Method for polishing silicon carbide substrate and polishing composition

Abstract

To provide a polishing method capable of reducing line defects on a surface of a silicon carbide substrate in polishing the substrate.SOLUTION: A method for polishing a silicon carbide substrate is provided. The polishing method includes a step of supplying a polishing composition to a substrate to be polished and polishing the substrate to be polished. The polishing composition includes abrasive grains. The abrasive grains have a zeta potential X [mV] in the polishing composition. A surface of the substrate to be polished has a zeta potential Y [mV]. Here, the zeta potential Y is measured for the surface of the substrate to be polished in the polishing composition using a solid zeta potential measuring device. The zeta potential X [mV] and the zeta potential Y [mV] satisfy X Y>250.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for polishing a silicon carbide substrate and a polishing composition. [Background technology]

[0002] Conventionally, polishing is performed using a polishing composition on the surface of materials such as metals, semimetals, nonmetals, and oxides thereof. For example, a polishing object having a surface made of a compound semiconductor material such as silicon carbide can be processed by polishing (lapping) by supplying diamond abrasive grains between the polishing platen that is in contact with the surface of the polishing object and the polishing object. However, lapping using diamond abrasive grains is prone to defects and distortions due to the occurrence and remaining of scratches and dents. Therefore, polishing (polishing) using a polishing pad that supplies a polishing liquid between the polishing pad and the polishing object after or instead of lapping using diamond abrasive grains is being considered.

[0003] Patent Document 1 describes that when polishing a sapphire substrate, the zeta potential X1 of the abrasive grains (colloidal silica) in the polishing composition and the zeta potential Y1 of the object to be polished have the relationship X1×Y1≦0. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-183530 A Summary of the Invention [Problem to be solved by the invention]

[0005] In general, from the viewpoint of manufacturing efficiency and cost, it is desired that the polishing removal rate when polishing an object to be polished by supplying a polishing liquid is sufficiently high for practical use. For example, in polishing an object to be polished made of a high-hardness material such as silicon carbide, it is desired to further improve the polishing removal rate from the viewpoint of improving the yield of the polished object. However, in a polishing composition designed for the purpose of improving the polishing removal rate, for example, line defects may occur due to the abrasive grains in the polishing composition. The required level of surface quality after polishing of silicon carbide substrates is increasing, and it is useful if a high-quality surface without line defects as described above can be realized together with a practical polishing removal rate.

[0006] In light of this background, the present inventors have clarified the zeta potential of the surface (surface to be polished) of a silicon carbide substrate to be polished by using a solid zeta potential measuring device in the research and development of silicon carbide substrate polishing. As a result of intensive research based on this knowledge, the present invention has been completed. That is, the present invention has an object to provide a polishing method capable of reducing line defects on the substrate surface in polishing a silicon carbide substrate. Another related object is to provide a polishing composition suitable for the above polishing method. [Means for solving the problem]

[0007] According to the present specification, a method for polishing a silicon carbide substrate is provided. This polishing method includes a step of supplying a polishing composition to a substrate to be polished to polish the substrate to be polished. The polishing composition includes abrasive grains. The abrasive grains have a zeta potential X [mV] in the polishing composition. The surface of the substrate to be polished has a zeta potential Y [mV]. Here, the zeta potential Y is a zeta potential measured for the surface of the substrate to be polished in the polishing composition using a solid zeta potential measuring device. The zeta potential X [mV] and the zeta potential Y [mV] satisfy X·Y>250. By polishing with a polishing composition designed so that the zeta potential X of the abrasive grains in the polishing composition and the zeta potential Y of the surface of the substrate to be polished in the polishing composition satisfy the relational formula: X·Y>250;, line defects on the surface after polishing are reduced, and preferably a polished surface free of line defects is realized.

[0008] In some preferred embodiments, the product (X·Y) of the zeta potential X [mV] and the zeta potential Y [mV] is within a range of 370 to 2000. By selecting the zeta potential X of the abrasive grains and the zeta potential Y of the substrate to be polished such that the X·Y is within a range of 370 to 2000, it is possible to preferably reduce line defects on the surface after polishing while realizing a practical polishing removal rate.

[0009] In some preferred embodiments, the zeta potential Y is lower than -25 mV and is equal to or higher than -50 mV. In embodiments in which the zeta potential Y of the surface of the substrate to be polished in the polishing composition measured using a solid zeta potential measuring device is within the above range, the techniques disclosed herein are preferably carried out.

[0010] In some preferred embodiments, the zeta potential X is lower than −10 mV and is −70 mV or higher. In an embodiment in which the zeta potential X of the abrasive grains in the polishing composition is within the above range, the techniques disclosed herein are preferably carried out.

[0011] In some preferred embodiments, the abrasive grains include alumina grains. In the embodiment in which alumina grains are used as abrasive grains, the technology disclosed herein is preferably implemented by designing the above-mentioned zeta potential relational expression to be satisfied. In addition, the polishing composition containing alumina grains as abrasive grains is likely to obtain a practical polishing removal rate.

[0012] In some embodiments, the polishing composition further comprises an oxidizing agent. In an embodiment in which the polishing composition comprises an oxidizing agent, the technique disclosed herein is preferably implemented by designing the composition to satisfy the above-mentioned zeta potential relational expression. In addition, a polishing composition containing an oxidizing agent is likely to provide a practical polishing removal rate. In particular, in an embodiment in which the oxidizing agent comprises a complex metal oxide (e.g., permanganic acid), the technique disclosed herein is more effectively implemented.

[0013] In some embodiments, the pH of the polishing composition is 8.0 or more and 12 or less. In embodiments in which the pH of the polishing composition is within the above range, the techniques disclosed herein are preferably carried out.

[0014] The present specification also provides a polishing composition for use in any of the polishing methods disclosed herein. The polishing composition contains abrasive grains. The abrasive grains have a zeta potential X [mV] in the polishing composition. The zeta potential X [mV] satisfies the relationship with the zeta potential Y [mV] of the surface of the substrate to be polished in the polishing composition measured using a solid zeta potential measuring device: X·Y>250. By using a polishing composition having such composition and characteristics for polishing a silicon carbide substrate, line defects on the surface after polishing are reduced, and preferably a polished surface free of line defects is realized. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention will be described below. Note that matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field.

[0016] <Zeta potential characteristics> The polishing composition disclosed herein is characterized in that, in polishing a substrate to be polished, the zeta potential X [mV] of the abrasive grains in the polishing composition and the zeta potential Y [mV] of the surface of the substrate to be polished in the polishing composition satisfy the relationship: X·Y>250. Here, the zeta potential Y is the zeta potential measured for the surface of the substrate to be polished in the polishing composition using a solid zeta potential measuring device. With a polishing composition designed so that the zeta potential X of the abrasive grains in the polishing composition and the zeta potential Y of the surface of the substrate to be polished in the polishing composition satisfy the above relationship, line defects on the surface of the silicon carbide substrate after polishing are reduced, and preferably a polished surface free of line defects is realized. The reason for this is that, when the polishing composition is supplied to the silicon carbide substrate, the abrasive grains in the polishing composition and the substrate to be polished have the same sign of zeta potential, and the product of the zeta potentials (X·Y) of the two is greater than 250, so that the abrasive grains and the substrate to be polished repel each other sufficiently to prevent line defects caused by the abrasive grains. The technology disclosed herein is not limited to the above interpretation. In addition, the zeta potential of the substrate to be polished has conventionally been evaluated using a powder made of the same material as the substrate, as described in Patent Document 1, for example, but this method does not allow the influence of the crystal orientation of the substrate to be polished to be confirmed, and the correlation with the actual polishing time is unclear. In the technology disclosed herein, the zeta potential of the surface (the surface to be polished, specifically the Si surface) of the silicon carbide substrate to be actually polished can be quantitatively evaluated by adopting a solid zeta potential measuring device. By quantitatively evaluating the zeta potential of the substrate surface in the polishing composition using this method, it has become possible to study and create a composition for a polishing composition that can achieve a practical polishing removal rate for the silicon carbide substrate to be polished and achieve a higher quality surface without line defects based on the zeta potential of the substrate surface and the zeta potential of the abrasive grains. By measuring the zeta potential of the silicon carbide substrate in the polishing composition, it is possible to accurately measure the zeta potential of the Si surface that is the surface to be polished of the silicon carbide substrate, and in the embodiment in which the polishing composition contains an oxidizing agent, it is possible to accurately measure the zeta potential of the Si oxidized surface, thereby obtaining the desired effect.

[0017] In some embodiments, the product (X·Y) of the zeta potential X [mV] and the zeta potential Y [mV] may be 300 or more, and from the viewpoint of better preventing the occurrence of line defects, it is preferably 370 or more, more preferably 400 or more, even more preferably 500 or more, even more preferably 700 or more, particularly preferably 800 or more, may be 1000 or more, may be 1200 or more, may be 1400 or more, or may be 1500 or more. In addition, the upper limit of the above X·Y is not particularly limited, and from the viewpoint of obtaining a practical polishing removal rate, in some embodiments, the above (X·Y) may be, for example, 5000 or less, 4000 or less, or 3000 or less. In some preferred embodiments, the above (X·Y) is 2000 or less, 1800 or less, 1600 or less, 1400 or less, 1200 or less, 1000 or less, or 900 or less.

[0018] The product (X·Y) of the zeta potential X [mV] and the zeta potential Y [mV] can be adjusted by the selection of abrasive grains used in the polishing composition, the selection and amount of additives such as an oxidizing agent used, adjustment of the pH, the silicon carbide substrate used, etc.

[0019] The zeta potential X of the abrasive grains in the polishing composition is appropriately set within a range that satisfies the above-mentioned relational expression: X·Y>250;, and is not particularly limited otherwise. In some embodiments, the absolute value |X| of the zeta potential X of the abrasive grains in the polishing composition is preferably greater than 10 mV, more preferably 15 mV or more, even more preferably 20 mV or more, particularly preferably 25 mV or more, and may be 30 mV or more, or may be 35 mV or more. The larger the |X|, the better the prevention of the occurrence of line defects. In some embodiments, the |X| is usually about 100 mV or less, and is suitably 80 mV or less. The smaller the |X|, the more the polishing removal rate tends to improve. From this viewpoint, in some preferred embodiments, the |X| is 70 mV or less, may be 60 mV or less, may be 50 mV or less, may be 40 mV or less, may be 30 mV or less, or may be 25 mV or less.

[0020] When the zeta potential Y of the surface of the substrate to be polished is a negative value, the abrasive grains in the polishing composition have a negative zeta potential X. In this embodiment, the zeta potential X of the abrasive grains in the polishing composition is preferably less than -10 mV, more preferably -15 mV or less, even more preferably -20 mV or less, particularly preferably -25 mV or less, and may be -30 mV or less, or may be -35 mV or less. When the zeta potential Y of the surface of the substrate to be polished is a negative value, the smaller the zeta potential X, the better the prevention of the occurrence of line defects. In some embodiments, the zeta potential X is approximately -100 mV or more, and suitably -80 mV or more. The smaller the absolute value of the zeta potential X, the more the polishing removal rate tends to improve. From this viewpoint, in some preferred embodiments, the zeta potential X is −70 mV or more, optionally −60 mV or more, optionally −50 mV or more, optionally −40 mV or more, optionally −30 mV or more, or optionally −25 mV or more.

[0021] The zeta potential X of the abrasive grains in the polishing composition is obtained by measuring the polishing composition containing the abrasive grains using a zeta potential meter. Specifically, it is measured by the method described in the Examples below. The zeta potential X can be adjusted by selecting the type of abrasive grains, modifying the surface of the abrasive grains, selecting and using the amount of additives such as an oxidizing agent, adjusting the pH, etc.

[0022] The zeta potential Y of the surface of the substrate to be polished in the polishing composition is appropriately set within a range that satisfies the above-mentioned relational expression: X·Y>250;, and is not particularly limited otherwise. In some embodiments, the absolute value |Y| of the zeta potential Y of the surface of the substrate to be polished in the polishing composition is preferably greater than 25 mV, more preferably 28 mV or more, even more preferably 30 mV or more, and even more preferably 32 mV or more. In some embodiments, the |Y| is usually about 50 mV or less, suitably 40 mV or less, may be 35 mV or less, or may be 30 mV or less. The smaller the |Y|, the more the polishing removal rate tends to improve.

[0023] Although not particularly limited, in some embodiments, the zeta potential Y of the polishing target substrate surface in the polishing composition is preferably lower than -25mV, more preferably -28mV or less, even more preferably -30mV or less, and even more preferably -32mV or less.In some embodiments, the zeta potential Y is about -50mV or more, appropriately -40mV or more, may be -35mV or more, or may be -30mV or more.The smaller the absolute value of the zeta potential Y, the more the polishing removal rate tends to improve.

[0024] Although not particularly limited, in some embodiments, the absolute value |XY| of the difference between the zeta potential X [mV] of the abrasive grains in the polishing composition and the zeta potential Y [mV] of the surface of the substrate to be polished is preferably 50 or less. By the difference between the zeta potential X and the zeta potential Y being within a predetermined range, the abrasive grains and the substrate tend to repel each other suitably, and the desired effect tends to be easily obtained. From this viewpoint, in some preferred embodiments, the above |XY| is 35 or less, may be 30 or less, may be 25 or less, may be 20 or less, may be 15 or less, or may be 10 or less.

[0025] The zeta potential Y of the surface of the substrate to be polished in the polishing composition is the zeta potential measured for the surface of the substrate to be polished in the polishing composition using a solid zeta potential measuring device.Specifically, it is measured by the method described in the examples below.The zeta potential Y can be adjusted by selecting the silicon carbide substrate to be used, the additives such as oxidizing agent, the amount of use, adjusting pH, etc.

[0026] <Polishing composition> (Abrasive grain) The polishing composition disclosed herein contains abrasive grains. The abrasive grains function to mechanically polish the substrate to be polished. The material and properties of the abrasive grains are not particularly limited, and various abrasive grains that can satisfy the above-mentioned zeta potential relational expression can be used. For example, the abrasive grains can be any of inorganic particles, organic particles, and organic-inorganic composite particles. For example, the abrasive grains can be substantially composed of any of 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 the like. The abrasive grains may be used alone or in combination of two or more types. Among them, 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 preferable 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 preferable, and alumina particles are particularly preferable.

[0027] Although not particularly limited, the abrasive grains may be surface-modified, for example, for the purpose of adjusting the zeta potential X. Although not particularly limited, the abrasive grains (e.g., alumina particles) can be surface-modified, for example, by chemical modification (e.g., modification with a coupling agent such as alkoxyaluminate, alkoxysilane, alkoxytitanate, etc.; modification by adsorption of a surface modifier such as polyacrylic acid ester, polyethylene glycol ester, polyethylene glycol ether, acrylic acid, methacrylic acid, etc.; functional group modification by immobilization of sulfonic acid, carboxylic acid (acetic acid, propionic acid, etc.), etc.) or by doping.

[0028] In some preferred embodiments, the polishing composition contains alumina particles (alumina abrasive particles) as abrasive particles. In the embodiment using alumina particles as abrasive particles, the effect of satisfying the above-mentioned zeta potential relational expression can be preferably exhibited. In addition, a polishing composition containing alumina particles as abrasive particles is likely to obtain a practical polishing removal rate. The alumina particles can be appropriately selected from various known alumina particles. Examples of such known alumina particles include α-alumina and intermediate alumina. Here, intermediate alumina is a general term for alumina particles other than α-alumina, and specific examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, χ-alumina, etc. In addition, alumina called fumed alumina (typically alumina fine particles produced when alumina salt is baked at high temperature) may be used based on classification by manufacturing method. Furthermore, alumina called colloidal alumina or alumina sol (for example, alumina hydrate such as boehmite) is also included in the above-mentioned known alumina particles. Furthermore, the alumina particles may be surface-modified. From the viewpoint of processability, it is preferable that the alumina particles contain α-alumina. The alumina particles may be used alone or in combination of two or more kinds.

[0029] When using alumina particles as abrasive grains, the proportion of alumina particles in the total abrasive grains used is generally more advantageous.For example, the proportion of alumina particles in the total abrasive grains is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, even more preferably 98% by weight or more, and particularly preferably 99% by weight or more.The technology disclosed herein can be preferably implemented in an embodiment in which substantially 100% by weight of the abrasive grains contained in polishing composition are alumina abrasive grains.

[0030] The particle size of the abrasive grains is not particularly limited and is selected so as to exhibit the desired polishing effect. From the viewpoint of polishing removal rate, etc., in some embodiments, the average secondary particle diameter of the abrasive grains (e.g., alumina grains) is suitable to be larger than 10 nm, preferably 50 nm or more, more preferably 100 nm or more, even more preferably 200 nm or more, even more preferably 300 nm or more, and particularly preferably 400 nm or more. The upper limit of the average secondary particle diameter of the abrasive grains (e.g., alumina grains) is not particularly limited, but in some embodiments, it is suitable to make it approximately 10 μm or less, and from the viewpoint of improving surface quality, it is preferably 5 μm or less, more preferably 3 μm or less, even more preferably 1000 nm or less, even more preferably 700 nm or less, and particularly preferably 500 nm or less, and may be 400 nm or less, 300 nm or less, or 250 nm or less.

[0031] The average secondary particle diameter of the abrasive grains can be measured as the volume average particle diameter (volume-based arithmetic mean diameter; Mv) for particles less than 500 nm by dynamic light scattering using, for example, a model "UPA-UT151" manufactured by Nikkiso Co., Ltd. For particles of 500 nm or more, the volume average particle diameter can be measured by a pore electrical resistance method using a model "Multisizer 3" manufactured by BECKMAN COULTER.

[0032] The content of abrasive grains in the polishing composition disclosed herein is not particularly limited.In some embodiments, the content of abrasive grains (e.g., alumina grains) in the polishing composition may be approximately 0.01% by weight or more, and from the viewpoint of improving the polishing removal rate, it is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, even more preferably 1% by weight or more, even more preferably 2% by weight or more, and particularly preferably 3% by weight or more.In addition, from the viewpoint of dispersibility, polishing stability, etc., the content of abrasive grains (e.g., alumina grains) in the polishing composition is usually appropriate to be 50% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, and may be 10% by weight or less, or 8% by weight or less.

[0033] In some embodiments, the polishing composition is preferably substantially free of diamond particles as abrasive grains. Diamond particles can be a limiting factor in improving smoothness due to their high hardness. In addition, diamond particles are generally expensive, so they are not considered to be advantageous materials in terms of cost performance, and from a practical standpoint, the dependency on high-priced materials such as diamond particles may be low. Here, the abrasive grains substantially free of diamond particles means that the proportion of diamond particles in the entire abrasive grains is 1% by weight or less, more preferably 0.5% by weight or less, typically 0.1% by weight or less, including the case where the proportion of diamond particles is 0% by weight. In such an embodiment, the application effect of the technology disclosed herein can be suitably exhibited.

[0034] (Oxidizing agent) In some embodiments, the polishing composition preferably contains an oxidizing agent. The oxidizing agent can reduce the hardness of the substrate to be polished (specifically, a silicon carbide substrate), weaken the substrate surface, and improve the polishing removal rate. In addition, according to the technology disclosed herein, in an embodiment in which the polishing composition contains an oxidizing agent (for example, a composite metal oxide described later), the effect of satisfying the above-mentioned zeta potential relational expression can be preferably exhibited. Examples of the oxidizing agent include metal nitrates, ferric acids, permanganic acids, chromic acids, vanadic acids, ruthenic acids, molybdic acids, perrhenic acids, and tungstic acids. Among them, ferric acids, permanganic acids, chromic acids, vanadic acids, molybdic acids, and tungstic acids are more preferred, and permanganic acids (for example, permanganates) and vanadic acids are even more preferred. The oxidizing agent can be used alone or in combination of two or more.

[0035] In some preferred embodiments, the polishing composition contains a complex metal oxide as an oxidizing agent. The polishing composition containing a complex metal oxide as an oxidizing agent is easy to improve the polishing performance. Specific examples of the complex metal oxide include metal nitrates such as iron nitrate and silver nitrate; iron acids such as potassium ferrate; permanganates such as sodium permanganate and potassium permanganate; chromates such as potassium chromate and potassium dichromate; vanadates such as sodium vanadate and potassium vanadate; ruthenic acids such as perruthenic acid salts; molybdic acids such as ammonium molybdate and disodium molybdate; rhenic acids such as perrhenic acid salts; and tungstic acids such as disodium tungstate. The complex metal oxides can be used alone or in combination of two or more.

[0036] In the embodiment in which a composite metal oxide is used as an oxidizing agent, it is more preferable to use a composite metal oxide having a monovalent or divalent metal element (excluding transition metal elements) and a fourth period transition metal element of the periodic table as the composite metal oxide. Suitable examples of the monovalent or divalent metal element include Na, K, Mg, and Ca. Of these, Na and K are more preferable. Suitable examples of the fourth period transition metal element of the periodic table include Fe, Mn, Cr, V, and Ti. Of these, Fe, Mn, and Cr are more preferable, and Mn is even more preferable. The composite metal oxide can effectively reduce the hardness and weaken the surface of silicon carbide, which is a high-hardness material. This can more preferably exhibit the effect of improving the polishing removal rate.

[0037] When the composite metal oxide is a salt (for example, permanganate), the composite metal oxide may be present in the polishing composition in the form of ions.

[0038] In the embodiment in which a composite metal oxide is used as an oxidizing agent, the polishing composition may or may not further contain an oxidizing agent other than the composite metal oxide. Examples of oxidizing agents other than composite metal oxides include peroxides such as hydrogen peroxide; periodic acids such as periodic acid and its salts, sodium periodate and potassium periodate; iodic acids such as iodic acid and its salts, ammonium iodate; bromic acids such as bromic acid and its salts, potassium bromate; persulfuric acids such as peroxomonosulfuric acid and peroxodisulfuric acid, and persulfuric acids such as ammonium persulfate and potassium persulfate; chloric acids and perchloric acids such as chloric acid and its salts, perchloric acid and its salts, potassium perchlorate; osmic acids such as perosmic acid and osmic acid; selenic acids such as perselenic acid and selenic acid; ammonium cerium nitrate; and the like. Oxidizing agents other than composite metal oxides can be used alone or in combination of two or more.

[0039] When using composite metal oxide as oxidizing agent, the proportion of composite metal oxide in the whole oxidizing agent used is generally higher, which is advantageous.For example, the proportion of composite metal oxide in the whole oxidizing agent is appropriate to be 50% by weight or more (for example, more than 50% by weight) from the viewpoint of effectively exerting the effect of containing composite metal oxide, and is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, even more preferably 98% by weight or more, and particularly preferably 99% by weight or more.The technology disclosed herein can be preferably implemented in an embodiment in which substantially 100% by weight of the oxidizing agent contained in the polishing composition is composite metal oxide.

[0040] In the embodiment in which the polishing composition contains an oxidizing agent, the content of the oxidizing agent is not particularly limited. In some embodiments, from the viewpoint of improving the polishing removal rate, the content of the oxidizing agent is about 0.1% by weight or more, preferably 0.3% by weight or more, more preferably 0.5% by weight or more, even more preferably 0.8% by weight or more, even more preferably 1.0% by weight or more (for example, more than 1.0% by weight), and may be 1.2% by weight or more, may be 1.4% by weight or more, or may be 1.6% by weight or more. In some embodiments, from the viewpoint of the surface quality after polishing, the content of the oxidizing agent in the polishing composition is about 30% by weight or less, preferably 10% by weight or less, more preferably 8% by weight or less, even more preferably 6% by weight or less, even more preferably 4% by weight or less, and particularly preferably 3% by weight or less.

[0041] In the embodiment in which the polishing composition contains an oxidizing agent, the content of the oxidizing agent can also be specified by the relative relationship with the content of abrasive grains. Although not particularly limited, in some embodiments, the ratio of the content of the oxidizing agent Wx [wt%] to the content of abrasive grains Wa [wt%], i.e., Wx / Wa, is, for example, approximately 0.01 or more, preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.25 or more. When Wx / Wa is larger, the contribution of chemical polishing to the contribution of mechanical polishing tends to be larger. In addition, from the viewpoint of increasing the contribution of mechanical polishing, in some embodiments, Wx / Wa is, for example, 100 or less, suitably 50 or less, preferably 10 or less, more preferably 5 or less, even more preferably 3 or less, and particularly preferably 1 or less.

[0042] (water) The polishing composition disclosed herein typically contains water. As the water, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water, etc. can be preferably used. The polishing composition disclosed herein may further contain an organic solvent (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water, if necessary. Usually, it is appropriate that 90% by volume or more of the solvent contained in the polishing composition is water, preferably 95% by volume or more is water, and more preferably 99 to 100% by volume is water.

[0043] (acid) The polishing composition may contain an acid as necessary for the purpose of pH adjustment, polishing acceleration, etc. As the acid, both inorganic and organic acids can be used. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, carbonic acid, etc. 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, and succinic acid, etc. These can be used alone or in combination of two or more. When an acid is used, the amount of the acid is not particularly limited, and can be determined according to the purpose of use (e.g., pH adjustment). Alternatively, in some embodiments, the polishing composition may be substantially free of acid.

[0044] (Basic compounds) The polishing composition may contain a basic compound as necessary for the purpose of pH adjustment, polishing acceleration, etc. Here, the basic compound refers to a compound that has the function of increasing the pH of the polishing composition by being added to the polishing composition. Examples of basic compounds include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; carbonates and bicarbonates such as ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, and sodium carbonate; ammonia; quaternary ammonium hydroxides such as quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide; and other amines. The basic compound may be used alone or in combination of two or more. When a basic compound is used, the amount used is not particularly limited, and may be the amount used depending on the purpose of use (e.g., pH adjustment). Alternatively, in some embodiments, the polishing composition may be substantially free of a basic compound.

[0045] (Dispersant) The polishing composition may contain a dispersant as necessary for the purpose of preventing the settling of abrasive grains and improving dispersion. The zeta potential X of the abrasive grains in the polishing composition may be adjusted by adding a dispersant to the polishing composition. Examples of dispersants include phosphorus-containing acids and their salts, sulfonic acid esters, polyoxyalkylene alkyl ethers, and the like. Examples of phosphorus-containing acids and their salts include inorganic phosphoric acids such as phosphoric acid (orthophosphoric acid), pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, and hexametaphosphoric acid; inorganic phosphates; organic phosphates such as methyl acid phosphate, ethyl acid phosphate, ethyl glycol acid phosphate, and isopropyl acid phosphate; phosphoric acid esters such as phytic acid (myo-inositol-1,2,3,4,5,6-hexaphosphate); nitrilotris(methylene phosphonate); Examples of the phosphonates include ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethanehydroxy-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, and methanehydroxyphosphonic acid; salts of phosphonates, etc. Examples of the sulfonic acid esters include alkylbenzenesulfonates and diallylsulfosuccinates.Examples of polyoxyalkylene alkyl ethers include polyoxyethylene glycol, polyoxyethylene propyl ether, polyoxyethylene butyl ether, polyoxyethylene pentyl ether, polyoxyethylene hexyl ether, polyoxyethylene octyl ether, polyoxyethylene-2-ethylhexyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene isodecyl ether, polyoxyethylene tridecyl ether, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene isostearyl ether, polyoxyethylene oleyl ether, polyoxyethylene phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, and polyoxyethylene dodecyl phenyl ether. Other examples of dispersants include carboxylic acid polymers and low molecular weight carboxylic acids. The carboxylic acid polymers referred to here are polymers containing carboxylic acid units such as acrylic acid, methacrylic acid, and maleic acid, and various carboxylic acid polymers that can be used as dispersants for abrasive grains can be used. The weight average molecular weight (Mw) of the carboxylic acid polymer is not particularly limited, but is within the range of about 1000 to 500000. The above Mw can be the weight average molecular weight (water-based, polyethylene glycol equivalent) determined by GPC. The low molecular weight carboxylic acid is a carboxylic acid having a molecular weight of less than 1000 (for example, 46 to less than 1000), and various low molecular weight carboxylic acids that can be used as dispersants for abrasive grains can be used. The dispersants can be used alone or in combination of two or more.

[0046] When a dispersant is used, the amount of the dispersant used is not particularly limited, and can be determined according to the purpose of use (e.g., prevention of settling of abrasive grains, improvement of dispersion, adjustment of the zeta potential X of the abrasive grains in the polishing composition). Alternatively, in some embodiments, the polishing composition may be substantially free of a dispersant.

[0047] (Other Ingredients) The polishing composition disclosed herein may further contain, as necessary, known additives that can be used in polishing compositions (specifically, polishing compositions used for polishing silicon carbide substrates), such as chelating agents, thickeners, surface protective agents, wetting agents, surfactants, rust inhibitors, preservatives, and antifungal agents, within the scope that does not impair the effects of the present invention. The content of the above additives may be appropriately set depending on the purpose of their addition, and detailed explanations are omitted since they do not characterize the present invention.

[0048] Although not particularly limited, the effect of the technology disclosed herein (specifically, the effect obtained based on the relational expression of zeta potential) can be preferably exhibited in an embodiment in which the polishing composition contains alumina particles as abrasive grains, an oxidizing agent (preferably a composite metal oxide), and water.From this viewpoint, the total content of alumina particles, oxidizing agent, and water in the polishing composition is preferably 90% by weight or more, more preferably 95% by weight or more, even more preferably 98% by weight or more, even more preferably 99% by weight or more, and may be 99.5% by weight or more, or may be 99.9% by weight or more.

[0049] (pH) The pH of the polishing composition is usually suitably about 2 to 12. When the pH is in the above range, a practical polishing removal rate is easily achieved in polishing the substrate to be polished. In some embodiments, the pH may be 2.5 or more, 3.0 or more, 4.0 or more, 5.0 or more, 6.0 or more, or 7.0 or more. In some preferred embodiments, the pH of the polishing composition is 8.0 or more, more preferably 8.5 or more. There is no particular limit to the upper limit of the pH, but in some embodiments, the pH is suitably 12.0 or less, 11.0 or less, 10.0 or less, or 9.0 or less (for example, less than 9.0). The zeta potential X and the zeta potential Y can be adjusted by changing the pH of the polishing composition.

[0050] (Preparation of Polishing Composition) The method of preparing the polishing composition disclosed herein is not particularly limited.For example, it is advisable to use a well-known mixing device such as a blade type agitator, an ultrasonic disperser, a homomixer, etc. to mix each component contained in the polishing composition.The manner of mixing these components is not particularly limited, and for example, all components may be mixed at once, or may be mixed in a suitably set order.

[0051] The polishing composition disclosed herein may be a one-component type or a multi-component type, including a two-component type. For example, the polishing composition may be configured so 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 to polish a substrate to be polished. These are stored separately, for example, before use, and can be mixed at the time of use to prepare a one-component polishing composition. When mixing, water for dilution or the like can be further mixed.

[0052] <Substrate to be polished> In the technology disclosed herein, a silicon carbide substrate that can have a zeta potential Y that satisfies the above zeta potential relational expression is used as the substrate to be polished. Silicon carbide (SiC) is expected to be a compound semiconductor substrate material with low power loss and excellent heat resistance, etc., and improving its surface properties is particularly advantageous in practical use. The silicon carbide substrate may have a single crystal surface of the above material that is mechanically and chemically stable. The technology disclosed herein can be particularly preferably applied to polishing the single crystal surface of silicon carbide.

[0053] <Polishing method> The polishing composition disclosed herein can be used to polish a substrate to be polished, for example, in an embodiment that includes the following steps. That is, prepare a polishing liquid (slurry) containing any of the polishing compositions disclosed herein. The preparation of the polishing liquid may include adjusting the concentration (e.g., dilution), adjusting pH, etc., of the polishing composition to prepare the polishing liquid. Alternatively, the polishing composition may be used as it is as the polishing liquid. In addition, in the case of a multi-agent type polishing composition, the preparation of the polishing liquid may include mixing the agents, diluting one or more agents before the mixing, diluting the mixture after the mixing, etc. Next, the polishing liquid is supplied to the substrate to be polished, and the substrate is polished by a conventional method used by those skilled in the art. For example, the substrate to be polished is set in a general polishing device, and the polishing liquid is supplied to the surface of the substrate to be polished through the polishing pad of the polishing device. Typically, the polishing liquid is continuously supplied, while the polishing pad is pressed against the surface of the substrate to be polished, and the two are moved relatively (for example, rotated). Through this polishing process, the polishing of the substrate is completed.

[0054] According to this specification, a polishing method for polishing a substrate to be polished (specifically, a silicon carbide substrate) is provided. The polishing method includes a step of polishing a substrate to be polished using the polishing composition disclosed herein. The polishing method is characterized in that the zeta potential X [mV] of the abrasive grains in the polishing composition and the zeta potential Y [mV] of the surface of the substrate to be polished in the polishing composition satisfy the relational expression: X·Y>250. The technical meaning, the numerical range of the relational expression, the numerical range of the zeta potentials X and Y, etc. are as described above, and therefore will not be described again.

[0055] In some preferred embodiments, the polishing method includes a step of performing pre-polishing (pre-polishing step) and a step of performing finish polishing (finish polishing step). In a typical embodiment, the pre-polishing step is a polishing step arranged immediately before the finish polishing step. The pre-polishing step may be a single-stage polishing step, or may be a multi-stage polishing step of two or more stages. The finish polishing step referred to here is a step of performing finish polishing on a substrate that has been subjected to pre-polishing, and refers to a polishing step arranged at the end (i.e., the most downstream side) of the polishing steps performed using a polishing slurry containing abrasive grains. In the polishing method including the pre-polishing step and the finish polishing step, the polishing composition disclosed herein may be used in the pre-polishing step, may be used in the finish polishing step, or may be used in both the pre-polishing step and the finish polishing step.

[0056] In a preferred embodiment, the polishing step using the above-mentioned polishing composition can be a preliminary polishing step.When the preliminary polishing step includes two or more stages of polishing steps, two or more of the polishing steps can be carried out using any of the polishing compositions disclosed herein.The polishing composition disclosed herein can be preferably applied to the preliminary polishing at the front stage (upstream side).For example, it can also be preferably used in the first preliminary polishing step after the lapping step described below, typically in the first polishing step.

[0057] In another preferred embodiment, the polishing process using the above-mentioned polishing composition is a finish polishing process.The polishing composition disclosed herein can reduce line defects on the surface after polishing, and is therefore suitable as a polishing composition (finish polishing composition) used in the finish polishing process of the surface of the substrate to be polished.

[0058] Preliminary polishing and finish polishing can be applied to both polishing using a single-sided polishing machine and polishing using a double-sided polishing machine. In a single-sided polishing machine, the substrate to be polished is attached to a ceramic plate with wax or held using a holder called a carrier, and a polishing pad is pressed against one side of the substrate to be polished while supplying a polishing composition, and the two are moved relatively to polish one side of the substrate to be polished. The movement is, for example, a rotational movement. In a double-sided polishing machine, the substrate to be polished is held using a holder called a carrier, and a polishing pad is pressed against the opposing side of the substrate to be polished while supplying a polishing composition from above, and the two are rotated in a relative direction to polish both sides of the substrate to be polished simultaneously.

[0059] The polishing pad used in each polishing step disclosed herein is not particularly limited. For example, any of nonwoven type, suede type, hard foam polyurethane type, abrasive type, abrasive type, and the like may be used. In some embodiments, a suede type polishing pad that does not contain abrasive particles may be preferably used.

[0060] The polished object polished by the method disclosed herein is typically washed after polishing. This washing can be performed using a suitable washing liquid. The washing liquid to be used is not particularly limited, and a known or commonly used one can be appropriately selected and used.

[0061] The polishing method disclosed herein may include any other steps in addition to the above-mentioned preliminary polishing step and finish polishing step. Such steps include a lapping step performed before the preliminary polishing step. The lapping step is a step of polishing the substrate to be polished by pressing the surface of a polishing platen, for example a cast iron platen, against the substrate to be polished. Therefore, a polishing pad is not used in the lapping step. The lapping step is typically performed by supplying abrasive grains between the polishing platen and the substrate to be polished. The abrasive grains are typically diamond abrasive grains. The polishing method disclosed herein may also include an additional step before the preliminary polishing step or between the preliminary polishing step and the finish polishing step. The additional step is, for example, a cleaning step or a polishing step.

[0062] <Method of manufacturing polished object> The technology disclosed herein may include a method for manufacturing an abrasive, which includes a polishing step using any of the polishing methods described above, and the provision of an abrasive manufactured by the method. The above-mentioned method for manufacturing an abrasive is specifically a method for manufacturing a silicon carbide substrate. That is, the technology disclosed herein provides a method for manufacturing an abrasive, which includes polishing a substrate to be polished (specifically a silicon carbide substrate) by applying any of the polishing methods disclosed herein, and a polished product manufactured by the method. The above manufacturing method can efficiently provide an abrasive, specifically a silicon carbide substrate, having improved surface quality.

[0063] The matters disclosed in this specification include the following. [1] A method for polishing a silicon carbide substrate, comprising: The polishing composition is supplied to a substrate to be polished, and the substrate is polished. The polishing composition contains abrasive grains, The abrasive grains have a zeta potential X [mV] in the polishing composition, the surface of the substrate to be polished has a zeta potential Y [mV] in the polishing composition as measured using a solid zeta potential measuring device; The polishing method, wherein the zeta potential X [mV] and the zeta potential Y [mV] satisfy X·Y>250. [2] The polishing method according to the above [1], wherein the product (X·Y) of the zeta potential X [mV] and the zeta potential Y [mV] is within the range of 370 to 2000. [3] The polishing method according to the above [1] or [2], wherein the zeta potential Y is lower than -25 mV and is equal to or higher than -50 mV. [4] The polishing method according to any one of the above [1] to [3], wherein the zeta potential X is lower than −10 mV and is equal to or higher than −70 mV. [5] The polishing method according to any one of the above [1] to [4], wherein the abrasive grains contain alumina particles. [6] The polishing method according to any one of the above [1] to [5], wherein the polishing composition further contains an oxidizing agent. [7] The polishing method according to [6] above, wherein the oxidizing agent contains a composite metal oxide. [8] The polishing method according to any one of the above [1] to [7], wherein the polishing composition has a pH of 8.0 or more and 12 or less.

[0064]

[11] Containing abrasive grains; The abrasive grains have a zeta potential X [mV] in the polishing composition, A polishing composition, wherein the zeta potential X [mV] satisfies the relationship with the zeta potential Y [mV] of the surface of the substrate to be polished in the polishing composition measured using a solid zeta potential measurement device: X·Y>250.

[12] The polishing composition according to

[11] above, wherein the product (X·Y) of the zeta potential X [mV] and the zeta potential Y [mV] is within the range of 370 to 2000.

[13] The polishing composition according to

[11] or

[12] above, wherein the zeta potential Y is lower than -25 mV and is -50 mV or higher.

[14] The polishing composition according to any one of the above

[11] to

[13] , wherein the zeta potential X is lower than −10 mV and is −70 mV or higher.

[15] The polishing composition according to any one of the above

[11] to

[14] , wherein the abrasive grains contain alumina particles.

[16] The polishing composition according to any one of

[11] to

[15] above, further comprising an oxidizing agent.

[17] The polishing composition according to

[16] above, wherein the oxidizing agent contains a composite metal oxide.

[18] The polishing composition according to any one of the above

[11] to

[17] , which has a pH of 8.0 or more and 12 or less.

[19] The polishing composition according to any one of

[11] to

[18] above, which is used in the polishing method according to any one of [1] to [8] above. EXAMPLES

[0065] Some examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "%" is based on weight unless otherwise specified.

[0066] <Preparation of Polishing Composition> (Examples 1 to 16) Alumina abrasive grains, potassium permanganate (KMnO4) as an oxidizing agent, and deionized water were mixed, and the pH was adjusted to prepare a polishing composition according to each example. The content of the alumina abrasive grains was 3%, and the content of potassium permanganate was 3%. The pH of the polishing composition was adjusted to the value shown in Table 1 using potassium hydroxide (KOH) as a pH adjuster. Five types of alumina (alumina A to E) shown in Table 1 were prepared and used as the alumina abrasive grains. Alumina modified by different functional group modifications was used as alumina B and C. In addition, in Examples 1 to 3, a carboxylic acid-based polymer (polyacrylic acid, molecular weight 10000, 1 wt%) was further added as a dispersant, and in Examples 10 to 12, a low molecular weight carboxylic acid (acetic acid, 1 wt%) was further added as a dispersant.

[0067] <Measurement of Zeta Potential X> For each polishing composition, the zeta potential [mV] was measured under the conditions of a liquid temperature of 20 to 25 °C using a high-concentration zeta potential meter "ZetaProbe" manufactured by Colloidal Dynamics. The obtained values were shown in the corresponding columns of Table 1 as the zeta potential X of the abrasive grains in the polishing composition.

[0068] <Measurement of zeta potential Y> An SiC wafer (conductivity type: n-type, crystal type 4H-SiC, off-angle with respect to the C-axis of the main plane (0001): 4°, 2 inches) was immersed in each polishing composition for 24 hours, and the zeta potential Y [mV] of the Si surface of the SiC wafer in a 1 mM KCl aqueous solution was measured using a solid zeta potential measuring device (zeta potential analyzer for solid surface analysis "Surpass3" manufactured by Anton Paar). The obtained values were shown in the corresponding columns of Table 1. The measurement was carried out in an environment of 25 °C ± 2.5 °C.

[0069] <Polishing of SiC wafer> Using diamond abrasive grains with an average particle size of 5 μm, lapping was preliminarily performed on the surface of the SiC wafer, and each polishing composition was directly used as a polishing liquid and polished under the following polishing conditions. [Polishing conditions] Polishing apparatus: Single-sided polishing apparatus manufactured by Nippon Engis Co., Ltd., model "EJ-380IN" Polishing pad: "SUBA800" manufactured by Nitta Haas Polishing pressure: 300 g / cm 2 Platen rotation speed: 80 rotations / min Polishing time: 1 hour Head rotation speed: 40 rotations / min Supply rate of polishing liquid: 20 mL / min (flow-through) Temperature of polishing liquid: 25 °C Substrate to be polished: Si surface of SiC wafer (conductivity type: n-type, crystal type 4H-SiC, off-angle with respect to the C-axis of the main plane (0001): 4°), 2 inches

[0070] <Evaluation of polishing removal rate> The polishing removal rate was calculated according to the following calculation formulas (1) and (2). (1) Polishing stock removal [cm] = Difference in weight of SiC wafer before and after polishing [g] / SiC density [g / cm 3 ](=3.21g / cm 3 ) / polished area [cm 2 ](=19.62cm 2 ) (2) Polishing removal rate [nm / h] = Polishing removal amount [cm] × 10 7 / Polishing time (=1 hour) The obtained values ​​are shown in the corresponding columns in Table 1.

[0071] <Evaluation of line defects> The polished SiC wafers were evaluated for the presence or absence of line defects of 2 cm or more in length across the entire surface of the wafer using the Lasertec SiC wafer defect inspection / review device "SICA-88." If there were no line defects, it was judged as "Good," and if line defects were found, it was judged as "Poor," and this is shown in the corresponding column in Table 1.

[0072] [Table 1]

[0073] As shown in Table 1, in Examples 2-3, 5-6, 8-9, 12, and 15-16 in which the zeta potential X [mV] of the abrasive grains in the polishing composition and the zeta potential Y [mV] of the substrate to be polished in the polishing composition satisfy X·Y>250, no line defects were observed on the surface after polishing. In addition, in the polishing using the polishing compositions of Examples 2-3, 5-6, 8-9, 12, and 15-16, practical polishing removal rates were obtained. On the other hand, in Examples 1, 4, 7, 10-11, and 13-14 in which X·Y>250 was not satisfied, line defects were observed on the surface after polishing. In this example, the effect of the present invention was confirmed in polishing the Si surface, but in polishing a SiC substrate, if the zeta potentials of the substrate and the abrasive grains have the same sign, a repulsive force acts between the substrate and the abrasive grains, suppressing the occurrence of line defects. Therefore, it is considered that the effect of the present invention can be obtained in polishing the C surface as long as X·Y>250 is satisfied.

[0074] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above.

Claims

1. 1. A method for polishing a silicon carbide substrate, comprising: The polishing composition is supplied to a substrate to be polished, and the substrate is polished. The polishing composition contains abrasive grains, The abrasive grains have a zeta potential X [mV] in the polishing composition, the surface of the substrate to be polished has a zeta potential Y [mV] in the polishing composition as measured using a solid zeta potential measuring device; The polishing method, wherein the zeta potential X [mV] and the zeta potential Y [mV] satisfy X·Y>250.

2. 2. The polishing method according to claim 1, wherein the product (X·Y) of the zeta potential X [mV] and the zeta potential Y [mV] is within a range of 370 to 2000.

3. 3. The polishing method according to claim 1, wherein the zeta potential Y is lower than −25 mV and is equal to or higher than −50 mV.

4. 3. The polishing method according to claim 1, wherein the zeta potential X is lower than −10 mV and is equal to or higher than −70 mV.

5. The polishing method according to claim 1 or 2, wherein the abrasive grains include alumina particles.

6. The polishing method according to claim 1 or 2, wherein the polishing composition further comprises an oxidizing agent.

7. The polishing method according to claim 6 , wherein the oxidizing agent comprises a complex metal oxide.

8. 3. The polishing method according to claim 1, wherein the polishing composition has a pH of 8.0 or more and 12 or less.

9. A polishing composition for use in the polishing method according to claim 1 or 2, Contains abrasive grains, The abrasive grains have a zeta potential X [mV] in the polishing composition, The zeta potential X [mV] satisfies the relationship with the zeta potential Y [mV] of the surface of the substrate to be polished in the polishing composition measured using a solid zeta potential measuring device: X·Y>250.

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