Polishing composition

Abstract

The present invention pertains to a polishing composition which comprises abrasive grains, an aqueous medium, and a polymer having a structural unit represented by formula (A) and / or a structural unit represented by formula (B) [in formula (A) and formula (B), X1 and X2 each independently represent -N(-H)- or -O-, R1 and R5 each independently represent a linear or branched alkylene group having 1-6 carbon atoms, R2, R3, R6, and R7 each independently represent a linear or branched alkyl group having 1-4 carbon atoms, and R4 and R8 each independently represent a hydrogen atom or a methyl group], and in which, when the polymer has the structural unit represented by formula (B) but does not have the structural unit represented by formula (A), the amount of a structural unit including a betaine structure in the polymer is 0-9 mol%.

Description

polishing composition

[0001] The present invention relates to a polishing composition.

[0002] In the semiconductor manufacturing process, a polishing process is performed to polish the surface of the wafer to improve its flatness. In particular, the CMP (Chemical Mechanical Polishing) process, which enables high-precision polishing, is an essential process in semiconductor manufacturing.

[0003] The CMP process is typically a process in which a wafer held by a top ring is pressed against a polishing pad while a polishing composition containing abrasive grains is supplied, and the top ring and the polishing pad are rotated to polish the wafer surface to a flat surface. The polishing composition used in the CMP process is also called a CMP slurry.

[0004] Various studies have been conducted on polishing compositions used in CMP processes, and for example, Patent Documents 1 to 7 describe polishing compositions containing cerium oxide particles, a specific water-soluble polymer compound, and an aqueous medium such as water. Patent Document 8 describes a method for producing silicon wafers that includes, together with other steps, a polishing step using a polishing composition containing silica particles, a specific water-soluble polymer, a nitrogen-containing basic compound, and an aqueous medium.

[0005] JP 2019-121641 A JP 2020-186367 A JP 2021-166254 A JP 2021-100126 A JP 2021-5631 A JP 2021-5704 A JP 2009-260236 A JP 2019-186346 A

[0006] Although various polishing compositions have been investigated as described above, there is still a demand for further improvement in the polishing rate, and also for achieving a high level of planarization effect after polishing.

[0007] Therefore, an object of the present invention is to provide a polishing composition that has sufficient planarizing ability and is capable of performing polishing treatment at a high polishing rate.

[0008] The present inventors have conducted extensive research to solve the above problems, and have found that the above problems can be solved by a polishing composition containing abrasive grains, a polymer having specific structural units, and an aqueous medium, thereby completing the present invention. That is, the present invention includes the following aspects.

[0009] [1] Abrasive grains and a constituent unit represented by formula (A) and / or a constituent unit represented by formula (B): [In formula (A) and formula (B), X １ and X ２ each independently represents —N(—H)— or —O—; R １ and R ５ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms; R ２ , R ３ , R ６ and R ７ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms; R ４ and R ８ each independently represent a hydrogen atom or a methyl group], and an aqueous medium, provided that when the polymer has a structural unit represented by formula (B) but does not have a structural unit represented by formula (A), the amount of structural units containing a betaine structure in the polymer is 0 to 9 mol %. [2] The polishing composition according to [1], wherein the weight-average molecular weight of the polymer is 1,000 to 1,000,000. [3] The polishing composition according to [1] or [2], wherein the amount of structural units represented by formula (A) and / or structural units represented by formula (B) in the polymer is 5 to 100 mol % based on the amount of all structural units in the polymer. [4] The polishing composition according to [1] or [2], wherein X in formulas (A) and (B) １ and X ２ [5] The polishing composition according to any one of [1] to [4], wherein the amount of the polymer contained in the polishing composition is 0.0005 to 5 mass % based on the total amount of the polishing composition. [6] The polishing composition according to any one of [1] to [5], wherein the abrasive grains are silica particles.

[0010] According to the present invention, it is possible to provide a polishing composition capable of performing a polishing treatment at a high polishing rate. According to a preferred embodiment of the present invention, it is possible to provide a polishing composition capable of achieving a high polishing rate while having sufficient planarization ability.

[0011] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention. Note that in this specification, the range of values ​​indicated by "to" includes the upper and lower limits.

[0012] [Polymer] The polishing composition of the present invention is a polishing composition containing abrasive grains, a specific polymer, and an aqueous medium. The specific polymer contains a structural unit represented by formula (A) and / or a structural unit represented by formula (B): [In formula (A) and formula (B), X １ and X ２ each independently represents —N(—H)— or —O—; R １ and R ５ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms; R ２ , R ３ , R ６ and R ７ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms; R ４ and R ８ each independently represent a hydrogen atom or a methyl group. In this specification, the structural unit represented by formula (A) is also referred to as structural unit (A), and the structural unit represented by formula (B) is also referred to as structural unit (B). The polymer contained in the polishing composition may be a polymer containing one type of structural unit (A) or structural unit (B), a polymer containing two or more types of structural units (A) or structural units (B), or a polymer containing one or more types of structural units (A) and one or more types of structural units (B). However, when the polymer contains structural unit (B) but does not contain structural unit (A), the amount of structural units containing a betaine structure in the polymer is 0 to 9 mol %.

[0013] X in formula (A) and formula (B) １ and X ２ Each independently represents —N(—H)— or —O—. １ and X ２ is preferably —N(—H)— from the viewpoint of the hydrolysis resistance of the copolymer.

[0014] R １ and R ５ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms. Examples of the linear or branched alkylene group having 1 to 6 carbon atoms include a methylene group, an ethylene group, an n-propylene group, an isopropylene group, an n-butylene group, a methylmethylene group, a methylethylene group, a dimethylethylene group, a methylpropylene group, an ethylpropylene group, a dimethylpropylene group, a methylbutylene group, an n-pentylene group, and an n-heptylene group. R １ and R ５ The number of carbon atoms in R is preferably 2 to 5, more preferably 2 to 4, from the viewpoints of solubility in an aqueous medium (water solubility) and ease of availability (availability). １ and R ５ preferably represents a linear alkylene group.

[0015] R ２ , R ３ , R ６ and R ７ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and an isobutyl group. From the viewpoints of water solubility and availability, R ２ , R ３ , R ６ and R ７ are each independently preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and even more preferably a methyl group.

[0016] R ４ and R ８ each independently represents a hydrogen atom or a methyl group.

[0017] When a polymer has the structural unit (B) but does not have the structural unit (A), the amount of structural units containing a betaine structure in the polymer is 0 to 9 mol % relative to the amount of all structural units contained in the polymer. Here, a betaine structure refers to a structure in which a positive charge and a negative charge are present at non-adjacent positions within the same molecule, and the structural unit as a whole has no charge. Furthermore, an amine oxide structure refers to a structure in which a positive charge and a negative charge are present at adjacent positions within the same molecule, and the structural unit as a whole has no charge. Therefore, a betaine structure and an amine oxide structure are distinguished as different structures.

[0018] In one embodiment of the present invention, the amount of structural units in the polymer that contain a betaine structure having a positive charge and a negative charge at non-adjacent positions within the same molecule is preferably 0 to 30 mol %, more preferably 0 to 20 mol %, even more preferably 0 to 10 mol %, and still more preferably 0 to 9 mol % relative to the amount of all structural units in the polymer. Note that the same applies to cases where the polymer has structural unit (B) but does not have structural unit (A).

[0019] The reason why the polishing rate is improved when using a polishing composition containing a polymer having a structural unit represented by formula (A) and / or a structural unit represented by formula (B) is not entirely clear, but it is believed to be due to the following reasons. Generally, abrasive grains such as silica particles and the surface of a workpiece to be polished such as a silicon substrate both have a negative zeta potential under basic conditions. Therefore, repulsive forces act between the abrasive grains and the surface of the workpiece to be polished, reducing the force the abrasive grains exert on the surface of the workpiece to be polished, or reducing the fluidity of the polishing composition, thereby reducing the number of times the abrasive grains come into contact with the surface of the workpiece to be polished, resulting in a decrease in the polishing rate. In the polishing composition of the present invention, the specific polymer described above reduces the zeta potentials of both the abrasive grains and the surface of the workpiece to be polished, thereby reducing the repulsive forces acting between them and improving the polishing rate. More specifically, the structural unit represented by formula (A) has the above-mentioned amine oxide structure, in which a positively charged atom and a negatively charged atom are directly bonded, which is believed to impart high hydration ability to the copolymer. Therefore, it is believed that the polymer having an amine oxide structure as a structural unit increases the hydrophilicity of the surface of the object to be polished, and the ammonium cation moiety reduces the zeta potential, thereby improving the fluidity of the polishing composition between the object to be polished and the polishing pad, and the number of times the abrasive grains come into contact with the object to be polished increases, resulting in an improved polishing rate.Similarly, the structural unit represented by formula (B) has a positive zeta potential, so that repulsion is less likely to occur between the abrasive grains and the surface of the object to be polished, making it difficult for the abrasive grains to reduce the force applied to the surface of the object to be polished, and making it difficult for the fluidity of the polishing composition to decrease, thereby improving the polishing rate.In addition, although the reason for the improved planarization ability is not entirely clear, it is believed that when the polymer having the structural unit represented by formula (A) and / or the structural unit represented by formula (B) is adsorbed on the surface of the object to be polished, it is adsorbed so as to fill in the unevenness of the object to be polished, thereby flattening the surface, and this flat surface is uniformly polished, thereby improving the planarization ability.

[0020] The amount of the structural unit represented by formula (A) and / or the structural unit represented by formula (B) in the polymer is preferably 5 to 100 mol %, more preferably 5 to 95 mol %, even more preferably 5 to 90 mol %, and even more preferably 5 to 85 mol % relative to the amount of all structural units of the polymer, from the viewpoint of the removal rate and planarization ability of the polishing composition. The molar ratio can be calculated, for example, from the ratio of each raw material (charge ratio) when polymerizing the specific copolymer. １ The molar ratio may be calculated using H-NMR or the like.

[0021] The weight-average molecular weight (Mw) of the polymer is preferably 1,000 to 1,000,000, more preferably 1,000 to 800,000, and even more preferably 1,000 to 600,000, from the viewpoint of achieving a high polishing rate while maintaining sufficient planarization ability. In one embodiment of the present invention, the weight-average molecular weight of the polymer may be preferably 10,000 to 200,000, more preferably 20,000 to 150,000, from the viewpoint of planarization and polishing rate. The weight-average molecular weight can be determined by gel permeation chromatography (hereinafter referred to as GPC). The weight-average molecular weight measured by GPC can be determined by the method described in the Examples below. From the viewpoint of improving the polishing rate, the weight-average molecular weight (Mw) of the polymer is preferably equal to or greater than the lower limit described above. From the viewpoint of planarization effect, the weight-average molecular weight (Mw) of the polymer is preferably equal to or less than the upper limit described above.

[0022] In addition to the structural unit represented by formula (A) and / or the structural unit represented by formula (B), the polymer may contain other structural units based on other monomers copolymerizable with the monomers that provide these structural units. Examples of other structural units include structural units corresponding to monomers having a polymerizable moiety such as a vinyl group or a (meth)acryloyl group. Examples include vinyl monomers such as vinyl alcohol and vinyl acetate, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, acrylonitrile, maleic acid and maleic acid esters, itaconic acid and itaconic acid esters, vinylamine, vinylpyridine, allylamine, vinylpyrrolidone, vinylcaprolactam, vinylmethylether, vinylmethyloxazolidinone, vinylformal, vinylacetal, vinylamine, vinylisobutylether, acrylamide, and methacrylamide. These structural units may be present in one or more monomers. The lower limit of the content of other structural units other than the structural unit (A) and / or the structural unit (B) in the polymer can be, for example, 1 mol% or more, 5 mol% or more, or 10 mol% or more, from the viewpoint of fully exhibiting the functions exerted by the other structural units. Similarly, the upper limit of the content of other structural units other than the structural unit (A) and / or the structural unit (B) in the polymer can be preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 30 mol% or less, based on the amount of all structural units of the polymer, from the viewpoint of fully exhibiting the functions exerted by the structural unit (A) and / or the structural unit (B). However, as mentioned above, when the polymer has a structural unit represented by formula (B) but does not have a structural unit represented by formula (A), the amount of structural units containing a betaine structure in the polymer is 0 to 9 mol%.

[0023] The method for producing a polymer containing the structural units represented by formula (A) and / or formula (B) is not particularly limited, and the polymer can be produced by a known polymerization method for producing a polymer, such as bulk polymerization, precipitation polymerization, suspension polymerization, emulsion polymerization, solution polymerization, etc. Furthermore, if a commercially available product is available, the commercially available product may be used.

[0024] In a preferred embodiment of the present invention, the polishing composition preferably contains at least a polymer containing a structural unit represented by formula (A) from the viewpoint of improving the storage stability of the polishing composition. The reason why the storage stability is improved when the polishing composition contains a polymer containing a structural unit represented by formula (A) is unclear, but it is thought that this is because the structural unit represented by formula (A) corresponds to the above-mentioned amine oxide monomer. Therefore, when the polymer containing the structural unit represented by formula (A) adheres to the abrasive grains, electrostatic repulsion occurs between the abrasive grains, making it easier to prevent the abrasive grains from aggregating. In particular, since the amine oxide structure has a direct bond between positively and negatively charged moieties, the degree of cationization on the nitrogen atom is low, which is thought to make negatively charged abrasive grains less likely to aggregate. Good storage stability of the polishing composition makes it easier to suppress the aggregation of abrasive grains and the like dispersed in the polishing composition. The presence of such aggregates in the polishing composition may cause defects on the surface of the object to be polished during the CMP process. However, this embodiment makes it possible to suppress the occurrence of such defects.

[0025] [Abrasive grains] The polishing composition of the present invention contains at least one type of abrasive grains. The abrasive grains are not particularly limited as long as they are particles that exhibit a polishing effect, and examples thereof include inorganic oxides, inorganic hydroxides, oxides of inorganic hydroxides, metal borides, metal carbides, metal nitrides, polymer particles, etc. The polishing composition may contain one type of abrasive grains or may contain two or more types of abrasive grains.

[0026] Examples of inorganic oxides include silica (SiO ２ ), alumina (Al ２ O ３ ), zirconia (ZrO ２ ), cerium oxide (ceria, CeO ２ ), manganese oxide (MnO２ ), titanium oxide (TiO ２ ), zinc oxide (ZnO), magnesium oxide (MgO), etc. Examples of inorganic hydroxides include aluminum hydroxide, etc. Examples of oxides of inorganic hydroxides include aluminum hydroxide oxide. Examples of metal borides, metal carbides, and metal nitrides include silicon carbide, silicon nitride, silicon carbonitride, boron carbide, tungsten carbide, zirconium carbide, aluminum boride, tantalum carbide, titanium carbide, etc. These abrasive grains may be, for example, organic polymer-coated oxide particles, inorganic-coated particles, etc. The abrasive grains are preferably inorganic oxides, more preferably at least one selected from the group consisting of silica, alumina, and ceria.

[0027] When the abrasive grains contain silica, the type of silica is not particularly limited, but from the viewpoint of wafer surface smoothness, colloidal silica is preferred.In addition, from the viewpoint of suppressing wafer contamination, silica obtained by hydrolysis of alkoxysilane is preferred, and colloidal silica obtained in the same manner is more preferred.

[0028] The average primary particle diameter of the abrasive grains is preferably 5 to 100 nm, more preferably 10 to 80 nm, and even more preferably 15 to 60 nm, from the viewpoint of planarization ability and polishing rate. The average primary particle diameter of the abrasive grains is determined by the specific surface area S (m ２ / g) and is measured according to the method specified in JIS-Z-8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption."

[0029] From the viewpoint of ensuring a high polishing rate and reducing surface defects (LPD) on the object to be polished, the degree of association of abrasive grains is preferably 1.1 or more and 3.0 or less, more preferably 1.8 or more and 2.5 or less. The degree of association of abrasive grains is a coefficient representing the shape of the abrasive grains, and is calculated by the following formula. The average secondary particle size is the particle size measured by dynamic light scattering, and can be measured, for example, using a commercially available dynamic light scattering device. Degree of association = average secondary particle size / average primary particle size

[0030] The lower limit of the average secondary particle diameter of the abrasive grains is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 30 nm or more, from the viewpoint of ensuring a high removal rate. The upper limit of the average secondary particle diameter of the abrasive grains is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less, from the viewpoint of reducing LPD. Therefore, the average secondary particle diameter of the abrasive grains measured by dynamic light scattering is preferably 10 to 250 nm, more preferably 20 to 200 nm, and even more preferably 30 to 150 nm.

[0031] The content of the abrasive grains is preferably 0.05 to 10 mass %, more preferably 0.1 to 8 mass %, and even more preferably 0.5 to 6 mass %, based on the total weight of the polishing composition, from the viewpoint of achieving a high polishing rate while maintaining sufficient planarization ability.

[0032] [Aqueous Medium] The polishing composition of the present invention contains at least one aqueous medium. The polishing composition may contain one type of aqueous medium or two or more types of aqueous media. Examples of aqueous media include water and mixtures of water and water-soluble solvents. Examples of water-soluble solvents include alcohols such as methanol, ethanol, and isopropanol. The water is not particularly limited, but from the viewpoint of improving safety during polishing, it is preferable to use water such as ion-exchanged water, distilled water, and ultrapure water.

[0033] The content of the aqueous medium in the polishing composition of the present invention is preferably 1.0 to 99.9 mass %, more preferably 80 to 98 mass %, and even more preferably 90 to 96 mass %, based on the total weight of the polishing composition, from the viewpoint of achieving a high removal rate while maintaining sufficient planarization ability, and from the viewpoint of the storage stability of the polishing composition.

[0034] [Other Components] The polishing composition of the present invention may optionally contain at least one other component in addition to the abrasive grains, the specific polymer, and the aqueous medium, as long as the effects of the present invention are not impaired. Examples of other components include known components that polishing compositions may contain, such as pH adjusters, polymers other than the specific polymers, polishing aids, silicon nitride polishing inhibitors, thickeners, dispersants, rust inhibitors, basic substances, and surfactants. The polishing composition may contain one other component, or two or more other components. From the viewpoint of obtaining the effects of adding these other components, the amount of these other components is preferably 0.001% by mass or more, more preferably 0.0025% by mass or more, and even more preferably 0.01% by mass or more, based on the total weight of the polishing composition. However, from the viewpoint of the polishing rate and planarization ability, it is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, based on the total weight of the polishing composition.

[0035] Examples of pH adjusters include acidic compounds, alkaline compounds, and salts thereof. The salts of acidic compounds are preferably at least one selected from alkali metal salts, ammonium salts, and amine salts of acidic compounds, more preferably ammonium salts of acidic compounds. The salts of basic compounds are preferably compounds having at least one counter ion selected from hydroxide ions, chloride ions, and iodide ions, more preferably at least one counter ion selected from hydroxide ions and chloride ions.

[0036] Examples of the acidic compound include inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid; and organic acids such as acetic acid, oxalic acid, citric acid, and malic acid. Among these, from the viewpoint of versatility, at least one selected from hydrochloric acid, nitric acid, and acetic acid is preferred, and at least one selected from hydrochloric acid and acetic acid is more preferred.

[0037] Examples of the alkaline compound include inorganic alkaline compounds such as ammonia and potassium hydroxide, and organic alkaline compounds such as alkylamines and alkanolamines. Among these, from the viewpoint of improving the quality of the semiconductor substrate, at least one selected from ammonia and alkylamines is preferred, and ammonia is more preferred.

[0038] Examples of the polishing aid include anionic surfactants and nonionic surfactants. Examples of the anionic surfactants include alkyl ether acetates, alkyl ether phosphates, and alkyl ether sulfates. Examples of the nonionic surfactants include nonionic polymers such as polyacrylamide, and polyoxyalkylene alkyl ethers.

[0039] [Polishing composition] The polishing composition can be produced by a production method that includes, for example, a dispersion containing abrasive grains and an aqueous medium, a polymer having structural unit (A) and / or structural unit (B), and, if necessary, other optional components, by a known method.The order in which these components are mixed is not particularly limited.Mixing can be carried out using, for example, a homomixer, a homogenizer, an ultrasonic disperser, a wet ball mill, etc.

[0040] From the viewpoint of achieving both an improved removal rate and storage stability, the pH of the polishing composition is preferably 8.0 to 14.0, more preferably 8.5 to 13.5, and even more preferably 9.0 to 13.0. The pH can be measured using a commercially available pH meter. For example, the pH may be adjusted to the above range by adding a pH adjuster to the polishing composition.

[0041] From the viewpoints of improving the removal rate and storage stability, the solid content of the polishing composition is preferably 1 to 40 wt %, more preferably 2 to 30 wt %, and even more preferably 4 to 20 wt %, based on the total weight of the polishing composition. The solid content can be measured, for example, by the charge ratio, and is the weight excluding the aqueous medium.

[0042] [Polishing Method] The composition of the present invention can be usefully used as a polishing composition in a polishing step in the manufacturing process of a semiconductor wafer. In particular, it can be preferably used as a CMP slurry in a CMP step, and may be used as a polishing composition in a known manufacturing process of a semiconductor wafer.

[0043] The present invention will be described in more detail below with reference to examples, but these examples are not intended to limit the scope of the present invention. In the examples, "%" and "parts" represent "% by mass" and "parts by mass", respectively, unless otherwise specified.

[0044] The physical properties of the polymer or polishing composition were measured by the following methods.

[0045] (Weight-average molecular weight) The weight-average molecular weight of each polymer was calculated based on the peaks in a chromatogram obtained by performing GPC under the following conditions: Apparatus: HLC-8320 GPC (Tosoh Corporation, detector integrated type) Column: Wakobeads-G50 + Wakobeads-G40 (both Fujifilm Wako Pure Chemical Industries, Ltd.) Eluent: distilled water: methanol: acetic acid: sodium acetate = 936:624:46.8:64 (mass ratio) Flow rate: 0.7 mL / min Column temperature: 30°C Differential refractive index detector: Schoddex RI SE-61 (Resonac Corporation) Standard substance: monodisperse polyethylene glycol with known molecular weight

[0046] (pH of polishing composition) This is a value measured using a commercially available pH meter (Castany ACT pH meter, manufactured by Horiba, Ltd.), and is the value measured 1 minute after immersing the measuring electrode of the pH meter in each polishing composition.

[0047] Synthesis Example 1: Synthesis of p-DMAPMA 136.8 g of ultrapure water, 7.2 g of isopropyl alcohol, and 16.0 g of N-(3-dimethylaminopropyl)methacrylamide (Tokyo Chemical Industry Co., Ltd.) were placed in a 200 mL three-neck flask equipped with a dropping tank, a thermometer, and a stirrer, and the temperature was raised to 80°C. 0.272 g of VA-044 (Fujifilm Wako Pure Chemical Industries, Ltd.) was then added, and the temperature was maintained. Stirring was then continued for 19.5 hours while maintaining the temperature, and the mixture was then returned to room temperature, yielding p-DMAPMA. The weight-average molecular weight of the resulting p-DMAPMA was 66,000.

[0048] (Synthesis Example 2: Synthesis of p-DMAPMA-O) p-DMAPMA was synthesized in the same manner as in Synthesis Example 1. 75.0 g of the obtained p-DMAPMA was placed in a 100 mL three-neck flask, and the temperature was raised to 75°C, and 4.27 g of 35% aqueous hydrogen peroxide (Tokyo Chemical Industry Co., Ltd.) was added dropwise over 2 hours. After the dropwise addition was completed, the temperature was raised to 80°C, and stirring was continued for 24 hours while maintaining the temperature, and then the temperature was returned to room temperature, thereby obtaining p-DMAPMA-O. The weight-average molecular weight of the obtained p-DMAPMA-O was 67,000.

[0049] Synthesis Example 3: Synthesis of p-MEB1 (Mw: 7,000) 125.3 g of ultrapure water and 34.7 g of N-(2-carboxyethyl)-N-methacryloxyethyl-N,N-dimethylammonium betaine (manufactured by Osaka Organic Chemical Industry Ltd.) were placed in a 200 mL three-neck flask equipped with a dropping tank, a thermometer, and a stirrer, and the temperature was raised to 80°C, after which 0.384 g of VA-044 was added dropwise. Stirring was continued for 24 hours while maintaining the temperature, and then the temperature was returned to room temperature, yielding p-MEB1. The weight-average molecular weight was 7,000.

[0050] Synthesis Example 4: Synthesis of p-MEB2 (Mw: 41,000) 125.3 g of ultrapure water and 34.7 g of N-(2-carboxyethyl)-N-methacryloxyethyl-N,N-dimethylammonium betaine (manufactured by Osaka Organic Chemical Industry Ltd.) were placed in a 200 mL three-neck flask equipped with a dropping tank, a thermometer, and a stirrer, and the temperature was raised to 90°C, after which 0.384 g of VA-044 was added dropwise. Stirring was continued for 22 hours while maintaining the temperature, and then the temperature was returned to room temperature, yielding p-MEB2. The weight-average molecular weight was 41,000.

[0051] (Synthesis Example 5: Synthesis of p-MEB3 (Mw: 126,000)) p-MEB3 was obtained in the same manner as in Synthesis Example 4, except that the temperature was 70°C instead of 80°C and the stirring time was 18 hours instead of 15 hours. The weight average molecular weight was 126,000.

[0052] (Synthesis Example 6: Synthesis of PVP (Mw: 36,000)) 144.0 g of ultrapure water and 16.0 g of 1-vinyl-2-pyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd.) were placed in a 200 mL three-neck flask equipped with a dropping tank, a thermometer, and a stirrer, and the temperature was raised to 90°C, after which 0.256 g of VA-044 was added dropwise. Stirring was continued for 16 hours while maintaining the temperature, and then the temperature was returned to room temperature, yielding PVP. The weight-average molecular weight was 36,000.

[0053] (Synthesis Example 7: Synthesis of p-DMAPAA-Q (Mw: 34,000)) 131.7 g of ultrapure water, 6.9 g of isopropyl alcohol, and 21.3 g of N-[3-(dimethylamino)propyl]acrylamide-methyl chloride quaternary salt (manufactured by KJ Chemicals Corporation) were placed in a 200 mL three-neck flask equipped with a dropping tank, a thermometer, and a stirrer, and the temperature was raised to 80°C, and 0.192 g of V-601 (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added dropwise. Stirring was continued for 16 hours while maintaining the temperature, and then the temperature was returned to room temperature, thereby obtaining p-DMAPAA-Q. The weight-average molecular weight was 34,000.

[0054] Preparation Example 1: Preparation of Silica Slurry Snowtex 30L (Nissan Chemical Industries, Ltd.) was diluted 6 times with ultrapure water to obtain a silica slurry containing 5% by mass of abrasive grains (silica). The average primary particle diameter of the silica was 45 nm.

[0055] (Examples 1 and 2, Comparative Examples 1 to 6) A polishing composition containing each polymer was prepared by diluting the polymer obtained in each of the above Synthesis Examples to a solids concentration of 500 mass ppm and the silica slurry obtained in Preparation Example 1 with ultrapure water to a solids concentration of 5.0 mass %. Comparative Example 1 did not contain the polymer according to each of the above Synthesis Examples.

[0056] (Polishing Step) Polishing compositions prepared according to the methods described in the above Examples and Comparative Examples were used as CMP slurries, and polishing was carried out using a polishing apparatus under the following conditions, and the polishing rate was calculated according to the following method. Polishing was carried out six times under the same conditions, and the average of the obtained polishing rates was taken as the polishing rate. The same applies to the Ra value. Polishing apparatus: SPL-15F (single-sided polishing machine) manufactured by Okamoto Machine Tool Works, Ltd. Polishing pad: SUBA-800 manufactured by Nitta DuPont Co., Ltd. Polishing object: silicon wafer Platen rotation speed: 60 rpm Head rotation speed: 60 rpm Polishing load: 10.6 kPa Polishing liquid supply rate: 20 mL / min Polishing time: 10 minutes

[0057] The polishing rate and flattening effect in the polishing step were evaluated according to the following methods, and the results are shown in Table 1.

[0058] (Polishing Rate) The weight of the object to be polished before and after polishing was measured using a precision balance, and the resulting weight difference was divided by the density, area, and polishing time of the silicon substrate to determine the single-side polishing rate per unit time. The weight of the object to be polished after polishing is the weight after the object to be polished after polishing was washed with ultrapure water and dried. Table 1 also shows the ratio of the polishing rate in each Example and Comparative Example, where the polishing rate in Comparative Example 1, in which no polymer was used, is set to 1. A larger ratio of the polishing rate indicates that the polishing rate was increased by using the resin. Polishing rate (μm / min) = {(weight of object before polishing [g] - weight of object after polishing [g]) × 10,000} / (density of object to be polished [g / cm ３] × area of ​​polished surface [cm ２ ]×Polishing time [min])

[0059] (Planarization effect) Using a white light interference microscope (Zygo NewView 7300), 17 points were measured on the surface (polished surface) of the polished object after polishing, and the average Ra value was calculated to calculate the surface roughness of the polished object after polishing. Table 1 also shows the ratio of the Ra values ​​in each example and comparative example, assuming that the Ra value in Comparative Example 1, which does not use a polymer, is 1. The smaller the Ra value, the higher the surface planarization effect, and the smaller the ratio of the Ra value, the more the planarization effect is improved by using the resin.

[0060]

[0061] It was confirmed that when the polishing composition described in the examples, which contains abrasive grains, a polymer having a structural unit represented by formula (A) and / or a structural unit represented by formula (B), and an aqueous medium, was used, the polishing rate was improved and the planarization effect was also high compared to when a polishing composition not containing a polymer was used.

Claims

1. An abrasive grain, a constitutional unit represented by formula (A) and / or a constitutional unit represented by formula (B): [In the formula (A) and the formula (B), X １ and X ２ each independently represents -N(-H)- or -O-; R １ and R ５ each independently represents a linear or branched alkylene group having 1 to 6 carbon atoms; R ２ , R ３ , R ６ and R ７ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms; R ４ and R ８ each independently represents a hydrogen atom or a methyl group], and an aqueous medium, provided that when the polymer has a structural unit represented by formula (B) but does not have a structural unit represented by formula (A), the amount of structural units containing a betaine structure in the polymer is 0 to 9 mol %.

2. The polishing composition according to claim 1, wherein the weight average molecular weight of the polymer is 1,000 to 1,000,000.

3. The polishing composition according to claim 1 or 2, wherein the amount of the structural unit represented by formula (A) and / or the structural unit represented by formula (B) in the polymer is 5 to 100 mol % based on the amount of all structural units of the polymer.

4. X in formula (A) and formula (B) １ and X ２ The polishing composition according to claim 1 or 2, wherein represents --N(--H)--.

5. The polishing composition according to claim 1 or 2, wherein the amount of the polymer contained in the polishing composition is 0.0005 to 5 mass % based on the total amount of the polishing composition.

6. The polishing composition according to claim 1 or 2, wherein the abrasive particles are silica particles.

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