Polishing method and polishing composition

Abstract

Provided are a polishing method and a polishing composition that are applied to polishing of silicon carbide and allows reduction of rise in pH of the polishing composition and increase in pad temperature during polishing. Provided is a method of polishing an object to be polished having a surface formed of silicon carbide. The method includes steps of preparing a polishing composition, and supplying the polishing composition to the object to be polished and polishing the object to be polished. The polishing composition contains permanganate, a metal salt A, and water. The metal salt A is a salt of a metal cation having a pKa of less than 7.0 in form of a hydrated metal ion, and an anion.

Description

Polishing method and polishing composition

[0001] The present invention relates to a polishing method and a polishing composition, and more particularly to a polishing method and a polishing composition for silicon carbide. This application claims priority to Japanese Patent Application No. 2021-016869 filed on February 4, 2021, and Japanese Patent Application No. 2021-162178 filed on September 30, 2021, the entire contents of which are incorporated herein by reference.

[0002] Polishing using a polishing composition has been used on the surfaces of materials such as metals, semimetals, nonmetals, and their oxides. For example, surfaces made of compound semiconductor materials such as silicon carbide, boron carbide, tungsten carbide, silicon nitride, titanium nitride, and gallium nitride are processed by polishing (lapping) by supplying diamond abrasive grains between the surface and a polishing table. However, lapping using diamond abrasive grains is prone to defects and distortion due to the generation and persistence of scratches and dents. Therefore, polishing (polishing) using a polishing pad and a polishing composition after lapping using diamond abrasive grains, or instead of lapping, has been considered. Examples of literature disclosing this type of prior art include Patent Documents 1 and 2.

[0003] International Publication No. WO 2018 / 174008 International Publication No. WO 2019 / 138846

[0004] Generally, from the viewpoint of manufacturing efficiency and cost-effectiveness, it is desirable that the polishing removal rate is sufficiently high for practical use.For example, in polishing a surface made of silicon carbide, which is a high-hardness material, an improvement in the polishing removal rate is strongly desired.Patent Documents 1 and 2 propose that the polishing rate be improved by adding an alkali metal salt and / or an alkaline earth metal salt as a polishing accelerator to a polishing composition containing water and an oxidizing agent, and not containing abrasive grains (Patent Document 1) or containing abrasive grains (Patent Document 2).

[0005] However, depending on the mode of use, the polishing composition using the techniques described in Patent Documents 1 and 2 may have difficulty in properly demonstrating its original polishing performance (for example, polishing removal rate) due to the fact that the pH of the polishing composition supplied to the object to be polished increases significantly during polishing.In addition, the polishing removal rate can also be improved by setting polishing conditions such as increasing the load applied to the polishing surface during polishing to increase the processing pressure or increasing the rotation speed of the platen of the polishing device.However, the polishing composition using the techniques described in Patent Documents 1 and 2 tends to cause a large increase in the temperature of the polishing pad during polishing (polishing) using the polishing composition.If the temperature increase of the polishing pad can be suppressed, it becomes possible to adopt more severe processing conditions, which is beneficial for further improving the polishing removal rate.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a polishing method and a polishing composition that can be applied to polishing silicon carbide and that can suppress an increase in the pH of the polishing composition and an increase in the pad temperature during polishing.

[0007] This specification provides a method for polishing an object having a silicon carbide surface. The method includes preparing a polishing composition and supplying the polishing composition to the object to be polished to polish it. The polishing composition contains permanganate, metal salt A, and water. Here, metal salt A is a salt of a metal cation having a pKa of less than 7.0 and an anion. By polishing silicon carbide using a polishing composition containing permanganate and metal salt A, increases in the pH of the polishing composition and increases in the temperature of the polishing pad (hereinafter also referred to as pad temperature) during polishing can be suppressed. This can improve the polishing removal rate and / or enable the use of more severe processing conditions. This can increase the productivity of the object (e.g., a silicon carbide substrate) obtained through polishing by the polishing method. This specification also provides a polishing composition for use in any of the polishing methods disclosed herein.

[0008] In some embodiments of the technology disclosed herein (including a polishing method, a polishing composition used in the method, a method for producing a polished object, etc.; the same applies hereinafter), the pH of the polishing composition supplied to the object to be polished (hereinafter also referred to as initial pH) is preferably 5.0 or less. In polishing using a polishing composition having such an initial pH, applying the technology disclosed herein can effectively suppress a rise in pH during polishing.

[0009] In some embodiments of the technology disclosed herein, the pH of the polishing composition supplied to the object to be polished when it flows out of the object to be polished (hereinafter also referred to as the pH during polishing) increases by less than 2.0 from the pH when the polishing composition was supplied to the object to be polished (i.e., the initial pH). In such embodiments, the effect of improving the polishing removal rate by suppressing the pH increase can be suitably exhibited.

[0010] In some embodiments, the polishing composition further comprises abrasive grains. The use of abrasive grains can improve the polishing removal rate. In addition, when polishing using a polishing composition containing abrasive grains, the pad temperature tends to be higher than when a polishing composition not containing abrasive grains is used, so it is more effective to suppress the increase in pad temperature by applying the technology disclosed herein.

[0011] In some embodiments, the metal cation in the metal salt A is a cation containing a metal belonging to Groups 3 to 16 of the periodic table. In such embodiments, increases in pH and pad temperature during polishing can be effectively suppressed.

[0012] This specification also provides a polishing composition for polishing an object having a surface composed of silicon carbide. The polishing composition contains a permanganate, a metal salt A, and water. Here, the metal salt A is a salt of a metal cation having a pKa of less than 7.0 and an anion. When used to polish the object, the polishing composition having such a composition can effectively suppress an increase in the pH of the polishing composition and an increase in the pad temperature during polishing.

[0013] Preferred embodiments of the present invention will be described below. It should be noted that matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.

[0014] <Polishing Composition> (Permanganate) The polishing composition in the technology disclosed herein contains a permanganate. In polishing silicon carbide, the permanganate typically functions as an oxidizing agent, thereby exhibiting the effect of improving the polishing removal rate. As the permanganate, for example, an alkali metal permanganate such as sodium permanganate or potassium permanganate is preferred, and potassium permanganate is particularly preferred. Note that the permanganate may be present in the polishing composition in the form of an ion.

[0015] The concentration (content) of permanganate in the polishing composition is not particularly limited, and can be appropriately set according to the purpose and mode of use of the polishing composition so as to achieve the desired effect.In some embodiments, from the viewpoint of improving the polishing removal rate, the concentration of permanganate is preferably about 5 mM or more (i.e., 0.005 mol / L or more).From the viewpoint of improving the polishing removal rate, the concentration of permanganate is preferably 10 mM or more, more preferably 30 mM or more, and may be 50 mM or more, 70 mM or more, or 90 mM or more.From the viewpoint of easily achieving a higher polishing removal rate, in some embodiments, the concentration of permanganate may be 120 mM or more, 140 mM or more, 160 mM or more, 180 mM or more, 200 mM or more, or 225 mM or more. The upper limit of the concentration of permanganate in the polishing composition is not particularly limited, but from the viewpoint of suppressing the rise in pad temperature, etc., it is appropriate to make it approximately 2500 mM or less, preferably 2000 mM or less, more preferably 1700 mM or less, and may be 1500 mM or less, may be 1000 mM or less, may be 750 mM or less, may be 500 mM or less, may be 400 mM or less, or may be 300 mM or less. In some embodiments, the concentration of permanganate may be 250 mM or less, may be 200 mM or less, may be 150 mM or less, may be 120 mM or less.

[0016] (Metal Salt A) The polishing composition of the technology disclosed herein contains metal salt A. Metal salt A is a salt of a metal cation having a pKa of less than 7.0 and an anion. In this specification, metal cation refers to a cation containing a metal. That is, the metal cation may be a cation composed of only a metal, or a cation composed of a metal and a non-metal. Metal salt A can be used alone or in combination of two or more. By adding metal salt A in addition to permanganate to a polishing composition used for polishing silicon carbide, it is possible to preferably suppress an increase in the pH of the polishing composition and an increase in pad temperature during polishing. Without wishing to be bound by theory, the reason for such effects is thought to be as follows. That is, in polishing (polishing) performed by supplying a polishing composition containing permanganate to an object having a surface composed of silicon carbide, the permanganate contained in the polishing composition can contribute to improving the polishing removal rate by oxidizing and embrittling the silicon carbide surface. However, this oxidation can cause an increase in the pH of the polishing composition supplied to the material to be polished. As a result, if the pH of the polishing composition supplied to the material to be polished rises from the initial pH (i.e., the pH of the polishing composition supplied to the material to be polished) during polishing of the material to be polished and falls outside the appropriate pH range, the chemical polishing performance of the polishing composition on the material to be polished will be reduced. It is believed that a decrease in the chemical polishing performance of the polishing composition reduces the polishing removal rate and increases the contribution of mechanical polishing performance, making the pad temperature more likely to rise. When a polishing composition containing permanganate contains a metal salt A containing a metal cation whose hydrated metal ion has a pKa of less than 7.0, the metal salt A exerts a buffering effect, suppressing the increase in the pH of the polishing composition and maintaining it within the appropriate pH range. This maintains the chemical polishing performance of the polishing composition, thereby suppressing the decrease in the polishing removal rate and suppressing the increase in pad temperature. However, the above considerations do not limit the scope of the present invention.

[0017] In some embodiments, a salt of a metal cation having a pKa of less than 6.0 as the hydrated metal ion and an anion can be preferably used as the metal salt A. Examples of metal cations having a pKa of less than 6.0 as the hydrated metal ion include Al ３＋ (pKa of hydrated metal ion is 5.0), Cr ３＋ (same 4.0), In ３＋ (4.0), Ga ３＋ (same as 2.6), Fe ３＋ (same as 2.2), Hf ４＋ (same -0.2), Zr ４＋ (same -0.3), Ce ４＋ (same -1.1), Ti ４＋ (same as -4.0), but are not limited thereto. In some embodiments, the pKa of the hydrated metal ion may be 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, or 3.0 or less. The lower limit of the pKa of the hydrated metal ion is suitably approximately -5.0 or more, may be -1.5 or more, may be -0.5 or more, preferably 0.0 or more, more preferably 0.5 or more, may be 1.0 or more, may be 1.5 or more, may be 2.0 or more, or may be 2.5 or more. The valence of the metal cation in metal salt A may be, for example, divalent to tetravalent. In some embodiments, metal salt A that is a salt of a cation containing a trivalent metal and an anion may be preferably used.

[0018] The metal cation in metal salt A may be, for example, a cation containing a metal belonging to Groups 3 to 16 of the periodic table, preferably a cation containing a metal belonging to Groups 4 to 14 of the periodic table, and more preferably a cation containing a metal belonging to Groups 6 to 14. The technology disclosed herein can be preferably practiced in an embodiment using metal salt A that is a salt of an anion and a cation containing, for example, a metal belonging to Group 13 of the periodic table.

[0019] In some embodiments, a metal salt that buffers the pH to 2.5 to 5.5 (e.g., 3.0 to 4.5) can be preferably used as metal salt A. The pH that metal salt A buffers can be determined by titrating an aqueous solution of metal salt A with sodium hydroxide.

[0020] The metal salt A 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, and salts of nitric acid, sulfuric acid, carbonic acid, silicic acid, boric acid, and phosphoric acid. Examples of organic acid salts include salts of 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, and salts of hydrochloric acid, nitric acid, and sulfuric acid are more preferred. The technology disclosed herein relates to, for example, salts of Al as the metal salt A. ３＋ , Cr ３＋ , Fe ３＋ , In ３＋ , Ga ３＋ and Zr ４＋ and a cation selected from the group consisting of nitrate ions (NO ３ － ), chloride ions (Cl － ), sulfate ions (SO ４ ２－ ) and acetate ions (CH ３ COO － This can be preferably carried out in an embodiment using a salt with an anion selected from the group consisting of:

[0021] The metal salt A is preferably a water-soluble salt. By using a water-soluble metal salt A, a good surface with few defects such as scratches can be efficiently formed.

[0022] The concentration (content) of metal salt A in the polishing composition is not particularly limited, and can be appropriately set so as to achieve the desired effect according to the purpose and mode of use of the polishing composition.The concentration of metal salt A may be, for example, approximately 1000 mM or less, may be 500 mM or less, or may be 300 mM or less.From the viewpoint of effectively suppressing the pH increase and the pad temperature increase during polishing, in some embodiments, the concentration of metal salt A is suitably 200 mM or less, preferably 100 mM or less, more preferably 50 mM or less, may be 40 mM or less, may be 30 mM or less, may be 20 mM or less, or may be 10 mM or less.The lower limit of the concentration of metal salt A may be, for example, 0.1 mM or more, and from the viewpoint of appropriately exhibiting the effect of use of metal salt A, it is advantageous to set it to 1 mM or more, preferably 5 mM or more, and more preferably 7 mM or more (for example, 8 mM or more). The technology disclosed herein can also be preferably practiced in an embodiment in which the concentration of metal salt A in the polishing composition is 10 mM or more, 20 mM or more, 25 mM or more, or 30 mM or more, for example.

[0023] Although not particularly limited, from the viewpoint of better exerting the effect of adding metal salt A to a polishing composition containing permanganate, the ratio (C2 / C1) of the concentration of metal salt A (if a plurality of metal salts A are contained, their total concentration) C2 [mM] to the concentration of permanganate (if a plurality of permanganates are contained, their total concentration) C1 [mM] in the polishing composition is suitably about 0.0002 or more, preferably 0.001 or more, more preferably 0.005 or more, and may be 0.01 or more, or may be 0.02 or more. From the viewpoint of enhancing the effect of suppressing the rise in pad temperature, in some embodiments, C2 / C1 may be, for example, 0.03 or more, preferably 0.04 or more, may be 0.05 or more, or may be 0.07 or more. The upper limit of C2 / C1 is not particularly limited, but is suitably about 200 or less, may be 100 or less, may be 75 or less, or may be 50 or less. In some preferred embodiments, C2 / C1 may be 20 or less, 10 or less, 5 or less, 1 or less, 0.6 or less, 0.5 or less, 0.3 or less, or 0.2 or less. With such a concentration ratio (C2 / C1) of metal salt A to permanganate, the suppression of an increase in pH and an increase in pad temperature by metal salt A can be preferably achieved.

[0024] (Abrasive grains) In some embodiments of the technology disclosed herein, the polishing composition contains abrasive grains. A polishing composition containing abrasive grains can achieve a higher polishing removal rate by exhibiting a primarily mechanical polishing action due to the abrasive grains in addition to the primarily chemical polishing action due to the permanganate and metal salt A. Furthermore, since the pad temperature tends to increase when the polishing composition contains abrasive grains, it is more effective to apply the technology disclosed herein to suppress the increase in pad temperature.

[0025] The material and properties of the abrasive grains are not particularly limited. For example, the abrasive grains may be inorganic particles, organic particles, or organic-inorganic composite particles. Examples include oxide particles such as silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and iron oxide particles; nitride particles such as silicon nitride particles and boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; and carbonates such as calcium carbonate and barium carbonate. One type of abrasive grain may be used alone, or two or more types may be used in combination. Among these, oxide particles such as silica particles, alumina particles, cerium oxide particles, chromium oxide particles, zirconium oxide particles, manganese dioxide particles, and iron oxide particles are preferred because they can form a good surface. Among these, silica particles, alumina particles, zirconium oxide particles, chromium oxide particles, and iron oxide particles are more preferred, and silica particles and alumina particles are particularly preferred. In an embodiment in which silica particles or alumina particles are used as abrasive grains, the effect of suppressing an increase in pad temperature can be suitably achieved by applying the technology disclosed herein.

[0026] In this specification, the phrase "consisting essentially of X" or "consisting essentially of X" in relation to the composition of the abrasive grains means that the proportion of X in the abrasive grains (purity of X) is 90% or more by weight. The proportion of X in the abrasive grains is preferably 95% or more, more preferably 97% or more, even more preferably 98% or more, for example, 99% or more.

[0027] The average primary particle size of the abrasive grains is not particularly limited. From the viewpoint of easily obtaining a desired polishing removal rate while suppressing an increase in pad temperature, the average primary particle size of the abrasive grains can be, for example, 5 nm or more, suitably 10 nm or more, preferably 20 nm or more, or even 30 nm or more. From the viewpoint of improving the polishing removal rate, in some embodiments, the average primary particle size of the abrasive grains may be 50 nm or more, 80 nm or more, 150 nm or more, 250 nm or more, 280 nm or more, or 350 nm or more. Furthermore, from the viewpoint of suppressing an increase in pad temperature, the average primary particle size of the abrasive grains can be, for example, 5 μm or less, preferably 3 μm or less, more preferably 1 μm or less, or may be 750 nm or less, or may be 500 nm or less. From the viewpoint of surface quality after polishing, in some embodiments, the average primary particle size of the abrasive grains may be 350 nm or less, 300 nm or less, 180 nm or less, 150 nm or less, 85 nm or less, or 50 nm or less.

[0028] In this specification, the average primary particle diameter is calculated from the specific surface area (BET value) measured by the BET method by the following formula: average primary particle diameter (nm) = 6000 / (true density (g / cm ３ ) × BET value (m ２ The specific surface area is the particle size (BET particle size) calculated by the formula: (1 / g / 2) / (2 / g). The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritics, trade name "Flow Sorb II 2300."

[0029] The average secondary particle diameter of the abrasive grains may be, for example, 10 nm or more, and from the viewpoint of easily increasing the polishing removal rate, it is preferably 50 nm or more, more preferably 100 nm or more, and may be 250 nm or more, or even 400 nm or more. From the viewpoint of ensuring a sufficient number per unit weight, the upper limit of the average secondary particle diameter of the abrasive grains is suitably set to approximately 10 μm or less. Furthermore, from the viewpoint of suppressing an increase in pad temperature, the average secondary particle diameter is preferably 5 μm or less, more preferably 3 μm or less, for example, 1 μm or less. From the viewpoint of surface quality after polishing, in some embodiments, the average secondary particle diameter of the abrasive grains may be 600 nm or less, 300 nm or less, 170 nm or less, or 100 nm or less.

[0030] The average secondary particle diameter of the abrasive grains can be measured as the volume average particle diameter (volume-based arithmetic mean diameter; Mv) for particles less than 500 nm by dynamic light scattering using, for example, a model "UPA-UT151" manufactured by Nikkiso Co., Ltd. Furthermore, for particles 500 nm or larger, the volume average particle diameter can be measured by, for example, a pore electrical resistance method using a model "Multisizer 3" manufactured by Beckman Coulter.

[0031] When alumina particles (alumina abrasive grains) are used as abrasive grains, they can be appropriately selected from various known alumina particles. Examples of such known alumina particles include α-alumina and intermediate alumina. Here, intermediate alumina is a general term for alumina particles other than α-alumina, and specific examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and χ-alumina. Fumed alumina (typically alumina fine particles produced by high-temperature calcination of alumina salts) may also be used, based on classification by production method. Furthermore, alumina called colloidal alumina or alumina sol (e.g., alumina hydrates such as boehmite) also fall within the scope of the known alumina particles. From the viewpoint of processability, α-alumina is preferred. The alumina abrasive grains disclosed herein may contain one type of such alumina particles alone or in combination of two or more types.

[0032] When alumina particles are used as abrasive grains, it is generally advantageous to have a higher proportion of alumina particles in the total abrasive grains used. For example, the proportion of alumina particles in the total abrasive grains is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and may be substantially 100% by weight.

[0033] The particle size of the alumina abrasive grains is not particularly limited and can be selected so as to achieve the desired polishing effect. From the viewpoint of improving the polishing removal rate, the average primary particle diameter of the alumina abrasive grains is preferably 50 nm or more, more preferably 80 nm or more, and may be 150 nm or more, 250 nm or more, 280 nm or more, 300 nm or more, or 350 nm or more. The upper limit of the average primary particle diameter of the alumina abrasive grains is not particularly limited, but from the viewpoint of suppressing an increase in pad temperature, it is appropriate to set it to approximately 5 μm or less. From the viewpoint of surface quality after polishing, it is preferably 3 μm or less, more preferably 1 μm or less, and may be 750 nm or less, 500 nm or less, 400 nm or less, or 350 nm or less.

[0034] When using alumina particles as abrasive grains, the polishing composition disclosed herein may further contain abrasive grains made of materials other than alumina (hereinafter also referred to as non-alumina abrasive grains) within the scope that does not impair the effects of the present invention.Examples of such non-alumina abrasive grains include abrasive grains that are substantially composed of any of oxide particles such as silica particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese oxide particles, zinc oxide particles, iron oxide particles, etc.; nitride particles such as silicon nitride particles, boron nitride particles, etc.; carbide particles such as silicon carbide particles, boron carbide particles, etc.; diamond particles; carbonates such as calcium carbonate, barium carbonate, etc.

[0035] The content of the non-alumina abrasive grains is suitably, for example, 30% by weight or less of the total weight of the abrasive grains contained in the polishing composition, preferably 20% by weight or less, and more preferably 10% by weight or less.

[0036] In another preferred embodiment of the technology disclosed herein, the polishing composition contains silica particles (silica abrasive particles) as abrasive particles. The silica abrasive particles can be appropriately selected from various known silica particles. Examples of such known silica particles include colloidal silica and dry process silica. Among these, colloidal silica is preferably used. Silica abrasive particles containing colloidal silica can suitably achieve good surface precision.

[0037] The shape (external shape) of the silica abrasive grains may be spherical or non-spherical. Specific examples of non-spherical silica abrasive grains include peanut-shaped (i.e., peanut shell-shaped), cocoon-shaped, confetti-shaped, and rugby ball-shaped. In the technology disclosed herein, the silica abrasive grains may be in the form of primary particles, or in the form of secondary particles in which a plurality of primary particles are aggregated. Furthermore, silica abrasive grains in the form of primary particles and silica abrasive grains in the form of secondary particles may be present together. In a preferred embodiment, at least a portion of the silica abrasive grains are contained in the polishing composition in the form of secondary particles.

[0038] As the silica abrasive grains, those having an average primary particle diameter of more than 5 nm can be preferably used. From the viewpoint of polishing efficiency, etc., the average primary particle diameter of the silica abrasive grains is preferably 15 nm or more, more preferably 20 nm or more, even more preferably 25 nm or more, and particularly preferably 30 nm or more. The upper limit of the average primary particle diameter of the silica abrasive grains is not particularly limited, but it is appropriate to set it to approximately 120 nm or less, preferably 100 nm or less, more preferably 85 nm or less. For example, from the viewpoint of achieving both polishing efficiency and surface quality at a higher level, silica abrasive grains having a BET diameter of 12 nm or more and 80 nm or less are preferred, and silica abrasive grains having a BET diameter of 15 nm or more and 75 nm or less are preferred.

[0039] The average secondary particle size of the silica abrasive grains is not particularly limited, but is preferably 20 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more, from the viewpoint of polishing efficiency, etc. Furthermore, from the viewpoint of obtaining a higher quality surface, the average secondary particle size of the silica abrasive grains is suitably 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, even more preferably 130 nm or less, and particularly preferably 110 nm or less (e.g., 100 nm or less).

[0040] The true specific gravity (true density) of the silica particles is preferably 1.5 or more, more preferably 1.6 or more, and even more preferably 1.7 or more. An increase in the true specific gravity of the silica particles tends to increase the physical polishing ability. The upper limit of the true specific gravity of the silica particles is not particularly limited, but is typically 2.3 or less, for example, 2.2 or less, 2.0 or less, or 1.9 or less. The true specific gravity of the silica particles can be measured by a liquid substitution method using ethanol as the substitution liquid.

[0041] The shape (outer shape) of silica particles is preferably spherical.Although not particularly limited, the average value of the long diameter / short diameter ratio of particles (average aspect ratio) is in principle 1.00 or more, and from the viewpoint of improving the polishing removal rate, it may be, for example, 1.05 or more, or 1.10 or more.In addition, the average aspect ratio of particles is suitably 3.0 or less, and may be 2.0 or less.From the viewpoint of improving the smoothness of the polished surface and reducing scratches, the average aspect ratio of particles is preferably 1.50 or less, may be 1.30 or less, or may be 1.20 or less.

[0042] The particle shape (external shape) and average aspect ratio can be determined, for example, by observation with an electron microscope. A specific procedure for determining the average aspect ratio involves, for example, using a scanning electron microscope (SEM) to extract the shapes of a predetermined number of particles (e.g., 200 particles). The smallest rectangle circumscribing each extracted particle shape is then drawn. The length of the long side (major axis value) of the rectangle drawn for each particle shape is then divided by the length of the short side (minor axis value) to calculate the major axis / minor axis ratio (aspect ratio). The average aspect ratio can be determined by arithmetically averaging the aspect ratios of the predetermined number of particles.

[0043] In the embodiment where the polishing composition contains silica abrasive grains, the polishing composition may further contain abrasive grains made of a material other than silica (hereinafter also referred to as non-silica abrasive grains).Examples of particles constituting such non-silica abrasive grains include oxide particles such as alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese oxide particles, zinc oxide particles, iron oxide particles, etc.; nitride particles such as silicon nitride particles, boron nitride particles, etc.; carbide particles such as silicon carbide particles, boron carbide particles, etc.; diamond particles; carbonates such as calcium carbonate and barium carbonate; etc. In some embodiments of the polishing composition containing silica abrasive grains and non-silica abrasive grains, the content of non-silica abrasive grains in the total weight of the abrasive grains contained in the polishing composition may be, for example, 30 wt% or less, 20 wt% or less, or 10 wt% or less.

[0044] The content of abrasive grains (e.g., silica abrasive grains, alumina abrasive grains, etc.) in the polishing composition disclosed herein is suitably less than 5 wt % from the viewpoint of suppressing an increase in pad temperature, advantageously less than 3 wt %, preferably less than 1 wt %, more preferably less than 0.5 wt %, and may be 0.3 wt % or less, or may be 0.2 wt % or less. In some embodiments, the content of abrasive grains in the polishing composition may be 0.1 wt % or less or less than 0.1 wt %, 0.05 wt % or less or less than 0.05 wt %, 0.04 wt % or less or less than 0.04 wt %, or 0.03 wt % or less or less than 0.03 wt %. The lower limit of the content of abrasive grains is not particularly limited, and may be, for example, 0.000001 wt % or more (i.e., 0.01 ppm or more). In order to enhance the effect of using the abrasive grains, in some embodiments, the content of the abrasive grains in the polishing composition may be 0.00001% by weight or more, 0.0001% by weight or more, 0.001% by weight or more, 0.002% by weight or more, or 0.005% by weight or more. When the polishing composition disclosed herein contains multiple types of abrasive grains, the content of the abrasive grains in the polishing composition refers to the total content of the multiple types of abrasive grains.

[0045] The polishing composition disclosed herein preferably does not substantially contain diamond particles as particles.Diamond particles have high hardness, which can be a limiting factor in improving smoothness.In addition, diamond particles are generally expensive, so they are not considered to be an advantageous material in terms of cost-effectiveness, and from a practical standpoint, it is acceptable to have a low dependency on expensive materials such as diamond particles.Here, "particles substantially do not contain diamond particles" means that the proportion of diamond particles in the total particles is 1% by weight or less, more preferably 0.5% by weight or less, typically 0.1% by weight or less, and includes the case where the proportion of diamond particles is 0% by weight.In such an embodiment, the application effect of the present invention can be suitably exhibited.

[0046] In a polishing composition containing abrasive grains, the relationship between the permanganate concentration and the abrasive grain content is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and mode of use. In some embodiments, the ratio of the permanganate concentration C1 [mM] to the abrasive grain content W1 [wt %], i.e., C1 / W1, can be, for example, 5 or more, suitably 50 or more, advantageously 100 or more, preferably 150 or more, and more preferably 200 or more or 250 or more. In other words, the linear relationship between C1 and W1 and the larger C1 / W1 tend to increase the contribution of chemical polishing relative to the contribution of mechanical polishing. In such a composition, the metal salt A can effectively suppress pad temperature rise. For example, polishing using a polishing composition satisfying 500≦C1 / W1 can effectively achieve both a high polishing removal rate and suppressed pad temperature rise. In some embodiments, C1 / W1 may be 300 or more, 400 or more, 500 or more, 700 or more, 1000 or more, or even 1500 or more, 3000 or more, 5500 or more, or 7500 or more. The upper limit of C1 / W1 is not particularly limited, but from the viewpoint of storage stability of the polishing composition, it can be, for example, about 100,000 or less, 75,000 or less, 50,000 or less, 20,000 or less, 10,000 or less, or 9,000 or less. In some embodiments, C1 / W1 may be 7,000 or less, 5,000 or less, or 3,000 or less. In the above "C1 / W1," "C1" represents the numerical portion when the concentration of permanganate in the polishing composition is expressed in units of "mM," and "W1" represents the numerical portion when the content of abrasive grains in the polishing composition is expressed in units of "wt %," and both C1 and W1 are dimensionless numbers.

[0047] In the polishing composition disclosed herein, the ratio of the permanganate concentration C1 [mM] to the square root of the abrasive grain content W1 [wt %], i.e., C1 / √(W1), is preferably 200 or more. In other words, the relationship between C1 and W1 is nonlinear, and as C1 / √(W1) increases, the contribution of chemical polishing to the contribution of mechanical polishing tends to increase. By improving the polishing removal rate in a composition that satisfies 200≦C1 / √(W1), it is possible to achieve both a high polishing removal rate and suppression of pad temperature increases. In some embodiments, C1 / √(W1) may be 300 or more, 750 or more, or even 1500 or more, 2500 or more, 3500 or more, or 4500 or more. The upper limit of C1 / √(W1) is not particularly limited, but from the viewpoint of storage stability of the polishing composition, it can be, for example, approximately 12,000 or less, or may be 10,000 or less, 8,000 or less, or 6,000 or less. In some embodiments, C1 / √(W1) may be 4,500 or less, 3,500 or less, or 2,500 or less.

[0048] In a polishing composition containing abrasive grains, the relationship between the concentration of metal salt A and the content of abrasive grains is not particularly limited and can be appropriately set so as to achieve the desired effect depending on the purpose and mode of use. The ratio of the concentration of metal salt A C2 [mM] to the content of abrasive grains W1 [wt %], i.e., C2 / W1, can be, for example, 5 or more, advantageously 10 or more, preferably 20 or more, more preferably 30 or more, and may be 50 or more, or even 80 or more. As C2 / W1 increases, the effect of suppressing pad temperature rise due to the use of metal salt A can be more effectively exerted. In some embodiments, C2 / W1 may be 150 or more, 200 or more, 300 or more, 500 or more, or 800 or more. The upper limit of C2 / W1 is not particularly limited, but from the viewpoint of storage stability of the polishing composition, it can be, for example, approximately 10,000 or less, or may be 5,000 or less, or may be 2,500 or less. In some embodiments, C2 / W1 may be 1000 or less, 800 or less, 600 or less, 450 or less, 350 or less, or 250 or less. In the above "C2 / W1," "C2" represents the numerical value when the concentration of metal salt A in the polishing composition is expressed in units of "mM," and "W1" represents the numerical value when the content of abrasive grains in the polishing composition is expressed in units of "wt %," and both C2 and W1 are dimensionless numbers.

[0049] (Alkaline Earth Metal Salt) The polishing composition disclosed herein may contain, as an optional component, at least one metal salt A selected from alkaline earth metal salts. EMS Metal salt A EMS As the alkaline earth metal salt, one kind of alkaline earth metal salt may be used alone, or two or more kinds of alkaline earth metal salts may be used in combination. EMS The use of the metal salt in combination with the above can better suppress the rise in pad temperature. EMS It is preferable that the alloy contains one or more of Mg, Ca, Sr, and Ba as an element belonging to alkaline earth metals. Of these, either Ca or Sr is preferable, and Ca is more preferable.

[0050] Metal salt AEMS The type of salt in is not particularly limited, and 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, and salts of nitric acid, sulfuric acid, carbonic acid, silicic acid, boric acid, and phosphoric acid. Examples of organic acid salts include salts of 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, and salts of hydrochloric acid and nitric acid are more preferred. The technology disclosed herein can be applied to, for example, a metal salt A EMS The method can be preferably carried out in an embodiment in which a nitrate or chloride of an alkaline earth metal is used as the catalyst.

[0051] Metal salt A EMS Specific examples of alkaline earth metal salts that can be selected from include chlorides such as magnesium chloride, calcium chloride, strontium chloride, and barium chloride; bromides such as magnesium bromide; fluorides such as magnesium fluoride, calcium fluoride, strontium fluoride, and barium fluoride; nitrates such as magnesium nitrate, calcium nitrate, strontium nitrate, and barium nitrate; sulfates such as magnesium sulfate, calcium sulfate, strontium sulfate, and barium sulfate; carbonates such as magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate; carboxylates such as calcium acetate, strontium acetate, calcium benzoate, and calcium citrate;

[0052] Metal salt A EMS is preferably a water-soluble salt. EMS By using the metal salt A contained in the polishing composition, a good surface with few defects such as scratches can be efficiently formed. EMS is preferably a compound that is not oxidized by the permanganate contained in the composition. EMS By appropriately selectingEMS The permanganate and the metal salt A can prevent the permanganate from being deactivated due to oxidation of the metal salt A by the permanganate, and can suppress deterioration of the performance of the polishing composition over time (for example, a decrease in the polishing removal rate). EMS An example of a preferred combination is a combination of potassium permanganate and calcium nitrate.

[0053] Metal salt A EMS In some embodiments, including metal salt A and metal salt A EMS The anion species of the metal salt A and the metal salt A may be the same. EMS The common anion species of the metal salt A may be, for example, a nitrate ion, a chloride ion, a sulfate ion, a phosphate ion, etc. EMS In some embodiments, including metal salt A and metal salt A EMS may have different anion species.

[0054] Metal salt A EMS In the polishing composition comprising the metal salt A EMS The concentration (content) of metal salt A is not particularly limited and can be appropriately set depending on the purpose and mode of use of the polishing composition so as to achieve the desired effect. EMS The concentration of may be, for example, about 1000 mM or less, 500 mM or less, or 300 mM or less. In some embodiments, in order to effectively achieve both an improvement in the polishing removal rate and suppression of an increase in the pad temperature when used in combination with metal salt A, metal salt A EMS The concentration of metal salt A is suitably 200 mM or less, preferably 100 mM or less, more preferably 50 mM or less, and may be 30 mM or less, 20 mM or less, or 10 mM or less. EMS The lower limit of the concentration of metal salt A may be, for example, 0.1 mM or more. EMS From the viewpoint of properly exerting the effect of use of the metal salt A in the polishing composition, the concentration is preferably 0.5 mM or more, more preferably 1 mM or more, and may be 2.5 mM or more, or may be 5 mM or more. EMSThe concentration of the compound may be preferably 0.5 mM to 100 mM or 1 mM to 50 mM.

[0055] Although not particularly limited, metal salt A EMS From the viewpoint of making it easier to properly exhibit the effect of using metal salt A in the polishing composition, EMS Concentration of metal salts A EMS The ratio (C3 / C1) of the concentration of permanganate (when a plurality of permanganates are contained, their total concentration) C3 [mM] to the concentration of permanganate (when a plurality of permanganates are contained, their total concentration) C1 [mM] is preferably 0.001 or more, more preferably 0.005 or more, and may be 0.01 or more, or 0.02 or more. In some embodiments, C3 / C1 may be, for example, 0.03 or more, 0.05 or more, or 0.07 or more. The upper limit of C3 / C1 is not particularly limited, but is suitably approximately 100 or less, and may be 50 or less, 10 or less, or 5 or less. In some preferred embodiments, C3 / C1 may be 1 or less, 0.5 or less, 0.3 or less, or 0.1 or less. Such metal salt A EMS and permanganate (C3 / C1), EMS The effect of further containing the compound can be preferably exhibited.

[0056] Metal salt A EMS The relationship between the concentration C3 [mM] of the metal salt A and the concentration C2 [mM] of the metal salt A is not particularly limited and can be set so that the combined effect of these two is appropriately exhibited. For example, C3 / C2 may be in the range of 0.001 to 1000. From the viewpoint of favorably achieving both an improvement in the polishing removal rate and suppression of an increase in pad temperature, in some embodiments, C3 / C2 is suitably approximately 0.01 or more, and preferably 0.05 or more (e.g., 0.1 or more). Furthermore, C3 / C2 is suitably approximately 100 or less, preferably 50 or less, and more preferably 25 or less (e.g., 10 or less).

[0057] In a polishing composition containing abrasive grains, metal salt A EMSThe relationship between the concentration of metal salt A and the content of abrasive grains is not particularly limited and can be appropriately set so as to achieve the desired effect depending on the purpose and mode of use. EMS The ratio of the concentration C3 [mM] of metal salt A to metal salt B, i.e., C3 / W1, can be, for example, 5 or more, preferably 10 or more, more preferably 30 or more, and may be 50 or more, or may be 80 or more. As C3 / W1 increases, the contribution of chemical polishing to the contribution of mechanical polishing tends to increase. In such a composition, EMS The combined use of these can favorably exert the effect of suppressing an increase in pad temperature. In some embodiments, C3 / W1 may be 100 or more, 150 or more, 200 or more, 300 or more, or 500 or more. The upper limit of C3 / W1 is not particularly limited, but from the viewpoint of the storage stability of the polishing composition, it can be, for example, about 5000 or less, 2500 or less, or 1000 or less. In some embodiments, C3 / W1 may be 900 or less, 700 or less, or 500 or less. Note that "C3" in the above "C3 / W1" refers to the ratio of metal salt A in the polishing composition. EMS It represents the numerical part when the concentration is expressed in units of "mM". Therefore, C3 is a dimensionless number.

[0058] (Water) The polishing composition disclosed herein contains water. Ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used as water. The polishing composition disclosed herein may further contain an organic solvent (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water, as needed. Generally, it is appropriate that 90% by volume or more of the solvent contained in the polishing composition is water, preferably 95% by volume or more, and more preferably 99 to 100% by volume.

[0059] (Acid) The polishing composition may contain an acid as needed for purposes such as adjusting the pH or improving the polishing removal rate. Both inorganic and organic acids can be used as the acid. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, and carbonic acid. Examples of organic acids include aliphatic carboxylic acids such as formic acid, acetic acid, and propionic acid, aromatic carboxylic acids such as benzoic acid and phthalic acid, citric acid, oxalic acid, tartaric acid, malic acid, maleic acid, fumaric acid, succinic acid, organic sulfonic acids, and organic phosphonic acids. These acids can be used alone or in combination of two or more. When an acid is used, the amount used is not particularly limited and can be determined according to the purpose of use (e.g., pH adjustment). Alternatively, some embodiments of the polishing composition disclosed herein may be substantially acid-free.

[0060] (Basic Compound) The polishing composition may contain a basic compound as needed for purposes such as adjusting the pH or improving the polishing removal rate. Here, the term "basic compound" refers to a compound that, when added to a polishing composition, increases the pH of the composition. Examples of basic compounds include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; carbonates and bicarbonates such as ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, and sodium carbonate; ammonia; quaternary ammonium compounds, such as quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide; and other compounds such as amines, phosphates, hydrogen phosphates, and organic acid salts. The basic compound may be used alone or in combination with two or more. When a basic compound is used, its amount is not particularly limited and can be adjusted depending on the purpose of use (e.g., pH adjustment). Alternatively, some embodiments of the polishing composition disclosed herein may be substantially free of a basic compound.

[0061] (Other Components) The polishing composition disclosed herein may further contain, as needed, known additives that can be used in polishing compositions (for example, polishing compositions used for polishing high-hardness materials such as silicon carbide), such as chelating agents, thickeners, dispersants, surface protective agents, wetting agents, surfactants, rust inhibitors, preservatives, and antifungal agents, within the scope that does not impair the effects of the present invention.The content of the above-mentioned additives can be appropriately set according to the purpose of addition, and since they do not characterize the present invention, detailed explanations will be omitted.

[0062] (pH) The pH of the polishing composition is suitably about 1.0 to 5.5. When a polishing composition having a pH in the above range is supplied to an object to be polished, a practical polishing removal rate is likely to be achieved. From the viewpoint of more easily exerting the effects of suppressing pH increase and pad temperature increase during polishing due to the buffering action of metal salt A, in some embodiments, the pH of the polishing composition is preferably less than 5.5, and may be 5.0 or less, less than 5.0, 4.0 or less, or less than 4.0 (e.g., 3.5 or less). The pH may be, for example, 1.0 or more, 1.5 or more, 2.0 or more, or 2.5 or more.

[0063] The method for preparing the polishing composition disclosed herein is not particularly limited. For example, the components contained in the polishing composition may be mixed using a well-known mixing device such as a blade mixer, ultrasonic disperser, or homomixer. The manner in which these components are mixed is not particularly limited. For example, all components may be mixed at once or in an appropriate order. The polishing composition disclosed herein may be a single-component type or a multi-component type, including a two-component type. For example, Part A containing some of the components of the polishing composition (e.g., components other than water) and Part B containing the remaining components may be mixed together and used to polish an object to be polished. These may be stored separately before use and mixed at the time of use to prepare a one-component polishing composition. When mixing, water for dilution or the like may be further added.

[0064] <Object to be polished> The polishing method disclosed herein is applied to polishing an object having a surface made of 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 improving the polishing removal rate is particularly great. The technology disclosed herein can be particularly preferably applied to polishing the surface of a silicon carbide single crystal. The silicon carbide may be conductive and doped with impurities, or insulating or semi-insulating and not doped with impurities.

[0065] <Polishing Method> The polishing method disclosed herein can be carried out using any of the polishing compositions described above, for example, in an embodiment including the following steps. 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 (e.g., diluting), adjusting the pH, or the like of the polishing composition to prepare the polishing liquid. Alternatively, the polishing composition may be used as is as the polishing liquid. In the case of a multi-component polishing composition, preparing the polishing liquid may include mixing the components, diluting one or more components before the mixing, or diluting the mixture after the mixing. The polishing liquid is then supplied to the object to be polished, and polished using a method commonly used by those skilled in the art. For example, the polishing liquid may be supplied to a polishing object placed in a conventional polishing apparatus, and the polishing liquid is supplied to the surface of the object to be polished via the polishing pad of the polishing apparatus. Typically, the polishing liquid is continuously supplied while the polishing pad is pressed against the surface of the object to be polished, causing relative movement (e.g., rotational movement) between the two. In this case, it is preferable that the pH of the polishing composition when it flows out from the object to be polished is maintained at a pH that is less than 2.0 (for example, an increase of -0.5 or more and 1.5 or less) from the pH when the polishing composition is supplied to the object to be polished. Polishing of the object to be polished is completed through this polishing step.

[0066] In addition, the above-mentioned contents and content ratios of each component that may be contained in the polishing composition in the technology disclosed herein typically mean the contents and content ratios in the polishing composition when actually supplied to the object to be polished (i.e., at the point of use), and therefore can be read as the contents and content ratios in the polishing liquid.

[0067] This specification provides a polishing method for polishing an object to be polished (typically, a material to be polished) and a method for manufacturing a polished product using the polishing method. The polishing method is characterized by including a step of polishing the object to be polished using the polishing composition disclosed herein. A preferred embodiment of the polishing method includes a step of performing pre-polishing (pre-polishing step) and a step of performing finish polishing (finish polishing step). In a typical embodiment, the pre-polishing step is a polishing step arranged immediately before the finish polishing step. The pre-polishing step may be a single-stage polishing step or may be a multi-stage polishing step consisting of two or more stages. The finish polishing step referred to here is a step of finish polishing the object to be polished after pre-polishing, and refers to the polishing step arranged last (i.e., most downstream) among polishing steps performed using a polishing slurry containing abrasive grains. In such a polishing method including a pre-polishing step and a finish polishing step, the polishing composition disclosed herein may be used in the pre-polishing step, in the finish polishing step, or in both the pre-polishing step and the finish polishing step.

[0068] Preliminary polishing and finish polishing can be applied to both polishing using a single-sided polishing machine and polishing using a double-sided polishing machine. In a single-sided polishing machine, the object to be polished is attached to a ceramic plate with wax or held using a holder called a carrier. While supplying a polishing composition, a polishing pad is pressed against one side of the object to be polished, and the two are moved relative to each other, thereby polishing one side of the object to be polished. The movement is, for example, rotational movement. In a double-sided polishing machine, the object to be polished is held using a holder called a carrier, and while supplying a polishing composition from above, a polishing pad is pressed against the opposing side of the object to be polished, and the two are rotated relative to each other, thereby simultaneously polishing both sides of the object to be polished.

[0069] The polishing conditions are not limited to specific conditions and are appropriately set based on the type of material to be polished, the desired surface properties (specifically, smoothness), the polishing removal rate, etc. For example, the polishing composition disclosed herein can be used over a wide pressure range, for example, from 10 kPa to 150 kPa. From the viewpoint of achieving both a high polishing removal rate and suppressing an increase in pad temperature, in some embodiments, the processing pressure may be, for example, 20 kPa or more, 30 kPa or more, or 40 kPa or more, and may be 100 kPa or less, 80 kPa or less, or 60 kPa or less. Polishing using the polishing method disclosed herein can be preferably performed at a processing pressure of, for example, 30 kPa or more, and the productivity of the target object (polished object) obtained through such polishing can be increased. Note that the processing pressure here is synonymous with the polishing pressure.

[0070] In the above-described polishing, the rotation speed of the platen and the rotation speed of the head of the polishing apparatus are not particularly limited and can be, for example, about 10 to 200 rpm. The rotation speed may be, for example, 20 rpm or more, or 30 rpm or more. From the viewpoint of easily achieving a higher polishing removal rate, in some embodiments, the rotation speed is preferably 55 rpm or more, more preferably 70 rpm or more, and may be 85 rpm or more, 100 rpm or more, or even 115 rpm or more. Since the use of metal salt A in the polishing composition containing permanganate can suppress an increase in pad temperature, polishing by the polishing method disclosed herein can be preferably carried out even at such a relatively high rotation speed, thereby increasing the productivity of the target object (polished object) obtained through such polishing. Furthermore, from the viewpoint of suppressing an increase in pad temperature and reducing the load on the polishing apparatus, in some embodiments, the rotation speed can be, for example, 180 rpm or less, or may be 160 rpm or less, or may be 140 rpm or less. The rotation speed of the surface plate and the rotation speed of the head may be approximately the same or different.

[0071] In the above polishing, the supply rate of the polishing composition to the object to be polished was 78.54 cm ２The supply rate per surface (corresponding to one side of a 4-inch wafer) can be, for example, 200 mL / min or less, or may be 150 mL / min or less, or may be 100 mL / min or less. The lower limit of the supply rate can be, for example, 5 mL / min or more, or may be 10 mL / min or more, or may be 15 mL / min or more. Reducing the supply rate of the polishing composition is preferable from the viewpoint of reducing the environmental load by reducing the amount of waste liquid and saving space in the polishing equipment. On the other hand, when the supply rate of the polishing composition is reduced, the time the polishing composition remains on the object to be polished generally becomes longer. For this reason, it can be said that the pH of the polishing composition on the object to be polished tends to increase easily. In addition, when the supply rate of the polishing composition is reduced, the amount of heat removed by the flow of the polishing composition generally tends to decrease, which is disadvantageous from the viewpoint of suppressing an increase in the pad temperature. In the polishing method disclosed herein, the use of metal salt A in the polishing composition containing permanganate can suppress an increase in the pH of the polishing composition on the object to be polished and can also suppress an increase in the pad temperature, so that polishing can be carried out suitably even if the supply rate of the polishing composition is relatively low. For example, when the polishing area is 78.54 cm ２ The supply rate can be preferably 50 mL / min or less, 35 mL / min or less, or even 25 mL / min or less.

[0072] The polishing pad used in each polishing step disclosed herein is not particularly limited. For example, any of nonwoven fabric, suede, and hard foam polyurethane types may be used. In some embodiments, nonwoven fabric polishing pads may be preferably used. In embodiments using the above polishing pad, the effect of suppressing pad temperature rise, which is an effect of the technology disclosed herein, is preferably exhibited. Note that the polishing pad used in the technology disclosed herein is a polishing pad that does not contain abrasive grains.

[0073] The object to be polished by the method disclosed herein is typically washed after polishing. This washing can be carried out using an appropriate washing liquid. The washing liquid to be used is not particularly limited, and a known or commonly used one can be appropriately selected and used.

[0074] The polishing method disclosed herein may include any other process in addition to the pre-polishing process and the finish polishing process. Examples of such processes include a mechanical polishing process or a lapping process performed before the pre-polishing process. The mechanical polishing process involves polishing the object to be polished using a liquid in which diamond abrasive grains are dispersed in a solvent. In some preferred embodiments, the dispersion does not contain an oxidizing agent. The lapping process involves pressing the surface of a polishing platen, such as a cast iron platen, against the object to be polished to polish it. Therefore, a polishing pad is not used in the lapping process. The lapping process is typically performed by supplying abrasive grains between the polishing platen and the object to be polished. The abrasive grains are typically diamond abrasive grains. The polishing method disclosed herein may also include an additional process before the pre-polishing process or between the pre-polishing process and the finish polishing process. The additional process may be, for example, a cleaning process or a polishing process.

[0075] <Method for manufacturing a polished product> The technology disclosed herein may include a method for manufacturing a polished product, which includes a polishing step using any of the polishing methods described above, and the provision of a polished product manufactured by this method. The method for manufacturing the polished product is, for example, a method for manufacturing a silicon carbide substrate. That is, the technology disclosed herein provides a method for manufacturing a polished product, which includes polishing an object having a surface made of a high-hardness material using any of the polishing methods disclosed herein, and a polished product manufactured by this method. The manufacturing method described above can efficiently provide a substrate manufactured through polishing, such as a silicon carbide substrate.

[0076] The matters disclosed by this specification include the following. [1] A method for polishing an object having a surface composed of silicon carbide, comprising the steps of preparing a polishing composition and supplying the polishing composition to the object to be polished to polish the object, wherein the polishing composition comprises a permanganate, a metal salt A, and water, and the metal salt A is a salt of a metal cation having a pKa of a hydrated metal ion of less than 7.0 and an anion. [2] The polishing method according to [1] above, wherein the pH of the polishing composition supplied to the object to be polished is 5.0 or less. [3] The polishing method according to [1] or [2] above, wherein, in the polishing step, the pH of the polishing composition supplied to the object to be polished when it flows out of the object to be polished increases by less than 2.0 from the pH when the polishing composition was supplied to the object to be polished. [4] The polishing method according to any of [1] to [3] above, wherein the polishing composition contains abrasive grains. [5] The polishing method according to any one of [1] to [4] above, wherein the metal salt A is a salt of a metal cation having a pKa of less than 6.0 as a hydrated metal ion and an anion. [6] The polishing method according to any one of [1] to [5] above, wherein the metal cation in the metal salt A is a cation containing a metal belonging to Groups 3 to 16 of the periodic table. [7] The polishing method according to any one of [1] to [5] above, wherein the metal cation in the metal salt A is a cation containing a metal belonging to Group 13 of the periodic table. [8] The polishing method according to any one of [1] to [7] above, wherein the metal cation in the metal salt A is a trivalent cation. [9] The polishing method according to any one of [1] to [8] above, wherein the anion in the metal salt A is a nitrate ion.

[10] A polishing composition for use in the polishing method according to any one of [1] to [9] above.

[0077]

[11] A polishing composition for polishing an object having a surface composed of silicon carbide, comprising a permanganate, a metal salt A, and water, wherein the metal salt A is a salt of a metal cation having a pKa of less than 7.0 as a hydrated metal ion, and an anion.

[12] The polishing composition according to

[11] above, having a pH of 5.0 or less.

[13] The polishing composition according to

[11] or

[12] above, further comprising abrasive grains.

[14] The polishing composition according to any one of

[11] to

[13] above, wherein the metal salt A is a salt of a metal cation having a pKa of less than 6.0 as a hydrated metal ion, and an anion.

[15] The polishing composition according to any one of

[11] to

[14] above, wherein the metal cation in the metal salt A is a cation containing a metal belonging to Groups 3 to 16 of the periodic table.

[16] The polishing composition according to any one of

[11] to

[14] above, wherein in the metal salt A, the metal cation is a cation containing a metal belonging to Group 13 of the periodic table.

[17] The polishing composition according to any one of

[11] to

[16] above, wherein in the metal salt A, the metal cation is a trivalent cation.

[18] The polishing composition according to any one of

[11] to

[17] above, wherein in the metal salt A, the anion is a nitrate ion.

[19] A method for polishing an object having a surface composed of silicon carbide, comprising the steps of: preparing the polishing composition according to any one of

[11] to

[18] above; and supplying the polishing composition to the object to be polished to polish the object.

[0078] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "%" is based on weight unless otherwise specified.

[0079] Experimental Example 1 Preparation of Polishing Composition Examples A1 and A2 Alumina abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the amounts shown in Table 1.

[0080] (Example A3) Alumina abrasive grains, potassium permanganate as a permanganate salt, indium nitrate trihydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the content shown in Table 1.

[0081] (Example A4) Alumina abrasive grains, potassium permanganate as permanganate, gallium nitrate octahydrate as metal salt A, and deionized water are mixed to prepare a polishing composition containing each component in the content shown in Table 1.

[0082] Comparative Example A1 A polishing composition according to this example was prepared in the same manner as in Example A1, except that aluminum nitrate nonahydrate was not used.

[0083] Comparative Example A2 A polishing composition according to this example was prepared in the same manner as in Comparative Example A1, except that the content of alumina abrasive grains was changed to 0.5%.

[0084] Comparative Example A3 Alumina abrasive grains, potassium permanganate, calcium nitrate tetrahydrate, and deionized water were mixed together to prepare a polishing composition containing each component in the amount shown in Table 1.

[0085] In the polishing compositions of each example in Experimental Example 1, α-alumina abrasive grains having an average primary particle size of 310 nm were used as the alumina abrasive grains. The pH (initial pH) of the polishing compositions of Examples A1 and A2 and Comparative Examples A1 to A3 was adjusted using nitric acid as shown in Table 1. The pH (initial pH) of the polishing compositions of Examples A3 and A4 was as shown in Table 1.

[0086] <Polishing of Object to be Polished> A SiC wafer was pre-polished using a preliminary polishing composition containing alumina abrasive grains. This pre-polished SiC wafer was used as the object to be polished, and the polishing composition according to each example was used as a polishing liquid as is to polish the object to be polished under the following polishing conditions. [Polishing Conditions] Polishing apparatus: Fujikoshi Machinery Co., Ltd., model "RDP-500" (platen diameter 20 inches) Polishing pad: Nitta Haas "SUBA800XY" (non-woven fabric type) Processing pressure: 44.1 kPa Platen rotation speed: 120 rpm Head rotation speed: 120 rpm Polishing liquid supply rate: 20 mL / min Polishing liquid usage method: Disposable Polishing time: 15 minutes Object to be polished: 4-inch SiC wafer (conductivity type: n-type, crystal type 4H-SiC, off-angle of main surface (0001) relative to the C-axis: 4°), 1 wafer / batch Polishing liquid temperature: 23°C

[0087] <Measurement and Evaluation> (Polishing Removal Rate) Under the above polishing conditions, a SiC wafer was polished using the polishing composition of each example, and then the polishing removal rate was calculated according to the following formulas (1) and (2): (1) Polishing stock removal [cm] = difference in weight of SiC wafer before and after polishing [g] / density of SiC [g / cm ３ ](=3.21g / cm ３ ) / polished area [cm ２ ] (=78.54cm ２ (2) Polishing removal rate [nm / h] = polishing removal amount [cm] × 10 ７ / Polishing time (= 15 / 60 hours)

[0088] The polishing removal rate obtained in each example was converted into a relative value when the rate of Comparative Example A2 was set to 100, and is shown in Table 1.

[0089] (Pad Temperature) The temperature of the polishing pad during polishing under the above polishing conditions was measured. When measuring the pad temperature, a template using a suede backing material as the wafer holding portion was used. During polishing, the wafer was kept in a state where water was applied to the suede material. The pad temperature was directly measured using the value output from the pad temperature measuring device (infrared thermal radiation thermometer) installed in the polishing apparatus. Measurements were taken from 5 minutes to 15 minutes after the start of polishing, and the average temperature during that period was taken as the pad temperature during polishing with the polishing composition of each example.

[0090] The obtained results were substituted into the following formula: ΔT [°C] = (pad temperature of Comparative Example A1) - (pad temperature of each example), and the pad temperature rise suppression effect was evaluated based on this ΔT (i.e., the amount of decrease in pad temperature relative to the pad temperature of Comparative Example A1) using the following four levels, which are shown in Table 1. A larger ΔT means a higher pad temperature rise suppression effect. AA: ΔT is 2.0°C or more A: ΔT is greater than 1.0°C and less than 2.0°C B: ΔT is greater than 0.3°C and less than 1.0°C C: ΔT is 0.3°C or less

[0091] (pH during polishing) During polishing under the above polishing conditions, the polishing liquid flowing down from the outer edge of the workpiece was sampled and its pH was measured. The polishing liquid was sampled 7 minutes after the start of polishing. The results are shown in Table 1.

[0092]

[0093] As shown in Table 1, metal cations with a pKa of 5.0 (Al ３＋ In Examples A1 and A2, in which polishing of SiC wafers was carried out using a polishing composition containing a metal salt A (aluminum nitrate nonahydrate), which is a salt of a hydrated metal ion having a pKa of 2.6, and an anion, the increase in pH during polishing was significantly suppressed, the polishing removal rate was significantly improved, and the increase in pad temperature was suppressed, compared to Comparative Examples A1 and A2, in which a polishing composition not containing a metal salt A was used. ３＋The same effect was obtained in Example A4, which used a polishing composition containing metal salt A (gallium nitrate octahydrate), which is a salt of a metal cation (In) with an anion. ３＋ In Example A3, a polishing composition containing metal salt A (indium nitrate trihydrate), which is a salt of indium nitrate trihydrate and an anion, was used, and the polishing removal rate was maintained at the same level as in Comparative Example A2, while the pH increase during polishing was significantly suppressed and the pad temperature increase was suppressed. ２＋ In Comparative Example A3, which used a polishing composition containing a salt of hydroxypropyltrimonials (HBr) and an anion, the effect of suppressing the increase in pH of the polishing composition during polishing was weak, and the effect of suppressing the increase in pad temperature was also weak.

[0094] Experimental Example 2 Preparation of polishing composition Examples S1 and S2 Silica abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the amounts shown in Table 2.

[0095] (Example S3) Silica abrasive grains, potassium permanganate as a permanganate salt, indium nitrate trihydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the content shown in Table 2.

[0096] (Example S4) Silica abrasive grains, potassium permanganate as permanganate, gallium nitrate octahydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the content shown in Table 2.

[0097] (Example S5) Silica abrasive grains, potassium permanganate as a permanganate salt, and zirconium acetate (Zr(OAc)) as a metal salt A ４ ) and deionized water were mixed to prepare a polishing composition containing each component in the amount shown in Table 2.

[0098] Comparative Example S1 A polishing composition according to this example was prepared in the same manner as in Example S1, except that aluminum nitrate nonahydrate was not used.

[0099] Comparative Example S2 Silica abrasive grains, potassium permanganate, calcium nitrate tetrahydrate, and deionized water were mixed together to prepare a polishing composition containing each component in the amount shown in Table 2.

[0100] In the polishing compositions of each example in Experimental Example 2, colloidal silica having an average primary particle size of 35 nm was used as the silica abrasive grains. The pH (initial pH) of the polishing compositions of Examples S1 and S2 and Comparative Examples S1 and S2 was adjusted using nitric acid as shown in Table 2. The pH (initial pH) of the polishing compositions of Examples S3 and S4 was as shown in Table 2.

[0101] <Polishing of object to be polished> A SiC wafer was pre-polished using a preliminary polishing composition containing alumina abrasive grains. The pre-polished SiC wafer was used as the object to be polished, and the polishing composition according to each example was used as a polishing liquid as is, and the above object to be polished was polished under the same polishing conditions as in Experimental Example 1.

[0102] <Measurement and Evaluation> (Polishing Removal Rate) Values ​​obtained by measurement in the same manner as in Experimental Example 1 were converted into relative values ​​when Comparative Example S1 was set at 100, and are shown in Table 2.

[0103] (Pad Temperature) The values ​​obtained by measurement in the same manner as in Experimental Example 1 were substituted into the following formula: ΔT [°C] = (pad temperature of Comparative Example S1) - (pad temperature of each example), and the pad temperature rise suppression effect was evaluated based on this ΔT (i.e., the degree of decrease in pad temperature relative to the pad temperature of Comparative Example S1) using the following four levels, which are shown in Table 2. AA: ΔT is 2.0°C or more A: ΔT is greater than 1.0°C and less than 2.0°C B: ΔT is greater than 0.3°C and less than 1.0°C C: ΔT is 0.3°C or less

[0104] (pH during polishing) Measurement was carried out in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0105]

[0106] As shown in Table 2, in Examples S1, S2, S3, S4, and S5 in which SiC wafers were polished using a polishing composition containing metal salt A (aluminum nitrate nonahydrate, indium nitrate trihydrate, gallium nitrate octahydrate, or zirconium acetate), the pH increase during polishing was significantly suppressed, the polishing removal rate was significantly improved, and the pad temperature increase was suppressed, compared to Comparative Example S1 in which a polishing composition not containing metal salt A was used. On the other hand, in Examples S1, S2, S3, S4, and S5 in which SiC wafers were polished using a polishing composition containing metal salt A (aluminum nitrate nonahydrate, indium nitrate trihydrate, gallium nitrate octahydrate, or zirconium acetate), the pH increase during polishing was significantly suppressed, the polishing removal rate was significantly improved, and the pad temperature increase was suppressed. On the other hand, in Examples S1, S2, S3, S4, and S5 in which a polishing composition not containing metal salt A was used instead, the metal cation (Ca ２＋ In Comparative Example S2, which used a polishing composition containing a salt of ) and an anion, the effect of suppressing the increase in pH of the polishing composition during polishing was weak, and the effect of suppressing the increase in pad temperature was also weak.

[0107] Experimental Example 3 Preparation of polishing composition Example A5 Alumina abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the amounts shown in Table 3.

[0108] Comparative Example A4 A polishing composition according to this example was prepared in the same manner as in Example A5, except that aluminum nitrate nonahydrate was not used.

[0109] (Example S6) Silica abrasive grains, potassium permanganate as permanganate, aluminum nitrate nonahydrate as metal salt A, and deionized water were mixed to prepare a polishing composition containing each component in the content shown in Table 4.

[0110] Comparative Example S3 A ​​polishing composition according to this example was prepared in the same manner as in Example S6, except that aluminum nitrate nonahydrate was not used.

[0111] <Polishing of object to be polished> A SiC wafer was pre-polished using a preliminary polishing composition containing alumina abrasive grains. The pre-polished SiC wafer was used as the object to be polished, and the polishing composition according to each example was used as a polishing liquid as is, and the above-mentioned object to be polished was polished under the following two types of polishing conditions. [Polishing condition 1] Polishing apparatus: Fujikoshi Machinery Co., Ltd., model "RDP-500" (platen diameter 20 inches) Polishing pad: Nitta Haas "IC-1000" (hard polyurethane type) Processing pressure: 29.4 kPa Platen rotation speed: 100 rpm Head rotation speed: 100 rpm Polishing liquid supply rate: 20 mL / min Polishing liquid usage method: disposable Polishing time: 15 minutes Polishing object: 4-inch semi-insulating SiC wafer (conductivity type: non-doped type, crystalline type 4H-SiC, off angle of main surface (0001) to the C-axis: 0°), 1 wafer / batch Polishing liquid temperature: 23°C [Polishing condition 2] Polishing apparatus: Fujikoshi Machinery Co., Ltd., model "RDP-500" (platen diameter 20 inches) Polishing pad: Nitta Haas "IC-1000" (hard polyurethane type) Processing pressure: 39.2 kPa Platen rotation speed: 120 rpm Head rotation speed: 120 rpm Polishing liquid supply rate: 20 mL / min Polishing liquid usage method: Disposable Polishing time: 15 minutes Polishing object: 4-inch semi-insulating SiC wafer (conductivity type: non-doped type, crystalline type 4H-SiC, off angle of main surface (0001) to the C-axis: 0°), 1 wafer / batch Polishing liquid temperature: 23°C

[0112] <Measurement and Evaluation> (Polishing Removal Rate) The values ​​obtained by measurement in the same manner as in Experimental Example 1 were converted into relative values ​​with Comparative Example A4 for Example A5 and Comparative Example S3 for Example S6 set to 100, and are shown in Tables 3 and 4, respectively.

[0113]

[0114]

[0115] As shown in Tables 3 and 4, a polishing composition containing metal salt A (aluminum nitrate nonahydrate) was found to have the effect of improving the polishing removal rate compared to a polishing composition not containing metal salt A, regardless of the polishing conditions, even when polishing semi-insulating SiC wafers.

[0116] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

Claims

1. A method for polishing an object to be polished having a surface composed of silicon carbide, the method comprising: preparing a polishing composition; and supplying the polishing composition to the object to be polished to polish the object to be polished, wherein the polishing composition contains a permanganate, a metal salt A, and water, and the metal salt A is a salt of a metal cation having a hydrated metal ion pKa of less than 7.0 and an anion.

2. The polishing method according to claim 1, wherein the pH of the polishing composition supplied to the object to be polished is 5.0 or less.

3. The polishing method according to claim 1 or 2, wherein in the polishing step, when the polishing composition supplied to the object to be polished flows out of the object to be polished, the pH rise from the pH when the polishing composition is supplied to the object to be polished is less than 2.

0.

4. The polishing method according to any one of claims 1 to 3, wherein the polishing composition contains abrasive grains.

5. The polishing method according to any one of claims 1 to 4, wherein in the metal salt A, the metal cation is a cation containing a metal belonging to Groups 3 to 16 of the periodic table.

6. A polishing composition used in the polishing method according to any one of claims 1 to 5.

7. A polishing composition for polishing an object to be polished having a surface composed of silicon carbide, the polishing composition containing a permanganate, a metal salt A, and water, and the metal salt A being a salt of a metal cation having a hydrated metal ion pKa of less than 7.0 and an anion.