Colloidal silica and method for producing same

Abstract

The present invention provides a colloidal silica having few fine particles. Also provided is a method for producing a colloidal silica.

Description

Colloidal silica and its manufacturing method

[0001] The present invention relates to colloidal silica with a low content of fine particles.

[0002] In the CMP (Chemical Mechanical Polishing) process used in semiconductor manufacturing, the residue of particles on the polished surface is a frequent problem, which can lead to a decrease in yield in semiconductor manufacturing.

[0003] As semiconductors become increasingly miniaturized, there is a demand for further reduction in the amount of particles remaining on the polished surface, and accordingly, there is a demand for a reduction in the amount of particles contained in CMP slurries.

[0004] Colloidal silica is used as an abrasive raw material for CMP slurries. Colloidal silica usually contains a small amount of fine particles that are smaller than the main particles, and these fine particles can cause the problem of remaining on the polishing surface.

[0005] Conventionally, methods for producing colloidal silica with few fine particles have been disclosed (Patent Documents 1 and 2). Patent Document 1 discloses that in the hydrolysis and condensation reaction of an alkoxysilane or its condensate, a silica sol with few fine particles can be obtained by adjusting the reaction conditions so that the electrical conductivity value does not change by 90% or more from 5 minutes after the start of the reaction when the electrical conductivity first reaches a maximum until the end of the reaction. Patent Document 2 discloses that in the hydrolysis and condensation reaction of a tetraalkoxysilane, a silica sol with few fine particles can be obtained by keeping the change in water concentration in the reaction system within 3% by mass from the start of the hydrolysis and condensation reaction to the end of the reaction.

[0006] Other methods disclosed include solvent substitution of produced colloidal silica by thermal distillation to reduce the organic solvent concentration to less than 1% by mass (Patent Document 3), addition of a neutral oxidizing agent (Patent Document 4), and ultrafiltration using an ultrafiltration membrane to reduce fine particles (Patent Document 5). Patent Document 3 discloses distilling off the organic solvent coexisting with colloidal silica produced by the sol-gel method to reduce the residual organic solvent concentration in the colloidal silica to less than 1% by mass, thereby obtaining colloidal silica with a number distribution ratio of fine particles having a particle size of 40% or less of the volume average particle size of 10% or less. Patent Document 4 discloses adding a neutral oxidizing agent (including hydrogen peroxide) to a silica sol produced by the sol-gel method to obtain a silica sol with a low intermediate product (unreacted material). Patent Document 5 discloses that intermediate products are removed by ultrafiltration of a silica sol obtained by subjecting tetraalkoxysilane to hydrolysis and condensation reaction using an ultrafiltration membrane with a molecular weight cutoff of 5,000 to 80,000.

[0007] Even with these conventional techniques, colloidal silica with reduced particulate content to a level that satisfies the requirements of semiconductor CMP processes at advanced technology nodes has not yet been obtained.

[0008] Japanese Patent Publication No. 2020-164351 Japanese Patent Publication No. 2022-109711 International Publication No. WO2016 / 117560A1 Japanese Patent Publication No. 2020-75830 Japanese Patent Publication No. 2021-116208

[0009] The present invention provides colloidal silica with few fine particles.

[0010] As a result of extensive research, the inventors of the present invention have developed a technology that enables the production of colloidal silica with a low content of fine particles by including a specific heat treatment in the colloidal silica production process.

[0011] The present invention encompasses the following colloidal silica and a method for producing colloidal silica.

[0012] Item 1. A method for producing colloidal silica, comprising the step of heat-treating a silica sol comprising water and silica particles at the boiling point of water under normal pressure.

[0013] Item 2. The pH of the silica sol during the heat treatment is pH 9.0 to pH 10.5, the heat treatment time is 11 hours to 35 hours, and the heat treatment is performed at 1 m of silica sol. 3 The stirring power per unit is 0.01kW / m 3 ~0.40kW / m 3 Item 2. The method for producing colloidal silica according to Item 1, wherein the silica sol is stirred under the following conditions:

[0014] Item 3. The method for producing colloidal silica according to Item 1 or 2, wherein the silica sol is obtained by: (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions where the addition rate of the alkoxysilane contained in solution B per 1 kg of solution A is 0.8 mol / hour / kg to 2.50 mol / hour / kg.

[0015] Item 4. The method for producing colloidal silica according to Item 1 or 2, wherein the silica sol is obtained by (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst, and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions in which the concentration of the alkoxysilane contained in solution B is 60% by mass to 98% by mass.

[0016] Item 5. Colloidal silica, wherein the fine particle content parameter 1, defined as follows, is 15.0 or less.

[0017] Definition of Fine Particle Content Parameter 1 (i) Colloidal silica is diluted with ultrapure water (hereinafter referred to as "ultrapure water") having an electrical resistivity of 18.2 MΩ or more to a silica concentration of 2 mass % (wt%) (diluted solution).

[0018] (ii) 9.1 g of the diluted solution is transferred to a centrifuge tube (model number: S303922A) manufactured by Eppendorf-Himac Technologies Co., Ltd., and centrifuged using a centrifugal rotor S58A and a centrifuge CS100FNX at a centrifugal speed of 50,000 rpm, a centrifugation temperature of 5°C, and a centrifugation time of 60 minutes (all manufactured by Eppendorf-Himac Technologies Co., Ltd.).

[0019] (iii) After centrifugation, 2 mL of the supernatant was collected from the centrifuge tube, and this 2 mL of the supernatant after centrifugation was mixed with silica sol prepared by diluting ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Co., Ltd. 10 times with ultra-pure water in the following mass ratio (mixture).

[0020] After centrifugation, the supernatant: 10-fold diluted solution of PL-3 = 9:1 (mass ratio) (iv) The particle size distribution of the resulting mixture is measured using a particle size distribution measuring device based on scanning electrical mobility diameter measurement method.

[0021] (v) The value calculated from the measured particle size distribution using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica.

[0022] Equation (1) Fine particle content parameter 1 = (total number of detected particles of 15 nm or less) ÷ (total number of detected particles of 25 nm or more) The colloidal silica of the present invention has a low fine particle content. When CMP is performed using the colloidal silica of the present invention as an abrasive, the amount of fine particles remaining on the polished surface is significantly reduced compared to when conventional colloidal silica is used as an abrasive, and the surface roughness of the polished surface can also be reduced.

[0023] The present invention can provide colloidal silica with few fine particles.

[0024] The present invention will be described in detail below.

[0025] The embodiments of the present invention are intended to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the content of the invention.

[0026] In this specification, the terms "comprise" and "contain" are concepts that encompass all of "comprise," "consist essentially of," and "consist only of."

[0027] In this specification, when a numerical range is expressed as "A to B," it means "A or more, and B or less."

[0028] In this specification, the expressions parts, % and the like are generally used.

[0029] In this specification, unless otherwise specified, all parts by mass or % by mass (wt%) are used.

[0030] [1] Method for Producing Colloidal Silica The present invention includes a method for producing colloidal silica.

[0031] The method for producing colloidal silica of the present invention includes a step of heat-treating a silica sol consisting of water and silica particles at the boiling point of water under normal pressure.

[0032] The pH of the silica sol during the heat treatment is preferably from pH 9.0 to pH 10.5.

[0033] The heat treatment time is preferably 11 to 35 hours.

[0034] The heat treatment is preferably carried out by heating the silica sol. 3 The stirring power per unit is 0.01kW / m 3 ~0.40kW / m 3 The silica sol is stirred under the conditions described above.

[0035] The silica sol (a silica sol composed of water and silica particles) is preferably a silica sol obtained by: (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under the conditions that the addition rate of the alkoxysilane contained in the solution B per 1 kg of the solution A is 0.8 mol / hour / kg to 2.50 mol / hour / kg.

[0036] The term "mol / hour / kg" indicates the mass of alkoxysilane added per hour to 1 kg of solution A, converted into the amount of silica.

[0037] The silica sol (a silica sol composed of water and silica particles) is preferably obtained by: (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions in which the concentration of the alkoxysilane contained in the solution B is 60% by mass to 98% by mass.

[0038] The colloidal silica of the present invention has a low content of fine particles. When CMP is performed using the colloidal silica obtained by the production method of the present invention as an abrasive, the amount of fine particles remaining on the polished surface is significantly reduced, and the surface roughness of the polished surface can also be reduced.

[0039] The method for producing colloidal silica of the present invention preferably involves a series of operations: (i) synthesizing silica particles by an alkoxide method (particle synthesis), (ii) concentrating the particle concentration by thermal distillation (thermal concentration), (iii) substituting the solvent with water by thermal distillation (heated water substitution), and (iv) reducing the fine particles by heat treatment (heat treatment), thereby enabling the production of colloidal silica with a small number of fine particles.

[0040] (1) Silica Particle Synthesis Step In the colloidal silica production method of the present invention, silica particles are preferably prepared by hydrolyzing and dehydrating condensation of an alkoxysilane to obtain a silica sol (particle synthesis step by the alkoxide method).

[0041] Three-liquid method (method for synthesizing silica particles) The synthesis of silica particles is preferably a three-liquid method, in which a solution B containing alkoxysilane (tetraalkoxysilane) and a solution C containing water are added to a solution A containing water, an alkali catalyst, and an alcohol, and the alkoxysilane (tetraalkoxysilane) is subjected to a hydrolysis reaction and a condensation reaction to synthesize silica particles. By preferably adopting the three-liquid method for synthesizing silica particles, excellent controllability of the hydrolysis reaction and the condensation reaction is achieved.

[0042] Solution A (Three-liquid Method) In the synthesis of silica particles, a three-liquid method is employed, and the water concentration (mass %, wt%) of Solution A is preferably 3 wt% to 25 wt%, more preferably 3 wt% to 23 wt%, even more preferably 3 wt% to 20 wt%, and most preferably 3 wt% to 18 wt%. By adjusting the water concentration of Solution A to preferably 3 wt% to 25 wt%, the solubility of silicic acid produced by the hydrolysis reaction in the reaction solution is excellent.

[0043] In the synthesis of silica particles, a three-liquid method is employed, and the alkali catalyst concentration (mass %, wt%) of Solution A is preferably 0.1 wt% to 3.0 wt%, more preferably 0.2 wt% to 2.5 wt%, even more preferably 0.3 wt% to 2.0 wt%, and most preferably 0.5 wt% to 1.6 wt%. By adjusting the alkali catalyst concentration of Solution A to preferably 0.1 wt% to 3.0 wt%, aggregation of silica particles is suppressed, and excellent dispersion stability of the silica particles in the dispersion is achieved.

[0044] The alkali catalyst is preferably an organic base catalyst containing no metal component, in order to avoid contamination with metal impurities, and more preferably an organic base catalyst containing nitrogen.

[0045] The alkaline catalyst is preferably ammonia.

[0046] The organic base catalyst is preferably ethylenediamine, diethylenetriamine, triethylenetetraamine, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, 3-ethoxypropylamine (3-EOPA), dipropylamine, triethylamine, or the like.

[0047] Ammonia is preferably used because it has an excellent catalytic action, is highly volatile, and can be easily removed in a subsequent step.

[0048] From the viewpoint of increasing the true specific gravity of the silica particles, it is preferable to select an organic base catalyst with a boiling point of 90°C or higher so that it is less likely to volatilize even when the reaction temperature is increased. Preferably, tetramethylammonium hydroxide, 3-ethoxypropylamine, etc. are used.

[0049] The alkali catalyst may be used alone or in the form of a mixture (blend) of two or more kinds.

[0050] The alcohol is preferably methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1,4-butanediol, or the like.

[0051] The alcohol may be used alone or in the form of a mixture (blend) of two or more kinds.

[0052] Solution B (three-component method) The silica sol is preferably obtained by: (a) adding solution B containing an alkoxysilane to solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions in which the concentration (mass %, wt %) of the alkoxysilane contained in solution B is 60 mass % to 98 mass %.

[0053] In the synthesis of silica particles, a three-liquid method is employed, and the alkoxysilane concentration in Solution B is preferably 60 wt% to 98 wt%, more preferably 65 wt% to 98 wt%, even more preferably 68 wt% to 98 wt%, and most preferably 70 wt% to 95 wt%. By adjusting the alkoxysilane concentration in Solution B to preferably 60 wt% to 98 wt%, the amount of solvent used can be reduced, resulting in excellent productivity of silica particles.

[0054] The silica sol is preferably a silica sol obtained by: (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions in which the addition rate of the alkoxysilane contained in the solution B per 1 kg of the solution A is 0.8 mol / hour / kg to 2.50 mol / hour / kg.

[0055] In the synthesis of silica particles, a three-liquid method is employed, and the addition rate (mol / hr / kg) of the alkoxysilane in Solution B is preferably 0.8 mol / hr / kg to 2.5 mol / hr / kg, more preferably 1.1 mol / hr / kg to 2.4 mol / hr / kg. By adjusting the addition rate of the alkoxysilane in Solution B to preferably 0.8 mol / hr / kg to 2.5 mol / hr / kg, the reaction time is shortened and productivity is excellent.

[0056] The term "mol / hour / kg" indicates the mass of alkoxysilane added per hour to 1 kg of solution A, converted into the amount of silica.

[0057] The alkoxysilane is preferably a tetra-C alkoxysilane such as tetramethoxysilane (TMOS), tetraethoxysilane, or tetraisopropoxysilane. 1-8 An alkoxysilane is used. The alkoxysilane is preferably tetra C 1-4 Alkoxysilane is used, and more preferably, tetramethoxysilane (TMOS), tetraethoxysilane, or the like is used.

[0058] The alkoxysilane may be used alone or in the form of a mixture (blend) of two or more kinds.

[0059] The alcohol is preferably methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1,4-butanediol, or the like.

[0060] The alcohol may be used alone or in the form of a mixture (blend) of two or more kinds.

[0061] Solution C (Three-component Method) In the synthesis of silica particles, a three-component method is used, and the alkali catalyst concentration (mass %, wt%) of Solution C is preferably 0 wt% to 9 wt%, more preferably 0 wt% to 8 wt%, even more preferably 0 wt% to 7 wt%, and most preferably 0 wt% to 6 wt%. By adjusting the alkali catalyst concentration of Solution C to preferably 0 wt% to 9 wt%, the reaction does not proceed excessively slowly, and excellent controllability is achieved.

[0062] The alkaline catalyst is preferably ammonia.

[0063] The organic base catalyst is preferably ethylenediamine, diethylenetriamine, triethylenetetraamine, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, 3-ethoxypropylamine, dipropylamine, triethylamine, or the like.

[0064] Ammonia is preferably used because it has an excellent catalytic action, is highly volatile, and can be easily removed in a subsequent step.

[0065] From the viewpoint of increasing the true specific gravity of the silica particles, it is preferable to select an organic base catalyst with a boiling point of 90°C or higher so that it is less likely to volatilize even when the reaction temperature is increased. Preferably, tetramethylammonium hydroxide, 3-ethoxypropylamine, etc. are used.

[0066] The alkali catalyst may be used alone or in the form of a mixture (blend) of two or more kinds.

[0067] Hydrolysis reaction and condensation reaction In the synthesis of silica particles, a three-liquid method is used, and the maximum water concentration (mass % (wt%)) in the reaction system from the start of the hydrolysis reaction and condensation reaction to the end of the reaction is preferably 28 wt% or less, more preferably 25 wt% or less, even more preferably 20 wt% or less, and most preferably 18 wt% or less. By adjusting the maximum water concentration in the reaction system from the start of the hydrolysis reaction and condensation reaction to the end of the reaction, preferably 28 wt% or less, the solubility of alkoxysilane (tetraalkoxysilane, etc.) in the reaction solution is improved, and the generation of fine silica particles can be suppressed.

[0068] In the synthesis of silica particles, a three-liquid method is used, and the change in water concentration (mass % (wt%)) in the reaction system from the start of the hydrolysis reaction and condensation reaction to the end of the reaction is preferably 15 wt% or less, more preferably 13 wt% or less, even more preferably 11 wt% or less, and most preferably 8 wt% or less. By adjusting the change in water concentration in the reaction system from the start of the hydrolysis reaction and condensation reaction to the end of the reaction, preferably 15 wt% or less, the solubility of silicic acid produced by the reaction is maintained, and the generation of fine silica particles can be suppressed.

[0069] In the synthesis of silica particles, a three-liquid method is employed, and the reaction temperature (°C) is preferably 10°C to 80°C, more preferably 12°C to 70°C, even more preferably 15°C to 60°C, and most preferably 18°C ​​to 55°C. By adjusting the reaction temperature for the synthesis of silica particles to preferably 10°C to 80°C, the reaction does not proceed excessively slowly, and excellent controllability is achieved.

[0070] In the method for producing colloidal silica of the present invention, in addition to a production method in which an alkoxysilane is hydrolyzed and subjected to dehydration condensation to obtain a silica sol (a method for synthesizing silica particles by the alkoxide method), a production method in which sodium silicate is ion-exchanged to prepare active silicic acid, and then condenses silicic acid species under basic conditions to obtain a silica sol may also be used.

[0071] (2) Heat Concentration Step The colloidal silica production method of the present invention preferably includes a heat concentration step, in which the particle concentration is concentrated by heat distillation. By including the heat concentration step in the colloidal silica production method, it is possible to reduce the number of fine silica particles contained in the colloidal silica.

[0072] In the heat concentration step, the Pv value (stirring power per unit volume) is preferably 0.01 kW / m 3 ~0.40kW / m 3 and more preferably 0.01 kW / m 3 ~0.30kW / m 3 and more preferably 0.01 kW / m 3 ~0.20kW / m 3 and most preferably 0.01 kW / m 3 ~0.10kW / m 3 The Pv value of the heat concentration treatment is preferably 0.40 kW / m 3 By adjusting the following, the concentration and temperature of the silica particles can be made uniform and the Pv value can be kept below a certain value, thereby suppressing aggregation of the silica particles.

[0073] The heating and concentration time (minutes, min) in the heating and concentration step is preferably 60 to 600 minutes. By adjusting the heating and concentration time in the heating and concentration step to preferably 60 to 600 minutes, it is possible to reduce the fineness of the silica particles without significantly changing the average secondary particle size or degree of association of the silica particles.

[0074] (3) Heating and Water Substitution Step (Production of Silica Sol Consisting of Water and Silica Particles) The colloidal silica to be subjected to the heat treatment is preferably one in which the silica particle concentration has been concentrated by heat distillation and the solvent has been substituted with water. By performing heat concentration and heat water substitution under the conditions below, the content of fine particles of 15 nm or less can be reduced from the level before the heat treatment. By heat treating the colloidal silica with a low fine particle content obtained by heat concentration and heat water substitution under the conditions below under the above conditions, colloidal silica with an even lower fine particle content can be obtained.

[0075] The method for producing colloidal silica of the present invention preferably includes a heated water substitution step in which the solvent is substituted with water by heated distillation. By including the heated water substitution step in the method for producing colloidal silica, it is possible to reduce the number of fine silica particles contained in the colloidal silica.

[0076] In the heated water replacement step, the Pv value (stirring power per unit volume) is preferably 0.01 kW / m 3 ~0.40kW / m 3 and more preferably 0.01 kW / m 3 ~0.30kW / m 3 and more preferably 0.01 kW / m 3 ~0.20kW / m 3 and most preferably 0.01 kW / m 3 ~0.10kW / m 3 The Pv value of the heated water replacement treatment is preferably 0.40 kW / m 3 By adjusting the following, the concentration and temperature of the silica sol can be made uniform and the Pv value can be kept below a certain value, thereby suppressing the aggregation of silica particles.

[0077] The hot water replacement time (minutes, min) in the hot water replacement step is preferably 60 to 600 minutes. By adjusting the hot water replacement time in the hot water replacement step to preferably 60 to 600 minutes, it is possible to reduce the fineness of the silica particles without significantly changing the average secondary particle size or degree of association of the silica particles.

[0078] In the heated water replacement step, the methanol concentration (ppm) after the heated water replacement is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, even more preferably 1,000 ppm or less, and most preferably 500 ppm or less. By adjusting the methanol concentration after the heated water replacement to preferably 10,000 ppm or less, it is possible to reduce the fine silica particles contained in the colloidal silica.

[0079] (4) Heat Treatment Step (Method for Producing Colloidal Silica) The colloidal silica to be subjected to the heat treatment is preferably obtained by concentrating the silica particles and substituting the solvent with water through heat distillation. By heat concentration and substituting with heated water, it is possible to reduce the content of silica particles of 15 nm or less from the point before the heat treatment. By heat treating the colloidal silica with a low content of silica particles obtained through heat concentration and substituting with heated water, it is possible to obtain colloidal silica with an even lower content of silica particles.

[0080] The method for producing colloidal silica of the present invention includes a step of heat-treating a silica sol composed of water and silica particles at the boiling point of water under normal pressure. In the method for producing colloidal silica of the present invention, the heat treatment can reduce the number of fine silica particles contained in the colloidal silica.

[0081] In the heat treatment step, the heating temperature is the boiling point of water under reflux, which makes it possible to reduce the fineness of the silica particles without significantly changing the average secondary particle size or degree of association of the silica particles.

[0082] In the heat treatment step, heating is performed at atmospheric pressure, which makes it possible to reduce the fineness of the silica particles without significantly changing the average secondary particle size or degree of association of the silica particles.

[0083] The pH of the silica sol during the heat treatment is preferably from pH 9.0 to pH 10.5.

[0084] The pH of the silica sol is preferably adjusted to pH 9.0 to pH 10.5 using 3-ethoxypropylamine (3-EOPA), ammonia, ethylenediamine, diethylenetriamine, or the like.

[0085] The minimum pH value of the silica sol during the heat treatment is preferably 9.0 or higher, more preferably 9.2 or higher, even more preferably 9.4 or higher, and most preferably 9.5 or higher. By adjusting the minimum pH value of the silica sol during the heat treatment to preferably 9.0 or higher, it is possible to reduce the number of fine silica particles contained in the colloidal silica.

[0086] The maximum pH value of the silica sol during the heat treatment is preferably 10.5 or less, more preferably 10.3 or less, even more preferably 10.1 or less, and most preferably 10.0 or less. By adjusting the maximum pH value of the silica sol during the heat treatment to preferably 10.5 or less, aggregation of silica particles can be suppressed.

[0087] The heat treatment is preferably carried out with 1 ml of silica sol. 3 The stirring power per unit (Pv value) is 0.01kW / m 3 ~0.40kW / m 3 The silica sol is stirred under the conditions described above.

[0088] In the heat treatment step, the Pv value (stirring power per unit volume) is preferably 0.01 kW / m 3 ~0.40kW / m 3 and more preferably 0.01 kW / m 3 ~0.30kW / m 3 and more preferably 0.01 kW / m 3 ~0.20kW / m 3 and most preferably 0.01 kW / m 3 ~0.10kW / m 3 The Pv value during the heat treatment is preferably 0.40 kW / m 3 By adjusting the following, the concentration and temperature of the silica sol can be made uniform and the Pv value can be kept below a certain value, thereby suppressing the aggregation of silica particles.

[0089] The heat treatment time is preferably 11 to 35 hours. In the heat treatment step, the heating time (hours) is preferably 11 to 35 hours, more preferably 12 to 30 hours, even more preferably 14 to 28 hours, and most preferably 15 to 25 hours. By adjusting the heat treatment time to preferably 11 to 35 hours, it is possible to reduce the fineness of the silica particles without significantly changing the average secondary particle size or degree of association of the silica particles.

[0090] In the heat treatment step, the concentration (mass % (wt%)) of the silica sol during heating is preferably 2 wt% to 50 wt%, more preferably 4 wt% to 45 wt%, even more preferably 6 wt% to 40 wt%, and most preferably 8 wt% to 35 wt%. By adjusting the concentration of the silica sol during heat treatment to preferably 2 wt% to 50 wt%, it is possible to reduce the fineness of the silica particles without significantly changing the average secondary particle size or degree of association of the silica particles.

[0091] [2] Colloidal silica The present invention includes colloidal silica.

[0092] The colloidal silica of the present invention has a fine particle content parameter 1 defined as follows: 15.0 or less.

[0093] Definition of Fine Particle Content Parameter 1 (i) Colloidal silica is diluted with ultrapure water (hereinafter referred to as "ultrapure water") having an electrical resistivity of 18.2 MΩ or more to a silica concentration of 2 mass % (wt%) (diluted solution).

[0094] (ii) 9.1 g of the diluted solution is transferred to a centrifuge tube (model number: S303922A) manufactured by Eppendorf-Himac Technologies Co., Ltd., and centrifuged using a centrifugal rotor S58A and a centrifuge CS100FNX at a centrifugal speed of 50,000 rpm, a centrifugation temperature of 5°C, and a centrifugation time of 60 minutes (all manufactured by Eppendorf-Himac Technologies Co., Ltd.).

[0095] (iii) After centrifugation, 2 mL of the supernatant was collected from the centrifuge tube, and this 2 mL of the supernatant after centrifugation was mixed with silica sol prepared by diluting ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Co., Ltd. 10 times with ultra-pure water in the following mass ratio (mixture).

[0096] Supernatant after centrifugation: 10-fold diluted solution of PL-3 = 9:1 (mass ratio)

[0097] (iv) The particle size distribution of the resulting mixture is measured using a particle size distribution measuring device based on scanning electrical mobility diameter measurement.

[0098] (v) The value calculated from the measured particle size distribution using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica.

[0099] Equation (1) Fine particle content parameter 1=(total number of detected particles of 15 nm or less)÷(total number of detected particles of 25 nm or more) The colloidal silica of the present invention has (i) an average secondary particle diameter of 20 nm to 250 nm, and (ii) a fine particle content parameter 1 of 15.0 or less.

[0100] The colloidal silica of the present invention has a low content of fine particles. When CMP is performed using the colloidal silica obtained by the production method of the present invention as an abrasive, the amount of fine particles remaining on the polished surface is significantly reduced, and the surface roughness of the polished surface can also be reduced.

[0101] The silica concentration (mass %, wt%) of the colloidal silica is preferably 2 wt% to 55 wt%, more preferably 2 wt% to 50 wt%, even more preferably 2 wt% to 45 wt%, and most preferably 3 wt% to 40 wt%. By adjusting the silica concentration of the colloidal silica to preferably 2 wt% to 55 wt%, an excellent polishing rate can be achieved.

[0102] [3] Method for Evaluating Physical Properties of Colloidal Silica In the present invention, the physical properties of silica particles are evaluated as follows.

[0103] (1-1) Method for measuring particle content parameter 1 (i) Add ultrapure water (hereinafter referred to as "ultrapure water") with an electrical resistivity of 18.2 MΩ or more to the colloidal silica sample to be measured, and dilute it to a silica concentration of 2 mass % (wt%) (diluted solution).

[0104] (ii) 9.1 g of the diluted solution is transferred to a centrifuge tube (model number: S303922A) manufactured by Eppendorf-Himac Technologies Co., Ltd., and centrifuged using a centrifugal rotor S58A and a centrifuge CS100FNX at a centrifugal speed of 50,000 rpm, a centrifugation temperature of 5°C, and a centrifugation time of 60 minutes (all manufactured by Eppendorf-Himac Technologies Co., Ltd.).

[0105] (iii) After centrifugation, 2 mL of the supernatant was collected from the centrifuge tube, and this 2 mL of the supernatant after centrifugation was mixed with silica sol prepared by diluting ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Co., Ltd. 10 times with ultra-pure water in the following mass ratio.

[0106] The supernatant after centrifugation: 10-fold diluted solution of PL-3 = 9:1 (mass ratio) The resulting mixture was designated as measurement sample 1.

[0107] (iv) The particle size distribution of the measurement sample 1 is measured using a particle size distribution measuring device based on a scanning electrical mobility diameter measurement method. An example of a particle size distribution measuring device based on a scanning electrical mobility diameter measurement method is the Liquid Nanoparticle Sizer System Model 9310 (LNS) manufactured by KANOMAX Corporation. Measurement is performed using the LNS under the following (1-2) particle size distribution measurement conditions.

[0108] (v) From the obtained particle size distribution measurement value, the fine particle content parameter 1 of the colloidal silica sample is calculated using the following formula:

[0109] Formula (1) Fine particle content parameter 1 = (total number of detected particles of 15 nm or less) ÷ (total number of detected particles of 25 nm or more)

[0110] (1-2) Particle size distribution measurement conditions (i) The air used for measurement is compressed air generated by a compressor and purified by an air filter (manufactured by CKD, FCS500-88-P90) to dry air.

[0111] (ii) Pre-measurement pre-operation is carried out for at least 24 hours with ultrapure water and the above-mentioned dry air supplied to the LNS device.

[0112] (iii) The inside of the measuring device is washed with ultrapure water. The particle concentration of the ultrapure water is measured under the conditions shown in Table 1, and the washing is completed when the total number of detected particles is less than 5.0E+11 (# / mL).

[0113] (iv) Under the measurement conditions shown in Table 1, measurement is performed using LNS Volumetric Standard manufactured by KANOMAX as the standard particle.

[0114] (v) Use ultrapure water to clean the inside of the measuring device. Measure the particle concentration of the ultrapure water under the conditions shown in Table 1, and end the cleaning when the total number of detected particles is less than 1.0E+11 (# / mL).

[0115] (vi) Measurement of measurement sample 1 is carried out under the measurement conditions shown in Table 1.

[0116] The colloidal silica has a particle content parameter 1 of 15.0 or less as measured by the above-mentioned measuring method.

[0117] The colloidal silica has a particle content parameter 1 measured by the above-mentioned measurement method of 15.0 or less, preferably 12.0 or less, more preferably 10.0 or less, and even more preferably 8.0 or less. By adjusting the particle content parameter 1 to 15.0 or less, the amount of particles remaining on the polished surface can be reduced.

[0118] (2-1) Method for measuring particle content parameter 2 (%) (i) Add ultrapure water (hereinafter referred to as "ultrapure water") with an electrical resistivity of 18.2 MΩ or more to the colloidal silica sample to be measured, and dilute it so that the silica concentration after dilution is 0.1 mass % (wt%). The resulting diluted solution is measurement sample 2.

[0119] (ii) The particle size distribution of the measurement sample 2 is measured using a particle size distribution measuring device based on a scanning electrical mobility diameter measurement method. An example of a particle size distribution measuring device based on a scanning electrical mobility diameter measurement method is the Liquid Nanoparticle Sizer System Model 9310 (LNS) manufactured by KANOMAX Corporation. Measurement is performed using the LNS under the following (2-2) particle size distribution measurement conditions.

[0120] (iii) From the obtained particle size distribution measurement value, the fine particle content parameter 2 of the colloidal silica sample is calculated using the following formula:

[0121] Equation (3) Fine particle content parameter 2 = (total number of particles detected of 15 nm or less) ÷ (total number of all particles detected) × 100 [%]

[0122] (2-2) Particle size distribution measurement conditions (i) The air used for measurement is compressed air generated by a compressor and purified by an air filter (manufactured by CKD, FCS500-88-P90) to dry air.

[0123] (ii) Pre-measurement pre-operation is carried out for at least 24 hours with ultrapure water and the above-mentioned dry air supplied to the LNS device.

[0124] (iii) The inside of the measuring device is washed with ultrapure water. The particle concentration of the ultrapure water is measured under the conditions shown in Table 1, and the washing is completed when the total number of detected particles is less than 5.0E+11 (# / mL).

[0125] (iv) Measurement is performed using the LNS Volumetric Standard manufactured by KANOMAX as the standard particle under the measurement conditions shown in Table 1 (LNS measurement conditions).

[0126] (v) Use ultrapure water to clean the inside of the measuring device. Measure the particle concentration of the ultrapure water under the conditions shown in Table 1, and end the cleaning when the total number of detected particles is less than 1.0E+11 (# / mL).

[0127] (vi) Measurement of measurement sample 2 is carried out under the measurement conditions shown in Table 1.

[0128] The colloidal silica has a fine particle content parameter 2 of 8.0% or less as measured by the above-mentioned measuring method.

[0129] The colloidal silica has a particle content parameter 2 measured by the above-mentioned measurement method of 8.0% or less, preferably 7.0% or less, more preferably 6.0% or less, and even more preferably 5.0% or less. By adjusting the particle content parameter 2 to 8.0% or less, the amount of particles remaining on the polished surface can be reduced.

[0130]

[0131] (3) Percentage of fine particle amount evaluated by SEM (%) (i) A dispersion liquid made by mixing 7.5 mL of methanol, 1.5 mL of water, 1 mL of 0.01M HCl, and 5 μL of 20% colloidal silica is dropped onto a sample stage and allowed to dry. This sample stage is then set in a scanning electron microscope (SEM) and an SEM image is taken.

[0132] (ii) Images of 1,000 silica particles taken with a scanning electron microscope were each approximated to an ellipse using image analysis software (Mitani Corporation's "WinRoof2018"), and the minor axis of the ellipse was measured.

[0133] (iii) In the number frequency distribution of the minor axis of an ellipse obtained by the SEM image analysis described above, particles whose minor axis of an ellipse is 25% or less of the average value are defined as fine particles, and the number ratio of fine particles is calculated.

[0134] The proportion of fine particles in the colloidal silica as evaluated by SEM is preferably 0.1% or less. By adjusting the proportion of fine particles in the colloidal silica as evaluated by SEM to 0.1% or less, the amount of fine particles remaining on the polished surface can be reduced.

[0135] (4) Average primary particle diameter (nm) After pre-drying the colloidal silica on a hot plate, heat-treat it at 800°C for 1 hour to prepare a measurement sample. The BET specific surface area is measured using the prepared measurement sample. Assuming the true specific gravity of silica is 2.2, the ratio of 2727 / BET specific surface area (m 2 / g) is converted to the average primary particle diameter (nm) of silica particles in the colloidal silica.

[0136] The average primary particle size of the colloidal silica is preferably 5 nm to 130 nm, more preferably 10 nm to 120 nm, even more preferably 12 nm to 110 nm, and most preferably 14 nm to 100 nm. By adjusting the average primary particle size of the colloidal silica to preferably 5 nm to 130 nm, it is possible to reduce the roughness of the polished surface.

[0137] (5) Average secondary particle diameter (nm) Colloidal silica was diluted with a 0.3% by mass aqueous solution of citric acid to a silica concentration of 1.0% by mass (wt%) (diluted solution).

[0138] The diluted solution is used as a measurement sample, and the average secondary particle diameter of the measurement sample is measured by dynamic light scattering (ELSZ-2000, manufactured by Otsuka Electronics Co., Ltd.).

[0139] The average secondary particle diameter (nm) of the colloidal silica is preferably 20 nm to 250 nm, more preferably 24 nm to 200 nm, even more preferably 27 nm to 170 nm, and most preferably 30 nm to 140 nm. By adjusting the average secondary particle diameter of the colloidal silica to preferably 20 nm to 250 nm, the roughness of the polished surface can be reduced.

[0140] (6) Association Ratio The association ratio of silica particles in colloidal silica is a value obtained by calculating the average secondary particle size / average primary particle size of silica particles in colloidal silica.

[0141] The association ratio of silica particles in colloidal silica is preferably 1.0 or more, more preferably 1.1 or more, even more preferably 1.2 or more, and most preferably 1.3 or more. By adjusting the lower limit of the association ratio of colloidal silica to 1.0 or more, the polishing rate when polishing with colloidal silica is further improved.

[0142] The association ratio of the colloidal silica is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less, and most preferably 2.9 or less. By adjusting the upper limit of the association ratio of the colloidal silica to 4.0 or less, it is possible to reduce the roughness of the polished surface when polished using colloidal silica.

[0143] (7) Silica concentration (mass % (wt%)) Colloidal silica was pre-dried on a hot plate, then heat-treated at 800°C for 1 hour, and the silica concentration was calculated from the remaining amount.

[0144] The silica concentration of the colloidal silica is preferably 2 wt% to 55 wt%, more preferably 2 wt% to 50 wt%, even more preferably 2 wt% to 45 wt%, and most preferably 3 wt% to 40 wt%. By adjusting the silica concentration of the colloidal silica to 2 wt% to 55 wt%, the polishing rate when polishing the colloidal silica is further improved.

[0145] (8) Silanol group density (number / nm 2 The silanol group density of colloidal silica can be determined by the Sears method. The Sears method was performed with reference to the description in GW Sears, Jr., "Determination of Specific Surface Area of ​​Colloidal Silica by Titration with Sodium Hydroxide," Analytical Chemistry, 28(12), 1981(1956). A 1% by mass (wt%) silica dispersion was used for measurement, and titration was carried out with a 0.1 mol / L aqueous sodium hydroxide solution, and the silanol group density was calculated using the following formula:

[0146] ρ=(a×f×6022)÷(c×S) In the above formula, ρ: Silanol group density (number / nm 2 ), a: Drop volume (mL) of 0.1 mol / L sodium hydroxide aqueous solution at pH 4-9, f: Factor of 0.1 mol / L sodium hydroxide aqueous solution, c: Mass of silica particles (g), S: BET specific surface area (m 2 / g).

[0147] The silanol group density of the silica particles in the colloidal silica is preferably 1.5 / nm 2 More preferably, 1.6 particles / nm 2 More preferably, it is 1.8 particles / nm 2 or more, and most preferably 2.0 particles / nm 2 The lower limit of the silanol group density is set to 1.5 / nm 2 By making the above adjustments, the occurrence of scratches on the workpiece can be further reduced.

[0148] The silanol group density is preferably 10.0 / nm 2 More preferably, 9.5 particles / nm 2 More preferably, 9.0 particles / nm 2 or less, and most preferably 8.8 particles / nm 2 The upper limit of the silanol group density is 10.0 / nm 2 By adjusting the following, the abrasiveness of colloidal silica can be further improved.

[0149] (9) True Specific Gravity In this specification, the true specific gravity can be measured by drying colloidal silica on a hot plate at 150°C, then storing it in a 300°C oven for 1 hour, and then using a liquid phase displacement method using ethanol.

[0150] The true specific gravity of the silica particles contained in the colloidal silica is preferably 1.0 or more, more preferably 1.2 or more, even more preferably 1.4 or more, and most preferably 1.5 or more. By adjusting the lower limit of the true specific gravity to 1.0 or more, the polishing properties of the colloidal silica of the present invention are further improved.

[0151] The true specific gravity is preferably 3.0 or less, more preferably 2.8 or less, even more preferably 2.5 or less, and most preferably 2.3 or less. By adjusting the upper limit of the true specific gravity to 3.0 or less, the occurrence of scratches on the object to be polished is further reduced.

[0152] (10) Metal impurity content (ppm) The metal impurity content was measured using an atomic absorption spectrometer. The metal impurity content was calculated as the sum of the contents of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the colloidal silica.

[0153] The content of metal impurities contained in colloidal silica is preferably 1 ppm or less. By adjusting the content of metal impurities contained in colloidal silica to 1 ppm or less, it is more suitable for use as a CMP slurry.

[0154] (11) Polished Surface Roughness RMS (nm) Colloidal silica was diluted with ultrapure water to a silica concentration of 3.0% by mass (wt%) to prepare a polishing composition.

[0155] Using the polishing composition obtained, a 3 cm square silicon wafer having a silicon oxide film formed on its surface is polished under the following conditions.

[0156] Polishing machine: NF-300CMP, manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TMPad, manufactured by Nitta DuPont Co., Ltd. Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min After polishing, the surface roughness of the polished surface of the wafer was evaluated using an atomic force microscope under the following conditions.

[0157] Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: OLYMPUS MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: 5 fields are observed per polished wafer.

[0158] Surface roughness calculation method: The average value of the root mean square roughness of five fields of view was taken as the polished surface roughness RMS.

[0159] The polished surface roughness RMS (nm) is preferably 3.00 nm or less.

[0160] (12) Number of particles remaining on the polished surface (particles / μm 2 ) The colloidal silica is diluted with ultrapure water to a silica concentration of 3.0 mass % (wt %) to prepare a polishing composition.

[0161] Using the polishing composition obtained, a 3 cm square silicon wafer having a silicon oxide film formed on its surface is polished under the following conditions.

[0162] Polishing machine: NF-300CMP, manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TMPad, manufactured by Nitta DuPont Co., Ltd. Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min After polishing, the silicon wafer is cleaned by scrubbing it in the scrubbing section built into the cleaning and drying device MAT ZAB-8S1M, where a PVA roll brush comes into contact with the wafer and the cleaning and drying device is scrubbed under the following conditions: To hold the silicon wafer in place, a jig is used with a frame made of glass epoxy resin and the wafer holding section made of polyurethane.

[0163] Brush: AION SCL BRUSH ROLLER 48 (40 / 26) x 224 mm, manufactured by AION Scrubbing time: 1 min Brush rotation speed: 200 rpm Spin rotation speed of silicon wafer fixing part: 50 rpm After scrubbing, ultrapure water was flowed over the polishing substrate at 750 mL / min for 1 minute, and then the substrate was treated for 20 seconds at 1800 rpm in the spin dryer built into the above equipment.

[0164] After drying, the number of particles remaining on the polished surface of the silicon wafer is measured using an SPM-9700HT manufactured by Shimadzu Corporation.

[0165] Number of particles remaining on the polished surface (particles / μm 2 ) is preferably 3 / μm 2 The following is the result.

[0166] [4] Polishing composition The present invention includes a polishing composition containing the colloidal silica of the present invention.

[0167] The polishing composition is useful for CMP applications.

[0168] The polishing composition contains colloidal silica and may further contain additives such as a diluent, an oxidizing agent, a pH adjuster, an anticorrosive agent, a stabilizer, and a surfactant.

[0169] The content of colloidal silica in the polishing composition (mass%, wt%, silica concentration) is preferably 0.01 wt% to 20 wt%, more preferably 0.1 wt% to 15 wt%, even more preferably 1 wt% to 10 wt%, and particularly preferably 2 wt% to 5 wt%.

[0170] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples and can be embodied in various forms without departing from the spirit and scope of the present invention.

[0171] The present invention will be specifically explained by showing examples.

[0172] However, the present invention is not limited to the examples.

[0173] [1] Production of colloidal silica (1) Example 1 (with heat treatment) Preparation of heated water-substituted silica sol To a solution A prepared by mixing 976 g of methanol, 97 g of water, and 58 g of 29 mass % ammonia water, a solution B prepared by mixing 190 g of methanol and 506 g of tetramethoxysilane (TMOS), and a solution C (pH = 7.85) containing 119 g of pure water were added at a constant rate over 75 minutes.

[0174] In preparing the reaction solution, the temperature of each solution before mixing was kept at 35°C, and the temperature of the reaction solution was adjusted so that it would decrease from an initial reaction temperature of 35°C at the start of addition of Solution B to Solution A (start of synthesis) to a final reaction temperature of 24.5°C at the end of addition (end of synthesis), while the temperature was being controlled. The total amounts of Solutions B and C were added to Solution A at a constant rate.

[0175] The reaction mixture was heated and concentrated under stirring, and the residue was replaced with heated water. After the replacement with heated water, the methanol concentration was 301 ppm.

[0176] To 100 parts by mass of the silica sol obtained above after the hot water substitution, 0.65 parts by mass of 3-ethoxypropylamine (3-EOPA) was added, the pH was adjusted to 9.9, and the silica sol was heated at 100°C under normal pressure while stirring. The heating treatment was started when the silica sol reached 100°C, and samples were taken every 0.5 hours from the start of the heating treatment to measure the pH.

[0177] 0.5 hours after the start of the heat treatment, the pH had reached 9.6, so 0.2 parts by mass of 3-EOPA was added again to adjust the pH to 9.9. The above procedure was repeated every 1.5 hours from the start of the heat treatment to the end of the heat treatment. 2.2 parts by mass of 3-EOPA were added from the start of the heat treatment to the end of the heat treatment.

[0178] The heat treatment was carried out for 16 hours to obtain colloidal silica.

[0179] Measurement of methanol concentration: A gas chromatograph (Thermo, FocusGC), an autosampler (Thermo, AS3000, or a device with equivalent or higher performance), and an air compressor (capable of supplying compressed air of 0.4 MPa or higher) were used. A 1 μL sample was drawn into a 10 μL syringe, and the syringe was set in the autosampler for measurement.

[0180] (2) Example 2 (with heat treatment) Preparation of heated water-substituted silica sol To solution A, which was a mixture of 7.7 g of pure water, 96.8 g of methanol, and 4.5 g of 29% by mass ammonia water, solution B, which was a mixture of 100 g of TMOS and 17.7 g of methanol, and solution C, which was a mixture of 31.7 g of pure water and 4.7 g of 29% by mass ammonia water, were added at a constant rate over 217 minutes while maintaining the liquid temperature at 36°C.

[0181] After the addition was completed, the reaction mixture was stirred for an additional 30 minutes while maintaining the temperature at 36°C.

[0182] The reaction mixture was heated and concentrated under stirring, and the residue was replaced with heated water. After the replacement with heated water, the methanol concentration was 212 ppm.

[0183] To 100 parts by mass of the silica sol obtained above after the hot water substitution, 0.6 parts by mass of 3-EOPA was added, the pH was adjusted to 9.8, and the silica sol was stirred and heated at 100°C under atmospheric pressure. The heating treatment was started when the silica sol reached 100°C, and samples were taken every 0.5 hours after the start of the heating treatment, and the pH was measured.

[0184] 0.5 hours after the start of the heat treatment, the pH had reached 9.6, so 0.12 parts by mass of 3-EOPA was added again to adjust the pH to 9.8. The above procedure was repeated every 1.0 hour from the start of the heat treatment to the end of the heat treatment. 2.76 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0185] The heat treatment was carried out for 23.0 hours to obtain colloidal silica.

[0186] (3) Example 3 (Example with Heat Treatment and Small Average Particle Size) Preparation of Silica Sol Substituted with Heated Water To Solution A, which was a mixture of 463.1 g of pure water, 104.8 g of 26% by mass ammonia water, and 4255.0 g of methanol, Solution B, which was a mixture of 3,044.4 g of TMOS and 229.4 g of methanol, and Solution C, which was a mixture of 643.2 g of pure water and 104.8 g of 26% by mass ammonia water, were added at a constant rate over 150 minutes while maintaining the liquid temperature at 50°C.

[0187] The reaction mixture was heated and concentrated under stirring, and the residue was replaced with heated water. After the replacement with heated water, the methanol concentration was 198 ppm.

[0188] To 100 parts by mass of the silica sol obtained above after the hot water substitution, 0.65 parts by mass of 3-EOPA was added, the pH was adjusted to 9.9, and the silica sol was stirred and heated at 100°C under normal pressure. The heating treatment was started when the silica sol reached 100°C, and samples were taken every 0.5 hours from the start of the heating treatment, and the pH was measured.

[0189] 0.5 hours after the start of the heat treatment, the pH had reached 9.6, so 0.2 parts by mass of 3-EOPA was added again to adjust the pH to 9.9. The above procedure was repeated every 1.0 hour from the start of the heat treatment to the end of the heat treatment. 3.2 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0190] The heat treatment was carried out for 24.5 hours to obtain colloidal silica.

[0191] (4) Example 4 (Example with Heat Treatment and Large Average Particle Size) Preparation of Silica Sol Substituted with Heated Water To Solution A, which was a mixture of 1,546.6 g of pure water, 340.6 g of 26% by mass ammonia water, and 8,363.2 g of methanol, Solution B, which was a mixture of 6,088.0 g of TMOS and 350.0 g of methanol, and Solution C, which was a mixture of 1,186.2 g of pure water and 340.6 g of 26% by mass ammonia water, were added at a constant rate over 100 minutes while maintaining the liquid temperature at 20°C.

[0192] The reaction mixture was heated and concentrated under stirring, and the residue was replaced with heated water. After the replacement with heated water, the methanol concentration was 196 ppm.

[0193] To 100 parts by mass of the silica sol obtained above after the hot water substitution, 0.65 parts by mass of 3-EOPA was added, the pH was adjusted to 9.9, and the silica sol was heated at 100°C under normal pressure while stirring. The heating treatment was started when the silica sol reached 100°C, and samples were taken every 0.25 hours from the start of the heating treatment, and the pH was measured.

[0194] 0.25 hours after the start of the heat treatment, the pH had reached 9.7, so 0.15 parts by mass of 3-EOPA was added again to adjust the pH to 9.9. The above procedure was repeated every 1.0 hour from the start of the heat treatment to the end of the heat treatment. 3.0 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0195] The heat treatment was carried out for 20.0 hours to obtain colloidal silica.

[0196] (5) Example 5 (Example with heat treatment and low silica concentration during heating) Preparation of silica sol substituted with heated water The reaction solution obtained in Example 1 was substituted with heated water under stirring conditions. The methanol concentration after the substitution with heated water was 387 ppm.

[0197] To 100 parts by mass of the silica sol obtained above after the hot water substitution, 0.65 parts by mass of 3-EOPA was added, the pH was adjusted to 9.9, and the silica sol was stirred and heated at 100°C under normal pressure. The heating treatment was started when the silica sol reached 100°C, and samples were taken every 0.5 hours from the start of the heating treatment, and the pH was measured.

[0198] 0.5 hours after the start of the heat treatment, the pH had reached 9.6, so 0.2 parts by mass of 3-EOPA was added again to adjust the pH to 9.9. The above procedure was repeated every 1.5 hours from the start of the heat treatment to the end of the heat treatment. 2.4 parts by mass of 3-EOPA were added from the start of the heat treatment to the end of the heat treatment.

[0199] The heat treatment was carried out for 18.0 hours to obtain colloidal silica.

[0200] (6) Example 6 (Example with heat treatment and high silica concentration during heating) Preparation of silica sol subjected to heated water substitution The reaction solution obtained in Example 1 was heated and concentrated under stirring conditions, and the mixture was substituted with heated water. The methanol concentration after the heated water substitution was 184 ppm.

[0201] To 100 parts by mass of the silica sol obtained above after the hot water substitution, 0.65 parts by mass of 3-EOPA was added, the pH was adjusted to 9.9, and the silica sol was stirred and heated at 100°C under normal pressure. The heating treatment was started when the silica sol reached 100°C, and samples were taken every 0.5 hours from the start of the heating treatment, and the pH was measured.

[0202] After 0.5 hours of heating, the pH had reached 9.6, so 0.2 parts by mass of 3-EOPA was added again to adjust the pH to 9.9. The above procedure was repeated every 1.5 hours from the start of the heating treatment to the end of the heating treatment. 2.0 parts by mass of 3-EOPA was added from the start of the heating treatment to the end of the heating treatment.

[0203] The heat treatment was carried out for 15.5 hours to obtain colloidal silica.

[0204] (7) Comparative Example 1 (without heat treatment) This is an example simulating the prior art (Patent Document 1: JP 2020-164351 A, and Patent Document 3: International Publication No. WO2016 / 117560A1).

[0205] Solution A was prepared by mixing 976 g of methanol, 97 g of water, and 58 g of 29% by mass aqueous ammonia. Solution B was prepared by mixing 190 g of methanol and 506 g of tetramethoxysilane (TMOS), and solution C (pH = 7.85) was prepared by mixing 119 g of pure water, and these were added at a constant rate over 75 minutes.

[0206] In preparing the reaction solution, the temperature of each solution before mixing was kept at 35°C, and the temperature of the reaction solution was controlled so that it would decrease from an initial reaction temperature of 35°C at the start of addition of Solution B to Solution A (start of synthesis) to a final reaction temperature of 24.5°C at the end of addition (end of synthesis), while the entire amounts of Solutions B and C were added to Solution A at a constant rate.

[0207] The reaction mixture was heated and concentrated under stirring, and then heated water was substituted to obtain colloidal silica.

[0208] (8) Comparative Example 2 (without heat treatment) This is an example simulating the prior art (Patent Document 2: JP 2022-109711 A and Patent Document 3).

[0209] Solution A was a mixture of 7.7 g of pure water, 96.8 g of methanol, and 4.5 g of 29% by mass ammonia water. Solution B was a mixture of 100 g of tetramethoxysilane and 17.7 g of methanol, and Solution C was a mixture of 31.7 g of pure water and 4.7 g of 29% by mass ammonia water. These were added at a constant rate over 217 minutes while the liquid temperature was maintained at 36°C.

[0210] After the addition was completed, the reaction mixture was stirred for an additional 30 minutes while maintaining the temperature at 36°C.

[0211] The reaction solution was heated and concentrated under stirring, and then heated water was substituted to obtain colloidal silica.

[0212] (9) Comparative Example 3 (without heat treatment) This is an example simulating the conventional technology (Patent Documents 2 to 3, and Patent Document 4: JP 2020-75830 A).

[0213] To the colloidal silica obtained in Comparative Example 2, 35% by mass of hydrogen peroxide was added so that the amount of hydrogen peroxide was 0.5 g per 100 g of tetraalkoxysilane converted into silica, thereby obtaining colloidal silica.

[0214] (10) Comparative Example 4 (without heat treatment) This is an example simulating the conventional technology (Patent Documents 2 to 4, and Patent Document 5: JP 2021-116208 A).

[0215] 120 g of the colloidal silica obtained in Comparative Example 3 was ultrafiltered using an ultrafiltration membrane with a molecular weight cutoff of 80,000 (Asahi Kasei Corporation's Lab Module AOP-0013) in a pencil-type module (PX-02001) manufactured by Asahi Kasei Corporation, L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MFLX07514-10) manufactured by Masterflex, and L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) manufactured by Masterflex, and a tube for silicon perhydrolysis (96400-25) manufactured by Masterflex, to obtain colloidal silica.

[0216] The amount of liquid that permeated the ultrafiltration membrane was 63.6 g, and the permeability was 53%.

[0217] (11) Comparative Example 5 (Example of long-term ultrafiltration without heat treatment) This is an example simulating the prior art (Patent Documents 2 to 5).

[0218] Colloidal silica (40 g) obtained in Comparative Example 4 was subjected to ultrafiltration using an ultrafiltration membrane with a molecular weight cutoff of 80,000 (Asahi Kasei Corporation Lab Module AOP-0013) in a pencil-type module (PX-02001) manufactured by Asahi Kasei Corporation, L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MFLX07514-10) manufactured by Masterflex, and L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) manufactured by Masterflex as pumps, and Masterflex silicon perhydrolysis tubing (96400-25) as tubing, to obtain colloidal silica.

[0219] During the ultrafiltration, ultrapure water was added to the colloidal silica to maintain the liquid amount of the colloidal silica constant.

[0220] The amount of liquid that permeated the ultrafiltration membrane was 220.5 g, and the time required for ultrafiltration was 152 minutes.

[0221]

[0222]

[0223] [2] Evaluation Results Examples 1 to 6 are colloidal silicas produced by a colloidal silica production method including a step of heat-treating a silica sol consisting of water and silica particles at the boiling point of water under normal pressure.

[0224] The colloidal silica of Examples 1 to 6 had (i) an average secondary particle diameter of 20 nm to 250 nm, and (ii) a fine particle content parameter 1 of 15.0 or less.

[0225] The colloidal silica of the examples was able to keep the content of fine particles low.

[0226] Comparative Examples 1 to 5 are colloidal silicas produced by a colloidal silica production method that does not include a heat treatment step.

[0227] Comparative Examples 1 to 5 are examples that simulate the prior art.

[0228] Comparative Example 1 is an example that simulates Patent Documents 1 and 3, and was unable to effectively reduce fine particles of 15 nm or less.

[0229] Comparative Example 2 is an example that simulates Patent Documents 2 and 3, and was unable to effectively reduce fine particles of 15 nm or less.

[0230] Comparative Example 3 is an example that simulates Patent Documents 2 to 4, and was unable to effectively reduce fine particles of 15 nm or less.

[0231] Comparative Example 4 is an example that simulates Patent Documents 2 to 5, and was unable to effectively reduce fine particles of 15 nm or less.

[0232] Comparative Example 5 is an example in which ultrafiltration was carried out for a long period of time in order to simulate Patent Documents 2 to 5 and to reduce the amount of fine particles, and an increase in the average secondary particle size due to particle aggregation was confirmed.

[0233] [3] Industrial Applicability The method for producing colloidal silica of the present invention includes a step of heat-treating a silica sol consisting of water and silica particles at the boiling point of water under normal pressure.

[0234] The colloidal silica of the present invention has (i) an average secondary particle diameter of 20 nm to 250 nm, and (ii) a fine particle content parameter 1 defined as below of 15.0 or less.

[0235] Definition of Fine Particle Content Parameter 1 (i) Colloidal silica is diluted with ultrapure water (hereinafter referred to as "ultrapure water") having an electrical resistivity of 18.2 MΩ or more to a silica concentration of 2 mass % (wt%) (diluted solution).

[0236] (ii) 9.1 g of the diluted solution is transferred to a centrifuge tube (model number: S303922A) manufactured by Eppendorf-Himac Technologies Co., Ltd., and centrifuged using a centrifugal rotor S58A and a centrifuge CS100FNX at a centrifugal speed of 50,000 rpm, a centrifugation temperature of 5°C, and a centrifugation time of 60 minutes (all manufactured by Eppendorf-Himac Technologies Co., Ltd.).

[0237] (iii) After centrifugation, 2 mL of the supernatant was collected from the centrifuge tube, and this 2 mL of the supernatant after centrifugation was mixed with silica sol prepared by diluting ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Co., Ltd. 10 times with ultra-pure water in the following mass ratio (mixture).

[0238] After centrifugation, the supernatant: 10-fold diluted solution of PL-3 = 9:1 (mass ratio) (iv) The particle size distribution of the resulting mixture is measured using a particle size distribution measuring device based on scanning electrical mobility diameter measurement method.

[0239] (v) The value calculated from the measured particle size distribution using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica.

[0240] Fine particle content parameter 1=(total number of particles of 15 nm or less detected)÷(total number of particles of 25 nm or more detected) Equation (1) The colloidal silica of the present invention has a low fine particle content.

[0241] When CMP is performed using the colloidal silica of the present invention as abrasive grains, the amount of fine particles remaining on the polished surface is significantly reduced, and the surface roughness of the polished surface can be reduced, compared to when conventional colloidal silica is used as abrasive grains.

Claims

1. A method for producing colloidal silica, comprising the step of heat-treating a silica sol consisting of water and silica particles at the boiling point of water under normal pressure.

2. The pH of the silica sol during the heat treatment is pH 9.0 to pH 10.5, the heat treatment time is 11 hours to 35 hours, and the heat treatment is performed at 1 ml of silica sol. 3 The stirring power per unit is 0.01kW / m 3 ~0.40kW / m 3 The method for producing colloidal silica according to claim 1, wherein the silica sol is stirred under the conditions of 3. The method for producing colloidal silica according to claim 1 or 2, wherein the silica sol is obtained by: (a) adding solution B containing an alkoxysilane to solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions in which the addition rate of the alkoxysilane contained in solution B per 1 kg of solution A is 0.8 mol / hour / kg to 2.50 mol / hour / kg.

4. The method for producing colloidal silica according to claim 1 or 2, wherein the silica sol is obtained by: (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst; and (b) hydrolyzing and dehydrating condensing the alkoxysilane under conditions in which the concentration of the alkoxysilane contained in solution B is 60% by mass to 98% by mass.

5. A colloidal silica having a fine particle content parameter 1, defined as follows, of 15.0 or less. Definition of microparticle content parameter 1 (i) Colloidal silica is diluted with ultrapure water (hereinafter referred to as "ultrapure water") having an electrical resistivity of 18.2 MΩ or more to give a silica concentration of 2 mass % (wt%) (diluted solution). (ii) 9.1 g of the diluted solution is placed in a centrifuge tube (model number: S303922A) manufactured by Eppendorf-Himac Technologies Co., Ltd., and centrifuged using a centrifuge rotor S58A and a centrifuge CS100FNX under the conditions of a centrifuge speed of 50,000 rpm, a centrifuge temperature of 5°C, and a centrifuge time of 60 minutes (all manufactured by Eppendorf-Himac Technologies Co., Ltd.). (iii) After centrifugation, 2 mL of the supernatant is collected from the centrifuge tube, and this 2 mL of the supernatant after centrifugation is mixed with silica sol obtained by diluting ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Co., Ltd. 10 times with ultra-pure water in the following mass ratio (mixture). Supernatant after centrifugation: 10-fold diluted solution of PL-3 = 9:1 (mass ratio) (iv) The particle size distribution of the resulting mixture is measured using a particle size distribution measuring device based on scanning electrical mobility diameter measurement. (v) The value calculated from the measured particle size distribution value obtained using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica. Formula (1) Fine particle content parameter 1 = (total number of detected particles of 15 nm or less) ÷ (total number of detected particles of 25 nm or more)

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