Polishing pad, polishing method, and method for manufacturing a polishing pad

Abstract

To provide a polishing pad that maintains high levels of global and local flatness while further suppressing burring at the edges of the workpiece. [Solution] The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following equations (1) and (2). 100[μm]≦D50≦200[μm] (1) |D80-D20| / D50≦1.2 ···(2) This polishing pad is characterized in that, on the surface where the bubble area ratio is maximum, the bubble area ratio is 70% to 95% and the Asker A hardness of the resin sheet, measured at 25°C, is 40 or higher.

Description

Technical Field

[0001] The present disclosure relates to a polishing pad, a polishing method, and a method for manufacturing a polishing pad.

Background Art

[0002] Conventionally, for precision polishing of the surfaces of glass substrates, semiconductor wafers containing compounds such as silicon and silicon carbide, gallium nitride, gallium oxide, diamond, etc. used in lenses, display mask blanks, etc., semiconductor devices containing metals such as silicon oxide insulating films and copper, tungsten, and other barrier metals, and workpieces to be polished such as hard disks for shape transfer or planarization, polishing with free abrasive grains has been carried out. In polishing with free abrasive grains, it is common to supply a slurry containing free abrasive grains between the workpiece to be polished and the polishing pad, and to oscillate and bring into contact while rotating the workpiece to be polished and the polishing pad individually.

[0003] In recent years, especially in free abrasive grain polishing related to semiconductors, due to the combined requirements of finer processing accuracy and improved productivity, the requirements for planarization of the workpiece to be polished have been increasing. Specifically, flatness refers to global flatness, which focuses on the overall height difference of the polished surface of the workpiece to be polished, local flatness, which focuses on the height difference within the plane after the chip is divided, and sag, etc., which is evaluated by focusing on the height difference between the end portion and the central portion of the polished surface of the workpiece to be polished, and the coexistence of these is required.

[0004] The deterioration of global flatness is mainly due to the slurry in the central portion of the workpiece to be polished being discharged and depleted due to sliding and the rotation of the polishing pad and the workpiece to be polished, resulting in non-uniform progress of polishing. Also, the deterioration of local flatness is due to the non-uniformity of the slurry holding amount caused by the non-uniformity of the pore diameter and the non-uniformity at the micro level of the contact points. Therefore, for example, in Patent Document 1, a polishing pad has been proposed that sharpens the bubble diameter distribution, equalizes the holding amount of the slurry at the micro level and the contact points, and enhances the slurry holding property by making the bubbles communicate.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-98103 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the configuration in Patent Document 1 had problems such as sagging at the end of the workpiece due to the ease with which the shape deformed under pressure because of the interconnected bubbles, and further improvements were needed.

[0007] The object of this disclosure is to provide a polishing pad that maintains high global and local flatness while further suppressing burr at the edges of the workpiece. The object of this disclosure is to provide a polishing method that maintains high global and local flatness while further suppressing burr at the edges of the workpiece. The object of this disclosure is to provide a method for manufacturing a polishing pad that maintains high global and local flatness while further suppressing burr at the edges of the workpiece. [Means for solving the problem]

[0008] To address the above issues, this disclosure provides: A polishing pad for polishing a workpiece with free abrasive particles, The polishing pad has a resin sheet having multiple air bubbles, When the cross-sectional area is determined by cutting the resin sheet perpendicular to its thickness direction based on the X-ray CT measurement results of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-sectional area to the area of ​​the cross-sectional area is defined as the bubble area ratio, The resin sheet has a surface among its cut surfaces where the air bubble area ratio is maximized. When the diameter corresponding to 20% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D80 [μm], The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following equations (1) and (2). 100[μm]≦D50≦200[μm] (1) |D80-D20| / D50≦1.2 ···(2) On the surface where the bubble area ratio is maximum, the bubble area ratio is 70% or more and 95% or less. The Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 40 or higher. This is a polishing pad characterized by the following features. Furthermore, this disclosure is, A polishing method using a polishing pad for polishing a workpiece with free abrasive particles, The polishing pad is the polishing pad described above. The polishing method includes a step of exposing the surface with the maximum bubble area ratio, or a surface near thereto, to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet. Furthermore, this disclosure is, The process includes introducing uncured resin into a coaxial centrifugal molding apparatus, forming an uncured resin layer on the inner surface of the coaxial centrifugal molding apparatus by centrifugal force, and then heating and curing the uncured resin layer to produce a resin sheet. The resin sheet has multiple air bubbles, When the cross-sectional area is determined by cutting the resin sheet perpendicular to its thickness direction based on the X-ray CT measurement results of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-sectional area to the area of ​​the cross-sectional area is defined as the bubble area ratio, The resin sheet has a surface with the largest bubble area ratio among the cut surfaces, When the diameter corresponding to 20% of the cumulative frequency of the equivalent circle diameters of the plurality of bubbles on the surface with the largest bubble area ratio is defined as D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent circle diameters of the plurality of bubbles on the surface with the largest bubble area ratio is defined as D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent circle diameters of the plurality of bubbles on the surface with the largest bubble area ratio is defined as D80 [μm], On the surface with the largest bubble area ratio, D20, D50, and D80 satisfy the following formulas (1) and (2), 100 [μm] ≤ D50 ≤ 200 [μm] ···(1) |D80 - D20| / D50 ≤ 1.2 ···(2) On the surface with the largest bubble area ratio, the bubble area ratio is 70 area% or more and 95 area% or less, A method for manufacturing a polishing pad, wherein the Asker A hardness of the resin sheet measured using a probe with a tip diameter of 0.79 mm at 25°C is 40 or more.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide a polishing pad and a polishing method that can suppress sagging at the end of the workpiece to be polished while maintaining high global flatness and local flatness.

Brief Description of the Drawings

[0010] [Figure 1] (a) Perspective view showing the concept of recesses and openings derived from bubbles of the present disclosure, (b) Cross-sectional view showing the concept of recesses and openings derived from bubbles of the present disclosure. [Figure 2] Conceptual diagram for explaining the equivalent circle diameter of the opening of the recess derived from bubbles. [Figure 3] Schematic diagram showing a configuration example of a centrifugal forming machine used for centrifugal forming. [Figure 4] Overview diagram of a method for defining a measurement surface in X-ray CT apparatus measurement and analysis.

Embodiments for Carrying Out the Invention

[0011] In the present disclosure, descriptions such as "XX or more and YY or less" and "XX to YY" representing numerical ranges mean numerical ranges including the lower limit and the upper limit which are the endpoints, unless otherwise specified.

[0012] 〔First Embodiment〕 The first embodiment relates to a polishing pad. The polishing pad of the present disclosure is a polishing pad for polishing an object to be polished with free abrasive grains, the polishing pad having a resin sheet with a plurality of air bubbles, from the measurement result of X-ray CT of the resin sheet, a cross-section obtained by cutting the resin sheet perpendicular to the thickness direction of the resin sheet is obtained, and when the ratio of the total area of the openings of the recesses derived from the plurality of air bubbles in the cross-section to the area of the cross-section is defined as the air bubble area ratio, the resin sheet has a surface in the cross-section where the air bubble area ratio is the maximum, when the diameter corresponding to 20% of the cumulative frequency of the equivalent circle diameters of the plurality of air bubbles on the surface where the air bubble area ratio is the maximum is defined as D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent circle diameters of the plurality of air bubbles on the surface where the air bubble area ratio is the maximum is defined as D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent circle diameters of the plurality of air bubbles on the surface where the air bubble area ratio is the maximum is defined as D80 [μm], the surface where the air bubble area ratio is the maximum satisfies the following formula (1) and the following formula (2) for the D20, the D50, and the D80, 100 [μm] ≦ D50 ≦ 200 [μm] ···(1) |D80 - D20| / D50 ≦ 1.2 ···(2) the air bubble area ratio on the surface where the air bubble area ratio is the maximum is 70 area% or more and 95 area% or less, the Asker A hardness of the resin sheet measured using a indenter with a tip diameter of 0.79 mm at 25°C is 40 or more, which is characterized by the above. In this disclosure, the nearby surface refers to the surface within a depth range of ±200 μm from the surface with the maximum bubble area ratio. Since the distribution of bubbles is continuous, the nearby surface is thought to have approximately the same number of bubble-derived depressions as the surface with the maximum bubble area ratio and to exert approximately the same effects.

[0013] According to the inventors' research, the above-mentioned polishing pad makes it possible to provide a polishing pad and polishing method that maintain high levels of global and local flatness while further suppressing burring at the edges of the workpiece. The details are described below.

[0014] As mentioned earlier, global flatness depends on the uniformity of slurry retention over a relatively macroscopic range of the pad, while local flatness depends on the slurry retention over a relatively microscopic range of the pad and the uniformity of the contact points.

[0015] In contrast to those, sag, another indicator related to flatness, is largely due to the elasticity and stiffness of the pad. Therefore, an approach to improve the material's stiffness can be considered, but in that case, there is a high possibility of adverse effects such as scratching.

[0016] Therefore, the pad needs to have a certain hardness while maintaining structural rigidity. The inventors believe that achieving global and local flatness through methods such as connecting air bubbles, which would reduce the rigidity of the pad, has inherent limitations as an approach to achieving both flatness and resistance to sagging.

[0017] From this perspective, improving local flatness by homogenizing the microstructure, that is, by sharpening the distribution of the diameter of the openings of depressions originating from air bubbles on the surface with the highest air bubble area ratio or its vicinity, can be achieved without reducing the rigidity of the pad and is an effective means of improving pad deformation above a certain hardness.

[0018] Therefore, the inventors investigated a structure that could improve slurry retention without reducing the rigidity of the pad, that is, by using closed cells instead of interconnected cells, thereby improving global flatness and reducing sagging.

[0019] In free abrasive polishing, slurry is constantly supplied between the polishing pad and the workpiece. The phenomenon of insufficient retention can be interpreted as an imbalance between the supply and discharge of slurry between the polishing pad and the workpiece, or rather, an over-discharge.

[0020] Therefore, the inventors sought a structure that not only enhances slurry retention and suppresses discharge, but also allows the supplied material to quickly penetrate from the periphery to the center of the pad, and found that this can be achieved in the presence of openings in recesses originating from air bubbles of a certain density or higher.

[0021] Although the details remain unclear, the inventors of this invention surmise the following: The slurry supplied between the polishing pad and the workpiece, or more precisely, the free abrasive particles, penetrate from the periphery to the center of the pad by moving between the depressions caused by air bubbles.

[0022] Therefore, if there are openings in depressions caused by bubbles above a certain density, the frequency of movement between these bubble-derived depressions increases non-linearly due to the increase in the number of bubbles and the decrease in the distance between them. This is thought to improve the penetration of the slurry into the center of the pad, thereby improving global flatness.

[0023] From the above studies, the inventors have found a configuration in which the distribution of opening diameters of depressions originating from air bubbles is sharp, and an area ratio of openings that can achieve sufficient inter-bubble movement of abrasive grains is realized using independent bubbles. As a result, for pads with a certain hardness or higher, it is possible to improve both global and local flatness while also improving sagging.

[0024] The details of this disclosure are described below. The polishing pad of this disclosure is a polishing pad for polishing an object to be polished with free abrasive particles. In this disclosure, the polishing pad has a resin sheet having a plurality of air bubbles.

[0025] In this disclosure, the cutting surface obtained by cutting the resin sheet perpendicular to the thickness direction of the resin sheet is determined from the measurement results of the X-ray CT of the resin sheet, and the bubble area ratio is defined as the ratio of the total area of ​​the openings of the multiple bubble-derived recesses on the cutting surface to the area of ​​the cutting surface. In this disclosure, the resin sheet has a surface on the cutting surface where the bubble area ratio is maximized.

[0026] Figures 1(a) and 1(b) schematically show bubbles on the surface with the maximum bubble area ratio or a nearby surface. As shown in the figures, bubbles on the surface with the maximum bubble area ratio or a nearby surface 3 have an opening 2 and a recess 1 originating from the bubble.

[0027] In this disclosure, when D50 [μm] is defined as the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the depressions originating from multiple bubbles on the surface where the bubble area ratio is maximum, the surface where the bubble area ratio is maximum satisfies the following equation (1). 100[μm]≦D50≦200[μm] (1) In this disclosure, D50 is preferably 101 μm or more and 194 μm or less.

[0028] When D50 is within the above range, the depressions caused by air bubbles can adequately hold the slurry, and since the slurry does not penetrate in the depth direction of the pad, phenomena such as the slurry being pushed out when the pad is pressurized, causing deformation and sagging, as can occur with continuous bubbles, are less likely to occur.

[0029] If D50 is greater than 100 μm, the opening diameter of the depressions caused by air bubbles is too small, preventing sufficient slurry retention and resulting in poor global flatness. If D50 is greater than 200 μm, the opening diameter is too large, leading to uneven contact with the workpiece between the center and edge of the opening, and reducing site flatness.

[0030] Here, Figure 2 shows a diagram illustrating the equivalent diameter of an equal-area circle opening of a bubble-derived recess in this disclosure. The equivalent diameter 6 of an equal-area circle opening of a bubble-derived recess can be determined by calculating the diameter of a circle (equal-area 5 of the bubble-derived recess opening) that has an equal area to the area of ​​the opening 4 of the bubble-derived recess, as in known methods.

[0031] In this disclosure, when the surface with the maximum bubble area ratio is defined as having a diameter corresponding to 20% of the cumulative frequency of the equivalent diameter of equiarea circles of recesses originating from multiple bubbles as D20 [μm], and a diameter corresponding to 80% of the cumulative frequency of the equivalent diameter of equiarea circles of recesses originating from multiple bubbles as D80 [μm], the surface with the maximum bubble area ratio satisfies the following equation (2) for D20, D50, and D80. |D80-D20| / D50≦1.2 ···(2)

[0032] In this disclosure, |D80-D20| / D50 represents the width of the distribution of equivalent diameters of equiarea circles of depressions originating from multiple air bubbles. A larger value results in a broader distribution, while a smaller value results in a sharper distribution. It is preferable that |D80-D20| / D50 is between 0.80 and 1.20, more preferably between 0.80 and 1.19, and particularly preferably between 0.80 and 1.18.

[0033] When |D80-D20| / D50 falls within the above range, the distribution of openings in the depressions caused by air bubbles becomes sharper, resulting in higher uniformity and improved site flatness. When |D80-D20| / D50 > 1.2, the distribution of openings in the depressions caused by air bubbles is broad, and the slurry retention and contact points become uneven, resulting in poor site flatness.

[0034] In this disclosure, the bubble area ratio on the surface where the bubble area ratio is maximum is 70 area% or more and 95 area% or less, preferably 70 area% or more and 90 area% or less, and more preferably 70 area% or more and 84 area% or less.

[0035] When the bubble area ratio is within the above range, inter-bubble movement of abrasive particles occurs actively, improving slurry penetration and resulting in good global flatness. If the ratio of the total area of ​​the openings is less than 70%, slurry penetration decreases, worsening global flatness. If it is greater than 95%, the rigidity of the surface with the maximum bubble area ratio or the surrounding surface decreases, worsening sagging.

[0036] In this disclosure, the Asker A hardness of the resin sheet, as measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 40 or higher. If the Asker A hardness is within the above range, it is possible to suppress sagging. If the Asker A hardness is less than 40, even with the aforementioned configuration of the openings in the recesses caused by air bubbles, deformation of the pad occurs, making it difficult to suppress sagging.

[0037] In this disclosure, if the surface with the maximum bubble area ratio is not exposed, it is preferable to expose the surface with the maximum bubble area ratio to the surface of the resin sheet, and then the average value (Dd) of the depths of the multiple bubble-derived recesses and D50 satisfy the following formula (3). 0.25 < Dd / D50 < 1 ···(3)

[0038] In this disclosure, Dd / D50 is more preferably 0.4 or more and 0.9 or less, and even more preferably 0.50 or more and 0.81 or less. When Dd / D50 is within the above range, deformation of the pad in the depth direction is suppressed while sufficient slurry retention is achieved, thereby improving global flatness while suppressing sagging.

[0039] In this disclosure, the maximum diameter of the bubble-derived recess on the surface with the highest bubble area ratio is preferably 100 μm or more and 500 μm or less, more preferably 125 μm or more and 475 μm or less, and even more preferably 150 μm or more and 475 μm or less. This prevents non-uniformity such as localized excess slurry and insufficient contact area, thereby improving site flatness.

[0040] [Second Embodiment] The second embodiment relates to a method for manufacturing an abrasive pad. The method for manufacturing an abrasive pad according to this disclosure is: The process includes introducing uncured resin into a coaxial centrifugal molding apparatus, forming an uncured resin layer on the inner surface of the coaxial centrifugal molding apparatus by centrifugal force, and then heating and curing the uncured resin layer to produce a resin sheet. The resin sheet has multiple air bubbles, When the cross-sectional area is determined by cutting the resin sheet perpendicular to its thickness direction based on the X-ray CT measurement results of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-sectional area to the area of ​​the cross-sectional area is defined as the bubble area ratio, The resin sheet has a surface among its cut surfaces where the air bubble area ratio is maximized. When the diameter corresponding to 20% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D80 [μm], The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following equations (1) and (2). 100[μm]≦D50≦200[μm] (1) |D80-D20| / D50≦1.2 ···(2) On the surface where the bubble area ratio is maximum, the bubble area ratio is 70% or more and 95% or less. The Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 40 or higher. Since the items described in the first embodiment overlap with those described in the second embodiment, explanations of resin sheets and the like may be omitted.

[0041] The present disclosure's method for manufacturing a polishing pad includes the steps of introducing uncured resin into a coaxial centrifugal molding apparatus, forming an uncured resin layer on the inner surface of the coaxial centrifugal molding apparatus by centrifugal force, and then heating and curing the uncured resin layer to produce a resin sheet. In this way, the bubble-derived recessed structure can be formed on the surface with the maximum bubble area ratio or on a surface near thereto.

[0042] In the method for manufacturing polishing pads according to this disclosure, the centrifugal force applied by the coaxial centrifugal molding apparatus in the process is 200 m / s 2 More than 4000m / s 2 Preferably, the viscosity of the uncured resin introduced into the coaxial centrifugal molding apparatus is 1,000 mPa·s or more and 20,000 mPa·s or less. By doing so, it is possible to form a distribution of bubbles that will form depressions originating from the bubbles on the surface of the resin sheet where the bubble area ratio is maximum or on a surface near thereto.

[0043] The materials for the resin sheets used in this disclosure will be described in detail below. The material for the resin sheet is not particularly limited as long as it is a thermosetting resin, but for example, one or more of the following can be used: polyurethane resin composition, polyacrylic resin composition, polycarbonate resin composition, polyamide resin composition, polyester resin composition, polyepoxy resin composition, etc.

[0044] The polyurethane resin composition contains a structure in which compounds containing active hydrogen groups and compounds containing isocyanate groups are alternately repeated as constituent units. The compound containing the active hydrogen group is an organic compound having an active hydrogen group that can react with an isocyanate group. Specific examples of the active hydrogen group include functional groups such as a hydroxyl group, a primary amino group, a secondary amino group, and a thiol group. The compound containing the active hydrogen group may have multiple types and multiple individuals of the active hydrogen group.

[0045] Examples of compounds containing the active hydrogen group include polyol compounds and polyamine compounds. Examples of polyol compounds include linear aliphatic glycols, branched aliphatic glycols, alicyclic diols, polyfunctional polyols, polyester polyols, polyester polycarbonate polyols, polyether polyols, polycarbonate polyols, and polyfunctional polyol polymers.

[0046] Examples of linear aliphatic glycols include 1,4-benzenedimethanol, 1,4-bis(2-hydroxyethoxy)benzene, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, and 1,9-nonanediol.

[0047] Examples of branched aliphatic glycols include neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and 2-methyl-1,8-octanediol.

[0048] Examples of alicyclic diols include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and bisphenol A with water. Examples of polyfunctional polyols include glycerin, trimethylolpropane, tributylolpropane, pentaerythritol, and sorbitol.

[0049] Examples of polyester polyols include polyethylene adipate glycol, polybutylene adipate glycol, polycaprolactone polyol, and polyhexamethylene adipate glycol.

[0050] Examples of polyester polycarbonate polyols include reaction products of polyester glycols such as polycaprolactone polyols and alkylene carbonates. Another example is a reaction product obtained by reacting a reaction mixture, which is formed by reacting ethylene carbonate with a polyhydric alcohol, with an organic dicarboxylic acid.

[0051] Examples of polyether polyols include polytetramethylene ether glycol, polypropylene glycol, polyethylene glycol, and ethylene oxide-added polypropylene polyol.

[0052] Examples of polycarbonate polyols include reaction products of diols such as 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene ether glycol with phosgene, diallyl carbonate (e.g., diphenyl carbonate), or cyclic carbonate (e.g., propylene carbonate).

[0053] Examples of polyamine compounds include 4,4'-methylenebis(2-chloroaniline) (MOCA), 4,4'-methylenedianiline, and trimethylene Examples include bis(4-aminobenzoate), 2-methyl4,6-bis(methylthio)benzene-1,3-diamine, 2-methyl4,6-bis(methylthio)-1,5-benzenediamine, 2,6-dichloro-p-phenylenediamine, 4,4'-methylenebis(2,3-dichloroaniline), 3,5-bis(methylthio)-2,4-toluenediamine, 3,5-bis(methylthio)-2,6-toluenediamine, 3,5-diethyltoluene-2,4-diamine, 3,5-diethyltoluene-2,6-diamine, trimethylene glycol-di-p-aminobenzoate, 1,2-bis(2-aminophenylthio)ethane, and 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane.

[0054] Compounds containing an isocyanate group include aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and urethane prepolymers. Examples of aromatic diisocyanates include tolylene diisocyanate (TDI), 1,5-naphthalene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate. Furthermore, examples of aromatic diisocyanates include diphenylmethane diisocyanate (MDI) and modified diphenylmethane diisocyanate (MDI).

[0055] Modified forms of diphenylmethane diisocyanate (MDI) include, for example, carbodiimide-modified forms, urethane-modified forms, allophanate-modified forms, urea-modified forms, biuret-modified forms, isocyanurate-modified forms, and oxazolidone-modified forms. Specifically, an example of such a modified form is carbodiimide-modified diphenylmethane diisocyanate (carbodiimide-modified MDI).

[0056] Examples of aliphatic diisocyanates include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate (HDI).

[0057] Examples of alicyclic diisocyanates include 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, and methylenebis(4,1-cyclohexylene) diisocyanate. The urethane prepolymer is a polymer formed by bonding a polyol and a polyisocyanate, and has isocyanate groups as terminal groups.

[0058] The resin sheet may contain a filler. Examples of fillers include inorganic powders such as aluminum oxide, cerium oxide, titanium oxide, germanium oxide, silicon carbide, calcium carbonate, silica, carbon black, diamond, talc, and clay; inorganic fibers such as glass fiber and carbon fiber; metal powders such as iron, copper, aluminum, and nickel; metal fibers such as iron fibers, copper fibers, and aluminum fibers; organic fibers such as polyimide fibers, Teflon® fibers, and polyester fibers; organic pigments such as azo pigments; and other materials commonly used in polymer chemistry, such as gases, fluids, and resin powders. Multiple types of these may be included simultaneously.

[0059] The filler is preferably in an amount of 0.1 parts by mass or more and 40.0 parts by mass or less per 100 parts by mass of resin. The particle size of the filler is preferably between 10 nm and 500 nm.

[0060] The resin sheet may contain a foam stabilizer. Examples of foam stabilizers include silicone-based surfactants, and one or more types can be used. Examples include "Toray Silicone SH-193," "Toray Silicone SH-192," and "Toray Silicone SH-190" manufactured by Toray Dow Corning Co., Ltd.

[0061] In addition to the materials mentioned above, stabilizers such as antioxidants, lubricants, pigments, fillers, antistatic agents, and other additives may be added to the resin sheet as needed. As a method for forming multiple bubble-derived recesses on the surface of the resin sheet of the polishing pad where the bubble area ratio is maximum, or on a surface near that surface, for example, mechanical foaming by mixing an inert gas into the uncured resin, chemical foaming by adding a foaming agent such as water, or by adding hollow microspheres that themselves become bubbles.

[0062] Examples of inert gases used in mechanical foaming include nitrogen, oxygen, carbon dioxide, noble gases such as helium and argon, and mixtures of these gases such as air. Any known stirring device can be used without particular limitation as a stirring device for dispersing inert gas in the form of fine bubbles by mechanical foaming. Specifically, examples include homogenizers, dissolvers, twin-screw planetary mixers, and mechanical floss foamers. The shape of the stirring blades of the stirring device is also not particularly limited, but examples include whip-type stirring blades.

[0063] Examples of foaming agents used in chemical foaming include water, foaming agents mainly composed of hydrocarbons having 5 or 6 carbon atoms, organic chemical foaming agents, and halogenated hydrocarbons. Examples of such hydrocarbons include chain hydrocarbons such as butane, n-pentane, and n-hexane, and alicyclic hydrocarbons such as cyclopentane and cyclohexane.

[0064] Examples of such organic chemical blowing agents include azo compounds, nitroso compounds, and sulfonyl hydrazide compounds. Examples of azo compounds include azodicarbonamide, azobisisobutyronitrile, diazoaminobenzene, and barium azodicarboxylate.

[0065] Examples of nitroso compounds include N,N'-dinitrosopentamethylenetetramine and N,N'-dinitroso-N,N'-dimethylterephthalamide. Examples of sulfonyl hydrazide compounds include p,p'-oxybis(benzenesulfonyl hydrazide) and p-toluenesulfonyl hydrazide. Examples of halogenated hydrocarbons include methylene chloride and HFCs (hydrofluorocarbons).

[0066] One example of a method for manufacturing the resin sheet of the polishing pad is centrifugal molding. Centrifugal molding is a method of forming a thin-walled cylindrical sheet by placing uncured resin sheet material into a cylindrical mold, rotating it at high speed to form a resin material layer on the inner surface by centrifugal force, and then heating and curing that layer. The cylindrical sheet thus obtained is removed from the cylindrical mold as a molded product, secondary crosslinking is performed as needed, and it is cut to the desired dimensions and shape as needed. Cutting methods include known methods such as sledgehammers, lasers, and cutters.

[0067] Figure 3 shows an example of the configuration of a centrifugal molding machine used for centrifugal molding. Specifically, the centrifugal molding machine can be configured to include a drive shaft 7 that rotates with a motor or the like, a cylindrical cup-shaped mold 8 (cylindrical mold 8) attached to the tip of the drive shaft and rotatably supported, a heat source 9 such as a heater fixedly arranged on the outer circumference of the cylindrical mold 8, and a hatch 10 opening in a case that covers these components.

[0068] The temperature of the cylindrical mold should be adjusted as appropriate based on the viscosity and foaming properties of the material being used. For example, if you want to speed up the curing process, you should increase the temperature, but the balance between foaming and curing varies depending on the material, so it needs to be adjusted according to the purpose.

[0069] The rotation speed of the cylindrical mold controls the effect of centrifugal force due to rotation, and this should also be adjusted appropriately based on the viscosity and foaming characteristics of the material used. For example, if you want to increase the foaming rate on the inner surface of a cylindrical mold for a resin sheet, you can increase the rotation speed to increase centrifugal force and promote the accumulation of bubbles. If you want to reduce the diameter of the bubbles, you can increase the rotation speed to increase centrifugal force and promote the bursting of large-diameter bubbles. The same applies if you want to equalize the distribution of bubble diameters. It is also possible to change the rotation speed in stages depending on the curing and foaming state of the resin. The rotation time of the cylindrical mold should be appropriately controlled to the extent that the centrifugal force effect described above is exerted.

[0070] The manufacturing method for the polishing pad of this disclosure preferably includes a step of exposing the surface with the maximum bubble area ratio or a nearby surface to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet. At a minimum, the surface with the maximum bubble area ratio or a nearby surface must be exposed to the surface of the resin sheet before use as a polishing pad. Any method that exposes the cross-section is acceptable.

[0071] [Third Embodiment] The third embodiment relates to a polishing method. The polishing method disclosed herein is A polishing method using a polishing pad for polishing a workpiece with free abrasive particles, The polishing pad is the polishing pad of the present disclosure, If the surface with the maximum bubble area ratio, or a surface near it, is not exposed to the surface of the resin sheet, the method includes a step of exposing the surface with the maximum bubble area ratio, or a surface near it, to the surface of the resin sheet. Since the items described in the first and second embodiments overlap with the descriptions in the third embodiment, explanations of resin sheets and the like may be omitted.

[0072] The polishing method described herein is a polishing method that uses a polishing pad to polish an object to be polished with free abrasive particles, wherein the polishing pad is the polishing pad described herein. A specific example thereof will be described.

[0073] First, the polishing method of this disclosure includes a step of exposing the surface with the maximum bubble area ratio or a nearby surface to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet. When polishing, it is necessary that the surface with the maximum bubble area ratio or a nearby surface is exposed to the surface of the resin sheet. Any method that exposes the cross-section is acceptable for this purpose.

[0074] Next, the workpiece to be polished is held in the holding platen of the polishing machine. Then, the polishing pad is attached to the polishing platen, which is positioned opposite the holding platen. If the polishing pad has double-sided tape and release paper, when attaching the polishing pad to the polishing platen, the release paper is peeled off from the double-sided tape to expose the adhesive layer of the double-sided tape, and then the exposed adhesive layer is brought into contact with the polishing platen and pressed down.

[0075] Then, a polishing slurry containing abrasive grains is supplied between the workpiece and the polishing pad as needed, and the workpiece is pressed towards the polishing pad with a predetermined polishing pressure while the polishing platen or holding platen is rotated, thereby polishing the workpiece with free abrasive grains.

[0076] The polishing slurry is not particularly limited and may be one used in conventional chemical mechanical polishing. As for the abrasive grains, general types can be used depending on the material to be polished, such as ceria, silica, alumina, manganese oxide, diamond, and organic-inorganic composite abrasive grains. The abrasive grains may be used individually or in combination of two or more types.

[0077] [Measurement and calculation methods for each physical property] The measurement and calculation methods for various physical properties of the polishing pad and material are described below. <Method for measuring diameters corresponding to a cumulative frequency of 20%, 50%, and 80%> • Acquisition of shape data The resin sheet (section 11 of the resin sheet for X-ray CT imaging), cut into strips 2 cm wide and 5 cm long, was placed in an X-ray CT scanner (TXS-32300FDHS, manufactured by Toshiba IT Control Systems Co., Ltd.), and X-ray CT measurements were performed. The measurement conditions are shown below. X-ray tube voltage [kV]: 75.000 X-ray tube voltage [mA]: 0.053 Data mode: CONE FC function: Laks Scan Mode: FULL Views: 2000 Slice distance: 0.004 Integral: 1 • Definition of measuring surface

[0078] In the above measurement, the shape data obtained for the X-ray CT imaging area 12 was analyzed using VGStudio Max 2.1, image processing software manufactured by Visual Science Volume Graphics Co., Ltd. A 4.0 mm × 4.0 mm area on the surface of the resin sheet with the largest surface area was sliced ​​every 4.0 μm in the thickness direction to obtain a measurement surface 13 that sliced ​​the X-ray CT imaging area. An overview of the method for defining the measurement surface up to this point is shown in Figure 4.

[0079] Each obtained cross-section was classified into bubble-derived openings and resin portions by binarization processing using contrast adjustment. The total area of ​​bubble-derived openings of 2 μm or larger (openings 14 of bubble-derived depressions on the measurement surface) was calculated and divided by the area of ​​the entire region to determine the percentage. In the binarization process, areas with a grayscale range of 129 or higher were considered to be the resin portion.

[0080] When the surface with the largest area ratio of the openings of the depressions caused by air bubbles was used as the measurement surface, the measurement surface was determined from the above data. Furthermore, when the outermost surface of the resin sheet was used as the measurement surface, the sheet was sliced ​​from the surface side, and the measurement surface was defined as the cut surface where no voids, each containing more than 10% of the sheet, were present, assuming the entire measurement surface was 100%.

[0081] • Measurement of the equivalent diameter of an area circle The 4.0 mm × 4.0 mm measurement surface data obtained from the above measurements was analyzed using ImageJ (Rasband, WS, US National Institutes of Health, Bethesda, Maryland, USA). By binarizing the data through contrast adjustment, the openings of depressions caused by air bubbles and the resin portion were classified, and the equivalent diameter of an equal-area circle was calculated for the openings of depressions caused by air bubbles larger than 2 μm on the 4.0 mm × 4.0 mm measurement surface. From the data on the openings of the depressions derived from the obtained air bubbles, the diameters corresponding to a cumulative frequency of 20%, 50%, and 80% were calculated.

[0082] <Method for calculating the ratio of the total area of ​​openings> • Acquisition of shape data Similar to the measurement of the diameter corresponding to a cumulative frequency of 20%, X-ray CT measurements were performed on the resin sheet to obtain measurement surface data of 4.0 mm × 4.0 mm. • Calculation of the ratio of the total area of ​​openings The 4.0 mm x 4.0 mm measurement surface data obtained from the above measurements was analyzed using VGStudio Max 2.1, image processing software manufactured by Visual Science Volume Graphics Co., Ltd. The total area of ​​the openings for depressions of 2 μm or larger originating from air bubbles on the 4.0 mm x 4.0 mm measurement surface was calculated, and the ratio was calculated by dividing this by the total area of ​​the entire region.

[0083] <Asker A hardness of the resin sheet at 25°C> If the thickness is 6 mm or more, the resin sheet is left at that thickness; if the thickness is 6 mm or less, the sheet is laminated to a thickness of 6 mm or more. After standing for 16 hours in a 25°C environment with a humidity of 50% ± 5%, the hardness was measured five times using a Type A durometer compliant with JIS K 6253 (Asker Type A, manufactured by Polymer Instruments Co., Ltd.), and the average value was taken as the Asker A hardness of the resin sheet.

[0084] <Method for measuring the average value (Dd) of the depth of depressions caused by air bubbles on the surface with the maximum air bubble area ratio or a nearby surface.> • Acquisition of shape data Shape data was obtained by performing X-ray CT measurements on the resin sheet, similar to the measurement of the diameter corresponding to a cumulative frequency of 20%. • Measurement of the average depth (Dd) of depressions caused by bubbles on the surface with the largest bubble area ratio or a nearby surface. The shape data obtained from the above measurements was analyzed using VGStudio Max 2.1, image processing software manufactured by Visual Science Volume Graphics Co., Ltd., and a 4.0 mm × 4.0 mm area viewed from the surface of the resin sheet was sliced ​​vertically at 4.0 μm intervals. Each obtained cross-section was classified into bubble-derived depressions and resin portions by binarization processing with contrast adjustment, and the depth from the opening to the lowest surface was calculated for bubble-derived depressions of 2 μm or more, and the average value (Dd) was obtained.

[0085] <Method for measuring resin viscosity> Viscosity was measured after 60 seconds using a HAAKE VP-500. The measurement equipment and conditions are as follows. Viscometer: Rotary viscometer Viscotester VT550 (HAAKE Corporation) Sensor system: NV cup / NV rotor Rotation speed: 8.3s -1 (500rpm) Circulating constant temperature bath: Open bath circulator DC5-K20 (manufactured by HAAKE) Set temperature: 70℃

[0086] <Methods for evaluating global flatness, local flatness, and sagging of polished workpieces> The surface of the fabricated polishing pad 1 was subjected to a so-called XY groove process (grid-like groove processing) with a width of 2.0 mm, a pitch of 15 mm, and a depth of 0.5 mm, and was mounted on the upper and lower platens of a double-sided polishing machine (manufactured by Fujikoshi Machinery Co., Ltd.).

[0087] The polishing time for each batch was set to 30 minutes. Twenty batches of polishing were performed on five 300mm diameter silicon single-crystal wafers (100) per batch. The flatness (global flatness, local flatness, and sagging) of the 20th batch was measured, and the average value was calculated for the five wafers. The polishing rate was also measured simultaneously. The slurry supplied was a colloidal silica-containing pH 10.5 alkaline solution (manufactured by Fujimi Incorporated) at a rate of 5 L / min. The polishing head and platen rotation speed was set to 30 rpm, and the polishing pressure was 70 g / cm². 2 That's what I decided.

[0088] Global flatness, local flatness, and sagging were evaluated using a flatness measuring device (Nanometoro300TT-A, manufactured by Kuroda Seiki Co., Ltd.) as GBIR (global backsurface-referenced ideal plane / range), SFQR (site front least squares range), and SFQR of the outer edge of the wafer (edge ​​SFQR in Table 2), respectively. Local flatness was measured at approximately 8.0 × 26.0 mm near the center of the wafer. 2 The SFQR was defined as the range within this area. Additionally, the dread was calculated by excluding the outermost 1 mm of the wafer and determining the SFQR for each section divided by radiation at 5° intervals starting from the center of the wafer, within the range from the outer edge to 35 mm inward. [Examples]

[0089] The present disclosure will be described in detail below with reference to examples, but these examples are not intended to limit the present disclosure in any way. In the following formulations, parts are by mass unless otherwise specified.

[0090] <Example 1> 237 parts by mass of 2,4-TDI (tolylene diisocyanate) was reacted with 412 parts by mass of PTMG (polytetramethylene ether glycol) with a number average molecular weight of approximately 1000 and 40 parts by mass of diethylene glycol. The mixture was degassed under heating and reduced pressure to obtain a prepolymer. This prepolymer had an isocyanate content of 9.1%.

[0091] An uncured resin solution was obtained by mixing 55.0 parts by mass of prepolymer, 45.0 parts by mass of diethyltoluenediamine (DETDA), 5.0 parts by mass of water, 0.006 parts by mass of Toyocat® ET (manufactured by Tosoh Corporation), and 2.0 parts by mass of silicone-based foam stabilizer SH-193.

[0092] 340 g of the uncured resin solution was poured onto a pre-formed silicone rubber release layer into a cylindrical mold with a diameter of 450 mm and a depth of 320 mm inside a centrifugal molding machine heated to 110°C and rotating at 1200 rpm. From the moment the pouring was completed, the machine was maintained at 1200 rpm for 30 minutes to heat-cur the solution. After that, the solution was demolded from the mold to obtain a resin sheet 1 with a thickness of 1.50 mm.

[0093] A polishing pad 1 was obtained by attaching a double-sided tape, which has adhesive layers (material: acrylic resin) on both sides of a PET substrate and release paper on one side, to the surface of the obtained resin sheet 1 on the side furthest from the cut surface at the depth where the air bubble area ratio is maximum, using the adhesive layer on the side opposite the release paper. The physical properties of the obtained polishing pad 1 are shown in Table 1.

[0094] [Table 1]

[0095] Table 2 shows the results of the evaluation of global flatness, local flatness, and sagging of the polished workpiece.

[0096] [Table 2]

[0097] <Examples 2-9> Polishing pads 2 to 9 were obtained in the same manner as in Example 1, except that the formulation, the rotation conditions of the cylindrical mold, and the rotation time were changed as shown in Table 3. The evaluation results for the polishing pads 2-9 are shown in Table 2.

[0098] [Table 3]

[0099] <Comparative Examples 1-6> Polishing pads 10 to 15 were obtained in the same manner as in Example 1, except that the formulation, the rotation conditions of the cylindrical mold, and the rotation time were changed as shown in Table 3. The evaluation results for the obtained polishing pads 10-15 are shown in Table 2.

[0100] Examples 1 to 9 showed good global flatness, local flatness, and sagging of the polished workpiece because the equivalent diameter of the equiarea circle of the bubble-derived depressions, their distribution, total area, and hardness all met the requirements of claim 1. Example 1 was particularly good.

[0101] In Comparative Examples 1 to 6, the equivalent diameter of the equiarea circle of the depressions originating from air bubbles, their distribution, total area, and hardness did not meet the requirements of Claim 1, and the polished workpiece showed low values ​​in either the global flatness, local flatness, or sagging.

[0102] This embodiment includes the following configurations and methods. (Composition 1) A polishing pad for polishing a workpiece with free abrasive particles, The polishing pad has a resin sheet having multiple air bubbles, When the cross-sectional area is determined by cutting the resin sheet perpendicular to its thickness direction based on the X-ray CT measurement results of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-sectional area to the area of ​​the cross-sectional area is defined as the bubble area ratio, The resin sheet has a surface among its cut surfaces where the air bubble area ratio is maximized. When the diameter corresponding to 20% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D80 [μm], The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following equations (1) and (2). 100[μm]≦D50≦200[μm] (1) |D80-D20| / D50≦1.2 ···(2) On the surface where the bubble area ratio is maximum, the bubble area ratio is 70% or more and 95% or less. The Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 40 or higher. A polishing pad characterized by the following features. (Configuration 2) The polishing pad according to configuration 1, wherein the surface with the maximum bubble area ratio is such that the average value (Dd) of the depths of the multiple bubble-derived recesses and D50 satisfy the following formula (3). 0.25 <Dd / D50<1 ···(3) (Composition 3) The polishing pad according to configuration 1 or 2, wherein the maximum diameter of the recesses originating from the bubbles on the surface where the bubble area ratio is maximum is 100 μm or more and 500 μm or less. (Method 1) A polishing method using a polishing pad for polishing a workpiece with free abrasive particles, The polishing pad is the polishing pad described in any one of items 1 to 3 of the configuration. A polishing method comprising the step of exposing the surface with the maximum bubble area ratio or a nearby surface to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet. (Method 2) The process includes introducing uncured resin into a coaxial centrifugal molding apparatus, forming an uncured resin layer on the inner surface of the coaxial centrifugal molding apparatus by centrifugal force, and then heating and curing the uncured resin layer to produce a resin sheet. The resin sheet has multiple air bubbles, When the cross-sectional area is determined by cutting the resin sheet perpendicular to its thickness direction based on the X-ray CT measurement results of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-sectional area to the area of ​​the cross-sectional area is defined as the bubble area ratio, The resin sheet has a surface among its cut surfaces where the air bubble area ratio is maximized. When the diameter corresponding to 20% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface with the maximum bubble area ratio is D80 [μm], The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following equations (1) and (2). 100[μm]≦D50≦200[μm] (1) |D80-D20| / D50≦1.2 ···(2) On the surface where the bubble area ratio is maximum, the bubble area ratio is 70% or more and 95% or less. A method for manufacturing an abrasive pad, wherein the Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 40 or higher. (Method 3) The aforementioned centrifugal force is 200 m / s². 2 More than 4000m / s 2 The following: The method for manufacturing an abrasive pad according to Method 2, wherein the viscosity of the uncured resin introduced is 1,000 mPa·s or more and 20,000 mPa·s or less. (Method 4) A method for manufacturing an abrasive pad according to method 2 or 3, comprising the step of exposing the surface with the maximum bubble area ratio or a nearby surface to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet. [Explanation of Symbols]

[0103] 1. Depression caused by air bubbles 2. Opening of a recess caused by an air bubble 3. The surface with the maximum bubble area ratio, or a surface near it. 4. Opening of recesses caused by air bubbles 5. Equi-area circles of openings in depressions caused by air bubbles. 6. Equivalent diameter of an equal-area circle at the opening of a recess caused by air bubbles. 7 Drive shaft 8. Cylindrical mold 9 Heat source 10 hatches 11 Sections of resin sheets for X-ray CT imaging 12 X-ray CT imaging area 13. Measurement surface obtained by slicing the X-ray CT imaging area. 14 Opening of recesses on the measurement surface caused by air bubbles

Claims

1. A polishing pad for polishing a workpiece with free abrasive particles, The polishing pad has a resin sheet having multiple air bubbles, When the X-ray CT measurement results of the resin sheet are used to determine the cross-section obtained by cutting the resin sheet perpendicular to the thickness direction of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-section to the area of ​​the cross-section is defined as the bubble area ratio, The resin sheet has a surface among its cut surfaces where the air bubble area ratio is maximized. When the diameter corresponding to 20% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface where the bubble area ratio is maximum is D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface where the bubble area ratio is maximum is D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface where the bubble area ratio is maximum is D80 [μm], The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following formulas (1) and (2). 100 [μm]≦D50≦200 [μm] (1) |D80-D20| / D50≦1.2...(2) On the surface where the bubble area ratio is maximum, the bubble area ratio is 70% or more and 95% or less. At 25°C, the Asker A hardness of the resin sheet is 40 or higher. A polishing pad characterized by the following features.

2. The polishing pad according to claim 1, wherein the surface with the maximum bubble area ratio satisfies the following formula (3) between the average value (Dd) of the depths of the depressions originating from the plurality of bubbles and D50. 0.25<Dd / D50<1...(3)

3. The polishing pad according to claim 1, wherein the maximum diameter of the recesses originating from the bubbles on the surface where the bubble area ratio is maximum is 100 μm or more and 500 μm or less.

4. A polishing method using a polishing pad for polishing a workpiece with free abrasive particles, The polishing pad is the polishing pad described in any one of claims 1 to 3, A polishing method comprising the step of exposing the surface with the maximum bubble area ratio or a nearby surface to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet.

5. The process includes introducing uncured resin into a coaxial centrifugal molding apparatus, forming an uncured resin layer on the inner surface of the coaxial centrifugal molding apparatus by centrifugal force, and then heating and curing the uncured resin layer to produce a resin sheet. The resin sheet has multiple air bubbles, When the X-ray CT measurement results of the resin sheet are used to determine the cross-section obtained by cutting the resin sheet perpendicular to the thickness direction of the resin sheet, and the ratio of the total area of ​​the openings of the multiple bubble-derived depressions on the cross-section to the area of ​​the cross-section is defined as the bubble area ratio, The resin sheet has a surface among its cut surfaces where the air bubble area ratio is maximized. When the diameter corresponding to 20% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface where the bubble area ratio is maximum is D20 [μm], the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface where the bubble area ratio is maximum is D50 [μm], and the diameter corresponding to 80% of the cumulative frequency of the equivalent diameters of the equiarea circles of the multiple bubbles on the surface where the bubble area ratio is maximum is D80 [μm], The surface with the maximum bubble area ratio is one in which D20, D50 and D80 satisfy the following formulas (1) and (2). 100 [μm]≦D50≦200 [μm] (1) |D80-D20| / D50≦1.2...(2) On the surface where the bubble area ratio is maximum, the bubble area ratio is 70% or more and 95% or less. A method for manufacturing an abrasive pad, wherein the resin sheet has an Asker A hardness of 40 or higher at 25°C.

6. The aforementioned centrifugal force is 200 m / s². ２ More than 4000m / s ２ The following: The method for manufacturing an abrasive pad according to claim 5, wherein the viscosity of the uncured resin introduced is 1,000 mPa·s or more and 20,000 mPa·s or less.

7. A method for manufacturing an abrasive pad according to claim 5, comprising the step of exposing the surface with the maximum bubble area ratio or a nearby surface to the surface of the resin sheet if that surface is not exposed to the surface of the resin sheet.

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