SLURRY COMPOSITION FOR POLISHING SiC SUBSTRATE AND POLISHING METHOD FOR SiC SUBSTRATE

Abstract

To provide a slurry composition for polishing a SiC substrate, which makes it possible to polish a SiC substrate with a high polishing rate.SOLUTION: A slurry composition for polishing a SiC substrate, comprises alumina abrasive grains, an oxidizing agent, and a dispersion medium, wherein the alumina abrasive grains include transition alumina having an α-conversion ratio of 80% or less, the alumina abrasive grains have an isoelectric point within a range of 8.0 to 10.0 inclusive, and the pH is within a range of 1 to 5 inclusive. The average secondary particle size of the transition alumina is preferably from 0.10 μm to 1.00 μm inclusive. The slurry composition for polishing a SiC substrate is preferably formulated to contain 1 mass% or more and 22 mass% or less of the alumina abrasive grains.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a slurry composition for polishing SiC substrates and a method for polishing SiC substrates. [Background technology]

[0002] The semiconductor material SiC (silicon carbide) is currently widely used as a substrate for devices. SiC substrates are produced, for example, by cutting a single-crystal SiC ingot produced by sublimation deposition and then performing chemical mechanical polishing (CMP) on the cut surface to remove irregularities, waviness, processing distortion, etc. from the cut surface and smooth the cut surface.

[0003] If the surface of a SiC substrate is uneven, wavy, or has residual processing damage, it becomes difficult to obtain the properties expected from the physical properties of SiC. Therefore, various slurries have been proposed for polishing SiC substrates to improve the smoothness of the SiC substrate.

[0004] For example, Patent Document 1 describes a CMP slurry containing alumina abrasive grains, an oxidizing agent, and a solvent, and having a pH of 0.5 to 6. The document also describes that a mixture of alpha alumina and transition alumina may be used as the alumina abrasive grains. The document also lists a SiC substrate as an object to be polished with the CMP slurry.

[0005] Patent Document 2 describes a polishing composition containing alumina abrasive grains and water. In the invention described in this document, the isoelectric point of the alumina abrasive grains is set to be less than 8.0 and lower than the pH of the polishing composition. This document lists alpha alumina and intermediate alumina as the alumina abrasive grains. This document also describes that the polishing composition is suitable for polishing silicon carbide.

[0006] Patent Document 3 describes a polishing composition containing abrasive grains, water, and a hydrophobic dispersion medium containing at least one selected from the group consisting of normal paraffin hydrocarbons, isoparaffin hydrocarbons, naphthenic hydrocarbons, and terpene hydrocarbons. The document also describes the use of aluminum oxide having an alpha conversion rate of 50% or more as the abrasive grains. The document also lists silicon carbide as an example of a material to be polished with the polishing composition.

[0007] A polishing composition for SiC substrates is required to be able to polish SiC substrates at a high removal rate and to provide the polished SiC substrate with a highly smooth surface. However, the inventions described in Patent Documents 1 to 3 do not fully satisfy this requirement.

[0008] Incidentally, Patent Document 4 describes a polishing slurry composition containing oxide abrasive grains, a dispersant containing an anionic organic dispersant or an inorganic dispersant, and an oxidizing agent, and having a pH of less than 7. The document also describes that it is preferable for the isoelectric point of the oxide abrasive grains to be higher than the pH of the polishing slurry, and that it is preferable to use α-alumina with an isoelectric point of 9.1 to 9.2 as the oxide abrasive grains. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2019-535146 [Patent Document 2] Japanese Patent Application Publication No. 2017-179221 [Patent Document 3] International Publication No. 2022 / 210744 [Patent Document 4] International Publication No. 2008 / 102672 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the polishing slurry composition described in Patent Document 4 is intended for polishing the surface of nitride crystals. The same document does not describe the use of the polishing slurry composition for polishing SiC substrates.

[0011] Therefore, an object of the present invention is to provide a slurry composition for polishing SiC substrates, which can polish SiC substrates at a high polishing rate and give the polished SiC substrates a highly smooth surface. [Means for solving the problem]

[0012] As a result of intensive research, the present inventors have found that by setting the pH of a slurry composition containing transition alumina having a specific alpha conversion rate and isoelectric point within a specific range, when the slurry composition is used to polish an SiC substrate, it is possible to improve the surface smoothness while maintaining a high polishing rate, and have thus completed the present invention. <1> ~ <8> This provides:

[0013] <1> A slurry composition for polishing SiC substrates, comprising alumina abrasive grains, an oxidizing agent, and a dispersion medium, The alumina abrasive grains contain transition alumina having an alpha conversion rate of 80% or less, The isoelectric point of the alumina abrasive grains is 8.0 or more and 10.0 or less, A slurry composition for polishing SiC substrates, having a pH of 1 or more and 5 or less.

[0014] <2> The average secondary particle diameter of the transition alumina is 0.1 μm or more and 1.0 μm or less. <1> 2. A slurry composition for polishing SiC substrates according to claim 1.

[0015] <3> The alumina abrasive grains are contained in an amount of 1 mass % or more and 22 mass % or less. <1> or <2> 2. A slurry composition for polishing SiC substrates according to claim 1.

[0016] <4> The oxidizing agent is at least one selected from the group consisting of permanganic acids, periodic acids, and peroxides. <1> ~ <3> 10. A slurry composition for polishing SiC substrates according to claim 1, wherein the slurry composition is a polishing agent.

[0017] <5> The oxidizing agent is contained in an amount of 0.1 mass % or more and 14 mass % or less. <1> ~ <4> 10. A slurry composition for polishing SiC substrates according to claim 1, wherein the slurry composition is a polishing agent.

[0018] <6> The pH is greater than 3 and not greater than 5, and is used for polishing the Si surface of a SiC substrate. <1> ~ <5> 10. A slurry composition for polishing SiC substrates according to claim 1, wherein the slurry composition is a polishing agent.

[0019] <7> The pH is 1 or more and 3 or less, and the polishing agent is used for polishing the C-face of a SiC substrate. <1> ~ <6> 10. A slurry composition for polishing SiC substrates according to claim 1, wherein the slurry composition is a polishing agent.

[0020] <8> 1. A method for polishing a SiC substrate, comprising: a step of contacting a SiC substrate with a slurry composition containing alumina abrasive grains, an oxidizing agent, and a dispersion medium, The alumina abrasive grains contain transition alumina having an alpha conversion rate of 80% or less, The isoelectric point of the alumina abrasive grains is 8.0 or more and 10.0 or less, A method for polishing a SiC substrate, wherein the pH of the slurry composition is 1 or more and 5 or less. [Effects of the Invention]

[0021] According to the slurry composition for polishing SiC substrates of the present invention, SiC substrates can be polished at a high polishing rate, and the polished SiC substrates have high smoothness. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail. The slurry composition for polishing SiC substrates of the present invention (hereinafter referred to as "the slurry composition of the present invention") contains alumina abrasive grains. In the present invention, the alumina abrasive grains contain transition alumina having an alpha conversion rate of 80% or less.

[0023] Transition alumina is alumina containing a crystalline phase other than the α-phase in its particles. In the present invention, transition alumina includes, as crystalline phases other than the α-phase, for example, χ-phase, κ-phase, γ-phase, δ-phase, and θ-phase. The transition alumina of the present invention may contain only one type of crystalline phase other than the α-phase, or may contain two or more types. Furthermore, the transition alumina of the present invention may contain an α-phase or may not contain an α-phase. Whether or not the alumina particles contain a crystalline phase other than the α-phase can be determined by whether or not a peak other than 57.5° is observed in the range of 2θ=55.8° to 58.9° in an X-ray diffraction pattern measured by powder X-ray diffractometry.

[0024] In the present invention, the alpha phase ratio of transition alumina is 80% or less. The alpha phase ratio is the proportion of the alpha phase in the alumina crystal phase of transition alumina. When transition alumina does not contain the alpha phase, the alpha phase ratio is 0%. When transition alumina contains the alpha phase, the alpha phase ratio is more than 0%. By setting the alpha phase ratio of transition alumina to 80% or less, it is possible to polish SiC substrates at a high polishing rate, and the smoothness of the polished SiC substrates is high. From the viewpoint of further enhancing the effects of the present invention, the alpha phase ratio of transition alumina is preferably 0% or more and 80% or less, more preferably 20% or more and 70% or less, and even more preferably 40% or more and 60% or less. The alpha phase ratio of transition alumina can be measured by the method described in the examples.

[0025] Transition alumina can be produced, for example, by calcining aluminum hydroxide, aluminum sulfate, alums such as aluminum potassium sulfate and aluminum ammonium sulfate, ammonium aluminum carbonate, etc. The gelatinization rate of transition alumina can be adjusted by adjusting the calcination time and calcination temperature of the raw material alumina, and the calcination time and calcination temperature can be appropriately determined depending on the desired gelatinization rate of transition alumina, and are matters within the scope of common technical knowledge of a person skilled in the art.

[0026] The alumina abrasive grains used in the present invention may contain other aluminas in addition to transition alumina having an alpha phase ratio of 80% or less. However, from the viewpoint of further enhancing the effects of the present invention, the content of other aluminas in the alumina abrasive grains is preferably less than the content of transition alumina having an alpha phase ratio of 80% or less. Specifically, the content of transition alumina having an alpha phase ratio of 80% or less in the alumina abrasive grains is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and the alumina abrasive grains may be substantially composed of only the above transition alumina. Examples of other aluminas include transition alumina having an alpha phase ratio of more than 80% and alpha alumina that does not contain any crystalline phase other than the alpha phase in the particles.

[0027] The alumina abrasive grains used in the present invention have an isoelectric point of 8.0 or more and 10.0 or less. By setting the isoelectric point within this range, SiC substrates can be polished at a high polishing rate, and the polished SiC substrates have high surface smoothness. From the viewpoint of further enhancing the effects of the present invention, the isoelectric point of the alumina abrasive grains is preferably 8.2 or more and 9.8 or less, and more preferably 8.5 or more and 9.5 or less. The isoelectric point of the alumina abrasive grains can be measured by the method described in the Examples. When the alumina abrasive grains used in the present invention consist solely of the above-mentioned transition alumina, the isoelectric point of the alumina abrasive grains is the isoelectric point of the above-mentioned transition alumina.

[0028] In the present invention, the isoelectric point of the alumina abrasive grains can be adjusted to the above-mentioned range by using, for example, a mineral acid (particularly nitric acid) such as nitric acid, sulfuric acid, or phosphoric acid as a dispersant when grinding the alumina abrasive grains. If, for example, oxalic acid or ammonium polyacrylate is used as a dispersant, the isoelectric point of the alumina abrasive grains will fall outside the above-mentioned range, as will be shown in the examples described below. There are no particular restrictions on the amount of dispersant used, and a known amount may be used.

[0029] The inventors of the present invention believe that the reason why the alumina abrasive grains of the present invention contain transition alumina with an alpha conversion rate of 80% or less and have an isoelectric point of 8.0 or more and 10.0 or less can polish SiC substrates at a high polishing rate and achieve high smoothness of the polished SiC substrates is as follows. It is known that the alpha conversion rate of alumina affects the hardness of alumina. It is also known that the isoelectric point is determined by the surface condition of alumina. The inventors speculate that by setting the alpha conversion rate and isoelectric point within specific ranges, the hardness and surface condition of the alumina abrasive grains can polish SiC substrates at a high polishing rate, and the polished SiC substrates have high smoothness.

[0030] From the viewpoint of further enhancing the effects of the present invention, the alumina abrasive grains of the present invention preferably have an average secondary particle size of 0.10 μm or more and 1.00 μm or less, more preferably 0.12 μm or more and 0.40 μm or less, and even more preferably 0.13 μm or more and 0.35 μm or less. The average secondary particle size of the alumina abrasive grains can be measured by the method described in the Examples.

[0031] There are no particular restrictions on the primary particle size of alumina abrasive grains, provided that the average secondary particle size is within the above-mentioned range. Secondary particles are particles formed by agglomeration of multiple primary particles that behave as if they were a single particle. Primary particles are objects that can be recognized as the smallest particle unit, judging from their external geometric shape.

[0032] There are no particular limitations on the shape of the primary particles of the alumina abrasive grains of the present invention, and they may have various shapes, such as spherical, flaky, and polyhedral shapes.

[0033] From the viewpoint of further enhancing the effects of the present invention, the content of alumina abrasive grains in the slurry composition of the present invention is preferably 1% by mass or more and 22% by mass or less, more preferably 2% by mass or more and 20% by mass or less, even more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 3% by mass or more and 10% by mass or less.

[0034] The slurry composition of the present invention contains an oxidizing agent. Any known oxidizing agent can be used as the oxidizing agent without any particular limitation. Specific examples of the oxidizing agent include peroxides, nitric acid compounds, persulfuric acid compounds, chlorine compounds, bromine compounds, periodic acids, ferric acids, permanganic acids, chromic acids, vanadic acids, molybdic acids, and tungstic acids. In the present invention, one of the oxidizing agents may be used alone, or two or more may be used in combination.

[0035] The peroxide may, for example, be hydrogen peroxide. Examples of nitric acid compounds include nitric acid, nitrates such as iron nitrate, silver nitrate and aluminum nitrate, and nitric acid complexes such as cerium ammonium nitrate. Persulfate compounds include persulfates such as peroxomonosulfuric acid and peroxodisulfuric acid; and persulfates such as ammonium persulfate and potassium persulfate. Examples of chlorine compounds include chloric acid, perchloric acid, and perchlorates such as potassium perchlorate. Bromine compounds include, for example, bromic acid and bromates such as potassium bromate. Examples of ferrates include ferric acid and ferrates such as potassium ferrate. Periodates include periodic acid and periodate salts such as sodium periodate and potassium periodate. Examples of permanganates include permanganic acid and permanganate salts such as sodium permanganate and potassium permanganate. Examples of chromates include chromic acid and chromates such as potassium chromate and potassium dichromate. Examples of vanadic acids include vanadic acid and vanadates such as ammonium vanadate, sodium vanadate, and potassium vanadate. Examples of molybdic acids include molybdic acid and molybdates such as ammonium molybdate and disodium molybdate. Examples of tungstic acids include tungstic acid and tungstates such as disodium tungstate.

[0036] From the viewpoint of further enhancing the effects of the present invention, the slurry composition of the present invention preferably contains, as an oxidizing agent, at least one selected from the group consisting of peroxides, permanganic acids, and periodic acids, more preferably contains permanganic acids, and even more preferably contains a permanganate.

[0037] From the viewpoint of further enhancing the effects of the present invention, the content of the oxidizing agent in the slurry composition of the present invention is preferably 0.1 mass % or more and 14 mass % or less, more preferably 0.3 mass % or more and 7 mass % or less, and even more preferably 0.4 mass % or more and 5 mass % or less.

[0038] The slurry composition of the present invention contains a dispersion medium. Specific examples of the dispersion medium include water and water-soluble organic solvents. Examples of water include tap water, distilled water, pure water, ultrapure water, and ion-exchanged water. Examples of water-soluble organic solvents include monohydric alcohols, glycols, amides, sulfoxides, and pyrrolidones.

[0039] Examples of monohydric alcohols include methanol, ethanol, isopropanol, n-butanol, and methylisocarbinol. Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, and polypropylene glycol. Examples of amides include N,N-dimethylformamide and N,N-dimethylacetamide. Examples of sulfoxides include dimethyl sulfoxide. Examples of pyrrolidones include pyrrolidones such as methylpyrrolidone and N-methyl-2-pyrrolidone.

[0040] The dispersion medium contained in the slurry composition of the present invention preferably does not contain a water-insoluble organic solvent. If a water-insoluble organic solvent is contained, the alumina abrasive grains and the oxidizing agent are difficult to disperse in the slurry composition, which results in a decrease in the polishing rate for the SiC substrate and a high possibility of reducing the surface smoothness of the SiC substrate after polishing. Examples of water-insoluble organic solvents include aromatic hydrocarbons, normal paraffin hydrocarbons, isoparaffin hydrocarbons, naphthenic hydrocarbons, and terpene hydrocarbons.

[0041] Examples of aromatic hydrocarbons include benzene, toluene, and xylene. Examples of normal paraffin hydrocarbons include linear hydrocarbons having 5 to 30 carbon atoms, liquid paraffin, kerosene, and light oil. Examples of isoparaffin hydrocarbons include branched hydrocarbons having 5 to 40 carbon atoms and liquid isoparaffin. Examples of naphthenic hydrocarbons include cyclic hydrocarbons having 5 to 40 carbon atoms. Examples of terpene hydrocarbons include chain terpene hydrocarbons such as myrcene, farnesene, and citral; and cyclic terpene hydrocarbons such as menthol, cineole, pinene, limonene, α-terpinene, γ-terpinene, camphene, phellandrene, terpinene, terpinolene, p-cymene, and cedrene.

[0042] From the viewpoint of further increasing the polishing rate for SiC substrates, the content of the dispersion medium in the slurry composition of the present invention is preferably 60% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 95% by mass or less, and even more preferably 75% by mass or more and 95% by mass or less.

[0043] The slurry composition of the present invention preferably contains a pH adjuster. The slurry composition of the present invention has a specific pH value, as described below. The pH adjuster is used to adjust the pH of the slurry composition. In the present invention, known pH adjusters can be used without any particular limitation. Specific examples of pH adjusters include inorganic acids such as nitric acid, sulfuric acid, and phosphoric acid, and organic acids such as acetic acid and citric acid. In the present invention, one of the pH adjusters may be used alone, or two or more may be used in combination. From the viewpoint of further enhancing the effects of the present invention, it is preferable to use an inorganic acid as the pH adjuster. There is no particular limitation on the content of the pH adjuster in the slurry composition of the present invention, and the content of the pH adjuster in the slurry composition can be appropriately determined depending on the desired pH.

[0044] The slurry composition of the present invention may contain a dispersing aid. Any known dispersing aid can be used without any particular limitation. Specific examples of dispersing aids include phosphate compounds such as potassium phosphate, sodium phosphate, ammonium phosphate, and calcium phosphate; hydrogen phosphate compounds such as potassium hydrogen phosphate, sodium hydrogen phosphate, ammonium hydrogen phosphate, and calcium hydrogen phosphate; and monopolymers of unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, or ammonium salts or amine salts of such monopolymers. One of the dispersing agents may be used alone, or two or more may be used in combination. The content of the dispersing aid in the slurry composition of the present invention is preferably 0.1 to 50 parts by weight, more preferably 0.1 to 20 parts by weight, and particularly preferably 0.1 to 10 parts by weight, per 100 parts by weight of the alumina abrasive grains.

[0045] As a result of extensive research, the present inventors have found that there is a pH suitable for polishing SiC substrates. That is, the pH of the slurry composition of the present invention is 1 or more and 5 or less. By setting the pH to 1 or more and 5 or less, it is possible to polish SiC substrates at a high polishing rate. The pH of the slurry composition in the present invention is a value measured at 25°C. For example, a pH meter D-51 manufactured by Horiba, Ltd. can be used for the measurement.

[0046] The slurry composition of the present invention is capable of polishing both the Si face and the C face of a SiC substrate at a high polishing rate. The present inventors further investigated the relationship between the pH of the slurry composition and the polishing rate of a SiC substrate and found that the polishing rates of the Si face and the C face of a SiC substrate can be further increased by adjusting the pH range. Specifically, when polishing the Si face of a SiC substrate, the polishing rate of the Si face can be further increased by adjusting the pH of the slurry composition of the present invention to more than 3 and not more than 5, preferably 3.2 or more and 4.8 or less, and more preferably 3.6 or more and 4.4 or less. When polishing the C-face of a SiC substrate, the polishing rate of the C-face can be further increased by adjusting the pH of the slurry composition of the present invention to 1 or more and 3 or less, preferably 1.3 or more and 2.7 or less, and more preferably 1.6 or more and 2.4 or less. The pH of the slurry composition can be adjusted by adding the pH adjusters described above to the slurry composition.

[0047] The slurry composition of the present invention is used as a polishing slurry when performing CMP treatment on a SiC substrate.

[0048] The slurry composition of the present invention can be produced, for example, by mixing a mixture prepared by adding transition alumina and an oxidizing agent, and optionally a dispersing aid and a pH adjuster, to a dispersion medium. In the present invention, the slurry composition may be prepared by simultaneously adding the transition alumina, the oxidizing agent, the dispersing aid, and the pH adjuster to the dispersion medium and mixing them. Alternatively, the slurry composition may be prepared by previously preparing a first liquid containing the transition alumina, the dispersing aid, the pH adjuster, and the dispersion medium, and a second liquid containing the oxidizing agent and the dispersion medium, and mixing the first liquid and the second liquid at the time of use. In the present invention, from the viewpoints of economy and ease of handling, it is preferable to prepare the slurry composition by mixing the first liquid and the second liquid. There are no particular limitations on the conditions for producing the slurry composition, and known conditions may be used.

[0049] Next, the method for polishing a SiC substrate of the present invention will be described. The method for polishing a SiC substrate of the present invention includes a step of bringing the slurry composition of the present invention into contact with the SiC substrate and polishing the SiC substrate when performing CMP on the SiC substrate. The conditions for contacting the slurry composition with the SiC substrate are not particularly limited, and known conditions may be used.

[0050] In the method for polishing a SiC substrate of the present invention, when polishing the Si face of a SiC substrate, the pH of the slurry composition is preferably adjusted to more than 3 and not more than 5, more preferably adjusted to 3.2 or more and not more than 4.8, and even more preferably adjusted to 3.6 or more and not more than 4.4. By setting the pH of the slurry composition within the above range, the polishing rate for the Si face can be increased.

[0051] In the method for polishing a SiC substrate of the present invention, when polishing the C-face of a SiC substrate, the pH of the slurry composition is preferably adjusted to 1 or more and 3 or less, more preferably 1.3 or more and 2.7 or less, and even more preferably 1.6 or more and 2.4 or less. By setting the pH of the slurry composition within the above range, the polishing rate for the C-face can be increased. [Example]

[0052] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0053] [Production Example 1] 1000 g of transition alumina consisting of the gamma phase and having a gelatinization rate of 0% and 11.5 g of nitric acid were added to water and pulverized using a wet bead mill to an average secondary particle diameter of 0.15 μm, producing transition alumina dispersion A-1. The gelatinization rate, isoelectric point, and average particle diameter of the transition alumina contained in transition alumina dispersion A-1 were measured by the following methods. The isoelectric point of transition alumina A-1 was 9.

[0054] [Production Example 2] Transition alumina dispersion A-2 was produced in the same manner as in Production Example 1, except that transition alumina having a gelatinization rate of 50% and the remainder being γ phase was used and pulverization was carried out under conditions such that the average secondary particle size became 0.20 μm. The transition alumina contained in transition alumina dispersion A-2 had an isoelectric point of 9.

[0055] [Production Example 3] Transition alumina dispersion A-3 was produced in the same manner as in Production Example 1, except that transition alumina having an 80% gelatinization rate and the remainder being γ phase was used and pulverization was carried out under conditions such that the average secondary particle size became 0.20 μm. The transition alumina contained in transition alumina dispersion A-3 had an isoelectric point of 9.

[0056] [Production Example 4] Transition alumina dispersion A'-1 was produced in the same manner as in Production Example 1, except that transition alumina having a gelatinization rate of 97% and the remainder being γ phase was used and pulverization was carried out under conditions such that the average secondary particle size became 0.25 μm. The transition alumina contained in transition alumina dispersion A'-1 had an isoelectric point of 9.

[0057] [Production Example 5] A transition alumina dispersion A'-2 was produced in the same manner as in Production Example 2, except that 50 g of oxalic acid was used instead of 11.5 g of nitric acid and pulverization was performed under conditions such that the average secondary particle diameter became 0.20 μm. The transition alumina contained in the transition alumina dispersion A'-2 had an isoelectric point of 5. [Production Example 6] A transition alumina dispersion A'-3 was produced in the same manner as in Production Example 2, except that 96 g of ammonium polyacrylate was used instead of 11.5 g of nitric acid and pulverization was performed under conditions such that the average secondary particle diameter became 0.20 μm. The transition alumina contained in the transition alumina dispersion A'-3 had an isoelectric point of 4.

[0058] [Method for measuring the alpha conversion rate] The transition alumina was analyzed by powder X-ray diffraction. The measurement conditions for powder X-ray diffraction were as follows. The following values ​​were determined from the diffraction spectrum. The measurement apparatus and measurement conditions are as follows. S: Peak integrated counts at 2θ = 55.8° to 58.9° Time required to measure TS:S BN1: Counts at 2θ = 55.8° BN2: Counts at 2θ=58.9° TBN: Time required to measure BN1 and BN2 From the obtained values, the peak area (SP) was calculated based on the following formula. SP = S - (BN1 + BN2) / 2 × (TS / TBN) The same measurement was also carried out on alumina with a gelatinization rate of 100% (product name CR1, manufactured by Baikowski SA), and the peak (S100) of the alumina was calculated. The gelatinization rate was calculated from the calculated SP and S100 using the following formula. αization rate (%)=(SP / S100)×100

[0059] Measurement conditions Equipment: Bruker D2 PHASER X-ray generating voltage: 30 kV Radiation: Cu-Kα1 line (λ=1.56060Å) Current: 10mA Scan Speed: 1.2 degrees / minute Measurement step width: 0.02 degrees / minute

[0060] [Method for measuring isoelectric point] The pH of an alumina dispersion with an abrasive concentration adjusted to 0.1% by mass was adjusted from 2 to 11 using HCl or NaOH, and the zeta potential was measured at each pH value. The pH at which the zeta potential was 0 mV was defined as the isoelectric point. An ELSZneo manufactured by Otsuka Electronics Co., Ltd. was used for the measurements.

[0061] [Method for measuring average secondary particle size] The slurry was adjusted to an appropriate concentration with pure water, and after two minutes of ultrasonic treatment, the average secondary particle size was measured using a Horiba LA-950.

[0062] In order to confirm the effects of the present invention, the following Studies 1 to 4 were conducted. The numerical values ​​in the columns for components in the following Tables 1 to 3 are in mass %. Transition aluminas A-1 to A-3 and A'-1 to A'-3 in Tables 1 to 3 refer to the following transition aluminas. The numerical values ​​in the columns for transition aluminas A-1 to A-3 and A'-1 to A'-3 in Tables 1 to 3 are the contents of transition alumina contained in the slurry composition.

[0063] Transition alumina A-1: ​​Transition alumina contained in transition alumina dispersion A-1 (alpha conversion rate: 0%, isoelectric point: 9) Transition alumina A-2: Transition alumina contained in transition alumina dispersion A-2 (alpha conversion rate: 50%, isoelectric point: 9) Transition alumina A-3: Transition alumina contained in transition alumina dispersion A-3 (alpha conversion rate: 80%, isoelectric point: 9) Transition alumina A'-1: Transition alumina contained in transition alumina dispersion A'-1 (alpha conversion rate: 97%, isoelectric point: 9) Transition alumina A'-2: Transition alumina contained in transition alumina dispersion A'-2 (alpha conversion rate: 50%, isoelectric point: 5) Transition alumina A'-3: Transition alumina contained in transition alumina dispersion A'-3 (alpha conversion rate: 50%, isoelectric point: 4)

[0064] [Consideration 1] In this study, we investigated the effect of the alpha conversion rate of alumina abrasive grains on the polishing rate and the surface roughness of SiC substrates after polishing.

[0065] [Preparation of Slurry Compositions of Examples 1 to 3 and Comparative Example 1] The transition alumina dispersions produced in the Production Examples, nitric acid, and water were mixed so that the contents of each component and pH were as shown in Table 1, to prepare the slurry compositions of Examples 1 to 3 and Comparative Example 1.

[0066] The prepared slurry composition was used to polish the C-face of a SiC wafer, and the polishing rate was calculated. The polishing conditions and the method for measuring the polishing rate are as follows. In addition, the center line average surface roughness (Ra) of the polished SiC wafer was measured by the method described below. The results are shown in Table 1.

[0067] [Polishing rate] The C-side of a φ4-inch SiC wafer was polished using the slurry composition. A φ15-inch single-side polisher manufactured by LAPMASTER was used as the polishing device, and a polyurethane pad was used as the polishing pad. The polishing conditions were as follows: The mass of the SiC wafer before and after polishing was measured using a precision balance (model name: AG0204, manufactured by Mettler Toledo), and the mass difference between the SiC wafer before and after polishing was calculated. The calculated mass difference was divided by the polishing time to calculate the polishing rate. The results are shown in Table 1.

[0068] [Polishing conditions] Polishing pad rotation speed: 50 rpm Wafer rotation speed: 30 rpm Polishing pressure: 200g / cm 2 Slurry supply rate: 10ml / min Polishing time: 45 minutes

[0069] [Surface roughness] The polished SiC wafer was washed and then dried. The centerline average surface roughness (Ra) of the dried SiC wafer was measured over a 10 μm × 10 μm area using an atomic force microscope (ICON, manufactured by Bruker). The results are shown in Table 1.

[0070] [Table 1]

[0071] As is clear from the results in Table 1, the slurry compositions of Examples 1 to 3 were able to polish SiC wafers at a polishing rate equivalent to that of the slurry composition of Comparative Example 1. Furthermore, the C-faces of the SiC wafers polished using the slurries of Examples 1 to 3 had smaller center line average surface roughness (Ra) than the C-face of the SiC wafer polished using the slurry composition of Comparative Example 1. This result demonstrates that by setting the alpha conversion rate of transition alumina to a value specified in the present invention, SiC substrates with high smoothness can be obtained at a high polishing rate.

[0072] [Consideration 2] In this study, the influence of the pH of the slurry composition on the polishing rate of the C-face of the SiC substrate and the influence on the surface smoothness of the C-face after polishing were evaluated.

[0073] Slurry compositions of Example 4 and Comparative Example 2 were prepared in the same manner as in Example 2, except that the amount of pH adjuster (nitric acid) used was adjusted so that the pH of the slurry composition would be the value shown in Table 2. The polishing rates of the slurry compositions of Example 4 and Comparative Example 2 were measured by the method described above. The results are shown in Table 2 together with the results of Example 2 and Comparative Example 1.

[0074] [Table 2]

[0075] As is clear from Table 2, the slurry compositions of Examples 2 and 4 had higher polishing rates for the C-face of the SiC wafer than the slurry composition of Comparative Example 2. Furthermore, the C-face of the SiC wafer polished using the slurries of Examples 2 and 4 had clearly smaller center line average surface roughness (Ra) than the C-face of the SiC wafer polished using the slurry composition of Comparative Example 1. This result shows that by adjusting the pH of the slurry composition to the value specified in the present invention, the C-face of the SiC substrate can be polished at a high polishing rate, and the C-face of the SiC substrate after polishing has high surface smoothness.

[0076] As is clear from Table 2, the slurry composition of Example 2 had a higher polishing rate for the C-face of the SiC wafer than the slurry composition of Example 4. Furthermore, the center line average surface roughness (Ra) of the C-face of the SiC wafer polished with the slurry composition of Example 2 was clearly smaller than the center line average surface roughness (Ra) of the C-face polished with the slurry composition of Example 4. This result indicates that by adjusting the pH of the slurry composition to 1 or more and 3 or less, the polishing rate for the C-face of the SiC wafer can be further increased, and the C-face of the polished SiC substrate can have a high surface smoothness.

[0077] [Consideration 3] In this study, the influence of the pH of the slurry composition on the polishing rate of the Si surface of the SiC substrate and the influence on the surface smoothness of the Si surface after polishing were evaluated.

[0078] The slurry compositions of Examples 5 and 6 and Comparative Examples 3 and 4 were prepared in the same manner as in Example 2, except that the amount of pH adjuster (nitric acid) used was adjusted so that the pH of the slurry composition would be the value shown in Table 3. The polishing rates of the Si surface and the centerline average surface roughness (Ra) of the polished Si surface were measured for the slurry compositions of Examples 5 and 6 and Comparative Examples 3 and 4. The polishing rates were measured by polishing the Si surface of a SiC substrate using the method described above. The centerline average surface roughness (Ra) of the Si surface was also measured using the method described above. The results are shown in Table 3.

[0079] [Table 3]

[0080] As is clear from Table 3, the slurry compositions of Examples 5 and 6 had higher polishing rates for the Si face of the SiC wafer than the slurry compositions of Comparative Examples 3 and 4. Furthermore, the Si faces of the SiC wafers polished using the slurries of Examples 5 and 6 had clearly smaller center line average surface roughness (Ra) than the Si faces of the SiC wafers polished using the slurry compositions of Comparative Examples 3 and 4. These results demonstrate that by adjusting the pH of the slurry composition to the value specified in the present invention, the Si face of the SiC substrate can be polished at a high polishing rate, and the Si face of the polished SiC substrate has a high surface smoothness.

[0081] As is clear from Table 3, the slurry composition of Example 6 had a higher polishing rate for the Si face of the SiC wafer than the slurry composition of Example 5. The center line average surface roughness (Ra) of the Si face of the SiC wafer polished with the slurry composition of Example 6 was almost the same as the center line average surface roughness (Ra) of the Si face polished with the slurry composition of Example 5. This result indicates that by adjusting the pH of the slurry composition to more than 3 and not more than 5, it is possible to further increase the polishing rate for the Si face of the SiC wafer while improving the surface smoothness of the Si face after polishing.

[0082] [Consideration 4] In this study, we evaluated the effect of the isoelectric point of alumina abrasive grains on the polishing rate of SiC substrates and the surface smoothness after polishing.

[0083] Slurry compositions of Comparative Examples 5 and 6 were prepared in the same manner as in Example 2, except that transition alumina A'-2 or transition alumina A'-3 was used instead of transition alumina A-2. The polishing rates of the slurry compositions of Comparative Examples 5 and 6 and the surface roughness of the polished C-face of the SiC wafer were measured by the methods described above. The results are shown in Table 4 together with the results of Example 2.

[0084] [Table 4]

[0085] As is clear from the results in Table 4, the slurry composition of Example 2 was able to polish the C-face of the SiC wafer at a higher polishing rate than the slurry compositions of Comparative Examples 5 and 6. Furthermore, the C-face of the SiC wafer polished with the slurry composition of Example 2 had a smaller center line average surface roughness (Ra) than the C-face of the SiC wafer polished with the slurry compositions of Comparative Examples 5 and 6. This result demonstrates that by setting the isoelectric point of transition alumina to the value specified in the present invention, it is possible to obtain a SiC substrate with high smoothness at a high polishing rate.

Claims

1. A slurry composition for polishing SiC substrates, comprising alumina abrasive grains, an oxidizing agent, and a dispersion medium, The alumina abrasive grains contain transition alumina having an alpha conversion rate of 80% or less, The isoelectric point of the alumina abrasive grains is 8.0 or more and 10.0 or less, A slurry composition for polishing SiC substrates, having a pH of 1 or more and 5 or less.

2. 2. The slurry composition for polishing SiC substrates according to claim 1, wherein the transition alumina has an average secondary particle size of 0.10 μm or more and 1.00 μm or less.

3. 2. The slurry composition for polishing SiC substrates according to claim 1, containing 1 mass % or more and 22 mass % or less of the alumina abrasive grains.

4. 2. The slurry composition for polishing SiC substrates according to claim 1, wherein the oxidizing agent is at least one selected from the group consisting of permanganic acids, periodic acids, and peroxides.

5. 2. The slurry composition for polishing SiC substrates according to claim 1, containing 0.1 mass % or more and 14 mass % or less of the oxidizing agent.

6. 2. The slurry composition for polishing SiC substrates according to claim 1, which has a pH greater than 3 and equal to or less than 5 and is used for polishing the Si surface of a SiC substrate.

7. 2. The slurry composition for polishing SiC substrates according to claim 1, which has a pH of 1 or more and 3 or less and is used for polishing the C-face of a SiC substrate.

8. 1. A method for polishing a SiC substrate, comprising: a step of contacting a SiC substrate with a slurry composition containing alumina abrasive grains, an oxidizing agent, and a dispersion medium, the method comprising: The alumina abrasive grains contain transition alumina having an alpha conversion rate of 80% or less, The isoelectric point of the alumina abrasive grains is 8.0 or more and 10.0 or less, A method for polishing a SiC substrate, wherein the pH of the slurry composition is 1 or more and 5 or less.

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