Colloidal silica and method for producing colloidal silica

Abstract

Provided is a colloidal silica which, when used as an abrasive grain for polishing, hardly leaves silica particles on the polished surface and can form a polished surface with reduced surface roughness. A colloidal silica in which silica particles are dispersed in a solvent, wherein the true specific gravity of the silica particles by the liquid phase substitution method is 1.60 or more and 2.20 or less, and the value of composite parameter 1 calculated by a specific formula is 10 or more and 200 or less.

Description

Technical Field

[0001] The present invention relates to colloidal silica and a method for producing the same.

Background Art

[0002] Colloidal silica is obtained by dispersing silica particles in a medium such as water, and is used as a physical property improver in fields such as paper, fibers, and steel. In addition, it has come to be used as a raw material for a polishing composition used in chemical mechanical polishing (CMP) of semiconductor devices such as semiconductor wafers.

[0003] In CMP performed during the manufacturing process of semiconductor devices, it is necessary to smooth the surface of the substrate after polishing at the nanometer level. If the smoothing of the substrate surface is insufficient, that is, if the surface of the substrate after polishing is rough, wiring disconnection and short circuits are likely to occur, and as a result, the electrical connection reliability of the semiconductor is likely to be impaired.

[0004] In addition, since the yield is likely to decrease due to the remaining silica particles on the surface of the substrate after polishing, there is a demand for a polishing composition that can smooth the surface of the substrate with high precision and in which particles hardly remain on the surface of the substrate.

[0005] As a method for producing colloidal silica in which silica particles hardly remain on the surface of the substrate after polishing, Patent Document 1 discloses that by adjusting the method of adding a basic catalyst during the synthesis of silica particles by hydrolysis and condensation reaction of alkoxysilane, as an index of the concentration of the silicon-containing compound, by controlling the Si concentration in the solvent of the colloidal silica, it is possible to produce colloidal silica that hardly remains on the substrate surface.

[0006] In addition, as a method for producing colloidal silica in which silica particles hardly remain on the surface of the substrate after polishing, Patent Document 2 discloses that after synthesizing silica particles by hydrolysis and condensation reactions of alkoxysilane, a pressure heat treatment (specifically, a heat treatment at 140 to 200 °C under the pressure conditions in the examples) is performed to control the density of silanol groups on the particle surface, whereby colloidal silica in which silica particles hardly remain on the substrate surface can be produced.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0008] However, as a result of the inventor's study, it has been found that even when using the colloidal silica obtained by the production method described in Patent Document 1, it is difficult to obtain a polishing composition in which silica particles hardly remain on the polishing surface. This is because polishing compositions using colloidal silica as a raw material are often adjusted to be basic from the viewpoint of the dispersion stability of particles, and generally silica particles are easily dissolved in a basic environment. Therefore, in order to prepare a polishing composition in which silica particles hardly remain on the substrate surface, colloidal silica with controlled Si concentration in the solvent in a basic environment is required.

[0009] In addition, as a result of the inventor's study, it has been found that although the polishing composition using the colloidal silica obtained by the production method described in Patent Document 2 hardly leaves silica particles on the polishing surface, it is difficult to obtain a polishing surface with reduced surface roughness. As described in Patent Document 2, colloidal silica obtained by subjecting it to high-temperature and high-pressure treatment using an autoclave apparatus has a large true specific gravity of silica particles and is likely to increase mechanical strength. Therefore, it was considered that when used in a polishing composition, the flatness of the polished surface was likely to be impaired.

[0010] An object of the present invention is to provide a colloidal silica and a method for producing the same, which can form a polished surface with reduced surface roughness and with little residual silica particles on the polished surface when used as abrasive grains for polishing.

Means for Solving the Problems

[0011] In order to solve the above technical problems, the present inventors conducted intensive studies and found that a colloidal silica in which silica particles are dispersed in a solvent, and the true specific gravity of the silica particles by the liquid phase replacement method is 1.60 or more and 2.20 or less, and the value of composite parameter 1 defined by a specific formula is 10 or more and 200 or less can solve the problem. Based on this finding, the present invention has been completed.

[0012] That is, the present invention is (1) A colloidal silica in which silica particles are dispersed in a solvent, the true specific gravity of the silica particles by the liquid phase replacement method is 1.60 or more and 2.20 or less, The following formula (1) JPEG0007706684000001.jpg9136(However, A: the silicon concentration (mass ppm) in the solvent after 24 hours have passed with the silica particle concentration adjusted to 10% by mass and the pH adjusted to 10.5, B: the silanol group density (number / nm 2 ) of the silica particles measured by the shear method, C: the average secondary particle diameter (nm) of the silica particles measured by the dynamic light scattering method.) The value of composite parameter 1 calculated by is 10 or more and 200 or less A colloidal silica characterized by (2) The colloidal silica according to (1) above, wherein the average secondary particle diameter of the silica particles measured by the dynamic light scattering method is 3 to 200 nm. (3) The colloidal silica according to (1) or (2) above, wherein the metal impurity content is less than 1 mass ppm, and (4) A method for producing the colloidal silica according to any one of (1) to (3) above, comprising: a reaction step of obtaining a reaction solution by bringing a mother liquor containing a basic catalyst, water, and alcohol into contact with a raw material solution containing alcohol and tetraalkoxysilane; an aging step of adjusting the water concentration of the reaction solution obtained in the reaction step to 0 to 6 mass%, and then heating and stirring the reaction solution at a temperature of 55 to 65 ° C for 50 hours or more under normal pressure. A method for producing colloidal silica, characterized by including the above steps. (5) The method for producing colloidal silica according to (4) above, wherein the basic catalyst is ammonia, the alcohol in the mother liquor is methanol, the alcohol in the raw material solution is methanol, and the tetraalkoxysilane is tetramethoxysilane. The present invention provides the above.

Effects of the Invention

[0013] According to the present invention, it is possible to provide a colloidal silica and a method for producing the colloidal silica that can form a polished surface with reduced surface roughness and with little residual silica particles on the polished surface when used as abrasive grains for polishing.

Embodiments for Carrying Out the Invention

[0014] First, the colloidal silica according to the present invention will be described. The colloidal silica according to the present invention is a colloidal silica in which silica particles are dispersed in a solvent, the true specific gravity of the silica particles by the liquid phase replacement method is 1.60 or more and 2.20 or less, the following formula (1) JPEG0007706684000002.jpg9136 (where A is the silicon concentration (ppm by mass) in the solvent after 24 hours with the silica particle concentration adjusted to 10% by mass and the pH adjusted to 10.5, B is the silanol group density (number / nm 2 ) of the silica particles measured by the shear method, and C is the average secondary particle diameter (nm) of the silica particles measured by dynamic light scattering method.) The value of the composite parameter 1 calculated by is 10 or more and 200 or less and is characterized by this.

[0015] The colloidal silica according to the present invention has a true specific gravity of 1.60 or more and 2.20 or less, preferably 1.70 or more and 2.18 or less, and more preferably 1.75 or more and 2.15 or less, by the liquid phase substitution method of the silica particles constituting the colloidal silica.

[0016] In the colloidal silica according to the present invention, when the true specific gravity of the silica particles constituting the colloidal silica is within the above range by the liquid phase substitution method, when the colloidal silica according to the present invention is used as abrasive grains for polishing, while exhibiting excellent polishing properties, a polished surface with reduced surface roughness can be easily formed.

[0017] In the present application documents, the true specific gravity by the liquid phase substitution method means the value measured by the liquid phase substitution method using ethanol after drying the measurement sample on a hot plate at 150 °C and heating and holding it in a furnace at 300 °C for 1 hour.

[0018] The colloidal silica according to the present invention is represented by the following formula (1) JPEG0007706684000003.jpg9136 (where A is the silicon concentration (ppm by mass) in the solvent after 24 hours with the silica particle concentration adjusted to 10% by mass and the pH adjusted to 10.5, B is the silanol group density (number / nm 2 ) of the silica particles measured by the shear method, and C is the average secondary particle diameter (nm) of the silica particles measured by dynamic light scattering method.) The value of the composite parameter 1 calculated thereby is 10 or more and 200 or less.

[0019] In the colloidal silica according to the present invention, the composite parameter 1 is 200 or less, preferably 185 or less, more preferably 155 or less, and still more preferably 100 or less. When the composite parameter 1 is less than or equal to the above value (upper limit value), when the colloidal silica according to the present invention is used as abrasive grains for polishing, the number of particles remaining on the polished surface can be suppressed.

[0020] In the colloidal silica according to the present invention, the composite parameter 1 is 10 or more, preferably 19 or more, more preferably 24 or more, and still more preferably 35 or more. When the composite parameter 1 is greater than or equal to the above value (lower limit value), when the colloidal silica according to the present invention is used as abrasive grains for polishing, the flatness of the polished surface can be further improved.

[0021] When colloidal silica is used as abrasive grains for polishing, it is considered that the silica particles constituting the colloidal silica bind to the polished surface with the silanol groups on the particle surface as reaction points and remain on the polished surface. The binding between the silica particles and the polished surface is considered to be promoted by a silicon (Si) compound dissolved in the solvent, and since the dissolution of the silica particles is promoted under basic conditions, it is considered that the binding between the silica particles and the polished surface is more promoted under basic conditions. In addition, the smaller the particle diameter of the silica particles constituting the colloidal silica, the more likely they are to remain on the polished surface.

[0022] Based on the above background, as a result of intensive studies by the present inventor, it has been found that colloidal silica in which the composite parameter 1 represented by the following formula (1) is controlled low within a predetermined range is less likely to have silica particles remaining on the polished surface when used as abrasive grains for polishing. JPEG0007706684000004.jpg9136 (However, A: the silicon concentration (mass ppm) in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to pass, B: the silanol group density (number / nm 2 ) of the silica particles measured by the shear method, C: the average secondary particle diameter (nm) of the silica particles measured by the dynamic light scattering method.)

[0023] In the colloidal silica according to the present invention, "A" constituting the composite parameter 1 means the silicon concentration (mass ppm) in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to pass. The silicon concentration in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to pass indicates the ease of dissolution of the silica particles under basic conditions. In the colloidal silica according to the present invention, the silicon concentration "A" in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to pass is preferably 5 mass ppm or more and 400 mass ppm or less.

[0024] In the colloidal silica according to the present invention, the silicon concentration "A" in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to pass is preferably 400 mass ppm or less, more preferably 350 mass ppm or less, still more preferably 300 mass ppm or less, and particularly preferably 275 mass ppm or less.

[0025] In the colloidal silica according to the present invention, when the silicon concentration "A" in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to pass is below the above value (upper limit value), when the colloidal silica according to the present invention is used as an abrasive grain for polishing, the remaining of the silica particles on the polished surface is likely to be suppressed.

[0026] In the colloidal silica according to the present invention, the silicon concentration "A" in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to elapse is preferably 5 ppm by mass or more, more preferably 20 ppm by mass or more, still more preferably 40 ppm by mass or more, and particularly preferably 60 ppm by mass or more.

[0027] In the colloidal silica according to the present invention, when the silicon concentration "A" in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to elapse is equal to or higher than the above value (lower limit value), the polishing performance can be further improved when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0028] In the present application documents, the silicon concentration "A" (ppm by mass) in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and allowing 24 hours to elapse means a value calculated by the following method. First, for the colloidal silica, a basic catalyst such as ultrapure water or aqueous ammonia is added and diluted to adjust the silica particle concentration to 10% by mass and the pH to 10.5. Next, the colloidal silica adjusted to a silica particle concentration of 10% by mass and a pH of 10.5 is allowed to stand in an incubator at 25°C and taken out after 24 hours have elapsed. 10 mL of the colloidal silica taken out from the incubator is aliquoted into a centrifuge tube, centrifuged at 260,000 G for 2 hours, and then 2 mL of the supernatant is collected from the upper part of the centrifuge tube. The silicon concentration (silicon atom concentration) in the obtained supernatant is measured with an inductively coupled plasma atomic emission spectrometry (ICP-AES) apparatus using the absolute calibration curve method, and the obtained value is taken as the silicon concentration "A" (ppm by mass) in the solvent.

[0029] In the colloidal silica according to the present invention, "B" constituting the composite parameter 1 means the silanol group density (number / nm 2 ) of the silica particles measured by the shear method. In the colloidal silica according to the present invention, the silanol group density "B" of the silica particles measured by the shear method is 1.5 pieces / nm 2 or more and 10.0 pieces / nm 2 or less is preferable.

[0030] In the colloidal silica according to the present invention, the silanol group density "B" (pieces / nm 2 ) of the silica particles measured by the shear method is preferably 10.0 pieces / nm 2 or less, more preferably 9.5 pieces / nm 2 or less, even more preferably 9.0 pieces / nm 2 or less, particularly preferably 8.8 pieces / nm 2 or less.

[0031] In the colloidal silica according to the present invention, when the silanol group density "B" of the silica particles measured by the shear method is equal to or less than the above value (upper limit value), when the colloidal silica according to the present invention is used as abrasive grains for polishing, the remaining of the silica particles on the polishing surface is likely to be suppressed.

[0032] In the colloidal silica according to the present invention, the silanol group density "B" (pieces / nm 2 ) of the silica particles measured by the shear method is preferably 1.0 piece / nm 2 or more, more preferably 1.5 pieces / nm 2 or more, even more preferably 1.7 pieces / nm 2 or more, particularly preferably 2.0 pieces / nm 2 or more.

[0033] In the colloidal silica according to the present invention, when the silanol group density "B" of the silica particles measured by the shear method is equal to or more than the above value (lower limit value), the polishing performance can be further improved when the colloidal silica of the present invention is used as abrasive grains for polishing.

[0034] In addition, in the present application documents, the silanol group density "B" (pieces / nm 2 ) of the silica particles measured by the shear method means the value calculated by the following method. That is, based on the Sears method described in G.W. Sears, Jr., “Determination of Specific Surface Area of Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981(1956), after adjusting the silica particle concentration of the colloidal silica to be measured to 1% by mass and titrating with a 0.1 mol / L aqueous sodium hydroxide solution, the silanol group density “B” (number / nm 2 ) is meant. B = (a × f × 6022) ÷ (c × S) B: Silanol group density (number / nm 2 ) a: Drop volume (mL) of 0.1 mol / L aqueous sodium hydroxide solution at pH 4 to pH 9 f: Factor of 0.1 mol / L aqueous sodium hydroxide solution c: Mass (g) of silica particles S: BET specific surface area (m 2 / g)

[0035] In the colloidal silica according to the present invention, “C” constituting the composite parameter 1 means the average secondary particle diameter (nm) of the silica particles measured by the dynamic light scattering method. In the colloidal silica according to the present invention, the average secondary particle diameter “C” of the silica particles measured by the dynamic light scattering method is preferably 3 nm or more and 200 nm or less.

[0036] In the colloidal silica according to the present invention, the average secondary particle diameter “C” (nm) of the silica particles measured by the dynamic light scattering method is preferably 200 nm or less, more preferably 175 nm or less, still more preferably 150 nm or less, and particularly preferably 100 nm or less.

[0037] In the colloidal silica according to the present invention, when the average secondary particle diameter "C" of the silica particles measured by the dynamic light scattering method is equal to or less than the above value (upper limit value), the flatness of the polished surface is likely to be improved when the colloidal silica according to the present invention is used as an abrasive grain for polishing.

[0038] In the colloidal silica according to the present invention, the average secondary particle diameter "C" (nm) of the silica particles measured by the dynamic light scattering method is preferably 3 nm or more, more preferably 5 nm or more, still more preferably 8 nm or more, and particularly preferably 10 nm or more.

[0039] In the colloidal silica according to the present invention, when the average secondary particle diameter "C" of the silica particles measured by the dynamic light scattering method is equal to or more than the above value (lower limit value), the polishing performance can be further improved when the colloidal silica according to the present invention is used as an abrasive grain for polishing.

[0040] In the present application documents, the average secondary particle diameter "C" (nm) of the silica particles measured by the dynamic light scattering method means a value calculated by the following method. That is, first, an aqueous citric acid solution of 0.3 mass% is added to the colloidal silica and diluted to a silica concentration of 0.8 mass%, and the resulting diluted solution is used as a measurement sample. Using the above measurement sample, the average particle diameter measured by the dynamic light scattering method using a zeta potential, particle size, and molecular weight measurement system "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd. is defined as the average secondary particle diameter (nm) of the silica particles.

[0041] In addition, the average primary particle diameter of the silica particles contained in the colloidal silica according to the present invention means a value measured by the BET method described below. First, the colloidal silica is pre-dried on a hot plate at 150 ° C and then heat-treated at 800 ° C for 1 hour to prepare a measurement sample. Using the obtained measurement sample, the specific surface area (BET specific surface area) S' by the BET method is measured. In the case of substantially spherical particles, the average primary particle diameter (nm) is represented by the following formula Average primary particle diameter (nm) = 6000 / (BET specific surface area S’ (m 2 / g) × true density (g / cm 3 )) can be determined, where the true density of the silica particles is 2.20 g / cm 3 , and the average primary particle diameter (nm) of the silica particles is given by the following formula Average primary particle diameter (nm) of silica particles = 2727 / BET specific surface area S’ (m 2 / g) can be determined.

[0042] In the colloidal silica according to the present invention, the following formula Aggregation ratio = average secondary particle diameter (nm) of silica particles ÷ average primary particle diameter (nm) of silica particles The aggregation ratio of the silica particles calculated by this is preferably 1.0 or more and 3.0 or less.

[0043] In the colloidal silica according to the present invention, the aggregation ratio of the silica particles is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.5 or less. In the colloidal silica according to the present invention, when the aggregation ratio is equal to or less than the above value (upper limit value), when the colloidal silica according to the present invention is used as abrasive grains for polishing, it becomes easier to improve the flatness of the polished surface.

[0044] In the colloidal silica according to the present invention, the aggregation ratio of the silica particles is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.4 or more. In the colloidal silica according to the present invention, when the aggregation ratio of the silica particles is equal to or more than the above value (lower limit value), it becomes easier to improve the polishing performance when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0045] The pH of the colloidal silica according to the present invention may be appropriately set according to its use and is not particularly limited, but is preferably 2.0 or more and 11.0 or less.

[0046] The pH of the colloidal silica according to the present invention is preferably 2.0 or more, more preferably 2.5 or more, and even more preferably 3.0 or more. When the pH of the colloidal silica according to the present invention is equal to or higher than the above value (lower limit value), the long-term dispersion stability of the silica particles of the colloidal silica according to the present invention is likely to be improved.

[0047] Also, the pH of the colloidal silica according to the present invention is preferably 11.0 or less, more preferably 10.7 or less, and even more preferably 10.5 or less. Even when the pH of the colloidal silica according to the present invention is equal to or lower than the above value (upper limit value), the long-term dispersion stability of the colloidal silica is likely to be improved.

[0048] In this application document, pH means the value measured by a desktop pH / water quality analyzer (F-2000PI manufactured by Horiba, Ltd.).

[0049] The content of the silica particles in the colloidal silica according to the present invention is not particularly limited, but when the content of the colloidal silica is 100% by mass, it is preferably 2% by mass or more and 50% by mass or less.

[0050] The content (silica particle concentration) of the silica particles in the colloidal silica according to the present invention is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more when the content of the colloidal silica is 100% by mass.

[0051] When the content of the silica particles in the colloidal silica according to the present invention is equal to or higher than the above value (lower limit value), the polishing performance when the colloidal silica according to the present invention is used as abrasive grains for polishing can be further improved.

[0052] The content (concentration of silica particles) of the silica particles in the colloidal silica according to the present invention is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less when the content of the colloidal silica is 100% by mass. When the content of silica particles in the colloidal silica according to the present invention is equal to or less than the above value (upper limit value), the long-term dispersion stability of the silica particles can be further improved.

[0053] In the present application documents, the content of silica particles (concentration of silica particles) in the colloidal silica according to the present invention means the value measured by the following measurement method. That is, after drying 10.0 g of colloidal silica on a hot plate at 150 °C and then heat-treating it at 800 °C for 1 hour to remove moisture, taking the amount of the obtained solid content as W g, it means the value calculated from the following formula. Content of silica particles in colloidal silica (mass %) = (W / 10.0) × 100

[0054] In the colloidal silica according to the present invention, the metal impurity content (total content of metal impurities) is preferably 1 mass ppm or less. When the metal impurity content is 1 mass ppm or less, the colloidal silica according to the present invention can be suitably used as abrasive grains for polishing electronic materials such as semiconductor wafers.

[0055] In the colloidal silica according to the present invention, examples of the metal impurities include one or more selected from sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, cobalt, and the like.

[0056] In the present application documents, the metal impurity content means the value measured using an atomic absorption spectrometer.

[0057] Next, a method for producing the colloidal silica according to the present invention will be described. The method for producing the colloidal silica according to the present invention is a reaction step of obtaining a reaction solution by bringing a mother liquor containing a basic catalyst, water, and alcohol into contact with a raw material solution containing alcohol and tetraalkoxysilane, The reaction solution obtained in the above reaction step is adjusted so that the water concentration of the reaction solution is 0 to 6% by mass, and then aged by heating and stirring at a temperature of 55 to 65°C for 50 hours or more under normal pressure. It is characterized by including the above.

[0058] In the method for producing colloidal silica according to the present invention, as the basic catalyst constituting the mother liquor, from the viewpoint of preventing the mixing of impurities, one or more selected from organic amines and ammonia are preferable, and in particular, one or more selected from ethylenediamine, diethylenetriamine, triethylenetetramine, 3-ethoxypropylamine (3-EOPOA), ammonia, urea, ethanolamine, and tetramethylammonium hydroxide are more preferable, and ammonia is even more preferable. In the method for producing colloidal silica according to the present invention, when the basic catalyst constituting the mother liquor is the above-mentioned one, it has excellent catalytic action, high volatility, and can be easily removed in the subsequent process.

[0059] In the method for producing colloidal silica according to the present invention, the concentration of the basic catalyst in the mother liquor is preferably 0.2 to 3.0% by mass, more preferably 0.3 to 2.5% by mass, and even more preferably 0.5 to 1.8% by mass. In the method for producing colloidal silica according to the present invention, when the concentration of the basic catalyst in the mother liquor is within the above range, the particle size of the silica particles in the obtained colloidal silica can be easily controlled within a desired range.

[0060] In the method for producing colloidal silica according to the present invention, as the water constituting the mother liquor, in order to reduce the mixing of metal impurities as much as possible, pure water or ultrapure water is preferable.

[0061] In the method for producing colloidal silica according to the present invention, the concentration of the water constituting the mother liquor is preferably 3.0 to 25.0% by mass, more preferably 5.0 to 20.0% by mass, and even more preferably 5.0 to 18.0% by mass. In the method for producing colloidal silica according to the present invention, while adjusting the concentration of water in the mother liquor within the above range, by controlling the mixing ratio of the mother liquor and the raw material solution, the hydrolysis and dehydration condensation reactions of tetraalkoxysilane described later can be preferably promoted more easily.

[0062] In the method for producing colloidal silica according to the present invention, as the alcohol constituting the mother liquor, one or more selected from methanol, ethanol, isopropanol, etc. are preferable.

[0063] In the method for producing colloidal silica according to the present invention, it is more preferable that the alcohol constituting the mother liquor is the same alcohol as the alcohol generated by the hydrolysis of tetraalkoxysilane described later. For example, when the tetraalkoxysilane described later is tetramethoxysilane (TMOS), methanol is preferable as the alcohol constituting the mother liquor. In the method for producing colloidal silica according to the present invention, by using the same alcohol as the alcohol generated by the hydrolysis of tetraalkoxysilane described later as the alcohol constituting the mother liquor, the recovery and reuse of alcohol can be easily performed.

[0064] In the method for producing colloidal silica according to the present invention, the concentration of the alcohol constituting the mother liquor is preferably 70 to 90% by mass, more preferably 72 to 88% by mass, and even more preferably 74 to 86% by mass. In the method for producing colloidal silica according to the present invention, when the concentration of the alcohol in the mother liquor is within the above range, the dispersibility of tetraalkoxysilane described later is excellent, and the hydrolysis reaction can be preferably promoted more easily.

[0065] In the method for producing colloidal silica according to the present invention, as the alcohol constituting the raw material solution, one or more selected from methanol, ethanol, isopropanol, etc. are preferable.

[0066] In the method for producing colloidal silica according to the present invention, it is more preferable that the alcohol constituting the raw material solution is the same alcohol as the alcohol generated by hydrolysis of tetraalkoxysilane described later. For example, when the tetraalkoxysilane described later is tetramethoxysilane (TMOS), methanol is preferable as the alcohol constituting the raw material solution. In the method for producing colloidal silica according to the present invention, by using the same alcohol as the alcohol generated by hydrolysis of tetraalkoxysilane described later as the alcohol constituting the raw material solution, recovery and reuse of the alcohol can be easily performed.

[0067] In the method for producing colloidal silica according to the present invention, as the tetraalkoxysilane constituting the raw material solution, the following general formula (1) Si(OR)4(1) (In the above general formula (1), the R group is an alkyl group having 1 to 8 carbon atoms.) Examples thereof include tetraalkoxysilane represented by the formula or a derivative thereof.

[0068] In the tetraalkoxysilane represented by the general formula (1) or a derivative thereof, the R group is an alkyl group having 1 to 8 carbon atoms, and preferably an alkyl group having 1 to 4 carbon atoms.

[0069] In the tetraalkoxysilane represented by the general formula (1) or a derivative thereof, examples of the R group include one or more selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, etc., and one or more selected from a methyl group, an ethyl group, a propyl group, an isopropyl group and a butyl group are preferable.

[0070] As the tetraalkoxysilane represented by the general formula (1), tetramethoxysilane in which the R group is a methyl group, tetraethoxysilane in which the R group is an ethyl group, or tetraisopropoxysilane in which the R group is an isopropyl group is preferable. In addition, examples of the derivative of the tetraalkoxysilane represented by the general formula (1) include low condensates obtained by partially hydrolyzing the tetraalkoxysilane represented by the general formula (1). As the tetraalkoxysilane or its derivative represented by the general formula (1), tetramethoxysilane (TMOS) is preferred in terms of easy control of the hydrolysis rate, easy obtainment of fine silica particles, and low residue of unreacted substances.

[0071] In the method for producing colloidal silica according to the present invention, the concentration of tetraalkoxysilane in the raw material solution is preferably 4.0 to 6.5 mol / L, more preferably 4.0 to 6.0 mol / L, and even more preferably 4.3 to 6.0 mol / L.

[0072] In the method for producing colloidal silica according to the present invention, when the concentration of tetraalkoxysilane in the raw material solution is within the above range, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane is facilitated.

[0073] In the method for producing colloidal silica according to the present invention, a reaction step is performed in which a mother liquor containing the basic catalyst, water, and alcohol is reacted with a raw material solution containing alcohol and tetraalkoxysilane to obtain a reaction solution.

[0074] In the method for producing colloidal silica according to the present invention, in the reaction step, the mother liquor containing the basic catalyst, water, and alcohol and the raw material solution containing alcohol and tetraalkoxysilane are preferably brought into contact such that the raw material solution is 5 to 45 parts by mass, more preferably 8 to 35 parts by mass, and even more preferably 10 to 30 parts by mass with respect to 100 parts by mass of the mother liquor.

[0075] In the method for producing colloidal silica according to the present invention, by controlling the contact amount of the raw material solution within the above range with respect to 100 parts by mass of the mother liquor, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane in the raw material solution is effectively facilitated.

[0076] In the method for producing colloidal silica according to the present invention, in the reaction step, the mother liquor containing the basic catalyst, water and alcohol and the raw material solution containing alcohol and tetraalkoxysilane are such that the content of water in the reaction solution constituting the mother liquor with respect to the content of tetraalkoxysilane in the reaction solution constituting the raw material solution (content of water in the reaction solution constituting the mother liquor / content of tetraalkoxysilane in the reaction solution constituting the raw material solution) is preferably reacted so as to be 5.0 to 20.0 in molar ratio, more preferably reacted so as to be 5.0 to 15.0, and even more preferably reacted so as to be 5.5 to 13.0.

[0077] In the method for producing colloidal silica according to the present invention, in the reaction step, by reacting so that the content of water in the reaction solution constituting the mother liquor / the content of tetraalkoxysilane in the reaction solution constituting the raw material solution is within the above range, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane in the raw material solution can be easily advanced, and the particle size of the silica particles in the obtained colloidal silica can be easily controlled within a desired range.

[0078] In the method for producing colloidal silica according to the present invention, in the reaction step, when adding the raw material solution to the mother liquor, the addition rate of the raw material solution to the mother liquor is preferably 0.0010 to 0.0080 parts by mass per minute, more preferably 0.0015 to 0.0070 parts by mass per minute, and even more preferably 0.0018 to 0.0060 parts by mass per minute per 1 part by mass of the mother liquor. When the addition rate of the raw material solution to the mother liquor is within the above range, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane can be easily advanced, and the particle size of the silica particles in the obtained colloidal silica can be easily controlled within a desired range.

[0079] In the method for producing colloidal silica according to the present invention, the reaction step can be carried out under any pressure conditions of reduced pressure, normal pressure, or increased pressure, but it is preferably carried out under normal pressure.

[0080] In the method for producing colloidal silica according to the present invention, in the reaction step, when adding the raw material solution to the mother liquor, it is preferable to complete the addition of the raw material solution within 10 minutes to 300 minutes, and more preferably within 30 minutes to 200 minutes.

[0081] In the method for producing colloidal silica according to the present invention, in the reaction step, the temperature (reaction temperature) when reacting the mother liquor and the raw material solution to obtain a reaction solution is preferably 10.0 to 85.0 °C, more preferably 12.0 to 65.0 °C, and even more preferably 15.0 to 40.0 °C. In the method for producing colloidal silica according to the present invention, when the reaction time and reaction temperature in the reaction step are within the above ranges, the reaction of alkoxysilane is suppressed, and it becomes easier to generate silica particles having a desired particle size under the liquid phase.

[0082] In the method for producing colloidal silica according to the present invention, in the reaction step, by bringing the mother liquor and the raw material solution into contact and mixing them, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane starts in the obtained mixed solution, and silica particles are synthesized.

[0083] In the method for producing colloidal silica according to the present invention, after adjusting the water concentration of the reaction solution obtained in the reaction step to 0 to 6% by mass, a ripening step of heating and stirring at a temperature of 55 to 65 °C for 50 hours or more under normal pressure is performed.

[0084] In the method for producing colloidal silica according to the present invention, in the ripening step, the water concentration of the reaction solution obtained in the reaction step is controlled to 0 to 6% by mass, preferably controlled to 0 to 5% by mass, and more preferably controlled to 0 to 4% by mass.

[0085] In the method for producing colloidal silica according to the present invention, in the aging step, by controlling the water concentration of the reaction solution within the above range, that is, after adjusting it to a concentration lower than the water concentration in the reaction solution during the hydrolysis and dehydration condensation reactions of conventionally known tetraalkoxysilane, (as will be described later) by heating at a predetermined temperature for a predetermined time, the value of the composite parameter 1 can be controlled within a desired range without significantly increasing the true specific gravity. Although the detailed mechanism is not clear, it is considered that due to the low water concentration in the reaction solution, hydrolysis of silica and dehydration condensation of the hydrolysis products proceed only in the vicinity of the silica particle surface, and dense siloxane bonds may be formed. Along with this, it is considered that the solubility of silica particles under basic conditions is suppressed and the density of silanol groups on the particle surface is controlled. In addition, it is presumed that since the location where dense siloxane bonds are formed is only on the particle surface, the true specific gravity is not significantly increased.

[0086] In the method for producing colloidal silica according to the present invention, the water concentration in the reaction solution in the aging step may be adjusted to the above range by adding alcohol while heating and distilling off the solvent of the reaction solution obtained in the reaction step, or in the reaction step, by controlling the composition of the mother liquor or the raw material solution or by controlling the mixing ratio of the mother liquor and the raw material solution, it may be adjusted to the above range.

[0087] In the method for producing colloidal silica according to the present invention, the heating and stirring in the aging step is carried out under normal pressure.

[0088] In the method for producing colloidal silica according to the present invention, in the aging step, the reaction solution (obtained by mixing the mother liquor and the raw material solution) is subjected to heat stirring treatment under temperature conditions of 55 to 65°C in a state where the water concentration is controlled, and it is preferably subjected to heat stirring treatment under temperature conditions of 57 to 65°C, and more preferably subjected to heat stirring treatment under temperature conditions of 60 to 65°C. In the method for producing colloidal silica according to the present invention, by performing heating and stirring in the aging step under normal pressure within the above temperature range, the true specific gravity of silica particles by the liquid phase substitution method in the obtained colloidal silica can be controlled within a desired range.

[0089] In the method for producing colloidal silica according to the present invention, in the aging step, the reaction solution (obtained by mixing the mother liquor and the raw material solution) is subjected to heat stirring treatment for 50 hours or more, preferably 55 hours or more, and more preferably 60 hours or more under the above temperature conditions after controlling the water concentration.

[0090] In the method for producing colloidal silica according to the present invention, in the aging step, after controlling the water concentration of the mixed solution (obtained by mixing the mother liquor and the raw material solution) to a low concentration, by performing heat stirring treatment for a long time as described above under the above temperature conditions, the solubility of silica particles under basic conditions and the density of silanol groups on the particle surface can be controlled to a desired level.

[0091] Therefore, in the method for producing colloidal silica according to the present invention, by performing the above aging step, the solubility of silica particles under basic conditions can be controlled without significantly increasing the true specific gravity. Therefore, in the obtained colloidal silica, the silicon concentration "A" in the solvent after adjusting the silica particle concentration to 10% by mass and the pH to 10.5 and passing 24 hours can be reduced. Further, in the method for producing colloidal silica according to the present invention, by performing the above aging step, the density of silanol groups on the particle surface can be controlled, and in the obtained colloidal silica, the density "B" of silanol groups of silica particles measured by the shear method can be reduced. Therefore, in the method for producing colloidal silica according to the present invention, the obtained colloidal silica has the following formula (1) JPEG0007706684000005.jpg9136(where A is the silicon concentration (mass ppm) in the solvent after 24 hours with the silica particle concentration adjusted to 10% by mass and the pH adjusted to 10.5, B is the silanol group density (number / nm 2 ) of the silica particles measured by the shear method, and C is the average secondary particle diameter (nm) of the silica particles measured by the dynamic light scattering method.) The composite parameter 1 calculated by can be easily controlled within a desired range.

[0092] In the method for producing colloidal silica according to the present invention, since the aged liquid obtained through the aging step contains an organic solvent such as alcohol in addition to water, in order to enhance the long-term storage stability, if necessary, the dispersion medium of the obtained reaction liquid may be replaced with water or subjected to a concentration treatment.

[0093] The method for replacing the organic solvent with water is not particularly limited. For example, a method of replacing the organic solvent with water by continuously adding water while membrane-concentrating the aged liquid obtained through the aging step using an ultrafiltration membrane can be mentioned.

[0094] In the method for producing colloidal silica according to the present invention, the method for concentrating the aged liquid obtained through the aging step is also not particularly limited, and examples thereof include a heating concentration method and a membrane concentration method.

[0095] In this way, in the method for producing colloidal silica according to the present invention, colloidal silica having desired properties can be obtained.

[0096] In the method for producing colloidal silica according to the present invention, from the viewpoint of not increasing the true specific gravity by the liquid phase replacement method of silica particles, it is preferably free from a pressure treatment under temperature conditions exceeding 100°C, that is, a pressure heating treatment under a pressure higher than atmospheric pressure.

[0097] The method for producing colloidal silica according to the present invention preferably does not include a firing step of silica particles from the viewpoint of not increasing the true specific gravity by the liquid phase replacement method of silica particles.

[0098] According to the present invention, when used as abrasive grains for polishing, a method for easily producing colloidal silica capable of forming a polished surface with reduced surface roughness and in which silica particles hardly remain on the polished surface can be provided.

Examples

[0099] Next, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited in any way by the following examples.

[0100] (Example 1) (1) 785 parts by mass of pure water, 193 parts by mass of 28% by mass ammonia water, and 5486 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1210 parts by mass of tetramethoxysilane (TMOS) and 326 parts by mass of methanol was continuously injected into the above mother liquor at a constant rate over 46 minutes while maintaining the liquid temperature in the reaction system at 20.5°C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration in the liquid reached 5.1% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 50 hours while maintaining the temperature at 60°C. The stirred solution was passed through a filtration module equipped with an ultrafiltration membrane, and the solvent was replaced with water by continuously adding pure water while removing methanol and ammonia. The addition of pure water was terminated when the pH reached 8 or less, and the removal of the solvent component by membrane concentration was continued. Membrane concentration was terminated when the silica particle concentration in the solution reached 20% by mass, and the target colloidal silica was prepared. The production conditions in this example are listed in Table 1. Also, the physical properties of the colloidal silica obtained in this example are listed in Table 2.

[0101] (Example 2) (1) 1079 parts by mass of pure water, 185 parts by mass of 28% ammonia water, and 5219 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1195 parts by mass of tetramethoxysilane (TMOS) and 322 parts by mass of methanol was injected at a constant rate into the above mother liquor over 90 minutes while maintaining the liquid temperature in the reaction system at 19.8 °C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 5.2% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 50 hours while maintaining the temperature at 63 °C. The stirred solution was passed through a filtration module equipped with an ultrafiltration membrane, and pure water was continuously added while removing methanol and ammonia to replace the solvent with water. The addition of pure water was terminated when the pH reached 8 or less, and the removal of the solvent components by membrane concentration was continued. Membrane concentration was terminated when the silica particle concentration in the solution reached 20% by mass to prepare colloidal silica. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0102] (Example 3) (1) 825 parts by mass of pure water, 254 parts by mass of 28% ammonia water, and 5383 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1211 parts by mass of tetramethoxysilane (TMOS) and 327 parts by mass of methanol was injected at a constant rate into the above mother liquor over 55 minutes while maintaining the liquid temperature in the reaction system at 19.4 °C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 4.9% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 55 hours while maintaining the temperature at 58 °C. The solution after stirring was passed through a filtration module equipped with an ultrafiltration membrane, and the solvent was replaced with water by continuously adding pure water while removing methanol and ammonia. When the pH reached 8 or lower, the addition of pure water was terminated, and the removal of the solvent components by membrane concentration was continued. When the silica particle concentration in the solution reached 20% by mass, the membrane concentration was terminated, and the target colloidal silica was prepared. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0103] (Example 4) (1) 879 parts by mass of pure water, 142 parts by mass of 28% aqueous ammonia, and 5411 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1235 parts by mass of tetramethoxysilane (TMOS) and 333 parts by mass of methanol was injected into the above mother liquor at a constant rate over 43 minutes while maintaining the liquid temperature in the reaction system at 22.1 °C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained reaction solution under normal pressure. The addition of methanol was terminated when the water concentration in the solution reached 5.8% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 70 hours while maintaining the temperature at 65 °C. The solution after stirring was passed through a filtration module equipped with an ultrafiltration membrane, and the solvent was replaced with water by continuously adding pure water while removing methanol and ammonia. When the pH reached 8 or lower, the addition of pure water was terminated, and the removal of the solvent components by membrane concentration was continued. When the silica particle concentration in the solution reached 20% by mass, the membrane concentration was terminated to prepare colloidal silica. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0104] (Example 5) (1) 258 parts by mass of pure water, 448 parts by mass of 28% ammonia water, and 6348 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 745 parts by mass of tetramethoxysilane (TMOS) and 201 parts by mass of methanol was injected into the above mother liquor at a constant rate over 48 minutes while maintaining the liquid temperature in the reaction system at 8.2 °C, to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 4.7% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 50 hours while maintaining the temperature at 55 °C. The stirred solution was passed through a filtration module equipped with an ultrafiltration membrane, and the solvent was replaced with water by continuously adding pure water while removing methanol and ammonia. The addition of pure water was terminated when the pH reached 8 or less, and the removal of the solvent component by membrane concentration was continued. Membrane concentration was terminated when the silica particle concentration in the solution reached 20% by mass, and the target colloidal silica was prepared. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0105] (Example 6) (1) 1222 parts by mass of pure water, 261 parts by mass of 28% ammonia water, and 5167 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1063 parts by mass of tetramethoxysilane (TMOS) and 287 parts by mass of methanol was injected into the above mother liquor at a constant rate over 90 minutes while maintaining the liquid temperature in the reaction system at 21.1 °C, to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 5.2% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 50 hours while maintaining the temperature at 63 °C. The solution after stirring was passed through a filtration module equipped with an ultrafiltration membrane, and pure water was continuously added while removing methanol and ammonia to replace the solvent with water. When the pH reached 8 or lower, the addition of pure water was terminated, and the removal of the solvent components by membrane concentration was continued. When the silica particle concentration in the solution reached 20% by mass, the membrane concentration was terminated to prepare the target colloidal silica. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0106] (Example 7) (1) 1151 parts by mass of pure water, 311 parts by mass of 28% aqueous ammonia, and 5026 parts by mass of methanol were mixed to prepare a mother liquor. Subsequently, a raw material solution containing 1191 parts by mass of tetramethoxysilane (TMOS) and 321 parts by mass of methanol was injected into the above mother liquor at a constant rate over 90 minutes while maintaining the liquid temperature in the reaction system at 20.7 °C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 4.8% by mass. Subsequently, the reaction solution with the adjusted water concentration was heated and stirred for 50 hours while maintaining the temperature at 60 °C. The solution after stirring was passed through a filtration module equipped with an ultrafiltration membrane, and pure water was continuously added while removing methanol and ammonia to replace the solvent with water. When the pH reached 8 or lower, the addition of pure water was terminated, and the removal of the solvent components by membrane concentration was continued. When the silica particle concentration in the solution reached 20% by mass, the membrane concentration was terminated to prepare the target colloidal silica. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0107] (Example 8) (1) 804 parts by mass of pure water, 179 parts by mass of 28% aqueous ammonia, and 6086 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 733 parts by mass of tetramethoxysilane (TMOS) and 198 parts by mass of methanol was injected at a constant rate into the above mother liquor over 33 minutes while maintaining the liquid temperature in the reaction system at 20.5 °C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration in the solution reached 5.4% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 50 hours while maintaining the temperature at 65 °C. The stirred solution was passed through a filtration module equipped with an ultrafiltration membrane, and pure water was continuously added while removing methanol and ammonia to replace the solvent with water. The addition of pure water was terminated when the pH became 8 or less, and the removal of the solvent components by membrane concentration was continued. Membrane concentration was terminated when the silica particle concentration in the solution reached 20% by mass, and the target colloidal silica was prepared. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0108] (Example 9) (1) 1310 parts by mass of pure water, 150 parts by mass of 28% aqueous ammonia, and 4899 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1292 parts by mass of tetramethoxysilane (TMOS) and 348 parts by mass of methanol was injected at a constant rate into the above mother liquor over 40 minutes while maintaining the liquid temperature in the reaction system at 19.9 °C to prepare a silica sol reaction solution using water and methanol as dispersion media. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 5.1% by mass. Next, the reaction solution was heated and stirred for 65 hours while maintaining the temperature at 60 °C. The solution after stirring was passed through a filtration module equipped with an ultrafiltration membrane, and the solvent was replaced with water by continuously adding pure water while removing methanol and ammonia. When the pH reached 8 or lower, the addition of pure water was terminated, and the removal of the solvent components by membrane concentration was continued. Membrane concentration was terminated when the silica particle concentration in the solution reached 20% by mass, and the target colloidal silica was prepared. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0109] (Example 10) (1) 713 parts by mass of pure water, 213 parts by mass of 28% aqueous ammonia, and 5535 parts by mass of methanol were mixed to prepare a mother liquor. Next, a raw material solution containing 1212 parts by mass of tetramethoxysilane (TMOS) and 327 parts by mass of methanol was injected into the above mother liquor at a constant rate over 49 minutes while maintaining the liquid temperature in the reaction system at 21.3°C, and a silica sol reaction solution using water and methanol as dispersion media was prepared. (2) Methanol was added while heating and distilling the obtained silica sol reaction solution under normal pressure, and the addition of methanol was terminated when the water concentration of the solution reached 4.9% by mass. Next, the reaction solution with the adjusted water concentration was heated and stirred for 65 hours while maintaining the temperature at 58°C. The solution after stirring was passed through a filtration module equipped with an ultrafiltration membrane, and the solvent was replaced with water by continuously adding pure water while removing methanol and ammonia. When the pH reached 8 or lower, the addition of pure water was terminated, and the removal of the solvent components by membrane concentration was continued. Membrane concentration was terminated when the silica particle concentration in the solution reached 20% by mass, and the target colloidal silica was prepared. The production conditions in this example are described in Table 1. Also, the physical properties of the colloidal silica obtained in this example are described in Table 2.

[0110] (Comparative Example 1) A silica sol reaction solution was obtained under the same conditions as in Example 4(1). The obtained silica sol reaction solution was concentrated while being heated and distilled under normal pressure. While keeping the volume constant, this concentrated solution was heated and distilled under normal pressure while adding pure water to replace methanol and ammonia in the concentrated solution with water. When the pH reached 8 or less, the dropping and heating of pure water were terminated, and colloidal silica with a silica particle concentration of 20% by mass was prepared. The physical properties of the colloidal silica obtained in this comparative example are shown in Table 3.

[0111] (Comparative Example 2) A silica sol reaction solution was obtained under the same conditions as in Example 8(1). The obtained silica sol reaction solution was concentrated while being heated and distilled under normal pressure. While keeping the volume constant, this concentrated solution was heated and distilled under normal pressure while adding pure water to replace methanol and ammonia in the concentrated solution with water. When the pH reached 8 or less, the dropping and heating of pure water were terminated, and colloidal silica with a silica particle concentration of 20% by mass was prepared. The physical properties of the colloidal silica obtained in this comparative example are shown in Table 3.

[0112] (Comparative Example 3) The colloidal silica obtained in Comparative Example 2 was placed in a pressure-resistant container, and was subjected to a pressure heat treatment for 5 hours while maintaining the internal pressure at 0.4 MPa and the temperature of the solution at 140 °C, thereby producing colloidal silica with a silica particle concentration of 20% by mass. The physical properties of the colloidal silica obtained in this comparative example are shown in Table 3.

[0113] (Comparative Example 4) The colloidal silica obtained in Comparative Example 2 was calcined in an air atmosphere at 950 to 1050 °C. The obtained calcined product was put into a ball mill and crushed using balls with a diameter of 3 mm. The crushed calcined product (silica particles) and pure water were mixed so that the silica particle concentration became 20% by mass, thereby dispersing the silica particles in water and preparing colloidal silica subjected to a calcination treatment. The physical properties of the colloidal silica obtained in this comparative example are shown in Table 3.

[0114] The colloidal silica obtained in each of the above examples and comparative examples was used as abrasive grains for polishing, and the number of residual particles on the polished surface and the surface roughness of the polished surface were evaluated by the following method. The results are shown in Tables 2 and 3.

[0115] <Number of residual particles on the polished surface> Ultra-pure water and 28 mass% aqueous ammonia were added to the colloidal silica and diluted to a silica concentration of 3.0 mass% and a pH of 10.5 to obtain a polishing composition. Using the obtained polishing composition, a 3 cm square silicon wafer with a silicon oxide film formed on its surface was polished under the following conditions. (Polishing conditions) Polishing machine: manufactured by Nanofactor Co., Ltd., NF-300CMP Polishing pad: manufactured by Nitto DuPont Co., Ltd., IC1000TMPad Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 minutes (Washing conditions) After polishing, the silicon wafer was cleaned by performing scrub cleaning in which a PVA roll brush was brought into contact with the scrubbing section built into the cleaning and drying apparatus MAT ZAB-8S1M under the following conditions. To fix the silicon wafer, a jig made of glass epoxy resin for the frame and polyurethane for the wafer fixing part was used. Brush: manufactured by AION Co., Ltd., AION SCL BRUSH ROLLER 48(40 / 26)×224 mm Scrub cleaning time: 1 min Brush rotation speed: 200 rpm Spin rotation speed of the silicon wafer fixing part: 50 rpm After scrub cleaning, ultrapure water was flowed at a flow rate of 750 mL / min for 1 minute on the upper side of the polishing substrate, and further processed at 1800 rpm for 20 seconds with the spin drying apparatus built into the above apparatus. (Particle counting conditions) Regarding the dried silicon wafer, the number of residual fine particles on the polished surface was measured using an atomic force microscope. Atomic force microscope: SPM-9700HT manufactured by Shimadzu Corporation 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: Five arbitrary fields per polished wafer were observed (observation range per field: 3 μm × 3 μm). In the five observation fields (five fields) on the wafer polished surface, the number of particles remaining on the polished surface was counted, and the total count number in the five fields was divided by the area of the five fields (45 μm 2 ) to obtain the number of residual particles on the polished surface (particles / μm 2 ). When the number of residual fine particles on the polished surface (particles / μm 2 ) is measured by the above method, if the number of residual fine particles on the polished surface is 2 (particles / μm 2 ) or less, it is determined that the residual amount of silica particles on the polished surface is small, and if the number of residual fine particles on the polished surface exceeds 2 (particles / μm 2 ), it is determined that the residual amount of silica particles on the polished surface is large.

[0116] <Evaluation method for polished surface roughness> For colloidal silica, ultrapure water and 28% by mass ammonia water were added and diluted to a silica particle concentration of 3.0% by mass and a pH of 10.5 to obtain a polishing composition. Using the obtained polishing composition, a 3 cm square silicon wafer with a silicon oxide film formed on its surface was polished under the following conditions. (Polishing conditions) Polishing machine: NF-300CMP manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TM Pad manufactured by Nitto 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 (Cleaning conditions) The silicon wafer after polishing was cleaned by performing scrub cleaning in which a PVA roll brush was brought into contact with the scrubbing section built into the cleaning and drying apparatus MAT ZAB-8S1M under the following conditions. At this time, in order to fix the silicon wafer, a jig was used in which the frame was made of glass epoxy resin and the wafer fixing portion was made of polyurethane. Brush: Manufactured by AION, AION SCL BRUSH ROLLER 48(40 / 26)×224 mm Scrub cleaning time: 1 min Brush rotation speed: 200 rpm Spin rotation speed of the silicon wafer fixing section: 50 rpm After scrub cleaning, ultrapure water was flowed at a flow rate of 750 mL / min for 1 minute above the polishing substrate, and further processed at 1800 rpm for 20 seconds with the spin drying apparatus built into the above device. (Measurement conditions for surface roughness) After the above cleaning treatment, the surface roughness of the polished surface was measured for the sufficiently dried wafer under the following conditions using an atomic force microscope. Atomic force microscope: SPM-9700HT manufactured by Shimadzu Corporation Cantilever: Manufactured by OLYMPUS, MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: Arbitrary 5 fields were observed per polished wafer (observation range per field 3 μm×3 μm). At 5 observation fields (5 fields) on the wafer polishing surface, the root mean square roughness x i (nm) was measured, and the arithmetic mean value of the root mean square roughness x i (nm) was defined as the polishing surface roughness Rms (nm). When the polished surface roughness Rms is 3.000 nm or less, the polished surface roughness is judged to be good, and when the polished surface roughness Rms exceeds 3.000 nm, the polished surface roughness is judged to be poor.

[0117]

Table 1

[0118]

Table 2

[0119]

Table 3

[0120] From Table 2, the colloidal silica obtained by a specific manufacturing method in Examples 1 to 10 has a true specific gravity of 1.60 or more and 2.20 or less by the liquid phase replacement method of silica particles, and the value of composite parameter 1 calculated by a specific formula is 10 or more and 200 or less. Therefore, when used as abrasive grains for polishing a silicon wafer, the number of residual fine particles on the polished surface is 2 (pieces / μm 2 ) or less, the residual amount of silica particles is small, and it can be seen that the surface roughness can be suppressed with a polished surface roughness Rms of 3.000 nm or less.

[0121] On the other hand, from Table 3, the colloidal silica obtained by a conventional manufacturing method in Comparative Example 1 and Comparative Example 2 has a value of composite parameter 1 calculated by a specific formula outside the predetermined range. Therefore, when used as abrasive grains for polishing a silicon wafer, the number of residual fine particles on the polished surface is 2 (pieces / μm 2 ) or more, and it can be seen that the residual amount of silica particles is large. Also, from Table 3, the colloidal silica obtained by a conventional manufacturing method in Comparative Example 3 and Comparative Example 4 has a true specific gravity by the liquid phase replacement method of silica particles outside the predetermined range. Therefore, when used as abrasive grains for polishing a silicon wafer, it can be seen that the surface roughness with a polished surface roughness Rms exceeding 3.000 nm is increased.

Industrial Applicability

[0122] According to the present invention, when used as abrasive grains for polishing, it is possible to provide colloidal silica and a method for producing colloidal silica that can form a polished surface with reduced surface roughness and in which silica particles hardly remain on the polished surface.

Claims

1. A colloidal silica in which silica particles are dispersed in a solvent, wherein the true specific gravity of the silica particles by the liquid phase replacement method is 1.60 or more and 2.20 or less, and the value of composite parameter 1 calculated by the following formula (1) (However, A: the silicon concentration (mass ppm) in the solvent after 24 hours have passed with the silica particle concentration adjusted to 10% by mass and the pH adjusted to 10.5, B: the silanol group density (number / nm ２ ) of the silica particles measured by the shear method, C: the average secondary particle diameter (nm) of the silica particles measured by the dynamic light scattering method.) is 10 or more and 200 or less. The colloidal silica is characterized by this.

2. The colloidal silica according to Claim 1, wherein the average secondary particle diameter of the silica particles measured by the dynamic light scattering method is 3 to 200 nm.

3. The colloidal silica according to Claim 1, wherein the metal impurity content is less than 1 mass ppm.

4. A method for producing the colloidal silica according to any one of Claims 1 to 3, comprising a reaction step of obtaining a reaction solution by bringing a mother liquor containing a basic catalyst, water and alcohol into contact with a raw material solution containing alcohol and tetraalkoxysilane, and an aging step of adjusting the water concentration of the reaction solution obtained in the reaction step to 0 to 6 mass%, and then heating and stirring at a temperature of 55 to 65 ° C for 50 hours or more under normal pressure. The method for producing colloidal silica is characterized by including this.

5. The method for producing colloidal silica according to Claim 4, wherein the basic catalyst is ammonia, the alcohol in the mother liquor is methanol, the alcohol in the raw material solution is methanol, and the tetraalkoxysilane is tetramethoxysilane.

Images