Composition for polishing and polishing method

Abstract

The present invention provides a polishing composition including fumed silica, an oxidizing agent, and a metal salt. The polishing composition includes more than 10 mmol / L of the metal salt.

Description

Technical Field

[0001] The present invention relates to a polishing composition and a polishing method. Specifically, it relates to a polishing composition and a polishing method suitable for polishing a high-hardness material having a Vickers hardness of 1500 Hv or more. This application claims priority based on Japanese Patent Application No. 2020-060913 filed on March 30, 2020, and the entire contents of that application are incorporated herein by reference.

Background Art

[0002] The surfaces of materials such as metals, semimetals, nonmetals, and their oxides are polished using a polishing composition. For example, a surface composed of a compound semiconductor material such as silicon carbide, boron carbide, tungsten carbide, silicon nitride, titanium nitride, or gallium nitride can be processed by lapping in which diamond abrasive grains are supplied between the surface and a polishing platen. However, in lapping using diamond abrasive grains, defects and distortions are likely to occur due to the generation, remaining, etc. of scratches and indentations. Therefore, polishing (polishing) using a polishing pad and a polishing composition is being considered after lapping using diamond abrasive grains or instead of such lapping. As a document disclosing the prior art of the polishing composition, Patent Document 1 can be cited. In Patent Document 1, a composition for polishing tantalum is being considered.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, from the viewpoints of manufacturing efficiency and cost effectiveness, it is desirable that the polishing removal rate is sufficiently large in practical use. For example, in the polishing of a surface composed of a high-hardness material such as silicon carbide, further improvement in the polishing removal rate is desired. As a polishing composition capable of expecting such an improvement in the polishing removal rate, a polishing composition containing fumed silica can be mentioned. Since fumed silica is more non-spherical than colloidal silica, it tends to have excellent processing power. On the other hand, problems such as alumina residue (stabbing, etc.) on the polishing surface like alumina abrasive grains are less likely to occur, which is preferable. Further, when the polishing composition contains an oxidizing agent, the oxidizing agent can alter the surface of the substrate, and the polishing removal rate can be improved.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to improve the polishing removal rate with a composition containing fumed silica and an oxidizing agent.

Means for Solving the Problems

[0006] According to this specification, a polishing composition containing fumed silica, an oxidizing agent, and a metal salt is provided. This polishing composition is characterized by containing more than 10 mmol / L of the metal salt. When the polishing composition contains more than 10 mmol / L of the above metal salt, the polishing removal rate is improved in the composition containing fumed silica and an oxidizing agent. Incidentally, although it will be described in detail later, the "metal salt" in this specification is defined as a compound different from the above "oxidizing agent", and specifically, it can be a normal salt formed by the neutralization of a strong acid and a strong base. The metal forming the above metal salt includes lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium or barium.

[0007] In some preferred embodiments of the technology disclosed herein (including a polishing composition, a polishing method, a method for manufacturing a substrate. The same shall apply hereinafter), the metal salt is a nitrate and / or a hydrochloride of an alkali metal and / or an alkaline earth metal. By using the above metal salt, the polishing removal rate is preferably improved.

[0008] In some preferred embodiments, the metal forming the metal salt is calcium. When the metal is calcium, the polishing removal rate is particularly preferably improved.

[0009] In some preferred embodiments, the metal forming the metal salt is potassium. When the metal is potassium, the polishing removal rate is particularly preferably improved.

[0010] In some preferred embodiments, the oxidizing agent contains a composite metal oxide. A composition containing a composite metal oxide as the oxidizing agent is likely to improve the polishing removal rate by containing more than 10 mmol / L of the metal salt.

[0011] In some preferred embodiments, the ratio (B / A) of the concentration B [mmol / L] of the metal salt to the concentration A [mmol / L] of the oxidizing agent is 0.01 or more and 10 or less. According to such a configuration, the effects of the technology disclosed herein are preferably exhibited.

[0012] In some preferred embodiments, the pH of the polishing composition is greater than 5.0 and less than 9.0. When the pH of the polishing composition is in the above range (a range close to the neutral range), the effects of the technology disclosed herein are preferably exhibited.

[0013] The polishing composition disclosed herein is preferably used for polishing a material having a Vickers hardness of 1500 Hv or more. According to the polishing composition, the polishing removal rate for a high-hardness material can be improved. Preferred examples of the high-hardness material include silicon carbide. When polishing silicon carbide, the effects of the technology disclosed herein are preferably exhibited.

[0014] According to this specification, furthermore, a method for polishing a substrate is provided. The polishing method includes a step of polishing the substrate using any of the polishing compositions disclosed herein. According to this polishing method, the polishing removal rate is improved.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention can be understood as design matters of those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the relevant field.

[0016] <Polishing composition> (Fumed silica) The polishing composition disclosed herein contains fumed silica. As the fumed silica, it can be appropriately selected and used from various known fumed silicas. The fumed silica can contain one kind of various known fumed silicas alone or in combination of two or more kinds.

[0017] The average primary particle diameter of the fumed silica is not particularly limited as long as the effects of the present invention are exhibited. From the viewpoint of improving the polishing removal rate and the like, it is preferably 10 nm or more, more preferably 15 nm or more, still more preferably 20 nm or more, and may be, for example, 30 nm or more. By increasing the average primary particle diameter, a higher polishing removal rate can be achieved. Also, from the viewpoint of the surface quality after polishing, the above average primary particle diameter is preferably 150 nm or less, more preferably 100 nm or less, still more preferably 80 nm or less, and may be, for example, 60 nm or less.

[0018] In the technology disclosed herein, the average primary particle diameter refers to the particle diameter (BET particle diameter) calculated by the formula: average primary particle diameter (nm) = 6000 / (true density (g / cm 3 ) × BET value (m 2 / g)) from the specific surface area (BET value) measured by the BET method. The measurement of the specific surface area can be performed, for example, using a surface area measuring device manufactured by Micromeritics, trade name "Flow Sorb II 2300".

[0019] The average secondary particle diameter of the fumed silica is not particularly limited as long as the effects of the present invention can be exhibited. For example, 15 nm or more is suitable. From the viewpoint of improving the polishing removal rate, etc., it is preferably 30 nm or more, more preferably 60 nm or more, still more preferably 80 nm or more, particularly preferably 100 nm or more (for example, 120 nm or more), and may be 150 nm or more. Further, the average secondary particle diameter of the above fumed silica can be, for example, 1000 nm or less. From the viewpoint of the surface quality after polishing, the above average secondary particle diameter is preferably 500 nm or less, and may be 300 nm or less. For example, fumed silica having an average secondary particle diameter of 120 nm or more and 220 nm or less can be preferably employed.

[0020] In the technology disclosed herein, the average secondary particle diameter of the fumed silica refers to the volume-based average particle diameter (50% volume average particle diameter) based on the dynamic light scattering method. The measurement of the particle diameter based on the dynamic light scattering method can be performed, for example, using "N4 Plus" manufactured by BECKMAN COULTER.

[0021] The aspect ratio of the fumed silica is not particularly limited and can be, for example, 1.5 or more. From the viewpoint of improving the polishing removal rate, the aspect ratio of the fumed silica may be 2.0 or more, 2.5 or more, or 3.0 or more. Further, the upper limit of the above aspect ratio is, for example, less than 8.0, and may be less than 6.0. In this specification, the "aspect ratio" of the fumed silica refers to the value of the ratio of the average secondary particle diameter / average primary particle diameter of the fumed silica.

[0022] The content of fumed silica in the polishing composition (when including multiple types of fumed silica, their total content) is not particularly limited as long as the effects of the present invention can be exerted. For example, it may be 0.01% by weight or more, and may be 0.05% by weight or more. From the perspective of improving the polishing rate, it is appropriate to set it at 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 0.8% by weight or more, and may also be 1% by weight or more, or 5% by weight or more. Also, from the perspectives of the dispersibility, stability over time, etc. of the polishing composition, the content of fumed silica is appropriately set to 50% by weight or less, preferably 20% by weight or less, and may also be 15% by weight or less, 10% by weight or less, 8% by weight or less, 3% by weight or less, 1.5% by weight or less, or for example, 0.3% by weight or less.

[0023] The polishing composition disclosed herein may contain silica abrasive grains other than fumed silica (hereinafter also referred to as non-fumed silica abrasive grains) and abrasive grains made of materials other than silica (hereinafter also referred to as non-silica abrasive grains) within a range that does not impair the effects of the present invention. Examples of non-fumed silica abrasive grains include colloidal silica and precipitated silica. Examples of non-silica abrasive grains include oxide grains such as aluminum oxide grains, cerium oxide grains, chromium oxide grains, titanium dioxide grains, zirconium oxide grains, magnesium oxide grains, manganese oxide grains, zinc oxide grains, and iron oxide grains; nitride grains such as silicon nitride grains and boron nitride grains; carbide grains such as silicon carbide grains and boron carbide grains; diamond grains; inorganic grains such as carbonates such as calcium carbonate and barium carbonate, and abrasive grains substantially composed of any of organic grains such as crosslinked or non-crosslinked polymethyl methacrylate, polyacrylonitrile, polystyrene, nylon, and silicone.

[0024] Generally, a higher proportion of fumed silica in the total abrasive grains used is advantageous. For example, the proportion of fumed silica in the total abrasive grains is appropriately more than 50% by weight, preferably 70% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, and may also be substantially 100% by weight.

[0025] In some embodiments, the polishing composition may substantially not contain diamond particles as abrasive grains. Since diamond particles have high hardness, they can be a limiting factor in improving smoothness. Also, since diamond particles are generally expensive, they are not an advantageous material in terms of cost-effectiveness, and in practical terms, the dependence on high-cost materials such as diamond particles may be low. Here, the abrasive grains substantially not containing diamond particles means that the proportion of diamond particles in the total abrasive grains is 1% by weight or less, more preferably 0.5% by weight or less, and typically 0.1% by weight or less, including the case where the proportion of diamond particles is 0% by weight. In such embodiments, the effects of the technology disclosed herein can be preferably exhibited.

[0026] (Oxidizing agent) The polishing composition disclosed herein contains an oxidizing agent. The oxidizing agent can cause an oxidation reaction with the substrate surface during the polishing process, lower the hardness of the surface, and make the surface vulnerable. By using an oxidizing agent, the polishing removal rate can be effectively improved. The oxidizing agent is not particularly limited as long as it is a substance having a redox potential sufficient to exert an action of oxidizing the substrate surface. For example, the oxidizing agent can be a substance having a redox potential higher than that of the substrate material at the pH at which polishing is carried out. Here, the pH at which the above polishing is carried out is usually the same as the pH of the polishing composition. The redox potential of the substrate material is the value measured using a commercially available redox potentiometer for the redox potential of a slurry prepared by dispersing the powder of the material in water and adjusting the slurry to the same pH as the polishing composition (redox potential with respect to the standard hydrogen electrode at a liquid temperature of 25°C). Note that the oxidizing agent in this specification does not include metal salts described later.

[0027] Specific examples of the oxidizing agent include peroxides such as hydrogen peroxide; nitrates such as iron nitrate, silver nitrate, and aluminum nitrate; persulfates such as peroxomonosulfuric acid and peroxodisulfuric acid; chlorates such as chloric acid; perchlorates such as perchloric acid; bromates such as bromic acid; iodates such as iodic acid; periodates; ferrates such as potassium ferrate; permanganates such as sodium permanganate and potassium permanganate; chromates such as potassium chromate and potassium dichromate; vanadates such as ammonium vanadate, sodium vanadate, and potassium vanadate; ruthenates such as perruthenic acid or its salts; molybdates such as molybdic acid, ammonium molybdate which is a salt thereof, and disodium molybdate; rhenates such as perrhenic acid or its salts; tungstates such as tungstic acid and disodium tungstate which is a salt thereof. These may be used alone or in appropriate combinations of two or more.

[0028] In some preferred embodiments, the polishing composition contains a composite metal oxide as the oxidizing agent. Examples of the composite metal oxide include nitrates, ferrates, permanganates, chromates, vanadates, ruthenates, molybdates, rhenates, and tungstates. Among them, ferrates, permanganates, and chromates are more preferred, and permanganates are even more preferred. The composite metal oxide may be used alone or in appropriate combinations of two or more.

[0029] The polishing composition disclosed herein may or may not further contain an oxidizing agent other than the above composite metal oxide. The technology disclosed herein can be preferably implemented in an embodiment that substantially does not contain an oxidizing agent other than the above composite metal oxide (for example, hydrogen peroxide).

[0030] The concentration (content) of the oxidizing agent in the polishing composition is suitably 0.001 mol / L or more. From the viewpoint of improving the polishing removal rate, in some embodiments, the concentration of the oxidizing agent is preferably 0.005 mol / L or more, more preferably 0.01 mol / L or more, and even more preferably 0.05 mol / L or more. In some preferred embodiments, the concentration of the oxidizing agent is 0.10 mol / L or more, may be 0.15 mol / L or more, may be 0.20 mol / L or more, for example, 0.25 mol / L or more. Also, from the viewpoint of the surface quality after polishing, it is suitable that the concentration of the oxidizing agent is 10 mol / L or less, preferably 5 mol / L or less, and more preferably 3 mol / L or less (for example, 1 mol / L or less, or 0.5 mol / L or less). In some embodiments, the concentration of the oxidizing agent may be 0.30 mol / L or less, may be 0.20 mol / L or less, may be 0.12 mol / L or less, or may be 0.09 mol / L or less.

[0031] The content of the oxidizing agent can also be specified by its relative relationship with the abrasive grains (typically fumed silica). Although not particularly limited, in some embodiments, the content of the oxidizing agent relative to 100 parts by weight of the abrasive grains can be, for example, 0.01 mol or more, suitably 0.05 mol or more from the viewpoint of effectively exerting the effect of using the oxidizing agent, may be 0.10 mol or more, may be 0.5 mol or more, may be 1 mol or more, may be 2.5 mol or more, or may be 5 mol or more. The content of the oxidizing agent relative to 100 parts by weight of the abrasive grains can be, for example, 50 mol or less (for example, 30 mol or less), and suitably 10 mol or less from the viewpoint of effectively exerting the mechanical polishing force by the abrasive grains, may be 6 mol or less, may be 3 mol or less, may be 1 mol or less, or may be 0.3 mol or less (for example, 0.1 mol or less).

[0032] (metal salt) The polishing composition disclosed herein contains a metal salt. By containing a metal salt in a predetermined amount or more, the polishing removal rate is improved. Specifically, the oxidizing agent contained in the polishing composition disclosed herein alters the surface of the substrate (particularly the surface of a substrate made of a high-hardness material such as silicon carbide), and the altered layer is removed by polishing. The metal salt exhibits an action of promoting or assisting the alteration and removal, and is considered to contribute to the improvement of the polishing removal rate. Note that the improvement of the polishing removal rate by the technology disclosed herein is not construed as being limited to the above mechanism. The "metal salt" disclosed herein is a compound different from the above "oxidizing agent", and specifically, it can be a normal salt formed by the neutralization of a strong acid and a strong base. As the above metal salt, those containing an element belonging to an alkali metal and / or an alkaline earth metal are preferable, and those containing any one or more of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) are more preferable. Among them, a metal salt containing any one of Na, K, Ca, and Sr is preferable, and a metal salt containing any one of K and Ca is particularly preferable.

[0033] The type of the salt in the above metal salt is not particularly limited, and it may be an inorganic acid salt or an organic acid salt. For example, examples of the inorganic acid salt include salts of hydrogen halide acids (e.g., hydrochloric acid, hydrobromic acid, hydrofluoric acid), nitric acid, sulfuric acid, carbonic acid, silicic acid, boric acid, phosphoric acid, etc. Examples of the organic acid salt include salts of carboxylic acids (e.g., formic acid, acetic acid, propionic acid, benzoic acid, glycine acid, butyric acid, citric acid, tartaric acid, trifluoroacetic acid), organic sulfonic acids (e.g., methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid), organic phosphonic acids (e.g., methylphosphonic acid, benzenephosphonic acid, toluenephosphonic acid), organic phosphoric acids (e.g., ethylphosphoric acid), etc. Among them, inorganic acid salts are preferable, hydrochloride salts and nitrate salts are more preferable, and nitrate salts are particularly preferably used.

[0034] Specific examples of the metal salt include chlorides such as lithium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride; bromides such as sodium bromide, potassium bromide, magnesium bromide, calcium bromide; fluorides such as lithium fluoride, sodium fluoride, potassium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride; nitrates such as lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate; carbonates such as potassium carbonate, potassium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate; carboxylates such as potassium acetate, sodium acetate, calcium acetate, strontium acetate, sodium benzoate, calcium benzoate, sodium citrate, calcium citrate; and metal salts substantially composed of any of these. The metal salt may be used alone or in combination of two or more kinds.

[0035] The metal salt may be dissolved or may be dispersed as a solid in the polishing composition. That is, the metal salt may be water-soluble or water-insoluble. Also, a part of the metal salt may be dissolved and the remainder may be dispersed as a solid in the polishing composition. In some preferred embodiments, the metal salt is a water-soluble salt. By using a water-soluble metal salt, a good surface with few defects such as scratches can be efficiently formed. Also, in some preferred embodiments, the metal salt is a salt that dissolves in water and exhibits a neutral range, and specifically may be a normal salt formed by the neutralization of a strong acid and a strong base. By using a metal salt whose aqueous solution exhibits a neutral range (for example, pH 6 to 8, preferably pH 6.5 to 7.5), a high-quality surface can be efficiently formed. Examples of metal salts whose aqueous solutions are neutral include chlorides such as sodium chloride, potassium chloride, calcium chloride, and strontium chloride, and nitrates such as sodium nitrate, potassium nitrate, calcium nitrate, and strontium nitrate. Among them, potassium chloride, sodium chloride, calcium chloride, strontium chloride, potassium nitrate, calcium nitrate, and strontium nitrate are preferred because they can efficiently form a good surface. Among them, potassium chloride, calcium chloride, potassium nitrate, and calcium nitrate are particularly preferred.

[0036] In the polishing composition disclosed herein, the concentration (content) of the metal salt is more than 10 mmol / L. Thereby, in a composition containing fumed silica and an oxidizing agent, the polishing removal rate is improved. In some embodiments, the concentration of the metal salt is preferably 12 mmol / L or more, more preferably 20 mmol / L or more, may be 30 mmol / L or more, and may be 50 mmol / L or more. In some other embodiments, a concentration of 80 mmol / L or more is suitable for the metal salt, and it may preferably be 150 mmol / L or more, may be 250 mmol / L or more, and may be 500 mmol / L or more.

[0037] The upper limit of the concentration of the metal salt is not particularly limited, and it is appropriate to set it to 10 mol / L or less. When the concentration of the metal salt is within a predetermined range, the polishing removal rate on the surface of the substrate material (especially high-hardness materials) can be improved to a higher level. From the perspective of improving the polishing removal rate and the like, the above concentration is preferably 5 mol / L or less, more preferably 3 mol / L or less, even more preferably 1000 mmol / L or less, and may be 600 mmol / L or less, 400 mmol / L or less, or 200 mmol / L or less. In some embodiments, the concentration of the metal salt may be 100 mmol / L or less, 70 mmol / L or less, or 25 mmol / L or less (for example, 20 mmol / L or less).

[0038] The concentration ratio of the oxidizing agent to the metal salt is not particularly limited as long as the effects of the present invention are exhibited. Assuming the action of exhibiting the effects of the present invention, it is considered preferable to set the amount of the metal salt within a predetermined range with respect to the amount of the oxidizing agent. From such a perspective, the ratio (B / A) of the concentration B [mmol / L] of the metal salt to the concentration A [mmol / L] of the oxidizing agent is, from the perspective of improving the polishing removal rate, for example, 0.01 or more, suitably 0.05 or more, may be 0.07 or more, or 0.10 or more (for example, 0.15 or more). In some embodiments, the above ratio (B / A) may be 0.30 or more, 1.0 or more, or 3.0 or more (for example, 6.0 or more). Further, the upper limit of the above ratio (B / A) is not particularly limited, and may be, for example, 15 or less, suitably 10 or less from the perspective of the polishing removal rate, preferably 5.0 or less, more preferably 1.0 or less, even more preferably 0.50 or less (for example, 0.20 or less), and may be 0.12 or less.

[0039] (Dispersion medium) The dispersion medium used in the polishing composition is not particularly limited as long as it can disperse fumed silica, an oxidizing agent, and a metal salt. The dispersion medium in this specification is generally a liquid (a medium that is liquid at 23°C), which is generally referred to as a dispersion medium or a solvent, and includes those that can be a solvent for an oxidizing agent or a metal salt. Water is preferably used as the dispersion medium. As water, for example, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used. The polishing composition disclosed herein may further contain an organic solvent (such as lower alcohol, lower ketone, etc.) that can be uniformly mixed with water, if necessary. It is preferable that 90% by volume or more of the solvent contained in the polishing composition is water, and more preferably 95% by volume or more (typically 99 - 100% by volume) is water.

[0040] (pH) The pH of the polishing composition is suitably about 2 to 12. When the pH is within the above range, a practical polishing removal rate is easily achieved when polishing the substrate. In some embodiments, the above pH may be 2.5 or more, 3.0 or more, 4.0 or more, 5.0 or more, 5.5 or more. The upper limit of the pH is not particularly limited. In some embodiments, the above pH may be 12.0 or less, 10.0 or less, 9.0 or less, 8.0 or less, 7.5 or less, 7.0 or less, 6.5 or less. In some preferred embodiments, the pH of the polishing composition is greater than 5.0 and less than 9.0, and may be, for example, less than 8.0 or less than 7.0. When the pH is within the above range, a higher polishing removal rate can be achieved. Although not to be construed in a particularly limiting manner, it is considered that both the cation and the anion in the metal salt contribute to the improvement of the polishing removal rate. Also, when the pH of the polishing composition is within the above range, there are advantages such as less damage to the polishing apparatus, for example.

[0041] (Other components) The polishing composition disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions (for example, polishing compositions for high-hardness materials, preferably polishing compositions for silicon carbide substrates), such as chelating agents, thickeners, dispersants, surface protectants, wetting agents, pH adjusters (organic acids, inorganic acids, basic compounds), surfactants, rust preventives, antiseptics, fungicides, etc., as long as the effects of the present invention are not impaired. The content of the above additives may be appropriately set according to the purpose of addition, and since it does not characterize the present invention, detailed description thereof is omitted.

[0042] <Preparation of Polishing Composition> The manufacturing method of the polishing composition disclosed herein is not particularly limited. For example, each component contained in the polishing composition may be mixed using a well-known mixing device such as a blade stirrer, an ultrasonic disperser, or a homomixer. The mode of mixing these components is not particularly limited, and for example, all components may be mixed at once, or they may be mixed in an appropriately set order.

[0043] The polishing composition disclosed herein may be of a single-agent type or a multi-agent type including a two-agent type. For example, a liquid A containing some of the constituent components of the polishing composition and a liquid B containing the remaining components may be stored separately, and may be configured such that the liquid A and the liquid B are mixed and used when polishing a substrate.

[0044] <Concentrate> The polishing composition disclosed herein may be in a concentrated form (that is, in the form of a concentrate of the polishing liquid) before being used for polishing. Such a concentrated form of the polishing composition is advantageous from the viewpoints of convenience and cost reduction during production, distribution, storage, etc.

[0045] <Substrate> The substrate polished using the polishing composition disclosed herein is not particularly limited. For example, the polishing composition disclosed herein can be applied to polishing a substrate having a surface composed of a compound semiconductor material, that is, a compound semiconductor substrate. The constituent material of the compound semiconductor substrate is not particularly limited. For example, it can be a Group II-VI compound semiconductor such as cadmium telluride, zinc selenide, cadmium sulfide, mercury cadmium telluride, cadmium zinc telluride, etc.; a Group III-V compound semiconductor such as gallium nitride, gallium arsenide, gallium phosphide, indium phosphide, aluminum gallium arsenide, indium gallium arsenide, indium gallium nitride arsenide, aluminum gallium indium phosphide, etc.; a Group IV-IV compound semiconductor such as silicon carbide, germanium silicide, etc. It may also be a substrate having a surface composed of a plurality of these materials. In some preferred embodiments, the polishing composition disclosed herein can be applied to polishing a substrate having a surface composed of a non-oxide (i.e., non-oxide) compound semiconductor material. When polishing a substrate having a surface composed of a non-oxide compound semiconductor material, the polishing promoting effect by the oxidizing agent contained in the polishing composition disclosed herein is preferably easily exerted.

[0046] The polishing composition disclosed herein can be preferably used, for example, to polish a substrate surface having a Vickers hardness of 500 Hv or more. The above Vickers hardness is preferably 700 Hv or more, for example 1000 Hv or more, and in some preferred embodiments, 1500 Hv or more. The Vickers hardness of the substrate material may be 1800 Hv or more, 2000 Hv or more, or 2200 Hv or more. The upper limit of the Vickers hardness of the substrate surface 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, the Vickers hardness can be measured based on JIS R 1610:2003. The international standard corresponding to the above JIS standard is ISO 14705:2000.

[0047] Examples of materials having a Vickers hardness of 1500 Hv or higher include silicon carbide, silicon nitride, titanium nitride, gallium nitride, and the like. The substrate in the technology disclosed herein can have a single-crystal surface of the above materials that is mechanically and chemically stable. Among them, the substrate surface is preferably composed of either silicon carbide or gallium nitride, and more preferably composed of silicon carbide. Silicon carbide is expected as a compound semiconductor substrate material with low power loss and excellent heat resistance, etc., and the practical advantages of efficiently making its surface smooth and flat are particularly great. The technology disclosed herein can be particularly preferably applied to polishing the single-crystal surface of silicon carbide.

[0048] <Polishing method> The polishing composition disclosed herein can be used when polishing a substrate, for example, in an embodiment including the following operations. That is, a polishing liquid (slurry) containing any of the polishing compositions disclosed herein is prepared. Preparing the polishing liquid may include adjusting the concentration of the polishing composition (for example, diluting the polishing composition), adjusting the pH of the polishing composition, etc. to prepare the polishing liquid. Alternatively, the polishing composition may be used as the polishing liquid as it is. In the case of a multi-agent type polishing composition, preparing the polishing liquid may include mixing those agents, diluting one or more agents before the mixing, diluting the mixture after the mixing, and the like. Next, the polishing liquid is supplied to the polishing surface and polished by a conventional method performed by those skilled in the art. For example, it is a method of setting a substrate on a general polishing apparatus and supplying the polishing liquid to the polishing surface of the substrate through the polishing pad of the polishing apparatus. Typically, while continuously supplying the polishing liquid, the polishing pad is pressed against the polishing surface of the substrate and the two are relatively moved (for example, rotationally moved). Through such a polishing process, the polishing of the substrate is completed.

[0049] According to this specification, a polishing method for polishing a substrate and a method for manufacturing a substrate using the polishing method are provided. The polishing method is characterized by including a step of polishing a substrate using the polishing composition disclosed herein. The polishing methods according to some preferred embodiments include a step of performing preliminary polishing (preliminary polishing step) and a step of performing finish polishing (finish polishing step). In some preferred embodiments, the preliminary polishing step is a polishing step arranged immediately before the finish polishing step. The preliminary polishing step may be a single-stage polishing step or a multi-stage polishing step of two or more stages. Further, the finish polishing step referred to herein is a step of performing finish polishing on the substrate on which the preliminary polishing has been performed, and refers to the polishing step that is arranged last (i.e., on the most downstream side) among the polishing steps performed using a polishing slurry containing abrasive grains. In the polishing method including the preliminary polishing step and the finish polishing step in this way, the polishing composition disclosed herein may be used in one step of the preliminary polishing step, may be used in the finish polishing step, or may be used in both the preliminary polishing step and the finish polishing step.

[0050] The preliminary polishing and the finish polishing can be carried out by either a single-sided polishing apparatus or a double-sided polishing apparatus. In a single-sided polishing apparatus, the substrate is attached to a ceramic plate with wax, the substrate is held using a holder called a carrier, and while supplying the polishing composition, a polishing pad is pressed against one side of the substrate and the two are relatively moved to polish one side of the object to be polished. The above movement is, for example, a rotational movement. In a double-sided polishing apparatus, the substrate is held using a holder called a carrier, and while supplying the polishing composition from above, a polishing pad is pressed against the opposing surfaces of the substrate, and they are rotated in opposite directions to polish both sides of the substrate simultaneously.

[0051] The polishing pads used in each of the polishing processes disclosed herein are not particularly limited. For example, any of a non-woven type, a suede type, a rigid foamed polyurethane type, those containing abrasive grains, those not containing abrasive grains, etc. may be used. In some embodiments, a non-woven type or a rigid foamed polyurethane type polishing pad not containing abrasive grains may be preferably employed.

[0052] The substrate polished by the method disclosed herein is typically cleaned after polishing. This cleaning can be performed using an appropriate cleaning liquid. The cleaning liquid to be used is not particularly limited, and known and commonly used ones can be appropriately selected and used.

[0053] Note that the polishing method disclosed herein may include any other processes in addition to the above-mentioned preliminary polishing process and finishing polishing process. Examples of such processes include a mechanical polishing process and a lapping process performed before the preliminary polishing process. In the above-mentioned mechanical polishing process, the substrate is polished using a liquid in which diamond abrasive grains are dispersed in a solvent. In some preferred embodiments, the above-mentioned dispersion liquid does not contain an oxidizing agent. The above-mentioned lapping process is a process of pressing the surface of a polishing platen, for example, a cast iron platen, against the substrate for polishing. Therefore, no polishing pad is used in the lapping process. The lapping process is typically performed by supplying abrasive grains between the polishing platen and the substrate. The above-mentioned abrasive grains are typically diamond abrasive grains. Further, the polishing method disclosed herein may include additional processes before the preliminary polishing process or between the preliminary polishing process and the finishing polishing process. The additional processes are, for example, a cleaning process and a polishing process.

[0054] <Method for manufacturing a substrate> The technology disclosed herein may include a method for manufacturing a substrate including a polishing step by any of the polishing methods described above, and a substrate manufactured by the method. The method for manufacturing the substrate is, for example, a method for manufacturing a silicon carbide substrate. That is, according to the technology disclosed herein, there are provided a method for manufacturing a substrate including polishing any of the substrates disclosed herein by any of the methods disclosed herein, and a substrate manufactured by the method. According to the manufacturing method, a substrate with improved surface quality, such as a silicon carbide substrate, can be efficiently provided.

Example

[0055] Hereinafter, some examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples. In the following description, “%” is based on weight unless otherwise specified.

[0056] <Preparation of Polishing Composition> (Example 1) Fumed silica, potassium permanganate (KMnO4) as an oxidizing agent, calcium nitrate as a metal salt, and deionized water were mixed to prepare the polishing composition of this example. The concentration of fumed silica was 1%, the concentration of potassium permanganate was 260 mmol / L, and the concentration of calcium nitrate was 15 mmol / L. The pH of the polishing composition was as shown in Table 1. As the fumed silica, one having an average primary particle diameter of 30 nm and an average secondary particle diameter of 150 nm was used.

[0057] (Examples 2 - 3) The polishing compositions of each example were prepared in the same manner as in Example 1 except that the concentration of calcium nitrate was the concentration shown in Table 1.

[0058] (Examples 4 - 6) The polishing compositions of each example were prepared in the same manner as in Example 1 except that the concentration of the oxidizing agent was 80 mmol / L and the concentration of calcium nitrate was the concentration shown in Table 1.

[0059] (Examples 7 - 8) The polishing compositions of each example were prepared in the same manner as in Example 4, except that the type and concentration of the metal salt were as shown in Table 1.

[0060] (Examples 9 to 11) The polishing compositions of each example were prepared in the same manner as in Example 4, except that the concentration of calcium nitrate was 15 mmol / L and the concentration of fumed silica was the concentration shown in Table 1.

[0061] (Examples 12 to 13) The polishing compositions of each example were prepared in the same manner as in Example 4, except that the type and concentration of the metal salt were as shown in Table 1.

[0062] (Comparative Examples 1 to 2) The polishing compositions of each example were prepared in the same manner as in Example 4, except that the concentration of calcium nitrate was the concentration shown in Table 1.

[0063] (Comparative Examples 3 to 4) The polishing compositions of each example were prepared in the same manner as in Example 4, except that the type and concentration of the metal salt were as shown in Table 1.

[0064] (Evaluation of Polishing Removal Rate) Preliminary polishing was performed in advance using a polishing liquid containing alumina abrasive grains. The surface of the SiC wafer after the preliminary polishing was polished under the following conditions using the polishing composition of each example as the polishing liquid as it was. Then, the polishing rate was calculated according to the following calculation formulas (1) and (2). The results are shown in the corresponding columns of Table 1. (1) Polishing removal amount [cm] = Difference in weight of the SiC wafer before and after polishing [g] / Density of SiC [g / cm 3 (= 3.21 g / cm 3 ) / Polishing target area [cm 2 (= 19.62 cm 2 ) (2) Polishing rate [nm / h] = Polishing removal amount [cm] × 10 7 / Polishing time (= 1 hour) (Polishing Conditions) Polishing apparatus: Single-sided polishing apparatus manufactured by Nippon Engis Co., Ltd., model "EJ-380IN-CH" Polishing pad: "SUBA800XY" manufactured by Nitta Haas Polishing pressure: 29.4 kPa Platen rotation speed: 80 revolutions per minute Head rotation speed: 40 revolutions per minute Supply rate of polishing liquid: 20 mL / min (flowing over) Temperature of polishing liquid: 25 °C Polishing time: 1 hour Object to be polished: SiC wafer (conductivity type: n-type, crystal type 4H-SiC, off-angle with respect to the C-axis of the main surface (0001): 4) 2 inches × 3 pieces

[0065]

Table 1

[0066] As shown in Table 1, according to the polishing compositions of Examples 1 to 13 containing fumed silica and an oxidizing agent and containing a metal salt in a proportion of more than 10 mmol / L, the polishing rate was improved as compared with Comparative Examples 1 to 4 in which the content of the metal salt was 10 mmol / L or less.

[0067] As described above, specific examples of the present invention have been described in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims

1. A polishing composition comprising fumed silica, an oxidizing agent, and a metal salt, wherein the oxidizing agent contains a composite metal oxide, and the content of the metal salt is more than 10 mmol / L.

2. A polishing composition used for polishing a material having a Vickers hardness of 1500 Hv or more, comprising fumed silica, an oxidizing agent, and a metal salt, wherein the content of the metal salt is more than 10 mmol / L.

3. The polishing composition according to claim 1 or 2, wherein the metal salt is a nitrate and / or hydrochloride of an alkali metal and / or an alkaline earth metal.

4. The polishing composition according to any one of claims 1 to 3, wherein the metal forming the metal salt is potassium.

5. The polishing composition according to any one of claims 1 to 3, wherein the metal forming the metal salt is calcium.

6. The polishing composition according to any one of claims 1 to 5, wherein the ratio (B / A) of the concentration B [mmol / L] of the metal salt to the concentration A [mmol / L] of the oxidizing agent is 0.01 or more and 10 or less.

7. The polishing composition according to any one of claims 1 to 6, wherein the pH is greater than 5.0 and less than 9.

0.

8. The polishing composition according to any one of claims 1 to 7, which is used for polishing silicon carbide.

9. A method for polishing a substrate, comprising a step of polishing the substrate using the polishing composition according to any one of claims 1 to 8.

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