Polishing composition and polishing method

Abstract

The present invention provides a polishing composition capable of improving polishing removal speed. The polishing composition includes a permanganate, a rare earth salt (excluding a rare earth salt containing cerium), and a salt of a metal cation and an anion having a pKa of 2 to 6, inclusive.

Description

Polishing composition and polishing method

[0001] The present invention relates to an abrasive composition and an abrasive method. This application claims priority to Japanese Patent Application No. 2024-167891, filed on 26 September 2024, the entire contents of which are incorporated herein by reference.

[0002] Polishing is performed on the surfaces of materials such as metals, metalloids, nonmetals, and their oxides using polishing compositions. For example, surfaces composed of compound semiconductor materials such as silicon carbide, boron carbide, tungsten carbide, silicon nitride, titanium nitride, and gallium nitride are processed by polishing (lapping) performed by supplying diamond abrasive grains between the surface and the polishing platen. However, lapping using diamond abrasive grains is prone to defects and distortions due to the occurrence and retention of scratches and dents. Therefore, polishing using a polishing pad and polishing composition is being considered after, or as an alternative to, lapping with diamond abrasive grains. Patent document 1 is an example of a document disclosing this type of prior art.

[0003] Strength Specification No. 10,655,035

[0004] Generally, from the standpoint of manufacturing efficiency and cost-effectiveness, a sufficiently high polishing removal rate is desirable for practical purposes. For example, in polishing surfaces made of high-hardness materials such as silicon carbide, an improvement in the polishing removal rate is strongly desired. To address this issue, polishing compositions containing strong oxidizing agents such as permanganates have been conventionally used.

[0005] For example, Patent Document 1 describes a salt solution prepared by adding 0.125% by weight potassium persulfate (4.76 mM) as a secondary oxidizing agent to a 2.00% by weight potassium permanganate aqueous solution (130.4 mM), to which aluminum nitrate, copper nitrate, iron nitrate, or zirconium sulfate was added as a metal cation source to a metal cation concentration of 3.43 mM. Using this solution, a polishing test of a silicon carbide (SiC) wafer was performed, and Fe ３＋ and Al ３＋ Al showed a superior material removal rate (MRR) compared to other metal cations.３＋ It is noted that Ra not only performed better than other metal cations tested, but also resulted in a lower scratch count (page 8, right column, line 51 to page 9, left column, line 12, Figure 1). Furthermore, the same document describes the use of aluminum nitrate in Al ３＋ The optimization of the concentration was also considered, and it was noted that among the concentrations tested, the MRR was best at 0% aluminum nitrate, and that the MRR tended to decrease as the aluminum nitrate concentration increased (page 9, left column, lines 13-36, Figure 2).

[0006] In polishing various objects to be polished, including substrates made of high-hardness materials such as silicon carbide, it would be practically significant to be able to achieve an even higher level of polishing removal speed. The inventors have confirmed that the polishing removal speed of SiC is improved by adding rare earth salts, and based on this finding, further investigations have revealed that by combining rare earth salts with specific metal salts, a higher polishing removal speed can be achieved than when each is used alone, thus completing the present invention. In other words, the present invention aims to provide a polishing composition that can improve the polishing removal speed in polishing objects. Another related object is to provide a method for polishing objects using such a polishing composition.

[0007] This specification provides an abrasive composition comprising a permanganate, a rare earth salt (excluding those containing cerium), and a salt of a metal cation and anion having a pKa of 2 to 6. The abrasive composition having the above composition can improve the abrasive removal rate.

[0008] In some preferred embodiments, the rare earth salt contains a group 17 element. Using such a rare earth salt makes it easier to obtain a better polishing and removal rate improvement effect. A rare earth salt containing a fluorine atom is preferably used as the rare earth salt.

[0009] In some embodiments, the metal cation having a pKa of 2 to 6 is selected from aluminum ions, indium ions, and gallium ions. By using a salt of the above metal cation and anion, the polishing removal rate improvement effect of the technology disclosed herein is preferably exhibited.

[0010] In some embodiments, the polishing composition further comprises abrasive grains. A polishing composition containing abrasive grains can achieve a high polishing removal rate based on the polishing action of the abrasive grains. Silica is preferably used as the abrasive grain. Silica abrasive grains can preferably achieve both a high polishing removal rate and good surface finish.

[0011] The polishing compositions disclosed herein are used, for example, for polishing materials with a Vickers hardness of 1500 Hv or higher. In polishing such high-hardness materials, the effects of the techniques disclosed herein can be preferably demonstrated. In some embodiments, the material with a Vickers hardness of 1500 Hv or higher is a non-oxide (i.e., a compound that is not an oxide). In polishing non-oxide materials to be polished, the effect of improving the polishing removal rate by the polishing compositions disclosed herein can be preferably realized.

[0012] The polishing compositions disclosed herein can be used, for example, for polishing silicon carbide. In polishing silicon carbide, the effects of the techniques disclosed herein can be favorably exhibited.

[0013] This specification further provides a polishing method comprising the step of polishing an object to be polished using any of the polishing compositions disclosed herein. Such a polishing method can improve the polishing removal rate, even when polishing an object to be polished made of a high-hardness material. This makes it possible to increase the productivity of the target product (polished material, such as a compound semiconductor substrate such as a silicon carbide substrate) obtained through polishing by the above polishing method.

[0014] 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.

[0015] <Polishing Composition> (Permanganate) The polishing composition disclosed herein contains a permanganate. In polishing materials to be polished (e.g., high-hardness non-oxide materials such as silicon carbide), the permanganate typically functions as an oxidizing agent, thereby improving the polishing removal rate. As the permanganate, alkali metal permanganates such as sodium permanganate and potassium permanganate are preferred, with potassium permanganate being particularly preferred. In some embodiments, the proportion of potassium permanganate in the total permanganate may be approximately 10% by weight or more, approximately 30% by weight or more, approximately 50% by weight or more (e.g., more than 50% by weight), approximately 70% by weight or more, approximately 90% by weight or more, or 99-100% by weight. One type of permanganate can be used alone or in combination of two or more types. The permanganate may exist in an ionic state in the polishing composition.

[0016] The permanganate content in any of the polishing compositions disclosed herein is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use of the polishing composition. In some embodiments, from the viewpoint of improving the polishing removal rate, the permanganate content is suitable to be approximately 0.1% by weight or more, preferably 0.5% by weight or more, more preferably 1% by weight or more, even more preferably 2% by weight or more, even more preferably 3% by weight or more, and may be 3.5% by weight or more. Also in some embodiments, from the viewpoint of surface quality after polishing, the permanganate content in the polishing composition is suitable to be approximately 30% by weight or less, may be 20% by weight or less, or 15% by weight or less. In some other embodiments, the permanganate content may be less than 12% by weight, may be 10% by weight or less (e.g., less than 10% by weight), may be 8% by weight or less, may be 6% by weight or less, or may be 5% by weight or less. Embodiments with a content of less than 12% by weight are suitable, for example, when potassium permanganate is used. By limiting the amount of permanganate used, it is possible to sufficiently dissolve the permanganate in the polishing composition and achieve a high polishing removal rate.

[0017] (Rare Earth Salts) The polishing compositions disclosed herein contain rare earth salts. Here, rare earth salts refer to salts containing rare earth elements. However, the rare earth salts disclosed herein do not contain cerium. By using such rare earth salts, a high polishing removal rate can be achieved. Polishing compositions containing permanganate and rare earth salts can improve the polishing removal rate. This is thought to be because, in the polishing composition, the rare earth salts act as Lewis acids, coordinating to the oxide layer formed on the surface of the object to be polished, thereby promoting the removal of atoms from the surface of the object to be polished. However, the above considerations do not limit the scope of the present invention. Rare earth salts can be used individually or in combination of two or more. Rare earth salts may typically exist in the polishing composition dissolved in a solvent such as water.

[0018] Examples of rare earth elements that make up rare earth salts include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Among these, La, Nd, Sm, Gd, and Yb are preferred, La, Nd, Gd, and Yb are more preferred, La, Nd, and Yb are even more preferred, and La is particularly preferred.

[0019] The type of salt in the rare earth salt is not particularly limited and 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, phosphoric acid, and trifluoromethanesulfonic acid are preferred, and salts of hydrochloric acid, nitric acid, sulfuric acid, and trifluoromethanesulfonic acid are more preferred. In some embodiments, the rare earth salt is preferably one that contains a group 17 element. Examples of rare earth salts containing Group 17 elements include those containing fluorine, chlorine, bromine, and iodine atoms. Among these, rare earth salts containing fluorine atoms are preferred. Such rare earth salts may be salts of trifluoromethanesulfonic acid. Rare earth salts typically do not contain ammonium ions or ammonia.

[0020] The concentration (content) of rare earth salts in the polishing 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 polishing composition. The concentration of rare earth salts in the polishing composition may be, for example, 0.1 mM or more (i.e., 0.1 mmol / L or more), and from the viewpoint of appropriately exhibiting the effect of using rare earth salts, it is advantageous to set it to 1 mM or more, preferably 5 mM or more, and it may also be 10 mM or more, 12 mM or more, 15 mM or more, 20 mM or more, or 25 mM or more. Furthermore, the upper limit of the concentration of rare earth salts may be, for example, approximately 1000 mM or less (i.e., 1 mol / L or less), 500 mM or less, or 300 mM or less. In some embodiments, the concentration of the rare earth salt is suitable to be 200 mM or less, preferably 100 mM or less, more preferably 50 mM or less, even more preferably 30 mM or less, even more preferably 25 mM or less, and may also be 20 mM or less, 17 mM or less, 15 mM or less, 12 mM or less, or 10 mM or less. By appropriately setting the amount of rare earth salt used within the above range, the polishing removal rate improvement effect of the technology disclosed herein can be preferably achieved.

[0021] The ratio (M2 / W1) of the concentration M2 [mM] of the rare earth salt in the polishing composition to the content W1 [wt%] of the permanganate is greater than 0, may be 0.01 or greater, 0.1 or greater, or 0.5 or greater. From the viewpoint of better exhibiting the effects of including the rare earth salt in the polishing composition containing the permanganate, in some embodiments, the ratio (M2 / W1) may be, for example, 1.0 or greater, 2.0 or greater, 2.5 or greater, 3.0 or greater, or 3.5 or greater. There is no particular upper limit to the ratio (M2 / W1), but it is appropriate to be approximately 500 or less, preferably 100 or less, and more preferably 50 or less. In some preferred embodiments, the ratio (M2 / W1) may be 25 or less, 20 or less, 10 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less.

[0022] (Salt of a metal cation and an anion with a pKa of 2 or more and 6 or less) The polishing composition disclosed herein contains a salt of a metal cation and an anion with a pKa of 2 or more and 6 or less. Hereinafter, the salt of a metal cation and an anion with a pKa of 2 or more and 6 or less may be abbreviated as metal salt A. Note that metal salt A does not include the aforementioned permanganate and rare earth salts. Metal salt A is a compound different from permanganate and rare earth salts. According to a polishing composition containing permanganate and further containing the aforementioned rare earth salt and metal salt A, the polishing removal rate can be improved more than when either the rare earth salt or metal salt A is combined with permanganate alone. Metal salt A can be used alone or in combination of two or more. Metal salt A can typically exist in a dissolved state in a solvent such as water in the polishing composition.

[0023] The metal cation with a pKa of 2 or more and 6 or less may be, for example, a cation containing a metal belonging to Groups 5 to 14 of the periodic table, preferably a cation containing a metal belonging to Groups 6 to 14 of the periodic table, and more preferably a cation containing a metal belonging to Group 13 of the periodic table. Specific examples of the metal cation with a pKa of 2 or more and 6 or less include aluminum ion (Al ３＋ , pKa 5.0), indium ion (In ３＋ , pKa 4.0), gallium ion (Ga ３＋ , pKa 2.6), chromium ion (Cr ３＋ , pKa 4.0), iron ion (Fe ３＋Examples include, but are not limited to, metal cations with a pKa of 2.2. Among these metal cations, aluminum ions, indium ions, and gallium ions are preferably used. In this specification, the pKa values ​​of metal cations shall be those listed in Inorganic Chemistry, GARY WULSBERG, University Science Books, 2000, p.59, Table 2.2 “Hydrolysis Constants for Metal Cations”. As metal salt A, for example, aluminum salts, indium salts, and gallium salts are preferably used, in which the metal cation with a pKa of 2 to 6 is an aluminum ion, an indium ion, or a gallium ion.

[0024] The type of salt in metal salt A is not particularly limited and 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. Suitable examples of such metal salt A include aluminum hydrochloride, aluminum nitrate, and aluminum sulfate.

[0025] The rare earth salt and metal salt A may have the same or different anionic species. In some preferred embodiments, the anionic species of the rare earth salt and metal salt A are the same. The anionic species common to the rare earth salt and metal salt A may be, for example, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, etc. In some other embodiments, the anionic species of the rare earth salt and metal salt A are different. For example, if the anionic species of the rare earth salt contains a group 17 element (e.g., trifluoromethanesulfonic acid), the anionic species of metal salt A may be nitric acid.

[0026] The concentration (content) of metal salt A in the polishing 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 polishing composition. 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 set it to 1 mM or more, and from the viewpoint of improving the polishing removal speed, it is preferable to set it to 5 mM or more, more preferably to 8 mM or more, even more preferably to 10 mM or more, even more preferably to 12 mM or more, and particularly preferably to 15 mM or more. The concentration of metal salt A in the polishing composition may be 20 mM or more, or 30 mM or more. Furthermore, the upper limit of the concentration of metal salt A may be, for example, approximately 1000 mM or less, or 500 mM or less, or 300 mM or less. 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, even more preferably 30 mM or less (e.g., less than 30 mM), even more preferably 25 mM or less, even more preferably 20 mM or less, particularly preferably 15 mM or less, and may also be 10 mM or less. In embodiments in which metal salt A is used in the amount limited as described above, the polishing removal rate improvement effect of the technology disclosed herein can be effectively exerted.

[0027] The ratio (M3 / W1) of the concentration M3 [mM] of metal salt A in the polishing composition to the concentration W1 [wt%] of permanganate is greater than 0, may be 0.01 or greater, 0.1 or greater, or 0.5 or greater. From the viewpoint of better exhibiting the effect of including metal salt A in the polishing composition containing permanganate, in some embodiments the ratio (M3 / W1) may be, for example, 1.0 or greater, 2.0 or greater, 2.5 or greater, 3.0 or greater, or 3.5 or greater. The upper limit of the ratio (M3 / W1) is not particularly limited, but is generally appropriate to be 500 or less, preferably 100 or less, and more preferably 50 or less. In some preferred embodiments the ratio (M3 / W1) may be 25 or less, 20 or less, 10 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1 or less.

[0028] The ratio (M3 / M2) of the concentration M2 [mM] of the rare earth salt to the concentration M3 [mM] of the metal salt A in the polishing composition can be appropriately set to achieve the desired effect depending on the purpose and manner of use of the polishing composition. The ratio (M3 / M2) may be 0.01 or greater, or 0.1 or greater. From the viewpoint of adding a predetermined amount of metal salt A to the rare earth salt and better exhibiting the effect based on the combined use of the rare earth salt and metal salt A, in some embodiments the ratio (M3 / M2) may be, for example, 0.3 or greater, 0.5 or greater, 0.7 or greater, 0.9 or greater, or 1 or greater. On the other hand, from the viewpoint of better exhibiting the effect of including the rare earth salt, in some embodiments the ratio (M3 / M2) may be, for example, approximately 100 or less, 10 or less, 3 or less, 2 or less, 1.5 or less, or 1.2 or less.

[0029] The total content (M2 + M3) of rare earth salts and metal salt A in the polishing composition is not particularly limited. The total content of rare earth salts and metal salt A may be, for example, 0.1 mM or more, and from the viewpoint of better exhibiting the effect of improving the polishing removal speed based on the combined use of rare earth salts and metal salt A, it is advantageous to have a total content of 1 mM or more, preferably 5 mM or more, more preferably 10 mM or more, even more preferably 15 mM or more, even more preferably 20 mM or more, and particularly preferably 25 mM or more. The total content of rare earth salts and metal salt A in the polishing composition may be 40 mM or more, or 50 mM or more. Furthermore, the upper limit of the total content of rare earth salts and metal salt A may be, for example, approximately 1000 mM or less, 500 mM or less, or 300 mM or less. In some embodiments, the total content of rare earth salts and metal salt A is suitable to be 200 mM or less, preferably 100 mM or less, more preferably 80 mM or less, even more preferably 60 mM or less (e.g., less than 60 mM), even more preferably 50 mM or less, even more preferably 40 mM or less, particularly preferably 30 mM or less, and may be 20 mM or less. By appropriately setting the total content of rare earth salts and metal salt A within the above range, the polishing removal rate improvement effect of the technology disclosed herein can be preferably achieved.

[0030] (Abrasive grains) The polishing compositions disclosed herein may or may not contain abrasive grains. In some embodiments, the polishing compositions contain abrasive grains. With polishing compositions 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, rare earth salts, and metal salt A.

[0031] 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; carbonates such as calcium carbonate and barium carbonate; and abrasive grains substantially composed of any of these. 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.

[0032] In this specification, "substantially consisting of X" or "substantially composed of X" means that the proportion of X in the abrasive grains (purity of X) is 90% or more by weight. Furthermore, the proportion of X in the abrasive grains is preferably 95% or more, more preferably 97% or more, even more preferably 98% or more, and for example, 99% or more.

[0033] The average primary particle size of the abrasive grains is not particularly limited. 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, and may be 30 nm or more. 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, or 350 nm or more. From the perspective of improving the polishing removal rate, it is preferable that the average primary particle size of the abrasive grains is large. Also, from the perspective of the surface quality after polishing, etc., 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, and may be 750 nm or less, or 500 nm or less. From the perspective of obtaining better surface quality, 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.

[0034] In this specification, the average primary particle size refers to the particle size (BET particle size) calculated by the formula: average primary particle size (nm) = 6000 / (true density (g / cm ３ ³) × BET value (m ２ ² / g)). The above specific surface area can be measured, for example, using a surface area measuring device manufactured by Micromeritics, trade name "Flow Sorb II 2300".

[0035] The average secondary particle size of the abrasive grains may be, for example, 10 nm or more. From the perspective of facilitating an increase in 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 400 nm or more. The upper limit of the average secondary particle size of the abrasive grains is suitably about 10 µm or less from the perspective of ensuring a sufficient number per unit weight. Also, from the perspective of the surface quality after polishing, etc., the above average secondary particle size is preferably 5 µm or less, more preferably 3 µm or less, and for example, 1 µm or less. From the perspective of obtaining better surface quality, in some embodiments, the average secondary particle size of the abrasive grains may be 600 nm or less, 300 nm or less, 170 nm or less, or 100 nm or less.

[0036] For particles with an average secondary particle diameter of less than 500 nm, for example, the volume average particle diameter (arithmetic mean diameter based on volume; Mv) can be measured by the dynamic light scattering method using a model "UPA-UT151" manufactured by Nikkiso Co., Ltd. For particles with a diameter of 500 nm or more, the volume average particle diameter can be measured by the pore electrical resistance method or the like using a model "Multisizer 3" manufactured by BECKMAN COULTER, Inc.

[0037] When using alumina particles (alumina abrasive grains) as the abrasive grains, they can be appropriately selected and used 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. Specifically, γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, χ-alumina, etc. are exemplified. Also, alumina called fumed alumina (typically alumina fine particles produced when an alumina salt is fired at a high temperature) based on classification by production method may be used. Furthermore, alumina called colloidal alumina or alumina sol (for example, alumina hydrates such as boehmite) is also included in the examples of the above-mentioned known alumina particles. From the viewpoint of workability, it is preferable to contain α-alumina. The alumina abrasive grains in the technology disclosed herein can contain one kind of such alumina particles alone or in combination of two or more kinds.

[0038] When using alumina particles as the abrasive grains, it is generally advantageous for the proportion of alumina particles in the total abrasive grains used to be higher. 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, still more preferably 95% by weight or more, and may be substantially 100% by weight.

[0039] 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, 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 surface quality after polishing, it is appropriate to be approximately 5 μm or less, 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.

[0040] 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.

[0041] 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.

[0042] In some preferred embodiments, the polishing composition contains 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.

[0043] When using silica abrasive grains, a higher proportion of silica abrasive grains to the total abrasive grains used is generally advantageous. For example, the proportion of silica abrasive grains 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 be substantially 100% by weight. In an abrasive composition that substantially does not contain abrasive grains other than silica abrasive grains, for example, if it substantially does not contain abrasive grains with a higher hardness than silica abrasive grains (e.g., alumina particles, zirconium oxide particles, chromium oxide particles), scratches and dents on the polished surface caused by the inclusion of such high-hardness abrasive grains are less likely to occur, and a better surface accuracy can be suitably achieved. Note that substantially not containing abrasive grains other than silica abrasive grains means that the proportion of abrasive grains other than silica abrasive grains in the total weight of abrasive grains contained in the abrasive composition is 1% by weight or less, for example 0.5% by weight or less, and even more preferably 0.1% by weight or less, and includes the case where the proportion of abrasive grains other than silica abrasive grains is 0% by weight.

[0044] 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.

[0045] 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 an average primary particle diameter of 12 nm to 80 nm are preferred, and silica abrasive grains with an average primary particle diameter of 15 nm to 75 nm are preferred.

[0046] 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).

[0047] 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.

[0048] The shape (outer form) of the silica particles is preferably spherical. Although not particularly limited, the average value of the ratio of the major axis to the minor axis of the particles (average aspect ratio) 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.

[0049] 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, a scanning electron microscope (SEM) is used to extract the shapes of a predetermined number of particles (e.g., 200). The smallest rectangle that circumscribes the shape of each extracted particle is drawn. Then, for the rectangle drawn for the shape of each particle, the ratio of the major axis to the minor axis is calculated 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.

[0050] In embodiments in which the polishing composition contains 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.

[0051] In an embodiment using 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.

[0052] The content of abrasive grains (e.g., silica abrasive grains) in the polishing compositions disclosed herein is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use of the polishing composition. The content of abrasive grains may be, for example, less than 5% by weight, less than 3% by weight, or less than 2% by weight. In some embodiments, the content of abrasive grains in the polishing composition is preferably less than 1% by weight, more preferably less than 0.5% by weight, more preferably 0.4% by weight or less, may be 0.3% by weight or less, or 0.2% by weight or less. In some embodiments, the content of abrasive grains in the polishing composition may be 0.1% by weight or less or less, 0.05% by weight or less or less, 0.04% by weight or less or less, or 0.03% by weight or less 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 using abrasive grains, in some embodiments, the abrasive 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. In some preferred embodiments, the abrasive content in the polishing composition may be 0.01% by weight or more, 0.02% by weight or more, 0.03% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.5% by weight or more, or 0.8% by weight or more. When the polishing composition disclosed herein contains multiple types of abrasive grains, the abrasive content in the polishing composition refers to the total content of the above multiple types of abrasive grains.

[0053] 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 degree of 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.

[0054] In embodiments of the polishing composition containing abrasive grains, the relationship between the abrasive grain content and the permanganate 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 permanganate content W1 [weight%] to the abrasive grain content Wa [weight%] (W1 / Wa) can be, for example, approximately 0.01 or more, preferably 0.1 or more, and may also be 1 or more. As the ratio (W1 / Wa) increases, the contribution of chemical polishing tends to increase relative to the contribution of mechanical polishing. In some embodiments, the ratio (W1 / Wa) is preferably 5 or more, may be 10 or more, may be 20 or more, and may also be 30 or more. There is no particular upper limit to the ratio (W1 / Wa), but from the viewpoint of storage stability of the polishing composition, it can be, for example, approximately 5000 or less, 1500 or less, 1000 or less, 800 or less, 400 or less, 250 or less, 100 or less, 80 or less, or 50 or less. In some embodiments, the ratio (W1 / Wa) can be 30 or less, 20 or less, or 10 or less.

[0055] In embodiments of the polishing composition containing abrasive grains, the relationship between the abrasive grain content and the concentration of the rare earth salt 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 the rare earth salt M2 [mM] to the abrasive grain content Wa [weight %] (M2 / Wa) is appropriately set to 0.1 or more, preferably 1 or more, more preferably 5 or more, and may be 10 or more. As the ratio (M2 / Wa) increases, the contribution of chemical polishing tends to increase relative to the contribution of mechanical polishing. In some embodiments, the ratio (M2 / Wa) may be 50 or more, 80 or more, 100 or more, 120 or more, 150 or more, 200 or more, or 250 or more. There is no particular upper limit to the ratio (M2 / Wa), but from the viewpoint of storage stability of the polishing composition, it can be, for example, approximately 20,000 or less, 10,000 or less, 5,000 or less, 2,500 or less, or 1,000 or less. In some embodiments, the ratio (M2 / Wa) may be 500 or less, 300 or less, 200 or less, or 100 or less.

[0056] In embodiments where the polishing composition contains abrasive grains, the relationship between the abrasive grain content and the concentration of metal salt A is not particularly limited and can be appropriately set according to the purpose and manner of use to achieve the desired effect. The ratio of the concentration of metal salt A M3 [mM] to the abrasive grain content Wa [weight%] (M3 / Wa) can be, for example, 5 or more, preferably 10 or more, more preferably 30 or more, may be 50 or more, may be 80 or more, may be 100 or more, may be 120 or more, may be 150 or more, may be 200 or more, or may be 250 or more. The upper limit of the ratio (M3 / Wa) is not particularly limited, but from the viewpoint of storage stability of the polishing composition, for example it can be approximately 10,000 or less, may be 5,000 or less, may be 2,500 or less, or may be 1,000 or less. In some embodiments, the ratio (M3 / Wa) may be 700 or less, 500 or less, 300 or less, 200 or less, or 100 or less.

[0057] (Water) The polishing compositions disclosed herein typically contain water. Deionized water, pure water, ultrapure water, distilled water, etc., can be preferably 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, 90% by volume or more of the solvent in the polishing composition is water, preferably 95% by volume or more, and more preferably 99-100% by volume.

[0058] (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 purpose of use (e.g., pH adjustment). Alternatively, some embodiments of the polishing composition disclosed herein may have a composition that is substantially free of acid.

[0059] (Basic Compounds) The polishing composition 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 the 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 is substantially free of basic compounds (e.g., ammonium ions and ammonia).

[0060] (Oxidizing agents other than permanganates) The polishing compositions disclosed herein may contain oxidizing agents other than permanganates, to the extent that they do not impair the effects of the present invention. Examples of compounds that can be selected as oxidizing agents other than permanganates include peroxides such as hydrogen peroxide, periodic acids, iodic acids, bromic acids, iron acids, chromic acids and dichromates, vanadic acids, ruthenic acids, molybdic acids, perrhenic acids, tungstic acids, persulfates, chloric acids and perchloric acids, osmium acids, selenic acids, and the like. Oxidizing agents other than permanganates may be used individually or in combination of two or more.

[0061] (Optional Salts) The polishing compositions disclosed herein may contain various salts other than permanganates, rare earth salts, and metal salt A, as long as they do not impair the effects of the present invention. Any salt other than permanganates, rare earth salts, and metal salt A is a salt of a metal cation and anion having a pKa of less than 2 or greater than 6, and which does not contain rare earth elements. Examples of such arbitrary metal salts (e.g., alkali metal salts, alkaline earth metal salts) 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; and so on. When the polishing composition contains arbitrary salts, examples of the anionic species of the arbitrary salt include those exemplified as the anionic species of the rare earth salt and metal salt A. The anionic species of the arbitrary salt may be the same as or different from at least one of the anionic species of the rare earth salt and metal salt A.

[0062] The total content of oxidizing agents other than permanganate and any salts in the polishing composition is, for example, less than 100% by weight, may be less than 50% by weight, less than 30% by weight, less than 10% by weight, less than 3% by weight, or less than 1% by weight, when the total content of permanganate, rare earth salts, and metal salt A is taken as 100% by weight. The techniques disclosed herein can preferably be carried out using polishing compositions that do not contain oxidizing agents other than permanganate and any salts.

[0063] (Other Components) 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.

[0064] (pH) The pH of the polishing composition is appropriately set to about 1 to 12. When the pH is within the above range, a practical polishing removal rate is easily achieved. In some embodiments, the above pH may be 12.0 or less, 11.0 or less, 10.0 or less, 9.0 or less, less than 9.0, 8.0 or less, less than 8.0, 7.0 or less, less than 7.0, or 6.0 or less. From the viewpoint of making it easier to exhibit the polishing removal rate improvement effect of permanganate, rare earth salts and metal salt A, in some embodiments, the pH of the polishing composition is preferably less than 6.0, 5.0 or less, less than 5.0, 4.0 or less, or less than 4.0. The above pH may be, for example, 1.0 or higher, 1.5 or higher, 2.0 or higher, or 2.5 or higher.

[0065] 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 agitator, 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 they may be mixed in an order set as appropriate. The polishing composition disclosed herein may be a single-component type or a multi-component type, including a two-component type. 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 and used for polishing an object to be polished. These can be stored separately before use, for example, and mixed at the time of use to prepare a single-component polishing composition. During mixing, water or the like for dilution may be further added.

[0066] <Objects to be Polished> The objects to be polished with the polishing compositions disclosed herein are not particularly limited. For example, the polishing compositions disclosed herein can be applied to polishing substrates having a surface made of compound semiconductor material, i.e., compound semiconductor substrates. The constituent materials of the compound semiconductor substrate are not particularly limited and may include, for example, II-VI compound semiconductors such as cadmium telluride, zinc selenide, cadmium sulfide, cadmium mercury telluride, zinc cadmium telluride; III-V compound semiconductors such as gallium nitride, gallium arsenide, gallium phosphide, indium phosphide, aluminum gallium arsenide, indium gallium arsenide, indium nitrogen gallium arsenide, and aluminum gallium phosphide; IV-IV compound semiconductors such as silicon carbide (SiC) and germanium silicide; and so on. These materials may be conductive with impurities doped, or insulating or semi-insulating without impurities doped. The object to be polished may be composed of a plurality of these materials. In a preferred embodiment, the polishing composition disclosed herein may be applied to polishing a substrate having a surface composed of a non-oxide (i.e., non-oxide) chemical semiconductor material. In polishing a substrate having a surface composed of a non-oxide chemical semiconductor material, the polishing-promoting effect of the oxidizing agent (typically a permanganate) contained in the polishing composition disclosed herein is readily exhibited.

[0067] The polishing compositions disclosed herein can be preferably used, for example, for polishing the surface of an object to be polished having a Vickers hardness of 500 Hv or more. The Vickers hardness is preferably 700 Hv or more, for example, 1000 Hv or more, or 1500 Hv or more. The Vickers hardness of the material to be polished may be 1800 Hv or more, 2000 Hv or more, or 2200 Hv or more. The upper limit of the Vickers hardness of the surface of the object to be polished is not particularly limited, and may be approximately 7000 Hv or less, 5000 Hv or less, or 3000 Hv or less. In this specification, Vickers hardness can be measured in accordance with JIS R 1610:2003. The international standard corresponding to the above JIS standard is ISO 14705:2000.

[0068] Materials having a Vickers hardness of 1500 Hv or higher include silicon carbide, silicon nitride, titanium nitride, and gallium nitride. The object to be polished in the technology disclosed herein may have a single-crystal surface of the above material that is mechanically and chemically stable. In particular, the surface of the object to be polished is preferably composed of either silicon carbide or gallium nitride, and more preferably 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 speed is particularly great. The technology disclosed herein can be particularly preferably applied to the polishing of a single-crystal surface of silicon carbide.

[0069] <Polishing Method> The polishing compositions disclosed herein can be used to polish an object to be polished in a manner that includes, for example, the following operations: 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., dilution) and pH 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 agents, diluting one or more agents before mixing, and diluting the mixture after mixing. The polishing liquid is then supplied to the object to be polished and polished in a manner that is common to those skilled in the art. For example, the object to be polished is set in a general polishing apparatus, and the polishing liquid is supplied to the surface of the object to be polished through the polishing pad of the apparatus. Typically, the polishing liquid is supplied continuously, and the polishing pad is pressed against the surface of the object to be polished, causing the two to move relative to each other (e.g., rotate). Polishing of the object to be polished is completed through this polishing process.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 improving the polishing removal rate, 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. The polishing composition disclosed herein can also be preferably used for polishing at processing conditions 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 the processing pressure as used herein is synonymous with polishing pressure.

[0074] The polishing pads used in each polishing step 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 rigid foamed polyurethane type polishing pad may be preferred. The polishing pads used in the technologies disclosed herein are polishing pads that do not contain abrasive particles.

[0075] 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.

[0076] 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.

[0077] <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 a polished product manufactured by said method. The method for manufacturing polished products is, for example, a method for manufacturing a silicon carbide substrate. 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 a polished product manufactured by said method. According to the manufacturing method, a substrate manufactured through polishing, such as a silicon carbide substrate, can be efficiently provided.

[0078] The matters disclosed in this specification include: [1] an abrasive composition comprising a permanganate, a rare earth salt (excluding one containing cerium), and a salt of a metal cation and anion having a pKa of 2 to 6; [2] the abrasive composition according to [1], wherein the rare earth salt comprises a Group 17 element; [3] the abrasive composition according to [1] or [2], wherein the rare earth salt comprises a fluorine atom; [4] the abrasive composition according to any one of [1] to [3], wherein the metal cation having a pKa of 2 to 6 is selected from aluminum ions, indium ions, and gallium ions; [5] the abrasive composition according to any one of [1] to [4], further comprising abrasive grains; [6] the abrasive composition according to [5], wherein the abrasive grains comprise silica; [7] the abrasive composition according to any one of [1] to [6], used for polishing materials with a Vickers hardness of 1500 Hv or higher. [8] An abrasive composition according to any one of [1] to [7] above, used for polishing silicon carbide. [9] A polishing method comprising the step of polishing an object to be polished using an abrasive composition according to any one of [1] to [8] above.

[0079] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0080] <Preparation of Polishing Compositions> (Examples 1-6) Polishing compositions were prepared by mixing silica abrasive grains, potassium permanganate, rare earth salts listed in Table 1, aluminum nitrate, and deionized water to obtain a composition containing 0.1% by weight of silica abrasive grains, 4% by weight of potassium permanganate, 15 mM of rare earth salts (calculated as rare earth elements), and 15 mM of aluminum nitrate (calculated as Al). Colloidal silica with an average primary particle diameter of 35 nm and an average secondary particle diameter of 70 nm was used as the silica abrasive grains. The pH of the polishing composition according to Example 1 was 3.10, the pH of the polishing composition according to Example 2 was 3.50, the pH of the polishing composition according to Example 3 was 3.50, the pH of the polishing composition according to Example 4 was 3.32, the pH of the polishing composition according to Example 5 was 3.76, and the pH of the polishing composition according to Example 6 was 3.73.

[0081] (Comparative Examples 1-3) The concentrations of rare earth salts and aluminum nitrate were changed to the concentrations (contents) shown in Table 1. The polishing compositions for each example were prepared in the same manner as in Example 1. In Comparative Example 1, no rare earth salt was added, and in Comparative Examples 2 and 3, no aluminum nitrate was added. In Comparative Example 3, cerium ammonium nitrate was used as the rare earth salt. The pH of the polishing composition for Comparative Example 1 was 3.49, the pH of the polishing composition for Comparative Example 2 was 5.47, and the pH of the polishing composition for Comparative Example 3 was 1.47.

[0082] <Polishing of the object to be polished> A SiC wafer was pre-polished using a pre-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 the polishing fluid to polish the object under the following polishing conditions. [Polishing conditions] Polishing equipment: Fujikoshi Machinery Co., Ltd., model "RDP-500" Polishing pad: Nitta DuPont "IC-1000" (made of hard polyurethane) Processing pressure: 490 gf / cm ２ Plate rotation speed: 130 rpm Head rotation speed: 130 rpm Polishing fluid supply rate: 20 mL / min Polishing fluid usage method: Discard polishing time: 10 minutes Polishing object: 4-inch SiC wafer (conductive type: n-type, crystalline type 4H-SiC, off-angle of main surface (0001) relative to the C axis: 4°), 1 wafer / batch Polishing fluid temperature: 23°C

[0083] For the polishing pad, a pad with a polishing surface that had been brush-dressed for 5 minutes, followed by diamond dressing for 3 minutes, and then brush-dressed again for 5 minutes was used. The brush-dressing and diamond dressing were performed before the polishing described above.

[0084] <Polishing Removal Rate> Under the above polishing conditions, after polishing the SiC wafer using the polishing composition for each example, the polishing removal rate was calculated according to the following formulas (1) and (2). (1) Polishing removal amount [cm] = Difference in weight of SiC wafer before and after polishing [g] / Density of SiC [g / cm³] ３ ](=3.21g / cm ３) / Polishing area [cm²] ２ ] (=78.54cm ２ (2) Polishing removal rate [nm / h] = Polishing allowance [cm] × 10 ７ / Polishing time (= 10 / 60) The polishing removal rate obtained in each example was converted to a relative value with Comparative Example 1 set to 100 and is shown in Table 1.

[0085]

[0086] As shown in Table 1, the polishing compositions according to Examples 1 to 6, which contain permanganate, a rare earth salt, and aluminum nitrate, a salt (metal salt) of a metal cation and anion with a pKa of 2 to 6, achieved a higher polishing removal rate than Comparative Examples 1 to 3, which used the rare earth salt and the metal salt individually, respectively. Comparative Example 3, which used cerium ammonium nitrate as the rare earth salt, had a polishing removal rate that was more than 20% lower than Comparative Example 1, which used lanthanum nitrate as the rare earth salt. It is thought that even if cerium ammonium nitrate is used in combination with the metal salt, the results will be similar to or lower than those of Comparative Example 1.

[0087] <Preparation of Polishing Compositions> (Examples 7 and 8) A polishing composition was prepared by mixing silica abrasive grains, potassium permanganate, rare earth salts listed in Table 2, aluminum nitrate, and deionized water to a concentration of 0.1% by weight of silica abrasive grains, 4% by weight of potassium permanganate, 15 mM of rare earth salts (calculated as rare earth elements), and 15 mM of aluminum nitrate (calculated as Al). Colloidal silica with an average primary particle diameter of 35 nm and an average secondary particle diameter of 70 nm was used as the silica abrasive grains. The pH of the polishing composition according to Example 7 was 3.5, and the pH of the polishing composition according to Example 8 was also 3.5.

[0088] (Comparative Example 4) Calcium nitrate was used instead of rare earth salts, and the concentrations (contents) of each component were changed to those shown in Table 2. The polishing composition was prepared in the same manner as in Example 7. The pH of the polishing composition according to Comparative Example 4 was 3.7.

[0089] <Polishing of the object to be polished> A SiC wafer was pre-polished using a pre-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 the polishing fluid to polish the object under the following polishing conditions. [Polishing conditions] Polishing equipment: Fujikoshi Machinery Co., Ltd., model "RDP-500" Polishing pad: Nitta DuPont "IC-1000" (made of hard polyurethane) Processing pressure: 490 gf / cm ２ Plate rotation speed: 130 rpm Head rotation speed: 130 rpm Polishing fluid supply rate: 20 mL / min Polishing fluid usage method: Discard polishing time: 10 minutes Polishing object: 4-inch SiC wafer (conductive type: n-type, crystalline type 4H-SiC, off-angle of main surface (0001) relative to the C axis: 4°), 1 wafer / batch Polishing fluid temperature: 23°C

[0090] For the polishing pad, a pad with a polishing surface that had been brush-dressed for 5 minutes, followed by diamond dressing for 3 minutes, and then brush-dressed again for 5 minutes was used. The brush-dressing and diamond dressing were performed before the polishing described above.

[0091] <Polishing Removal Rate> Under the above polishing conditions, after polishing the SiC wafer using the polishing composition for each example, the polishing removal rate was calculated according to the following formulas (1) and (2). (1) Polishing removal amount [cm] = Difference in weight of SiC wafer before and after polishing [g] / Density of SiC [g / cm³] ３ ](=3.21g / cm ３ ) / Polishing area [cm²] ２ ] (=78.54cm ２ (2) Polishing removal rate [nm / h] = Polishing allowance [cm] × 10 ７ / Polishing time (= 10 / 60) The polishing removal rate obtained in each example was converted to a relative value with Comparative Example 4 set to 100 and is shown in Table 2.

[0092]

[0093] As shown in Table 2, the polishing compositions according to Examples 7-8, which contain permanganate, a rare earth salt, and aluminum nitrate, a salt of a metal cation and anion with a pKa of 2 to 6, achieved a higher polishing removal rate than Comparative Example 4, which did not use a rare earth salt and instead used a combination of the above metal salt and calcium nitrate, a salt of a metal cation and anion with a pKa of less than 2 or greater than 6. Furthermore, the polishing composition according to Example 8, which used a rare earth salt containing a Group 17 element, showed an even greater improvement in the polishing removal rate.

[0094] 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 polishing composition comprising permanganate, rare earth salts (excluding those containing cerium), and a salt of a metal cation and anion having a pKa of 2 to 6.

2. The polishing composition according to claim 1, wherein the rare earth salt comprises a Group 17 element.

3. The polishing composition according to claim 1 or 2, wherein the rare earth salt contains a fluorine atom.

4. The polishing composition according to claim 1 or 2, wherein the metal cation having a pKa of 2 or more and 6 or less is selected from aluminum ions, indium ions, and gallium ions.

5. The polishing composition according to claim 1 or 2, further comprising abrasive grains.

6. The polishing composition according to claim 5, wherein the abrasive grains contain silica.

7. The polishing composition according to claim 1 or 2, used for polishing materials with a Vickers hardness of 1500 Hv or higher.

8. The polishing composition according to claim 1 or 2, used for polishing silicon carbide.

9. A polishing method comprising the step of polishing an object to be polished using the polishing composition described in claim 1 or 2.

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