Silica fine particle dispersion liquid and production method thereof

Abstract

To provide silica fine particle dispersion liquid which has a low impurity content and a high polishing speed as used in polishing applications.SOLUTION: Silica fine particle dispersion liquid includes silica fine particles dispersed in a solvent which satisfies the following [1] to [5]: [1] a specific surface area equivalent sphere conversion particle diameter D(nm) of the silica fine particles satisfies 5≤D≤100; [2] an area of a peak based on each of Q0 to Q4 structures in a spectrum obtained by a 29Si-NMR analysis for the silica fine particles is determined and is represented as corresponding S0 to S4, the ratio R4 (R4=S4 / (S0+S1+S2+S3+S4)×100) of S4 to the sum of them satisfies a specific equation using the particle diameter D; [3] the particle density of the silica fine particles is in a specific range; [4] the carbon content in the silica fine particles is less than 0.1 mass% per SiO2; and [5] the impurity content in the silica fine particles is low.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silica fine particle dispersion suitable for polishing various electronic materials such as silicon wafers, silicon carbide wafers, sapphire wafers, compound semiconductor wafers, and magnetic disks, and particularly to a high-purity silica fine particle dispersion with a reduced impurity content, and to a method for producing the same. [Background technology]

[0002] In the manufacturing process of semiconductor devices, polishing is performed using an abrasive containing an abrasive dispersion to planarize the surface of electronic materials such as semiconductor silicon wafers. If the abrasive contains metal impurities (e.g., Fe, Cr, Ni, Cu, etc.), the metal impurities may diffuse into the surface or interior of the silicon wafer during polishing, potentially causing surface defects in the silicon wafer. Furthermore, the metal impurities may form impurity levels in the silicon wafer, potentially adversely affecting the period during which the semiconductor silicon wafer can exhibit stable performance. Therefore, it is necessary to further reduce the content of metal impurities in the abrasive. Here, silica microparticle dispersions are widely used as abrasive dispersions for planarizing the surface of electronic materials such as semiconductor silicon wafers, and there is a demand for reducing the content of metal impurities in these silica microparticles.

[0003] Known methods for producing highly purified silica microparticles (silica microparticle dispersions) with reduced metal impurity content include a method for producing silica microparticle dispersions by synthesizing silica microparticle dispersions using tetraalkoxysilanes as raw materials, and a method for producing silica microparticle dispersions by using water glass (aqueous sodium silicate solution) as raw material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 05-097422 [Patent Document 2] Japanese Patent Application Publication No. 04-002606 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-044224 [Patent Document 4] Patent Publication No. 2021-134098 [Patent Document 5] Japanese Patent Publication No. 2022-100932 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Documents 1 and 2, a strong acid is added to a silicic acid solution obtained from an alkali metal silicate, followed by heat treatment, followed by cation exchange, anion exchange, and then, preferably, another cation exchange, to obtain a high-purity silicic acid solution. However, when the strong acid is removed using an ion exchange resin, it is difficult to control the pH, and if there are areas with a high pH, ​​gel will form and be mixed into the obtained silicic acid solution, ultimately resulting in problems of reduced quality and stability of the silica sol.

[0006] In Patent Document 3, a silicic acid solution is obtained from a diluted solution of water glass by electrodialysis, and is further purified by cation exchange. In this method, gel formed during the process of changing the pH from alkaline to acidic remains in the silicic acid solution. Even if such a silicic acid solution is used as a raw material, it is not easy to obtain uniform silica microparticles suitable for use in abrasives. Furthermore, since water glass is electrodialyzed, the efficiency of removing metal ions is low, making it impossible to obtain a highly pure silicic acid solution.

[0007] Both Patent Documents 4 and 5 provide impurity-free silica fine particle dispersions that can be preferably used as abrasives, but there has been a demand for even higher purity silica fine particles.

[0008] A conventional method for removing impurities from silica is to neutralize water glass, a raw material for silica synthesis, to obtain a gel, which is then leached with acid and washed to remove the impurities before being used for silica synthesis. In this method, since the gel is washed while undergoing solid-liquid separation, it is necessary to generate a gel of a certain size in advance and use it for washing. When a silica particle dispersion is synthesized using such a gel as a raw material, the resulting silica particle dispersion tends to contain many coarse particles and have a wide particle size distribution. On the other hand, when a fine gel is generated and redissolved in an alkali to obtain purified water glass and use it for synthesizing silica particles, the fine gel is not suitable for solid-liquid separation, and it is difficult to properly wash the gel.

[0009] In particular, polishing abrasive dispersions used for polishing semiconductor devices must be free of unstable impurities other than silica fine particles, such as gel-like substances (silica oligomer aggregates). To achieve this, the silicic acid solution used as the raw material for producing the silica fine particle dispersion must be gel-free. The present inventors conducted extensive research and discovered that, in the process of purifying the silicic acid solution by acid leaching the metal impurities contained in the silicic acid solution used as the raw material for producing the silica fine particle dispersion under heating, adding an amount of acid ranging from 300 to 10,000 ppm further promotes the ionization of the metal impurities and prevents gelation of the silicic acid. Furthermore, Ti, which is particularly difficult to remove among metal impurities, can be further reduced by performing air bubbling under specific conditions during the acid leaching process, thereby completing the present invention. [Means for solving the problem]

[0010] The present invention includes the following (1) to (5). (1) A silica fine particle dispersion liquid in which silica fine particles satisfying the following [1] to [5] are dispersed in a solvent. [1] The particle diameter D (nm) of the silica fine particles, calculated by converting the specific surface area into an equivalent sphere, satisfies the relationship 5≦D≦100. [2] Regarding the silica particles 29In the spectrum obtained by Si-NMR analysis, the areas of the peaks based on the Q0 structure, Q1 structure, Q2 structure, Q3 structure, and Q4 structure are determined, and when these are designated as S0, S1, S2, S3, and S4, the ratio R4 of S4 to the total of these (R4=S4 / (S0+S1+S2+S3+S4)×100) satisfies the following formula using the particle diameter D. 0.97≦(2.9×In(D)+73.7) / R4≦1.03 [3] The particle density of the silica fine particles is 2.2±0.20 g / cm 3 Range. [4] The carbon content in the silica fine particles is less than 0.1% by mass per SiO2. [5] The content of Al, Fe, and Na per SiO2 contained in the silica microparticles is 5 ppm or less (metal equivalent), the content of Ti per SiO2 is 10 ppm or less (metal equivalent), and the content of Cu and Ni per SiO2 is 20 ppb or less (metal equivalent). (2) The silica fine particle dispersion according to (1) above, wherein the silica fine particles further satisfy the following [6]: [6] Ratio of the sum of the areas of S2+S3 to the sum of the areas of each peak (S0+S1+S2+S3+S4) 2+3 (R 2+3 = (S2+S3) / (S0+S1+S2+S3+S4) × 100) satisfies the following formula using the particle diameter D. 0.87≦(-4×In(D)+30) / R 2+3 ≦1.13 (3) The silica fine particle dispersion according to (1) or (2) above, wherein the silica fine particles are prepared using an alkali silicate as a raw material. (4) A method for producing a silica fine particle dispersion, comprising the following steps 1 to 4: Step 1: A step of bubbling air into an acidic silicic acid solution (silica concentration 1.0 to 6.0 mass %, pH 2.0 to 3.0) to adjust the dissolved oxygen concentration to 6.0 to 9.0 mg / L. Step 2: Following the previous step, while continuing air bubbling, hydrochloric acid is added to the acidic silicic acid solution so that the hydrochloric acid concentration becomes 300 ppm to 10,000 ppm, and then the solution is maintained at a temperature in the range of 50°C to 80°C, and further cation exchange is performed to obtain a purified acidic silicic acid solution. (Here, air bubbling into the acidic silicic acid solution is continued until just before cation exchange, but is not performed during cation exchange.) Step 3: Electrodialysis is carried out so that the conductivity of the purified acidic silicic acid solution obtained in the previous step becomes 0.5 to 2.0 ms / cm, and while continuing electrodialysis, an aqueous sulfuric acid solution is added so that the SO4 concentration of the purified acidic silicic acid solution becomes 300 to 10,000 ppm, and electrodialysis is continued until the conductivity becomes 0.5 to 1.0 ms / cm, and further cation exchange is carried out to obtain a high-purity silicic acid solution. Step 4: Add an alkaline aqueous solution to the high-purity silicic acid solution obtained in the previous step, and heat and maintain at 40 to 98°C to mature it. Subsequently, another high-purity silicic acid solution and an alkaline aqueous solution are added continuously or intermittently to obtain a silica microparticle dispersion. (5) The method for producing a silica fine particle dispersion according to (4) above, further comprising repeating the following step 5 at least once: Step 5: An alkaline aqueous solution is added to the silica microparticle dispersion obtained in the previous step to form core particles, and then another high-purity silicic acid solution and alkali are added continuously or intermittently to obtain a silica microparticle dispersion. [Effects of the Invention]

[0011] High-purity silica particles with a low impurity content are known to be synthesized by hydrolysis of alkoxysilane (high-purity silica particles derived from alkoxysilane).In contrast, the present invention provides extremely high-purity silica particles, silica particle dispersions, and methods for producing the same, which are synthesized using water glass, which is economically cheaper than alkoxysilane, as a raw material. According to the method for producing a silica microparticle dispersion of the present invention, the nickel content contained in the silica microparticles is superior to that of high-purity silica microparticles derived from alkoxysilanes, the copper content and aluminum content are at the same level as those of the same high-purity silica microparticles, and the sodium, iron and titanium contents can be made to levels that are almost comparable to those of the same high-purity silica microparticles. When the silica fine particles or silica fine particle dispersion of the present invention is used for polishing, polishing can be performed at a higher polishing rate than when conventional high-purity silica fine particles are used for polishing. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a graph showing the relationship between particle diameter and R4 obtained in Examples 1 to 5. [Figure 2] FIG. 1 is a graph showing the relationship between particle diameter and R2+3 obtained in Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will now be described. The present invention provides a silica fine particle dispersion in which silica fine particles satisfying the following [1] to [5] are dispersed in a solvent. [1] The particle diameter D (nm) of the silica fine particles, calculated by converting the specific surface area into an equivalent sphere, satisfies the relationship 5≦D≦100. [2] Regarding the silica particles 29 In the spectrum obtained by Si-NMR analysis, the areas of the peaks based on the Q0 structure, Q1 structure, Q2 structure, Q3 structure, and Q4 structure are determined, and when these are designated as S0, S1, S2, S3, and S4, the ratio R4 of S4 to the total of these (R4=S4 / (S0+S1+S2+S3+S4)×100) satisfies the following formula using the particle diameter D. 0.97≦(2.9×In(D)+73.7) / R4≦1.03 [3] The particle density of the silica fine particles is 2.2±0.20 g / cm 3 Range. [4] The carbon content in the silica fine particles is less than 0.1% by mass per SiO2. [5] The content of Al, Fe, and Na per SiO2 contained in the silica microparticles is 5 ppm or less (metal equivalent), the content of Ti per SiO2 is 10 ppm or less (metal equivalent), and the content of Cu and Ni per SiO2 is 20 ppb or less (metal equivalent). Such a silica fine particle dispersion will be hereinafter referred to as the "dispersion of the present invention." The silica fine particles contained in the dispersion of the present invention are also referred to as "silica fine particles of the present invention."

[0014] The present invention is a method for producing a silica fine particle dispersion liquid, which includes the following steps 1 to 4. Step 1: A step of bubbling air into an acidic silicic acid solution (silica concentration 1.0 to 6.0 mass %, pH 2.0 to 3.0) to adjust the dissolved oxygen concentration to 6.0 to 9.0 mg / L. Step 2: Following the previous step, while continuing air bubbling, hydrochloric acid is added to the acidic silicic acid solution so that the hydrochloric acid concentration becomes 300 ppm to 10,000 ppm, and then the solution is maintained at a temperature in the range of 50°C to 80°C, and further cation exchange is performed to obtain a purified acidic silicic acid solution. (Here, air bubbling into the acidic silicic acid solution is continued until just before cation exchange, but is not performed during cation exchange.) Step 3: Electrodialysis is carried out so that the conductivity of the purified acidic silicic acid solution obtained in the previous step becomes 0.5 to 2.0 ms / cm, and while continuing the electrodialysis, an aqueous sulfuric acid solution is added so that the SO4 concentration of the purified acidic silicic acid solution becomes 300 to 10,000 ppm, and electrodialysis is continued until the conductivity becomes 0.5 to 1.0 ms / cm, and further cation exchange is carried out to obtain a high-purity silicic acid solution. Step 4: Add an alkaline aqueous solution to the high-purity silicic acid solution obtained in the previous step, and heat and maintain at 40 to 98°C to mature it. Subsequently, another high-purity silicic acid solution and an alkaline aqueous solution are added continuously or intermittently to obtain a silica microparticle dispersion. Such a method for producing a silica fine particle dispersion liquid is hereinafter also referred to as the "production method of the present invention."

[0015] The dispersion of the present invention is preferably obtained by the production method of the present invention.

[0016] <Silica microparticles and silica microparticle dispersion of the present invention> [Silica Microparticles Overview] The silica microparticles of the present invention are substantially free of carbon, 29 The chemical shift of the Q4 structure in Si-NMR analysis appears in the region of -100.0 to -120.0 ppm, and the ratio of the measured area value to the specific surface area-equivalent particle diameter (D) of the silica microparticles satisfies certain conditions, and the silica microparticles are in a specific particle density range. When silica microparticles that satisfy these conditions are used for polishing, superior polishing performance (high polishing rate) can be obtained compared to when silica microparticles produced from alkoxysilanes are used for polishing. This is thought to be because silica microparticles that satisfy these conditions have a higher particle density and are harder at the same particle diameter than silica microparticles produced using alkoxysilane as a raw material, and therefore, when used as polishing abrasive grains, can transmit high kinetic energy to the polishing substrate.

[0017] [Chemical shift and average particle size] The silica microparticles of the present invention preferably have a specific surface area-equivalent particle diameter (D) of 5 to 100 nm. This range provides a high particle density and is particularly suitable as abrasive grains. When the specific surface area-equivalent particle diameter (D) is less than 5 nm, the silica cannot exist as silica particles and is dissolved in water. When the specific surface area-equivalent particle diameter (D) exceeds 100 nm, the relationship between the particle diameter and the degree of polymerization of the silica particles becomes balanced, and the particle density becomes saturated. It is more preferable that the specific surface area-equivalent particle diameter (D) of the silica microparticles be in the range of 10 to 80 nm. The measurement and calculation methods for the specific surface area-equivalent particle diameter (D) are as described below.

[0018] Silica fine particles of the present invention 29In the spectrum obtained by Si-NMR analysis, the areas of the peaks based on the Q0 structure, Q1 structure, Q2 structure, Q3 structure, and Q4 structure are determined, and when these are designated as S0, S1, S2, S3, and S4, the ratio R4 of S4 to the total of these (R4=S4 / (S0+S1+S2+S3+S4)×100) satisfies the following formula using the particle diameter D. 0.97≦(2.9×In(D)+73.7) / R4≦1.03

[0019] Regarding silica fine particles 29 In the spectrum obtained by Si-NMR analysis, the area of ​​the peak due to the Q0 structure is S0, the area of ​​the peak due to the Q1 structure is S1, the area of ​​the peak due to the Q2 structure is S2, the area of ​​the peak due to the Q3 structure is S3, and the area of ​​the peak due to the Q4 structure is S4. Then, let R1 = S1 / (S0 + S1 + S2 + S3 + S4) × 100, R2 = S2 / (S0 + S1 + S2 + S3 + S4) × 100, R3 = S3 / (S0 + S1 + S2 + S3 + S4) × 100, and R4 = S4 / (S0 + S1 + S2 + S3 + S4) × 100.

[0020] Each of the Q0 structure, Q1 structure, Q2 structure, Q3 structure and Q4 structure means the following structure.

[0021] [ka]

[0022] Here, (2.9 × In(D) + 73.7) / R4 represents the degree of development of the Q4 structure in the silica fine particles of the present invention. When the degree of polymerization of the silica fine particles is high (the particle density is high), 29 The Q4 peak area ratio of Si-NMR becomes higher. Here, (2.9×In(D)+73.7) represents the degree of development of the siloxane structure in the silica fine particles, and R4 represents the degree of development of the siloxane structure in the silica fine particles of the present invention. Silica fine particles synthesized using alkoxysilane as a raw material have a low particle density, and therefore the value in the above formula is greater than 1.03.

[0023] The abundance ratio of silicon in the Q0 to Q4 structures is as follows: 29 It can be determined by Si-NMR (nuclear magnetic resonance). 29 The silica sol containing the silica particles of the present invention is prepared using silicon containing Si, and for example, polydimethylsiloxane is used as a reference material. 29 Si-NMR analysis revealed that the chemical shifts of the Q0 to Q4 structures were in the range of -73.0 to -120.0 ppm. Specifically, the chemical shift of the Q0 structure was in the range of -73.0 to -73.5 ppm, the chemical shift of the Q1 structure was in the range of -73.5 to -78.0 ppm, the chemical shift of the Q2 structure was in the range of -82.0 to -100.0 ppm, the chemical shift of the Q3 structure was in the range of -90.0 to -110.0 ppm, and the chemical shift of the Q4 structure was in the range of -100.0 to -120.0 ppm.

[0024] The area of ​​the chemical shift peaks appearing in each region (S0, S1, S2, S3, S4) corresponds to the number of moles of silicon with Q0 to Q4 structures contained in the siloxane structure, so the peak area ratio of the chemical shift peaks of Q4 and Q3 structures to the total peak area (S0 + S1 + S2 + S3 + S4) in the chemical shift range of -73.0 to 120.0 ppm (i.e., R4, R3) represents the molar ratio of silicon with Q4 and Q3 structures contained in the siloxane structure. Therefore, silicon microparticles with a high ratio of the peak area ratio of the chemical shift peaks of the Q4 and Q3 structures (R4, R3) have a high density and can be said to exhibit an excellent polishing rate.

[0025] From this viewpoint, the silica fine particles of the present invention are prepared by using polydimethylsiloxane as a reference substance and preparing a silica sol containing the silica particles. 29The ratio of the area of ​​Q4 to the total peak area in the chemical shift range of -73.0 to -120.0 ppm in the spectrum obtained by Si-NMR analysis (i.e., R4) is preferably 79% or more, and the ratio of the area of ​​Q3 (i.e., R3) is preferably 18% or less. In other words, the total content of silicon having Q3 and Q4 structures is preferably in the range of 97% to 100% of the entire Q0 to Q4 structures, while the content of Q3 alone is preferably not more than 18%.

[0026] [Particle density] The silica fine particles of the present invention have a particle density of 2.2±0.20 g / cm 3 The particle density of the silica fine particles of the present invention is preferably in the range of 2.2±0.20 g / cm. Since the silica fine particles of the present invention do not contain carbon components derived from alkoxy groups, a Q4 structure in which Si is surrounded by four Si-O groups is formed, resulting in a particle density higher than that of silica fine particles produced using alkoxysilane as a raw material. The particle density is 2.2±0.20 g / cm. 3 Within this range, the skeleton of the silica particles is developed to a sufficient degree when used as polishing abrasive grains, and the particles can exhibit strength and hardness, so that such silica fine particles are highly practical as polishing abrasive grains. The particle density of the silica fine particles is 2.2±0.20 g / cm 3 If the density is less than the lower limit of 2.2±0.20 g / cm, the silica skeleton will not be sufficiently developed and the density of the silica fine particles will be 2.2±0.20 g / cm. 3 If the upper limit of the above is exceeded, the degree of polymerization will be higher than that of ordinary silica fine particles, the particle density will be too high, and the particles will tend to be coarse and hard. The method for measuring particle density will be described later.

[0027] [Carbon content] The carbon content in the silica fine particles of the present invention is preferably less than 0.1 mass% per SiO2. The silica fine particles of the present invention have such a low carbon content because the raw materials for producing them generally do not contain organic substances. Silica microparticles having a carbon content of 0.1% by mass or more are silica microparticles produced using alkoxysilane as a raw material, and have a carbon content of, for example, 0.4% by mass. These have a lower particle density than the silica microparticles of the present invention, and when used for polishing, the polishing rate is lower than that of the silica microparticles of the present invention.

[0028] The silica fine particles of the present invention preferably further satisfy the following [6]. [6] Ratio of the sum of the areas of S2+S3 to the sum of the areas of each peak (S0+S1+S2+S3+S4) 2+3 (R 2+3 = (S2+S3) / (S0+S1+S2+S3+S4) × 100) satisfies the following formula using the particle diameter D. 0.87≦(-4×In(D)+30) / R 2+3 ≦1.13 (-4×In(D)+30) represents the degree to which the Q2 and Q3 structures are not developed in ordinary silica particles, and R 2+3 represents the degree to which the Q2 structure and Q3 structure are not developed in the silica fine particles of the present invention. (-4×In(D)+30) / R 2+3 If the value is between 0.87 and 1.13, the silica microparticles have an appropriate particle density for use as polishing abrasive grains, which is preferable. If the value is less than 0.87, the particle density is low, and if the value is more than 1.13, the particle density is higher than that of ordinary silica microparticles, and the particles tend to be coarse and hard. (-4×In(D)+30) / R 2+3 The value is preferably in the range of 0.90 to 1.10.

[0029] [High-purity silica particles] The content of Al, Fe, and Na per SiO2 contained in the silica microparticles of the present invention is 5 ppm or less (metal equivalent), the content of Ti per SiO2 is 10 ppm or less (metal equivalent), and the content of Cu and Ni per SiO2 is 20 ppb or less (metal equivalent).

[0030] [Silica particle dispersion] The silica concentration of the dispersion of the present invention is not particularly limited, but is generally preferably in the range of 1% by mass to 50% by mass, and more preferably in the range of 10 to 40% by mass.

[0031] [solvent] Examples of the dispersion solvent contained in the dispersion of the present invention include alcohols such as methanol, ethanol, isopropanol, n-butanol, and methyl isocarbinol; ketones such as acetone, 2-butanone, ethyl amyl ketone, diacetone alcohol, isophorone, and cyclohexanone; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; ethers such as diethyl ether, isopropyl ether, tetrahydrofuran, 1,4-dioxane, and 3,4-dihydro-2H-pyran; glycol ethers such as 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, and ethylene glycol dimethyl ether; Examples of organic solvents that can be used include glycol ether acetates such as 2-ethoxyethyl acetate, 2-ethoxyethyl acetate, and 2-butoxyethyl acetate; esters such as methyl acetate, ethyl acetate, isobutyl acetate, amyl acetate, ethyl lactate, and ethylene carbonate; aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, heptane, isooctane, and cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,2-dichloroethane, dichloropropane, and chlorobenzene; sulfoxides such as dimethyl sulfoxide; and pyrrolidones such as N-methyl-2-pyrrolidone and N-octyl-2-pyrrolidone. These may also be used in combination with water.

[0032] [Raw material for silica particle dispersion] The dispersion of the present invention is preferably prepared using an alkali silicate as a raw material. Here, the alkali silicate is preferably, for example, an aqueous solution of alkali silicate having a solid content concentration in the range of 1 to 6 mass %. Although the type of the aqueous solution of alkali silicate is not particularly limited, it is preferably at least one selected from the group consisting of sodium silicate, potassium silicate, lithium silicate, and ammonium silicate, and more preferably sodium silicate and / or potassium silicate. The silica microparticles of the present invention are prepared using alkali silicate as a raw material, and have a lower carbon content and higher particle density than silica microparticles synthesized using alkoxysilane as a raw material, and can achieve an excellent polishing rate when used as a polishing abrasive.

[0033] <Production Method of the Present Invention> The production method of the present invention is a method for producing a silica fine particle dispersion liquid, which includes the following steps 1 to 4. Step 1: A step of bubbling air into an acidic silicic acid solution (silica concentration 1.0 to 6.0 mass %, pH 2.0 to 3.0) to adjust the dissolved oxygen concentration to 6.0 to 9.0 mg / L. Step 2: Following the previous step, while continuing air bubbling, hydrochloric acid is added so that the hydrochloric acid concentration becomes 300 ppm to 10,000 ppm, and then the temperature is maintained in the range of 50°C to 80°C, followed by cation exchange to obtain a purified acidic silicic acid solution. (Here, air bubbling into the acidic silicic acid solution is continued until just before cation exchange, but is not performed during cation exchange.) Step 3: Electrodialysis is carried out so that the conductivity of the purified acidic silicic acid solution obtained in the previous step becomes 0.5 to 2.0 ms / cm, and while continuing the electrodialysis, an aqueous sulfuric acid solution is added so that the SO4 concentration of the purified acidic silicic acid solution becomes 300 to 10,000 ppm, and electrodialysis is continued until the conductivity becomes 0.5 to 1.0 ms / cm, and further cation exchange is carried out to obtain a high-purity silicic acid solution. Step 4: Add an alkaline aqueous solution to the high-purity silicic acid solution obtained in the previous step, and heat and maintain at 40 to 98°C to mature it. Subsequently, another high-purity silicic acid solution and an alkaline aqueous solution are added continuously or intermittently to obtain a silica microparticle dispersion.

[0034] [Preferred manufacturing method] The production method of the present invention preferably further includes repeating the following step 5 one or more times. Step 5: An alkaline aqueous solution is added to the silica microparticle dispersion obtained in the previous step to form core particles, and then another high-purity silicic acid solution and alkali are added continuously or intermittently to obtain a silica microparticle dispersion.

[0035] [Process 1] In step 1, air is bubbled into an acidic silicic acid solution (silica concentration 1.0-6.0% by mass, pH 2.0-3.0) to adjust the dissolved oxygen concentration to 6.0-9.0 mg / L. The air bubbling is performed to promote ionization of metal impurities through oxidation. The ionized metal impurities are extracted and reduced or removed by the action of acid in a later step. The dissolved oxygen concentration is preferably in the range of 6.0 to 9.0 mg / L. This range is preferable because it promotes the ionization of metal impurities. If the dissolved oxygen concentration is less than 6.0 mg / L, the ionization of metal impurities is insufficient, and if it exceeds 9.0 mg / L, the effect of promoting ionization tends to saturate. A dissolved oxygen concentration in the range of 7.5 to 8.5 mg / L is recommended. Air bubbling is preferably performed using air. This is because air bubbling using air containing oxygen is effective for the ionization. However, bubbling using oxygen alone raises safety concerns because oxygen is a flammable gas. On the other hand, the ionization effect may not be achieved if a gas containing no oxygen (e.g., nitrogen gas) is used.

[0036] [Process 2] In step 2, following the previous step, hydrochloric acid is added while continuing air bubbling of the acidic silicic acid solution so that the hydrochloric acid concentration becomes 300 ppm to 10,000 ppm, and then the temperature is maintained in the range of 50°C to 80°C, followed by further cation exchange to obtain a purified acidic silicic acid solution. (Here, air bubbling of the acidic silicic acid solution is continued until just before cation exchange, but is not performed during cation exchange.) The hydrochloric acid is added for the purpose of acid leaching (the dissolution of impurity elements in silica into the dispersion medium using acid). The hydrochloric acid is preferably added so that the hydrochloric acid concentration in the acidic silicic acid solution is in the range of 300 ppm to 10,000 ppm. A hydrochloric acid concentration in the acidic silicic acid solution of 300 ppm to 10,000 ppm is preferred because it promotes the dissolution of metal impurities contained in silica. If the hydrochloric acid concentration in the acidic silicic acid solution is less than 300 ppm, the dissolution of metal impurities is insufficient. Similarly, if the hydrochloric acid concentration in the acidic silicic acid solution exceeds 10,000 ppm, the tendency for the metal impurities to dissolve in acid is saturated. The hydrochloric acid concentration in the acidic silicic acid solution is preferably in the range of 2,000 to 5,000 ppm. After the addition of hydrochloric acid, the solution is maintained at a temperature in the range of 50 to 80°C, and further cation exchange is carried out to obtain a purified acidic silicic acid solution. The temperature at which the acidic silicic acid solution is maintained after the addition of hydrochloric acid is preferably 50 to 80°C. This range is preferred because the acid dissolution of metal impurities proceeds without the silicic acid solution gelling. If the temperature is below 50°C, the acid dissolution of metal impurities may be insufficient, while if the temperature exceeds 80°C, there is a risk of the silicic acid solution gelling. The time for maintaining the acidic silicic acid solution within this temperature range is not particularly limited, but is typically 30 minutes to 8 hours. The temperature at which the acidic silicic acid solution is maintained is more preferably in the range of 60 to 70° C. During the addition of hydrochloric acid and the maintenance at 50 to 80° C., it is desirable to continue air bubbling in order to promote ionization by oxidation of metal impurities, as in the previous step.

[0037] The acidic silicic acid solution is then subjected to cation exchange to obtain a purified acidic silicic acid solution, preferably using a strongly acidic cation exchange resin. Here, for example, a strongly acidic cation exchange resin refers to an ion exchange resin having a sulfonic acid group. Although acidic ion exchange resins without sulfonic acid groups have been available, these do not qualify as the strongly acidic cation exchange resins used in the production method of the present invention. Strongly acidic cation exchange resins dissociate over the entire pH range and therefore have ion exchange capacity over the entire pH range. However, other ion exchange resins, such as weakly acidic ion exchange resins having carboxylic acid groups as exchange groups, do not dissociate on the acidic side and therefore lack ion exchange capacity, making them unsuitable for the production method of the present invention.

[0038] Cation exchange can be carried out by known methods. For example, ion exchange can be carried out by passing an acidic silicic acid solution through a column packed with a conventionally known strongly acidic cation exchange resin. Here, the liquid passing rate is not particularly limited, but it is preferable to set it to a liquid passing rate such that the spatial velocity is, for example, 2 to 18. Although it depends on the shape and size of the column, it is preferable to set the liquid passing rate to a relatively high spatial velocity within the above range. Ion exchange can also be carried out by adding a strongly acidic cation exchange resin to an aqueous alkali silicate solution and stirring it.

[0039] [Process 3] In step 3, electrodialysis is carried out so that the conductivity of the purified acidic silicic acid solution obtained in the previous step becomes 0.5 to 2.0 ms / cm. While continuing the electrodialysis, an aqueous sulfuric acid solution is added so that the SO4 concentration of the purified acidic silicic acid solution becomes 300 to 10,000 ppm. Electrodialysis is continued until the conductivity becomes 0.5 to 1.0 ms / cm, and further cation exchange is carried out to obtain a high-purity silicic acid solution. The electrodialysis is carried out for the purposes of reducing the Cl concentration and replacing SO4 with Cl. In the cation exchange process, ionized metal impurities are removed using a cation exchange resin in the previous step, but the presence of excess acid here makes it easy for alkali metals to desorb from the ion exchange resin, and some of the alkali metals tend to remain in the purified acidic silicic acid solution. Therefore, the excess acid is removed and the pH of the purified acidic silicic acid solution is adjusted to about 2, creating conditions that make it difficult for alkali metals to desorb from the ion exchange resin, before conducting another ion exchange. It is preferable to carry out electrodialysis so that the conductivity of the purified acidic silicic acid solution obtained in the previous step is 0.5 to 2.0 ms / cm, thereby adjusting the Cl concentration in the purified acidic silicic acid solution to 50 to 200 ppm. When the silica microparticle dispersion of the present invention is applied to CMP applications, residual Cl in the silica microparticle dispersion can cause corrosion of the silicon substrate, so it is necessary to remove Cl from the purified acidic silicic acid solution to a predetermined electrical conductivity, and then add sulfuric acid to replace the Cl.

[0040] When the electrodialysis in step 3 is carried out using, for example, an electrodialysis apparatus equipped with a deionization compartment, a concentration compartment, and an electrode solution tank, the purified acidic silicic acid solution is poured into the deionization compartment, pure water is poured into the concentration compartment, and an aqueous sulfuric acid solution is poured into the electrode solution tank. Here, electrodialysis is preferably carried out until the electrical conductivity of the purified acidic silicic acid solution reaches 0.5 to 2.0 ms / cm. If electrodialysis is carried out until the electrical conductivity of the purified acidic silicic acid solution reaches this range, the Cl content in the purified acidic silicic acid solution is appropriate, and the viscosity of the purified acidic silicic acid solution does not increase. If the electrical conductivity is less than 0.5 ms / cm, the Cl content is too low, causing the viscosity of the purified acidic silicic acid solution to increase and make it more susceptible to gelation. If the electrical conductivity of the purified acidic silicic acid solution exceeds 2.0 ms / cm, the Cl content is high, resulting in residual Cl remaining in the silica microparticle dispersion obtained by the production method of the present invention. A more preferable range for the electrical conductivity is 0.7 to 1.0 ms / cm.

[0041] After the purified acidic silicic acid solution has been adjusted to an electrical conductivity of 0.5 to 2.0 ms / cm, an aqueous sulfuric acid solution is added while continuing electrodialysis so that the SO4 concentration in the purified acidic silicic acid solution becomes 300 to 10,000 ppm. Electrodialysis is continued until the electrical conductivity becomes 0.5 to 1.0 ms / cm, and further cation exchange is performed to obtain a high-purity silicic acid solution. Here, it is desirable to add an aqueous sulfuric acid solution to bring the SO4 concentration of the purified acidic silicic acid solution to 300 to 10,000 ppm. This range is preferable because Cl is replaced by SO4. If the SO4 concentration of the purified acidic silicic acid solution is less than 300 ppm, the replacement of Cl by SO4 will be insufficient, and if it exceeds 10,000 ppm, the replacement of Cl by SO4 will saturate. A more desirable SO4 concentration range is 1,000 to 5,000 ppm.

[0042] Electrodialysis is continued until the conductivity of the purified acidic silicic acid solution reaches 0.5 to 1.0 ms / cm. Here, if the conductivity of the purified acidic silicic acid solution is within this range, the SO4 content is optimal and preferred. If the conductivity of the purified acidic silicic acid solution is less than 0.5 ms / cm, the SO4 content is too low, causing the viscosity of the silicic acid solution to increase and make it prone to gelation. If the conductivity exceeds 1.0 ms / cm, the replacement of Cl by SO4 is insufficient, resulting in Cl remaining in the silica microparticle dispersion. The conductivity range of the purified acidic silicic acid solution here is more preferably 0.7 to 1.0 ms / cm.

[0043] Next, the purified acidic silicic acid solution is subjected to cation exchange to obtain a purified acidic silicic acid solution. Here, a strongly acidic cation exchange resin is preferably used for the cation exchange. The selection of the ion exchange resin, the liquid flow rate, the ion exchange method, etc. for the cation exchange performed in step 3 are the same as those in step 2.

[0044] [Step 4] In step 4, an alkaline aqueous solution is added to the high-purity silicic acid liquid obtained in the previous step, and the mixture is aged by heating and maintaining at 40 to 98°C. Subsequently, another high-purity silicic acid liquid and an alkaline aqueous solution are added continuously or intermittently to obtain a silica microparticle dispersion liquid. In step 4, the high-purity silicic acid liquid is aggregated to form core particles, and the high-purity silicic acid liquid and an alkaline aqueous solution are added to the core particles to grow the particles, thereby obtaining a silica fine particle dispersion.

[0045] More specifically, in step 4, an alkaline aqueous solution is added to the high-purity silicic acid liquid obtained in the previous step, heated to a temperature in the range of 40°C to 98°C, and maintained at a temperature in the range of 40°C to 98°C (preferably for 20 minutes or more), and then a high-purity silicic acid liquid similar to the high-purity silicic acid liquid obtained in step 3 and an alkaline aqueous solution are added continuously or intermittently (preferably simultaneously) to obtain a silica microparticle dispersion liquid. The high-purity silicic acid liquid obtained in the previous step and used in step 4 is also called a "seed liquid" (seed particle dispersion liquid). The high-purity silicic acid liquid added to the seed liquid in step 4 is also called a "feed liquid."

[0046] In step 4, it is preferable to first add an alkaline aqueous solution to the high-purity silicic acid solution to adjust the pH of the high-purity silicic acid solution to a range of 10.0 to 13.0. This range is preferable because silica nucleation occurs during the subsequent treatment (at a temperature of 40°C to 98°C, preferably maintained within this temperature range for 20 minutes or more), and an optimal seed solution (seed particle dispersion) is obtained. If the pH of the high-purity silicic acid solution is less than 10.0, silica nucleation may occur too quickly, resulting in a seed solution containing very small nuclei, which may prevent the production of silica microparticles of the desired size. If the pH of the high-purity silicic acid solution is greater than 13.0, the nuclei generated may be large and the distribution may be broad, resulting in silica microparticles containing coarse particles with a wide particle size distribution. The pH range of the high-purity silicic acid solution is preferably between 11.0 and 12.5.

[0047] The high-purity silicic acid solution to which alkali has been added is heated to a temperature in the range of 40°C to 98°C, more preferably 50°C to 98°C, and even more preferably 60°C to 98°C. After the temperature is raised, the temperature is maintained for a predetermined time, and then the high-purity silicic acid solution is added to form silica fine particles and promote particle growth. Furthermore, the recommended holding time after the temperature rise is 20 minutes or more, and preferably 25 minutes or more.

[0048] The type of alkali is not particularly limited, but examples include potassium hydroxide, sodium hydroxide, and organic alkalis. The alkali is preferably used in an amount that allows the pH of the seed solution to be adjusted to a range of 10 to 13. The amount of the feed liquid used is such that the ratio of parts by mass of seed liquid to parts by mass of feed liquid is 100:100 to 100:10,000 in terms of silica [parts by mass] relative to the seed liquid.

[0049] Furthermore, the seed liquid and the feed liquid can be mixed by adding the feed liquid and the alkaline aqueous solution (preferably simultaneously). The amount of aqueous alkali solution used here is determined based on the amount of inorganic acid contained in the high-purity silicic acid solution used as the feed solution. When the inorganic acid is a monovalent inorganic acid, an equimolar amount is used; when the inorganic acid is a divalent inorganic acid, an amount twice as large as the inorganic acid; and when the inorganic acid is a trivalent inorganic acid, an amount three times as large as the inorganic acid. The rate of addition of the aqueous alkali solution is not particularly limited, as it varies depending on the concentration of the aqueous alkali solution. The type of aqueous alkali solution is not particularly limited, but examples include potassium hydroxide and sodium hydroxide. The aqueous alkali solution is added to maintain a sufficiently alkaline pH in the preparation, thereby dissolving the added high-purity silicic acid solution and depositing it on the surface of the core particles or silica particles. The aqueous alkali solution is added to maintain the pH of the system consisting of the seed solution, alkali, and feed solution, preferably in the range of 10 to 13 during the addition of the feed solution. Here, the temperature of the feed liquid is preferably in the range of 1°C or more and 30°C or less, more preferably in the range of 1°C or more and 20°C or less, and the feed liquid is added to the seed liquid.

[0050] [Step 5] Preferably, the feed liquid is gradually added to the seed liquid adjusted to the pH and temperature as described above, whereby silica microparticles grow in the seed liquid and a silica microparticle dispersion liquid (silica sol) is obtained. After the feed liquid is added to the seed liquid, it is preferable to maintain the temperature in the range of about 50°C to 98°C for several tens of minutes to several hours, since this allows the added high-purity silicic acid liquid to be sufficiently deposited on the silica microparticles, facilitating the growth of the silica microparticles. [Example]

[0051] 1.<Measurement of the average particle size of silica particles> The particle diameter D of the silica fine particles obtained in each of the Examples and Comparative Examples was calculated by substituting the value of the specific surface area measured by the method described below into the following formula and converting it into an equivalent sphere. D(nm)=6000 / (ρ·SA) where ρ is particle density, 2.20 g / cm 3 , SA: Specific surface area (m 2 / g).

[0052] 2.<Measurement of specific surface area (SA)> The specific surface area (SA) of the silica fine particles obtained in each of the Examples and Comparative Examples was measured. The method for measuring the specific surface area (BET specific surface area) will now be described. First, the silica fine particle dispersion was dried at 105° C. to obtain a powdered sample (silica fine particles). Next, the dried sample (0.2 g) is placed in a measurement cell and degassed in a nitrogen gas flow at 250°C for 40 minutes. The sample is then kept at liquid nitrogen temperature in a mixed gas flow of 30% by volume of nitrogen and 70% by volume of helium, and nitrogen is adsorbed onto the sample in equilibrium. Next, the temperature of the sample is gradually raised to room temperature while the mixed gas is being passed through, and the amount of nitrogen desorbed during this period is detected, and the specific surface area of ​​the sample is measured using a calibration curve prepared in advance. Such a BET specific surface area measurement method (nitrogen adsorption method) can be carried out using, for example, a conventionally known surface area measurement device. In the examples and comparative examples, a device manufactured by Mountec Co., Ltd., named Macsorb-1220, was used.

[0053] 3. Measurement of SiO₂ Content The silica particle dispersion was subjected to ignition loss at 1000 °C, and the obtained solid content was weighed to determine the mass, and the solid content concentration of the silica particle dispersion was determined. Further, the amount of impurities (in terms of oxide) determined by the method described below was subtracted from the solid content mass, and the obtained value was taken as the SiO₂ content contained in the silica particle dispersion.

[0054] 4. Measurement of Impurity Concentration The contents of Al, Na, Cu, Fe, Ti, and Ni (silica dry basis) in the silica particles obtained in each of the examples and comparative examples were measured. As the measuring device, an ICP plasma emission spectrometer (manufactured by SII, SPS5520) was used. The content rate of each element shall be measured by the following method. Approximately 1 g (adjusted to a solid content of 20 mass%) of the silica particle dispersion is collected in a platinum dish. 3 ml of phosphoric acid, 5 ml of nitric acid, and 10 ml of hydrofluoric acid are added, and it is heated on a sand bath. After drying, a small amount of water and 50 ml of nitric acid are added and dissolved, and it is placed in a 100 ml volumetric flask and diluted to 100 ml with water. For Na in this solution, it is measured with an atomic absorption spectrophotometer (for example, manufactured by Hitachi, Z-2310). Next, the operation of collecting 10 ml of aliquot from the solution placed in 100 ml into a 20 ml volumetric flask is repeated 5 times to obtain 5 aliquots of 10 ml. Then, using these, measurements of Cu, Ni, Al, Fe, Na, and Ti are performed by the standard addition method with an ICP plasma emission spectrometer. Here, a blank is also measured by the same method, and the blank portion is subtracted and adjusted to obtain the measured value for each element. Then, based on the mass of SiO₂ determined by the method described above, the mass ratio (ppm) of each component to SiO₂ was determined.

[0055] 5. Measurement of Cl and SO₄ Concentrations In each of the examples and comparative examples, the Cl concentration of the purified acidic silicic acid solution when performing electrodialysis and the Cl and SO₄ contents (mass ratio to SiO₂) of the high-purity silicic acid solution obtained by cation exchange were measured by ion chromatography. Specifically, 1 to 2 g of sample is taken and made into 200 ml of water to create a sample solution. Next, using a standard sample, the areas of chloride ions and sulfate ions are measured and a calibration curve is created. The areas of the sample solution are then measured to determine the concentrations of chloride ions and sulfate ions.

[0056] 6.<Measurement of carbon content> The silica microparticle dispersions obtained in each Example and Comparative Example were adjusted to 10°C and then centrifuged at 1,370,000 rpm (1,000,000 G) for 30 minutes using a small ultracentrifuge (Hitachi Koki Co., Ltd., CS150GXL). The precipitate was then collected and vacuum dried at 120°C for 24 hours to obtain a particle powder. The carbon content of this particle powder was measured using a carbon-sulfur analyzer (LECO Japan, CS844), and the mass ratio (mass %) of the carbon content to the SiO2 content in the silica microparticles was calculated.

[0057] 7.<Dissolved oxygen concentration> The dissolved oxygen in the acidic silicic acid solution was measured while air bubbling. The dissolved oxygen concentration was measured using a DO meter (model: OM-51) and a DO electrode (model: 9552-50D) manufactured by Horiba Ltd.

[0058] 8.<Particle density> Particle density (T D ) was performed in accordance with JIS Z 8807 "Method for measuring density and specific gravity of solids." The details are described below. The silica particle dispersion was placed in a crucible and dried on a hot plate at 150°C. After drying, it was further heated at 300°C for 1 hour and then cooled in a desiccator to prevent moisture absorption. It was then removed from the desiccator and crushed in a mortar. Approximately 10 g of the crushed sample was used for measurement. The 25 ml pycnometer and its stopper were then washed with ethanol and dried. The pycnometer was stoppered and weighed on a balance, and the mass was designated as W1. Next, the sample prepared as described above was placed in a pycnometer, the bottle was stoppered, and the bottle was weighed on a balance, and the mass was designated as W2. 20 ml of ethanol was added to the pycnometer containing the sample, and the pycnometer was degassed at 0.02 MPa or less for 30 minutes. After degassing, the pycnometer was filled with ethanol and placed in a constant temperature bath at 25°C without a stopper for 30 minutes. Next, the pycnometer was removed from the constant temperature bath, the stopper was put back on, the overflowing ethanol was wiped off, and the mass was weighed on a balance, and the mass was taken as W3. In addition, the density ρ of ethanol at that temperature was e The volume (V) of the pycnometer was calculated from the literature value. The obtained value is then substituted into the formula to obtain the density of the silica particles (T D ) was sought. T D =(W2-W1) / [V-(W3-W2) / ρ e ]

[0059] 9.< 29 Si-NMR measurement> Approximately 100 mg of dried silica particles was densely packed in a zirconia rotor with a 5 mm diameter, and the base magnetic field was set to 14.1 T in an NMR apparatus (Agilent VNMRS-600, 1 H resonance frequency 600MHz) 29 Measurements were carried out for the Si nucleus (119.2MHz). NMR measurements were performed using a single-pulse non-decoupling method, with 128 accumulations and a waiting time of 400 seconds. Polydimethylsiloxane (-34.44 ppm) was used as the reference material. Waveform analysis was performed on the obtained spectrum to determine the chemical shift and integral value of each signal. From these chemical shifts, the Q0, Q1, Q2, Q3, and Q4 structures were assigned. The peak areas (integral values) based on each were calculated, and these were designated S0, S1, S2, S3, and S4. The ratio (area percentage) of each to the total (S0 + S1 + S2 + S3 + S4) was then calculated.

[0060] <Polishing evaluation> The silica fine particle dispersion obtained in each of the Examples and Comparative Examples was diluted with pure water to 0.23 mass % and the pH was adjusted to 10 with ammonia to prepare a polishing liquid. A silicon wafer was used as the polishing substrate and set in a polishing machine (NF300, manufactured by Nanofactor Co., Ltd.). Using a SUBA600 polishing pad, the silicon wafer was polished for 1 minute at a substrate load of 15 kPa, a table rotation speed of 30 rpm, a spindle speed of 30 rpm, and while supplying the polishing solution at a rate of 250 ml / min. The substrate was then washed with pure water and air-dried. The weight loss of the polishing substrate was then measured, and the polishing rate was calculated.

[0061] In the following description of the Examples and Comparative Examples, the notation "(Step 1)" means that it corresponds to "Step 1" in the production method of the present invention. This relationship also applies to "(Step 2)" and "Step 2," "(Step 3)" and "Step 3," and "(Step 4)" and "Step 4."

[0062] <Synthesis Example 1> [Preparation of acidic silicic acid solution] No. 3 sodium silicate was diluted with pure water to prepare 10 kg of a diluted solution (aqueous sodium silicate solution [silica concentration 5% by mass]) and cooled to a liquid temperature of 10°C. Next, a column (volume 1,700 ml) was densely packed with a strong acid cation exchange resin (SK 1B manufactured by Mitsubishi Chemical), and the diluted solution (aqueous sodium silicate solution [silica concentration 5% by mass]) was introduced into the column at a space velocity of 9 hr. -1 The liquid was passed through the column at 100° C. to obtain 9,500 g of an acidic silicic acid liquid (1) (silica concentration: 4.8% by mass, pH: 2.6).

[0063] Example 1 (Process 1) 7,500 g of the acidic silicic acid solution (1) was placed in a 10 L separable flask lined with Teflon, and air bubbling was performed at a flow rate of 7 L / min to adjust the dissolved oxygen concentration to 7.5 mg / L.

[0064] (Process 2) Next, hydrochloric acid (concentration 10% by mass) was added to the acidic silicic acid solution (1) so that the Cl content was 3000 ppm, and then heating was started with a mantle heater to heat the solution to 70° C. After the solution temperature reached 70° C., the solution was maintained at 70° C. for 30 minutes for heat treatment. The air bubbling was continued at a flow rate of 7 L / min until the end of the heat treatment. Next, 1,500 g of a strong acid cation exchange resin (SK 1B manufactured by Mitsubishi Chemical, washed with pure water and then thoroughly drained) was gradually added to the acid silicic acid solution (1) after the heat treatment, and an ion exchange treatment was carried out while maintaining the liquid temperature at 70°C. During this time, air bubbling was not performed. The ion exchange resin was separated to obtain a purified acid silicic acid solution (2).

[0065] (Step 3) Next, the purified acidic silicic acid solution (2) prepared in (Step 2) was cooled to 15 ° C., and 3,500 g of the purified acidic silicic acid solution (2) was placed in the desalting compartment of the electrodialysis device. 3,000 g of pure water was placed in the concentration compartment, and 3,000 g of an aqueous sulfuric acid solution (concentration 1% by mass) was placed in the electrode solution tank. Electrodialysis was started under conditions of a transmembrane voltage of 4.5 V and a liquid circulation flow rate of 4 L / min, and dialysis was performed until the conductivity decreased to 0.9 mS / cm. At this point, the Cl concentration became 100 ppm. Next, an aqueous sulfuric acid solution (sulfuric acid concentration 10% by mass) was added to the purified acidic silicic acid solution (2) flowing into the desalination tank so that the SO content was 1000 ppm, and electrodialysis was continued until the conductivity decreased to 0.6 ms / cm, thereby obtaining a purified acidic silicic acid solution (3). This operation was carried out in two batches to obtain a total of 6900 g of purified acidic silicic acid solution (3). The Cl concentration of the purified acidic silicic acid solution (3) at this time was 0 ppm and the SO4 concentration was 80 ppm. The electrodialysis device used here was a CH-0 model manufactured by AGC Engineering Co., Ltd. The dialysis membrane was configured with 10 pairs of cation membrane / anion membrane. To 6,900 g of the purified acidic silicic acid solution (3), 1,380 g of a strong acidic cation exchange resin (SK 1B manufactured by Mitsubishi Chemical, washed with pure water and then thoroughly drained) was gradually added to carry out ion exchange, and then the ion exchange resin was separated to obtain a high-purity silicic acid solution (1) (silica concentration 4.5% by mass).

[0066] (Step 4) 117g of the high-purity silicic acid solution (1) (silica concentration 4.5% by mass) prepared in (step 3) and 428g of pure water were poured into a 10L stainless steel container equipped with a Liebig condenser, stirred and mixed to prepare a diluted high-purity silicic acid solution, and then 199g of ammonia water (concentration 15% by mass) was added thereto and stirred and mixed for 10 minutes, and then heated to 83 ° C. and held for 30 minutes for heat aging. Then, a total of 6,390g of the high-purity silicic acid solution (1) prepared in step 3 was added at an addition rate of 7.1g / min, and a total of 990g of ammonia water (concentration 1% by mass) was added at an addition rate of 1.1g / min. After the addition of the high-purity silicic acid solution (1) and the ammonia water was completed, the solution was heated and aged for 60 minutes while maintaining the liquid temperature at 83 ° C. After the heat aging was completed, the liquid temperature was cooled to below 40°C, and the liquid was concentrated to a silica concentration of 11% by mass using an ultrafiltration membrane (SIP1013 manufactured by Asahi Kasei), and further concentrated to a silica concentration of 40% by mass using a rotary evaporator to obtain a silica microparticle dispersion (silica concentration 20% by mass). The silica fine particle dispersion thus obtained was subjected to BET specific surface area measurement, metal impurity measurement, anion concentration measurement, NMR measurement, particle density measurement, carbon content measurement, and polishing test. The particle diameter D of these silica microparticles was 17 nm. The ratios (area percentages) of the peak areas (S0, S1, S2, S3, and S4) based on the Q0, Q1, Q2, Q3, and Q4 structures to the total (S0 + S1 + S2 + S3 + S4) were calculated. These data are shown in Table 1. Graphs based on these data are shown in Figures 1 and 2. Further measurement results and measurement methods are shown in Tables 2, 3 and 4.

[0067] <Example 2> (Step 5(1)) 210 g of the same silica particle dispersion (silica concentration 20 mass %) as prepared in Example 1 and 440 g of pure water were poured into a 10 L stainless steel vessel equipped with a Liebig condenser and mixed with stirring. Next, 61 g of aqueous ammonia (concentration: 3% by mass) was added to the container and mixed with stirring for 10 minutes, and then the temperature was raised to 87°C and maintained at that temperature for 30 minutes for thermal aging. Next, a total of 6,890 g of the same high-purity silicic acid solution (1) (silica concentration: 4.5% by mass) as prepared in step 3 of Example 1 was added at a rate of 6.4 g / min. Simultaneously, a total of 1,239 g of aqueous ammonia (concentration: 1% by mass) was added at a rate of 1.1 g / min. After the addition of the high-purity silicic acid liquid (1) and aqueous ammonia was completed, the liquid was heated and aged for 60 minutes while maintaining the liquid temperature at 87°C. After the heat aging was completed, the liquid was cooled to 40°C or below, concentrated using an ultrafiltration membrane (SIP1013 manufactured by Asahi Kasei) to a silica concentration of 11% by mass, and further concentrated using a rotary evaporator to a silica concentration of 20% by mass to obtain a silica microparticle dispersion. The silica fine particle dispersion thus obtained was subjected to BET specific surface area measurement, metal impurity measurement, anion concentration measurement, NMR measurement, particle density measurement, carbon content measurement, and polishing test. The particle diameter D of these silica microparticles was 40 nm. The ratios (area percentages) of the peak areas (S0, S1, S2, S3, and S4) based on the Q0, Q1, Q2, Q3, and Q4 structures to the total (S0 + S1 + S2 + S3 + S4) were calculated. These data are shown in Table 1. Graphs based on these data are shown in Figures 1 and 2. Further measurement results and measurement methods are shown in Tables 2, 3 and 4.

[0068] Example 3 (Step 5(2)) 588 g of a silica fine particle dispersion similar to that prepared in Example 2 (silica concentration 20% by mass) and 1373 g of pure water were poured into a 10 L stainless steel vessel equipped with a Liebig condenser and mixed with stirring. Next, 34 g of 15% by mass ammonia water was added thereto, and the mixture was stirred and mixed for 10 minutes. The temperature was then raised to 87°C and heat-aged for 30 minutes. Subsequently, a total of 5163 g of the high-purity silicic acid solution (1) (silica concentration 4.5% by mass) prepared in step 3 of Example 1 was added at an addition rate of 4.8 g / min. A total of 930 g of ammonia water (concentration 1% by mass) was simultaneously added at an addition rate of 1 g / min. After the addition of the high-purity silicic acid solution (1) and ammonia water (concentration 1% by mass) was completed, the solution was heat-aged by maintaining the liquid temperature at 87°C for 60 minutes. After the heating and aging process was completed, the liquid temperature was cooled to below 40°C, and then the liquid was concentrated using an ultrafiltration membrane (SIP1013 manufactured by Asahi Kasei) to a silica concentration of 11% by mass, and further concentrated using a rotary evaporator to a silica concentration of 20% by mass to obtain a silica microparticle dispersion. The particle diameter D of the silica fine particle dispersion thus obtained was 60 nm.

[0069] (Step 5(3)) 785 g of the silica microparticle dispersion (silica concentration 20% by mass) prepared in step 5(2) and 1,833 g of pure water were poured into a 10 L stainless steel vessel equipped with a Liebig condenser and stirred. 46 g of ammonia water (concentration 15% by mass) was then added to the vessel and stirred for 10 minutes. The mixture was then heated to 87°C and maintained at this temperature for 30 minutes for thermal aging. Next, a total of 4,287 g of high-purity silicic acid solution (1) (silica concentration 4.5 mass%) similar to that prepared in step 3 of Example 1 was added at a rate of 4.0 g / min. Simultaneously, a total of 771 g of aqueous ammonia (concentration 1 mass%) was added at a rate of 0.7 g / min. After the addition of the high-purity silicic acid liquid (1) and aqueous ammonia was completed, the liquid was heated and aged for 60 minutes while maintaining the liquid temperature at 87°C. After the heat-aging was completed, the liquid temperature was cooled to 40°C or less, and then the liquid was concentrated using an ultrafiltration membrane (SIP1013 manufactured by Asahi Kasei) to a silica concentration of 11% by mass, and further concentrated using a rotary evaporator to a silica concentration of 20% by mass to obtain a silica microparticle dispersion. The silica fine particle dispersion thus obtained was subjected to BET specific surface area measurement, metal impurity measurement, anion concentration measurement, NMR measurement, particle density measurement, carbon content measurement, and polishing test. The particle diameter D of these silica microparticles was 80 nm. The ratios (area percentages) of the peak areas (S0, S1, S2, S3, and S4) based on the Q0, Q1, Q2, Q3, and Q4 structures to the total (S0 + S1 + S2 + S3 + S4) were calculated. These data are shown in Table 1. Graphs based on these data are shown in Figures 1 and 2. Further measurement results and measurement methods are shown in Tables 2, 3 and 4.

[0070] Example 4 117 g of the high-purity silicic acid solution (1) (silica concentration 4.5% by mass) prepared in Example 1 (step 3) and 428 g of pure water were poured into a 10 L stainless steel container equipped with a Liebig condenser, stirred and mixed to prepare a diluted high-purity silicic acid solution, and then 199 g of ammonia water (concentration 15% by mass) was added thereto and stirred and mixed for 10 minutes, and then heated to 83 ° C. and held for 30 minutes for heat aging. Then, a total of 4,136 g of the high-purity silicic acid solution (1) prepared in step 3 was added at an addition rate of 7.1 g / min, and a total of 1,020 g of ammonia water (concentration 1% by mass) was added at an addition rate of 1.8 g / min. After the addition of the high-purity silicic acid solution (1) and the ammonia water was completed, the liquid temperature was maintained at 83 ° C. for 60 minutes for heat aging. After the heat aging was completed, the liquid temperature was cooled to below 40°C, and the liquid was concentrated to a silica concentration of 11% by mass using an ultrafiltration membrane (SIP1013 manufactured by Asahi Kasei), and further concentrated to a silica concentration of 40% by mass using a rotary evaporator to obtain a silica microparticle dispersion (silica concentration 20% by mass). The silica fine particle dispersion thus obtained was subjected to BET specific surface area measurement, metal impurity measurement, anion concentration measurement, NMR measurement, particle density measurement, and carbon content measurement. The particle diameter D of these silica microparticles was 11 nm. The ratios (area percentages) of the peak areas (S0, S1, S2, S3, and S4) based on the Q0, Q1, Q2, Q3, and Q4 structures to the total (S0 + S1 + S2 + S3 + S4) were calculated. These data are shown in Table 1. Graphs based on these data are shown in Figures 1 and 2. Further measurement results and measurement methods are shown in Tables 2, 3 and 4.

[0071] <Example 5> (Step 5(1)) 699 g of the same silica particle dispersion (silica concentration 20% by mass) as prepared in Example 1 and 1,468 g of pure water were poured into a 10 L stainless steel vessel equipped with a Liebig condenser and mixed with stirring. Next, 203 g of aqueous ammonia (concentration: 3% by mass) was added to the container and mixed with stirring for 10 minutes, and then the temperature was raised to 87°C and maintained at that temperature for 30 minutes for thermal aging. Next, a total of 4,715 g of the same high-purity silicic acid solution (1) (silica concentration 4.5% by mass) as that prepared in step 3 of Example 1 was added at a rate of 4.4 g / min. Simultaneously, a total of 849 g of aqueous ammonia (concentration 1% by mass) was added at a rate of 0.8 g / min. After the addition of the high-purity silicic acid liquid (1) and aqueous ammonia was completed, the liquid was heated and aged for 60 minutes while maintaining the liquid temperature at 87°C. After the heat aging was completed, the liquid was cooled to 40°C or below, concentrated using an ultrafiltration membrane (SIP1013 manufactured by Asahi Kasei) to a silica concentration of 11% by mass, and further concentrated using a rotary evaporator to a silica concentration of 20% by mass to obtain a silica microparticle dispersion. The silica fine particle dispersion thus obtained was subjected to BET specific surface area measurement, metal impurity measurement, anion concentration measurement, NMR measurement, particle density measurement, carbon content measurement, and polishing test. The particle diameter D of these silica microparticles was 25 nm. The ratios (area percentages) of the peak areas (S0, S1, S2, S3, and S4) based on the Q0, Q1, Q2, Q3, and Q4 structures to the total (S0 + S1 + S2 + S3 + S4) were calculated. These data are shown in Table 1. Graphs based on these data are shown in Figures 1 and 2. Further measurement results and measurement methods are shown in Tables 2, 3 and 4.

[0072] <Comparative Example 1> A silica microparticle dispersion was obtained under the same conditions and operations as in Example 1, except that neither air bubbling into the acidic silicic acid liquid (1) in step 1 of Example 1 nor air bubbling in the heat treatment step after adding hydrochloric acid in step 2 was performed.

[0073] <Comparative Example 2> A silica fine particle dispersion was obtained under the same conditions and procedures as in Example 1, except that in step 2 of Example 1, air bubbling was not performed in the heat treatment step after the addition of hydrochloric acid.

[0074] <Comparative Example 3> A silica fine particle dispersion was obtained under the same conditions and procedures as in Example 1, except that in steps 1 and 2 of Example 1, N2 bubbling was performed instead of air bubbling, and the dissolved oxygen concentration was left as it was.

[0075] <Comparative Example 4> (Dispersion liquid preparation process) A raw material solution was prepared by mixing 540.0 g of tetramethoxysilane (manufactured by Tama Chemicals Co., Ltd. (the same applies hereinafter)) and 180.0 g of methanol. A reaction vessel was charged with 5,400 g of a mixed solvent of methanol, water, and ammonia. The water concentration in this mixed solvent was 15% by mass, and the ammonia concentration was 1% by mass. The raw material solution was added dropwise to the reaction vessel at a uniform rate over 25 minutes while adjusting the liquid temperature so that the reaction solvent temperature was maintained at 20°C, to obtain a silica particle dispersion liquid with a silica particle concentration of 3.5 mass %. (Preconcentration step) The dispersion (silica concentration: 3.5% by mass) obtained in the dispersion preparation step was concentrated by a heat concentration method. Specifically, the dispersion obtained in the dispersion preparation step was heated at normal pressure to evaporate the organic solvent and water, and a silica particle dispersion (silica concentration 3.5% by mass) that had been prepared in advance was added so that the liquid volume remained constant, thereby concentrating the dispersion. (Water replacement process) Water substitution was carried out by a heat substitution method at atmospheric pressure while adding water to the concentrated dispersion. When the liquid temperature reached 96°C, the water substitution step was completed. (Particle surface conditioning process) After the water replacement step was completed, the solution was heated at a pH of 7 or higher while maintaining the liquid temperature at 96°C under normal pressure. In this step, the same amount of water as the amount of liquid to be distilled off was added, and heating was continued for 30 hours while maintaining a constant silica concentration in the system. (concentration process) After it was confirmed that the pH was below 7, the addition of water was stopped and the mixture was concentrated at 96°C under normal pressure until the silica particle concentration reached 20% by mass, thereby preparing a silica particle fine particle dispersion.

[0076] <Comparative Example 5> (Preparation of the bedding solution) 692 g of pure water and 462 g of methanol were mixed to prepare a mixture of the two (hereinafter referred to as "soaking solution"). (Preparation of additive solution A) 4885 g of methanol and 2571 g of TEOS (tetraethoxysilane) were mixed to prepare a mixture of the two (hereinafter referred to as "additive solution A"). (Preparation of additive solution B) 7625 g of pure water and 64.5 g of aqueous ammonia (concentration: 29% by mass) were mixed to prepare a mixture of the two (hereinafter referred to as "additive solution B"). (Preparation of Silica Microparticles) Next, 1154 g of the saturating solution was placed in a 20 L stainless steel vessel equipped with a Liebig condenser, and stirring was started at 200 rpm, and the temperature was raised to 65°C. Next, additive solution A and additive solution B were added simultaneously to the above-mentioned bedding solution. Here, a total of 7456 g of additive solution A was added at an addition rate of 3.4 g / min. Additionally, additive solution B was added at a rate of 3.5 g / min in a total amount of 7690 g. After the addition was completed, the mixture was aged at 65°C for 3 hours. Then, the mixture was concentrated to 6.7 L using an ultrafiltration membrane. The mixture was then concentrated with a rotary evaporator to a silica concentration of 15% by mass to obtain a silica fine particle dispersion.

[0077] <Comparative Example 6> (Preparation of the bedding solution) A drench solution was prepared by mixing 474.5 g of pure water and 316.3 g of methanol. (Preparation of additive solution A) Additive solution A was prepared by mixing 2999 g of methanol and 1579 g of TEOS (tetraethoxysilane). (Preparation of additive solution B) Additive solution B was prepared by mixing 1624 g of pure water and 114 g of 29 mass % ammonia water. (Preparation of Silica Microparticles) Next, 790.8 g of the saturating solution was placed in a 10 L stainless steel vessel equipped with a Liebig condenser, and stirring was started at 160 rpm, and the temperature was raised to 65°C. Next, additive solution A and additive solution B were added simultaneously to the above-mentioned bedding solution. Here, a total of 4578 g of additive solution A was added at a rate of 19.1 g / min. Furthermore, a total of 1738 g of additive solution B was added at a rate of 7.0 g / min. After the addition was completed, the mixture was aged at 65°C for 3 hours. Then, the mixture was concentrated to 4.1 L using an ultrafiltration membrane. The mixture was then concentrated with a rotary evaporator to a silica concentration of 15% by mass to obtain a silica fine particle dispersion.

[0078] [Table 1]

[0079] [Table 2]

[0080]

Table 3

[0081]

Table 4

Claims

1. A silica fine particle dispersion liquid in which silica fine particles satisfying the following [1] to [5] are dispersed in a solvent. [1] The particle diameter D (nm) of the silica fine particles, calculated by converting the specific surface area into an equivalent sphere, satisfies the relationship 5≦D≦100. [2] Regarding the silica fine particles 29 In the spectrum obtained by Si-NMR analysis, Q 0 structure, Q 1 structure, Q 2 structure, Q 3 Structure and Q 4 The areas of the peaks based on each structure were calculated and grouped into S 0 , S 1 , S 2 , S 3 and S 4 When these are summed, S 4 Ratio R 4 (R 4 = S 4 / (S 0 +S 1 +S 2 +S 3 +S 4 ) × 100) satisfies the following formula using the particle diameter D. 0.97≦(2.9×In(D)+73.7) / R 4 ≦1.03 [3] The particle density of the silica fine particles is 2.2±0.20 g / cm 3 Range. [4] The carbon content in the silica fine particles is SiO 2 The content of the saturation agent is less than 0.1% by mass per saturation agent. [5] SiO of Al, Fe, and Na contained in the silica fine particles 2 The content of Ti in each of the SiO 2 The content of Cu and Ni is 10 ppm or less (metal conversion) per SiO 2 The content per unit of metal is 20 ppb or less (metal equivalent).

2. 2. The silica fine particle dispersion according to claim 1, wherein the silica fine particles further satisfy the following [6]: [6] Sum of the areas of each peak (S 0 +S 1 +S 2 +S 3 +S 4 ) for S 2 +S 3 The ratio of the sum of 2+3 (R 2+3 = (S 2 +S 3 ) / (S 0 +S 1 +S 2 +S 3 +S 4 ) × 100) satisfies the following formula using the particle diameter D. 0.87≦(-4×In(D)+30) / R 2+3 ≦1.13

3. 3. The silica fine particle dispersion according to claim 1, wherein the silica fine particles are prepared using an alkali silicate as a raw material.

4. A method for producing a silica fine particle dispersion, comprising the following steps 1 to 4: Step 1: A step of bubbling air into an acidic silicic acid solution (silica concentration 1.0 to 6.0 mass%, pH 2.0 to 3.0) to adjust the dissolved oxygen concentration to 6.0 to 9.0 mg / L. Step 2: Following the previous step, while continuing air bubbling, hydrochloric acid is added to the acidic silicic acid solution so that the hydrochloric acid concentration becomes 300 ppm to 10,000 ppm, and then the solution is maintained at a temperature in the range of 50°C to 80°C, and further subjected to cation exchange to obtain a purified acidic silicic acid solution. (Here, air bubbling into the acidic silicic acid solution is continued until just before cation exchange, but is not performed during cation exchange.) Step 3: Electrodialysis is carried out so that the conductivity of the purified acidic silicic acid solution obtained in the previous step becomes 0.5 to 2.0 ms / cm, and the SO of the purified acidic silicic acid solution is further removed while continuing the electrodialysis. 4 A process in which an aqueous sulfuric acid solution is added so that the concentration becomes 300 to 10,000 ppm, electrodialysis is continued until the conductivity becomes 0.5 to 1.0 ms / cm, and further cation exchange is performed to obtain a high-purity silicic acid solution. Step 4: A step in which an alkaline aqueous solution is added to the high-purity silicic acid liquid obtained in the previous step, and the mixture is aged by heating and maintaining at 40 to 98°C, and then another high-purity silicic acid liquid and an alkaline aqueous solution are added continuously or intermittently to obtain a silica fine particle dispersion.

5. 5. The method for producing a silica fine particle dispersion according to claim 4, further comprising repeating the following step 5 one or more times: Step 5: An alkaline aqueous solution is added to the silica microparticle dispersion obtained in the previous step to form core particles, and then another high-purity silicic acid solution and alkali are added continuously or intermittently to obtain a silica microparticle dispersion.

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