Polishing method and polishing composition

Abstract

Provided are a polishing method and a polishing composition that are applied for polishing silicon carbide and that enable suppression of an increase in pH of the polishing composition and an increase in the temperature of a pad during polishing. Provided is a method for polishing a polishing target having a surface formed from silicon carbide. The method comprises a step for preparing a polishing composition, and a step for supplying the polishing composition to the polishing target and polishing said polishing target. The polishing composition contains a permanganate, a metal salt A, and water. The metal salt A is formed between an anion, and a metal cation the hydrated metal ion thereof having a pKa less than 7.0.

Description

Technical Field

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

Background Art

[0002] Polishing using a polishing composition is performed on the surfaces of materials such as metals, semimetals, nonmetals, and their oxides. For example, the surface formed of a compound semiconductor material such as silicon carbide, boron carbide, tungsten carbide, silicon nitride, titanium nitride, or gallium nitride is processed by polishing (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, after lapping using diamond abrasive grains or instead of such lapping, polishing (polishing) using a polishing pad and a polishing composition has been considered. As documents disclosing this kind of prior art, for example, Patent Documents 1 and 2 can be cited.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, from the viewpoints of manufacturing efficiency and cost effectiveness, it is desired that the polishing removal rate is sufficiently large in practical use. For example, in the polishing of a surface composed of silicon carbide, which is a high-hardness material, an improvement in the polishing removal rate is strongly desired. In Patent Documents 1 and 2, it has been proposed to improve the polishing rate 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 usage mode, the pH of the polishing composition supplied to the polishing object may greatly increase during polishing in the polishing composition applying the techniques described in Patent Documents 1 and 2, making it difficult to appropriately exhibit the original polishing performance (e.g., polishing removal rate). Also, although the polishing removal rate can 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 rotational speed of the surface plate of the polishing apparatus, in the polishing composition applying the techniques described in Patent Documents 1 and 2, the temperature rise of the polishing pad during polishing (polishing) using the polishing composition tends to be large. If the temperature rise 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 view of such circumstances, and an object thereof is to provide a polishing method and a polishing composition that can be applied to the polishing of silicon carbide and suppress the increase in pH of the polishing composition and the increase in pad temperature during polishing.

Means for Solving the Problems

[0007] This specification provides a method for polishing an object having a surface composed of silicon carbide. The method comprises the steps of preparing a polishing composition and supplying the polishing composition to the object to be polished to polish the object. The polishing composition comprises a permanganate, a metal salt A, and water. Here, the metal salt A is a salt of a metal cation with a hydrated metal ion pKa less than 7.0 and an anion. By polishing silicon carbide using a polishing composition containing permanganate and metal salt A, it is possible to suppress the rise in pH of the polishing composition and the rise in temperature of the polishing pad (hereinafter also referred to as pad temperature) during polishing. This makes it possible to improve the polishing removal rate and / or to employ harsher processing conditions. This makes it possible to increase the productivity of the target object (polished object, e.g., silicon carbide substrate) obtained through polishing by the above polishing method. Furthermore, this specification provides polishing compositions to be used in any of the polishing methods disclosed herein.

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

[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 (hereinafter also referred to as the pH during polishing) is less than 2.0 above the pH at which the polishing composition was supplied to the object (i.e., the initial pH). In such embodiments, the effect of improving the polishing removal rate by suppressing the rise in pH can be suitably achieved.

[0010] In some embodiments, the polishing composition further includes abrasive particles. The use of abrasive particles can improve the polishing removal rate. Furthermore, since polishing using a polishing composition containing abrasive particles tends to result in a higher pad temperature compared to polishing using a polishing composition without abrasive particles, it is more effective to suppress the rise in pad temperature by applying the techniques 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, the rise in pH and the rise in pad temperature during polishing can be effectively suppressed.

[0012] Furthermore, this specification provides a polishing composition for polishing an object having a surface composed of silicon carbide. The polishing composition comprises a permanganate, a metal salt A, and water. Here, the metal salt A is a salt of a metal cation with a pKa of less than 7.0 of the hydrated metal ion and an anion. A polishing composition of this composition can be used to polish the object to be polished and can preferably suppress the rise in pH of the polishing composition and the rise in pad temperature during polishing. [Modes for carrying out the invention]

[0013] Preferred embodiments of the present invention will be described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the contents disclosed herein and common technical knowledge in the art.

[0014] <Polishing composition> (Permanganate) The polishing composition in the technology disclosed herein contains a permanganate. In the polishing of silicon carbide, the permanganate can improve the polishing removal rate by typically functioning as an oxidizing agent. As the permanganate, alkali metal permanganates such as sodium permanganate and potassium permanganate are preferred, with potassium permanganate being particularly preferred. The permanganate may exist in an ionic state in the polishing composition.

[0015] The concentration (content) of permanganate in the abrasive composition is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use of the abrasive composition. In some embodiments, from the viewpoint of improving the abrasive removal rate, the concentration of permanganate is appropriate to be approximately 5 mM or more (i.e., 0.005 mol / L or more). From the viewpoint of improving the abrasive removal rate, the concentration of permanganate is preferably 10 mM or more, more preferably 30 mM or more, and may also be 50 mM or more, 70 mM or more, or 90 mM or more. From the viewpoint of making it easier to achieve a higher abrasive 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. There is no particular upper limit to the concentration of permanganate in the polishing composition, but from the viewpoint of suppressing the rise in pad temperature, it is appropriate to set it to approximately 2500 mM or less, preferably 2000 mM or less, more preferably 1700 mM or less, and may also be 1500 mM or less, 1000 mM or less, 750 mM or less, 500 mM or less, 400 mM or less, or 300 mM or less. In some embodiments, the concentration of permanganate may be 250 mM or less, 200 mM or less, 150 mM or less, or 120 mM or less.

[0016] (Metal salt A) The polishing composition in the technology disclosed herein contains metal salt A. Metal salt A is a salt of a metal cation with a hydrated metal ion pKa less than 7.0 and an anion. In this specification, metal cation means a cation containing metal. That is, the metal cation may be a cation composed solely of metal, or a cation composed of metal and nonmetal. Metal salt A can be used alone or in combination of two or more. By including metal salt A in addition to permanganate in a polishing composition used for polishing silicon carbide, it is desirable to suppress the rise in pH of the polishing composition and the rise in pad temperature during polishing. Although we do not wish to be constrained by theory, the reason why such effects are obtained can be considered as follows, for example. That is, in polishing performed by supplying a polishing composition containing permanganate to an object to be polished 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 making the surface of silicon carbide brittle. However, the above oxidation can be a factor in increasing 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 and falls outside the appropriate pH range, the chemical polishing performance of the polishing composition on the material to be polished will decrease. When the chemical polishing performance of the polishing composition decreases, the polishing removal rate decreases, and the contribution of mechanical polishing performance becomes relatively larger, which is thought to make it easier for the pad temperature to rise. If a metal salt A containing a metal cation with a pKa of hydrated metal ions less than 7.0 is added to a polishing composition containing permanganate, it is thought that the metal salt A will exert a buffering effect, suppressing the rise in pH of the polishing composition and maintaining it within the appropriate pH range. This will maintain the chemical polishing performance of the polishing composition, suppressing the decrease in the polishing removal rate and also suppressing the rise in pad temperature. However, the above considerations do not limit the scope of the present invention.

[0017] In some embodiments, as the metal salt A, a salt of a metal cation with a pKa of the hydrated metal ion less than 6.0 and an anion may be preferably employed. Examples of the metal cation with a pKa of the hydrated metal ion less than 6.0 include Al 3+ (pKa of the hydrated metal ion is 5.0), Cr 3+ (the same is 4.0), In 3+ (the same is 4.0), Ga 3+ (the same is 2.6), Fe 3+ (the same is 2.2), Hf 4+ (the same is -0.2), Zr 4+ (the same is -0.3), Ce 4+ (the same is -1.1), Ti 4+ (the same is -4.0), but are not limited thereto. In some embodiments, the pKa of the above 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. Also, the lower limit of the pKa of the above hydrated metal ion is suitably about -5.0 or more, may be -1.5 or more, may be -0.5 or more, is 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 above metal cation in the metal salt A can be, for example, divalent to tetravalent. In some embodiments, a metal salt A which is a salt of a trivalent metal-containing cation and an anion may be preferably employed.

[0018] The above metal cation in the 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 of the periodic table. The technology disclosed herein can be preferably implemented in an embodiment using a metal salt A which is a salt of a cation containing a metal belonging to Group 13 of the periodic table and an anion.

[0019] In some embodiments, metal salt A may preferably be one that buffers the pH to 2.5 to 5.5 (for example, 3.0 to 4.5). The buffered pH of metal salt A can be determined by titrating an aqueous solution of metal salt A with sodium hydroxide.

[0020] Metal salt A may be an inorganic salt or an organic salt. Examples of inorganic salts include salts of hydrohalogens 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 salts include salts of carboxylic acids such as formic acid, acetic acid, propionic acid, benzoic acid, glycinic 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 ethyl phosphoric 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, for example, uses Al as metal salt A. 3+ , Cr 3+ Fe 3+ In 3+ , Ga 3+ and Zr 4+ A cation selected from the group consisting of and a nitrate ion (NO3 - ), chloride ions (Cl - ), sulfate ions (SO4 2- ) and acetate ions (CH3COO - This can preferably be carried out in a manner that uses 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 according to the purpose and manner of use of the polishing composition so as to achieve the desired effect. The concentration of metal salt A may be, for example, approximately 1000 mM or less, 500 mM or less, or 300 mM or less. From the viewpoint of effectively achieving both suppression of pH rise and suppression of pad temperature rise during polishing, in some embodiments, the concentration of metal salt A is suitable to be 200 mM or less, preferably 100 mM or less, more preferably 50 mM or less, may also be 40 mM or less, may also be 30 mM or less, may also be 20 mM or less, or may also 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 using metal salt A, it is advantageous to be 1 mM or more, preferably 5 mM or more, and more preferably 7 mM or more (e.g., 8 mM or more). The techniques disclosed herein can also be preferably implemented in embodiments in which, for example, 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.

[0023] While not particularly limited, from the viewpoint of better exhibiting the effects of including metal salt A in a polishing composition containing permanganate, the ratio (C2 / C1) of the concentration of metal salt A (total concentration if multiple metal salts A are included) C2 [mM] to the concentration of permanganate (total concentration if multiple permanganates are included) C1 [mM] in the polishing composition is appropriately set to approximately 0.0002 or higher, preferably 0.001 or higher, more preferably 0.005 or higher, and may also be 0.01 or higher or 0.02 or higher. 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 higher, preferably 0.04 or higher, may also be 0.05 or higher, and may also be 0.07 or higher. The upper limit of C2 / C1 is not particularly limited, but is generally appropriate to be 200 or less, may also be 100 or less, may also be 75 or less, and may also 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, suppression of pH rise and suppression of pad temperature rise by metal salt A can be preferably achieved.

[0024] (Abrasive grains) In some embodiments of the technology disclosed herein, the polishing composition includes abrasive grains. With a polishing composition containing abrasive grains, a higher polishing rate can be achieved by providing a primarily mechanical polishing action by the abrasive grains in addition to the primarily chemical polishing action by the permanganate and metal salt A. Furthermore, since the pad temperature tends to rise when abrasive grains are included in the polishing composition, it is more effective to suppress the rise in pad temperature by applying the technology disclosed herein.

[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 of abrasive grains 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; carbonates such as calcium carbonate and barium carbonate; etc. The abrasive grains may be used individually or in combination of two or more types. 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 embodiments where silica particles or alumina particles are used as abrasive grains, the technology disclosed herein can be suitably applied to suppress the rise in pad temperature.

[0026] In this specification, "substantially composed of X" or "substantially made of X" means that the proportion of X in the abrasive grain (purity of X) is 90% or more by weight. Furthermore, the proportion of X in the abrasive grain is preferably 95% or more, more preferably 97% or more, even more preferably 98% or more, and for example, 99% or more.

[0027] The average primary particle diameter of the abrasive grains is not particularly limited. From the viewpoint of suppressing the rise in pad temperature while making it easier to obtain a desired polishing removal rate, the average primary particle diameter of the abrasive grains can be, for example, 5 nm or more, 10 nm or more is appropriate, preferably 20 nm or more, and may also be 30 nm or more. From the viewpoint of improving the polishing removal rate, in some embodiments, the average primary particle diameter 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. Also, from the viewpoint of suppressing the rise in pad temperature, the average primary particle diameter of the abrasive grains can be, for example, 5 μm or less, preferably 3 μm or less, more preferably 1 μm or less, and may also be 750 nm or less, or 500 nm or less. From the viewpoint of surface quality after polishing, in some embodiments, the average primary particle diameter 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 as follows: Average primary particle diameter (nm) = 6000 / (True density (g / cm³) 3 ) × BET value (m 2 This refers to the particle size (BET particle size) calculated by the formula ( / g). The specific surface area can be measured, for example, using a surface area measuring device manufactured by Micromeritex, product name "Flow Sorb II 2300".

[0029] The average secondary particle diameter of the abrasive grains may be, for example, 10 nm or more, preferably 50 nm or more, more preferably 100 nm or more, and may also be 250 nm or more, or 400 nm or more, from the viewpoint of easily increasing the polishing removal rate. The upper limit of the average secondary particle diameter of the abrasive grains is appropriately set to approximately 10 μm or less from the viewpoint of ensuring a sufficient number of particles per unit weight. Furthermore, from the viewpoint of suppressing the rise in pad temperature, the above 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, etc., 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 abrasive grains can be measured as the volume-average particle diameter (volume-based arithmetic mean diameter; Mv) for particles smaller than 500 nm using, for example, the dynamic light scattering method with the "UPA-UT151" model manufactured by Nikkiso Co., Ltd. For particles larger than 500 nm, the volume-average particle diameter can be measured using methods such as the pore electrical resistance method with the "Multisizer 3" model manufactured by Beckman Coulter.

[0031] When using alumina particles (alumina abrasive grains) as abrasive grains, various known alumina particles can be appropriately selected and used. 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 specifically, examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, χ-alumina, etc. In addition, alumina called fumed alumina (typically alumina fine particles produced when alumina salt is calcined at high temperature) based on the manufacturing method may be used. Furthermore, alumina called colloidal alumina or alumina sol (for example, alumina hydrate such as boehmite) is also included in the examples of known alumina particles. From the viewpoint of processability, it is preferable to include α-alumina. The alumina abrasive grains in the technology disclosed herein may contain one type of such alumina particle alone or in combination of two or more types.

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

[0033] The particle size of the alumina abrasive grains is not particularly limited and can be selected to achieve the desired polishing effect. From the viewpoint of improving the polishing removal speed, the average primary particle diameter of the alumina abrasive grains is preferably 50 nm or more, more preferably 80 nm or more, and may also 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 the rise in pad temperature, it is appropriate to keep it at approximately 5 μm or less, and from the viewpoint of surface quality after polishing, it is preferably 3 μm or less, more preferably 1 μm or less, and may also be 750 nm or less, 500 nm or less, 400 nm or less, or 350 nm or less.

[0034] When alumina particles are used as abrasive grains, the polishing compositions disclosed herein may further contain abrasive grains made of materials other than alumina (hereinafter also referred to as non-alumina abrasive grains), to the extent that they do not impair the effects of the present invention. Examples of such non-alumina abrasive grains include 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, 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 abrasive grains substantially composed of carbonates such as calcium carbonate and barium carbonate.

[0035] The content of the non-alumina abrasive grains is appropriately set to, for example, 30% by weight or less of the total weight of 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 comprises silica particles (silica abrasive grains) as abrasive grains. The silica abrasive grains can be appropriately selected from various known silica particles. Examples of such known silica particles include colloidal silica and dry-processed silica. Among these, the use of colloidal silica is preferred. With silica abrasive grains containing colloidal silica, good surface accuracy can be suitably achieved.

[0037] The shape (outer form) of silica abrasive grains may be spherical or non-spherical. For example, specific examples of non-spherical silica abrasive grains include peanut shape (i.e., the shape of a peanut shell), cocoon shape, konpeito shape, rugby ball shape, etc. In the technology disclosed herein, silica abrasive grains may be in the form of primary particles or in the form of secondary particles formed by the association of multiple primary particles. Furthermore, silica abrasive grains in the form of primary particles and silica abrasive grains in the form of secondary particles may be mixed. In one preferred embodiment, at least some of the silica abrasive grains are included in the polishing composition in the form of secondary particles.

[0038] As silica abrasive grains, those with an average primary particle diameter greater than 5 nm can preferably be used. From the viewpoint of polishing efficiency, 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. There is no particular upper limit to the average primary particle diameter of the silica abrasive grains, but it is appropriate to keep it generally 120 nm or less, preferably 100 nm or less, and more preferably 85 nm or less. For example, from the viewpoint of achieving a higher level of both polishing efficiency and surface quality, silica abrasive grains with a BET diameter of 12 nm to 80 nm are preferred, and silica abrasive grains with a BET diameter of 15 nm to 75 nm are preferred.

[0039] The average secondary particle diameter of the silica abrasive grains is not particularly limited, but from the viewpoint of polishing efficiency, it is preferably 20 nm or more, more preferably 50 nm or more, and even more preferably 70 nm or more. Furthermore, from the viewpoint of obtaining a higher quality surface, the average secondary particle diameter of the silica abrasive grains is suitable to be 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 (for example, 100 nm or less).

[0040] The true specific gravity (true density) of silica particles is preferably 1.5 or higher, more preferably 1.6 or higher, and even more preferably 1.7 or higher. The physical polishing ability tends to increase with increasing true specific gravity of silica particles. There is no particular upper limit to the true specific gravity of silica particles, but it is typically 2.3 or lower, for example, 2.2 or lower, 2.0 or lower, or 1.9 or lower. The true specific gravity of silica particles can be measured using a liquid displacement method with ethanol as the displacement solution.

[0041] The shape (outer form) of the silica particles is preferably spherical. Although not particularly limited, the average aspect ratio of the major axis to minor axis of the particles is, in principle, 1.00 or more, and from the viewpoint of improving the polishing removal speed, it may be, for example, 1.05 or more, or 1.10 or more. Furthermore, the average aspect ratio of the particles is appropriately 3.0 or less, but may also be 2.0 or less. From the viewpoint of improving the smoothness of the polished surface and reducing scratches, the average aspect ratio of the particles is preferably 1.50 or less, but may also be 1.30 or less, or 1.20 or less.

[0042] The shape (outer shape) and average aspect ratio of particles can be determined, for example, by electron microscopy observation. A specific procedure for determining the average aspect ratio is as follows: For example, use a scanning electron microscope (SEM) to extract the shapes of a predetermined number of particles (e.g., 200). Draw the smallest rectangle that circumscribes the shape of each extracted particle. Then, for the rectangle drawn for the shape of each particle, calculate the ratio of the major axis to the minor axis by dividing the length of the major side (major axis value) by the length of the minor side (minor axis value). The average aspect ratio can be obtained by taking the arithmetic mean of the aspect ratios of the predetermined number of particles.

[0043] In embodiments of the polishing composition containing silica abrasive grains, the polishing composition may further contain abrasive grains made of materials 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, 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; carbonates such as calcium carbonate and barium carbonate; and particles substantially composed of any of these. 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 abrasive grains contained in the polishing composition may be, for example, 30% by weight or less, 20% by weight or less, or 10% by weight or less.

[0044] The abrasive content (e.g., silica abrasive grains, alumina abrasive grains, etc.) in the polishing compositions disclosed herein is appropriately less than 5% by weight, advantageously less than 3% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, and may be 0.3% by weight or less, or 0.2% by weight or less. In some embodiments, the abrasive content in the polishing composition may be 0.1% by weight or less, 0.05% by weight or less, 0.04% by weight or less, or 0.03% by weight or less. The lower limit of the abrasive content is not particularly limited and may be, for example, 0.000001% by weight or more (i.e., 0.01 ppm or more). From the viewpoint of enhancing the effectiveness of abrasive grains, in some embodiments, the abrasive grain content 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 abrasive grain content in the polishing composition refers to the total content of the above multiple types of abrasive grains.

[0045] The polishing compositions disclosed herein preferably contain substantially no diamond particles. Diamond particles have high hardness and can be a limiting factor in improving smoothness. Furthermore, since diamond particles are generally expensive, they are not a cost-effective material, and from a practical standpoint, the reliance on high-priced materials such as diamond particles may be low. Here, "substantially containing no 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, and typically 0.1% by weight or less, and includes the case where the proportion of diamond particles is 0% by weight. In such embodiments, the effects of the present invention can be suitably demonstrated.

[0046] In polishing compositions containing abrasive grains, the relationship between the concentration of permanganate and the abrasive grain content is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use. In some embodiments, the ratio of the concentration of permanganate C1 [mM] to the abrasive grain content W1 [wt%], i.e., C1 / W1, can be, for example, 5 or more, 50 or more is appropriate, 100 or more is advantageous, 150 or more is preferred, and 200 or more or 250 or more is more preferred. In other words, the relationship between C1 and W1 is linear, and as C1 / W1 increases, the contribution of chemical polishing tends to increase compared to the contribution of mechanical polishing. In such compositions, the effect of suppressing the rise in pad temperature by metal salt A can be suitably exhibited. For example, polishing using a polishing composition satisfying 500 ≤ C1 / W1 can suitably achieve both a high polishing removal rate and suppression of the rise in pad temperature. In some embodiments, C1 / W1 may be 300 or more, 400 or more, 500 or more, 700 or more, 1000 or more, and even 1500 or more, 3000 or more, 5500 or more, or 7500 or more. There is no particular upper limit to C1 / W1, but from the viewpoint of storage stability of the polishing composition, for example, it may be approximately 100000 or less, 75000 or less, 50000 or less, 20000 or less, 10000 or less, or 9000 or less. In some embodiments, C1 / W1 may be 7000 or less, 5000 or less, or 3000 or less. In the above "C1 / W1", "C1" represents the numerical part when the concentration of permanganate in the abrasive composition is expressed in "mM", and "W1" represents the numerical part when the abrasive content in the abrasive composition is expressed in "weight%". Both C1 and W1 are dimensionless numbers.

[0047] In the polishing compositions disclosed herein, the ratio of the concentration of permanganate C1 [mM] to the square root of the abrasive 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 tends to increase relative to the contribution of mechanical polishing. By improving the polishing removal rate in compositions that satisfy 200 ≤ C1 / √(W1), a high polishing removal rate and suppression of pad temperature rise can be suitably achieved simultaneously. In some embodiments, C1 / √(W1) may be 300 or more, 750 or more, 1500 or more, 2500 or more, 3500 or more, or 4500 or more. There is no particular upper limit to C1 / √(W1), but from the viewpoint of storage stability of the polishing composition, it can be, for example, approximately 12000 or less, 10000 or less, 8000 or less, or 6000 or less. In some embodiments, C1 / √(W1) can be 4500 or less, 3500 or less, or 2500 or less.

[0048] In an abrasive composition containing abrasive grains, the relationship between the concentration of metal salt A and the abrasive grain content is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use. The ratio of the concentration of metal salt A C2 [mM] to the abrasive grain content W1 [wt%], i.e., C2 / W1, can be, for example, 5 or more, is advantageous if 10 or more, is preferable if 20 or more, is more preferable if 30 or more, may be 50 or more, or may be 80 or more. When C2 / W1 is larger, the effect of suppressing the pad temperature rise due to the use of metal salt A can be more favorably exhibited. In some embodiments, C2 / W1 may be 150 or more, may be 200 or more, may be 300 or more, may be 500 or more, or may be 800 or more. There is no particular upper limit to C2 / W1, but from the viewpoint of storage stability of the abrasive composition, for example, it can be approximately 10000 or less, may be 5000 or less, or may be 2500 or less. In some aspects, 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 part when the concentration of metal salt A in the abrasive composition is expressed in units of "mM", and "W1" represents the numerical part when the abrasive content in the abrasive composition is expressed in units of "weight%". Both C2 and W1 are dimensionless numbers.

[0049] (Alkaline earth metal salts) The polishing compositions disclosed herein optionally include at least one metal salt A selected from alkaline earth metal salts. EMS It may contain metal salt A. EMS For example, one type of alkaline earth metal salt may be used alone, or two or more types of alkaline earth metal salts may be used in combination. EMS When used in combination with the following, the rise in pad temperature can be better suppressed. Metal salt A EMS It is preferable that the mixture contains one or more elements belonging to the alkaline earth metals, specifically Mg, Ca, Sr, and Ba. Of these, Ca and Sr are preferred, with Ca being more preferred.

[0050] Metal salt A EMS The type of salt used is not particularly limited and may be an inorganic or organic salt. Examples of inorganic salts include salts of hydrohalogens 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 salts include salts of carboxylic acids such as formic acid, acetic acid, propionic acid, benzoic acid, glycinic 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 ethyl phosphoric 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 is, for example, a metal salt A EMS This can preferably be carried out in a manner in which alkaline earth metal nitrates or chlorides are used.

[0051] Metal salt A EMS Specific examples of alkaline earth metal salts that could be used as options 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; and carboxylates such as calcium acetate, strontium acetate, calcium benzoate, and calcium citrate.

[0052] Metal salt A EMS Preferably, it is a water-soluble salt. Water-soluble metal salt A EMS By using this method, a good surface with few defects such as scratches can be efficiently formed. Furthermore, metal salt A contained in the polishing composition EMS It is preferable that the compound is not oxidized by the permanganate contained in the composition. From this viewpoint, the permanganate and metal salt A EMS By appropriately selecting metal salt A EMS This prevents the deactivation of the permanganate due to oxidation by the permanganate, and suppresses the deterioration of the performance of the polishing composition over time (e.g., a decrease in polishing removal rate). Permanganate and metal salt A EMS One example of a preferred combination is the combination of potassium permanganate and calcium nitrate.

[0053] Metal salt A EMS In some embodiments, including metal salt A and metal salt A EMS This means that the anion species may be the same. Metal salt A and metal salt A EMS Common anion species may include, for example, nitrate ions, chloride ions, sulfate ions, phosphate ions, etc. Also, metal salt A EMS In some embodiments, including metal salt A and metal salt A EMSThe anion species may be different.

[0054] Metal salt A EMS In an abrasive composition containing metal salt A EMS The concentration (content) of the abrasive composition is not particularly limited and can be appropriately set to achieve the desired effect depending on the intended use and manner of use of the abrasive composition. EMS The concentration of may be, for example, approximately 1000 mM or less, 500 mM or less, or 300 mM or less. In some embodiments, in order to effectively achieve both improved polishing removal speed and suppression of pad temperature rise when used in combination with metal salt A, metal salt A EMS The concentration of is appropriately 200 mM or less, preferably 100 mM or less, more preferably 50 mM or less, and may also be 30 mM or less, 20 mM or less, or 10 mM or less. Metal salt A EMS The lower limit of the concentration may be, for example, 0.1 mM or higher, and metal salt A EMS From the viewpoint of appropriately exhibiting the effects of use, it is preferable to have a concentration of 0.5 mM or more, more preferably 1 mM or more, and may also be 2.5 mM or more, or 5 mM or more. The technology disclosed herein is, for example, a metal salt A in an abrasive composition. EMS This can preferably be carried out in a manner in which the concentration is 0.5 mM to 100 mM, or in a manner in which it is 1 mM to 50 mM.

[0055] While not particularly limited, metal salt A EMS From the viewpoint of making it easier to properly exert the effects of using metal salt A in the polishing composition, EMS Concentration of (multiple metal salts A) EMSIf it contains (total concentration of) C3 [mM], the ratio (C3 / C1) of the concentration of the permanganate (if it contains multiple permanganates, the total concentration of) C1 [mM] is preferably 0.001 or more, more preferably 0.005 or more, and may also 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 it is generally appropriate to be 100 or less, and may also 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. EMS In the concentration ratio (C3 / C1) of metal salt A to permanganate, EMS Further inclusion of this ingredient may preferably exhibit beneficial effects.

[0056] Metal salt A EMS The relationship between the concentration C3 [mM] of the compound and the concentration C2 [mM] of metal salt A is not particularly limited and can be set so as to appropriately exhibit the effects of using them together. For example, C3 / C2 may be in the range of 0.001 to 1000. From the viewpoint of suitably achieving both improved polishing removal speed and suppression of pad temperature rise, in some embodiments, C3 / C2 is appropriate to be approximately 0.01 or higher, and preferably 0.05 or higher (e.g., 0.1 or higher). Furthermore, C3 / C2 is appropriate to be approximately 100 or less, preferably 50 or less, and more preferably 25 or less (e.g., 10 or less).

[0057] In an abrasive composition containing abrasive grains, metal salt A EMS The relationship between the concentration and the abrasive content is not particularly limited and can be appropriately set according to the purpose and manner of use to achieve the desired effect. Metal salt A relative to the abrasive content W1 [weight %] EMSThe ratio of the concentrations C3 [mM] of the metals, 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 80 or more. As C3 / W1 increases, the contribution of chemical polishing tends to increase relative to the contribution of mechanical polishing. In such a composition, metal salt A and metal salt A EMS The combination of these elements can effectively suppress the rise 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. There is no particular upper limit to C3 / W1, but from the viewpoint of storage stability of the polishing composition, it may be approximately 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. In addition, "C3" in "C3 / W1" above refers to metal salt A in the polishing composition. EMS This represents the numerical part when the concentration is expressed in units of "mM". Therefore, C3 is a dimensionless number.

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

[0059] (acid) The polishing composition may contain an acid as needed for purposes such as pH adjustment or improving the polishing removal rate. Both inorganic and organic acids can be used. 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 acid, and organic phosphonic acid. These can be used individually or in combination of two or more. When using an acid, the amount used is not particularly limited and can be adjusted according to the intended use (e.g., pH adjustment). Alternatively, some embodiments of the polishing composition disclosed herein may contain substantially no acid.

[0060] (Basic compounds) Polishing compositions may contain basic compounds as needed for purposes such as pH adjustment or improving the polishing removal rate. Here, a basic compound refers to a compound that, when added to a polishing composition, has the function of increasing 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 tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide; and others such as amines, phosphates, hydrogen phosphates, and organic acid salts. Basic compounds can be used individually or in combination of two or more. When using basic compounds, the amount used is not particularly limited and can be adjusted according to the purpose of use (e.g., pH adjustment). Alternatively, some embodiments of the polishing compositions disclosed herein may have a composition that substantially does not contain basic compounds.

[0061] (Other ingredients) The polishing compositions disclosed herein may further contain, as necessary, 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 protectants, wetting agents, surfactants, rust inhibitors, preservatives, and fungicides, to the extent that they do not impair the effects of the present invention. The content of the above additives can be appropriately set according to their purpose of addition and does not characterize the present invention, so a detailed explanation is omitted.

[0062] (pH) The pH of the polishing composition is appropriately set to approximately 1.0 to 5.5. When a polishing composition with a pH within the above range is supplied to the object to be polished, a practical polishing removal rate is easily achieved. From the viewpoint of making it easier to exert the effects of suppressing pH rise and pad temperature rise during polishing due to the buffering effect of metal salt A, in some embodiments, the pH of the polishing composition is preferably less than 5.5, may be 5.0 or less, may be less than 5.0, may be 4.0 or less, or may be less than 4.0 (e.g., 3.5 or less). The above pH may be, for example, 1.0 or higher, may be 1.5 or higher, may be 2.0 or higher, or may be 2.5 or higher.

[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 vane stirrer, an ultrasonic disperser, or a homomixer. The manner in which these components are mixed is not particularly limited; for example, all components may be mixed at once, or they may be mixed in an order set as appropriate. The polishing compositions disclosed herein may be mono-component or multi-component, including two-component types. For example, the polishing composition may be configured such that part A, containing some of the components (e.g., components other than water), and part B, containing the remaining components, are mixed together for use in polishing an object. These can be stored separately before use, for example, and mixed at the time of use to prepare a one-component polishing composition. During mixing, water or other diluents may be further added.

[0064] <Object to be polished> The polishing method disclosed herein is applicable to polishing workpieces having a surface composed 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 increasing the polishing removal speed is particularly significant. 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 with impurities doped, or it may be insulating or semi-insulating without impurities doped.

[0065] <Polishing method> The polishing methods disclosed herein can be carried out using any of the polishing compositions described above, for example, in embodiments including the following operations. In other words, a polishing solution (slurry) containing any of the polishing compositions disclosed herein is prepared. Preparing the polishing solution may involve adjusting the concentration (e.g., dilution), adjusting the pH, or performing other operations on the polishing composition. Alternatively, the polishing composition may be used as is as a polishing solution. In the case of a multi-component polishing composition, preparing the polishing solution may involve mixing the agents, diluting one or more agents before mixing, diluting the mixture after mixing, and so on. Next, the polishing solution is supplied to the object to be polished, and the object is polished in a manner that is common practice for those skilled in the art. For example, the object to be polished is set in a general polishing apparatus, and the polishing solution is supplied to the surface of the object to be polished through the polishing pad of the apparatus. Typically, the polishing solution is supplied continuously, while the polishing pad is pressed against the surface of the object to be polished and the two are moved relative to each other (e.g., rotated). At this time, it is preferable that the pH of the polishing composition when it flows out of the object to be polished is kept below 2.0 (for example, an increase of -0.5 or more and 1.5 or less) from the pH when the polishing composition was supplied to the object to be polished. Polishing of the object is completed through this polishing process.

[0066] Furthermore, the above-mentioned content and content ratio for each component that may be included in the polishing composition in the technology disclosed herein typically refers to the content and content ratio in the polishing composition when actually supplied to the object to be polished (i.e., at the point of use), and therefore can be interpreted as the content and content ratio in the polishing solution.

[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 object 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 polishing method according to a preferred embodiment 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 that is placed immediately before the finish polishing step. The pre-polishing step may be a single polishing step or a multi-step polishing step of two or more steps. The finish polishing step, as used herein, is a step of performing finish polishing on the object to be polished that has been pre-polished, and is the last (i.e., furthest downstream) polishing step among the polishing steps that are performed using a polishing slurry containing abrasive particles. In 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] Pre-polishing and finish polishing are applicable to both single-sided and double-sided polishing. In a single-sided polishing device, the object to be polished is attached to a ceramic plate with wax, or held using a holder called a carrier. Polishing is performed by supplying a polishing composition and pressing a polishing pad against one side of the object, then moving the two relative to each other. This movement is, for example, rotational movement. In a double-sided polishing device, the object to be polished is held using a holder called a carrier. Polishing composition is supplied from above, and polishing pads are pressed against opposing sides of the object. Both sides of the object are polished simultaneously by rotating them in relative directions.

[0069] The polishing conditions described above are not limited to specific conditions, as they are appropriately set based on the type of material to be polished, the target surface properties (specifically smoothness), the polishing removal rate, etc. For example, regarding the processing pressure, the polishing composition disclosed herein can be used in a wide pressure range of, for example, 10 kPa to 150 kPa. From the viewpoint of suitably achieving both a high polishing removal rate and suppression of pad temperature rise, 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 also be 100 kPa or less, 80 kPa or less, or 60 kPa or less. Polishing by the polishing method disclosed herein can preferably be carried out at processing pressures of, for example, 30 kPa or more or higher, and the productivity of the target product (polished product) obtained through such polishing can be increased. Note that processing pressure as used herein is synonymous with polishing pressure.

[0070] In the polishing described above, the rotational speed of the polishing platen and the head of the polishing apparatus are not particularly limited and can be, for example, around 10 rpm to 200 rpm. The rotational speed may be, for example, 20 rpm or more, or 30 rpm or more. From the viewpoint of easily obtaining a higher polishing removal speed, in some embodiments, the rotational 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 115 rpm or more. Polishing by the polishing method disclosed herein can be preferably carried out even at such relatively high rotational speeds because the rise in pad temperature can be suppressed by the use of metal salt A in the polishing composition containing permanganate, and the productivity of the target product (polished product) obtained through such polishing can be increased. Furthermore, from the viewpoint of suppressing the rise in pad temperature and reducing the load on the polishing apparatus, in some embodiments, the rotational speed may be, for example, 180 rpm or less, 160 rpm or less, or 140 rpm or less. The rotational speed of the platen and the rotational speed of the head may be the same or different.

[0071] In the above polishing process, the supply rate of the polishing composition to the object to be polished is 78.54 cm². 2 The supply rate per side (equivalent to one side of a 4-inch wafer) can be, for example, 200 mL / min or less, 150 mL / min or less, or 100 mL / min or less. The lower limit of the supply rate can be, for example, 5 mL / min or more, 10 mL / min or more, or 15 mL / min or more. Reducing the supply rate of the polishing composition is preferable from the viewpoint of reducing environmental impact by decreasing the amount of wastewater and saving space in the polishing equipment. On the other hand, when the supply rate of the polishing composition is reduced, the time that the polishing composition remains on the object to be polished is generally longer. Therefore, it can be said that an increase in the pH of the polishing composition on the object to be polished tends to occur more easily. Also, 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 be smaller, which is disadvantageous from the viewpoint of suppressing the rise in pad temperature. In the polishing method disclosed herein, the use of metal salt A in the polishing composition containing permanganate can suppress the rise in pH of the polishing composition on the object to be polished and can also suppress the rise in pad temperature, so it can be suitably implemented even with a relatively small supply rate of the polishing composition. For example, polishing area 78.54 cm² 2 The procedure can also be preferably carried out at supply rates of 50 mL / min or less, 35 mL / min or less, and even 25 mL / min or less.

[0072] The polishing pads used in each polishing process disclosed herein are not particularly limited. For example, nonwoven fabric type, suede type, or rigid foamed polyurethane type may be used. In some embodiments, a nonwoven fabric type polishing pad may be preferred. In embodiments using the above-mentioned polishing pad, the effect of suppressing pad temperature rise, which is an effect of the technology disclosed herein, is preferably exhibited. The polishing pads used in the technology disclosed herein are polishing pads that do not contain abrasive grains.

[0073] Workpieces polished by the methods disclosed herein are typically cleaned after polishing. This cleaning can be carried out using a suitable cleaning solution. The cleaning solution used is not particularly limited, and known and conventional solutions can be appropriately selected and used.

[0074] The polishing method disclosed herein may include any other steps in addition to the pre-polishing and finish-polishing steps described above. Such steps include mechanical polishing and lapping steps performed before the pre-polishing step. The mechanical polishing step involves polishing the workpiece using a solution in which diamond abrasive particles are dispersed in a solvent. In some preferred embodiments, the dispersion does not contain an oxidizing agent. The lapping step involves polishing the workpiece by pressing the surface of a polishing plate, such as a cast iron plate, against it. Therefore, no polishing pad is used in the lapping step. The lapping step is typically performed by supplying abrasive particles between the polishing plate and the workpiece. The abrasive particles are typically diamond abrasive particles. The polishing method disclosed herein may also include additional steps before the pre-polishing step or between the pre-polishing and finish-polishing steps. Additional steps may include, for example, cleaning and polishing steps.

[0075] <Method for manufacturing polished products> The technologies disclosed herein may include a method for manufacturing polished products, which includes a polishing step by any of the polishing methods described herein, and the provision of polished products manufactured by such method. The method for manufacturing polished products is, for example, a method for manufacturing silicon carbide substrates. That is, the technologies disclosed herein provide a method for manufacturing polished products, which includes polishing an object to be polished having a surface made of a high-hardness material by applying any of the polishing methods disclosed herein, and polished products manufactured by such method. According to the manufacturing method, substrates manufactured through polishing, such as silicon carbide substrates, can be efficiently provided.

[0076] The matters disclosed in this specification include the following: [1] A method for polishing an object having a surface made of silicon carbide, The process involves preparing an abrasive composition, A step of supplying the above-mentioned polishing composition to the object to be polished and polishing the object to be polished. Includes, The above polishing composition contains permanganate, metal salt A, and water. The above metal salt A is a salt of a metal cation with a pKa of less than 7.0 of the hydrated metal ion and an anion, in a polishing method. [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 when the polishing composition supplied to the object to be polished flows out of the object to be polished is less than 2.0 above the pH at which the polishing composition was supplied to the object to be polished. [4] The polishing method according to any one 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 with a pKa of less than 6.0 of the 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 in the metal salt A, the metal cation 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 in the metal salt A, the metal cation is a trivalent cation. [9] The polishing method according to any one of [1] to [8] above, wherein in the metal salt A above, the anion is a nitrate ion.

[10] An abrasive composition used in any of the abrasive methods described in [1] to [9] above.

[0077]

[11] A polishing composition for polishing an object to be polished having a surface made of silicon carbide, It contains permanganate, metal salt A, and water. The above metal salt A is a polishing composition in which a metal cation with a pKa of less than 7.0 of the hydrated metal ion is a salt of an anion.

[12] The polishing composition described in

[11] above, wherein the pH is 5.0 or less.

[13] The polishing composition according to

[11] or

[12] , 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 with a pKa of less than 6.0 of the 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 the metal cation in the metal salt A 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 above, the anion is a nitrate ion.

[19] A method for polishing an object having a surface made of silicon carbide, A step of preparing the polishing composition described in any of the above

[11] to

[18] , A step of supplying the above-mentioned polishing composition to the object to be polished and polishing the object to be polished. Polishing methods, including those mentioned above. [Examples]

[0078] The following describes several embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments. In the following description, "%" refers to weight unless otherwise specified.

[0079] ≪Experimental Example 1≫ <Preparation of polishing composition> (Examples A1, A2) A polishing composition containing each component in the amounts shown in Table 1 was prepared by mixing alumina abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water.

[0080] (Example A3) A polishing composition containing each component in the amounts shown in Table 1 was prepared by mixing alumina abrasive grains, potassium permanganate as a permanganate salt, indium nitrate trihydrate as metal salt A, and deionized water.

[0081] (Example A4) A polishing composition containing each component in the amounts shown in Table 1 was prepared by mixing alumina abrasive grains, potassium permanganate as a permanganate salt, gallium nitrate octahydrate as metal salt A, and deionized water.

[0082] (Comparative Example A1) The 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) The polishing composition for this example was prepared in the same manner as for Comparative Example A1, except that the alumina abrasive content was changed to 0.5%.

[0084] (Comparative example A3) A polishing composition containing each component in the amounts shown in Table 1 was prepared by mixing alumina abrasive grains, potassium permanganate, calcium nitrate tetrahydrate, and deionized water.

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

[0086] <Polishing of the object to be polished> A SiC wafer was pre-polished using a pre-polishing composition containing alumina abrasive particles. This pre-polished SiC wafer was then used as the polishing target, and the polishing composition according to each example was used as the polishing solution to polish the target under the polishing conditions described below. [Polishing conditions] Polishing equipment: Fujikoshi Machinery Co., Ltd., Model "RDP-500" (plate diameter 20 inches) Polishing pad: Nitta Haas "SUBA800XY" (non-woven fabric type) Processing pressure: 44.1 kPa Plate rotation speed: 120 rpm Head rotation speed: 120 rpm Polishing solution supply rate: 20 mL / min How to use the polishing solution: Disposable Polishing time: 15 minutes Object to be polished: 4-inch SiC wafer (conductivity type: n-type, crystalline type: 4H-SiC, off-angle of main surface (0001) relative to the C axis: 4°), 1 wafer / batch Polishing solution temperature: 23℃

[0087] <Measurement and Evaluation> (Polishing removal rate) Under the polishing conditions described above, SiC wafers were polished using the polishing compositions of each example, and then the polishing removal rate was calculated according to the following formulas (1) and (2). (1) Polishing allowance [cm] = Difference in weight of SiC wafer before and after polishing [g] / Density of SiC [g / cm³] 3 ](=3.21g / cm 3 ) / Polishing area [cm 2 ](=78.54cm 2 ) (2) Polishing removal rate [nm / h] = Polishing allowance [cm] × 10 7 Polishing time (= 15 / 60 hours)

[0088] The polishing and removal rates obtained in each example were converted to relative values ​​with Comparative Example A2 set to 100 and are shown in Table 1.

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

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

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

[0092] [Table 1]

[0093] As shown in Table 1, metal cations (Al) have a pKa of 5.0 for hydrated metal ions. 3+In Examples A1 and A2, where SiC wafers were polished using a polishing composition containing metal salt A (aluminum nitrate nonahydrate), which is a salt of metal cation (Ga) and anion, the rise in pH during polishing was significantly suppressed, the polishing removal rate was significantly improved, and the rise in pad temperature was suppressed compared to Comparative Examples A1 and A2, which used a polishing composition without metal salt A. 3+ Similar effects were obtained in Example A4, which used a polishing composition containing metal salt A (gallium nitrate octahydrate), which is a salt of ) and anion. 3+ In Example A3, which used an abrasive composition containing metal salt A (indium nitrate trihydrate), which is a salt of ) and anion, the effect of significantly suppressing the rise in pH during polishing and suppressing the rise in pad temperature was obtained while maintaining the same polishing removal rate as in Comparative Example A2. On the other hand, metal cations (Ca) do not contain metal salt A, but instead have a hydrated metal ion pKa of 12.8. 2+ In Comparative Example A3, which used an abrasive composition containing a salt of ) and an anion, the effect of suppressing the rise in pH of the abrasive composition during polishing was weak, and the effect of suppressing the rise in pad temperature was also weak.

[0094] ≪Experimental Example 2≫ <Preparation of polishing composition> (Examples S1, S2) A polishing composition containing silica abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water was prepared by mixing these components in the amounts shown in Table 2.

[0095] (Example S3) A polishing composition containing silica abrasive grains, potassium permanganate as a permanganate salt, indium nitrate trihydrate as metal salt A, and deionized water was prepared by mixing these components in the amounts shown in Table 2.

[0096] (Example S4) A polishing composition containing silica abrasive grains, potassium permanganate as a permanganate salt, gallium nitrate octahydrate as metal salt A, and deionized water was prepared by mixing these components in the amounts shown in Table 2.

[0097] (Example S5) A polishing composition containing silica abrasive grains, potassium permanganate as a permanganate salt, zirconium acetate (Zr(OAc)4) as metal salt A, and deionized water was prepared by mixing these with the amounts of each component shown in Table 2.

[0098] (Comparative Example S1) The 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) A polishing composition containing silica abrasive grains, potassium permanganate, calcium nitrate tetrahydrate, and deionized water was prepared by mixing these components in the amounts shown in Table 2.

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

[0101] <Polishing of the object to be polished> A SiC wafer was pre-polished using a pre-polishing composition containing alumina abrasive particles. This pre-polished SiC wafer was then used as the polishing target, and the polishing composition according to each example was used as the polishing solution to polish the target under the same polishing conditions as in Experimental Example 1.

[0102] <Measurement and Evaluation> (Polishing removal rate) The values ​​obtained by measurement in the same manner as in Experimental Example 1 were converted to relative values ​​with Comparative Example S1 set to 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 equation: ΔT[°C]=(Pad temperature of Comparative Example S1)-(Pad temperature of each example); and the effect of suppressing pad rise was evaluated at the following four levels based on this ΔT (i.e., the decrease in pad temperature relative to the pad temperature of Comparative Example S1), and the results are shown in Table 2. AA: ΔT is 2.0℃ or higher A: ΔT is greater than 1.0℃ and less than 2.0℃ B: ΔT is greater than 0.3℃ and less than 1.0℃ C:ΔT is 0.3℃ or less

[0104] (pH during polishing) The measurements were taken in the same manner as in Experimental Example 1. The results are shown in Table 2.

[0105] [Table 2]

[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 rise in pH during polishing was significantly suppressed, the polishing removal rate was significantly improved, and the rise in pad temperature was suppressed compared to Comparative Example S1, which used a polishing composition without metal salt A. On the other hand, metal cations (Ca) do not contain metal salt A, but instead have a hydrated metal ion pKa of 12.8. 2+ In Comparative Example S2, which used an abrasive composition containing a salt of ) and an anion, the effect of suppressing the rise in pH of the abrasive composition during polishing was weak, and the effect of suppressing the rise in pad temperature was also weak.

[0107] ≪Experimental Example 3≫ <Preparation of polishing composition> (Example A5) A polishing composition containing each component in the amounts shown in Table 3 was prepared by mixing alumina abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water.

[0108] (Comparative example A4) The 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) A polishing composition containing silica abrasive grains, potassium permanganate as a permanganate salt, aluminum nitrate nonahydrate as metal salt A, and deionized water was prepared by mixing these components in the amounts shown in Table 4.

[0110] (Comparative Example S3) The 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 the object to be polished> A SiC wafer was pre-polished using a pre-polishing composition containing alumina abrasive particles. This pre-polished SiC wafer was then used as the object to be polished, and the polishing composition according to each example was used as the polishing solution to polish the object under the following two types of polishing conditions. [Polishing Condition 1] Polishing equipment: Fujikoshi Machinery Co., Ltd., Model "RDP-500" (plate diameter 20 inches) Polishing pad: Nitta Haas Co., Ltd. "IC-1000" (hard polyurethane type) Processing pressure: 29.4 kPa Plate rotation speed: 100 revolutions / minute Head rotation speed: 100 revolutions / minute Polishing solution supply rate: 20 mL / min How to use the polishing solution: Disposable Polishing time: 15 minutes Polishing target: 4-inch semi-insulating SiC wafer (conductive type: non-doped, crystalline 4H-SiC, off-angle of main surface (0001) relative to the C axis: 0°), 1 wafer / batch Polishing solution temperature: 23℃ [Polishing Condition 2] Polishing equipment: Fujikoshi Machinery Co., Ltd., Model "RDP-500" (plate diameter 20 inches) Polishing pad: Nitta Haas Co., Ltd. "IC-1000" (hard polyurethane type) Machining pressure: 39.2 kPa Plate rotation speed: 120 rpm Head rotation speed: 120 rpm Polishing solution supply rate: 20 mL / min How to use the polishing solution: Disposable Polishing time: 15 minutes Polishing target: 4-inch semi-insulating SiC wafer (conductive type: non-doped, crystalline 4H-SiC, off-angle of main surface (0001) relative to the C axis: 0°), 1 wafer / batch Polishing solution temperature: 23℃

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

[0113] [Table 3]

[0114] [Table 4]

[0115] As shown in Tables 3 and 4, the polishing composition containing metal salt A (aluminum nitrate nonahydrate) showed an improvement in polishing removal speed compared to the polishing composition without 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 in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above.

Claims

1. A method for polishing an object having a surface made of silicon carbide, The process involves preparing an abrasive composition, A step of supplying the polishing composition to the object to be polished and polishing the object to be polished. Includes, In the polishing process, the pH of the polishing composition supplied to the object to be polished when it flows out of the object to be polished is less than 2.0 above the pH at which the polishing composition was supplied to the object to be polished. The aforementioned polishing composition comprises permanganate, metal salt A, and water. The polishing method wherein the metal salt A is a salt of a metal cation with a pKa of less than 7.0 of the hydrated metal ion 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 the concentration of the metal salt A in the polishing composition is 8 mM or more.

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

5. The polishing method according to claim 4, wherein the abrasive grain is at least one selected from the group consisting of silica, cerium oxide, chromium oxide, titanium dioxide, zirconium oxide, magnesium oxide, manganese dioxide, zinc oxide, iron oxide, silicon nitride, boron nitride, calcium carbonate, and barium carbonate.

6. The polishing method according to claim 4, wherein the abrasive grain is silica.

7. The polishing method according to claim 4, wherein the abrasive grains include alumina.

8. The polishing method according to claim 4, wherein the average primary particle diameter of the abrasive grains is 150 nm or more and 5 μm or less.

9. The polishing method according to any one of claims 4 to 8, wherein the content of the abrasive grains in the polishing composition is less than 0.5% by weight.

10. The polishing method according to any one of claims 1 to 9, 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.

11. A polishing composition used in the polishing method according to any one of claims 1 to 10.

12. A polishing composition for polishing an object to be polished having a surface made of silicon carbide, It contains permanganate, metal salt A, and water. The aforementioned metal salt A is a salt of a metal cation with a hydrated metal ion pKa less than 7.0 and an anion. An abrasive composition wherein the pH of the abrasive composition when it flows out of the object to be polished after being supplied to the object to be polished is less than 2.0 above the pH at which it was supplied to the object to be polished.

13. The polishing composition according to claim 12, wherein the concentration of the metal salt A is 8 mM or more.

14. The polishing composition according to claim 12 or 13, further comprising abrasive grains.

15. The polishing composition according to claim 14, wherein the abrasive grain is at least one selected from the group consisting of silica, cerium oxide, chromium oxide, titanium dioxide, zirconium oxide, magnesium oxide, manganese dioxide, zinc oxide, iron oxide, silicon nitride, boron nitride, calcium carbonate, and barium carbonate.

16. The polishing composition according to claim 14, wherein the abrasive grains are silica.

17. The polishing composition according to claim 14, wherein the abrasive grains include alumina.

18. The polishing composition according to claim 14, wherein the average primary particle diameter of the abrasive grains is 150 nm or more and 5 μm or less.

19. The polishing composition according to any one of claims 14 to 18, wherein the content of the abrasive grains is less than 0.5% by weight.

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