Polishing composition

Abstract

[Problem] The present invention addresses the problem of providing a polishing composition which is capable of further improving the polishing speed of an object to be polished such as silicon carbide, and is capable of maintaining the properties of the polishing composition even if stored at relatively high temperatures. [Solution] The present invention provides a polishing composition which contains an oxidizing agent, a zirconium (IV) salt that serves as a metal salt, and an aqueous medium.

Description

polishing composition

[0001] The present invention relates to a polishing composition.

[0002] Silicon carbide (SiC) semiconductors have higher breakdown fields, electron saturation drift velocities, and thermal conductivities than silicon semiconductors. Therefore, research and development is being conducted to realize power devices that can operate at higher temperatures and speeds than conventional silicon devices. In particular, the development of highly efficient switching elements for use in power sources for driving motors in electric motorcycles, electric vehicles, hybrid cars, and the like is attracting attention. To realize such power devices, silicon carbide single crystal substrates with smooth surfaces are required for epitaxially growing high-quality silicon carbide semiconductor layers.

[0003] Furthermore, blue laser diodes have been attracting attention as light sources for recording information at high density, and there is also a growing need for white diodes as light sources to replace fluorescent lamps and incandescent lamps.

[0004] Such light-emitting devices are fabricated using gallium nitride (GaN) semiconductors, and silicon carbide single crystal substrates are used as substrates for forming high-quality gallium nitride semiconductor layers.

[0005] Silicon carbide single crystal substrates for such applications require high processing precision in terms of substrate flatness, substrate surface smoothness, etc. However, silicon carbide single crystals have extremely high hardness, making them difficult to process when fabricating substrates.

[0006] Therefore, Patent Document 1 attempts to solve the above problem by providing an abrasive for chemically and mechanically polishing a silicon carbide (SiC) single crystal substrate, which comprises an oxidizing agent that is permanganate ions, silica particles having an average secondary particle size of 0.2 μm or less, and a dispersion medium, wherein the content of the oxidizing agent is 0.25% by mass or more and 5% by mass or less, and the content of the silica particles is 0.01% by mass or more and less than 20% by mass.

[0007] Furthermore, Patent Document 2 attempts to achieve a high removal rate of amorphous carbon by providing a slurry for chemical mechanical polishing (CMP) that contains an aqueous liquid carrier, a transition metal oxy-compound such as an oxy-nitrate, and a per-based oxidizing agent.

[0008] International Publication No. 2013 / 035539 Special Publication No. 2023-512216

[0009] However, it was found that the polishing composition of Patent Document 1 could not sufficiently increase the removal rate, and that the properties of the polishing composition changed when stored at a relatively high temperature. It was also found that the polishing composition of Patent Document 2 had poor properties that could be maintained.

[0010] Therefore, an object of the present invention is to provide a polishing composition that can further improve the polishing rate of an object to be polished, such as silicon carbide, and can maintain the properties of the polishing composition even when stored at a relatively high temperature.

[0011] The above-mentioned problems are solved by providing a polishing composition containing an oxidizing agent, a zirconium (IV) salt as a metal salt, and an aqueous medium.

[0012] According to the present invention, it is possible to provide a polishing composition that can further improve the polishing rate of an object to be polished, such as silicon carbide, and can maintain the properties of the polishing composition even when stored at a relatively high temperature.

[0013] The present invention is described in detail below. In this specification, "X to Y" means "X or more and Y or less," with the numerical values ​​(X and Y) before and after it being used as upper and lower limits. When multiple "X to Y" are described, for example, when "X1 to Y1 or X2 to Y2" is described, disclosures with each numerical value as an upper limit, disclosures with each numerical value as a lower limit, and combinations of these upper and lower limits are all disclosed (i.e., serve as legitimate grounds for amendment). Specifically, amendments to X1 or more, amendments to Y2 or less, amendments to X1 or less, amendments to Y2 or more, amendments between X1 and X2, amendments between X1 and Y2, etc., must all be deemed legitimate. Furthermore, when features or aspects of the present disclosure are described in terms of a Markush group, those skilled in the art will recognize that the present disclosure is thereby described in terms of any individual component or subgroup of components of the Markush group. Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20-25°C) and a relative humidity of 40-50% RH. The concentrations described herein may be concentrations at the point of use (POU) or concentrations before dilution to the POU concentration. The dilution ratio may be 2-10 times. It should be understood that all combinations of embodiments and descriptions disclosed herein are disclosed in this application. In other words, they should be understood as a basis for correction. Furthermore, when the content or concentration of each component is described, if two or more components are included, it may be the total amount.

[0014] The present invention provides a polishing composition comprising an oxidizing agent, a zirconium (IV) salt as a metal salt, and an aqueous medium. This composition can further improve the polishing rate of a polishing object such as silicon carbide, and can maintain the properties of the polishing composition even when stored at a relatively high temperature. The composition of the polishing composition of the present invention will be described in detail below.

[0015] [Metal Salt] The metal salt disclosed in this specification is a compound composed of a metal cation and an anion. The polishing composition of the present invention contains a zirconium (IV) salt as the metal salt. The zirconium in the zirconium (IV) salt of the present invention becomes a cation in the polishing composition. In addition, in the present invention, the cation is composed of a single zirconium atom. In other words, the zirconium cation is a cation composed solely of zirconium. By using a polishing composition containing a zirconium (IV) salt as a metal salt in addition to an oxidizing agent, the polishing rate of a polishing object such as silicon carbide can be further improved, and the properties of the polishing composition can be maintained even when stored at a relatively high temperature.

[0016] In some embodiments, the zirconium (IV) salt may be an inorganic acid salt or an organic acid salt. Examples of inorganic acid salts include salts of hydrohalic acids such as hydrochloric acid, hydrobromic acid, and hydrofluoric acid, as well as salts of nitric acid, sulfuric acid, carbonic acid, silicic acid, boric acid, and phosphoric acid. In some embodiments, examples of organic acid salts include salts of organic carboxylic acids such as formic acid, acetic acid, propionic acid, benzoic acid, glycine acid, butyric acid, citric acid, tartaric acid, and trifluoroacetic acid; organic sulfonic acids such as methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, and toluenesulfonic acid; organic phosphonic acids such as methylphosphonic acid, benzenephosphonic acid, and toluenephosphonic acid; and organic phosphoric acids such as ethylphosphoric acid. Among these, salts of hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid are preferred, salts of hydrochloric acid, nitric acid, and sulfuric acid are more preferred, and salts of hydrochloric acid and nitric acid are even more preferred.

[0017] In some embodiments, the metal salt may comprise a zirconium cation and a nitrate ion (NO ３－ ) and chloride anion (Cl － ) is used. The zirconium cation, which is a cation composed of zirconium alone, is different from the zirconyl ZrO ion used in the comparative example. To give a specific example, the structure of zirconium nitrate is Zr(NO ３ ) ４ As shown in the figure, the central metal is IV-valent Zr, while the structure of zirconyl nitrate is OZr(NO ３ )２ As shown in the formula (1), the divalent moiety of the central metal Zr is oxidized with oxygen atoms, and the remaining divalent moiety forms a salt with 2 moles of nitrate ions. By using a zirconium cation, which is a cation composed solely of zirconium, as in the present invention, the properties of the polishing composition can be maintained even when stored at a relatively high temperature.

[0018] In some embodiments, the zirconium (IV) salt is at least one of zirconium nitrate and zirconium chloride.

[0019] In some embodiments, the concentration of the metal salt (particularly zirconium (IV) salt) in the polishing composition is preferably 0.1 mM or more, 0.5 mM or more, 1 mM or more, 5 mM or more, 7 mM or more, 10 mM or more, 15 mM or more, 20 mM or more, or 25 mM or more. In some embodiments, the concentration of the metal salt (particularly zirconium (IV) salt) in the polishing composition is 7 mM or more. In some embodiments, the concentration of the metal salt (particularly zirconium (IV) salt) in the polishing composition is preferably 1000 mM or less, 850 mM or less, 500 mM or less, 300 mM or less, 200 mM or less, 100 mM or less, 50 mM or less, or 40 mM or less.

[0020] From the above, the concentration of the metal salt (particularly zirconium (IV) salt) in the polishing composition is preferably 0.1 mM or more and 1000 mM or less, 0.5 mM or more and 850 mM or less, 1 mM or more and 500 mM or less, 5 mM or more and 300 mM or less, 7 mM or more and 300 mM or less, 10 mM or more and 200 mM or less, 15 mM or more and 100 mM or less, 20 mM or more and 50 mM or less, or 25 mM or more and 40 mM or less. Note that 1 mM = 1 mmol / L. When the concentration of the metal salt (particularly zirconium (IV) salt) in the polishing composition is particularly 7 mM or more, the properties of the polishing composition can be maintained even when stored at a relatively high temperature.

[0021] According to some embodiments, the polishing composition contains at least 80 wt%, 85 wt%, 90 wt%, 95 wt%, 98 wt%, 99 wt%, 99.5 wt%, or 99.9 wt% or more of the metal salts (up to 100 wt%) of zirconium (IV) salts. According to some embodiments, the polishing composition contains at least 90 wt%, 95 wt%, 98 wt%, 99 wt%, 99.5 wt%, or 99.9 wt% or more of the metal salts (up to 100 wt%) of zirconium nitrate and / or zirconium chloride.

[0022] The metal salt contained in the polishing composition may be prepared by purchasing a commercially available product or by synthesis.

[0023] [Oxidizing Agent] The polishing composition of the present invention contains an oxidizing agent. The oxidizing agent causes an oxidation reaction with the substrate (e.g., SiC) surface during the polishing process, which can reduce the hardness of the surface and make the surface brittle. The use of an oxidizing agent can effectively improve the polishing rate.

[0024] The oxidizing agent is not particularly limited as long as it has a redox potential sufficient to oxidize the substrate surface. For example, the oxidizing agent may be a substance having a redox potential higher than that of the substrate material at the pH at which polishing is performed. Here, the pH at which the polishing is performed is usually the same as the pH of the polishing composition. The redox potential of the substrate material is determined by dispersing powder of the material (e.g., SiC) in water to form a slurry, adjusting the slurry to the same pH as the polishing composition, and then measuring the redox potential of the slurry (the redox potential relative to a standard hydrogen electrode at a liquid temperature of 25°C) using a commercially available redox potentiometer. Among the metal salts that can be contained in the polishing composition, substances that also have a redox potential sufficient to oxidize the substrate surface are included in the category of oxidizing agents in this specification.

[0025] In some embodiments, the polishing composition contains a complex metal oxide as an oxidizing agent. Examples of the complex metal oxide include nitric acids such as iron nitrate, silver nitrate, and aluminum nitrate; ferric acids such as potassium ferrate; permanganic acids such as sodium permanganate and potassium permanganate; chromic acids such as potassium chromate and potassium dichromate; vanadic acids such as ammonium vanadate, sodium vanadate, and potassium vanadate; ruthenic acids such as perruthenic acid and its salts; molybdic acids such as molybdic acid and its salts, ammonium molybdate and disodium molybdate; rhenic acids such as perrhenic acid and its salts; and tungstic acids such as tungstic acid and its salt, disodium tungstate. Among these, ferric acids, permanganic acids, and chromic acids are more preferred, and permanganic acids are even more preferred. In some embodiments, the polishing composition contains a permanganic acid as an oxidizing agent. The complex metal oxide may be used alone or in combination of two or more. In this specification, the term "class" can be read as "compound."

[0026] In some embodiments, the polishing composition contains an oxidizing agent other than the composite metal oxide. Specific examples of oxidizing agents other than composite metal oxides include peroxides such as hydrogen peroxide; persulfates such as peroxomonosulfuric acid, peroxodisulfuric acid, and the like; chloric acids such as chloric acid; perchloric acids such as perchloric acid; bromic acids such as bromic acid; iodic acids such as iodic acid; periodic acids; ruthenic acids such as perruthenic acid or its salt; and the like. These may be used alone or in appropriate combination of two or more.

[0027] In some embodiments, the polishing composition is substantially free of oxidizing agents (e.g., hydrogen peroxide) other than the composite metal oxide. "Substantially free" means that no oxidizing agents (e.g., hydrogen peroxide) other than the composite metal oxide are contained, or, if contained, the amount of oxidizing agents is 100 ppm by mass or less in the polishing composition.

[0028] In some embodiments, the content of the oxidizing agent (particularly permanganates such as potassium permanganate) in the polishing composition is preferably 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 1.5% by mass or more, 2% by mass or more, 2.5% by mass or more, 3% by mass or more, or 3.5% by mass or more. In some embodiments, the content of the oxidizing agent (particularly permanganates such as potassium permanganate) in the polishing composition is preferably 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 7.5% by mass or less, or 5% by mass or less.

[0029] From the above, it is preferable that the content of the oxidizing agent (especially permanganates such as potassium permanganate) in the polishing composition be 0.01 mass% or more and 40 mass% or less, 0.05 mass% or more and 35 mass% or less, 0.1 mass% or more and 30 mass% or less, 0.5 mass% or more and 25 mass% or less, 1 mass% or more and 20 mass% or less, 1.5 mass% or more and 15 mass% or less, 2 mass% or more and 10 mass% or less, 3 mass% or more and 7.5 mass% or less, or 3.5 mass% or more and 5 mass% or less.

[0030] According to some embodiments, the oxidizing agent contained in the polishing composition is 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, or 99.9% by mass or more (upper limit: 100% by mass). According to some embodiments, the oxidizing agent contained in the polishing composition is 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, or 99.9% by mass or more (upper limit: 100% by mass).

[0031] [Abrasive Grains] According to some embodiments, the polishing composition contains abrasive grains. The abrasive grains have the function of mechanically polishing the object to be polished (e.g., SiC).

[0032] Specific examples of abrasive grains used in the present invention include metal oxides such as silicon oxide (silica), aluminum oxide (alumina), silicon oxide (silica), cerium oxide (ceria), zirconium oxide, titanium oxide (titania), and manganese oxide; metal carbides such as silicon carbide and titanium carbide; metal nitrides such as silicon nitride and titanium nitride; and metal borides such as titanium boride and tungsten boride. These abrasive grains may be used alone or in combination. Among silicon oxides (silica), colloidal silica is preferred. Colloidal silica can be produced by the sol-gel method. For example, it can be obtained by hydrolysis and condensation reaction using a hydrolyzable silicon compound (e.g., alkoxysilane or its derivative) as a raw material.

[0033] Among these abrasive grains, at least one selected from the group consisting of metal oxides and metal carbides is preferred from the viewpoint of obtaining an excellent polishing rate. According to some embodiments, the abrasive grains preferably contain at least one of silica and alumina from the viewpoint of obtaining an excellent polishing rate.

[0034] According to some embodiments, the average secondary particle diameter of the abrasive grains (particularly silicon oxide and colloidal silica) is preferably 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, or 52 nm or more. As the average secondary particle diameter of the abrasive grains increases, the polishing rate of the object to be polished can be improved. Furthermore, the average secondary particle diameter of the abrasive grains (particularly silicon oxide and colloidal silica) is preferably 105 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, or 60 nm or less. As the average secondary particle diameter of the abrasive grains decreases, it becomes easier to obtain a surface with fewer defects and less roughness.

[0035] From the above, it is preferable that the average secondary particle diameter of the abrasive grains (particularly silicon oxide and colloidal silica) is 10 nm or more and 105 nm or less, 15 nm or more and 100 nm or less, 20 nm or more and 95 nm or less, 25 nm or more and 90 nm or less, 30 nm or more and 85 nm or less, 35 nm or more and 80 nm or less, 40 nm or more and 75 nm or less, 45 nm or more and 70 nm or less, 50 nm or more and 65 nm or less, or 52 nm or more and 60 nm or less.

[0036] Unless otherwise specified, the average secondary particle size of abrasive grains in this specification is measured by a laser diffraction / scattering method. Specifically, the measurement can be performed using a laser diffraction / scattering particle size distribution analyzer (product name "LA-950") manufactured by Horiba, Ltd.

[0037] According to some embodiments, the content of abrasive grains (particularly silicon oxide and colloidal silica) in the polishing composition is preferably 0.001% by mass or more, 0.003% by mass or more, 0.005% by mass or more, 0.007% by mass or more, 0.01% by mass or more, 0.03% by mass or more, 0.05% by mass or more, 0.07% by mass or more, or 0.09% by mass or more. As the content of abrasive grains increases, the polishing rate can increase. According to some embodiments, the content of abrasive grains (particularly silicon oxide and colloidal silica) in the polishing composition is preferably 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, or 0.5% by mass or less. As the content of abrasive grains decreases, it becomes easier to obtain a surface with fewer defects such as scratches by polishing with the polishing composition.

[0038] From the above, it is preferable that the content of abrasive grains (especially silicon oxide and colloidal silica) in the polishing composition is 0.001 mass% or more and 30 mass% or less, 0.003 mass% or more and 25 mass% or less, 0.005 mass% or more and 20 mass% or less, 0.007 mass% or more and 15 mass% or less, 0.01 mass% or more and 10 mass% or less, 0.03 mass% or more and 5 mass% or less, 0.05 mass% or more and 3 mass% or less, 0.07 mass% or more and 1 mass% or less, or 0.09 mass% or more and 0.5 mass% or less.

[0039] According to some embodiments, the colloidal silica accounts for 90% by mass or more, 95% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, or 99.9% by mass or more of the abrasive grains contained in the polishing composition (upper limit: 100% by mass).

[0040] According to some embodiments, the surfaces of the abrasive grains (particularly silicon oxide and colloidal silica) contained in the polishing composition have not been treated to chemically bond a treating agent such as an organic acid (e.g., sulfonic acid).

[0041] [Aqueous Medium] The polishing composition of the present invention contains an aqueous medium for dissolving and dispersing each component. Water is preferred as the aqueous medium. From the viewpoint of suppressing the inhibition of the action of other components, water containing as few impurities as possible is preferred. Specifically, pure water or ultrapure water obtained by removing impurity ions with an ion exchange resin and then passing through a filter to remove foreign matter, or distilled water is preferred.

[0042] According to some embodiments, the aqueous medium contained in the polishing composition comprises water at least 80% by weight, at least 85% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, at least 99% by weight, at least 99.5% by weight, or at least 99.9% by weight (upper limit: 100% by weight).

[0043] [pH of Polishing Composition] According to some embodiments, the lower limit of the pH of the polishing composition is preferably 0.5 or more, greater than 0.5, 0.6 or more, greater than 0.6, 0.7 or more, greater than 0.7, 0.8 or more, greater than 0.8, 0.9 or more, greater than 0.9, 1.0 or more, greater than 1.0, 1.1 or more, greater than 1.1, 1.2 or more, greater than 1.2, 1.3 or more, greater than 1.3, 1.4 or more, greater than 1.4, 1.5 or more, greater than 1.5, 1.6 or more, or greater than 1.6, or 1.7 or more. According to some embodiments, the upper limit of the pH of the polishing composition is preferably less than 7.0, 6.5 or less, less than 6.5, 6.0 or less, less than 6.0, 5.5 or less, less than 5.5, 5.0 or less, less than 5.0, 4.5 or less, less than 4.5, 4.0 or less, less than 4.0, 3.5 or less, less than 3.5, 3.0 or less, less than 3.0, 2.5 or less, less than 2.5, 2.0 or less, less than 2.0, 1.9 or less, or 1.8 or less. According to some embodiments, the pH of the polishing composition is 4.5 or less.

[0044] From the above, the pH of the polishing composition is preferably 0.5 or more and less than 7.0, more than 0.5 and less than 6.5, more than 0.6 and less than 6.0, more than 0.7 and less than 5.5, more than 0.8 and less than 4.5, more than 0.9 and less than 4.0, more than 1.0 and less than 3.5, more than 1.1 and less than 3.0, more than 1.2 and less than 2.5, more than 1.3 and less than 2.0, 1.4 or more and less than 1.9, 1.5 or more and less than 1.9, or 1.6 or more and less than 1.8. According to some embodiments, the pH of the polishing composition is 0.5 or more and less than 2.5. Such embodiments more significantly enhance the effect of maintaining the properties of the polishing composition even when stored at relatively high temperatures. The pH can be measured using a pH meter (for example, a glass electrode hydrogen ion concentration indicator (model F-23) manufactured by Horiba, Ltd.).

[0045] According to some embodiments, the pH of the polishing composition may be adjusted to a desired value by adjusting the content of an oxidizing agent, a zirconium (IV) salt as a metal salt, and, if necessary, abrasive grains in an aqueous medium (particularly water), or by separately adding a pH adjuster such as those described below. Alternatively, the pH of the polishing composition may be adjusted to a desired value by adjusting the content of an oxidizing agent, a zirconium (IV) salt as a metal salt, and, if necessary, abrasive grains, without separately adding a pH adjuster such as those described below.

[0046] According to some embodiments, there is provided a polishing composition comprising an oxidizing agent, a zirconium (IV) salt as a metal salt, and an aqueous medium, wherein 80 mass% or more of the oxidizing agent is a permanganate such as potassium permanganate, and 80 mass% or more of the metal salt (excluding those that function as oxidizing agents as described above) is a zirconium (IV) salt.

[0047] [Other Components] According to some embodiments, the polishing composition may contain or may be substantially free of “other components” as needed. “Substantially free” means that the component is not contained, or if contained, the content of the component in the polishing composition is 100 ppm by mass or less.

[0048] According to some embodiments, other components include, but are not limited to, acids or their salts or bases or their salts (pH adjusters) that adjust the pH of the polishing composition, water-soluble polymers that act on the surface of the object to be polished or the surface of the abrasive grains, anticorrosives and chelating agents that suppress corrosion of the object to be polished, preservatives and antifungal agents that have other functions, etc.

[0049] The acid may be either an inorganic acid or an organic acid. Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, phenoxyacetic acid, methanesulfonic acid, ethanesulfonic acid, sulfosuccinic acid, benzenesulfonic acid, toluenesulfonic acid, phenylphosphonic acid, and hydroxyethane-1,1-diphosphonic acid. Examples of salts include Group 1 element salts, Group 2 element salts, aluminum salts, ammonium salts, amine salts, and quaternary ammonium salts. These acids or salts can be used alone or in combination. Among these, nitric acid and hydrochloric acid are preferred.

[0050] The content of the acid or its salt in the polishing composition may be appropriately adjusted so that the pH falls within the above range.

[0051] Examples of the base or its salt include amines such as aliphatic amines and aromatic amines, organic bases such as quaternary ammonium hydroxide, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, hydroxides of Group 2 elements such as magnesium hydroxide and calcium hydroxide, and ammonia.

[0052] The content of the base or its salt in the polishing composition may be appropriately adjusted so that the pH falls within the above range.

[0053] Examples of water-soluble polymers include polycarboxylic acids such as polyacrylic acid, polyphosphonic acids, polysulfonic acids such as polystyrene sulfonic acid, polysaccharides such as xanthan gum and sodium alginate, cellulose derivatives such as hydroxyethyl cellulose and carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, sorbitan monooleate, and oxyalkylene polymers having a single or multiple oxyalkylene units. Also suitable as water-soluble polymers are at least one of poly(t-butylacrylamidosulfonic acid) (= polyATBS) and poly(acrylic acid / t-butylacrylamidosulfonic acid) copolymers. Salts of the above compounds can also be used as water-soluble polymers.

[0054] Examples of the anticorrosive agent include amines, pyridines, tetraphenylphosphonium salts, benzotriazoles, triazoles, tetrazoles, and benzoic acid. Examples of the chelating agent include carboxylic acid chelating agents such as gluconic acid, amine chelating agents such as ethylenediamine, diethylenetriamine, and trimethyltetraamine, polyaminopolycarboxylic chelating agents such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, and diethylenetriaminepentaacetic acid, organic phosphonic acid chelating agents such as 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri(methylenephosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), diethylenetriaminepenta(methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, methanehydroxyphosphonic acid, and 1-phosphonobutane-2,3,4-tricarboxylic acid, phenol derivatives, and 1,3-diketones.

[0055] Examples of preservatives include sodium hypochlorite, etc. Examples of antifungal agents include oxazolines such as oxazolidine-2,5-dione, etc.

[0056] In some embodiments, the polishing composition contains no layered compounds, or less than 0.01 wt % layered compounds.

[0057] [Method for producing polishing composition] The method for producing the polishing composition of the present invention is not particularly limited, and can be obtained, for example, by stirring and mixing an oxidizing agent, a zirconium (IV) salt as a metal salt, an aqueous medium, and optionally abrasive grains, and optionally other components in an aqueous medium. The above descriptions of the oxidizing agent, metal salt, aqueous medium, abrasive grains, and other components can be applied.

[0058] The temperature at which the components are mixed is not particularly limited, but is preferably 10° C. to 40° C. Heating may be performed to increase the dissolution rate. The mixing time is also not particularly limited.

[0059] [Object to be polished] The polishing composition of the present invention is applied to the object to be polished to polish it. The object to be polished of the present invention is not particularly limited, but may be, for example, a substrate having a surface made of a semiconductor material, i.e., a semiconductor substrate. Examples of materials constituting the semiconductor substrate include semiconductors made of Group 14 elements such as silicon and germanium; compound semiconductors such as SiC, SiGe, ZnS, ZnSe, InP, AlN, GaAs, GaN, AlGaAs, InGaAs, GaP, ZnTe, and CdTd; and the like. Among these, compound semiconductors are preferred, and SiC (silicon carbide) is more preferred. According to some embodiments, the polishing composition is used to polish a semiconductor substrate, and the semiconductor substrate is a compound semiconductor substrate.

[0060] Furthermore, the material contained in the object to be polished of the present invention has a Vickers hardness of, for example, 500 Hv or more. The Vickers hardness is preferably 700 Hv or more, for example, 1000 Hv or more, or 1500 Hv or more. The Vickers hardness of the material contained in the object to be polished may be 1800 Hv or more, 2000 Hv or more, or 2200 Hv or more. The upper limit of the Vickers hardness of the material contained in the object to be polished is not particularly limited, and may be, for example, approximately 7000 Hv or less, 5000 Hv or less, or 3000 Hv or less. In this specification, Vickers hardness can be measured based on JIS R 1610:2003. The international standard corresponding to the above JIS standard is ISO 14705:2000.

[0061] From the above, the Vickers hardness of the material contained in the object to be polished of the present invention may be 700 Hv or more and 7000 Hv or less, 1000 Hv or more and 5000 Hv or less, or 1500 Hv or more and 3000 Hv or less. In some embodiments, the Vickers hardness of the material contained in the object to be polished may be 1800 Hv or more and 3000 Hv or less, or 2000 Hv or more and 3000 Hv or less.

[0062] Examples of materials having a Vickers hardness of 1500 Hv or more include silicon carbide, silicon nitride, titanium nitride, and gallium nitride. The object to be polished in the technology disclosed herein may have a single crystal surface of the above material, which is mechanically and chemically stable. The surface of the object to be polished is preferably composed of either silicon carbide or gallium nitride, and more preferably silicon carbide. Silicon carbide is expected to be a compound semiconductor substrate material with low power loss and excellent heat resistance, and the practical advantage of improving productivity by increasing the polishing rate is particularly great. The technology disclosed herein is particularly suitable for polishing the single crystal surface of silicon carbide.

[0063] [Polishing Method, Semiconductor Substrate Manufacturing Method] The polishing composition of the present invention is suitable for use in polishing semiconductor substrates. Thus, in some embodiments, a polishing method is provided comprising the step of polishing a semiconductor substrate using the polishing composition. In some embodiments, a method for manufacturing a semiconductor substrate using such a polishing method is also provided. Polishing an object to be polished using the polishing composition of the present invention can be carried out using equipment and conditions typically used for polishing. Common polishing apparatuses include single-sided polishing apparatuses and double-sided polishing apparatuses. In single-sided polishing apparatuses, a holder called a template is used to hold the object to be polished (preferably a substrate-like object to be polished), and one side of the object to be polished is polished by pressing a platen with an abrasive cloth affixed to one side of the object to be polished and rotating the platen while supplying a polishing composition. In double-sided polishing apparatuses, a holder called a carrier is used to hold the object to be polished, and a platen with an abrasive cloth affixed to the opposite side of the object to be polished is pressed against the opposite side of the object to be polished while supplying a polishing composition from above, and the two plates are rotated relative to each other to polish both sides of the object to be polished. At this time, polishing is carried out by the physical action of friction between the polishing pad and the polishing composition and the object to be polished, and the chemical action of the polishing composition on the object to be polished.

[0064] The polishing pads used in the polishing method using the polishing composition of the present invention vary in material, such as polyurethane type, foamed polyurethane type, nonwoven fabric type, suede type, etc., as well as in physical properties such as hardness and thickness, and further include those containing abrasive grains and those not containing abrasive grains, and these can be used without restriction.

[0065] When using the polishing composition of the present invention to polish an object to be polished, the polishing composition that has been used for polishing can be recovered and used again for polishing.As an example of the method for reusing polishing composition, the polishing composition that is discharged from polishing equipment can be recovered in a tank, and circulated back into the polishing equipment for use.The recycling of polishing composition is useful in that it can reduce the amount of polishing composition that is discharged as waste liquid, thereby reducing environmental load, and can reduce the amount of polishing composition that is used, thereby reducing the manufacturing cost required for polishing an object to be polished.

[0066] When the polishing composition of the present invention is recycled, a part or all of the abrasive grains, oxidizer, zirconium (IV) salt as a metal salt, and other additives consumed or lost during polishing can be added as a composition adjuster during recycling.In this case, the composition adjuster may be a mixture of the oxidizer, zirconium (IV) salt as a metal salt, optionally abrasive grains, and some or all of the other additives in any mixing ratio.By adding additional composition adjuster, the polishing composition is adjusted to a composition suitable for reuse, and polishing is maintained favorably.The concentrations of the oxidizer, zirconium (IV) salt as a metal salt, optionally abrasive grains, and other additives contained in the composition adjuster are arbitrary and not particularly limited, but are preferably adjusted appropriately according to the size of the circulation tank and the polishing conditions.

[0067] The polishing composition of the present invention may be a one-component type or a multi-component type such as a two-component type. The polishing composition of the present invention may also be prepared by diluting the stock solution of the polishing composition with a diluent such as water, for example, 1.5 times or more, 5 times or more, 10 times or more (for example, 1.5 times or more and 20 times or less).

[0068] Although the embodiments of the present invention have been described in detail, it is clear that this is by way of illustration and example only and not of limitation, and that the scope of the present invention should be interpreted by the appended claims.

[0069] The present invention encompasses the following aspects and embodiments: 1. A polishing composition comprising an oxidizing agent, a zirconium (IV) salt as a metal salt, and an aqueous medium; 2. A polishing composition comprising a nitrate ion (NO ) as the anion of the metal salt; ３ － ) and chloride anion (Cl －3. The polishing composition according to 1. above, which contains a permanganate as the oxidizing agent; 4. The polishing composition according to any one of 1. to 3. above, which further contains abrasive grains; 5. The polishing composition according to 4. above, which contains at least one of silica and alumina as the abrasive grains; 6. The polishing composition according to any one of 1. to 5. above, which contains the metal salt at a concentration of 7 mM or more; 7. The polishing composition according to any one of 1. to 6. above, which has a pH of 4.5 or less; 8. The polishing composition according to any one of 7. above, which has a pH of 0.5 or more and less than 2.5; 9. The polishing composition according to any one of 1. to 8. above, which is used for polishing a semiconductor substrate, the semiconductor substrate being a compound semiconductor substrate; 10. A polishing method comprising a step of polishing a semiconductor substrate with the polishing composition according to any one of 1. to 9. above; 11. 10. A method for manufacturing a semiconductor substrate using the polishing method described above.

[0070] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. In the following, unless otherwise specified, the operations were carried out under the conditions of room temperature (25°C) and relative humidity of 40 to 50% RH.

[0071] <Preparation of Polishing Composition> Each polishing composition was prepared by mixing potassium permanganate as an oxidizing agent, colloidal silica (average secondary particle diameter: 57 nm) as abrasive grains, a metal salt shown in Table 1, and a pH adjuster shown in Table 1 in water as an aqueous medium at room temperature (25°C) so as to obtain the contents shown in Table 1. Note that the notation "-" indicates that the corresponding component was not added.

[0072] The average secondary particle size of the abrasive grains was measured using a laser diffraction / scattering particle size distribution analyzer LA-950 manufactured by Horiba, Ltd. The pH was measured using a pH meter (a glass electrode hydrogen ion concentration indicator (model number F-23) manufactured by Horiba, Ltd.) and three-point calibration was performed using standard buffer solutions (phthalate pH buffer solution pH: 4.01 (25°C), neutral phosphate pH buffer solution pH: 6.86 (25°C), carbonate pH buffer solution pH: 10.01 (25°C)). The glass electrode was then placed in the polishing composition to be measured. The pH can be determined by measuring the value after the measured value has stabilized.

[0073] Using each polishing composition, an object to be polished was polished under the following polishing conditions.

[0074] <Polishing conditions> Polishing apparatus: RDP-500 (manufactured by Fujikoshi Machinery Co., Ltd.) Polishing pad: IC-1000 (manufactured by Nitta DuPont Co., Ltd.) Polishing load: 490 gf / cm ２ Platen rotation speed: 130 rpm Flow rate: 20 ml / min Polishing time: 10 min.

[0075] After polishing, the platen rotation speed was set to 50 rpm, and the surface was brushed with water using a PVA brush for 5 minutes, then water was run over the surface using a diamond dresser at the same rotation speed for 3 minutes, and then the surface was brushed again with water using a PVA brush for 5 minutes.

[0076] <Polished object> SiC substrate: 4 inch N-type 4H-SiC 4° off Vickers hardness 2000 to 2400 Hv.

[0077] <Polishing removal rate (RR)> The polishing removal rate was calculated from the difference in mass of the object before and after polishing. The unit of the polishing rate is nm / h (hours).

[0078] <Maintenance of Properties of Polishing Composition> Each polishing composition was allowed to stand in an environment of 43° C. for 12 days, and the polishing composition was evaluated for any change in properties according to the following criteria.

[0079] ◯: No change in properties △: A small amount of black foreign matter was found ×: A large amount of black foreign matter was found.

[0080]

[0081] It is clear that the polishing compositions of the examples can improve the removal rate of an object to be polished, such as silicon carbide, and can maintain their properties even when stored at a relatively high temperature.

[0082] Comparing Example 1 and Example 2, it is clear that the use of zirconium nitrate as the metal salt can significantly improve the polishing rate for polishing an object such as silicon carbide.

[0083] Comparative Examples 1 and 2 are examples in which zirconium is not used as the metal. It can be seen that the polishing compositions of Comparative Examples 1 and 2 cannot improve the polishing rate of an object to be polished, such as silicon carbide. In particular, the polishing composition of Comparative Example 2, which was adjusted to a pH substantially the same as that of the example, was unable to maintain its properties, and a small amount of black foreign matter was generated.

[0084] In Comparative Example 3, a zirconyl (ZrO) cation is used instead of a zirconium cation, which is a cation composed solely of zirconium. Although the polishing composition of this example was able to improve the polishing rate of an object to be polished, such as silicon carbide, to some extent, the polishing composition was very poor in maintaining its properties.

[0085] No metal salt was contained in the polishing composition of Comparative Example 4. The polishing composition of this example was unable to improve the removal rate of an object to be polished, such as silicon carbide, and the maintenance of the properties of the polishing composition was also very poor.

[0086] Although not shown in Table 1, an example in which zirconium nitrate in Example 1 was replaced with zirconium sulfate was also evaluated, and the effect was slightly weaker than the effect of improving the polishing rate in Examples 1 and 2. The maintenance of the properties of the polishing composition was as good as in the case of zirconium nitrate.

[0087] This application is based on Japanese Patent Application No. 2023-162426, filed on September 26, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A polishing composition comprising: an oxidizing agent; a zirconium (IV) salt as a metal salt; and an aqueous medium.

2. The anion of the metal salt is a nitrate ion (NO ３ － ) and chloride anion (Cl － 2. The polishing composition according to claim 1, comprising at least one of the following:

3. The polishing composition according to claim 1, wherein the oxidizing agent comprises a permanganate.

4. The polishing composition according to claim 1, further comprising abrasive grains.

5. The polishing composition according to claim 4, wherein the abrasive grains include at least one of silica and alumina.

6. The polishing composition according to claim 1, wherein the concentration of the metal salt is 7 mM or more.

7. The polishing composition according to claim 1, having a pH of 4.5 or less.

8. The polishing composition according to claim 1, having a pH of 0.5 or more and less than 2.

5.

9. The polishing composition according to claim 1, which is used for polishing a semiconductor substrate, the semiconductor substrate being a compound semiconductor substrate.

10. A polishing method comprising the step of polishing a semiconductor substrate with the polishing composition according to claim 1.

11. A method for manufacturing a semiconductor substrate, comprising using the polishing method according to claim 10.

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