Polishing composition and polishing method

Abstract

Provided is a polishing composition capable of exhibiting a high polishing removal rate and having improved storage stability. The polishing composition contains a permanganate (S1), a salt (S2) containing a group 4 element of the periodic table, and a salt (S3) of a metal cation and an anion, the salt (S3) having a pKa of 2 to 6, inclusive.

Description

Abrasive composition and polishing method

[0001] The present invention relates to an abrasive composition and a polishing method. This application claims priority based on Japanese Patent Application No. 2024-167890 filed on September 26, 2024, and the entire contents of that application are incorporated herein by reference.

[0002] Polishing using an abrasive composition is performed on the surfaces of materials such as metals, semi-metals, non-metals, and their oxides. 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) 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 an abrasive composition has been considered.

[0003] Patent Document 1 describes that salts such as zirconyl nitrate and aluminum nitrate can be used in the preparation of an aqueous abrasive composition having a specific composition used for polishing copper on a semiconductor wafer (paragraph 0011).

[0004] U.S. Patent Application Publication No. 2005 / 0104048

[0005] Generally, from the viewpoints of production efficiency and cost effectiveness, it is desired that the polishing removal rate is sufficiently large in practical use. For example, in polishing a surface composed of a high-hardness material such as silicon carbide, an improvement in the polishing removal rate is strongly desired. To address this problem, abrasive compositions containing strong oxidizing agents such as permanganate have conventionally been used. Also, the abrasive composition preferably has little change in state during storage before use and good storage stability.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a polishing composition that can exhibit a high polishing removal rate and can improve storage stability. Another related object is to provide a method for polishing a polishing target using such a polishing composition.

[0007] According to the present specification, there is provided a polishing composition containing a permanganate (S1), a salt containing a Group 4 element of the periodic table (S2), and a salt of a metal cation and an anion having a pKa of 2 or more and 6 or less (S3). According to the polishing composition having the above composition, a high polishing removal rate can be exhibited, and the storage stability can be improved.

[0008] In some embodiments, the salt (S2) is a salt containing an element selected from titanium, zirconium, and hafnium. In the embodiment using the salt (S2) containing the Group 4 element of the periodic table as described above, the technology disclosed herein is preferably implemented.

[0009] In some embodiments, the salt (S3) is a salt of a metal cation and an anion selected from aluminum ions, indium ions, and gallium ions. In the embodiment using the above salt (S3), the technology disclosed herein is preferably implemented.

[0010] In some embodiments, the polishing composition further contains abrasive grains. According to the polishing composition containing abrasive grains, a high polishing removal rate can be realized based on the polishing action of the abrasive grains. Silica is preferably used as the abrasive grains. According to silica abrasive grains, a high polishing removal rate and good surface accuracy can be preferably achieved simultaneously.

[0011] The polishing composition disclosed herein is used, for example, for polishing a material having a Vickers hardness of 1500 Hv or more. In the polishing of such a high-hardness material, the effects of the technology disclosed herein can be preferably exhibited. In some embodiments, the material having a Vickers hardness of 1500 Hv or more is a non-oxide (that is, a compound that is not an oxide). In the polishing of a polishing target material that is a non-oxide, a high polishing removal rate by the polishing composition 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 makes it possible to achieve a high 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, for example, 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 (S1)) The polishing composition disclosed herein contains permanganate (S1). Permanganate (S1) can improve the polishing removal rate by typically functioning as an oxidizing agent in polishing materials to be polished (e.g., high-hardness non-oxide materials such as silicon carbide). As permanganate (S1), 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 (S1) 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. Permanganate (S1) can be used alone or in combination of two or more types. Furthermore, permanganate (S1) may exist in an ionic state in the polishing composition.

[0016] The content of permanganate (S1) 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 content of permanganate (S1) 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 content of permanganate (S1) in the polishing composition is suitable to be approximately 30% by weight or less, may be 20% by weight or less, and may be 15% by weight or less. In some other embodiments, the content of permanganate (S1) may be less than 12% by weight, may be 10% by weight or less (for example, less than 10% by weight), may be 8% by weight or less, may be 6% by weight or less, and may be 5% by weight or less. An embodiment in which the content is less than 12% by weight is preferred, for example, when potassium permanganate is used. By limiting the amount of permanganate (S1) used, it is possible to sufficiently dissolve permanganate (S1) in the polishing composition and achieve a high polishing removal rate.

[0017] (Salt (S2) Containing Group 4 Element of the Periodic Table) The polishing composition disclosed herein contains a salt (S2) containing a Group 4 element of the periodic table. Hereinafter, the salt (S2) containing a Group 4 element of the periodic table may be abbreviated as salt (S2). The salt (S2) is typically a salt of a cation containing a metal (transition metal) belonging to Group 4 of the periodic table and an anion. By using the permanganate (S1) and the salt (S2), it is possible to suppress a decrease in the polishing removal rate and the like, and to achieve a high polishing removal rate. It is considered that the use of the salt (S2) suppresses the deterioration of the performance of the polishing composition (for example, a decrease in the polishing removal rate and the like) due to the pH fluctuation of the polishing composition in the polishing of the polishing object. However, the above considerations do not limit the scope of the present invention. The salt (S2) can be used alone or in combination of two or more. The salt (S2) can typically exist in a dissolved state in a solvent such as water in the polishing composition.

[0018] Examples of the Group 4 element include titanium, zirconium, and hafnium. Among them, the use of a salt containing zirconium as the Group 4 element is preferable. As the cation constituting the salt (S2), Ti ４＋ , Hf ４＋ , Zr ４＋ and other single-atom transition metal cations; TiO ＋ , TiO ２＋ , ZrO ２＋ , ZrO ＋ , HfO ＋ and other oxy-transition metal cations; ZrOH ＋ , HfOH ＋ and other transition metal hydroxide cations; and the like, but are not limited thereto. The salt (S2), which is a salt of such a cation and an anion, forms a hydrated metal cation in water and is likely to suppress the deterioration of the performance of the polishing composition over time.

[0019] The type of salt in salt (S2) is not particularly limited and may be an inorganic salt or an organic salt. Examples of inorganic salts include hydrohalogen acids such as hydrochloric acid, hydrobromic acid, and hydrofluoric acid, and inorganic salts such as nitric acid, sulfuric acid, carbonic acid, silicic acid, boric acid, and phosphoric acid; sulfides; oxides; oxyhalides such as oxychlorides, oxybromids, and oxyfluorides; oxyinorganic salts such as oxynitrates, oxysulfates, oxycarbonates, oxysilicates, oxyborates, and oxyphosphates; and oxysulfides. Examples of organic salts include 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; organic phosphoric acids such as ethyl phosphoric acid; and organic oxyacids such as oxyacetate. 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 techniques disclosed herein can preferably be carried out, for example, in the form of an oxy transition metal salt, which is a salt of an oxy transition metal cation and an anion, as the salt (S2). Some preferred embodiments include TiO ＋ , TiO ２＋ , ZrO ２＋ , ZrO ＋ , HfO ＋ One of the oxy transition metal cations and a nitrate ion (NO ３ － ), sulfate ions (SO ４ ２－ ) or chloride ions (Cl － This can preferably be carried out in a manner that uses a salt of ).

[0020] The salt (S2) dissolves in a solvent such as water to form a multinuclear transition metal complex consisting of a Group 4 element, which is a transition metal, and an oxygen atom and / or hydrogen. For example, when a salt containing a Group 4 element, such as zirconyl nitrate, zirconium sulfate, or zirconium chloride, is dissolved in water, a multinuclear transition metal complex consisting of zirconium and an oxygen atom and / or hydrogen is formed. The techniques disclosed herein can also be preferably carried out in a form in which the salt (S2) is dissolved in a solvent, and the resulting multinuclear transition metal complex consisting of a Group 4 element and an oxygen atom and / or hydrogen is included. A preferred multinuclear transition metal complex is one in which zirconium is composed of an oxygen atom and / or hydrogen.

[0021] The salt (S2) is preferably a compound that is not easily oxidized by the permanganate (S1). Examples of preferred salts (S2) include zirconyl nitrate.

[0022] The concentration (content) of the salt (S2) 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 the salt (S2) 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 the salt (S2), it is advantageous to set it to 1 mM or more, preferably 5 mM or more, and 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 salt (S2) concentration 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 salt (S2) 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 the salt (S2) is used in the amount limited as described above, the effects of the techniques disclosed herein (specifically, achieving both high polishing removal rate and storage stability) can be effectively demonstrated.

[0023] Concentration M of salt (S2) in the abrasive composition Ｓ２ [mM] and the content W of permanganate (S1) Ｓ１ Ratio to [weight %] (M Ｓ２ / W Ｓ１ ) may be greater than 0, 0.01 or greater, 0.1 or greater, or 0.5 or greater. From the viewpoint of better exhibiting the effect of including a salt (S2) in an abrasive composition containing permanganate (S1), in some embodiments, the ratio (M Ｓ２ / W Ｓ１ ) 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. Ratio (M Ｓ２ / W Ｓ１The upper limit of ) 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 (M Ｓ２ / W Ｓ１ ) 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.

[0024] (Salt (S3) of a metal cation and anion with a pKa of 2 to 6) The polishing composition disclosed herein contains a salt (S3) of a metal cation and anion with a pKa of 2 to 6. Hereinafter, the salt (S3) of a metal cation and anion with a pKa of 2 to 6 may be abbreviated as salt (S3). The polishing composition containing salt (S3) in addition to permanganate (S1) and salt (S2) can achieve a high polishing removal rate while improving storage stability (shelf life). This is thought to be because the pKa of the metal cation is 6 or less, so that it acts well on the object to be polished as an acid due to acid dissociation in the polishing composition, and because the pKa of the metal cation is 2 or more, so that the acid dissociation is not too strong and proton dissociation equilibrium occurs. However, the above considerations do not limit the scope of the present invention. Salt (S3) can be used alone or in combination of two or more types. The salt (S3) may typically be present in the polishing composition dissolved in a solvent such as water.

[0025] A 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. A specific example of a metal cation with a pKa of 2 or more and 6 or less is 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 ions (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 the 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 for the salt (S3), for example, aluminum salts, indium salts, and gallium salts are preferably used, where the metal cation with a pKa of 2 to 6 is an aluminum ion, an indium ion, or a gallium ion.

[0026] The type of salt in salt (S3) 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 salts (S3) include aluminum hydrochloride, aluminum nitrate, and aluminum sulfate.

[0027] The anionic species of salt (S2) and salt (S3) may be the same or different. In some preferred embodiments, the anionic species of salt (S2) and salt (S3) are the same. The anionic species common to salt (S2) and salt (S3) may be, for example, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, etc.

[0028] The concentration (content) of the salt (S3) 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 the salt (S3) may be, for example, 0.1 mM or more, and from the viewpoint of appropriately exhibiting the effect of using the salt (S3), it is advantageous to set it to 1 mM or more, and from the viewpoint of storage stability, 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 the salt (S3) in the polishing composition may be 20 mM or more, or 30 mM or more. Furthermore, the upper limit of the concentration of the salt (S3) 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 the salt (S3) 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 the salt (S3) is used in the amount limited as described above, the effects of the techniques disclosed herein (specifically, achieving both high polishing removal rate and storage stability) can be effectively demonstrated.

[0029] Concentration M of salt (S3) in the abrasive composition Ｓ３ [mM] and the concentration W of permanganate (S1) Ｓ１ Ratio to [weight %] (M Ｓ３ / W Ｓ１ ) may be greater than 0, 0.01 or greater, 0.1 or greater, or 0.5 or greater. From the viewpoint of better exhibiting the effect of including a salt (S3) in the polishing composition containing permanganate (S1), in some embodiments, the ratio (M Ｓ３ / W Ｓ１ ) 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. Ratio (M Ｓ３ / W Ｓ１The upper limit of ) 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 (M Ｓ３ / W Ｓ１ ) 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.

[0030] Concentration M of salt (S2) in the abrasive composition Ｓ２ [mM] and the concentration M of the salt (S3) Ｓ３ Here, the ratio with mM (M Ｓ３ / M Ｓ２ The ratio (M) can be appropriately set according to the purpose and manner of use of the polishing composition so as to achieve the desired effect. Ｓ３ / M Ｓ２ ) may be 0.01 or greater, or 0.1 or greater. From the viewpoint of better exhibiting the effect of including salt (S3), in some embodiments, the ratio (M Ｓ３ / M Ｓ２ ) may be, for example, 0.3 or more, 0.5 or more, 0.7 or more, 0.9 or more, or 1 or more. On the other hand, from the viewpoint of better exhibiting the effects of including salt (S2), in some embodiments, the ratio (M Ｓ３ / M Ｓ２ ) 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.

[0031] Total content of salt (S2) and salt (S3) in the abrasive composition (M Ｓ２ +M Ｓ３The salts (S2) and (S3) are not particularly limited. The total content of salt (S2) and salt (S3) may be, for example, 0.1 mM or more, and it is advantageous to have a total content of 1 mM or more from the viewpoint of appropriately exhibiting the effects of using salt (S2) and salt (S3). From the viewpoint of storage stability, it is preferable to have a total content of 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 salt (S2) and salt (S3) in the polishing composition may be 40 mM or more, or 50 mM or more. Furthermore, the upper limit of the total content of salt (S2) and salt (S3) 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 salt (S2) and salt (S3) is appropriately 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. The effects of the techniques disclosed herein (specifically, achieving both high polishing removal rate and storage stability) can be more effectively realized by using both salt (S2) and salt (S3) in limited amounts. Furthermore, in a composition containing salt (S2) and salt (S3) in the limited amounts described above, the above ratio (M Ｓ３ / M Ｓ２ By appropriately setting ), the effects of the technologies disclosed herein can be particularly effectively realized.

[0032] (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 (S1), salt (S2), and salt (S3).

[0033] 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.

[0034] 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.

[0035] The average primary particle diameter of the abrasive grains is not particularly limited. For example, the average primary particle diameter of the abrasive grains can be 5 nm or more, 10 nm or more is appropriate, preferably 20 nm or more, and may also be 30 nm or more. 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, or 350 nm or more. From the viewpoint of improving the polishing removal speed, a larger average primary particle diameter of the abrasive grains is preferable. Also, from the viewpoint of surface quality after polishing, 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 obtaining better surface quality, 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.

[0036] In this specification, the average primary particle diameter is calculated by the following formula, derived from the specific surface area (BET value) measured by the BET method: Average primary particle diameter (nm) = 6000 / (True density (g / cm³) ３ ) × BET value (m ２ This refers to the particle diameter (BET particle diameter) calculated by the formula ( / g). The specific surface area can be measured, for example, using a surface area measuring device manufactured by Micromeritex, Inc., product name "Flow Sorb II 2300".

[0037] 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 surface quality after polishing, 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 obtaining even better surface quality, 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.

[0038] For particles smaller than 500 nm, the average secondary particle diameter of abrasive grains can be measured as the volume-average particle diameter (volume-based arithmetic mean diameter; Mv) using dynamic light scattering, for example, with a Nikkiso Co., Ltd. model "UPA-UT151". For particles larger than 500 nm, the volume-average particle diameter can be measured using methods such as the pore electrical resistance method with a Beckman Coulter model "Multisizer 3".

[0039] 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 a combination of two or more types.

[0040] When using alumina particles as abrasive grains, it is generally advantageous for the proportion of alumina particles to the total amount of abrasive grains used to be higher. For example, the proportion of alumina particles to the total amount of 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] In embodiments in which the abrasive composition contains abrasive grains, the relationship between the abrasive grain content and the permanganate (S1) content is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use. The content of permanganate (S1) relative to the abrasive grain content Wa [weight %] is W. Ｓ１ [Weight %] ratio (W Ｓ１ The ratio (W) can be, for example, approximately 0.01 or more, it is appropriate to set it to 0.1 or more, and it may also be 1 or more. Ｓ１ As the ratio (W) increases, the contribution of chemical polishing tends to increase relative to the contribution of mechanical polishing. In some embodiments, the ratio (W) Ｓ１ The ratio (W) is preferably 5 or more, may be 10 or more, may be 20 or more, or may be 30 or more. Ｓ１ The upper limit of the ratio (W) is not particularly limited, 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 (W) Ｓ１ / Wa) may be 30 or less, 20 or less, or 10 or less.

[0057] In embodiments in which the abrasive composition contains abrasive grains, the relationship between the abrasive grain content and the salt (S2) concentration is not particularly limited and can be appropriately set to achieve the desired effect depending on the purpose and manner of use. The concentration of salt (S2) M relative to the abrasive grain content Wa [weight %] Ｓ２ [mM] ratio (M Ｓ２ The ratio (M) is appropriately set to 0.1 or higher, preferably 1 or higher, more preferably 5 or higher, and may also be 10 or higher. Ｓ２ As the ratio ( / Wa) increases, the contribution of chemical polishing tends to increase relative to the contribution of mechanical polishing. In some embodiments, the ratio (M Ｓ２ / 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. Ratio (M Ｓ２ The upper limit of ( / Wa) is not particularly limited, 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 (M Ｓ２ / Wa) may be 500 or less, 300 or less, 200 or less, or 100 or less.

[0058] In embodiments in which the abrasive composition contains abrasive grains, the relationship between the abrasive grain content and the salt (S3) concentration is not particularly limited and can be appropriately set according to the purpose and manner of use to achieve the desired effect. The concentration of salt (S3) M relative to the abrasive grain content Wa [weight %] Ｓ３ [mM] ratio (M Ｓ３ / 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, and may be 250 or more. Ratio (M Ｓ３ The upper limit of ( / Wa) is not particularly limited, but from the viewpoint of storage stability of the polishing composition, it can be, for example, approximately 10,000 or less, 5,000 or less, 2,500 or less, or 1,000 or less. In some embodiments, the ratio (MＳ３ / Wa) may be 700 or less, 500 or less, 300 or less, 200 or less, or 100 or less.

[0059] (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.

[0060] (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.

[0061] (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 substantially does not contain basic compounds.

[0062] (Optional Oxidizing Agents) The polishing compositions disclosed herein may contain oxidizing agents other than permanganate (S1) as long as they do not impair the effects of the present invention. Examples of compounds that may be selected as oxidizing agents other than permanganate (S1) 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, cerium ammonium nitrate, and the like. Oxidizing agents other than permanganate (S1) may be used individually or in combination of two or more.

[0063] (Optional Salts) The polishing compositions disclosed herein may contain various salts other than permanganates (S1), salts (S2), and salts (S3), as long as they do not impair the effects of the present invention. Any salt other than permanganates (S1), salts (S2), and salts (S3) may include salts containing metals other than Group 4 elements of the periodic table (e.g., transition metals), or salts of metal cations and anions with a pKa of less than 2 or greater than 6. 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 arbitrary salt anionic species include those exemplified as the anionic species of salt (S2) and salt (S3). The anionic species of arbitrary salt may be the same as or different from at least one of the anionic species of salt (S2) and salt (S3).

[0064] The total content of oxidizing agents other than permanganate (S1) and any salts in the polishing composition is, for example, less than 30% by weight, preferably less than 10% by weight, and may be less than 3% by weight or even less than 1% by weight, when the total content of permanganate (S1), salt (S2), and salt (S3) 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 (S1) and any salts.

[0065] (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.

[0066] (pH) The pH of the polishing composition is preferably around 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 effects based on the inclusion of salt (S2) and salt (S3) (achieving both polishing removal rate and storage stability), in some embodiments, the pH of the polishing composition is preferably less than 6.0, more preferably 5.0 or less or less than 5.0, even more preferably 4.0 or less or less than 4.0, and may also be 3.0 or less or less than 3.0, or 2.5 or less. The above pH may be, for example, 1.0 or higher, 1.5 or higher, or 2.0 or higher.

[0067] 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.

[0068] <Concentrated Solution> The polishing composition disclosed herein may be in a concentrated form (i.e., in the form of a concentrated polishing solution) before being supplied to the object to be polished. Such a concentrated form of the polishing composition is advantageous in terms of convenience and cost reduction during manufacturing, distribution, and storage. The concentration ratio is not particularly limited and can be, for example, 1.1 to 50 times by volume, and usually 1.5 to 40 times (for example, 2 to 30 times) is appropriate. Such a concentrated solution can be used by diluting it at a desired timing to prepare a polishing solution (working slurry) and supplying the polishing solution to the substrate. The above dilution can be performed, for example, by adding water to the concentrated solution and mixing it.

[0069] <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.

[0070] 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.

[0071] 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.

[0072] <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 solution (slurry) is prepared using any of the polishing compositions disclosed herein. Preparing the polishing solution may include adjusting the concentration (e.g., dilution) or pH of the polishing composition to prepare the polishing solution. Alternatively, the polishing composition may be used as is as the polishing solution. In the case of a multi-component polishing composition, preparing the polishing solution may include mixing the agents, diluting one or more agents before mixing, or diluting the mixture after mixing. The polishing solution 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 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). Polishing of the object to be polished is completed through this polishing process.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] <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.

[0081] The following are disclosed in this specification: [1] A polishing composition comprising a permanganate (S1), a salt containing a group 4 element of the periodic table (S2), and a salt of a metal cation and anion having a pKa of 2 to 6 (S3). [2] The polishing composition according to [1], wherein the salt (S2) comprises an element selected from titanium, zirconium, and hafnium. [3] The polishing composition according to [1] or [2], wherein the metal cation of the salt (S3) is selected from aluminum ions, indium ions, and gallium ions. [4] The polishing composition according to any one of [1] to [3], further comprising abrasive grains. [5] The polishing composition according to [4], wherein the abrasive grains comprise silica. [6] The polishing composition according to any one of [1] to [5], used for polishing materials with a Vickers hardness of 1500 Hv or higher. [7] The polishing composition according to any one of [1] to [6], used for polishing silicon carbide. [8] A polishing method comprising the step of polishing an object to be polished using any of the polishing compositions described in [1] to [7] above.

[0082] 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.

[0083] <Preparation of Polishing Composition> (Example 1) A polishing composition was prepared by mixing silica abrasive grains, potassium permanganate, zirconyl nitrate, aluminum nitrate, and deionized water to a concentration of 0.1% by weight of silica abrasive grains, 4% by weight of potassium permanganate, 30 mM of zirconyl nitrate (Zr equivalent), and 30 mM of aluminum nitrate (Al equivalent). The pH of the polishing composition was 1.6. 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.

[0084] (Example 2, Comparative Examples 1-2) The concentrations of zirconyl nitrate 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. The pH of the polishing composition for Example 2 was 2.2. The pH of the polishing composition for Comparative Example 1 was 1.9, and the pH of the polishing composition for Comparative Example 2 was 3.9. Aluminum nitrate was not added in Comparative Example 1, and zirconyl nitrate was not added in Comparative Example 2.

[0085] <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

[0086] 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.

[0087] <Measurement and Evaluation> (Polishing Removal Rate) Under the above polishing conditions, SiC wafers were polished using the polishing compositions of each example, and the polishing removal rate was calculated according to the following formulas (1) and (2). (1) Polishing 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 ] (=78.54cm２ (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 2 set to 100 and is shown in Table 1.

[0088] (Storage Stability) The storage stability of the polishing compositions prepared above was evaluated by conducting an accelerated test under storage conditions of 40°C. Specifically, the polishing composition for each example was filled into a transparent polyethylene resin container and sealed. The container was left undisturbed under conditions of 40°C, and the pH of the polishing composition was measured at approximately 3-day intervals. The number of days until the pH of the polishing composition in the container rose to 0.8 or higher was recorded as the storage stability. The results are shown in the corresponding column of Table 1.

[0089]

[0090] As shown in Table 1, the polishing composition according to Comparative Example 1, which contains potassium permanganate and zirconyl nitrate, achieved a significantly higher polishing removal rate compared to Comparative Example 2, which uses aluminum nitrate instead of zirconyl nitrate. However, Comparative Example 1's storage stability evaluation result (6 days) was inferior to that of Comparative Example 2 (storage stability of over 15 days). Although not shown in the experimental results, it was confirmed that increasing the amount of aluminum nitrate to 30 mM in Comparative Example 2 did not significantly improve the polishing removal rate. In Examples 1 and 2, which further contain aluminum nitrate in addition to potassium permanganate and zirconyl nitrate, storage stability was improved to 10 days or more while maintaining a high polishing removal rate based on the content of potassium permanganate and zirconyl nitrate to some extent. In particular, in Example 2, storage stability was improved by more than 60% compared to Comparative Example 1 while maintaining a high polishing removal rate equivalent to that of Comparative Example 1. It is thought that by using appropriate amounts of both zirconyl nitrate and aluminum nitrate in limited quantities, the effect of improving storage stability while maintaining a high polishing removal rate was effectively achieved. From the above results, it can be seen that a polishing composition containing permanganate, a salt containing a Group 4 element of the periodic table, and a salt of a metal cation and anion with a pKa of 2 to 6 can improve storage stability while maintaining a high polishing removal rate based on the content of permanganate and a salt containing a Group 4 element.

[0091] 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 a permanganate (S1), a salt containing a group 4 element of the periodic table (S2), and a salt of a metal cation and anion having a pKa of 2 to 6 (S3).

2. The polishing composition according to claim 1, wherein the salt (S2) comprises an element selected from titanium, zirconium, and hafnium.

3. The polishing composition according to claim 1 or 2, wherein the metal cation of the salt (S3) is selected from aluminum ions, indium ions, and gallium ions.

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

5. The polishing composition according to claim 4, wherein the abrasive grains contain silica.

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

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

8. 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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