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

Abstract

To provide a polishing pad that achieves relatively high flatness and polishing rate while preventing fracture during polishing. [Solution] The minimum value of the bubble area ratio distribution curve is in the range where the depth is between 10% and 80%, and the surface where the bubble area ratio is maximum is such that D50 satisfies the following equation (1). 20[μm]≦D50≦200[μm] (1) This polishing pad is characterized in that the Asker A hardness of the resin sheet, measured at 25°C, is 60 or higher.

Description

Technical Field

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

Background Art

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

[0003] As one of the performances required for a polishing pad, in order to improve the flatness of the workpiece, it is necessary to impart cushioning properties to the polishing pad and enhance the adhesion to the workpiece. However, an improvement in cushioning properties may cause sagging at the edges of the workpiece. Therefore, a polishing pad in which a polishing layer with relatively high rigidity is laminated under the polishing layer, and further, a cushioning layer is laminated under that has been proposed in Patent Document 1 and the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, with the increasing demand for energy conservation, the hardness of materials to be polished, such as power semiconductors, has been increasing. As a result, conventional polishing pads have a low polishing rate, and there is a need for high-performance polishing pads. Furthermore, with the need to improve the production cycle time of polishing pads and the increasing demand for difficult-to-process materials such as compound semiconductors, there is a need for polishing pads that can withstand increased rotational speeds and polishing pressures for both the polishing pad and the material being polished.

[0006] However, when polishing with the polishing pad described in Patent Document 1, if the rotation speed of the polishing pad and the workpiece, and the polishing pressure between the polishing pad and the workpiece are set higher than conventional conditions in order to improve the polishing rate, the pad may experience strong shear stress, which can lead to fracture at the laminated interface. Therefore, the polishing rate and other conditions are limited, and there has been a need for a polishing pad that does not experience fracture at the laminated interface.

[0007] Therefore, the object of this disclosure is to provide a polishing pad that achieves relatively high flatness and polishing rate while not fracturing during polishing. Furthermore, the object of this disclosure is to provide a polishing method that achieves relatively high flatness and polishing rate while not fracturing the polishing pad. Furthermore, the object of this disclosure is to provide a method for manufacturing a polishing pad that achieves relatively high flatness and polishing rate while not fracturing during polishing. [Means for solving the problem]

[0008] This disclosure is, A polishing pad for polishing a workpiece with free abrasive particles, The polishing pad has a resin sheet having multiple air bubbles, The resin sheet is a one-piece molded product, Based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at 4 μm intervals, parallel to the surface of the workpiece being polished, and extending to the opposite surface of the workpiece being polished. The sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio. The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, Regarding the depth of the surface where the bubble area ratio is maximum, assume that the depth is 0%. Of the multiple cross-sections, if we consider the depth of the cross-section furthest from the surface with the maximum bubble area ratio to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, the surface where the bubble area ratio is maximum is such that D50 satisfies the following formula (1), 20[μm]≦D50≦200[μm] (1) This polishing pad is characterized in that the Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 60 or higher. 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 is a one-piece molded product, The resin sheet has multiple air bubbles, Based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at 4 μm intervals, parallel to the surface on which the workpiece is being polished, and extending to the opposite surface on the same side. When the sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio, The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, The depth of the surface where the bubble area ratio is maximum is defined as the percentage where the depth is 0. Of the multiple cross-sections, if we consider the depth of the cross-section furthest from the surface with the maximum bubble area ratio to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, D50 satisfies the following formula (1): 20[μm]≦D50≦200[μm] (1) A method for manufacturing an abrasive pad, characterized in that the Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 60 or higher. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a highly durable polishing pad and a polishing method for the polishing pad that achieves flatness and polishing rate equal to or better than conventional polishing pads, while preventing breakage even under conditions where the rotation speed of the polishing pad and the workpiece, and the polishing pressure between the polishing pad and the workpiece are higher than conventional conditions. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view of the polishing pad related to this disclosure. [Figure 2](a) Perspective view schematically depicting recesses and openings derived from bubbles on the surface where the gas bubble area ratio according to the present disclosure is maximum or on a surface in its vicinity, (b) Cross-sectional view schematically depicting recesses and openings derived from bubbles on the surface where the gas bubble area ratio according to the present disclosure is maximum or on a surface in its vicinity. [Figure 3] Figure for explaining the equivalent circle diameter of the opening of the recess derived from bubbles according to the present disclosure. [Figure 4] Schematic diagram showing a configuration example of a centrifugal forming machine used for centrifugal forming according to the present disclosure. [Figure 5] Figure showing an overview of the method for defining the measurement surface.

Mode for Carrying Out the Invention

[0011] In the present disclosure, the description of "XX or more and YY or less" or "XX to YY" representing a numerical range means a numerical range 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. According to the study by the present inventors, one of the causes of breakage occurring at the laminated interface in the polishing pad according to Patent Document 1 was presumed to be due to the structure of the polishing pad according to Patent Document 1 being a laminated molded product. That is, it is a laminated molded product composed of three layers, and the compressibility in each layer is different, and strong shear stress is applied at the interface between the layers. Therefore, when polishing is performed using such a polishing pad under high rotational speed and polishing pressure, the polishing pad may break.

[0013] The present inventors recognized that in polishing a workpiece with free abrasive grains under high rotational speed and high polishing pressure of the polishing pad and the workpiece, it is necessary to develop a technology for making an integrally molded product instead of a laminated molded product, which is considered to be the cause of breakage. Therefore, as a result of repeated studies to prevent the occurrence of breakage, it was found that the following polishing pad can well achieve the purpose.

[0014] The polishing pad of the present disclosure is A polishing pad for polishing a workpiece with free abrasive particles, The polishing pad has a resin sheet having multiple air bubbles, The resin sheet is a one-piece molded product, Based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at 4 μm intervals, parallel to the surface of the workpiece being polished, and extending to the opposite surface of the workpiece being polished. The sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio. The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, The depth of the surface where the bubble area ratio is maximum is defined as the percentage where the depth is 0. Of the multiple cross-sections, if we consider the depth of the cross-section furthest from the surface with the maximum bubble area ratio to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, the surface where the bubble area ratio is maximum is such that D50 satisfies the following formula (1), 20[μm]≦D50≦200[μm] (1) The resin sheet is characterized by having an Asker A hardness of 60 or higher, as measured at 25°C using an indenter with a tip diameter of 0.79 mm.

[0015] The above-mentioned polishing pad makes it possible to provide a highly durable polishing pad that exhibits a polishing rate higher than conventional pads while preventing breakage or other damage. The inventors speculate that this is the reason for the following:

[0016] The polishing pad of this disclosure is a polishing pad for polishing a workpiece with free abrasive grains, and the polishing pad has a resin sheet having multiple air bubbles, and the resin sheet is a single-piece molded product. In order to suppress breakage of the polishing pad, it is important that the polishing pad is a single-piece molded product and not a laminated molded product. Figure 1 shows a schematic cross-sectional view of the polishing pad 1 of this disclosure. The resin sheet of the polishing pad 1 contains air bubbles 2 as shown in Figure 1.

[0017] In other words, a one-piece molded product is a continuous component made from a single material and consisting of a single layer. When subjected to shear stress during polishing, if there is no interface within the polishing pad, stress concentration is less likely to occur, making it less prone to fracture.

[0018] In this disclosure, based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined from the surface on which the workpiece is to be polished to the opposite surface, using multiple planes at 4 μm intervals parallel to the plane when the workpiece is placed on a plane with the opposite side facing downwards, and the sum of the area of ​​the openings of the multiple depressions originating from bubbles per unit area in each of the multiple cross-sections is defined as the bubble area ratio. In this disclosure, the resin sheet has a surface among the multiple cross-sections that has the maximum bubble area ratio.

[0019] Figures 2(a) and 2(b) schematically show bubbles on the surface with the maximum bubble area ratio or a nearby surface. Although the figures show a single bubble-derived recess, in reality, there are multiple bubble-derived recesses. As shown in the figures, the bubble on the surface with the maximum bubble area ratio or a nearby surface 5 has both an opening 4 and a bubble-derived recess 3.

[0020] Thus, the bubble area ratio is defined as the ratio of the sum of the equal-area circles of the openings of depressions originating from multiple bubbles per unit area in each of the multiple cross-sections obtained at 4 μm depths, with the side of the workpiece opposite to the side being polished fixed to a flat surface plate, and multiple cross-sections parallel to the surface plate taken up to the opposite side of the surface of the workpiece being polished.

[0021] In this disclosure, the horizontal axis represents depth as the distance between multiple cross-sections starting from the surface with the maximum bubble area ratio, and the vertical axis represents the bubble area ratio of the multiple cross-sections. In the bubble area ratio distribution curve created, when the depth of the surface with the maximum bubble area ratio is set to 0%, and the depth of the cross-section furthest from the surface with the maximum bubble area ratio is set to 100%, the minimum value of the bubble area ratio distribution curve lies in a depth range of 10% to 80%, preferably in a depth range of 30% to 80%, and more preferably in a depth range of 30.3% to 79.4%.

[0022] Because the minimum value of the bubble area ratio distribution curve lies within a depth range of 10% to 80%, even though it is a single-piece molded product, the area around the minimum value becomes a pseudo-rigid layer, similar to a laminated molded product, allowing for the formation of pseudo-polished layers and pseudo-sponge layers above and below it. As a result, fracture can be suppressed while achieving high flatness and a high polishing rate.

[0023] Furthermore, in this disclosure, when D50 [μm] is defined as the diameter corresponding to 50% of the cumulative frequency of the equivalent diameters of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, the surface where the bubble area ratio is maximum satisfies the following formula (1). 20[μm]≦D50≦200[μm] (1) In this disclosure, D50 is preferably 60 μm or more and 160 μm or less, and more preferably 101 μm or more and 151 μm or less.

[0024] If D50 is within the above range, the polishing rate will be maintained over a long period of time. If D50 is less than 20 μm, the polishing pad will not be able to hold enough abrasive grains, and the polishing rate will decrease. On the other hand, if D50 exceeds 200 μm, the rigidity of the polishing pad cannot be maintained, and flatness decreases.

[0025] Here, Figure 3 shows a diagram illustrating the equivalent diameter of an equal-area circle opening of a bubble-derived recess in this disclosure. The equivalent diameter 8 of an equal-area circle opening of a bubble-derived recess can be determined by fitting an equal-area circle 7 of an opening of a bubble-derived recess to the opening 6 of the bubble-derived recess, as in known methods.

[0026] Furthermore, the polishing pad of this disclosure has an Asker A hardness of 60 or higher, preferably 90 or higher, of the resin sheet measured at 25°C using an indenter with a tip diameter of 0.79 mm. This allows for a high polishing rate while suppressing fracture. On the other hand, if the Asker A hardness is less than 60, the polishing pad or the workpiece may fracture under high rotational speed and high polishing pressure conditions.

[0027] Furthermore, in this disclosure, in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region with a depth of 0% to 20% (average bubble area ratio) is preferably 30% to 95%, more preferably 30% to 50%, and even more preferably 32.0% to 45.4%. By doing so, fracture can be suppressed while achieving a high polishing rate.

[0028] Furthermore, in this disclosure, in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region with a depth of 20% to 50% (average bubble area ratio) is preferably 0% to 10%, more preferably 3% to 10%, and even more preferably 3.4% to 9.5%. By doing so, high rigidity can be achieved and sagging at the edges can be effectively suppressed.

[0029] In this disclosure, in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region with a depth of 50% to 100% (average bubble area ratio) is preferably 15% to 50%, more preferably 15% to 35%, and even more preferably 16.3% to 33.3%. By doing so, the overall cushioning of the polishing pad can be maintained at a high level, resulting in improved flatness. By setting the polishing pad within the above range, it is possible to achieve a higher level of both flatness and polishing rate without causing the sheet to break, which is preferable.

[0030] [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 is a one-piece molded product, The resin sheet has multiple air bubbles, Based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at 4 μm intervals, parallel to the surface on which the workpiece is being polished, and extending to the opposite surface on the same side. When the sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio, The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, The depth of the surface where the bubble area ratio is maximum is defined as the percentage where the depth is 0. Of the multiple cross-sections, if we consider the depth of the cross-section furthest from the surface with the maximum bubble area ratio to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, D50 satisfies the following formula (1): 20[μm]≦D50≦200[μm] (1) The resin sheet is characterized by having an Asker A hardness of 60 or higher, as measured at 25°C using an indenter with a tip diameter of 0.79 mm. Regarding the items described in the first embodiment, explanations may be omitted to avoid repetition.

[0031] 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 minimum value of the bubble area ratio distribution curve can be made to exist in a depth range of 10% to 80%.

[0032] Furthermore, in the manufacturing method of the polishing pad of this disclosure, the centrifugal force applied by the coaxial centrifugal molding apparatus is 200 m / s 2 More than 4000m / s 2 Preferably, the following conditions are met, and it is preferable that the viscosity of the uncured resin introduced into the coaxial centrifugal molding apparatus is 1000 mPa·s or more and 20000 mPa·s or less. By doing so, a bubble distribution can be formed to create bubble-derived depressions on the surface of the resin sheet where the bubble area ratio is maximum or on the surface near thereto. In this disclosure, the surface near thereto refers to the surface in the depth direction ±200 μm of the surface where the bubble area ratio is maximum. Since the bubble distribution is continuous, it is considered that the surface near thereto also has bubble-derived depressions that are almost the same as those on the surface where the bubble area ratio is maximum, and thus exhibits almost the same effects.

[0033] The control of the bubble distribution as described above is achieved by comprehensively controlling the foaming caused by heating from the surface of the cylindrical mold of the coaxial centrifugal molding machine and the movement of bubbles due to centrifugal force, using prescriptive factors such as resin viscosity, foaming amount and timing, and control of the ratio of competitive reactions between curing and foaming, as well as operating conditions such as the centrifugal force intensity level and the duration for which centrifugal force is applied.

[0034] The materials of the resin sheets described herein 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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. Examples of alicyclic diols include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and bisphenol A with water.

[0039] Examples of polyfunctional polyols include glycerin, trimethylolpropane, tributylolpropane, pentaerythritol, and sorbitol. Examples of polyester polyols include polyethylene adipate glycol, polybutylene adipate glycol, polycaprolactone polyol, and polyhexamethylene adipate glycol.

[0040] 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.

[0041] Examples of polyether polyols include polytetramethylene ether glycol, polypropylene glycol, polyethylene glycol, and ethylene oxide-added polypropylene polyol.

[0042] 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).

[0043] 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.

[0044] 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).

[0045] 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).

[0046] Examples of aliphatic diisocyanates include ethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate (HDI).

[0047] Examples of alicyclic diisocyanates include 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, and methylenebis(4,1-cyclohexylene) diisocyanate.

[0048] The urethane prepolymer is a polymer formed by bonding a polyol and a polyisocyanate, and has isocyanate groups as terminal groups. 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.

[0049] 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.

[0050] 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. 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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. Examples of nitroso compounds include N,N'-dinitrosopentamethylenetetramine and N,N'-dinitroso-N,N'-dimethylterephthalamide.

[0055] 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).

[0056] Hollow microspheres can be either already expanded or unexpanded. Unexpanded microspheres are heat-expandable microspheres and can be expanded by heating. Examples of commercially available hollow microspheres include, but are not limited to, the Expancel series (product name of Akzo Nobel Corporation) and Matsumoto Microspheres (product name of Matsumoto Oil & Fat Co., Ltd.).

[0057] Alternatively, materials obtained by synthesis using conventional methods may be used. The material of the outer shell of the hollow microsphere 4A is not particularly limited, but examples include polyvinyl alcohol, polyvinylpyrrolidone, poly(meth)acrylic acid, polyacrylamide, polyethylene glycol, polyhydroxyether acrylate, maleic acid copolymer, polyethylene oxide, polyurethane, poly(meth)acrylonitrile, polyvinylidene chloride, polyvinyl chloride, and organosilicon resins, as well as copolymers obtained by combining two or more monomers that constitute these resins.

[0058] 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.

[0059] Figure 4 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 10 that rotates with a motor or the like, a cylindrical cup-shaped mold 11 that is attached to the tip of the drive shaft and rotatably supported, a heat source 12 such as a heater fixedly arranged on the outer circumference of the cylindrical mold 11, and a hatch 9 opening in a case that covers these components.

[0060] 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.

[0061] Furthermore, 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. Also, 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. 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.

[0062] 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. Here, the nearby surface refers to the surface in the depth direction ±200 μm of 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 effect.

[0063] [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. Some items described in the first and second embodiments may be omitted from this explanation to avoid repetition.

[0064] 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.

[0065] 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. Here, the nearby surface refers to the surface within a depth range of ±200 μm from the surface with the maximum bubble area ratio.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] [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 the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of an equiarea circle at the opening of a depression caused by air bubbles, method for measuring the air bubble area ratio, and method for plotting the air bubble area ratio distribution curve> The resin sheet (section 13 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

[0070] The shape data obtained for the X-ray CT imaging area 14 in the above measurement 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 15 that was a slice of the X-ray CT imaging area. An overview of the method for defining the measurement surface up to this point is shown in Figure 5.

[0071] Each obtained cross-section was classified into bubble-derived depressions and resin portions by binarization processing using contrast adjustment. For bubble-derived depressions of 2 μm or larger (openings 16 of bubble-derived depressions on the measurement surface), the equivalent diameter of an equal-area circle was calculated, and the diameter corresponding to a cumulative frequency of 50% was calculated.

[0072] Furthermore, each obtained cross-section was classified into bubble-derived recesses and resin portions by binarization processing using contrast adjustment. The total area of ​​the openings was calculated and divided by the area of ​​the entire region to calculate the bubble area ratio, which is the ratio of the area of ​​openings caused by bubble recesses. The surface with the highest bubble area ratio was designated as the measurement surface, and the measurement surface was determined from this data. Furthermore, a bubble area ratio distribution curve was plotted by plotting the depth of each of the multiple cross-sections, starting from the surface with the maximum bubble area ratio, on the horizontal axis, and the bubble area ratio of each cross-section on the vertical axis.

[0073] <Asker A hardness of resin sheets at 25°C> To eliminate the influence of the sheet stand on the measurement values, the resin sheets, laminated to a thickness of 6 mm or more, were left standing for 16 hours in a 25°C environment with a humidity of 50% ± 5%. Then, they were 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.

[0074] <Evaluation of the fragility of polishing pads, and evaluation method for local flatness, sagging, and polishing rate of the workpiece> First, if the surface of the resin sheet of the prepared polishing pad 1 did not have the surface with the maximum air bubble area ratio or a nearby surface exposed, the surface with the maximum air bubble area ratio or a nearby surface was exposed. Then, a so-called XY groove processing (lattice-like groove processing) with a width of 2.0 mm, a pitch of 15 mm, and a depth of 0.5 mm was applied to the surface of the prepared polishing pad 1, and it was mounted on the upper and lower platens of a double-sided polishing machine (manufactured by Nachi-Fujikoshi Machinery Industries Co., Ltd.).

[0075] Next, the rotation speed of the polishing head and surface plate is set to 30 rpm, and the polishing pressure is set to 70 g / cm². 2 Under these conditions, a #100 diamond plate was attached to the head, and the pads were initially dressed for 1 minute. No further dressing was performed throughout the evaluation.

[0076] Next, the rotation speed of the polishing head and surface plate was set to 30 rpm, and the polishing pressure was set to 210 g / cm². 2 Under these conditions, the polishing time per batch was set to 30 minutes, and 20 batches of polishing were performed on five 300mm diameter silicon single crystal wafers (100). The flatness (local flatness, sagging) of the 20th batch was measured, and the average value was calculated for the five wafers. The polishing rate was also measured at the same time. The slurry supplied was a colloidal silica-containing pH 10.5 alkaline solution (manufactured by Fujimi Incorporated) at a rate of 5 L / min.

[0077] Local flatness and sagging were evaluated using a flatness measuring device (Nanometoro300TT-A, manufactured by Kuroda Seiki Co., Ltd.) as SFQR (site front least squares range) and SFQR of the outer edge of the wafer, respectively. Local flatness was evaluated 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. In addition, 80 more batches were polished using the same process as described above, and the cross-sections of the pads were observed to check for any internal fractures or cracks. [Examples]

[0078] 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.

[0079] <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 heated and degassed under reduced pressure to obtain a prepolymer. This prepolymer had an isocyanate content of 9.1%.

[0080] 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.

[0081] 340 g of the uncured resin solution was heated to 110°C on a pre-formed silicone rubber release layer and poured into a cylindrical mold with a diameter of 450 mm and a depth of 320 mm inside a centrifugal molding machine 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 resin. After that, the mold was demolded to obtain a resin sheet 1 with a thickness of 1.50 mm.

[0082] On the side of the obtained resin sheet 1 opposite to the side with the maximum air bubble area ratio or a nearby side, a double-sided tape made of PET with adhesive layers (material: acrylic resin) on both sides and release paper on one side was attached using the adhesive layer opposite to the release paper. The sheet was then cut into a circular shape with a diameter of 300 mm to obtain a polishing pad 1. The formulation and manufacturing conditions of the obtained polishing pad 1 are shown in Table 1. The physical properties of the obtained polishing pad 1 are shown in Table 2.

[0083] [Table 1]

[0084] [Table 2]

[0085] Table 3 shows the results of the evaluation of the ease with which the polishing pad breaks, as well as the evaluation of the local flatness, sagging, and polishing rate of the workpiece.

[0086] [Table 3]

[0087] <Examples 2-7> Polishing pads 2 to 7 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 1. The physical properties of the obtained polishing pads 2 to 7 are shown in Table 2. The evaluation results for the polishing pads 2-7 are shown in Table 3.

[0088] <Comparative Examples 1-4> Polishing pads 8 to 11 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 physical properties of the obtained polishing pads 8 to 11 are shown in Table 2. The evaluation results for the polishing pads 8-11 obtained are shown in Table 3.

[0089] <Comparative Example 5> A T-die with a lip width of 700 mm and a lip gap of 1.5 mm was attached to the tip of a feed block type extruder, which consisted of three extruders with a barrel diameter of 50 mm and an L / D ratio of 32. Thermoplastic polyurethane (product name: Rezamin P4070EX) manufactured by Dainichi Seika Co., Ltd. was hot-air dried at 100°C for 4 hours and then fed into the hopper of each extruder.

[0090] First, the extruder for the first layer (hereinafter referred to as the first extruder), the extruder for the second layer (hereinafter referred to as the second extruder), the extruder for the third layer (hereinafter referred to as the third extruder), and the die are all set to a temperature of 180°C, and the sheet is extruded at a discharge speed of 27.3 kg / hr.

[0091] When a steady state was reached, the internal pressures of the first, second, and third extruders were 11.2 MPa, 11.5 MPa, 11.3 MPa, and 11.3 MPa, respectively. Carbon dioxide, pressurized to 25 MPa by a pump, was injected from approximately the center of each extruder. Simultaneously, the temperature of the first extruder was changed to 155°C, the second extruder to 160°C, the third extruder to 165°C, and the die temperatures were changed to 155°C for the first layer, 160°C for the second layer, and 165°C for the third layer. In the steady state after carbon dioxide injection, the internal pressures of the first extruder were 17.8 MPa, the second extruder to 12.8 MPa, and the third extruder to 9.7 MPa.

[0092] After the temperature and internal pressure of the extruder and die stabilized and the discharge state stabilized, the sheet exiting the die was passed through a cooling roll controlled to 10°C, and then taken up by a take-up machine to obtain a resin sheet 13.

[0093] On the side of the obtained resin sheet 13 opposite to the side with the maximum air bubble area ratio or a nearby side, a double-sided tape made of PET with adhesive layers (material: acrylic resin) on both sides and release paper on one side was attached using the adhesive layer opposite to the release paper. The sheet was then cut into a circular shape with a diameter of 300 mm to obtain a polishing pad 12. The physical properties of the obtained polishing pad 12 are shown in Table 2. The evaluation results of the obtained polishing pad 12 are shown in Table 3.

[0094] Examples 1 to 7 and Comparative Examples 1 to 4 were integrally molded products and satisfied Claim 1, so pad breakage was suppressed. Comparative Example 5 did not satisfy Claim 1, which is an integrally molded product, so pad breakage was observed. In addition, Examples 1 to 7 satisfied Claim 1 in terms of bubble diameter, hardness, and the depth of the minimum value of the bubble area ratio distribution curve, and the local flatness, sagging, and polishing rate of the polished workpiece were also good. Example 1 was particularly good. Comparative Examples 1 to 4 did not satisfy Claim 1 in terms of bubble diameter, hardness, and the depth of the minimum value of the bubble area ratio distribution curve, and the local flatness and sagging of the polished workpiece were not good.

[0095] 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, The resin sheet is a one-piece molded product, Based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at 4 μm intervals, parallel to the surface of the workpiece being polished, and extending to the opposite surface of the workpiece being polished. The sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio. The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, The depth of the surface where the bubble area ratio is maximum is defined as the percentage where the depth is 0. Of the multiple cross-sections, if we consider the depth of the cross-section furthest from the surface with the maximum bubble area ratio to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, the surface where the bubble area ratio is maximum is such that D50 satisfies the following formula (1), 20[μm]≦D50≦200[μm] (1) An abrasive pad characterized in that the Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 60 or higher. (Configuration 2) The polishing pad according to configuration 1, wherein in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region where the depth is 0% or more and 20% or less is 30% or more and 95% or less. (Composition 3) The polishing pad according to configuration 1 or 2, wherein, in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region where the depth is 20% or more and 50% or less is 0% or more and 10% or less. (Composition 4) The polishing pad according to any one of configurations 1 to 3, wherein, in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region where the depth is 50% or more and 100% or less is 15% or more and 50% 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 4 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 is a one-piece molded product, The resin sheet has multiple air bubbles, Based on the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at 4 μm intervals, parallel to the surface on which the workpiece is being polished, and extending to the opposite surface on the same side. When the sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio, The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, The depth of the surface where the bubble area ratio is maximum is defined as the percentage where the depth is 0. Of the multiple cross-sections, if we consider the depth of the cross-section furthest from the surface with the maximum bubble area ratio to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, D50 satisfies the following formula (1): 20[μm]≦D50≦200[μm] (1) A method for manufacturing an abrasive pad, characterized in that the Asker A hardness of the resin sheet, measured at 25°C using an indenter with a tip diameter of 0.79 mm, is 60 or higher. (Method 3) The aforementioned centrifugal force is 200 m / s 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]

[0096] 1. Polishing pad 2 bubbles 3. Depressions caused by air bubbles 4. Opening of recesses caused by air bubbles 5. The surface with the maximum bubble area ratio, or a surface near it. 6. Opening of a recess caused by an air bubble 7. Equi-area circles of openings in depressions caused by air bubbles. 8. Equivalent diameter of an equal-area circle at the opening of a recess caused by an air bubble. 9 hatches 10 Drive shaft 11 Cylindrical mold 12 Heat source 13 Sections of resin sheets for X-ray CT imaging 14 X-ray CT imaging area 15 Measurement surface obtained by slicing the X-ray CT imaging area 16 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, The resin sheet is a one-piece molded product, From the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at depths of 4 μm each, parallel to the surface on which the workpiece is being polished, and extending to the opposite surface on the same side. When the sum of the area of ​​the openings of the multiple depressions originating from the bubbles per unit area in each of these multiple cross-sections is defined as the bubble area ratio, The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, Regarding the depth of the surface where the bubble area ratio is maximum, assume that the depth is 0%. Of the multiple cross-sections, if the depth of the cross-section furthest from the surface with the maximum bubble area ratio is considered to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, the surface where the bubble area ratio is maximum is such that D50 satisfies the following formula (1), 20 [μm]≦D50≦200 [μm] (1) A polishing pad characterized in that the resin sheet has an Asker A hardness of 60 or higher at 25°C.

2. The polishing pad according to claim 1, wherein in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region where the depth is 0% or more and 20% or less is 30% or more and 95% or less.

3. The polishing pad according to claim 1, wherein in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region where the depth is 20% or more and 50% or less is 0% or more and 10% or less.

4. The polishing pad according to claim 1, wherein in the bubble area ratio distribution curve, the average value of the bubble area ratio in the region where the depth is 50% or more and 100% or less is 15% or more and 50% or less.

5. 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 4. 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.

6. 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 is a one-piece molded product, The resin sheet has multiple air bubbles, From the X-ray CT measurement results of the resin sheet, multiple cross-sections are determined at depths of 4 μm, parallel to the surface on which the workpiece is being polished, and extending to the opposite surface on the same side. When the sum of the area of ​​the openings of the multiple bubble-derived recesses per unit area in each of these multiple cross-sections is defined as the bubble area ratio, The resin sheet has a surface among the multiple cross-sections that has the largest air bubble area ratio, In a bubble area ratio distribution curve created with the horizontal axis representing the depth, which is the distance between the multiple cross-sections starting from the surface where the bubble area ratio is maximum, and the vertical axis representing the bubble area ratio of the multiple cross-sections, The depth of the surface where the bubble area ratio is maximum is defined as the percentage where the depth is 0. Of the multiple cross-sections, if the depth of the cross-section furthest from the surface with the maximum bubble area ratio is considered to be 100%, The minimum value of the bubble area ratio distribution curve is located in the range where the depth is between 10% and 80%. When D50 [μm] is the diameter corresponding to 50% of the cumulative frequency of the equivalent diameter of the equiarea circles of the plurality of bubbles on the surface where the bubble area ratio is maximum, D50 satisfies the following formula (1): 20 [μm]≦D50≦200 [μm] (1) A method for manufacturing an abrasive pad, characterized in that the Asker A hardness of the resin sheet at 25°C is 60 or higher.

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

8. A method for manufacturing an abrasive pad according to claim 6, 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 the surface with the maximum bubble area ratio or a nearby surface is not exposed to the surface of the resin sheet.

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