Polishing composition, polishing method, and method for manufacturing semiconductor substrate

Abstract

To provide means capable of polishing a carbon film at a high polishing speed.SOLUTION: A polishing composition contains abrasive grains, a pH adjuster, and water. The average secondary particle diameter of the abrasive grains exceeds 120 nm. The abrasive grains include cationic modified silica, and the pH is 7 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polishing composition, a polishing method, and a method for producing a semiconductor substrate. [Background technology]

[0002] In recent years, semiconductor integrated circuits (Large-Scale Integration, hereinafter referred to as "LSI") have become increasingly highly integrated and performant. In particular, dynamic random access memory (DRAM) and 3D-NAND have achieved dramatic improvements in storage capacity through miniaturization and multi-layering. This progress in miniaturization and multi-layering has made it necessary to form contact holes with larger aspect ratios.

[0003] Contact holes can be formed by lithography and dry etching. When forming patterns with particularly large aspect ratios, hard masks are used. Hard masks are films that have high etching resistance against dry etching. Silicon nitride films have traditionally been used as hard masks, but carbon films, which have even higher etching resistance, are also being used.

[0004] Carbon films proposed for use as hard masks include amorphous carbon films, nanocrystalline diamond films, and graphene films. These films can be formed by chemical vapor deposition (hereinafter also referred to as "CVD"), physical vapor deposition (hereinafter also referred to as "PVD"), spin coating, and the like.

[0005] Carbon films are more likely to experience increased surface roughness during film formation than conventionally used silicon nitride films. A rough carbon film surface can cause problems during lithography or dry etching processes, potentially resulting in malfunctions of devices. Therefore, if the surface of the carbon film can be smoothed by polishing it, it is expected that malfunctions of devices can be reduced and productivity can be increased. In order to smooth the surface of a carbon film, it is necessary to sufficiently remove at least the surface layer of the carbon film, which necessitates high-speed polishing of the carbon film.

[0006] As a technique for polishing a carbon film, for example, Patent Document 1 discloses a polishing liquid containing abrasive grains, tetravalent cerium ions, and water. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2021 / 084706 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the technique described in Patent Document 1 has a problem in that the removal rate of the carbon film is low.

[0009] Therefore, an object of the present invention is to provide a means for polishing a carbon film at a high polishing rate. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by a polishing composition containing abrasive grains, a pH adjuster, and water, wherein the abrasive grains have an average secondary particle size of more than 120 nm, the abrasive grains contain cation-modified silica, and the pH is 7 or less, thereby completing the present invention. [Effects of the Invention]

[0011] According to the present invention, a means is provided that enables a carbon film to be polished at a high polishing rate. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention provides a polishing composition containing abrasive grains, a pH adjuster, and water, wherein the abrasive grains have an average secondary particle size of more than 120 nm, the abrasive grains contain cation-modified silica, and the pH is not more than 7. The polishing composition according to one embodiment of the present invention having such a configuration is capable of polishing a carbon film at a high removal rate.

[0013] Although the details of why the polishing composition of the present invention achieves the above-mentioned effects are unclear, the following mechanism is thought to be the cause: The abrasive grains of the present invention have an average secondary particle diameter of more than 120 nm, which is thought to enable the mechanical action of the abrasive grains to be sufficiently transmitted to the carbon film, thereby improving the removal rate of the carbon film.

[0014] The polishing composition of the present invention also contains cation-modified silica as abrasive grains. Abrasive grains having such a composition have a positive zeta potential and are therefore likely to approach a carbon film having a negative zeta potential, thereby improving the removal rate of the carbon film.

[0015] Furthermore, since the abrasive grains contain cation-modified silica, when the polished object (polished object) is subjected to surface treatment such as cleaning or rinse polishing after polishing is completed, it has the advantage of being possible to obtain a polished object with less residue derived from the abrasive grains.

[0016] The above mechanism is based on speculation, and the present invention is not limited to this mechanism in any way.

[0017] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0018] In this specification, unless otherwise specified, operations and measurements of physical properties are carried out at room temperature (20° C. or higher and 25° C. or lower) and at a relative humidity of 40% RH or higher and 50% RH or lower.

[0019] [Polished object] The object to be polished according to the present invention preferably includes a carbon film. Here, the term "carbon film" is not limited to films made of elemental carbon, but also includes carbon films containing atoms other than carbon atoms (such as hydrogen atoms and oxygen atoms). Examples of carbon films include amorphous carbon films (hereinafter also referred to as "amorphous carbon films"), diamond-like carbon films (hereinafter also referred to as "DLC"), nanocrystalline diamond films, graphene films, SiC films, and SiOC films. These films may be used alone or in combination. Among these, amorphous carbon films, diamond-like carbon films, nanocrystalline diamond films, and graphene films are preferred. These films can be formed by CVD, PVD, spin coating, or the like.

[0020] The carbon atom content in the carbon film is preferably 10 mass % or more, 30 mass % or more, 50 mass % or more, 60 mass % or more, 70 mass % or more, 80 mass % or more, 90 mass % or more, 92 mass % or more, 95 mass % or more, 97 mass % or more, 98 mass % or more, and 99 mass % or more, based on the total mass of the carbon film. The carbon film may be substantially composed of carbon (the carbon atom content is substantially 100 mass %).

[0021] The object to be polished according to the present invention may further contain other materials in addition to the carbon film, such as silicon nitride, silicon oxide, single crystal silicon, polycrystalline silicon (polysilicon), amorphous silicon, polycrystalline silicon doped with n-type or p-type impurities, amorphous silicon doped with n-type or p-type impurities, titanium nitride, elemental metals, and SiGe.

[0022] Examples of polishing objects containing silicon oxide include TEOS (Tetraethyl Orthosilicate) type silicon oxide surfaces (hereinafter also referred to as "TEOS" or "TEOS films") produced using tetraethyl orthosilicate as a precursor, HDP (High Density Plasma) films, USG (Undoped Silicate Glass) films, PSG (Phosphorus Silicate Glass) films, BPSG (Boron-Phospho Silicate Glass) films, and RTO (Rapid Thermal Oxidation) films.

[0023] Examples of elemental metals include tungsten, copper, cobalt, hafnium, nickel, gold, silver, platinum, palladium, rhodium, ruthenium, iridium, and osmium.

[0024] [Abrasive grain] The polishing composition of the present invention contains cation-modified silica (silica having a cationic group) as abrasive grains. The cation-modified silica may be used alone or in combination of two or more.

[0025] The cation-modified silica is preferably cation-modified colloidal silica (colloidal silica having a cationic group).

[0026] Here, cation-modified refers to a state in which cationic groups (e.g., amino groups or quaternary ammonium groups) are bonded to the surface of silica (preferably colloidal silica). According to a preferred embodiment of the present invention, the cation-modified silica particles are amino-modified silica particles, more preferably amino-modified colloidal silica particles. According to such an embodiment, the above-mentioned effects can be further improved.

[0027] The cation-modified silica may be a commercially available product or a synthetic product, but it is preferable to use one obtained by a method of cation-modifying a silica raw material with a silane coupling agent as described below. A method for producing cation-modified silica according to a preferred embodiment will be described below.

[0028] [Method of manufacturing cation-modified silica] [Silica raw material] The silica raw material is a raw material before being cation-modified (modified) using a predetermined silane coupling agent described later, and contains silica particles. The silica raw material is preferably colloidal silica. Hereinafter, colloidal silica as the silica raw material will also be referred to as "raw colloidal silica," and a detailed description will be given of an example in which the silica raw material is raw colloidal silica.

[0029] The raw colloidal silica may be produced, for example, by a sol-gel method. Raw colloidal silica produced by the sol-gel method is preferred because it contains a low content of metal impurities that are diffusible in semiconductors and corrosive ions such as chloride ions. The production of raw colloidal silica by the sol-gel method can be carried out using a conventionally known method. Specifically, raw colloidal silica can be obtained by using a hydrolyzable silicon compound (e.g., alkoxysilane or its derivative) as a raw material and carrying out a hydrolysis-condensation reaction. One type of silicon compound may be used alone, or two or more types may be used in combination. Furthermore, the raw colloidal silica may be produced by a method other than the sol-gel method.

[0030] In one embodiment, the silicon compound is preferably an alkoxysilane represented by the following general formula (1) or a derivative thereof.

[0031] [ka]

[0032] In general formula (1), R is an alkyl group, preferably a lower alkyl group having 1 to 8 carbon atoms, more preferably a lower alkyl group having 1 to 4 carbon atoms. Examples of R include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl groups. Preferred are tetramethoxysilane in which R is a methyl group, tetraethoxysilane in which R is an ethyl group, and tetraisopropoxysilane in which R is an isopropyl group. Examples of alkoxysilane derivatives include low condensates obtained by partially hydrolyzing alkoxysilanes.

[0033] The silicon compound is hydrolyzed and condensed in a reaction solvent to form colloidal silica. Water or a water-containing organic solvent can be used as the reaction solvent. Examples of the organic solvent include hydrophilic organic solvents such as alcohols (e.g., methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, ethylene glycol, propylene glycol, and 1,4-butanediol), and ketones (e.g., acetone and methyl ethyl ketone). Among these organic solvents, alcohols (e.g., methanol, ethanol, and isopropanol) are particularly preferred. From the perspective of post-treatment of the reaction solvent, it is more preferable to use alcohols with the same alkyl group (R) as the starting silicon compound (e.g., methanol for tetramethoxysilane). These organic solvents may be used alone or in combination. While the amount of organic solvent used is not particularly limited, a range of 5 to 50 moles per mole of silicon compound is preferred. Amounts of 5 moles or more ensure sufficient compatibility with the silicon compound, while amounts of 50 moles or less prevent a decrease in production efficiency. The amount of water added to the organic solvent is not particularly limited, as long as it is an amount necessary for the hydrolysis of the silicon compound, and is preferably about 2 to 15 moles per mole of the silicon compound. The amount of water mixed with the organic solvent significantly affects the particle size of the colloidal silica formed. By increasing the amount of water added, the particle size of the colloidal silica can be increased. By decreasing the amount of water added, the particle size of the colloidal silica can be decreased. Therefore, by changing the mixing ratio of water to organic solvent, the particle size of the colloidal silica produced can be adjusted as desired.

[0034] A basic catalyst is preferably added to the reaction solvent for the hydrolysis and condensation reaction of a silicon compound to obtain colloidal silica, to adjust the reaction solvent to alkaline (Stober method). This adjusts the reaction solvent to a pH of preferably 8 to 11, more preferably 8.5 to 10.5, allowing for the rapid formation of colloidal silica. From the viewpoint of preventing the incorporation of impurities, organic amines and ammonia are preferred as basic catalysts, with particularly preferred examples including ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide.

[0035] To hydrolyze and condense a silicon compound in a reaction solvent, the raw material silicon compound is added to an organic solvent and stirred at a temperature between 0°C and 100°C, preferably between 0°C and 50°C. By hydrolyzing and condensing the silicon compound while stirring in an organic solvent containing water, colloidal silica with a uniform particle size can be obtained.

[0036] Silica particles contained in the silica raw material usually exist in the form of secondary particles, which are aggregates of primary particles. The average particle size of the secondary particles of the silica particles (average secondary particle size) is not particularly limited, but is preferably more than 120 nm and not more than 500 nm, more preferably more than 150 nm and not more than 500 nm, and even more preferably 200 nm or more and less than 300 nm. As described in the Examples section below, the value of the average secondary particle size is measured as the volume average particle size by dynamic light scattering using a particle size distribution analyzer (UPA-UT151, manufactured by Nikkiso Co., Ltd.).

[0037] The lower limit of the average primary particle diameter of the silica particles contained in the silica raw material is preferably 50 nm or more, more preferably 60 nm or more, and even more preferably 70 nm or more. The upper limit of the average primary particle diameter of the silica particles is preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 100 nm or less. That is, as described in the Examples section below, the average primary particle diameter of the silica raw material is calculated based on the specific surface area (SA) of the silica particles calculated by the BET method, assuming that the shape of the silica particles is a sphere, and SA = 4πR 2 It can be calculated using the formula:

[0038] The concentration of silica particles in the silica raw material is not particularly limited as long as it is adjusted depending on the purpose of using the silica. However, from the viewpoint of productivity, it is preferably 5% by mass or more, more preferably 10% by mass to 60% by mass or less, and even more preferably 10% by mass to 50% by mass or less. Meanwhile, the remainder of the silica raw material, excluding the silica content, is water as a dispersion medium and a very small amount of catalyst. Considering the above-mentioned range of silica particle concentration, the concentration of the dispersion medium in the silica raw material is preferably 95% by mass or less, more preferably 40% by mass to 90% by mass or less, and even more preferably 50% by mass to 90% by mass or less. As mentioned above, the smaller the content of organic solvent in the dispersion medium, the more preferable. From this viewpoint, the proportion of the water content when the total amount of the dispersion medium is 100% by mass is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 100% by mass. When the dispersion medium contains an organic solvent, examples of such an organic solvent include the above-mentioned organic solvents such as methanol, ethanol, isopropanol, etc. Among them, it is preferable to use the same type of alcohol as the alcohol produced by hydrolysis of the above-mentioned silicon compound. This is because using the same type of alcohol as the alcohol produced by hydrolysis of the silicon compound can facilitate recovery and reuse of the solvent.

[0039] In the manufacturing method of this embodiment, a silica raw material is used that has a negative zeta potential. There is no particular limitation on the specific value of the zeta potential of the silica raw material, but the value immediately before the reaction with the silane coupling agent described below is preferably -10 mV or less, more preferably -20 mV or less, and even more preferably -30 mV or less. There is no particular limitation on the lower limit of this zeta potential value, and it is usually about -60 mV or more. The value of the zeta potential in this specification is the value measured by the method described in the Examples section below.

[0040] If the silica raw material already has a negative zeta potential when prepared or obtained, the silica raw material can be directly subjected to a reaction with a silane coupling agent, which will be described later, without any special treatment. On the other hand, if the zeta potential of the silica raw material when prepared or obtained is equal to or greater than zero, it is necessary to adjust the zeta potential of the silica raw material to a negative value before reacting with a silane coupling agent, which will be described later. Here, when the zeta potential of the silica raw material is equal to or greater than zero, there are no particular limitations on the method for adjusting the zeta potential of the silica raw material to a negative value. For example, an alkali may be added to the silica raw material to convert hydroxyl groups (-OH groups) present on the surface of silica particles contained in the silica raw material to -O - Group and H + and dissociate into -O - A method for increasing the exposure of silica raw material by anion exchange to convert hydroxyl groups (-OH groups) present on the surface of silica particles contained in the silica raw material to -O - Group and H + and dissociate into -O - Examples of such methods include a method of increasing the exposure of the silica raw material, and a method of introducing an anionic group into the silica raw material. Among these, the method of adding an alkali is preferably adopted from the viewpoint of excellent productivity.

[0041] In the method for producing cation-modified silica according to the present embodiment, the pH of the silica raw material to be reacted is determined as a result of the control of the zeta potential described above, and therefore it is difficult to unequivocally specify a preferred range. However, it is usually about 5 or more and 11 or less, preferably 6 or more and 10.5 or less, and more preferably 7 or more and 10 or less.

[0042] Furthermore, if necessary, the silica raw material prepared as described above may be subjected to various further treatment processes. An example of such a treatment process is a process of reducing the viscosity of the silica raw material. A process of reducing the viscosity of the silica raw material may include, for example, adding an alkaline solution (aqueous solution of various bases such as ammonia water) or an organic solvent to the silica raw material. There are no particular restrictions on the amount of alkaline solution or organic solvent added, and the amount may be appropriately determined taking into account the viscosity of the silica raw material obtained after the addition. Thus, performing a process of reducing the viscosity of the silica raw material has the advantages of improving the initial dispersibility of the silane coupling agent in the silica raw material and suppressing aggregation of silica particles.

[0043] [Silane coupling agent] In the method for producing cation-modified silica according to this embodiment, the silica raw material prepared above (which has a negative zeta potential) is mixed with a silane coupling agent having an amino group or a quaternary cationic group. This causes a reaction between the silica raw material (the hydroxyl groups present on the surface) and the hydrolyzable silyl groups of the silane coupling agent. As a result, one end of the silane coupling agent is bonded or adsorbed to the surface of the silica particles contained in the silica raw material, and the other end (the amino group or the quaternary cationic group) is exposed in large numbers on the surface of the silica particles. As a result, it has been confirmed that the zeta potential of the abrasive grains of cation-modified silica is more positive than that of the silica raw material.

[0044] Examples of the silane coupling agent used in this case include N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-triethoxysilyl-N-(α,γ-dimethyl-butylidene)propylamine, N-phenyl-γ-aminopropyltrimethoxysilane, N-(vinylbenzyl)-β-aminoethyl-γ-aminopropyltriethoxysilane hydrochloride, and octadecyldimethyl-(γ-trimethoxysilylpropyl)-ammonium chloride. Among them, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane are preferred because of their good reactivity with silica raw material, and γ-aminopropyltriethoxysilane, which is a primary amine / ethoxy coupling agent (a silane coupling agent having a primary amino group and an ethoxy group), is more preferably used.In the present invention, the silane coupling agent may be used alone or in combination of two or more.

[0045] [Mixing and reaction of silica raw material with silane coupling agent] In this production method, the silane raw material and the silane coupling agent are mixed and reacted with each other, thereby introducing cationic groups as modifying groups onto the surfaces of silica particles, thereby obtaining cation-modified silica.

[0046] When mixing and reacting the silica raw material with the silane coupling agent having an amino group or a quaternary cation group, it is preferable to use the silane coupling agent without dilution or in the form of a solution (aqueous dispersion) with a concentration of 5% by mass or more.Here, if "adding without dilution" is considered to be adding at a concentration of "100% by mass", the concentration of the silane coupling agent added is preferably 5% by mass or more, more preferably 50% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass (adding without dilution).In addition, when the silane coupling agent is added to the silica raw material in the form of a solution, there is no particular limitation on the solvent that constitutes the solution containing the silane coupling agent, but from the viewpoint of preventing gelation, it is preferable to use a solvent that does not contain water.

[0047] In the production method of this embodiment, the method for mixing the silica raw material and the silane coupling agent is not particularly limited, but from the viewpoint of suppressing gelation, a method in which the silane coupling agent is added to the silica raw material is preferred.

[0048] When adding a silane coupling agent to a silica raw material, the silane coupling agent may be added all at once, dividedly, or continuously, but it is preferable to add it dropwise at a constant dropwise rate.The dropwise rate is also appropriately adjusted according to the concentration of silica particles, the concentration of silane coupling agent, etc., but for example, when the total amount added is about 10 mL, it is 1 mL / min or more and 10 mL / min or less.

[0049] The amount of silane coupling agent added is difficult to define uniquely because the optimal amount varies depending on the conditions such as the specific surface area of ​​silica particles on the silica raw material side and the conditions such as the molecular weight of the silane coupling agent side. For example, it is preferably 0.05% by mass or more, more preferably 0.05% by mass or more and 20% by mass or less, even more preferably 0.1% by mass or more and 10% by mass or less, for example, 0.2% by mass or more and 5% by mass or less, based on 100% by mass of silica particles contained in the silica raw material.

[0050] In this manufacturing method, the mixing and reaction temperatures of the silica raw material and the silane coupling agent are not particularly limited, but are preferably in the range from room temperature to the boiling point of the solvent. In this embodiment, since the reaction can proceed even at room temperature, it is preferable to carry out the reaction at a temperature near room temperature (e.g., 20°C to 35°C). In other words, this manufacturing method preferably does not include a step of heating the reaction system between the silica raw material and the silane coupling agent. Even at temperatures near room temperature (15°C to 25°C), the extremely simple operation of stirring the reaction system for several hours has the advantage that almost all of the added silane coupling agent reacts with the silica particles in the silica raw material, leaving almost no unreacted coupling agent. By utilizing these advantages, the amount of the silane coupling agent added can be appropriately adjusted taking into account the zeta potential profile desired for the resulting cation-modified silica. The stirring speed during mixing and reaction is not particularly limited.

[0051] The reaction time between the silica raw material and the silane coupling agent is not particularly limited, but is preferably 10 minutes to 10 hours, more preferably 30 minutes to 5 hours. From the viewpoint of efficiently proceeding with the reaction, it is advisable to carry out the reaction while stirring the reaction system. There are no particular limitations on the stirring means or stirring conditions used in this case, and conventionally known knowledge can be referred to as appropriate. Furthermore, the pressure of the reaction system may be normal pressure (atmospheric pressure), elevated pressure, or reduced pressure. However, since the reaction according to the present invention can proceed under normal pressure (atmospheric pressure), the reaction may be carried out under normal pressure (atmospheric pressure).

[0052] If the cation-modified silica obtained according to the above method contains a solvent other than water, the dispersion medium, mainly the reaction solvent, may be replaced with water as needed to improve the long-term storage stability of the cation-modified silica. The method for replacing the solvent other than water with water is not particularly limited, and an example is a method in which a fixed amount of water is added dropwise while heating the cation-modified silica. Another example is a method in which the cation-modified silica is separated from the solvent other than water by precipitation, separation, centrifugation, or the like, and then redispersed in water.

[0053] The shape of the abrasive grains is not particularly limited and may be spherical or non-spherical. Specific examples of non-spherical shapes include polygonal prisms such as triangular prisms and quadrangular prisms, cylinders, bale-shaped cylinders in which the center is bulged out more than the ends, doughnut-shaped discs with a central hole, plate-shaped discs, cocoon-shaped discs with a central constriction, associative spheres in which multiple particles are integrated, confetti-shaped discs with multiple protrusions on the surface, and rugby ball-shaped discs, and are not particularly limited.

[0054] The average secondary particle diameter of the abrasive grains according to the present invention exceeds 120 nm. When the average secondary particle diameter of the abrasive grains exceeds 120 nm, the polishing rate of the object to be polished is significantly improved. The average secondary particle diameter of the abrasive grains is preferably greater than 130 nm, more preferably greater than 150 nm, even more preferably greater than 175 nm, even more preferably greater than 190 nm, and particularly preferably greater than 200 nm. On the other hand, the upper limit of the average secondary particle diameter of the abrasive grains is not particularly limited, but is preferably 500 nm or less, more preferably 450 nm or less, even more preferably 400 nm or less, even more preferably 350 nm or less, preferably 300 nm or less, and may be 250 nm or less. That is, the average secondary particle diameter of the abrasive grains is preferably more than 120 nm and not more than 500 nm, more preferably more than 130 nm and not more than 450 nm, even more preferably more than 150 nm and not more than 400 nm, even more preferably more than 175 nm and not more than 350 nm, particularly preferably more than 190 nm and not more than 300 nm, and may be more than 200 nm and not more than 250 nm. Note that the average secondary particle diameter of the abrasive grains is a value measured in the same manner as for the silica raw material described above, specifically, a value measured by the method described in the Examples.

[0055] The average primary particle size of the abrasive grains is preferably 50 nm or more, more preferably 60 nm or more, even more preferably 65 nm or more, even more preferably 70 nm or more, and particularly preferably 75 nm or more. The average primary particle size of the abrasive grains is preferably 300 nm or less, more preferably 250 nm or less, even more preferably 200 nm or less, even more preferably 150 nm or less, particularly preferably 100 nm or less, and most preferably 95 nm or less. That is, the average primary particle size of the abrasive grains is preferably 50 nm or more and 300 nm or less, more preferably 60 nm or more and 250 nm or less, even more preferably 65 nm or more and 200 nm or less, even more preferably 70 nm or more and 150 nm or less, particularly preferably 75 nm or more and 100 nm or less, and most preferably 75 nm or more and 95 nm or less. When the average primary particle size of the abrasive grains is within the above range, the polishing rate of the object to be polished, including the carbon film, can be further improved.

[0056] The average primary particle size of the abrasive grains is calculated based on the specific surface area (SA) of the abrasive grains calculated by the BET method, as in the case of the average primary particle size of the silica raw material, assuming that the abrasive grains are spherical, as follows: SA = 4πR 2 It can be calculated using the formula:

[0057] The ratio of the average secondary particle size to the average primary particle size of the abrasive grains (average secondary particle size / average primary particle size, hereinafter also referred to as "average degree of association") is preferably greater than 1.0, more preferably 1.1 or greater, and even more preferably 1.2 or greater. The average degree of association of the abrasive grains is preferably 4 or less, more preferably 3.5 or less, and even more preferably 3 or less. That is, the average degree of association of the abrasive grains is preferably greater than 1.0 and 4 or less, more preferably 1.1 or greater but 3.5 or less, and even more preferably 1.2 or greater but 3 or less.

[0058] The average degree of association of the abrasive grains can be obtained by dividing the average secondary particle size of the abrasive grains by the average primary particle size of the abrasive grains.

[0059] The lower limit of the aspect ratio of the abrasive grains in the polishing composition is not particularly limited, but is preferably greater than 1.0, more preferably greater than 1.1, and even more preferably greater than 1.2. The upper limit of the aspect ratio of the abrasive grains in the polishing composition is preferably 4 or less, more preferably 3.5 or less, and even more preferably 3 or less. That is, the aspect ratio of the abrasive grains is preferably greater than 1.0 and less than 4, more preferably 1.1 or more and less than 3.5, and even more preferably 1.2 or more and less than 3. Within these ranges, defects on the surface of the object to be polished can be further reduced. The aspect ratio is the average of the values ​​obtained by taking the smallest rectangle circumscribing the image of the abrasive grains using a scanning electron microscope and dividing the length of the long side of the rectangle by the length of the short side of the same rectangle, and can be determined using general image analysis software. The lower limit of the aspect ratio of the cation-modified silica in the polishing composition is not particularly limited, but is preferably 1.0 or more.

[0060] In the particle size distribution of abrasive grains measured by laser diffraction scattering, the ratio of particle diameter (D90) when the cumulative particle weight from the fine particle side reaches 90% of the total particle weight to particle diameter (D50) when the cumulative particle weight of all particles reaches 50% of the total particle weight of all particles, D90 / D50, is not particularly limited, but is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more.In addition, in the particle size distribution of abrasive grains in a polishing composition measured by laser diffraction scattering, the ratio of particle diameter (D90) when the cumulative particle weight from the fine particle side reaches 90% of the total particle weight to particle diameter (D50) when the cumulative particle weight of all particles reaches 50% of the total particle weight of all particles, D90 / D50, is not particularly limited, but is preferably 2.0 or less, more preferably 1.7 or less, and even more preferably 1.5 or less.Within this range, defects on the surface of the object to be polished can be further reduced.

[0061] The size of the abrasive grains (average primary particle diameter, average secondary particle diameter, aspect ratio, D90 / D50, etc.) can be appropriately controlled by selecting the silica raw material, the method for manufacturing the abrasive grains, etc.

[0062] The lower limit of the zeta potential of the abrasive grains in the polishing composition is preferably 10 mV or more, more preferably 20 mV or more, and even more preferably 30 mV or more.The upper limit of the zeta potential of the abrasive grains in the polishing composition is preferably 70 mV or less, more preferably 65 mV or less, and even more preferably 60 mV or less.That is, the zeta potential of the abrasive grains in the polishing composition is preferably 4 mV or more and 70 mV or less, more preferably 4.5 mV or more and 65 mV or less, and even more preferably 5 mV or more and 60 mV or less.

[0063] Abrasive grains having the above-mentioned zeta potential can polish a carbon film at a higher polishing rate.

[0064] In this specification, the zeta potential of the abrasive grains is a value measured by the method described in the Examples. The zeta potential of the abrasive grains can be adjusted by the amount of cationic groups in the abrasive grains, the pH of the polishing composition, etc.

[0065] The content (concentration) of abrasive grains in the polishing composition is not particularly limited, but is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the total mass of the polishing composition.The upper limit of the content of abrasive grains in the polishing composition is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and particularly preferably less than 4% by mass, based on the total mass of the polishing composition.That is, the content of abrasive grains is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.2% by mass or more and 5% by mass or less, even more preferably 0.5% by mass or more and 4% by mass or less, and particularly preferably more than 0.5% by mass and less than 4% by mass, based on the total mass of the polishing composition.

[0066] When the content of the abrasive grains is within this range, the carbon film can be polished at a higher removal rate. When the polishing composition contains two or more types of abrasive grains, the content of the abrasive grains refers to the total amount of these.

[0067] The polishing composition of the present invention may further contain abrasive grains other than cation-modified silica, provided that the effects of the present invention are not impaired. Such other abrasive grains may be inorganic particles, organic particles, or organic-inorganic composite particles. Specific examples of inorganic particles include unmodified silica, particles made of metal oxides such as alumina, ceria, and titania, silicon nitride particles, silicon carbide particles, and boron nitride particles. Specific examples of organic particles include polymethyl methacrylate (PMMA) particles. The other abrasive grains may be used alone or in combination of two or more types. Furthermore, the other abrasive grains may be commercially available products or synthetic products.

[0068] However, the content of the other abrasive grains is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 1% by mass or less, based on the total mass of the abrasive grains. Most preferably, the content of other abrasive grains is 0% by mass, i.e., the abrasive grains are composed only of cation-modified silica.

[0069] [pH and pH adjusters] The pH of the polishing composition of the present invention is 7 or less. When the pH is 7 or less, the zeta potential of the abrasive grains becomes an appropriate value, and the polishing rate of the object to be polished, including the carbon film, is improved. The pH is preferably 6 or less, more preferably 5.5 or less, and even more preferably 5 or less. The lower limit of the pH is preferably 1 or more, more preferably 2 or more, even more preferably 2.5 or more, and even more preferably 3 or more. That is, the pH of the polishing composition of the present invention is preferably 1 or more and 7 or less, more preferably 2 or more and 6 or less, even more preferably 2.5 or more and 5.5 or less, and even more preferably 3 or more and 5 or less.

[0070] The polishing composition of the present invention contains a pH adjuster for adjusting the pH. The pH adjuster may be any of an inorganic acid, an organic acid, and a base, and may also be any of an inorganic compound and an organic compound. The pH adjuster may be used alone or in combination of two or more.

[0071] Specific examples of inorganic acids that can be used as pH adjusters include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, boric acid, carbonic acid, hypophosphorous acid, phosphorous acid, and phosphoric acid. Among these, hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid are preferred.

[0072] Specific examples of organic acids that can be used as pH adjusters include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, and phenoxyacetic acid. Organic sulfuric acids such as methanesulfonic acid, ethanesulfonic acid, and isethionic acid may also be used. Among these, dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid and tartaric acid, and tricarboxylic acids such as citric acid are preferred.

[0073] Instead of or in combination with inorganic or organic acids, salts such as alkali metal salts of inorganic or organic acids may be used as pH adjusters. Combinations of a weak acid and a strong base, a strong acid and a weak base, or a weak acid and a weak base can be expected to have a pH buffering effect.

[0074] Specific examples of bases that can be used as pH adjusters include ammonia, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, etc. The amount of pH adjuster added is not particularly limited, and may be appropriately adjusted so that the polishing composition has a desired pH.

[0075] The pH of the polishing composition can be measured, for example, with a pH meter, specifically by the method described in the Examples.

[0076] [water] The polishing composition of the present invention contains water for dispersing each component. According to a more preferred embodiment of the present invention, the dispersion medium consists essentially of water. The term "substantially" as used above means that a dispersion medium other than water may be included as long as the effects of the present invention can be achieved. More specifically, the dispersion medium preferably consists of 90% by mass to 100% by mass of water and 0% by mass to 10% by mass of a dispersion medium other than water, more preferably 99% by mass to 100% by mass of water and 0% by mass to 1% by mass of a dispersion medium other than water. Most preferably, the dispersion medium consists solely of water.

[0077] Examples of dispersion media other than water include alcohols such as methanol, ethanol, and ethylene glycol; ketones such as acetone; and mixtures thereof.

[0078] In order not to inhibit the action of the components contained in the polishing composition, it is preferable that the water contains as few impurities as possible. Specifically, pure water or ultrapure water obtained by removing impurity ions with an ion exchange resin and then passing through a filter to remove foreign matter, or distilled water is more preferable.

[0079] [Other ingredients] The polishing composition of the present invention may further contain known additives that can be used in polishing compositions, such as an oxidizing agent, a complexing agent, an antiseptic, an antifungal agent, etc., within the range that does not impair the effects of the present invention. Among these, it is preferable to contain an oxidizing agent.

[0080] The oxidizing agent has the effect of oxidizing the surface of the object to be polished, and can further improve the polishing rate of the object to be polished with the polishing composition.

[0081] Examples of oxidizing agents include hydrogen peroxide, sodium peroxide, barium peroxide, ozone water, silver (II) salts, iron (III) salts, permanganic acid, chromic acid, dichromate, peroxodisulfuric acid, peroxolinic acid, peroxosulfuric acid, peroxoboric acid, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypochlorous acid, hypobromous acid, hypoiodous acid, chloric acid, chlorous acid, perchloric acid, bromic acid, iodic acid, periodic acid, persulfuric acid, dichloroisocyanuric acid, and salts thereof (e.g., potassium salts, sodium salts, ammonium salts, etc.). These oxidizing agents can be used alone or in combination. Among these, hydrogen peroxide, ammonium persulfate, periodic acid, hypochlorous acid, and sodium dichloroisocyanurate are preferred, with hydrogen peroxide being more preferred.

[0082] The lower limit of the content of the oxidizing agent in the polishing composition is preferably 0.001% by mass or more, and more preferably 0.01% by mass or more. By setting the lower limit in this way, the polishing rate can be further improved. Furthermore, the upper limit of the content of the oxidizing agent in the polishing composition is preferably 30% by mass or less, and more preferably 10% by mass or less. By setting the upper limit in this way, it is possible to reduce the material cost of the polishing composition and also to reduce the burden of treating the polishing composition after use in polishing, i.e., waste liquid treatment. Furthermore, it is possible to reduce the risk of excessive oxidation of the surface of the object to be polished by the oxidizing agent.

[0083] [Electrical conductivity] The electrical conductivity of the polishing composition of the present invention is preferably 0.1 mS / cm or more, more preferably 0.2 mS / cm or more, and even more preferably 0.3 mS / cm or more. The electrical conductivity of the polishing composition is preferably 10 mS / cm or less, more preferably 5.0 mS / cm or less, and even more preferably 2.0 mS / cm or less. If the electrical conductivity is within this range, the polishing rate of the object to be polished can be further improved. The electrical conductivity can be measured by the method described in the Examples.

[0084] In the present invention, there is no particular limitation on the method for controlling the electrical conductivity of the polishing composition to a desired value, and for example, this can be achieved by adding an electrical conductivity adjuster to the polishing composition. The electrical conductivity adjuster is not particularly limited as long as it can control the electrical conductivity to a desired value, and salt compounds such as acid salts and base salts are suitable. The content of the electrical conductivity adjuster in the polishing composition is not particularly limited as long as it is a content that can adjust the electrical conductivity to a desired value.

[0085] [Method for producing polishing composition] The method for producing the polishing composition of the present invention is not particularly limited, and can be obtained, for example, by stirring and mixing abrasive grains containing cation-modified silica, a pH adjuster, and other additives as necessary in water. The details of each component are as described above.

[0086] The temperature at which the components are mixed is not particularly limited, but is preferably 10° C. to 40° C. Heating may be used to increase the dissolution rate. The mixing time is also not particularly limited as long as uniform mixing is achieved.

[0087] [Polishing method and semiconductor substrate manufacturing method] As described above, the polishing composition of the present invention is suitable for use in polishing an object having a carbon film. Thus, the present invention provides a polishing method for polishing an object having a carbon film with the polishing composition of the present invention. The present invention also provides a method for producing a semiconductor substrate, comprising polishing a semiconductor substrate having a carbon film by the polishing method.

[0088] As the polishing device, a general polishing device can be used, which is equipped with a holder for holding a substrate or the like having an object to be polished, a motor whose rotation speed can be changed, and a polishing platen onto which a polishing pad (polishing cloth) can be attached.

[0089] The polishing pad may be made of any material, including ordinary nonwoven fabric, polyurethane, porous fluororesin, etc. The polishing pad is preferably provided with grooves to allow the polishing liquid to accumulate.

[0090] Regarding the polishing conditions, for example, the rotation speed of the polishing platen is 10 rpm (0.17 s -1 ) or more 500rpm (8.33s -1 The pressure (polishing pressure) applied to the substrate having the object to be polished is preferably 0.5 psi (3.4 kPa) or more and 10 psi (68.9 kPa) or less.

[0091] The method for supplying the polishing composition to the polishing pad is not particularly limited, and for example, a method of continuously supplying the polishing composition using a pump, etc. There is no limit to the amount of the polishing composition supplied, but it is preferable that the surface of the polishing pad is always covered with the polishing composition of the present invention.

[0092] After polishing, the substrate is washed with running water, and water droplets adhering to the substrate are removed by a spin dryer or the like, followed by drying, to obtain a substrate having a metal-containing layer.

[0093] The polishing composition according to the present invention may be a one-component type or a multi-component type including a two-component type. Further, the polishing composition according to the present invention may be prepared by diluting the stock solution of the polishing composition with a diluent such as water, for example, by a factor of 10 times or more.

Examples

[0094] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. Unless otherwise specified, “%” and “parts” mean “mass %” and “parts by mass”, respectively.

[0095] [Measurement methods for various physical properties] In this example, various physical properties were measured by the following methods.

[0096] [Measurement of particle size] The value of the average secondary particle size of the abrasive grains was adopted as the volume average particle size measured by the dynamic light scattering method using a particle size distribution measuring apparatus (UPA-UT151, manufactured by Nikkiso Co., Ltd.). Also, the value of the average primary particle size of the abrasive grains was calculated based on the specific surface area (SA) of the abrasive grains calculated from the BET method, assuming that the shape of the abrasive grains is a true sphere, using the formula SA = 4πR 2 and calculated using the formula.

[0097] [Measurement of zeta potential] The zeta potential of the abrasive grains was measured using a zeta potential measuring apparatus (trade name “ELS-Z”) manufactured by Otsuka Electronics Co., Ltd.

[0098] [Measurement of pH] The pH of the polishing composition was measured using a pH meter (manufactured by Horiba, Ltd., model number: F-71).

[0099] [Measurement of electrical conductivity] The electrical conductivity of the polishing composition was measured using a desktop electrical conductivity meter (manufactured by Horiba, Ltd., model number: DS-71).

[0100] [Preparation of polishing composition] Example 1 Colloidal silica (silica particle concentration: 20 mass %, average primary particle diameter: 90 nm, average secondary particle diameter: 210 nm) was prepared as a silica raw material.

[0101] To the colloidal silica prepared above, γ-aminopropyltriethoxysilane (hereinafter also referred to as “APTES”) was added dropwise at a rate of 1 mL / min without dilution while stirring at a stirring speed of 600 rpm. The amount of APTES added was 1% by mass relative to 100% by mass of silica particles contained in the silica raw material.

[0102] Thereafter, the reaction system was stirred for 3 hours at room temperature (25°C) without heating, to obtain cation-modified (amino group-modified) colloidal silica in which amino groups were introduced onto the surfaces of the silica particles.

[0103] The cation-modified colloidal silica obtained above as abrasive grains was added to pure water as a dispersion medium at room temperature (25° C.) so as to have a final concentration of 2 mass % to obtain a mixed liquid.

[0104] Thereafter, nitric acid was added to the mixture as a pH adjuster, and the mixture was stirred and mixed at room temperature (25° C.) for 30 minutes to prepare a polishing composition.

[0105] The pH of the obtained polishing composition was 5.0.The zeta potential of the cation-modified colloidal silica in the obtained polishing composition was measured according to the above-mentioned method, and was found to be +35mV.The particle size of the cation-modified colloidal silica in the polishing composition was the same as the particle size of the raw material colloidal silica used.

[0106] Example 2 A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 50 mass%, average primary particle diameter: 200 nm, average secondary particle diameter: 300 nm) was used as the silica raw material.

[0107] Example 3 A polishing composition was prepared in the same manner as in Example 2, except that nitric acid was added so that the pH of the polishing composition was 3.0.

[0108] Example 4 A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 100 nm, average secondary particle diameter: 160 nm) was used as the silica raw material.

[0109] Example 5 A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 90 nm, average secondary particle diameter: 210 nm) was used as the silica raw material and the amount of APTES added was 0.5 mass% relative to 100 mass% of the silica particles contained in the silica raw material.

[0110] Example 6 A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 80 nm, average secondary particle diameter: 135 nm) was used as the silica raw material.

[0111] (Comparative Example 1) A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 80 nm, average secondary particle diameter: 120 nm) was used as the silica raw material.

[0112] (Comparative Example 2) A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 35 nm, average secondary particle diameter: 70 nm) was used as the silica raw material.

[0113] (Comparative Example 3) A polishing composition was prepared in the same manner as in Example 1, except that nitric acid was added so that the pH of the polishing composition was 8.0.

[0114] Comparative Example 4 Colloidal silica (silica particle concentration: 20% by mass, average primary particle diameter: 90 nm, average secondary particle diameter: 210 nm) was prepared as a silica raw material. 5 mL of 3-mercaptopropyltrimethoxysilane mixed with 20 mL of ethanol was added to 900 mL of the ion-exchanged colloidal silica and heated at 70°C for 18 hours. 80 mL of a 31% by mass hydrogen peroxide solution was then added and heated at 65°C for 18 hours. After heating, the ethanol was removed using an evaporator to prepare anion-modified colloidal silica.

[0115] (Comparative Example 5) A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 90 nm, average secondary particle diameter: 210 nm) was used as the abrasive grains without being subjected to cation modification treatment.

[0116] (Comparative Example 6) A polishing composition was prepared in the same manner as in Example 1, except that colloidal silica (silica particle concentration: 20 mass%, average primary particle diameter: 45 nm, average secondary particle diameter: 90 nm) was used as the silica raw material.

[0117] (Comparative Example 7) A polishing composition was prepared in the same manner as in Example 1, except that cerium oxide having an average secondary particle size of 250 μm was used instead of the cation-modified colloidal silica.

[0118] (Comparative Example 8) A polishing composition was prepared in the same manner as in Example 1, except that α-alumina having an average secondary particle size of 300 μm was used instead of the cation-modified colloidal silica.

[0119] [Polishing speed] A silicon wafer (Advantec Corporation, 200 mm wafer, SKA, P-type) with an amorphous carbon film formed on its surface to a thickness of 5000 Å was prepared. The prepared wafer was polished using the polishing composition obtained above under the following polishing conditions, and the removal rate was measured: (polishing conditions) Polishing machine: EJ-380IN-CH (Engis Japan Co., Ltd.) Polishing pad: Hard polyurethane pad (Rohm and Haas, IC1010) Polishing pressure: 1.0 psi (1 psi = 6894.76 Pa) Platen rotation speed: 80 rpm Head (carrier) rotation speed: 60 rpm Flow rate of polishing composition: 100 ml / min Polishing time: 60 seconds.

[0120] (polishing speed) The polishing rate was calculated using the following formula.

[0121]

number

[0122] The film thickness was measured using an optical interference film thickness measuring device (manufactured by SCREEN Holdings Co., Ltd., model number: Lambda Ace VM-2030), and the polishing rate was calculated by dividing the difference in film thickness before and after polishing by the polishing time.

[0123] The composition of the polishing composition of each Example and Comparative Example and the evaluation results are shown in Table 1 below.

[0124] [Table 1]

[0125] As is clear from Table 1 above, it was found that the polishing compositions of the Examples can polish objects containing carbon films at a high polishing rate. Furthermore, when a polishing test was conducted in the same manner as in Example 1, except that potassium permanganate was added as an additive to the mixed solution of Example 1 to a final concentration of 0.1 mass % before adding the pH adjuster, the polishing rate was 233 Å / min. As is clear from this, it was found that the polishing rate of the polishing compositions of the Examples can be further improved by adding an oxidizing agent.

[0126] On the other hand, when the polishing compositions of the comparative examples were used, it was found that the polishing rate of the object to be polished containing a carbon film decreased. In Comparative Example 7, in which cerium oxide was used as the abrasive grains, the polishing rate decreased presumably due to the poor dispersibility of cerium oxide and the low hardness of cerium oxide. In Comparative Example 8, in which α-alumina was used as the abrasive grains, the polishing rate decreased presumably due to the poor dispersibility of α-alumina.

[0127] [Cleaning evaluation] The polished wafers of Example 1, Comparative Example 7, and Comparative Example 8 were washed with pure water (cleaning method: rinse polishing was performed on a separate platen while pure water was flowing at 300 ml / min under the same polishing conditions except for the flow rate. Then, the surface was scrubbed with a PVA sponge for 3 minutes while the pure water was flowing.) and the wafer surfaces were then observed with a scanning electron microscope (SEM, Hitachi High-Tech Corporation, model number: SU8000). Specifically, nine 1 μm square areas were randomly selected on the wafer surface, and the number of abrasive grain residues observed in each 1 μm square area was counted. The average number of abrasive grain residues at the nine measured locations was calculated and evaluated according to the following criteria: ○: The average number of abrasive grain residues is less than 3 ×: The average number of abrasive grain residues is 3 or more.

[0128] The results are shown in Table 2 below.

[0129] [Table 2]

[0130] As is clear from Table 2 above, it was found that the number of abrasive grain residues was small on the wafer surface after polishing and cleaning using the polishing composition of Example 1. On the other hand, it was found that the number of abrasive grain residues was large on the wafer surface after polishing and cleaning using the polishing compositions of Comparative Examples 7 and 8.

Claims

1. Contains abrasive grains, a pH adjuster, and water; The average secondary particle diameter of the abrasive grains exceeds 120 nm, the abrasive grains include cation-modified silica; A polishing composition having a pH of 5 or more and 7 or less.

2. Abrasive grains, a pH adjuster, and water are contained, The average secondary particle diameter of the abrasive grains exceeds 120 nm, the abrasive grains include cation-modified silica; A polishing composition having a pH of 7 or less, A polishing composition used for polishing an object to be polished, the object comprising at least one carbon film selected from the group consisting of an amorphous carbon film, a diamond-like carbon film, a nanocrystalline diamond film, and a graphene film.

3. 3. The polishing composition according to claim 2, having a pH of 2 or more and 6 or less.

4. 4. The polishing composition according to claim 2, having a pH of 5 or more and 7 or less.

5. 5. The polishing composition according to claim 1, wherein the abrasive grains have an average secondary particle size of more than 150 nm.

6. 6. The polishing composition according to claim 1, wherein the abrasive grains in the polishing composition have a zeta potential of 20 mV or more.

7. A polishing method comprising a step of polishing an object to be polished that includes a carbon film using the polishing composition according to any one of claims 1 to 6, The polishing method, wherein the carbon film comprises at least one film selected from the group consisting of an amorphous carbon film, a diamond-like carbon film, a nanocrystalline diamond film, and a graphene film.

8. A method for manufacturing a semiconductor substrate, comprising a step of polishing a semiconductor substrate including the carbon film by the polishing method described in claim 7.

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