Polishing pad and method for polishing object to be polished

Abstract

A polishing pad according to the present invention is provided with a polishing layer containing a composition that contains a hydrolyzable resin and abrasive grains having a median diameter of less than 2 μm.

Description

Polishing pad and method for polishing object

[0001] The present invention relates to a polishing pad and a method for polishing an object to be polished.

[0002] In the manufacturing process of substrates used in semiconductor devices, a cylindrical single crystal (ingot) is sliced ​​into discs to form wafers, which are then roughly polished (lapping, primary polishing) to ensure that both sides of the wafer are parallel and to the specified thickness. The roughly polished wafers then undergo chemical etching and precision mechanical polishing (secondary polishing, mechanical polishing) to create a highly flat, mirror-like surface. Finally, they undergo final polishing (chemical mechanical polishing, CMP), which also incorporates chemical action, to achieve atomic-level flatness.

[0003] In precision mechanical polishing in semiconductor substrate manufacturing processes, a known method uses a fixed-abrasive polishing pad having an abrasive layer containing a binder resin and abrasive grains fixed thereto, and the binder resin is typically a curable resin such as a phenolic resin, an epoxy resin, or an acrylic phenolic resin (see, for example, Patent Document 1).

[0004] JP 2018-51733 A

[0005] In general precision mechanical polishing, a hard metal surface plate is used to polish the substrate while supplying a slurry containing abrasive grains, which can easily cause microcracks and scratches on the surface of the substrate, resulting in the formation of a damaged layer.

[0006] In particular, substrates such as silicon carbide (SiC) and gallium nitride (GaN) used in next-generation power semiconductor devices are not only highly hard but also chemically stable, unlike silicon (Si) substrates. Therefore, if a damaged layer is formed by precision mechanical polishing, the damaged layer cannot be easily removed by chemical techniques such as chemical etching, and a long time of finish polishing is required, which increases the wafer processing cost.

[0007] On the other hand, the polishing pad using the binder resin as described above is softer and has a lower elastic modulus than the polishing pad using metal or ceramic, so it is expected that precision mechanical polishing can be performed on highly brittle substrates such as SiC substrates with less damage.In addition, in order to reduce the damage caused by precision mechanical polishing, it is desirable to use micro-abrasive particles with a small abrasive particle size as much as possible.In precision mechanical polishing, micro-abrasive particles with a median diameter of 3 μm or less are generally used.However, according to the study by the present inventors, when micro-abrasive particles are fixed with the binder resin as described above, there is a problem that the polishing speed is significantly reduced.

[0008] Therefore, it is desirable that fixed abrasive polishing pads using fine abrasive grains be able to reduce the damaged layer while minimizing the decrease in polishing rate, and preferably be able to remove the damaged layer while minimizing the decrease in polishing rate even without dressing (sharpening).

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a polishing pad that can reduce the damaged layer while minimizing the decrease in polishing rate, and a polishing method for an object to be polished using the same.

[0010] [1] A polishing pad comprising a polishing layer containing a hydrolyzable resin and abrasive grains having a median diameter (D50) of less than 2 μm. [2] The polishing pad according to [1], wherein the hydrolyzable resin is primarily composed of glycolic acid polymer. [3] The polishing pad according to [1] or [2], wherein the abrasive grain content is 55 mass% or less relative to the total mass of the polishing layer. [4] A method for polishing an object to be polished, comprising the step of polishing the object to be polished by sliding the polishing pad and the object to be polished relative to each other 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]. [5] The method for polishing an object to be polished according to [4], wherein the object to be polished comprises silicon carbide or gallium nitride. [6] The method for polishing an object to be polished according to [4] or [5], wherein the polishing liquid is an alkaline aqueous solution.

[0011] According to the present invention, it is possible to provide a polishing pad that can reduce the damaged layer while minimizing the decrease in polishing rate, and a method for polishing an object using the same.

[0012] Fig. 1A is a schematic plan view of a polishing pad according to one embodiment of the present invention, and Fig. 1B is a schematic cross-sectional view of the polishing pad taken along line 1B-1B of Fig. 1A. Fig. 2 is a schematic cross-sectional view showing a polishing method for a polished object according to one embodiment of the present invention. Figs. 3A to 3C are schematic cross-sectional views showing a manufacturing method of a polishing pad in an example.

[0013] The reason why the polishing speed drops significantly when micro-abrasive grains are fixed with a conventional binder resin is thought to be as follows: Micro-abrasive grains have small protruding heights and small chip pockets (the gap between the workpiece and the binder resin, which serves to discharge shavings), so even a small amount of shavings can easily cause clogging. In addition, the binder resin described above is not hydrolyzable, so it has no dressing effect and is unlikely to change. These factors are thought to be the reason why the polishing speed drops significantly.

[0014] The present inventors have investigated various binder resins for fixing abrasive grains in polishing pads and found that hydrolyzable resins such as glycolic acid polymers exhibit a dressing effect, making them less susceptible to clogging even when using fine abrasive grains. They have also found that even when using fine abrasive grains, a decrease in polishing rate can be minimized without a dressing treatment, which was difficult with previous resins. Furthermore, the present inventors have also investigated the size of the abrasive grains and found that a median diameter of less than 2 μm can significantly reduce the damage layer, leading to the invention.

[0015] That is, the polishing pad according to one embodiment of the present invention includes a polishing layer containing a hydrolyzable resin and abrasive grains having a median diameter of less than 2 μm. The configuration of the polishing pad will be described in detail below.

[0016] 1. Polishing Pad FIG. 1A is a schematic plan view of a polishing pad 100 according to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of the polishing pad 100 of FIG. 1A taken along line 1B-1B.

[0017] The polishing pad 100 according to this embodiment includes a polishing layer 110 (see FIG. 1B).

[0018] 1-1. Abrasive Layer In this embodiment, abrasive layer 110 includes a composition including matrix 111 containing a hydrolyzable resin and abrasive grains 112 fixed by matrix 111 (see FIG. 1B).

[0019] 1-1-1. Hydrolyzable Resin The hydrolyzable resin is not particularly limited as long as it is a resin that exhibits hydrolysis. The hydrolyzable resin may or may not be a biodegradable resin.

[0020] The hydrolyzable resin includes polyester having ester bond in the main chain, polycarbonate having carbonate bond in the main chain, etc. Examples of the hydrolyzable resin include lactic acid polymer, glycolic acid polymer, hydroxybutyric acid polymer, hydroxyvaleric acid polymer, caprolactone polymer, ethylene succinate polymer, butylene succinate polymer (such as polybutylene succinate, polybutylene succinate adipate, polybutylene succinate terephthalate, polyethylene succinate, polybutylene succinate carbonate, etc.), dioxanone polymer, trimethylene carbonate polymer, etc. Among these, lactic acid polymer and glycolic acid polymer are preferred, and glycolic acid polymer is preferred from the viewpoint of having higher strength and hydrolysis rate and being easier to adjust the protruding height of the abrasive grains of the polishing layer. That is, the hydrolyzable resin preferably contains glycolic acid polymer as the main component. "Containing a glycolic acid polymer as a main component" means that the content of glycolic acid polymer relative to the total amount of hydrolyzable resin is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0021] Glycolic acid polymers are made up of structural units derived from glycolic acid (-(-O-CH ２The glycolic acid polymer is a polymer containing a structural unit derived from glycolic acid, and is a polymer containing 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 therewith.

[0022] Examples of copolymerizable monomers include: glycols such as ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 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'-diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, and 5-tetrabutylphosphonium isophthalic acid; hydroxycarboxylic acids such as lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, and hydroxybenzoic acid; lactides; Lactones such as caprolactone, valerolactone, propiolactone, undecalactone, and 1,5-oxepan-2-one; and carbonates such as trimethylene carbonate.

[0023] The term "mainly composed of glycolic acid-derived structural units" means that the content of glycolic acid-derived structural units is 50% by mass or more relative to the total amount of structural units constituting the glycolic acid polymer. The content of glycolic acid-derived structural units is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more. When the content of the structural units constituting the glycolic acid polymer is 50% by mass or more, the strength of the glycolic acid polymer can be better maintained, so that sufficient strength can be obtained when used in a polishing pad. Furthermore, when the content of the structural units constituting the glycolic acid polymer is 70% by mass or more, hydrolysis is more likely to proceed, so that the decrease in polishing rate can be reduced.

[0024] Among these, from the viewpoint of higher strength and ease of hydrolysis, the glycolic acid polymer is preferably a homopolymer of glycolic acid.

[0025] The weight-average molecular weight of the glycolic acid polymer is not particularly limited, but is preferably 70,000 or more and 500,000 or less. A glycolic acid polymer having a weight-average molecular weight of 70,000 or more can increase the strength of the glycolic acid polymer, thereby further improving the retention and durability of abrasive grains. Furthermore, sufficient strength is obtained for handling, such as when removing the polishing pad from the mold during molding or when attaching the polishing pad to the platen of a polishing apparatus. Furthermore, when the polishing pad is brought into contact with the workpiece and a load is applied, abrasive grains protruding from the surface are less likely to be pushed back into the base material. This makes it possible to further reduce the decrease in polishing rate, even when using small abrasive grains. A glycolic acid polymer having a weight-average molecular weight of 500,000 or less can not only further maintain moldability, but also shorten the time until disintegration by hydrolysis. From the same perspective, the weight-average molecular weight of the glycolic acid polymer is more preferably 110,000 or more and 400,000 or less.

[0026] The weight-average molecular weight of the glycolic acid polymer can be measured by gel permeation chromatography (GPC). The measurement conditions can be as follows: (Measurement conditions) Apparatus: "Shodex-104" manufactured by Showa Denko Column: Two HFIP-606M columns connected in series with one HFIP-G column as a pre-column Column temperature: 40°C Eluent: HFIP solution containing 5 mM sodium trifluoroacetate Flow rate: 0.6 mL / min Detector: RI (differential refractive index) detector Molecular weight calibration: Five types of standard polymethyl methacrylate with different molecular weights

[0027] The content 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, even 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 composition).When the content of the hydrolyzable resin is 20% by mass or more, the strength of the polishing layer containing abrasive grains is increased, which is preferable.When the content of the hydrolyzable resin is 99% by mass or less, the proportion of abrasive grains is not too small, and the polishing rate is not too slow, which is preferable.When the content of the hydrolyzable resin is above this level, excessive collapse of the polishing layer is suppressed, and a more stable polishing rate is easily obtained due to the dressing effect.

[0028] 1-1-2. Abrasive Grains As described above, in this embodiment, abrasive grains with a median diameter of less than 2 μm are used. When the median diameter of the abrasive grains is less than 2 μm, even highly brittle workpieces such as SiC substrates can be easily processed ductilely, effectively reducing the damaged layer. The lower limit of the median diameter of the abrasive grains is not particularly limited, but from the viewpoint of adjusting the protruding height of the abrasive grains to a suitable height for polishing and further increasing the polishing rate, it is preferably 0.01 μm or more. From the same viewpoint, the median 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, even 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.

[0029] The median diameter of the abrasive grains can be determined from the particle size distribution measured in accordance with particle size analysis - laser diffraction and scattering method (ISO 13320:2020). Specifically, it can be measured using a laser diffraction particle size analyzer (e.g., Malvern Mastersizer 3000) at a measurement temperature of 21°C, using ion-exchanged water as the dispersion medium, with a refractive index of 1.330, and using the Mie theory as the light scattering model.

[0030] The material of the abrasive grains is not particularly limited, and examples thereof include 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. Among these, diamond, boron carbide, and boron nitride are preferred from the viewpoint of further increasing the polishing rate, and diamond is more preferred from the viewpoint of facilitating processing of high-hardness substrates such as SiC substrates.

[0031] The shape of the abrasive grains is not particularly limited and may be spherical, polyhedral, or irregular. The abrasive grains may be surface-treated to impart friability, or may be coated to enhance the retention of the hydrolyzable resin.

[0032] The content of abrasive grains is not particularly limited, but is preferably 1.0% by mass or more and 80% by mass or less relative to the polishing layer (or the total amount of the composition). If the content of abrasive grains is 80% by mass or less, when the polishing pad is brought into contact with the workpiece and a load is applied, the load is not too dispersed, and an appropriate load is applied to each abrasive grain, making it easier for the abrasive grains to cut into the workpiece. This makes it possible to further increase the polishing rate even when using fine abrasive grains. In addition, it is possible to further improve the formability or processability of the polishing pad. From the same perspective, the content of abrasive grains is more preferably 5.0% by mass or more and 70% by mass or less relative to the polishing layer (or the total amount of the composition), even more 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.

[0033] The content of abrasive grains can be measured by thermogravimetric analysis (TGA).Specifically, on the surface of the polishing layer of unused polishing pad, when any straight line passing through the center O of the polishing layer is designated as line L, and the straight line passing through the center O of the polishing layer perpendicular to line L is designated as line M, the center O of the polishing layer, the midpoint between the center O of the polishing layer and the end of the polishing layer on line L are designated as a1 and a2, and the midpoint between the center O of the polishing layer and the end of the polishing layer on line M are designated as b1 and b2, then, from the range including the measurement points of O, a1, a2, b1 and b2, 100 mg or more of measurement samples are taken from the polishing layer, and suitably pulverized, and used as the measurement samples from each measurement point.20 mg±2 of measurement sample is placed in a platinum pan, and in an air atmosphere, heated from room temperature to 800 ° C at a rate of 10 ° C / min, and kept at 800 ° C for 30 minutes, components other than abrasive grains are burned off, and the remaining sample weight is divided by the mass of the measurement sample to determine the content of abrasive grains in the polishing layer at each measurement point. In the present application, the arithmetic mean value of the abrasive grain content at each of the five points was taken as the representative value of the abrasive grain content of the polishing layer.

[0034] 1-1-3. Other Components The base material containing a hydrolyzable resin may be composed solely of the hydrolyzable resin, or may further contain other components in addition to the hydrolyzable resin. Examples of other components include resins other than the hydrolyzable resin and hydrolysis accelerators. In particular, from the viewpoint of further increasing the polishing rate, it is preferable that the polishing layer further contains a hydrolysis accelerator. One type of hydrolysis accelerator may be used alone, or two or more types may be used in combination.

[0035] The hydrolysis accelerator is a compound that accelerates the hydrolysis reaction of the hydrolyzable resin, and is preferably a compound that dissolves in the polishing liquid to accelerate the penetration of the solution into the hydrolyzable resin, and more preferably a compound that generates an acid or alkali in the presence of water. Examples of such decomposition accelerators include carboxylic acid anhydrides, phosphorus compounds, cyclic esters, and basic metal oxides.

[0036] Examples of carboxylic acid 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'-benzophenonetetracarboxylic dianhydride, diphenylsulfonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, ethylene glycol bisanhydrotrimellitate, and glycerin bisanhydrotrimellitate monoacetate. Among these, phthalic anhydride, trimellitic anhydride, benzoic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and benzene-1,2,4,5-tetracarboxylic anhydride (pyromellitic anhydride) are preferred.

[0037] The phosphorus compound is preferably an organic phosphorus compound such as a phosphate ester or a phosphite ester, 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 pentaerythritol skeleton.

[0038] Examples of phosphate esters having a long-chain alkyl group having 8 to 24 carbon atoms include mono- or di-stearyl acid phosphate or a mixture thereof, and di-2-ethylhexyl acid phosphate. Examples of phosphites having an aromatic ring include tris(nonylphenyl)phosphite. Examples of phosphites having a pentaerythritol skeleton include cyclic neopentanetetraylbis(2,6-di-tert-butyl-4-methylphenyl)phosphite, cyclic neopentanetetraylbis(2,4-di-tert-butylphenyl)phosphite, and cyclic neopentanetetraylbis(octadecyl)phosphite.

[0039] Examples of cyclic esters include glycolide, lactide, ε-caprolactone, γ-valerolactone, δ-valerolactone, diglycolic anhydride, and glutaric anhydride.

[0040] Examples of basic metal oxides include magnesium oxide, zinc oxide, calcium oxide, sodium oxide, and copper oxide.

[0041] Among these, cyclic esters are preferred, and glycolide is more preferred, from the viewpoint of being relatively stable during molding and further promoting the hydrolysis of hydrolyzable resins such as glycolic acid polymers within the polishing layer once water has penetrated therein.

[0042] The content of the hydrolysis accelerator is preferably 0.5% by mass or more and 50% by mass or less relative to the total amount of the hydrolyzable resin. When the content of the hydrolysis accelerator is 0.5% by mass or more, the hydrolysis of the hydrolyzable resin can be further accelerated, and the decrease in the polishing rate can be further reduced. When the content of the hydrolysis accelerator is 50% by mass or less, not only can the bleed-out of the hydrolysis accelerator be more unlikely to occur, but excessive collapse due to excessive hydrolysis can also be further suppressed. From the same viewpoint, the content of the hydrolysis accelerator is more preferably 1% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less.

[0043] 1-1-4. Physical Properties As described above, from the viewpoint of preventing a decrease in the polishing rate even when fine abrasive grains are used, it is preferable that the hydrolysis rate and strength of the base material containing the hydrolyzable resin are appropriately high.

[0044] (Thickness reduction rate) The hydrolysis rate of the base material can be expressed, for example, by the thickness reduction rate. When a molded body of the base material is immersed in water at 60°C, the thickness reduction rate is preferably 12 μm / h or more. A polishing layer containing a base material having such a thickness reduction rate is easily hydrolyzed by supplying a polishing liquid, and the dressing effect is more easily obtained. There is no particular limit on the upper limit of the thickness reduction rate, but 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, even more preferably 500 μm / h or less, and particularly preferably 100 μm / h or less.

[0045] The rate of thickness reduction can be measured by the following procedure. 1) The above composition containing no abrasive grains is injection molded to obtain a 10 mm x 10 mm x 120 mm prism, and a cubic test piece (molded body) with a side length of 10 mm is obtained from the prism. Molded bodies of the above composition containing no abrasive grains can also be obtained by heating and melting a molded body of a composition containing abrasive grains, i.e., the abrasive layer. The abrasive layer is heated and melted, and the resulting molten material is passed through a filter to separate the abrasive grains and the composition containing the other hydrolyzable resin, i.e., the composition not containing abrasive grains, and the abrasive-free composition is molded to produce a molded body, which can be used as a test piece. 2) Next, the test piece is placed in a 1 L autoclave, the autoclave is filled with water (deionized water) at 60°C, and the test piece is completely immersed at normal pressure. The above procedure is repeated to prepare immersion test pieces with different immersion times. Each immersion test piece is cut to expose the cross section. After drying, the thickness of the core (hard part) of the test piece is measured. The thickness reduction is measured from the difference with the thickness (10 mm) before immersion. 3) The time change in the thickness reduction of the test piece is determined based on the measured values ​​of the thickness reduction of the test piece measured after different immersion times. Then, the thickness reduction rate of the 10 mm test piece is calculated (unit: mm / h) from the time change in the thickness reduction of the test piece within the range where the time change in the thickness reduction of the test piece is linear.

[0046] The rate of thickness reduction of the base material can be adjusted, for example, by the type and content of the hydrolyzable resin and the type and content of the hydrolysis promoter. For example, when the hydrolyzable resin contains a glycolic acid polymer, the rate of thickness reduction tends to be high. Furthermore, when the content of the hydrolysis promoter is high, the rate of thickness reduction tends to be high.

[0047] (Tensile strength) The tensile strength of the base material at 25°C is preferably 55 MPa or more. If the tensile strength is 55 MPa or more, the abrasive grain retention force can be further increased. From the same viewpoint, the tensile strength of the base material is more preferably 60 MPa or more. There is no particular upper limit to the tensile strength of the base material, but it can be, for example, 1000 MPa or less. The tensile strength can be measured in accordance with ISO 527.

[0048] (Tensile Modulus) The tensile modulus of the base material at 25°C is preferably 1 GPa or more. When the tensile modulus is 1 GPa or more, when the polishing pad is brought into contact with the workpiece and a load is applied, the abrasive grains protruding from the surface are less likely to be pushed back into the base material. This makes it possible to reduce the decrease in polishing rate even when using small abrasive grains. In addition, it is possible to reduce the edge sagging of the workpiece after polishing (a phenomenon in which the edge is intensively scraped, resulting in a decrease in dimensional accuracy). From the same perspective, the tensile modulus of the base material is more preferably 3 GPa or more, and even more preferably 5 GPa or more. The upper limit of the tensile modulus of the base material is not particularly limited, but can be, for example, 50 GPa or less. The tensile modulus can be measured in accordance with ISO 527.

[0049] The tensile strength and tensile modulus of the base material can be adjusted by the type and content of the hydrolyzable resin, the type and content of the hydrolysis promoter, the weight average molecular weight, the cooling step during molding, etc. For example, if the content of the hydrolysis promoter is low, the tensile strength and tensile modulus tend to be large.

[0050] (Thickness) The thickness of the polishing layer is not particularly limited, but for example, when used for processing the substrate of semiconductor device, it is preferably 0.01mm or more and 50mm or less, more preferably 0.1mm or more and 30mm or less, even more preferably 0.3mm or more and 10mm or less, and particularly preferably 0.5mm or more and 5mm or less.If the thickness of the polishing layer is 0.01mm or more, it is preferable from the viewpoint that the polishing layer can sufficiently hold abrasive grains.

[0051] 1-2. Other Layers As described above, the polishing pad 100 may further include other layers as necessary. Examples of the other layers include a substrate layer and an adhesive layer. The substrate layer may be, for example, a resin film. The adhesive layer may be an adhesive layer for attaching the polishing pad 100 to a polishing platen (platen 210, described below).

[0052] 2. Method for Manufacturing Polishing Pad The polishing pad according to this embodiment can be manufactured by any method. For example, the polishing pad can be manufactured through the steps of 1) obtaining a composition containing a hydrolyzable resin and abrasive grains, and 2) molding the obtained composition.

[0053] The composition can be obtained by any method. For example, the composition can be obtained by kneading a hydrolyzable resin with abrasive grains. Examples of kneading machines that can be used include rolls, kneaders, Banbury mixers, and extruders (single-screw or multi-screw).

[0054] From the viewpoint of improving processability, the kneading is preferably carried out under heating. The heating temperature can be, for example, 150° C. or higher and 270° C. or lower. In particular, when the composition contains a hydrolysis accelerator, the heating temperature is preferably a temperature at which the hydrolysis accelerator can be dispersed in a stable state.

[0055] The form of the resulting composition is not particularly limited, and may be, for example, pellets, powder, or filaments.

[0056] Step 2) Next, the obtained composition is molded into a predetermined shape. The molding method is not particularly limited, and may be, for example, any of injection molding, melt extrusion molding, solidification extrusion molding, vacuum molding, transfer molding, and compression molding. Molding may also be performed using a 3D printer.

[0057] When producing a molded product by compression molding, pellets of the composition are fed into a mold, and the mold temperature is set to 150°C or higher and 270°C or lower, followed by press molding to obtain a polishing pad containing the molded product.

[0058] In addition, as will be described later, grooves may be formed on the surface of the polishing layer obtained by molding. The method for forming grooves is not particularly limited, and grooves may be formed by cutting the surface of the molded product of the composition, or by molding the composition using a mold or die on which a pattern corresponding to the grooves is formed. In addition, annealing may be performed as necessary from the viewpoint of improving the dimensional stability of the molded product.

[0059] 2 is a schematic diagram showing a polishing apparatus 200 using the polishing pad 100 according to the present embodiment. In this figure, detailed illustration of the polishing pad 100 is omitted.

[0060] 2, polishing apparatus 200 includes polishing pad 100, a disc-shaped surface plate 210 that supports polishing pad 100, a disc-shaped polishing head 230 that holds workpiece 220, a weight 240, and a supply nozzle 250 that supplies polishing liquid W. Surface plate 210 is rotatable by a rotation shaft (not shown), and polishing head 230 is rotatable by a rotation shaft 230A.

[0061] In this embodiment, the polishing pad 100 and the object to be polished 220 are slid relative to each other while a polishing liquid W containing water is supplied to the surface of the polishing pad 100, thereby polishing the object to be polished 220.

[0062] Specifically, first, the polishing pad 100 is attached to the surface plate 210. Next, the workpiece 220 held by the polishing head 230 is pressed against the polishing surface of the polishing pad 100, and the surface plate 210 and / or the polishing head 230 are rotated while supplying the polishing liquid W from the supply nozzle 250. This causes the polishing pad 100 and the workpiece 220 to slide relative to each other, polishing the processed surface (surface to be polished) of the workpiece 220.

[0063] The material of the object to be polished 220 is not particularly limited and may be a ceramic material, a glass material, or the like. Examples of ceramic materials include Si (silicon), SiC (silicon carbide), GaN (silicon nitride), GaAs (gallium arsenide), sapphire, and the like, with SiC and GaN being preferred. Specific examples of the object to be polished 220 include materials for semiconductor devices and electronic components, particularly Si substrates, SiC substrates, GaAs substrates, glass, and substrates for hard disks and LCDs (liquid crystal displays). Among these, semiconductor wafers are preferred, and SiC substrates, sapphire substrates, or GaN substrates used in power devices are more preferred, with SiC substrates or GaN substrates being even more preferred.

[0064] The polishing liquid W contains at least water. When the polishing pad 100 contains a glycolic acid polymer as a hydrolyzable resin, the polishing liquid W is preferably an alkaline or acidic aqueous solution, and an alkaline aqueous solution is more preferred, from the viewpoint of promoting hydrolysis of the glycolic acid polymer and further enhancing the dressing effect. In an alkaline aqueous solution, the carboxylic acid terminals generated by hydrolysis remain as carboxylate ions, and oligomers of the polymer generated by hydrolysis are easily eluted into the liquid. Therefore, an alkaline aqueous solution can promote hydrolysis more than an acidic aqueous solution.

[0065] The alkaline aqueous solution contains water and an alkaline substance. Examples of the alkaline substance include alkali metal hydroxides such as sodium hydroxide (NaOH) and potassium hydroxide (KOH), and organic alkalis such as tetramethylammonium hydroxide. From the viewpoint of further promoting the hydrolysis of the glycolic acid polymer, the pH of the alkaline aqueous solution is preferably 9 or higher, more preferably 12 or higher, and even more preferably 13 or higher. The upper limit of the pH can be, for example, 14. The pH is a value measured with a pH meter at 20°C. The pH of the alkaline aqueous solution can be adjusted by the amount of the alkaline substance.

[0066] The temperature of the polishing liquid W is not particularly limited, but can be set to 1°C or higher and 60°C or lower.

[0067] The polishing liquid W may further contain other components than those mentioned above, for example, a hydrolysis accelerator.

[0068] In the above embodiment, the surface of the polishing layer is flat, but this is not limiting and grooves may be provided. This allows the polishing liquid to be easily distributed over the entire surface of the polishing layer through the grooves, and also allows shavings generated by hydrolysis of the hydrolyzable resin to be easily discharged to the outside through the grooves.

[0069] The grooves may be arranged so as to allow the supply or discharge of the polishing liquid and the discharge of shavings of the hydrolyzable resin generated by hydrolysis. The planar shape of the grooves may be annular, radial, lattice-like, or linear. Furthermore, the convex portions of the concave-convex pattern formed by the grooves may be arranged in an island shape.

[0070] In the above embodiment, the polishing pad is composed of only the polishing layer, but is not limited thereto and may further include other layers. When the polishing pad further includes a base layer, the polishing layer may be disposed uniformly on the base layer or may be disposed in a pattern.

[0071] In the above embodiment, the median diameter of the abrasive grains is set to less than 2 μm in order to highly prevent the formation of a damaged layer, but this is not limiting. For example, if it is only necessary to make the depth of the damaged layer thinner than before, the median diameter of the abrasive grains may be 3 μm or less, for example, 0.01 μm or more and 3 μm or less.

[0072] The present disclosure will be described below with reference to examples, which should not be construed as limiting the scope of the present disclosure.

[0073] 1. Materials 1-1. Binder resin - PGA (homopolymer of glycolic acid, weight average molecular weight 298,000, thickness reduction rate 12.3 μm / h, tensile strength 112.8 MPa)

[0074] The weight average molecular weight, thickness reduction rate and tensile strength of the PGA were measured by the following methods.

[0075] (Measurement of Weight-Average Molecular Weight) The weight-average molecular weight was measured by gel permeation chromatography (GPC). The measurement conditions were as follows: Apparatus: "Shodex-104" manufactured by Showa Denko K.K. Column: Two HFIP-606M columns connected in series with one HFIP-G column as a pre-column Column temperature: 40°C Eluent: HFIP solution containing 5 mM sodium trifluoroacetate Flow rate: 0.6 mL / min Detector: RI (differential refractive index) detector Molecular weight calibration: Five types of standard polymethyl methacrylate with different molecular weights

[0076] (Measurement of Thickness Reduction Rate) The PGA was injection molded to obtain a 10 mm x 10 mm x 120 mm square pillar, and then a cubic test piece (molded article) with a side length of 10 mm was obtained from the square pillar.

[0077] The obtained test specimens were placed in a 1 L autoclave. The autoclave was then filled with water (deionized water) at 60°C, and the test specimens were completely immersed at normal pressure to perform an immersion test. Test specimens with different immersion times were prepared by removing the test specimens at predetermined time intervals, and each test specimen was cut to expose its cross section. After leaving the specimens to dry overnight in a dry room, the thickness of the core (hard part) of each test specimen was measured. The thickness loss was measured as the difference from the thickness before immersion (initial thickness, specifically 10 mm). The time change in the thickness loss of the test specimen was calculated based on the measured values ​​of the thickness loss of the test specimens measured for different immersion times. The thickness loss rate of a 10 mm thick test specimen was calculated (unit: mm / h) from the time change in the thickness loss of the test specimen within the range in which the time change in the thickness loss of the test specimen was linear.

[0078] (Measurement of Tensile Strength) The tensile strength of the PGA was measured in accordance with ISO527.

[0079] 1-2. Abrasive Grains Abrasive Grain 1: Polycrystalline diamond powder (Kemet Japan, median diameter 0.25 μm, irregular shape) Abrasive Grain 2: Polycrystalline diamond powder (Kemet Japan, median diameter 3.0 μm, irregular shape)

[0080] (Method for measuring median diameter) The median diameter of abrasive grains is measured by the following method.That is, using a laser diffraction particle size measuring instrument Mastersizer3000 (Malvern), the measurement temperature is 21 ° C, the dispersion medium is ion-exchanged water, the dispersion medium refractive index 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, and the measurement is performed under these conditions.The amount of abrasive grains added to the dispersion medium is adjusted so that the laser scattering intensity is 4% or more and 10% or less.

[0081] 2. Preparation and Evaluation of Polishing Pads (Tests 1 to 3) (1) Preparation of Polishing Pads (Kneading Process) The above PGA as a binder resin and the abrasive grains shown in Table 1 were weighed out to obtain the ratios shown in Table 1, and kneaded using a Laboplastomill (manufactured by Toyo Seiki Seisakusho) to obtain a composition. Kneading was performed at a predetermined heater temperature with a preheating time of 1 minute, a kneading time of 5 minutes, and a rotation speed of 50 rpm. The heater temperature was set to 250 ° C.

[0082] (Forming Process) Fig. 3 is a schematic diagram showing the components of a forming device 300 used in the examples. In the drawing, reference numeral 301 denotes a ferroelectric plate, and 302 denotes an aluminum foil.

[0083] A 0.5 mm thick SUS mold 303 with a 150 mm diameter hole was arranged as shown in Figure 3, and the kneaded composition 304 was set in the SUS mold 303 and press-molded to obtain a polishing pad 100 consisting of a polishing layer with a thickness of 0.5 mm, as shown in Figure 1. The temperature of the press was set to the same temperature as the heater temperature of the Labo Plastomill.

[0084] (2) Evaluation (Pretreatment of Polishing Pad) Since the abrasive grains of the polishing pad immediately after molding are embedded in the resin, the pad was sharpened with an #800 grindstone before a polishing test was carried out.

[0085] (Pre-processing of workpiece) The surface of a 20 x 20 mm square SiC substrate, which was the workpiece, was roughly polished on a copper surface plate using a slurry containing polycrystalline diamond with a median diameter of 1 µm, and then subjected to lapping.

[0086] 2, the polishing test was performed by mounting a polishing pad on a polishing apparatus 200. Specifically, the polishing pad was attached to a surface plate 210 (polishing plate) using a double-sided adhesive film (e.g., AS ONE OCA50-A4). The double-sided adhesive sheet was attached using a rubber roller or the like to prevent air bubbles from being trapped when attached to the polishing pad and polishing plate.

[0087] Next, the SiC substrate (20 x 20 mm square) that had been subjected to the above pre-processing as the workpiece 220 was pressed against the rotating polishing pad to perform polishing. The polishing conditions were as follows. At this time, the load of the jig (polishing head 230) and weight 240 was applied to the substrate. (Polishing conditions) Polishing device: Dialap ML-150P (manufactured by Marutoh Co., Ltd.) Polishing disc rotation speed: 100 rpm Polishing disc diameter: 150 mm diameter Forced drive or oscillation of workpiece: None Surface pressure: 250 gf / cm ２ Polishing liquid flow rate: 75 mL / h Polishing liquid: NaOH aqueous solution (20 ° C) with pH = 13

[0088] The polishing rate, the surface roughness of the workpiece and the depth of the damaged layer were measured by the following methods.

[0089] (1) Polishing Rate The thickness of the polished object was measured using an electric micrometer Millimar 1240 (manufactured by Mahr) while the object was attached to a jig. The thickness of the object was measured at five locations and the average value was used. The polishing rate was calculated from the polishing time (min) and the thickness reduction value (removal amount, μm).

[0090] (2) Surface Roughness of the Workpiece The arithmetic mean height Sa (μm) of the surface of the SiC substrate, which was the workpiece, after 2 hours of polishing was measured using a laser microscope VK-X260 (manufactured by Keyence Corporation) and used as the surface roughness. The measurement was performed using an objective lens with a magnification of 20 and an N.A. of 0.46.

[0091] Furthermore, the arithmetic mean height Sa (μm) of the surface of the SiC substrate after polishing was measured using an atomic force microscope (AFM) (scanning probe microscope SPI-3800 / SPA-300HV, manufactured by Seiko Instruments Inc.) under the following conditions: cantilever: SI-AF01, scanning area: 5000 nm × 5000 nm, scanning frequency: 1.00 Hz, atmosphere: air, temperature: room temperature (21° C.), and bias voltage: 0 V.

[0092] (3) Depth of Damaged Layer The cross section of the SiC substrate after 2 hours of polishing was observed using a transmission electron microscope (TEM), and the depth of the damaged layer was estimated from the obtained TEM image. Specifically, the measurement was performed using the following procedure. (Cross-Sectional TEM Sample) The cross-sectional TEM sample was prepared by microsampling and thinning using a focused ion beam device. Sampling was performed by taking a cross section perpendicular to the streak formed near the center of the polished surface. (TEM Observation) The TEM device used was a JEM-2100F field emission transmission electron microscope manufactured by JEOL Ltd. The acceleration voltage was 200 kV. The depth of the damaged layer was determined by reading the maximum depth from the scale bar in the observed image.

[0093] (Test 4) For comparison, a SiC substrate was polished using a tin surface plate (manufactured by Marutoh Co., Ltd., high polishing surface plate) used in precision polishing processes. In the polishing using the tin surface plate, a slurry (manufactured by Marutoh Co., Ltd.) containing abrasive grain 1 (polycrystalline diamond with a median diameter of 0.25 μm) was used as the polishing liquid. (Polishing conditions) Polishing device: Dialap ML-150P (manufactured by Marutoh Co., Ltd., tin surface plate) Polishing plate rotation speed: 100 rpm Polishing plate diameter: 150 mm diameter Forced drive or oscillation of the workpiece: None Surface pressure: 250 gf / cm ２ Flow rate of slurry: 50 g / h Then, in the same manner as above, the polishing rate, the surface roughness of the workpiece to be polished, and the depth of the damaged layer were measured by the following methods.

[0094] The construction of the polishing pads in Tests 1 to 4 and the evaluation results are shown in Table 1.

[0095]

[0096] As shown in Table 1, in Test 4, even though a polycrystalline diamond slurry with an average particle size of 0.25 μm was used, the depth of the damaged layer was as large as 120 nm. In contrast, in Test 1, it was found that the depth of the damaged layer could be reduced to 10 nm while suppressing a decrease in the polishing rate.

[0097] It is also clear that the surface roughness of the SiC substrate can be reduced by reducing the median diameter of the abrasive grains (comparison between Tests 1 and 2), and that the polishing rate can be increased by reducing the amount of abrasive grains (comparison between Tests 1 and 3).

[0098] This application claims priority based on Japanese Patent Application Nos. 2023-91781 and 2023-091782, filed June 2, 2023, and Japanese Patent Application No. 2023-119986, filed July 24, 2023. The contents of the specifications and drawings of these applications are incorporated herein by reference in their entirety.

[0099] According to the present invention, it is possible to provide a polishing pad that can reduce the damaged layer while suppressing a decrease in the polishing rate, and a method for polishing an object using the same.

[0100] REFERENCE SIGNS LIST 100 Polishing pad 110 Polishing layer 111 Base material 112 Abrasive grains 200 Polishing device 210 Surface plate 220 Object to be polished 230 Polishing head 230A Rotating shaft 240 Weight 250 Supply nozzle 301 Ferro plate 302 Aluminum foil 303 SUS mold 304 Composition

Claims

1. The polishing layer includes a composition containing a hydrolyzable resin and abrasive grains having a median diameter of less than 2 μm. Polishing pad.

2. The hydrolyzable resin is composed mainly of glycolic acid polymer. The polishing pad of claim 1 .

3. The content of the abrasive grains is 55% by mass or less relative to the total mass of the polishing layer. The polishing pad of claim 1 .

4. The method includes a step of polishing an object by sliding the polishing pad and the object to be polished relatively while supplying a polishing liquid containing water to the surface of the polishing layer of the polishing pad according to any one of claims 1 to 3. A method for polishing an object.

5. The object to be polished includes silicon carbide or gallium nitride. The method for polishing an object to be polished according to claim 4.

6. The polishing liquid is an alkaline aqueous solution. The method for polishing an object to be polished according to claim 4.