Grinding method for grinding pad and workpiece

Abstract

The abrasive pad of the present invention has an abrasive layer comprising a composition containing a hydrolyzable resin and abrasive grains with a median particle size of less than 2 µm.

Description

A Grinding Pad and a Grinding Method for a Workpiece to be Ground The present invention relates to a grinding pad and a grinding method for a workpiece to be ground. In the processing of a substrate used in a semiconductor device or the like, after a cylindrical single crystal (ingot) is cut into a disk shape to form a wafer shape, rough grinding (lapping, primary grinding) is performed to adjust the parallelism of both sides of the wafer while adjusting it to a specified thickness. The roughly ground wafer is further subjected to chemical etching and precision mechanical grinding (secondary grinding, mechanical polishing) for forming a mirror surface with high flatness. Finally, fine grinding (chemical mechanical polishing, CMP) that also adds a chemical action is performed to obtain atomic-level planarization. In such precision mechanical grinding in the semiconductor substrate processing, a grinding method using a fixed abrasive grinding pad is known. The fixed abrasive grinding pad has a grinding layer containing a binder resin and abrasive grains fixed by it. As the above-mentioned binder resin, curable resins such as phenolic resin, epoxy resin, and acrylic phenolic resin are usually used (for example, refer to Patent Document 1). [Prior Art Documents] [Patent Documents] Patent Document 1: Japanese Patent Laid-Open No. 2018-51733 Problems to be Solved by the Invention In addition, in general precision mechanical grinding, a hard metal platen is used, and grinding is performed while supplying a slurry containing abrasive grains. Therefore, it is easy to generate minute cracks or scratches on the surface layer of the substrate, and it is easy to form a damaged layer. In particular, substrates such as silicon carbide (SiC) and gallium nitride (GaN) used in next-generation power semiconductor devices are different from silicon (Si) substrates. They not only have high hardness but also are chemically stable. Therefore, if a damaged layer is formed due to precision mechanical grinding, it is not easy to remove the damaged layer by chemical methods such as chemical etching, and long-time fine grinding is required, resulting in an increase in the processing cost of the wafer. In contrast, the above-mentioned grinding pad using a binder resin is softer than a grinding pad using metal or ceramic, and has a low elastic modulus. Therefore, it is expected that precision mechanical grinding can be performed on a highly brittle substrate such as an SiC substrate with less damage. In addition, in order to reduce the damage generated by precision mechanical grinding, it is ideal to use as small abrasive grains as possible. Precision mechanical grinding usually uses fine abrasive grains with a median particle size of 3 µm or less. However, according to the research of the present inventors, when fixing fine abrasive grains using the above-mentioned binder resin, there is a problem that the grinding speed significantly decreases. Therefore, for a fixed abrasive grinding pad using fine abrasive grains, it is desired to reduce the decrease in the grinding speed while reducing the damaged layer. Preferably, even without dressing (filing), the decrease in the grinding speed is small, and the damaged layer can be removed. The present invention has been completed in view of the above circumstances, and an object thereof is to provide a polishing pad that reduces a decrease in polishing speed while reducing a damaged layer, and a polishing method for a workpiece to be polished using the same. Technical means for solving the problem [1] A polishing pad comprising a polishing layer containing a hydrolyzable resin and abrasive grains having a median particle diameter (D50) of less than 2 µm. [2] The polishing pad according to [1], wherein the hydrolyzable resin is mainly composed of a glycolic acid polymer. [3] The polishing pad according to [1] or [2], wherein the content of the abrasive grains is 55% by mass or less relative to the total mass of the polishing layer. [4] A polishing method for a workpiece to be polished, comprising the following steps: while supplying a polishing liquid containing water to the surface of the polishing layer of the polishing pad according to any one of [1] to [3], relatively sliding the polishing pad and the workpiece to be polished to polish the workpiece to be polished. [5] The polishing method for a workpiece to be polished according to [4], wherein the workpiece to be polished contains silicon carbide or gallium nitride. [6] The polishing method for a workpiece to be polished according to [4] or [5], wherein the polishing liquid is an alkaline aqueous solution. Effects of the invention According to the present invention, it is possible to provide a polishing pad that reduces a decrease in polishing speed while reducing a damaged layer, and a polishing method for a workpiece to be polished using the same. When fixing fine abrasive grains with a conventional adhesive resin, the reason for a significant decrease in the polishing speed is considered as follows. Since the protrusion height of the fine abrasive grains is small, the chip pocket (the gap between the workpiece to be polished and the adhesive resin. It has the function of discharging chips) is also small. Therefore, even if a small amount of chips are generated, they are easily clogged. In addition, since the above-mentioned adhesive resin does not have hydrolyzability, there is no dressing effect, and it is also difficult to generate replacement of abrasive grains. Therefore, it is considered that the polishing speed will significantly decrease. The inventors of the present invention studied various adhesive resins used for fixing abrasive grains in the polishing pad, and found that resins having hydrolyzability such as glycolic acid polymers showed a dressing effect. Therefore, even when using fine abrasive grains, clogging is not likely to occur. Therefore, it was found that even when using fine abrasive grains that were difficult to use with conventional resins, it was possible to reduce the decrease in the polishing speed without performing a dressing treatment. Moreover, the inventors of the present invention also studied the size of the abrasive grains, and found that by making the median particle diameter less than 2 µm, the damaged layer can be significantly reduced, and thus the present invention was conceived. That is, a polishing pad according to an embodiment of the present invention includes a polishing layer containing a hydrolyzable resin and abrasive grains having a median particle diameter of less than 2 µm. Hereinafter, the configuration of the polishing pad will be described in detail. 1. Polishing pad FIG. 1A is a schematic top view of a polishing pad 100 according to an embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view taken along line 1B-1B of the polishing pad 100 of FIG. 1A. The polishing pad 100 of the present embodiment includes a polishing layer 110 (refer to FIG. 1B). 1-1. Polishing layer In the present embodiment, the polishing layer 110 includes a base material 111 containing a hydrolyzable resin and a composition of abrasive grains 112 fixed by the base material 111 (refer to FIG. 1B). 1-1-1. Hydrolyzable resin The hydrolyzable resin is not particularly limited as long as it is a resin showing hydrolyzability. The hydrolyzable resin may be a biodegradable resin or may not be a biodegradable resin. Examples of the hydrolyzable resin include polyesters having an ester bond in the main chain, polycarbonates having a carbonate bond in the main chain, etc. Examples of the hydrolyzable resin include lactic acid polymers, glycolic acid polymers, hydroxybutyric acid polymers, hydroxypentanoic acid polymers, caprolactone polymers, ethylene succinate polymers, butylene succinate polymers (for example, including polybutylene succinate, polybutylene adipate succinate, polybutylene terephthalate succinate, polyethylene succinate, polybutylene carbonate succinate, etc.), dioxanone polymers, trimethylene carbonate polymers, etc. Among them, lactic acid polymers and glycolic acid polymers are preferred, and glycolic acid polymers are preferred from the viewpoint of having higher strength and hydrolysis rate and being easier to adjust the protrusion height of the abrasive grains in the polishing layer. That is, the hydrolyzable resin preferably contains a glycolic acid polymer as a main component. The term "containing a glycolic acid polymer as a main component" means that the content rate of the glycolic acid polymer is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total amount of the hydrolyzable resin. The glycolic acid polymer is a polymer containing a structural unit derived from glycolic acid (-(-O-CH 2 -CO-)-), and is a polymer having a structural unit derived from glycolic acid as a main component. The glycolic acid polymer may be a homopolymer of glycolic acid or a copolymer of glycolic acid and a monomer copolymerizable with it. Examples of copolymerizable monomers include: glycols such as ethylene glycol, propylene glycol, butylene glycol, heptylene glycol, hexylene glycol, octylene glycol, nonylene glycol, decylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; dicarboxylic acids such as oxalic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, anthracenedicarboxylic acid, 4,4'-diphenylether dicarboxylic acid, sodium 5-sulfoisophthalate, and isophthalic acid-5-tetrabutylphosphonium; hydroxycarboxylic acids such as lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxypentanoic acid, hydroxyhexanoic acid, and hydroxybenzoic acid; lactide of lactic acid; lactones such as epsilon-caprolactone, valerolactone, propiolactone, undecanolide, and 1,5-oxepan-2-one; and carbonates such as trimethylene carbonate. The fact that the structural unit derived from glycolic acid is the main component means that the content of the structural unit derived from glycolic acid is 50% by mass or more relative to the total amount of the structural units constituting the glycolic acid polymer. The content of the structural unit derived from glycolic acid is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. If the above content of the structural unit constituting the glycolic acid polymer is 50% by mass or more, the strength of the glycolic acid polymer can be further maintained, and thus more sufficient strength can be obtained when used for a polishing pad. In addition, if the above content of the structural unit constituting the glycolic acid polymer is 70% by mass or more, hydrolysis is more likely to occur, and thus the decrease in the polishing rate can be further reduced. Among them, from the viewpoint of higher strength and easier hydrolysis, the glycolic acid polymer is preferably a homopolymer of glycolic acid. The weight average molecular weight of the glycolic acid polymer is not particularly limited, and is preferably 70,000 or more and 500,000 or less. If the weight average molecular weight of the glycolic acid polymer is 70,000 or more, the strength of the glycolic acid polymer can be further improved, and thus the retention and durability of abrasive grains can be further improved. Moreover, more sufficient strength can be obtained for operations such as removing the polishing pad from the mold during molding and attaching the polishing pad to the platen of the polishing apparatus. In addition, when the object to be polished is brought into contact with the polishing pad and a load is applied, it is difficult for the abrasive grains protruding on the surface to be pressed back into the base material. Thereby, even when using fine abrasive grains, the decrease in the polishing rate can be further suppressed. If the weight average molecular weight of the glycolic acid polymer is 500,000 or less, not only the moldability can be further maintained, but also the time until disintegration by hydrolysis can be further shortened. From the same viewpoint, the weight average molecular weight of the glycolic acid polymer is more preferably 110,000 or more and 400,000 or less. The weight-average molecular weight of the glycolic acid polymer can be measured by gel permeation chromatography (GPC). The measurement conditions can be set as follows. (Measurement conditions) Device: "Shodex-104" manufactured by Showa Denko K.K. Column: Two HFIP-606M columns and one HFIP-G column as a pre-column are connected in series. Column temperature: 40 °C Eluent: HFIP solution dissolved with 5 mM sodium trifluoroacetate Flow rate: 0.6 mL / min Detector: RI (differential refractive index) detector Molecular weight calibration: Five standard polymethyl methacrylates with different molecular weights The content rate of the hydrolyzable resin is preferably 20% by mass or more and 99% by mass or less, more preferably 30% by mass or more and 95% by mass or less, still more preferably 50% by mass or more and 90% by mass or less, and particularly preferably 70% by mass or more and 90% by mass or less, relative to the polishing layer (or the total amount of the above composition). If the content rate of the hydrolyzable resin is 20% by mass or more, the strength of the polishing layer containing abrasive grains is higher, so it is preferred. If the content rate of the hydrolyzable resin is 99% by mass or less, the ratio of abrasive grains is not too small and the polishing rate is not too small, so it is preferred. If the hydrolyzable resin is at the above content rate, while suppressing the excessive disintegration of the polishing layer, it is easy to obtain a more stable polishing rate by the dressing effect. 1-1-2. Abrasive grains In this embodiment, abrasive grains with a median particle diameter of less than 2 µm are used as described above. If the median particle diameter of the abrasive grains is less than 2 µm, even for a brittle workpiece such as an SiC substrate, it is easy to process in a ductile manner, thereby effectively reducing the damaged layer. The lower limit of the median particle diameter of the abrasive grains is not particularly limited, and from the viewpoint of adjusting the protrusion height of the abrasive grains suitable for polishing and further increasing the polishing rate, it is preferably 0.01 µm or more. From the same viewpoint, the median particle diameter of the abrasive grains is preferably 0.01 µm or more and less than 2 µm, more preferably 0.05 µm or more and 1 µm or less, still more preferably 0.1 µm or more and 0.5 µm or less, and particularly preferably 0.2 µm or more and 0.3 µm or less. The median particle diameter of the abrasive grains can be obtained from the particle size distribution measured by the particle size analysis - laser diffraction scattering method (ISO 13320:2020). Specifically, a laser diffraction particle size analyzer (for example, Mastersizer3000 manufactured by Malvern) can be used, and the measurement is carried out under the conditions that the measurement temperature is 21 °C, the dispersion medium is ion-exchanged water, the refractive index of the dispersion medium is 1.330, and the light scattering model is the Mie theory. The material of the abrasive grains is not particularly limited. For example, diamond, silicon carbide, boron carbide, boron nitride, silicon nitride, cerium oxide, aluminum oxide, zirconium oxide, silicon oxide, iron oxide, manganese oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, titanium oxide, chromium oxide, barium carbonate, calcium carbonate, etc. may be cited. Among them, from the viewpoint of further improving the polishing rate, diamond, boron carbide, and boron nitride are preferred, and from the viewpoint of easily processing substrates with high hardness such as SiC substrates, diamond is more preferred. The shape of the abrasive grains is not particularly limited and may be spherical, polyhedral, or irregular. In addition, a surface treatment for imparting crushability may be performed on the abrasive grains, or a coating for improving the holding force of the hydrolyzable resin may be performed on the abrasive grains. The content rate of the abrasive grains is not particularly limited. Relative to the polishing layer (or the total amount of the above composition), it is preferably 1.0% by mass or more and 80% by mass or less. When the above content rate of the abrasive grains is 80% by mass or less, when the object to be polished is brought into contact with the polishing pad and a load is applied, the load will not be overly dispersed, an appropriate load is applied to each abrasive grain, and the abrasive grains can easily cut into the object to be polished. Thereby, even when using fine abrasive grains, the polishing rate can be further improved. Moreover, the moldability or workability of the polishing pad can be further improved. From the same viewpoint, the content rate of the abrasive grains relative to the polishing layer (or the total amount of the above composition) is more preferably 5.0% by mass or more and 70% by mass or less, further preferably 10% by mass or more and 50% by mass or less, and particularly preferably 10% by mass or more and 30% by mass or less. The content rate of the abrasive grains can be measured by a thermogravimetric analysis (TGA) device. Specifically, on the surface of the polishing layer of the unused polishing pad, when an arbitrary straight line passing through the center O of the polishing layer is set as straight line L and a straight line perpendicular to straight line L and passing through the center O of the polishing layer is set as straight line M, the center O of the polishing layer is set. When the midpoints of the center O of the polishing layer and the end of the polishing layer on straight line L are set as a1 and a2, and the midpoints of the center O of the polishing layer and the end of the polishing layer on straight line M are set as b1 and b2, measurement samples of 100 mg or more are taken from the polishing layer within the range of each measurement point including O, a1, a2, b1, and b2, appropriately crushed, and set as measurement samples from each measurement point. 20 mg ± 2 of the measurement sample is placed in a platinum flat pan, heated from room temperature to 800 °C at a rate of 10 °C / min in an air environment, and held at 800 °C for 30 minutes to burn off components other than the abrasive grains. The weight of the remaining sample is divided by the mass of the measurement sample to obtain the content rate of the abrasive grains in the polishing layer at each measurement point. In this case, the arithmetic average of the abrasive grain content rates of the above five points is set as the representative value of the abrasive grain content rate of the polishing layer. 1-1-3. Other components The base material containing a hydrolyzable resin may consist only of the hydrolyzable resin or may further contain other components other than the hydrolyzable resin. Examples of other components include other resins other than the hydrolyzable resin and hydrolysis accelerators. Among them, from the viewpoint of further increasing the polishing rate, it is preferable that the polishing layer further contains a hydrolysis accelerator. The hydrolysis accelerator may be used alone or two or more kinds may be used simultaneously. The hydrolysis accelerator is a compound that promotes the hydrolysis reaction of the hydrolyzable resin. For example, it is preferably a compound that promotes the penetration of the solution into the hydrolyzable resin by dissolving into the polishing liquid, and more preferably a compound that generates an acid or a base in the presence of water. Examples of such decomposition accelerators include carboxylic anhydrides, phosphorus compounds, cyclic esters, and basic metal oxides. Examples of carboxylic anhydrides include hexanoic anhydride, octanoic anhydride, decanoic anhydride, lauric anhydride, myristic anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, tetrahydrophthalic anhydride, butanetetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, diphenyl sulfone tetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, ethylene glycol bis(dehydrated trimellitate), and glycerol bis(dehydrated trimellitate) monoacetate. Among them, phthalic anhydride, trimellitic anhydride, benzoic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and benzene-1,2,4,5-tetracarboxylic dianhydride (pyromellitic dianhydride) are preferable. As the phosphorus compound, organic phosphorus compounds such as phosphoric acid esters and phosphorous acid esters are preferable, and more preferably an organic phosphorus compound having at least one selected from the group consisting of a long-chain alkyl group having 8 to 24 carbon atoms, an aromatic ring, and a neopentyl glycol skeleton. Examples of phosphoric acid esters having a long-chain alkyl group having 8 to 24 carbon atoms include mono- or di-stearyl acidic phosphoric acid esters or mixtures thereof and di-2-ethylhexyl acidic phosphoric acid ester. Examples of phosphorous acid esters having an aromatic ring include tris(nonylphenyl) phosphite. Examples of phosphorous acid esters having a neopentyl glycol skeleton include cyclic neopentanetetrayl bis(2,6-di-tert-butyl-4-methylphenyl) phosphite, cyclic neopentanetetrayl bis(2,4-di-tert-butylphenyl) phosphite, and cyclic neopentanetetrayl bis(octadecyl) phosphite. Examples of cyclic esters include glycolide, lactide, ε-caprolactone, γ-valerolactone, δ-valerolactone, diglycolic anhydride, and glutaric anhydride. Examples of basic metal oxides include magnesium oxide, zinc oxide, calcium oxide, sodium oxide, and copper oxide. Among them, from the viewpoint of relatively stable existence during molding and further promoting the hydrolysis of hydrolyzable resins such as glycolic acid polymers in the polishing layer through which water penetrates, cyclic esters are preferable, and glycolide is more preferable. The content rate of the hydrolysis accelerator is preferably 0.5% by mass or more and 50% by mass or less with respect to the total amount of the hydrolyzable resin. If the above content rate of the hydrolysis accelerator is 0.5% by mass or more, the hydrolysis of the hydrolyzable resin can be further promoted, and the decrease in the polishing rate can be further reduced. If the above content rate of the hydrolysis accelerator is 50% by mass or less, not only the exudation of the hydrolysis accelerator is less likely to occur, but also the excessive chipping caused by the excessive progress of hydrolysis can be further suppressed. From the same point of view, the above content rate of the hydrolysis accelerator is more preferably 1% by mass or more and 30% by mass or less, and further preferably 10% by mass or more and 20% by mass or less. 1-1-4. Physical properties As described above, from the viewpoint of further making it difficult for the polishing rate to decrease even when using fine abrasive grains, the hydrolysis rate and strength of the base material containing the hydrolyzable resin are preferably moderately high. (Rate of thickness reduction) The hydrolysis rate of the base material can be represented by, for example, the rate of thickness reduction. The rate of thickness reduction when the molded body of the above base material is immersed in water at 60°C is preferably 12 µm / h or more. The polishing layer containing the base material having such a rate of thickness reduction is easily hydrolyzed by supplying the polishing liquid, and thus it is easier to obtain a dressing effect. The upper limit of the rate of thickness reduction is not particularly limited, and from the viewpoint of extending the life of the polishing pad, it is preferably 2 mm / h or less, more preferably 1 mm / h or less, further preferably 500 µm / h or less, and particularly preferably 100 µm / h or less. The rate of thickness reduction can be measured in the following order. 1) A prism of 10 mm × 10 mm × 120 mm is obtained by injection molding the above composition without abrasive grains, and a test piece (molded body) in the form of a cube with one side of 10 mm is obtained from the prism. The molded body of the above composition without abrasive grains can also be obtained by heating and melting the molded body of the composition containing abrasive grains, i.e., the polishing layer. The polishing layer can be heated and melted, and the obtained melt can be passed through a filter to be separated into abrasive grains and a composition containing a hydrolyzable resin other than these, i.e., a composition without abrasive grains, and a molded body can be produced by molding the aforementioned composition without abrasive grains and used as a test piece. 2) Then, the aforementioned test piece is placed in a 1 L autoclave, and the autoclave is filled with water (deionized water) at 60°C. The aforementioned test piece is completely immersed under normal pressure, and the above operation is repeated to produce immersed test pieces with different immersion times. Each immersed test piece is cut to expose the cross section. After drying, the thickness of the core part (harder part) of the test piece is measured. The reduced thickness is measured based on the difference from the thickness before immersion (10 mm). 3) Based on the measured values of the reduced thickness of the test pieces measured at different immersion times, the time change of the reduced thickness of the test pieces is obtained. Then, based on the time change of the reduced thickness of the test pieces within the linear range of the time change of the reduced thickness of the test pieces, the rate of thickness reduction (unit: mm / h) of the test piece with a thickness of 10 mm is calculated. The reduction rate of the thickness of the above-mentioned base material can be adjusted, for example, by the type and content of the hydrolyzable resin, and the type and content of the hydrolysis accelerator. For example, when the hydrolyzable resin contains a glycolic acid polymer, the reduction rate of the thickness tends to be large. In addition, when the content of the hydrolysis accelerator is high, the reduction rate of the thickness tends to be large. (Tensile strength) The tensile strength of the above-mentioned base material at 25°C is preferably 55 MPa or more. If the tensile strength is 55 MPa or more, the holding force of the abrasive grains can be further improved. From the same point of view, the tensile strength of the above-mentioned base material is more preferably 60 MPa or more. The upper limit of the tensile strength of the above-mentioned base material is not particularly limited, and can be set to 1000 MPa or less, for example. The tensile strength can be measured according to ISO527. (Tensile modulus) The tensile modulus of the above-mentioned base material at 25°C is preferably 1 GPa or more. If the above-mentioned tensile modulus is 1 GPa or more, when the workpiece to be polished is brought into contact with the polishing pad and a load is applied, it is difficult for the abrasive grains protruding on the surface to be pressed back into the base material. Thereby, even when using fine abrasive grains, the decrease in the polishing rate can be further reduced. In addition, the edge sag of the workpiece to be polished after polishing (the phenomenon that the edge is concentratedly ground and the dimensional accuracy decreases) can be reduced. From the same point of view, the tensile modulus of the above-mentioned base material is more preferably 3 GPa or more, and further preferably 5 GPa or more. The upper limit of the tensile modulus of the above-mentioned base material is not particularly limited, and can be set to 50 GPa or less, for example. The tensile modulus can be measured according to ISO527. The tensile strength and tensile modulus of the above-mentioned base material can be adjusted by the type and content of the hydrolyzable resin, the type and content of the hydrolysis accelerator, the weight average molecular weight, the cooling process during molding, etc. For example, the lower the content of the hydrolysis accelerator, the easier it is for the above-mentioned tensile strength and tensile modulus to increase. (Thickness) The thickness of the polishing layer is not particularly limited. For example, when processing a substrate for a semiconductor device, it is preferably 0.01 mm or more and 50 mm or less, more preferably 0.1 mm or more and 30 mm or less, further preferably 0.3 mm or more and 10 mm or less, and particularly preferably 0.5 mm or more and 5 mm or less. If the thickness of the polishing layer is 0.01 mm or more, it is preferable from the viewpoint that the polishing layer can sufficiently hold the abrasive grains. 1-2. Other layers As described above, the polishing pad 100 may further contain other layers as needed. Examples of other layers include a base material layer and an adhesive layer. The base material layer can be a resin film, for example. The adhesive layer can be an adhesive layer for mounting the polishing pad 100 on a polishing platen (the chuck platen 210 described later). 2. Manufacturing method of the polishing pad The polishing pad of the present embodiment can be manufactured by any method. For example, it can be manufactured through 1) a process of obtaining a composition containing a hydrolyzable resin and abrasive grains and 2) a process of molding the obtained composition. The process of 1) The above composition can be obtained by any method. For example, the above composition can be obtained by kneading a hydrolyzable resin and abrasive grains. As a kneader, for example, a roll, a kneader, a Banbury mixer, an extruder (single-screw, multi-screw), etc. can be used. From the viewpoint of improving workability, kneading is preferably carried out under heating. The heating temperature can be set, for example, to 150°C or higher and 270°C or lower. In particular, when the above composition contains a hydrolysis accelerator, the heating temperature is preferably a temperature at which the hydrolysis accelerator can be stably dispersed. The form of the obtained composition is not particularly limited, and it can be, for example, granular, powdery, or filamentous. The process of 2) Then, the obtained composition is molded into a specified shape. The molding method is not particularly limited, and it can be, for example, any one of an injection molding method, a melt extrusion molding method, a solidification extrusion molding method, a vacuum molding method, a transfer molding method, and a compression molding method. In addition, molding can also be performed by 3D printing. When manufacturing a molded body by a compression molding method, the granules of the above composition are supplied into a mold. Then, the mold temperature is set to 150°C or higher and 270°C or lower, and pressure molding is performed to obtain a polishing pad containing a molded product. In addition, as described later, grooves can also be formed on the surface of the polished layer obtained by molding. The method of forming grooves is not particularly limited, and grooves can be formed by performing cutting processing or the like on the surface of the molded body of the above composition, or grooves can be formed by molding the above composition using a mold or a casting mold having a pattern corresponding to the grooves. In addition, from the viewpoint of improving the dimensional stability of the molded product, annealing can also be performed as needed. 3. Polishing method of the object to be polished FIG. 2 is a schematic diagram showing a polishing apparatus 200 using the polishing pad 100 of the present embodiment. In this figure, detailed illustration of the polishing pad 100 is omitted. As shown in FIG. 2, the polishing apparatus 200 includes a polishing pad 100, a disk-shaped platen 210 that supports the polishing pad 100, a disk-shaped polishing head 230 that holds the object to be polished 220, a weight 240, and a supply nozzle 250 that supplies a polishing liquid W. The platen 210 can be rotated by a rotating shaft (not shown), and the polishing head 230 can be rotated by a rotating shaft 230A. Moreover, in the present embodiment, while supplying a polishing liquid W containing water to the surface of the above polishing pad 100, the polishing pad 100 and the object to be polished 220 are relatively slid to polish the object to be polished 220. Specifically, first, the polishing pad 100 is installed on the platen 210. Then, the workpiece 220 held by the polishing head 230 is pressed against the polishing surface of the polishing pad 100, and while the polishing liquid W is supplied from the supply nozzle 250, the platen 210 and / or the polishing head 230 is rotated. Thereby, the polishing pad 100 and the workpiece 220 slide relative to each other to polish the processing surface (polished surface) of the workpiece 220. The material of the workpiece 220 is not particularly limited and can be a ceramic material, a glass material, etc. In the example of the ceramic material, it includes Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), sapphire, etc., and preferably SiC, GaN. Specifically, as the workpiece 220, materials such as semiconductor devices and electronic components can be cited, especially Si substrates, SiC substrates, GaAs substrates, glass, hard disks, substrates for LCD (liquid crystal displays), etc. Among them, a semiconductor wafer is preferred, and more preferably a SiC substrate, a sapphire substrate or a GaN substrate for power devices, and further preferably a SiC substrate or a GaN substrate. The polishing liquid W contains at least water. When the polishing pad 100 contains glycolic acid polymer as a hydrolyzable resin, from the viewpoint of promoting the hydrolysis of the glycolic acid polymer and further improving the dressing effect, the polishing liquid W is preferably an alkaline or acidic aqueous solution, and more preferably an alkaline aqueous solution. In the alkaline aqueous solution, the carboxylic acid terminal generated by hydrolysis remains in the form of carboxylate ions, so that the oligomers of the polymer generated by hydrolysis are easily dissolved in the liquid. Therefore, compared with the acidic aqueous solution, the alkaline aqueous solution can further promote hydrolysis. The alkaline aqueous solution contains water and an alkaline substance. In the example of the alkaline substance, it includes alkali metal hydroxides such as sodium hydroxide (NaOH), potassium hydroxide (KOH), and organic bases such as tetramethylammonium hydroxide. From the viewpoint of further promoting the hydrolysis of the glycolic acid polymer, the pH value of the alkaline aqueous solution is preferably 9 or more, more preferably 12 or more, and further preferably 13 or more. The upper limit of the pH value can be set to 14, for example. The pH value is the value measured by a pH meter at 20°C. The pH value of the alkaline aqueous solution can be adjusted by the amount of the alkaline substance. The temperature of the polishing liquid W is not particularly limited and can be set to 1°C or more and 60°C or less. The polishing liquid W can further contain other components other than the above, such as a hydrolysis accelerator. 4. Variation In addition, in the above embodiment, the surface of the polishing layer is flat, but it is not limited thereto, and grooves can also be arranged. Thereby, the polishing liquid can easily spread over the entire surface of the polishing layer through the grooves, and the chips generated by the hydrolysis of the hydrolyzable resin can be easily discharged to the outside through the grooves. The grooves only need to be arranged in such a way that the supply or discharge of the abrasive liquid and the discharge of the chips of the hydrolyzable resin generated by hydrolysis can be carried out. The top view shape of the grooves can be annular, radial, grid-like, or linear. In addition, the convex portions of the concavo-convex pattern formed by the grooves can also be arranged in an island shape. In addition, in the above-described embodiment, the polishing pad is composed only of the polishing layer, but it is not limited thereto, and other layers may be further included. When the polishing layer further includes a substrate layer, the polishing layer can be uniformly arranged on the substrate layer or arranged in a pattern. In addition, in the above-described embodiment, from the viewpoint of not easily forming a damaged layer in height, the median particle diameter of the abrasive grains is set to be less than 2 µm, but it is not limited thereto. For example, when only the depth of the damaged layer is thinner than before, the median particle diameter of the abrasive grains can also be 3 µm or less, for example, it can be 0.01 µm or more and 3 µm or less. Examples Hereinafter, the present invention will be described with reference to examples. The scope of the present invention is not construed in a limiting sense by the examples. 1. Materials 1-1. Adhesive resin • PGA (homopolymer of glycolic acid, weight average molecular weight 298,000, thickness reduction rate 12.3 µm / h, tensile strength 112.8 MPa) The weight average molecular weight, thickness reduction rate, and tensile strength of the above PGA were measured by the following methods. (Measurement of weight average molecular weight) The weight average molecular weight was measured by gel permeation chromatography (GPC). The measurement conditions are as follows. Apparatus: "Shodex-104" manufactured by Showa Denko K.K. Columns: Two HFIP-606M columns and one HFIP-G column as a pre-column are connected in series. Column temperature: 40°C. Eluent: HFIP solution dissolved with 5 mM sodium trifluoroacetate. Flow rate: 0.6 mL / min. Detector: RI (differential refractive index) detector. Molecular weight calibration: Five standard polymethyl methacrylates with different molecular weights. (Measurement of thickness reduction rate) After injection molding the above PGA to obtain a prism of 10 mm × 10 mm × 120 mm, a test piece (molded body) in the form of a cube with a side of 10 mm was obtained from the prism. Place the obtained test pieces in a 1 L autoclave. Then, fill the autoclave with water (deionized water) at a temperature of 60 °C, and completely immerse the above test pieces under normal pressure to conduct an immersion test. Take out the immersed test pieces at regular time intervals to produce test pieces with different immersion times. Cut each test piece to expose the cross-section. Then, place it in a drying room overnight to dry, and measure the thickness of the core (harder part) of the test piece. Measure the reduced thickness based on the difference from the thickness before immersion (initial thickness, specifically 10 mm). Based on the measured values of the reduced thickness of the test pieces measured at different immersion times, obtain the time change of the reduced thickness of the test pieces. Then, calculate the thickness reduction rate (unit: mm / h) of the test piece with a thickness of 10 mm based on the time change of the reduced thickness of the test piece within the linear range of the time change of the reduced thickness of the test piece. (Measurement of Tensile Strength) Measure the tensile strength of the above PGA according to ISO527. 1-2. Abrasive Grains Abrasive Grain 1: Polycrystalline diamond powder (manufactured by Kemet Japan Co., Ltd., median particle size 0.25 µm, amorphous) Abrasive Grain 2: Polycrystalline diamond powder (manufactured by Kemet Japan Co., Ltd., median particle size 3.0 µm, amorphous) (Method for Measuring Median Particle Size) The median particle size of the abrasive grains is measured by the following method. That is, using a laser diffraction particle size analyzer Mastersizer3000 (Malvern), the measurement is carried out under the conditions that the measurement temperature is 21 °C, the dispersion medium is ion-exchanged water, the refractive index of the dispersion medium is 1.330, the light scattering model is Mie theory, the particle absorption rate of polycrystalline diamond powder is 0.100, and the particle refractive index is 2.418. The addition amount of the abrasive grains in the dispersion medium is adjusted so that the laser scattering intensity is 4% or more and 10% or less. 2. Fabrication and Evaluation of Polishing Pads (Tests 1 to 3) (1) Fabrication of Polishing Pads (Kneading Process) Weigh the above PGA as the binder resin and the abrasive grains shown in Table 1 in the ratio shown in Table 1, and use a closed kneader (manufactured by Toyo Seiki Seisakusho Co., Ltd.) to knead to obtain a composition. The kneading is carried out at a specified heater temperature, a preheating time of 1 minute, a kneading time of 5 minutes, and a rotation speed of 50 rpm. In addition, the heater temperature is set to 250 °C for the kneading. (Molding Process) Figure 3 is a schematic diagram showing the components of the molding device 300 used in the examples. In this figure, reference numeral 301 represents an iron plate, and 302 represents an aluminum foil. Arrange a SUS mold 303 with a thickness of 0.5 mm and a hole with a diameter of 150 mm as shown in Fig. 3. Place the above-mentioned kneaded composition 304 on the SUS mold 303 and perform compression molding to obtain a polishing pad 100 composed of a polishing layer with a thickness of 0.5 mm as shown in Fig. 1. The temperature of the press is set to the same temperature as the heater temperature of the above-mentioned closed kneader. (2) Evaluation (Pre-treatment of the polishing pad) Since the abrasive grains of the polishing pad just after molding are buried by the resin, after filing with an #800 grindstone, a polishing test is carried out. (Pre-processing of the workpiece to be polished) Use a slurry containing polycrystalline diamond with a median grain size of 1 µm, and perform rough lapping on the surface of a 20×20 mm square SiC substrate as the workpiece to be polished using a copper platen. (Polishing test) As shown in Fig. 2, the polishing test is carried out by installing the polishing pad on a polishing device 200. Specifically, use a double-sided adhesive film (such as AS ONE OCA50-A4) to install the polishing pad on the platen 210 (polishing disk). When attaching the double-sided adhesive sheet to the polishing pad and the polishing disk, use a rubber roller or the like to attach it without mixing air bubbles. Then, press the rotating polishing pad against the SiC substrate (20×20 mm square) that has undergone the above-mentioned pre-processing as the workpiece to be polished 220 for polishing. The polishing conditions are as follows. At this time, a load of a jig (polishing head 230) and a heavy object 240 is applied to the substrate. (Polishing conditions) Polishing device: Dia-Lap ML-150P (manufactured by Maruto Co., Ltd.) Rotation speed of the polishing disk: 100 rpm Polishing disk diameter: 150 mm in diameter Forced drive and shaking of the workpiece to be polished: None Surface pressure: 250 gf / cm 2 Flow rate of the polishing liquid: 75 mL / h Polishing liquid: NaOH aqueous solution with pH = 13 (20°C) Next, use the following method to measure the polishing speed, surface roughness of the workpiece to be polished, and depth of the damaged layer. (1) Polishing speed Measure the thickness of the workpiece to be polished with an electric micrometer Millimar1240 (manufactured by Mahr) in the state where the workpiece to be polished is attached to the jig. The thickness of the workpiece to be polished is measured at 5 positions and set as the average value of them. The polishing speed is calculated based on the polishing time (min) and the thickness reduction value (removal amount, µm). (2) Surface roughness of the workpiece to be polished Using a laser microscope VK-X260 (manufactured by Keyence Corporation), the arithmetic mean height Sa (μm) of the surface of the SiC substrate as the object to be polished was measured after 2 hours of polishing, and this was defined as the surface roughness. The measurement was carried out using an objective lens with a magnification of 20 times and N.A. = 0.46. In addition, regarding the arithmetic mean height Sa (μm) of the surface of the SiC substrate after the above polishing, an atomic force microscope (AFM) (scanning probe microscope SPI-3800 / SPA-300HV, manufactured by Seiko Instruments Inc.) was used. The measurement was carried out under the conditions of cantilever: SI-AF01, scanning range: 5000 nm × 5000 nm, scanning frequency: 1.00 Hz, environment: atmosphere, temperature: room temperature (21 °C), bias voltage: 0 V. (3) Depth of the damaged layer A transmission electron microscope (TEM) was used to observe the cross-section of the SiC substrate after 2 hours of polishing, and the depth of the damaged layer was estimated based on the obtained TEM image. Specifically, the measurement was carried out in the following order. (Cross-section TEM specimen) The cross-section TEM specimen was fabricated by micro-sampling using a focused ion beam device and thinning. The sampling was performed on the stripes formed near the center of the polished surface, and a cross-section orthogonal to the stripes was taken. (TEM observation) As the TEM device, a JEM-2100F type field emission transmission electron microscope manufactured by JEOL Ltd. was used. The acceleration voltage was set to 200 kV. The depth of the damaged layer was obtained by reading the maximum depth according to the scale in the observed image. (Experiment 4) For comparison, a tin chuck (manufactured by Maruto Co., Ltd., high-polish chuck) used in the precision polishing process was used to polish the SiC substrate. In the polishing using the tin chuck, a slurry (manufactured by Maruto Co., Ltd.) containing abrasive grain 1 (polycrystalline diamond with a median grain size of 0.25 µm) was used as the polishing liquid. (Polishing conditions) Polishing device: Dia-Lap ML-150P (manufactured by Maruto Co., Ltd., tin chuck) Rotation speed of the polishing disk: 100 rpm Diameter of the polishing disk: 150 mm in diameter Forced drive and shaking of the object to be polished: None Surface pressure: 250 gf / cm 2 Flow rate of the slurry: 50 g / h Then, in the same manner as above, the polishing rate, the surface roughness of the object to be polished, and the depth of the damaged layer were measured using the following methods. The compositions of the polishing pads and the evaluation results of Experiments 1 to 4 are shown in Table 1. [Table 1] ※ Volume % relative to the total volume of the polishing layer As shown in Table 1, in Test 4, although a polycrystalline diamond slurry with an average particle size of 0.25 µm was used, the depth of the damaged layer was relatively large, at 120 nm. In contrast, in Test 1, while suppressing the decrease in the polishing rate, the depth of the damaged layer could be reduced to 10 nm. In addition, it can be seen that by further reducing the median particle size of the abrasive grains, the surface roughness of the SiC substrate can be further reduced (comparison between Tests 1 and 2). In addition, it can be seen that by reducing the amount of abrasive grains, the polishing rate can be further increased (comparison between Tests 1 and 3). This application claims priority based on Japanese Patent Application No. 2023-91781 and Japanese Patent Application No. 2023-091782 filed on June 2, 2023, and Japanese Patent Application No. 2023-119986 filed on July 24, 2023. All the contents described in the specification and drawings of that application are incorporated herein by reference. Industrial Applicability According to the present invention, there can be provided a polishing pad that suppresses a decrease in the polishing rate and reduces the damaged layer, and a polishing method for an object to be polished using the same. 100: Polishing pad 110: Polishing layer 111: Base material 112: Abrasive grains 200: Polishing device 210: Platen 220: Object to be polished 230: Polishing head 230A: Rotating shaft 240: Weight 250: Supply nozzle 301: Iron plate 302: Aluminum foil 303: SUS mold 304: Composition W: Polishing liquid [Fig. 1A] is a schematic top view of a polishing pad according to an embodiment of the present invention, and [Fig. 1B] is a schematic cross-sectional view taken along line 1B-1B of the polishing pad of Fig. 1A. [Fig. 2] is a schematic cross-sectional view showing a polishing method for an object to be polished according to an embodiment of the present invention. [Figs. 3A] to [3C] are schematic cross-sectional views showing a method for manufacturing a polishing pad in an example. 100: Polishing pad 110: Polishing layer 111: Base material 112: Abrasive grains

Claims

1. A polishing pad for precision mechanical grinding, comprising a polishing layer including a base material containing a hydrolyzable resin and diamond abrasive grains with a median particle size of less than 2 µm fixed by the base material, wherein the hydrolyzable resin is mainly composed of a glycolic acid polymer with a weight average molecular weight of 70,000 to 500,000, the base material has a tensile modulus of 1 GPa or more at 25°C, and the polishing layer has a thickness of 0.5 mm or more.

2. The abrasive pad of claim 1, wherein the content of the aforementioned diamond abrasive grains is 55% by mass or less relative to the total mass of the aforementioned abrasive layer.

3. The abrasive pad as claimed in claim 1, wherein the thickness of the aforementioned abrasive layer is more than 0.5 mm and less than 5 mm.

4. The abrasive pad according to any one of claims 1 to 3, wherein the thickness reduction rate when the molded body of the above-mentioned base material is immersed in water at 60°C is 12 µm / h or more.

5. A grinding method for a workpiece, comprising the following steps: while supplying an abrasive liquid containing water to the surface of the abrasive layer of an abrasive pad as claimed in any one of claims 1 to 4, the abrasive pad is slid relative to the workpiece to grind the workpiece.

6. The grinding method for the workpiece as described in claim 5, wherein the workpiece contains silicon carbide, sapphire, or gallium nitride.

7. The grinding method for the workpiece as described in claim 5, wherein the aforementioned grinding fluid is an alkaline aqueous solution.

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