles when attaching the polishing pad to the polishing platen, and improves workability.

[0035] (Average hole diameter) In this specification and the claims, the average hole diameter refers to the average of the circle equivalent diameters calculated based on the area of ​​minute holes present on the polished surface. The hole diameter can be calculated by binarizing an image of the polished surface taken with a scanning electron microscope (SEM) using image processing software to confirm the number of apertures, determining the circle equivalent diameter from the area of ​​each hole, and taking the average value of these values ​​as the average hole diameter. The polished surface is preferably a polished surface after buffing a polyurethane sheet. In the first embodiment, preferably embodiment 1-1, the average hole diameter of the holes present on the polished surface is preferably 20 to 60 μm, more preferably 25 to 55 μm, even more preferably 30 to 50 μm, and even more preferably 35 to 45 μm.

[0036] (Pore Ratio) In this specification and the claims, the porosity ratio means the ratio (%) of the pore area to the polished surface. The polished surface is preferably the polished surface after buffing the polyurethane sheet. The porosity ratio can be determined by binarizing an image of the polished surface taken with a scanning electron microscope (SEM) using image processing software, determining the area of ​​each pore, and then determining the ratio of the pore area per unit area of ​​the polished surface as the porosity ratio (%). In the first embodiment, preferably embodiment 1-1, the porosity ratio of the polyurethane sheet in the polishing pad is preferably in the range of 10 to 30%, more preferably 12 to 25%, even more preferably 15 to 25%, and even more preferably 15 to 20%.

[0037] (Applications) The polishing pad of the first embodiment, preferably embodiment 1-1, can be suitably used as a polishing pad for polishing (chemical mechanical polishing (CMP)) workpieces such as semiconductor devices, semiconductor wafers, silicon, and glass. Among these, the polishing pad of the first embodiment, preferably embodiment 1-1, can be suitably used as a polishing pad for semiconductor devices. Furthermore, the polishing pad of the first embodiment, preferably embodiment 1-1, can be suitably used as a polishing pad for polishing metal pattern wafers such as copper, and as a polishing pad for polishing barrier metals. Furthermore, the polishing pad of the first embodiment, preferably embodiment 1-1, can be suitably used for polishing workpieces using a polishing slurry (chemical mechanical polishing). Among these, the polishing pad of the first embodiment, preferably embodiment 1-1, can be suitably used for polishing workpieces using a slurry containing silicon atom-containing abrasive grains, and can be particularly suitably used for polishing workpieces using an alkaline slurry containing silicon atom-containing abrasive grains (chemical mechanical polishing).

[0038] <Effect> In the first embodiment, preferably embodiment 1-1, the polishing pad contains 1 to 50% by mass of anionic polyurethane resin in the polyurethane resin constituting the polyurethane sheet. By including 1 to 50% by mass of anionic polyurethane resin, it is possible to obtain a polishing pad that is less likely to have abrasive particles, especially silicon (Si) components, adhere to it in the slurry. However, if the proportion of anionic polyurethane resin in the polyurethane resin becomes too high, conversely, abrasive particles, especially silicon (Si) components, in the slurry will adhere more easily to the surface of the polishing pad. The reason for this is not entirely clear, but it is speculated that if the proportion of anionic polyurethane resin in the polyurethane resin becomes too high, the film-forming ability during wet film formation will decrease, the properties of the polishing surface will change, and the performance in preventing abrasive particles, especially silicon (Si) components, from adhering to the polishing surface will decrease (comparison of Example 1 and Comparative Example 3 of this embodiment). On the other hand, it is speculated that if the proportion of anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass, the above problem will not occur and the adhesion of abrasive particles can be reduced. Furthermore, the polishing pad described in Patent Document 2 is a nonwoven fabric type polishing pad. When polyurethane resin is impregnated into it, the nonwoven fabric acts as a framework, and the resin solidifies while adhering to the nonwoven fabric. As a result, problems with film formation and changes in the properties of the polished surface are less likely to occur. In particular, the surface condition is due to the unevenness of the fibers. On the other hand, since wet-formation type polishing pads do not have a framework, the influence of the foaming state is extremely large. Thus, wet-formation type polishing pads differ greatly in properties from nonwoven fabric type polishing pads, and it is impossible to recognize the above problems in wet-formation type polishing pads and their solutions from the disclosure in Patent Document 2 concerning nonwoven fabric type polishing pads. The effect of the polyurethane resin constituting the polyurethane sheet of the wet-formation type polishing pad containing 1 to 50% by mass of anionic polyurethane resin, which makes it difficult for abrasive particles in the slurry, especially silicon (Si) components, to adhere to the polishing pad, is remarkable.

[0039] Furthermore, the polishing pad of the first embodiment, preferably embodiment 1-1, is soft because it has multiple teardrop-shaped bubbles, and can be used for finish polishing. Unlike the initial polishing stage where nonwoven fabric type polishing is used, finish polishing is the final stage, so it is necessary to reduce the risk of scratches and particles. As described above, the polishing pad of the first embodiment, preferably embodiment 1-1, can suppress the adhesion, accumulation, and aggregation of abrasive grains in the slurry, especially silicon (Si) components, on the surface of the polishing pad. Therefore, it is expected that problems such as fine scratches caused by polishing the workpiece with aggregates of abrasive grains adhering to the surface of the polishing pad can be reduced. In addition, in finish polishing, if aggregates of abrasive grains containing Si adhere to the workpiece after polishing, it becomes a major problem as it results in defects (particles), but the polishing pad of the first embodiment, preferably embodiment 1-1, is less likely to allow aggregates containing Si to adhere to the polishing surface, so it is expected that the risk of defects caused by the transfer of aggregates from the polishing surface to the workpiece can also be reduced.

[0040] <Aspect 1-2> In the first aspect of the polishing pad, it is also preferable that the polyurethane resin contains a cationic polyurethane resin (as an ionic polyurethane resin). That is, another preferred aspect 1-2 of the polishing pad of the first aspect is a polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, and the polyurethane resin contains a cationic polyurethane resin. The following description will focus on this preferred aspect 1-2 of the polishing pad.

[0041] Polyurethane sheets have multiple teardrop-shaped bubbles. The term "teardrop-shaped bubbles" refers to bubbles formed inside the polyurethane sheet by the wet deposition method (anisotropic bubbles with a structure where the diameter increases from the top (the side in contact with the workpiece) to the bottom of the resin sheet), and is used to distinguish them from the roughly spherical bubbles found in dry molding. Therefore, a polyurethane sheet with multiple teardrop-shaped bubbles can be described as a polyurethane sheet formed by the wet deposition method. The wet deposition method involves dissolving the resin to be deposited in an organic solvent, applying the resin-containing solution to a sheet-like substrate, then passing it through a coagulation solution that dissolves the organic solvent but not the resin to replace the organic solvent, allowing it to coagulate, and finally drying it to form a foamed layer. Typically, when a polyurethane sheet is manufactured by the wet deposition method, multiple roughly teardrop-shaped macrobubbles (teardrop-shaped bubbles) are generated inside the polyurethane sheet. Furthermore, when polyurethane sheets are manufactured by a wet film deposition method, a large number of bubbles (microbubbles, minute bubbles) that are much finer than macrobubbles are usually formed in addition to macrobubbles. In this specification and the claims, a polyurethane sheet means a sheet whose main component is polyurethane resin (50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more of the total resin constituting the polyurethane sheet is polyurethane resin, and the polyurethane resin may be 100% by mass), and is clearly distinguished from sheets whose main component is other resins (such as silicone resin). In this specification and the claims, a polishing layer is a layer having a surface (polishing surface) that comes into contact with the object to be polished when polishing an object to be polished, such as a semiconductor device. A polishing pad may have other layers, such as a cushion layer, on the opposite side from the polishing layer. In this specification and the claims, a polyurethane sheet does not contain nonwoven fabric.

[0042] <Polyurethane Resin> Polyurethane sheets contain polyurethane resin. There are no particular restrictions on the type of polyurethane resin; it can be selected from various polyurethane resins according to the intended use. For example, polyester-based, polyether-based, or polycarbonate-based polyurethane resins can be used. Examples of polyester-based resins include polymers of polyester polyols, such as ethylene glycol or butanediol, and adipic acid, and diisocyanates such as diphenylmethane-4,4'-diisocyanate. Examples of polyether-based resins include polymers of polyether polyols, such as polytetramethylene ether glycol or polypropylene glycol, and isocyanates such as diphenylmethane-4,4'-diisocyanate. Examples of polycarbonate-based resins include polymers of polycarbonate polyols and isocyanates such as diphenylmethane-4,4'-diisocyanate. These resins may be commercially available resins such as "Crisbon" manufactured by DIC Corporation, "Samplen" manufactured by Sanyo Chemical Industries, Ltd., or "Rezamin" manufactured by Dainichi Seika Kogyo Co., Ltd., or a resin with the desired properties may be manufactured in-house.

[0043] As described above, cationic polyurethane resin is a polyurethane resin having cationic properties. Preferably, a cationic polyurethane resin is a polyurethane resin that contains a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines (or contains a group containing such nitrogen atom as a cationic ionic group) in its structure. As described above, anionic polyurethane resin is a polyurethane resin having anionic properties. Preferably, an anionic polyurethane resin is a polyurethane resin that contains an anionic ionic group in its structure. Examples of anionic ionic groups include carboxyl groups, sulfo groups, phosphate groups, phenolic hydroxyl groups, etc., with carboxyl groups being preferred. As described above, nonionic polyurethane resin is a polyurethane resin having nonionic properties, and preferably, a polyurethane resin that does not contain a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines, nor an anionic ionic group, in its structure. There are no particular restrictions on the method for producing a polyurethane resin whose structure contains nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, and known methods may be used as appropriate. For example, a compound containing nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines can be prepared as a component in the prepolymer that will be used as a raw material for the polyurethane resin and / or as a chain extender, or a compound containing nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines can be prepared by reacting the components in the prepolymer and / or the chain extender with a compound containing nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, and then these raw materials can be reacted to produce the polyurethane resin.

[0044] <Cationic Polyurethane Resin> The polyurethane resin in Embodiment 1-2 includes a cationic polyurethane resin. The proportion of cationic polyurethane resin in the polyurethane resin is preferably 1 to 50% by mass, more preferably 2 to 45% by mass, even more preferably 3 to 40% by mass, even more preferably 3 to 35% by mass, even more preferably 3 to 30% by mass, even more preferably 3 to 20% by mass, even more preferably 3 to 10% by mass, even more preferably 3 to 8% by mass, and even more preferably 4 to 6% by mass. When the proportion of cationic polyurethane resin in the polyurethane resin is within the above range, abrasive particles, especially silicon (Si) components in slurries, particularly acidic slurries, are less likely to adhere, and a polishing pad with excellent polishing surface properties can be obtained. Such a polishing pad can preferably be used to polish an object to be polished using an acidic slurry containing silicon atom-containing abrasive particles. The cationic polyurethane resin is preferably a polyurethane resin containing nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, and more preferably a polyurethane resin containing nitrogen atoms derived from a tertiary amine. These nitrogen atoms function as cations. The statement that a cationic polyurethane resin contains nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines can also be rephrased as saying that the cationic polyurethane resin contains at least one amine selected from the group consisting of primary to tertiary amines (hereinafter, groups having primary to tertiary amines may be referred to as primary to tertiary amino groups, respectively). The statement that a polyurethane resin contains nitrogen atoms derived from a primary amine means that the polyurethane resin contains a nitrogen atom in a primary amine whose three bonds are bonded to a hydrogen atom, and the remaining bond is bonded to a group other than a hydrogen atom. The statement that a polyurethane resin contains nitrogen atoms derived from a secondary amine means that the polyurethane resin contains a nitrogen atom in a secondary amine whose three bonds are bonded to a hydrogen atom, and the remaining two bonded to a group other than a hydrogen atom.The fact that the polyurethane resin contains a nitrogen atom derived from a tertiary amine means a polyurethane resin containing, in its structure, a nitrogen atom in the tertiary amine, where none of the three bonds of the nitrogen atom is bonded to a hydrogen atom and the remaining three are bonded to groups other than hydrogen atoms. The nitrogen atom may be contained in the main chain structure of the polyurethane resin or in the side chain structure, but is preferably contained in the main chain structure. The cationic polyurethane resin preferably contains a nitrogen atom derived from at least one amine selected from primary to tertiary amines in the polyol compound constituting the polyurethane resin. The polyol compound may be the polyol compound (A) constituting the prepolymer or the polyol compound (A') used as the chain extender (C). The nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines may be contained in the structure of the polyurethane resin by bonding of one or more groups other than the above-mentioned hydrogen atoms bonded to the nitrogen atom to a structural unit such as a polyol constituting the polyurethane resin, or may be contained in the structure of the polyurethane resin as a polyol unit (in the prepolymer or chain extender) constituting the polyurethane resin by having one or more groups other than the above-mentioned hydrogen atoms have two or more hydroxyl groups.

[0045] A nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines may be included in any structural unit constituting the polyurethane resin. Generally, polyurethane resins are obtained by reacting a prepolymer consisting of a polyol compound (A) (hereinafter sometimes referred to as component (A)) and a polyisocyanate compound (B) (hereinafter sometimes referred to as component (B)) with a chain extender (C) (hereinafter sometimes referred to as component (C)). The cationic ionic group may be included in the polyol compound (A) or in the chain extender (C) (for example, the polyol compound (A') in the chain extender (C)). Preferably, the cationic ionic group is included in the chain extender (C). When manufacturing polyurethane resin, the polyol compound (A), polyisocyanate compound (B), and chain extender (C) may be mixed and reacted at once, or the polyol compound (A) and polyisocyanate compound (B) may be reacted to produce a urethane bond-containing isocyanate compound (prepolymer), and then the prepolymer and chain extender (C) may be mixed and reacted. The individual components will be described below.

[0046] (Polyol Compound (A)) In this specification and the claims, polyol compound (A) means a compound having two or more alcoholic hydroxyl groups in its molecule. Examples of polyol compound (A) include polyester polyols, polyether polyols, polycarbonate polyols, polyacrylic polyols, polybutadiene polyols, hydrogenated polybutadiene polyols, dimer ols, and the like. Diol compounds are preferred as polyol compound (A), with polyester diols, polyether diols, and polycarbonate diols being more preferred, and polyester diols being particularly preferred. These polyol compounds may be used individually or in combination of multiple polyol compounds.

[0047] (Polyisocyanate compound (B)) In this specification and the claims, polyisocyanate compound (B) means a compound having two or more isocyanate groups in its molecule. Polyisocyanate compound (B) is not particularly limited as long as it has two or more isocyanate groups in its molecule. For example, diisocyanate compounds having two isocyanate groups in their molecule include m-phenylenediisocyanate, p-phenylenediisocyanate, 2,6-tolylenediisocyanate (2,6-TDI), 2,4-tolylenediisocyanate (2,4-TDI), naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), 4,4'-methylene-bis(cyclohexyl isocyanate) (hydrogenated MDI), 3,3'-dimethoxy-4,4'-biphenyldiisocyanate, 3,3'-dimeth Examples of polyisocyanate compounds include diphenylmethane-4,4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, cyclohexylene-1,4-diisocyanate, p-phenylene diisothiocyanate, xylylene-1,4-diisothiocyanate, and ethyridine diisothiocyanate. Diisocyanate compounds are preferred as polyisocyanate compounds, with MDI, 2,4-TDI, and 2,6-TDI being more preferred, and MDI being particularly preferred. These polyisocyanate compounds may be used individually or in combination of multiple polyisocyanate compounds.

[0048] (Chain extender (C)) As the chain extender (C), for example, a polyol compound (A') having a lower molecular weight than the above polyol compound (A) and / or a polyamine compound (D) can be used. Specific examples of the low molecular weight polyol compound (A') include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, and the like. In the present specification and claims, the polyamine compound (D) means a compound having two or more amino groups in the molecule. Specific examples of the low molecular weight polyamine compound (D) include ethylenediamine, 1,2-propanediamine, 1,6-hexamethylenediamine, piperazine, 2,5-dimethylpiperazine, isophoronediamine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, 4,4'-dicyclohexylmethanediamine, 3,3'-dimethyl-4,4'-dicyclohexylmethanediamine, hydrazine, and the like.

[0049] <Nitrogen Atoms Derived from Amines> Nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines may be included, for example, in a polyol compound (component (A) and / or component (A')). That is, structural units derived from the polyol compound of a cationic polyurethane resin may have nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines. By using a polyol compound having nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, the nitrogen atoms can be included (introduced) into the polyurethane resin, and a cationic polyurethane resin can be obtained. Examples of polyols having nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines include triethylenetetramine, diethylenetriamine, N-alkyldialkanolamines such as N-methyldiethanolamine and N-ethyldiethanolamine, and N-alkyldiaminoalkylamines such as N-methyldiaminoethylamine and N-ethyldiaminoethylamine. A compound containing a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines may be used as a chain extender (C) (component (A')) or as a polyol compound (component (A)), but it is preferable to use it as a chain extender (C).

[0050] There are no particular restrictions on the proportion of structural units derived from a compound having a nitrogen atom from at least one amine selected from the group consisting of primary to tertiary amines to the total structural units constituting the cationic polyurethane resin. However, among the total structural units constituting the cationic polyurethane resin (structural units derived from polyol compounds, structural units derived from polyisocyanate compounds, structural units derived from chain extenders, and compounds derived from a compound having a nitrogen atom from at least one amine selected from the group consisting of primary to tertiary amines), the proportion of structural units derived from a compound having a nitrogen atom from at least one amine selected from the group consisting of primary to tertiary amines (preferably a polyol compound) is preferably in the range of 0.1 to 30 mol%, more preferably in the range of 0.5 to 20 mol%, even more preferably in the range of 1 to 15 mol%, and still more preferably in the range of 5 to 15 mol%. Furthermore, the proportion is particularly preferably 8 to 12 mol%, and most preferably 10 mol%. Furthermore, when a compound having a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines is used as a chain extender, the proportion of structural units derived from the compound having a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines among the total structural units derived from the chain extender of the cationic polyurethane resin is preferably 1 to 50 mol%, more preferably 3 to 40 mol%, and even more preferably 5 to 30 mol%. Furthermore, when a compound having a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines is used as a chain extender, the proportion of structural units derived from the compound having a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines among the total structural units derived from the chain extender of the cationic polyurethane resin is preferably 5 to 65% by mass, more preferably 10 to 60% by mass, even more preferably 15 to 55% by mass, even more preferably 15 to 45% by mass, even more preferably 15 to 35% by mass, and particularly preferably 15 to 25% by mass. Furthermore, the aforementioned ratio is also preferably 25 to 35% by mass.Furthermore, when using a compound having nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines as a chain extender, the mass ratio of structural units derived from a compound having nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines to structural units derived from a compound that does not have nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines (preferably also does not have cationic ionic groups) is preferably 100:10 to 70, more preferably 100:15 to 65, even more preferably 100:15 to 60, even more preferably 100:15 to 50, even more preferably 100:15 to 40, and particularly preferably 100:20 to 30 (structural units derived from a compound that does not have nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines: structural units derived from a compound having nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines). Furthermore, the mass ratio is preferably 100:40 to 60, and particularly preferably 100:50. The structural units derived from the chain extender of the cationic polyurethane resin are preferably composed of structural units derived from a compound having a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines, and structural units derived from a compound that does not have a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines (preferably also does not have an anionic ionic group). In addition, the compound having a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines in the chain extender may have the same structure as the chain extender that does not have a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines, except that it contains a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines, or it may have a different structure.

[0051] <Polyurethane resins other than cationic polyurethane resins> The polyurethane resin in 1-2 preferably includes a cationic polyurethane resin and a polyurethane resin other than a cationic polyurethane resin. The mass ratio of the cationic polyurethane resin to the polyurethane resin other than a cationic polyurethane resin in the polyurethane resin is preferably 1:99 to 50:50, more preferably 2:98 to 45:55, even more preferably 3:97 to 40:60, even more preferably 3:97 to 35:65, even more preferably 3:97 to 30:70, even more preferably 3:97 to 20:80, even more preferably 3:97 to 10:90, even more preferably 3:97 to 8:92, and even more preferably 4:96 to 6:94. When the mass ratio of the cationic polyurethane resin to the polyurethane resin other than a cationic polyurethane resin in the polyurethane resin is within the above range, it is possible to reduce the adhesion of abrasive particles in the slurry to the polishing surface of the polishing pad.

[0052] There are no particular restrictions on polyurethane resins other than cationic polyurethane resins; any known polyurethane resin may be used. Examples of polyurethane resins other than cationic polyurethane resins include polyurethane resins that do not contain nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, and polyurethane resins that do not contain (have not introduced) nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, nor anionic ionic groups selected from the group consisting of carboxyl groups, sulfo groups, phosphate groups, and phenolic hydroxyl groups. Examples of polyurethane resins other than cationic polyurethane resins include anionic polyurethane resins and nonionic polyurethane resins. Among these, polyurethane resins other than cationic polyurethane resins are preferably polyurethane resins that do not contain nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, more preferably polyurethane resins that do not contain nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, and anionic ionic groups selected from the group consisting of carboxyl groups, sulfo groups, phosphoric acid groups, and phenolic hydroxyl groups, even more preferably polyurethane resins that do not contain nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, and anionic ionic groups, and still more preferably polyurethane resins that do not contain anionic ionic groups or cationic ionic groups.Furthermore, among polyurethane resins other than cationic polyurethane resins, it is preferable to have the same structural units as cationic polyurethane resins, except that structural units derived from compounds containing nitrogen atoms from at least one amine selected from the group consisting of primary to tertiary amines are replaced with structural units derived from compounds that do not contain nitrogen atoms from at least one amine selected from the group consisting of primary to tertiary amines. More preferable are polyurethane resins that have the same structural units as cationic polyurethane resins in the same proportions, except that structural units derived from compounds containing nitrogen atoms from at least one amine selected from the group consisting of primary to tertiary amines are replaced with structural units derived from compounds that do not contain nitrogen atoms from at least one amine selected from the group consisting of primary to tertiary amines.

[0053] <Zeta Potential> Zeta potential can be measured by the flow potential method, which measures the potential difference caused by the pressure difference, or by electrophoresis, which measures the mobility of tracer particles, and measurement by the flow potential method is preferred. In addition, to measure the zeta potential of polyurethane resin, a dry film with a thickness of about 200 μm is prepared by spreading the polyurethane resin (solution) thinly and drying it, and the zeta potential of this dry film is measured. In embodiment 1-2, the zeta potential of the polyurethane resin is preferably in the range of 5 to 50 mV at pH 2.9 to 3.1 (preferably pH 2.9), more preferably 10 to 35 mV, and even more preferably 13 to 32 mV.

[0054] (Modulus) Modulus is an index that represents the hardness of a resin, and is the value obtained by dividing the load applied when a non-foamed resin sheet is stretched to 100% (stretched to twice its original length) by the cross-sectional area (hereinafter sometimes referred to as 100% modulus). The higher this value, the harder the resin is. The polyurethane resin in embodiment 1-2 preferably has a 100% modulus of 1 to 10 MPa, more preferably 3 to 8 MPa, and even more preferably 3 to 5 MPa. When the 100% modulus is within the above range, it tends to be easier to balance the polishing rate and polishing scratches.

[0055] <Hydrophobic Additives> It is preferable that polyurethane sheets contain hydrophobic additives. Hydrophobic additives act as film-forming aids and can improve the film-forming properties of polyurethane sheets. Various conventional hydrophobic additives can be used as hydrophobic additives. Examples of hydrophobic additives include paraffinic hydrocarbons and nonionic hydrocarbons. Among these, it is preferable to include paraffinic hydrocarbons. Examples of paraffinic hydrocarbons include straight-chain hydrocarbons with 5 to 30 carbon atoms, normal paraffinic hydrocarbons such as liquid paraffin, kerosene, and light oil, branched hydrocarbons with 5 to 40 carbon atoms, and isoparaffinic hydrocarbons such as liquid isoparaffin. There are no particular restrictions on the amount of hydrophobic additives contained in the polyurethane sheet as long as a film can be formed on the polyurethane sheet, and any amount can be used as appropriate according to the properties of the polyurethane resin. In general, as the proportion of cationic polyurethane resin in the polyurethane resin increases, the film-forming properties deteriorate, so the amount of hydrophobic additives may be adjusted to facilitate film formation. Among these, the amount of hydrophobic additive is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 18 parts by mass or less, and even more preferably 16 parts by mass or less, per 100 parts by mass of polyurethane resin. On the other hand, there is no particular lower limit on the amount of hydrophobic additive. For example, it may be 0.01 parts by mass or more, 0.1 parts by mass or more, 0.5 parts by mass or more, 1 part by mass or more, 2 parts by mass or more, 4 parts by mass or more, 6 parts by mass or more, 8 parts by mass or more, 10 parts by mass or more, or 12 parts by mass or more, per 100 parts by mass of polyurethane resin. The amount of hydrophobic additive is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, preferably 1 to 20 parts by mass, and even more preferably 10 to 20 parts by mass, per 100 parts by mass of polyurethane resin.

[0056] <Cellulose Derivatives> The resin sheet preferably contains a cellulose derivative. By including a cellulose derivative, a microcell structure can be sufficiently formed when a polyurethane resin-containing solution applied to a film-forming substrate is wet-coated. In addition, the brittleness of the polishing pad is less likely to increase, and physical properties such as elongation are less likely to decrease. Examples of cellulose derivatives include ester-based cellulose derivatives, ether-based cellulose derivatives, ether-ester-based cellulose derivatives, and aromatic-containing cellulose conductors. Among these, ester-based cellulose derivatives are more preferred. Examples of ester-based cellulose derivatives include acetylcellulose, triacetylcellulose, acetylbutylcellulose, diacetylcellulose, acetylpropylcellulose, ethylcellulose, cellulose propionate, cellulose butyrate, nitrocellulose, cellulose sulfate, cellulose phosphate, cellulose acetate butyrate, cellulose nitrate acetate, and cellulose acetate propionate. Among these, acetylcellulose, triacetylcellulose, acetylbutylcellulose, diacetylcellulose, and acetylpropylcellulose are preferred, and those in which some or all of the OH groups of cellulose, such as acetylcellulose and triacetylcellulose, are esterified with acetate (particularly acetylcellulose with a substitution degree of 2.41) are more preferred. There are no particular restrictions on the amount of cellulose derivative contained in the polyurethane sheet, but it is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, and even more preferably 0.5 to 5 parts by mass per 100 parts by mass of polyurethane resin.

[0057] <Other Components> In the first embodiment, preferably embodiment 1-2, the polishing pad may contain components other than those mentioned above in the polyurethane sheet, as long as it does not impair the effects of the present invention. Examples of components other than those mentioned above include fillers such as carbon black.

[0058] (Thickness) There are no particular restrictions on the thickness of the polyurethane sheet in the polishing pad of the first embodiment, preferably embodiment 1-2, but it can be used in the range of 0.3 to 3.0 mm, preferably 0.5 to 2.0 mm, and more preferably 0.7 to 1.5 mm.

[0059] (Other layers) The polishing pad of the first embodiment, preferably embodiment 1-2, is based on the premise that the surface of the polyurethane sheet (polishing surface) is in contact with the workpiece to be polished, and therefore no other resin layers exist on the polishing surface of the polyurethane sheet. On the other hand, in the polishing pad of the first embodiment, preferably embodiment 1-2, other resin layers (underlayer, support layer) may or may not be bonded to the surface of the polyurethane sheet opposite to the surface that polishes the workpiece to be polished (polishing surface). The characteristics of the other resin layer are not particularly limited, but it is preferable that a layer harder than the polyurethane sheet (a layer with high hardness such as Shore A hardness or Shore D hardness) is bonded. By providing a layer harder than the polyurethane sheet, it is possible to avoid the fine irregularities of the polishing platen affecting the shape of the polishing surface, and the polishing flatness is further improved. In addition, the overall rigidity of the polishing pad is increased, which suppresses the occurrence of wrinkles when attaching the polishing pad to the polishing platen, and improves workability.

[0060] (Average hole diameter) In this specification and the claims, the average hole diameter refers to the average of the circle equivalent diameters calculated based on the area of ​​minute holes present on the polished surface. The hole diameter can be calculated by binarizing an image of the polished surface taken with a scanning electron microscope (SEM) using image processing software to confirm the number of apertures, determining the circle equivalent diameter from the area of ​​each hole, and taking the average value of these values ​​as the average hole diameter. The polished surface is preferably a polished surface after buffing a polyurethane sheet. In the first embodiment, preferably embodiment 1-2, the average hole diameter of the holes present on the polished surface is preferably 20 to 60 μm, more preferably 30 to 55 μm, even more preferably 38 to 50 μm, and even more preferably 40 to 45 μm.

[0061] (Pore Ratio) In this specification and the claims, the porosity ratio means the ratio (%) of the pore area to the polished surface. The polished surface is preferably the polished surface after buffing the polyurethane sheet. The porosity ratio can be determined by binarizing an image of the polished surface taken with a scanning electron microscope (SEM) using image processing software, determining the area of ​​each pore, and then determining the ratio of the pore area per unit area of ​​the polished surface as the porosity ratio (%). In the first embodiment, preferably embodiment 1-2, the porosity ratio of the polyurethane sheet in the polishing pad is preferably in the range of 10 to 50%, more preferably 16 to 50%, even more preferably 16 to 45%, and even more preferably 17 to 42%.

[0062] (Applications) The polishing pad of the first embodiment, preferably embodiment 1-2, can be suitably used as a polishing pad for polishing (chemical mechanical polishing (CMP)) of workpieces such as semiconductor devices, semiconductor wafers, silicon, and glass. Among these, the polishing pad of the first embodiment, preferably embodiment 1-2, can be suitably used as a polishing pad for semiconductor devices. Furthermore, the polishing pad of the first embodiment, preferably embodiment 1-2, can be suitably used as a polishing pad for polishing metal pattern wafers such as copper, and for polishing barrier metals. Furthermore, the polishing pad of the first embodiment, preferably embodiment 1-2, can be suitably used for polishing workpieces using a polishing slurry (chemical mechanical polishing). Among these, the polishing pad of the first embodiment, preferably embodiment 1-2, can be suitably used for polishing workpieces using a slurry containing silicon atom-containing abrasive grains, and can be particularly suitably used for polishing workpieces using an acidic slurry containing silicon atom-containing abrasive grains (chemical mechanical polishing).

[0063] <Effect> In the first embodiment, preferably embodiment 1-2, the polishing pad contains a cationic polyurethane resin in the polyurethane resin constituting the polyurethane sheet. By including the cationic polyurethane resin, it is possible to obtain a polishing pad that is less likely to have abrasive particles, especially silicon (Si) components, adhere to it in the slurry. In particular, by including 1 to 50% by mass of the cationic polyurethane resin, the adhesion of abrasive particles, especially silicon (Si) components, in the slurry can be significantly suppressed. The reason why the adhesion of silicon components can be suppressed by including 1 to 50% by mass of the cationic polyurethane resin compared to the case where the cationic polyurethane resin is included in more than 50% by mass is not entirely clear, but it is speculated that if the proportion of cationic polyurethane resin in the polyurethane resin becomes too high, the film-forming ability during wet film formation will decrease, the properties of the polishing surface will change, and the performance in preventing the adhesion of abrasive particles, especially silicon (Si) components, in the slurry to the polishing surface will decrease (comparison of Example A1 and Example A3 of this embodiment). On the other hand, if the cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass, the above problems will not occur, and it is presumed that the adhesion of abrasive particles to the polishing pad in acidic slurries can be significantly reduced. The polishing pad in Patent Document 3 aims to obtain a high polishing speed when polishing with an alkaline slurry of pH 12, and since it is a hard polishing pad that does not have air bubbles inside, problems with film formation and changes in the properties of the polished surface are less likely to occur. On the other hand, the wet-film-forming type polishing pad of the present invention is a soft polishing pad that has multiple large teardrop-shaped air bubbles, so the effect of the foaming state is extremely large. Thus, the properties of the wet-film-forming type polishing pad differ greatly from those of the non-foaming type polishing pad, and it is impossible to recognize the above problems and solutions in the wet-film-forming type polishing pad from the disclosure of Patent Document 3, which deals with a different problem than the present invention and relates to a non-foaming type polishing pad. The fact that the polyurethane resin constituting the polyurethane sheet of a wet-film-forming type polishing pad contains a cationic polyurethane resin (preferably 1 to 50% by mass) is remarkable because it makes it difficult for abrasive particles in the slurry, especially those in acidic slurries, preferably silicon (Si) components, to adhere to the polishing pad.

[0064] Furthermore, the polishing pad of the first embodiment, preferably embodiment 1-2, is soft because it has multiple teardrop-shaped bubbles, and can be used for finish polishing. Unlike the initial polishing stage where nonwoven fabric type polishing is used, finish polishing is the final stage, so it is necessary to reduce the risk of scratches and particles. As described above, the polishing pad of the first embodiment, preferably embodiment 1-2, can suppress the adhesion, accumulation, and aggregation of abrasive grains in the slurry, especially silicon (Si) components, on the surface of the polishing pad. Therefore, it is expected that problems such as fine scratches caused by polishing the workpiece with aggregates of abrasive grains adhering to the surface of the polishing pad can be reduced. In addition, in finish polishing, if aggregates of abrasive grains containing Si adhere to the workpiece after polishing, it becomes a major problem as it results in defects (particles), but the polishing pad of the first embodiment, preferably embodiment 1-2, is less likely to allow aggregates containing Si to adhere to the polishing surface, so it is expected that the risk of defects caused by the transfer of aggregates from the polishing surface to the workpiece can also be reduced.

[0065] The polishing pad of the first embodiment, preferably embodiment 1-1 or embodiment 1-2, can be manufactured, for example, by the following method.

[0066] <<Method for Manufacturing an Abrasive Pad (Second Embodiment)>> The second embodiment of the present invention is a manufacturing method comprising the steps of applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate, and immersing the film-forming substrate coated with the resin solution composition in a solidifying solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin contains an ionic polyurethane resin.

[0067] <Aspect 2-1> In addition, in the manufacturing method of the second aspect, it is preferable that the polyurethane resin contains an anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass. That is, preferred aspect 2-1 of the manufacturing method of the second aspect is a manufacturing method comprising the steps of applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate, and immersing the film-forming substrate to which the resin solution composition has been applied in a solidification solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin contains anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass. The manufacturing method of aspect 2-1 is preferred as a manufacturing method for the polishing pad of aspect 1-1. The steps of preferred aspect 2-1 will be described below.

[0068] <Step of applying the resin solution composition to the film-forming substrate> In the step of applying the resin solution composition to the film-forming substrate, a resin solution composition containing polyurethane resin and an organic solvent is prepared and applied to the film-forming substrate.

[0069] (Polyurethane Resin) The resin solution composition contains polyurethane resin, which is the material for the polyurethane sheet. The polyurethane resin includes anionic polyurethane resin. The polyurethane resin, anionic polyurethane resin, and their respective content ratios can be those listed in the description of the polishing pad.

[0070] (Organic solvent) Any organic solvent that can dissolve the polyurethane resin and is miscible with water can be used without particular limitations. Examples include N,N-dimethylformamide (DMF), methyl ethyl ketone, N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and acetone. Among these, DMF or DMAc are preferred. The organic solvent is preferably contained in the polyurethane resin-containing solution in an amount such that the solid content concentration in the polyurethane resin-containing solution is preferably 10 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 30% by mass. If the concentration is within the above range, the polyurethane resin-containing solution will have appropriate fluidity and can be uniformly applied to the film-forming substrate in the subsequent coating process.

[0071] (Hydrophobic Additive) The resin solution composition preferably contains a hydrophobic additive. As the hydrophobic additive, the hydrophobic additives listed in the description of the polishing pad can be used. The amount of hydrophobic additive contained in the resin solution composition is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and even more preferably 18 parts by mass or less, per 100 parts by mass of polyurethane resin. Furthermore, the amount of hydrophobic additive is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, even more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, even more preferably 10 parts by mass or more, and even more preferably 12 parts by mass or more, per 100 parts by mass of polyurethane resin. The amount of hydrophobic additive is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, preferably 1 to 20 parts by mass, and even more preferably 10 to 20 parts by mass, per 100 parts by mass of polyurethane resin.

[0072] (Cellulose derivatives) The resin solution composition may contain cellulose derivatives in addition to the above components. As the cellulose derivative, the cellulose derivatives listed in the description of the polishing pad can be used. The amount of cellulose derivative contained in the resin solution composition is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, even more preferably 0.5 to 5 parts by mass, even more preferably 0.5 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass per 100 parts by mass of polyurethane resin.

[0073] (Other Components) The resin solution composition may further contain other components besides those listed above, as long as they do not impair the effects of the present invention. Other components that can be used include those listed in the description of the polishing pad. The resin solution composition obtained above is continuously applied to the film-forming substrate in a substantially uniform manner, for example, by a knife coater, a reverse coater, etc. The film-forming substrate can be any substrate that is commonly used in the art without particular limitations. Examples of film-forming substrates include flexible polymer films such as polyester films and polyolefin films, and nonwoven fabrics impregnated and fixed with elastic resin, among which polyester films are preferred.

[0074] <Solidification Process> The film-forming substrate coated with the resin solution composition is immersed in a solidification solution mainly composed of water, which is a poor solvent for polyurethane resin. As the solidification solution, water, a mixed solution of water and a polar solvent such as DMF can be used. Examples of polar solvents include water-miscible organic solvents used to dissolve the polyurethane resin, such as DMF, DMAc, THF, DMSO, NMP, and acetone. The concentration of the polar solvent in the mixed solvent is preferably 0.5 to 30% by mass. There are no particular restrictions on the temperature of the solidification solution or the immersion time; for example, immersion at 5 to 80°C for 5 to 60 minutes is sufficient.

[0075] <Washing and Drying> If necessary, the sheet-like polyurethane resin obtained by solidifying in a solidification bath is washed and dried after being peeled off the film-forming substrate, or without peeling. The washing process removes any organic solvents remaining in the polyurethane resin. Water is an example of a washing solution used for washing. After washing, the polyurethane resin is dried. The drying process can be carried out using conventional methods, for example, by drying in a dryer at 80 to 150°C for about 5 to 60 minutes. A polyurethane sheet can be obtained through the above process.

[0076] In the above method for manufacturing the polishing pad, the polishing surface of the polyurethane sheet and / or the surface opposite to the polishing surface may be polished (buffed) as needed. Furthermore, grooves, embossing, and / or holes (punching) may be applied to the polishing surface of the polyurethane sheet, and a base material may be bonded to the polyurethane sheet. Additionally, a light-transmitting portion may be provided on the polyurethane sheet and / or the polishing pad. There are no particular restrictions on the polishing method, and it can be polished using known methods. Specifically, polishing with sandpaper is an example. There are no particular restrictions on the shape of the grooves and embossing, and examples include grid, concentric, and radial shapes. When bonding base materials to form a multi-layer structure, the multiple layers may be bonded and fixed together using double-sided tape or adhesive, applying pressure as needed. There are no particular restrictions on the double-sided tape or adhesive used, and any known double-sided tape or adhesive in the art can be arbitrarily selected and used.

[0077] Subsequently, double-sided tape is applied to the side of the polyurethane sheet opposite to the abrasive surface, or to the side opposite to the surface bonded to the polyurethane sheet of the base material. The sheet is then cut into a predetermined shape, preferably a disc shape, to complete the abrasive pad. There are no particular restrictions on the double-sided tape; any double-sided tape known in the art can be arbitrarily selected and used.

[0078] <Aspect 2-2> In addition, the manufacturing method of the second aspect is also preferable in which the polyurethane resin includes a cationic polyurethane resin. That is, another preferred aspect 2-2 of the manufacturing method of the second aspect is a manufacturing method comprising the steps of applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate, and immersing the film-forming substrate to which the resin solution composition has been applied in a solidifying solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin includes a cationic polyurethane resin. The manufacturing method of aspect 2-2 is preferred as a manufacturing method for the polishing pad of aspect 1-2. The steps of the preferred aspect 2-2 will be described below.

[0079] <Step of applying the resin solution composition to the film-forming substrate> In the step of applying the resin solution composition to the film-forming substrate, a resin solution composition containing polyurethane resin and an organic solvent is prepared and applied to the film-forming substrate.

[0080] (Polyurethane Resin) The resin solution composition contains polyurethane resin, which is the material for the polyurethane sheet. The polyurethane resin includes cationic polyurethane resin. The polyurethane resin, cationic polyurethane resin, and their respective content ratios can be those listed in the description of the polishing pad.

[0081] (Organic solvent) Any organic solvent that can dissolve the polyurethane resin and is miscible with water can be used without particular limitations. Examples include N,N-dimethylformamide (DMF), methyl ethyl ketone, N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and acetone. Among these, DMF or DMAc are preferred. The organic solvent is preferably contained in the polyurethane resin-containing solution in an amount such that the solid content concentration in the polyurethane resin-containing solution is preferably 10 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 15 to 30% by mass. If the concentration is within the above range, the polyurethane resin-containing solution will have appropriate fluidity and can be uniformly applied to the film-forming substrate in the subsequent coating process.

[0082] (Hydrophobic Additive) The resin solution composition preferably contains a hydrophobic additive. As the hydrophobic additive, the hydrophobic additives listed in the description of the polishing pad can be used. The amount of hydrophobic additive contained in the resin solution composition is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, and even more preferably 18 parts by mass or less, per 100 parts by mass of polyurethane resin. Furthermore, the amount of hydrophobic additive is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, even more preferably 4 parts by mass or more, even more preferably 6 parts by mass or more, even more preferably 8 parts by mass or more, even more preferably 10 parts by mass or more, and even more preferably 12 parts by mass or more, per 100 parts by mass of polyurethane resin. The amount of hydrophobic additive is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, preferably 1 to 20 parts by mass, and even more preferably 10 to 20 parts by mass, per 100 parts by mass of polyurethane resin.

[0083] (Cellulose derivatives) The resin solution composition may contain cellulose derivatives in addition to the above components. As the cellulose derivative, the cellulose derivatives listed in the description of the polishing pad can be used. The amount of cellulose derivative contained in the resin solution composition is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 8 parts by mass, even more preferably 0.5 to 5 parts by mass, even more preferably 0.5 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass per 100 parts by mass of polyurethane resin.

[0084] (Other Components) The resin solution composition may further contain other components besides those listed above, as long as they do not impair the effects of the present invention. Other components that can be used include those listed in the description of the polishing pad. The resin solution composition obtained above is continuously applied to the film-forming substrate in a substantially uniform manner, for example, by a knife coater, a reverse coater, etc. The film-forming substrate can be any substrate that is commonly used in the art without particular limitations. Examples of film-forming substrates include flexible polymer films such as polyester films and polyolefin films, and nonwoven fabrics impregnated and fixed with elastic resin, among which polyester films are preferred.

[0085] <Solidification Process> The film-forming substrate coated with the resin solution composition is immersed in a solidification solution mainly composed of water, which is a poor solvent for polyurethane resin. As the solidification solution, water, a mixed solution of water and a polar solvent such as DMF can be used. Examples of polar solvents include water-miscible organic solvents used to dissolve the polyurethane resin, such as DMF, DMAc, THF, DMSO, NMP, and acetone. The concentration of the polar solvent in the mixed solvent is preferably 0.5 to 30% by mass. There are no particular restrictions on the temperature of the solidification solution or the immersion time; for example, immersion at 5 to 80°C for 5 to 60 minutes is sufficient.

[0086] <Washing and Drying> If necessary, the sheet-like polyurethane resin obtained by solidifying in a solidification bath is washed and dried after being peeled off the film-forming substrate, or without peeling. The washing process removes any organic solvents remaining in the polyurethane resin. Water is an example of a washing solution used for washing. After washing, the polyurethane resin is dried. The drying process can be carried out using conventional methods, for example, by drying in a dryer at 80 to 150°C for about 5 to 60 minutes. A polyurethane sheet can be obtained through the above process.

[0087] In the above method for manufacturing the polishing pad, the polishing surface of the polyurethane sheet and / or the surface opposite to the polishing surface may be polished (buffed) as needed. Furthermore, grooves, embossing, and / or holes (punching) may be applied to the polishing surface of the polyurethane sheet, and a base material may be bonded to the polyurethane sheet. Additionally, a light-transmitting portion may be provided on the polyurethane sheet and / or the polishing pad. There are no particular restrictions on the polishing method, and it can be polished using known methods. Specifically, polishing with sandpaper is an example. There are no particular restrictions on the shape of the grooves and embossing, and examples include grid, concentric, and radial shapes. When bonding base materials to form a multi-layer structure, the multiple layers may be bonded and fixed together using double-sided tape or adhesive, applying pressure as needed. There are no particular restrictions on the double-sided tape or adhesive used, and any known double-sided tape or adhesive in the art can be arbitrarily selected and used.

[0088] Subsequently, double-sided tape is applied to the side of the polyurethane sheet opposite to the abrasive surface, or to the side opposite to the surface bonded to the polyurethane sheet of the base material. The sheet is then cut into a predetermined shape, preferably a disc shape, to complete the abrasive pad. There are no particular restrictions on the double-sided tape; any double-sided tape known in the art can be arbitrarily selected and used.

[0089] <Polishing Method (Third Aspect)> The third aspect of the present invention is a method for polishing an object to be polished, comprising the step of polishing the object to be polished using the above-described polishing pad in the presence of a slurry containing silicon atom-containing abrasive particles.

[0090] <Aspect 3-1> A preferred aspect of the polishing method of the third aspect is a method for polishing an object to be polished, comprising the step of polishing the object to be polished using the polishing pad of aspect 1-1 in the presence of a slurry containing silicon atom-containing abrasive grains. In aspect 3-1, it is preferable that the slurry containing silicon atom-containing abrasive grains is an alkaline slurry. The following description will focus on aspect 3-1.

[0091] In a third embodiment, preferably the polishing method of embodiment 3-1, the workpiece may be held using a holding pad while polishing with a polishing pad. When using a polishing pad, the polishing pad is attached to the polishing platen of the polishing machine so that the polishing surface of the polyurethane sheet faces the workpiece. Then, while supplying polishing slurry onto the polishing pad or the workpiece, the polishing platen is rotated to polish the processed surface of the workpiece. Examples of workpieces (held workpieces) include semiconductor devices, semiconductor wafers, silicon, and glass. Among these, semiconductor devices are preferred as workpieces. Examples of semiconductor device materials include silicon, polysilicon, silicon oxide film, silicon nitride, and metals such as Cu, W, Al, Ta, and TiN. The polishing pad can be suitably used as a polishing pad for polishing metal pattern wafers such as copper, or as a polishing pad for polishing barrier metals. Examples of polishing slurries include slurries for barrier metals, slurries for oxide films, and slurries for Cu. The slurry preferably contains silicon atom-containing abrasive particles. The slurry may also contain other abrasive particles, oxidizing agents, components to protect the workpiece, etching agents, chelating agents, etc. The abrasive (abrasive particles) of the polishing slurry is preferably silicon atom-containing abrasive particles, among which silica (SiO2) is preferred, and colloidal silica is more preferred. Examples of components to protect the workpiece include triazole compounds, pyrazole compounds, pyramidine compounds, imidazole compounds, guanidine compounds, thiazole compounds, and tetrazole compounds, which act as metal corrosion inhibitors. Furthermore, the liquid properties of the polishing slurry in the third embodiment, preferably embodiment 3-1, may be an acidic slurry or an alkaline slurry, but an alkaline slurry is preferred. The liquid properties of the polishing slurry can be adjusted by adding acidic components such as sulfuric acid and phosphoric acid, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, organic alkali compounds such as tetramethylammonium hydroxide and choline, and alkaline components such as ammonia to the slurry as needed.

[0092] <Aspect 3-2> Another preferred aspect 3-2 of the polishing method of the third aspect is a method for polishing a workpiece, comprising the step of polishing the workpiece using the polishing pad of aspect 1-2 in the presence of a slurry containing silicon atom-containing abrasive grains. In aspect 3-2, it is preferable that the slurry containing silicon atom-containing abrasive grains is an acidic slurry. The following description will focus on aspect 3-2. In the polishing method of the third aspect, preferably aspect 3-2, when polishing, the workpiece may be held using a holding pad while polishing with the polishing pad. When using a polishing pad, the polishing pad is attached to the polishing platen of the polishing machine so that the polishing surface of the polyurethane sheet faces the workpiece. Then, while supplying abrasive slurry onto the polishing pad or onto the workpiece, the polishing platen is rotated to polish the processed surface of the workpiece. Examples of workpieces (held workpieces) include semiconductor devices, semiconductor wafers, silicon, and glass. Among these, semiconductor devices are preferred as workpieces. Materials for semiconductor devices include silicon, polysilicon, silicon oxide films, silicon nitrides, and metals such as Cu, W, Al, Ta, and TiN. Polishing pads can be suitably used as polishing pads for polishing metal pattern wafers such as copper, or as polishing pads for polishing barrier metals. Examples of polishing slurries include slurries for barrier metals, slurries for oxide films, and slurries for Cu. The slurry preferably contains silicon atom-containing abrasive particles. The slurry may also contain other abrasive particles, oxidizing agents, components to protect the workpiece, etching agents, chelating agents, etc. The abrasive (abrasive particles) in the polishing slurry is preferably silicon atom-containing abrasive particles, among which silica (SiO2) is preferred, and colloidal silica is more preferred. Examples of components to protect the workpiece include triazole compounds, pyrazole compounds, pyramidine compounds, imidazole compounds, guanidine compounds, thiazole compounds, and tetrazole compounds, which act as metal corrosion inhibitors.Furthermore, the liquid properties of the polishing slurry in the third embodiment, preferably embodiment 3-2, may be an acidic slurry or an alkaline slurry, but an acidic slurry is preferred. The liquid properties of the polishing slurry can be adjusted by adding acidic components such as sulfuric acid or phosphoric acid, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, organic alkali compounds such as tetramethylammonium hydroxide and choline, and alkaline components such as ammonia to the slurry as needed.

[0093] The following embodiments of the present invention are also preferred. [A1] A polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, the polyurethane resin contains an anionic polyurethane resin, and the proportion of the anionic polyurethane resin to the polyurethane resin is 1 to 50% by mass. [A2] The polishing pad according to [A1], wherein the anionic polyurethane resin is a polyurethane resin containing anionic ionic groups. [A3] The polishing pad according to [A2], wherein the anionic ionic group contains at least one selected from the group consisting of a carboxyl group, a sulfo group, a phosphate group, and a phenolic hydroxyl group. [A4] The polishing pad according to [A3], wherein the anionic ionic group contains a carboxyl group. [A5] The polishing pad according to any one of [A1] to [A4], wherein the anionic polyurethane resin contains anionic ionic groups in the polyol compound constituting the polyurethane resin. [A6] The polishing pad according to any one of [A1] to [A5], wherein the polyurethane resin comprises the anionic polyurethane resin and a polyurethane resin other than the anionic polyurethane resin, and the mass ratio of the anionic polyurethane resin to the polyurethane resin other than the anionic polyurethane resin in the polyurethane resin is 1:99 to 50:50. [A7] The polishing pad according to [A6], wherein the polyurethane resin other than the anionic polyurethane resin is a polyurethane resin that does not contain a cationic ionic group selected from a group containing a nitrogen atom derived from at least one amine selected from the group consisting of primary amines to tertiary amines. [A8] The polishing pad according to any one of [A1] to [A7], wherein the porosity of the polishing surface of the polyurethane sheet is 15 to 20%. [A9] The polishing pad according to any one of [A1] to [A8], wherein the polyurethane sheet further comprises a hydrophobic additive. [A10] The polishing pad according to [A9], wherein the hydrophobic additive comprises a paraffinic hydrocarbon. [A11] A polishing pad according to any one of [A1] to [A10] for polishing an object to be polished using an alkaline slurry containing silicon atom-containing abrasive grains.[A12] A method for producing an abrasive pad according to any one of [A1] to [A11], comprising the steps of: applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate; and immersing the film-forming substrate coated with the resin solution composition in a solidifying solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin contains an anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass. [A13] A method for polishing an object to be polished, comprising the step of polishing the object to be polished using an abrasive pad according to any one of [A1] to [A11] in the presence of a slurry containing silicon atom-containing abrasive particles. [A14] The polishing method according to [A13], wherein the slurry is an alkaline slurry.

[0094] [B1] A polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, and the polyurethane resin contains a cationic polyurethane resin. [B2] The polishing pad according to [B1], wherein the proportion of cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass. [B3] The polishing pad according to [B1] or [B2] for polishing an object to be polished using an acidic slurry containing silicon atom-containing abrasive particles. [B4] The polishing pad according to any one of [B1] to [B3], wherein the cationic polyurethane resin is a polyurethane resin containing nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines. [B5] The polishing pad according to [B4], wherein the cationic polyurethane resin contains nitrogen atoms derived from a tertiary amine. [B6] The polishing pad according to any one of [B1] to [B5], wherein the cationic polyurethane resin contains a nitrogen atom derived from at least one amine selected from primary to tertiary amines in the polyol compound constituting the polyurethane resin. [B7] The polishing pad according to any one of [B1] to [B6], wherein the polyurethane resin comprises the cationic polyurethane resin and a polyurethane resin other than the cationic polyurethane resin, and the mass ratio of the cationic polyurethane resin to the polyurethane resin other than the cationic polyurethane resin in the polyurethane resin is 1:99 to 50:50. [B8] The polishing pad according to [B7], wherein the polyurethane resin other than the cationic polyurethane resin is a polyurethane resin that does not contain a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines, nor an anionic ionic group selected from the group consisting of carboxyl groups, sulfo groups, and phosphate groups. [B9] The polishing pad according to any one of [B1] to [B8], wherein the porosity of the polishing surface of the polyurethane sheet is 16 to 50%. [B10] The polishing pad according to any one of [B1] to [B9], wherein the polyurethane sheet further comprises a hydrophobic additive. [B11] The polishing pad according to [B10], wherein the hydrophobic additive comprises a paraffinic hydrocarbon.[B12] A method for producing an abrasive pad according to any one of [B1] to [B11], comprising the steps of: applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate; and immersing the film-forming substrate coated with the resin solution composition in a solidifying solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin contains a cationic polyurethane resin. [B13] The method for producing an abrasive pad according to [B12], wherein the proportion of cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass. [B14] A method for polishing an object to be polished, comprising the step of polishing the object to be polished using an abrasive pad according to any one of [B1] to [B11] in the presence of an acidic slurry containing silicon atom-containing abrasive particles.

[0095] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In Examples 1-2, Comparative Examples 1-3, Examples A1-A3, and Comparative Examples A1-A2, unless otherwise specified, "parts" means "parts by mass."

[0096] <Comparative Example 1> A polyurethane resin-containing solution was obtained by mixing 100 parts of a polyester-based polyurethane resin solution A (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa with 40 parts of DMF, 2 parts of water, 5 parts of polyether-modified silicone, and 2 parts of cellulose acetate. Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied to it using a knife coater. The film was then immersed in a solidification bath (solidification liquid was water) to solidify the polyurethane resin-containing solution. After that, the film-forming substrate was peeled off, washed, and dried to obtain a polyurethane sheet. Subsequently, the skin layer was buffed to open the surface, and a polyethylene terephthalate (PET) sheet was bonded to the side of the polyurethane sheet opposite to the buffed surface. Finally, the buffed surface was embossed with a grid-shaped mold to obtain the polishing pad of Comparative Example 1.

[0097] <Comparative Example 2> A polyurethane resin-containing solution was obtained by mixing 100 parts of a polyester-based polyurethane resin solution A (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa with 40 parts of DMF, 2 parts of water, 5 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation) and 2 parts of cellulose acetate. Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied to it using a knife coater. The film was then immersed in a solidification bath (solidification liquid was water) to solidify the polyurethane resin-containing solution. After that, the film-forming substrate was peeled off, washed and dried to obtain a polyurethane sheet. Subsequently, the skin layer was buffed to open the surface, and a polyethylene terephthalate (PET) sheet was bonded to the side of the polyurethane sheet opposite to the buffed surface. Then, the buffed surface was embossed with a grid-shaped mold to obtain the polishing pad of Comparative Example 2.

[0098] <Example 1> A polyurethane resin-containing solution was obtained by mixing 95 parts of a polyester-based polyurethane resin solution A (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa, 5 parts of a charge-adjusted polyester-based polyurethane resin solution B (solid content concentration 30% by mass) with a 100% modulus of 4.1 MPa, 40 parts of DMF, 5 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation), and 0.5 parts of cellulose acetate. The polishing pad of Example 1 was obtained in the same manner as in Comparative Example 2. The polyester polyurethane resin A and the charge-modified polyester polyurethane resin B used were composed of the same polyol compound (A) and polyisocyanate compound (B) (MDI), but differed in the composition of the chain extender (C) (polyol compound (A')). (In polyester polyurethane resin A, the ratio of chain extender without anionic functional groups to chain extender with anionic functional groups (carboxyl groups) was 100:0 (weight ratio), while in polyester polyurethane resin B, the ratio of chain extender without anionic functional groups to chain extender with anionic functional groups was 100:25 (weight ratio)). The proportion of structural units derived from the chain extender with anionic functional groups in the total structural units constituting the charge-modified polyester polyurethane resin solution B was 5 mol%.

[0099] <Example 2> A polyurethane resin-containing solution was obtained by mixing 70 parts of a polyester-based polyurethane resin solution A (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa, 30 parts of a charge-adjusted polyester-based polyurethane resin solution B (solid content concentration 30% by mass) with a 100% modulus of 4.1 MPa, 40 parts of DMF, 5.5 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation), and 0.5 parts of cellulose acetate. The polishing pad of Example 2 was obtained in the same manner as in Comparative Example 2.

[0100] <Comparative Example 3> A polyurethane resin-containing solution was obtained by mixing 100 parts of a charge-adjusted polyester polyurethane resin solution B (solid content concentration 30% by mass) with a 100% modulus of 4.1 MPa with 40 parts of DMF, 7 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation), and 0.5 parts of cellulose acetate. The polishing pad of Comparative Example 3 was obtained in the same manner as in Comparative Example 2.

[0101] <Test 1: Zeta Potential Measurement> For zeta potential measurement, polyurethane resin solution A and / or polyurethane resin solution B were mixed in the ratios used in Comparative Examples 1-3 and Examples 1-2, respectively. Each polyurethane resin was rolled thinly and dried with hot air to produce a dry film with a thickness of approximately 200 μm. The zeta potential of the obtained film surface was measured by the flow potential method in a 1 mM KCl aqueous solution while changing the pH from alkaline to neutral. HCl aqueous solution and KOH aqueous solution were used to adjust the pH. The results for pH 8.8-8.9 are shown in Table 1.

[0102]

[0103] <Test 2: Measurement of Si Adhesion Amount After Polishing Test> For each of the polishing pads of Comparative Examples 1-3 and Examples 1-2, a pad break (pre-use polishing surface preparation treatment using a dresser) was performed, and 10 workpieces were polished continuously under the polishing conditions described below. Then, the amount of Si component, which is an abrasive grain, was evaluated by performing energy-dispersive X-ray analysis on the central part of the land (area surrounded by embossed grooves) on the polishing surface of the polishing pad using a scanning electron microscope (SEM-EDX) equipped with an energy-dispersive X-ray spectrometer, for a region (0.4 mm × 0.3 mm) of the SEM image of the polishing pad surface. The amount of Si adhesion was evaluated according to the following criteria, with B or higher being considered acceptable. A: Si adhesion amount of 6.0 mass% or less B: Si adhesion amount greater than 6.0 mass% to 6.4 mass% or less C: Si adhesion amount greater than 6.4 mass% to 6.8 mass% or less D: Si adhesion amount greater than 6.8 mass% The results are shown in Table 2.

[0104] <Test Conditions> Dresser: 3M Diamond Dresser A188 Bad Break: 30N x 30 minutes Polishing Slurry: Strongly alkaline (pH 10-11) colloidal silica slurry Workpiece: TEOS coated silicon wafer Polishing Pressure: 2 psi Polishing Time: 1 minute Slurry Flow Rate: 200 mL / min Conditioning: Ex-situ 30N, 4 scans, 16 seconds

[0105]

[0106] <Result 1> Considering the zeta potential, Comparative Example 3 (in the case of 100% by mass of charge-adjusting resin) is expected to have the lowest adhesion amount. However, as can be seen from the results of Test 2, the polishing pad of Comparative Example 3, which has the smallest zeta potential (largest negative), had a larger adhesion amount compared to the polishing pads of Examples 1 and 2, and also a larger adhesion amount compared to Comparative Example 2 (Table 2).

[0107] (Test 3: Measurement of Average Hole Diameter & Hole Ratio) The average hole diameter and hole ratio of the polishing pads of Comparative Examples 1-3 and Examples 1-2 were calculated by observing nine locations on the polishing surface of a polyurethane sheet at 100x magnification using a scanning electron microscope (JEOL Ltd., JMS-5500LV), and then binarizing these images using image processing software (Nikon Corporation, ImageAnalyzer V20LAB Ver. 1.3). The average hole diameter was calculated by checking the number of openings after binarization, determining the equivalent diameter of a circle from the area of ​​each opening, and taking the average value. The hole ratio was calculated by determining the area of ​​each opening after binarization and taking the ratio of the opening area per unit area of ​​the polishing surface as the hole ratio (%). The results are shown in Table 3 and Figures 1-5.

[0108]

[0109] <Test 4: Measurement of Si adhesion after immersion test> For the polyester-based polyurethane resin solution A and charge-adjusted polyurethane resin solution B used in Comparative Examples 1-3 and Examples 1-2, the polyurethane resin solution was spread thinly and dried with hot air, similar to Test 1, to produce a dry film with a thickness of approximately 200 μm. The obtained film (3 cm × 5 cm) was immersed and shaken in 60 mL of alkaline colloidal silica slurry at 100 rpm for 2 hours, and then washed by immersion in 60 mL of 1 mM KOH aqueous solution for 5 minutes. The washed film was ultrasonically immersed in 30 mL of 0.1 M KOH aqueous solution for 1 hour, and after filtering the obtained solution, 20 mL of the filtrate was subjected to an ICP emission spectrometer (PerkinElmer Avio 500) to measure the Si content. The results are shown in Table 4.

[0110]

[0111] <Result 2> As described above, considering the zeta potential, it was thought that Comparative Example 3 (100% charge-adjusting resin) would have the lowest amount of adhesion. However, when comparing Examples 1-2 and Comparative Example 3, the polishing pad of Comparative Example 3 actually had the highest amount of adhesion (Table 2). Therefore, in Test 3, the polished surfaces of the polishing pads of Examples 1-2 and Comparative Examples 1-3 were examined after buffing. The polishing pad of Comparative Example 3 had a worse surface condition compared to the polishing pads of Examples 1-2 and Comparative Example 2 (insufficient pores were not formed by buffing, resulting in an uneven polished surface (Table 3, Figure 5)). Furthermore, in Test 4, when the amount of Si adhesion was examined by forming a film without wet deposition using only polyurethane resin solution A or polyurethane resin solution B, so that there were no teardrop-shaped bubbles or surface pores and the surface condition did not deteriorate, the amount of Si adhesion was smaller with resin solution B containing anionic polyurethane resin than with resin solution A (Table 4). From the above results, it is presumed that in polishing pads obtained by wet deposition, if the proportion of anionic polyurethane resin is too high, the surface condition after wet deposition deteriorates, and the amount of adhesion increases due to factors such as an increase in the specific surface area of ​​the polishing surface. On the other hand, the polishing pads of Examples 1 and 2, in which the proportion of anionic polyurethane resin to the polyurethane resin was 5% by mass and 30% by mass, respectively, did not show significant deterioration of the polishing surface, and the amount of Si adhesion was significantly reduced compared to the polishing pads of Comparative Examples 1 to 3. Therefore, it is considered that the polishing pads of Examples 1 and 2 can suppress the adhesion of abrasive particles in the slurry, such as colloidal silica.

[0112] <Comparative Example A1> A polyurethane resin-containing solution was obtained by mixing 100 parts of a polyester-based polyurethane resin solution A' (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa with 40 parts of DMF, 2 parts of water, 5 parts of polyether-modified silicone, and 2 parts of cellulose acetate. Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied to it using a knife coater. The film was then immersed in a solidification bath (solidification liquid was water) to solidify the polyurethane resin-containing solution. After that, the film-forming substrate was peeled off, washed, and dried to obtain a polyurethane sheet. Subsequently, the skin layer was buffed to open the surface, and a polyethylene terephthalate (PET) sheet was bonded to the side of the polyurethane sheet opposite to the buffed surface. Then, the buffed surface was embossed with a grid-shaped mold to obtain the polishing pad of Comparative Example A1. Comparative Example A1 is the same as Comparative Example 1.

[0113] <Comparative Example A2> A polyurethane resin-containing solution was obtained by mixing 100 parts of a polyester-based polyurethane resin solution A' (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa with 40 parts of DMF, 2 parts of water, 5 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation) and 2 parts of cellulose acetate. Next, a PET film was prepared as a film-forming substrate, and the polyurethane resin-containing solution was applied to it using a knife coater. The film was then immersed in a solidification bath (solidification liquid was water) to solidify the polyurethane resin-containing solution. After that, the film-forming substrate was peeled off, washed and dried to obtain a polyurethane sheet. Subsequently, the skin layer was buffed to open the surface, and a polyethylene terephthalate (PET) sheet was bonded to the side of the polyurethane sheet opposite to the buffed surface. Then, the buffed surface was embossed with a grid-shaped mold to obtain the polishing pad of Comparative Example A2. Comparative Example A2 is identical to Comparative Example 2.

[0114] <Example A1> A polyurethane resin-containing solution was obtained by mixing 95 parts of a polyester-based polyurethane resin solution A' (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa, 5 parts of a charge-adjusted polyester-based polyurethane resin solution C' (solid content concentration 30% by mass) with a 100% modulus of 4.1 MPa, 40 parts of DMF, 5 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation), and 0.5 parts of cellulose acetate. The polishing pad of Example A1 was obtained in the same manner as in Comparative Example A2. The polyester polyurethane resin A and the charge-modified polyester polyurethane resin C used consisted of the same polyol component and isocyanate component (MDI), but differed in the composition of their chain extenders (in polyester polyurethane resin A', the chain extender without nitrogen atoms derived from tertiary amines: chain extender having nitrogen atoms derived from tertiary amines in the main chain = 100:0 (weight ratio), while in polyester polyurethane resin C', the chain extender without nitrogen atoms derived from tertiary amines: chain extender having nitrogen atoms derived from tertiary amines = 100:50 (weight ratio)). The proportion of structural units (polyols) derived from the chain extender having nitrogen atoms derived from tertiary amines in the total structural units constituting the charge-modified polyester polyurethane resin solution C' was 10 mol%.

[0115] <Example A2> A polyurethane resin-containing solution was obtained by mixing 70 parts of a polyester-based polyurethane resin solution A' (solid content concentration 30% by mass) with a 100% modulus of 4.0 MPa, 30 parts of a charge-adjusted polyester-based polyurethane resin solution C' (solid content concentration 30% by mass) with a 100% modulus of 4.1 MPa, 40 parts of DMF, 5.5 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation), and 0.5 parts of cellulose acetate. The polishing pad of Example A2 was obtained in the same manner as in Comparative Example A2.

[0116] <Example A3> A polyurethane resin-containing solution was obtained by mixing 100 parts of a charge-adjusted polyester polyurethane resin solution C' (solid content concentration 30% by mass) with a 100% modulus of 4.1 MPa with 40 parts of DMF, 7 parts of isoparaffinic hydrocarbon (Crisbon Assister SD-8i manufactured by DIC Corporation), and 0.5 parts of cellulose acetate. The polishing pad of Example A3 was obtained in the same manner as in Comparative Example A2.

[0117] <Test A1: Zeta Potential Measurement> For zeta potential measurement, polyurethane resin solution A' and / or polyurethane resin solution C' were mixed in the ratios used in Comparative Examples A1-A2 and Examples A1-A3, respectively. Each polyurethane resin was thinly rolled out and dried with hot air to produce a dry film with a thickness of approximately 200 μm. The zeta potential of the obtained film surface was measured by the flow potential method in a 1 mM KCl aqueous solution while changing the pH from alkaline to neutral. HCl aqueous solution and KOH aqueous solution were used to adjust the pH. The results for pH 2.9-3.1 are shown in Table 5.

[0118]

[0119] <Test A2: Measurement of Si Adhesion Amount After Polishing Test> For each of the polishing pads of Comparative Examples A1-A2 and Examples A1-A3, a pad break (pre-use polishing surface preparation treatment using a dresser) was performed, and 10 workpieces were polished continuously under the polishing conditions described below. Then, the amount of Si component, which is an abrasive grain, was evaluated by performing energy-dispersive X-ray analysis on the central part of the land (area surrounded by embossed grooves) on the polishing surface of the polishing pad using a scanning electron microscope (SEM-EDX) equipped with an energy-dispersive X-ray spectrometer, for a region (0.4 mm × 0.3 mm) of the SEM image of the polishing pad surface. The amount of Si adhesion was evaluated according to the following criteria, with B or higher being considered acceptable. A: Si adhesion amount of 5.0 mass% or less B: Si adhesion amount greater than 5.0 mass% to 5.5 mass% or less C: Si adhesion amount greater than 5.5 mass% to 6.0 mass% or less D: Si adhesion amount greater than 6.0 mass% The results are shown in Table 6.

[0120] <Test Conditions> Dresser: 3M Diamond Dresser A188 Bad Break: 30N x 30 minutes Polishing Slurry: Strongly acidic (pH 2-3) colloidal silica slurry Workpiece: TEOS coated silicon wafer Polishing pressure: 2 psi Polishing time: 1 minute Slurry flow rate: 200 mL / min Conditioning: Ex-situ 30N, 4 scans, 16 seconds

[0121]

[0122] <Result A1> Compared to the polishing pads of Comparative Examples A1 to A2, the polishing pads of Examples A1 to A3 containing cationic polyurethane resin showed less silicon component adhesion and were found to suppress abrasive particle adhesion. Furthermore, considering the zeta potential, Example A3 (100% by mass of charge-adjusting resin) was expected to show the greatest reduction in adhesion, but as can be seen from the results of Test A2, the unexpected result was obtained that the polishing pads of Examples A1 to A2 showed less adhesion than the polishing pad of Example A3, which had the highest zeta potential (Table 6).

[0123] (Test A3: Measurement of Average Hole Diameter & Hole Ratio) The average hole diameter and hole ratio of the polishing pads of Comparative Examples A1-A2 and Examples A1-A3 were calculated by observing nine locations on the polishing surface of a polyurethane sheet at 100x magnification using a scanning electron microscope (JEOL Ltd., JMS-5500LV), and then binarizing these images using image processing software (Nikon Corporation, ImageAnalyzer V20LAB Ver. 1.3). The average hole diameter was calculated by checking the number of openings after binarization, determining the equivalent diameter of a circle from the area of ​​each opening, and taking the average value. The hole ratio was calculated by determining the area of ​​each opening after binarization and taking the ratio of the opening area per unit area of ​​the polishing surface as the hole ratio (%). The results are shown in Table 7 and Figures 6-10.

[0124]

[0125] <Test A4: Measurement of Si adhesion after immersion test> For the polyester-based polyurethane resin solution A' and charge-adjusted polyurethane resin solution C' used in comparative examples A1-A2 and examples A1-A3, the polyurethane resin solution was thinly spread and dried with hot air, similar to Test A1, to produce a dry film with a thickness of approximately 200 μm. The obtained film (3 cm × 5 cm) was immersed and shaken in 60 mL of acidic colloidal slurry at 100 rpm for 2 hours, and then washed by immersion in 60 mL of 1 mM HNO3 aqueous solution for 5 minutes. The washed film was ultrasonically immersed in 30 mL of 1 M HNO3 aqueous solution for 1 hour, and the obtained solution was filtered. 20 mL of the filtrate was subjected to an ICP emission spectrometer (PerkinElmer Avio 500) to measure the Si content. The results are shown in Table 8.

[0126]

[0127] <Result 2> The polishing pads of Examples A1 and A2, in which the proportion of cationic polyurethane resin to the polyurethane resin was 5% by mass and 30% by mass, respectively, did not show significant deterioration of the polished surface compared to the polishing pad of Example A3, in which the proportion of cationic polyurethane resin was 100% by mass (Figures 8 to 10). As mentioned above, considering the zeta potential, it was thought that Example A3 (100% charge-adjusting resin) would have the lowest adhesion amount, but in reality, when comparing Examples A1 to A2 and Example A3, the polishing pads of Examples A1 to A2 had less adhesion than the polishing pad of Example A3 (Table 6). Therefore, in Test A3, when the polished surfaces of the polishing pads of Examples A1 to A3 and Comparative Examples A1 to A2 were examined after buffing, the surface condition of the polishing pad of Example A3 was worse than that of the polishing pads of Examples A1 to A2 and Comparative Example A2 (sufficient pores were not formed by buffing, resulting in an uneven polished surface (Table 7, Figure 10)). Furthermore, in Test A4, when film deposition was performed without wet deposition using only polyurethane resin solution A' or polyurethane resin solution C', and the surface condition was not deteriorated without teardrop-shaped bubbles or surface pores, the amount of Si adhesion was examined. The resin solution C' containing cationic polyurethane resin showed a slightly smaller amount of Si adhesion than resin solution A' which does not contain cationic polyurethane resin (Table 8). From these results, it is presumed that in polishing pads obtained by wet deposition, if the proportion of cationic polyurethane resin is too high, the surface condition after wet deposition deteriorates, and the amount of adhesion increases due to an increase in the specific surface area of ​​the polishing surface. From the above, it is considered that the polishing pads of Examples A1 to A3 containing cationic polyurethane resin can reduce the adhesion of abrasive grains during polishing of the workpiece, and the polishing pads of Examples A1 to A2, in which the proportion of cationic polyurethane resin is 1 to 50% by mass, do not cause significant deterioration of the polishing surface and can further significantly reduce the amount of abrasive grain adhesion.

[0128] According to the present invention, it is possible to suppress the adhesion of abrasive particles, particularly silicon (Si) components, from the slurry to the surface of the polishing pad. Therefore, the polishing pad and its manufacturing method according to the present invention have industrial applicability.

Claims

1. A polishing pad comprising a polishing layer having a polyurethane sheet containing a plurality of teardrop-shaped bubbles, wherein the polyurethane sheet contains a polyurethane resin, and the polyurethane resin contains an ionic polyurethane resin.

2. The polishing pad according to claim 1, wherein the polyurethane resin includes an anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

3. The polishing pad according to claim 2, wherein the anionic polyurethane resin is a polyurethane resin containing an anionic ionic group in the polyol compound constituting the polyurethane resin.

4. The polishing pad according to claim 3, wherein the anionic ionic group includes a carboxyl group.

5. The polishing pad according to claim 2, wherein the polyurethane resin comprises the anionic polyurethane resin and a polyurethane resin other than the anionic polyurethane resin, the mass ratio of the anionic polyurethane resin to the polyurethane resin other than the anionic polyurethane resin in the polyurethane resin is 1:99 to 50:50, and the polyurethane resin other than the anionic polyurethane resin is a polyurethane resin that does not contain anionic ionic groups selected from the group consisting of carboxyl groups, sulfo groups, phosphate groups, and phenolic hydroxyl groups, nor cationic ionic groups selected from groups containing a nitrogen atom derived from at least one amine selected from the group consisting of primary amines to tertiary amines.

6. The polishing pad according to claim 2, wherein the porosity of the polishing surface of the polyurethane sheet is 15 to 20%.

7. The polishing pad according to claim 2, wherein the polyurethane sheet further comprises a paraffinic hydrocarbon.

8. The polishing pad according to claim 2, for polishing an object to be polished using an alkaline slurry containing silicon atom-containing abrasive particles.

9. The polishing pad according to claim 1, wherein the polyurethane resin comprises a cationic polyurethane resin.

10. The polishing pad according to claim 9, wherein the proportion of cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

11. The polishing pad according to claim 9, for polishing an object to be polished using an acidic slurry containing silicon atom-containing abrasive particles.

12. The polishing pad according to claim 9, wherein the cationic polyurethane resin is a polyurethane resin containing a nitrogen atom derived from at least one amine selected from the group consisting of primary to tertiary amines.

13. The polishing pad according to claim 12, wherein the cationic polyurethane resin contains nitrogen atoms derived from a tertiary amine in the polyol compound constituting the polyurethane resin.

14. The polishing pad according to claim 9, wherein the polyurethane resin comprises the cationic polyurethane resin and a polyurethane resin other than the cationic polyurethane resin, the mass ratio of the cationic polyurethane resin to the polyurethane resin other than the cationic polyurethane resin in the polyurethane resin is 1:99 to 50:50, and the polyurethane resin other than the cationic polyurethane resin is a polyurethane resin that does not contain nitrogen atoms derived from at least one amine selected from the group consisting of primary to tertiary amines, nor an anionic ionic group selected from the group consisting of carboxyl groups, sulfo groups, phosphate groups, and phenolic hydroxyl groups.

15. The polishing pad according to claim 9, wherein the porosity of the polishing surface of the polyurethane sheet is 16 to 50%.

16. The polishing pad according to claim 9, wherein the polyurethane sheet further comprises a paraffinic hydrocarbon.

17. A method for producing an abrasive pad according to any one of claims 1 to 16, comprising the steps of: applying a resin solution composition containing a polyurethane resin and an organic solvent to a film-forming substrate; and immersing the film-forming substrate coated with the resin solution composition in a solidifying solution to solidify the resin solution composition and obtain a polyurethane sheet, wherein the polyurethane resin contains an ionic polyurethane resin.

18. The manufacturing method according to claim 17, wherein the polyurethane resin contains an anionic polyurethane resin, and the proportion of the anionic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

19. The manufacturing method according to claim 17, wherein the polyurethane resin includes a cationic polyurethane resin.

20. The manufacturing method according to claim 19, wherein the proportion of cationic polyurethane resin in the polyurethane resin is 1 to 50% by mass.

Images