Method for producing water-dispersed surface-treated colloidal silica

Abstract

To provide water-dispersed colloidal silica, which does not contain metal impurities and a dispersant and which shows little viscosity increase in long-term storage.SOLUTION: Provided is a method for producing water-dispersed surface-treated colloidal silica, comprising the following steps (A1), (A2), and (A3). Step (A1): a synthesis step of obtaining colloidal silica from a tetra-functional silane compound or the like represented by the following formula (I), Si(OR1)4 (I) (In the formula, each R1 independently represents a primary hydrocarbon group having a carbon atom number of 1 to 6.) Step (A2): a surface treatment step by a tri-functional silane compound or the like represented by the following formula (II), R2Si(OR3)3 (II) (In the formula, R2 represents a substituted or unsubstituted primary hydrocarbon group having a carbon atom number of 1 to 20 and each R3 represents independently a monovalent hydrocarbon group having a carbon atom number of 1 to 6.) Step (A3): a dispersion medium substitution step.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing water-dispersed surface-treated colloidal silica. [Background technology]

[0002] With the remarkable miniaturization of semiconductor devices in recent years, colloidal silica, which has small silica particles, is used in processes such as silicon wafer polishing and chemical mechanical polishing (hereinafter referred to as "CMP") of semiconductor devices.

[0003] As colloidal silica for CMP process, high purity colloidal silica with very little metal impurities is required for the reason of preventing contamination of silicon wafers, etc. Patent Document 1 discloses a method for producing colloidal silica modified with a silane coupling agent having a cationic group, which has a low content of metal impurities. However, the presence of cationic groups on the silica surface may cause hydrogen bonds between the cationic groups and silanol groups, or the cationic groups may act as a condensation catalyst between silanol groups, causing aggregation of silica particles.

[0004] In addition, producing colloidal silica having a high silica concentration is preferable not only because it improves production efficiency but also because it improves storage and transportation efficiency and allows the blending of the abrasive used in polishing to be freely adjusted, thereby increasing the degree of freedom in blending. On the other hand, when colloidal silica is used in the CMP process, there is a problem that the viscosity of the colloidal silica increases when it is reused, and therefore the effectiveness of the colloidal silica as an abrasive cannot be fully demonstrated. Therefore, there is a demand for colloidal silica that is highly concentrated and has a small increase in viscosity over a long period of time.

[0005] Therefore, Patent Document 2 discloses a method of adding an inorganic or organic acid dispersant, such as sulfuric acid, nitric acid, or citric acid, to colloidal silica in order to improve the dispersibility of high-concentration colloidal silica. By using these dispersants, it is possible to improve the dispersibility of colloidal silica while preventing the inclusion of metal impurities, but there are cases in which silica aggregates or viscosity increases due to changes in pH value during long-term storage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2005-162533 A [Patent Document 2] Patent No. 5270344 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a water-dispersed colloidal silica which is free of metal impurities and dispersants, has a high concentration, and exhibits little increase in viscosity during long-term storage. [Means for solving the problem]

[0008] As a result of intensive research conducted by the present inventors in order to achieve the above-mentioned object, it was discovered that by treating a part of the surface of water-dispersed colloidal silica obtained by a sol-gel method in the presence of a hydrophilic organic solvent with a trifunctional silane compound or the like, and then replacing the dispersion medium with water, it is possible to obtain a surface-treated water-dispersed colloidal silica which is free of metal impurities and dispersants, has a high concentration, and exhibits little increase in viscosity over a long period of time, and thus completed the present invention.

[0009] That is, the present invention provides the following method for producing a water-dispersed surface-treated colloidal silica.

[0010] [1] A method for producing a water-dispersed surface-treated colloidal silica, comprising the following steps (A1), (A2), and (A3): Step (A1): A step of obtaining colloidal silica by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), a partial hydrolysis condensate thereof, or a mixture thereof in a mixed liquid containing a hydrophilic organic solvent and water in the presence of a basic substance. Si(OR 1 ) 4 (I) (In the formula, R 1 each independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms. Step (A2): A trifunctional silane compound represented by the following formula (II), a partial hydrolysis condensate thereof, or a mixture thereof is added to the colloidal silica obtained in step (A1), and R is formed on the surface of the colloidal silica. 2 SiO 3 / 2 A step of introducing units to obtain surface-treated colloidal silica. R 2 Si(OR 3 ) 3 (II) (In the formula, R 2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, R 3 each independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms. Step (A3): A step of replacing the hydrophilic organic solvent in the dispersion medium of the surface-treated colloidal silica obtained in step (A2) with water. [2] In step (A2), the amount of the trifunctional silane compound represented by formula (II), its partial hydrolysis condensate or a mixture thereof added is such that the amount of SiO in the colloidal silica obtained in step (A1) is 2 The method for producing the water-dispersed surface-treated colloidal silica according to [1], wherein the amount of the attenuated colloidal silica per mole of unit is 0.001 to 1 mole. [3] The method for producing a water-dispersed, surface-treated colloidal silica according to [1] or [2], wherein the produced water-dispersed, surface-treated colloidal silica has a metal impurity concentration of 0 to 1 ppm by mass. [4] The method for producing a water-dispersed, surface-treated colloidal silica according to any one of [1] to [3], wherein the concentration of the hydrophilic organic solvent in the produced water-dispersed, surface-treated colloidal silica is 0 to 1 mass %. [5] The method for producing a water-dispersed, surface-treated colloidal silica according to any one of [1] to [4], wherein the produced water-dispersed, surface-treated colloidal silica has a solid content of 15 to 50 mass %. [6] The kinematic viscosity of the water-dispersed surface-treated colloidal silica at 25°C is 1 to 100 mm 2 The method for producing a water-dispersed surface-treated colloidal silica according to any one of [1] to [5], wherein the total amount of the surface-treated colloidal silica is 100 / s. Effect of the Invention

[0011] The water-dispersed surface-treated colloidal silica obtained by the production method of the present invention is free of metal impurities and dispersants, has a high concentration, and exhibits little increase in viscosity during long-term storage, and therefore can be suitably used as abrasive grains in the polishing of silicon wafers, the CMP process of semiconductor devices, and the like. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below. The method for producing a water-dispersed, surface-treated colloidal silica of the present invention is a method for producing a water-dispersed, surface-treated colloidal silica, which includes the following steps (A1), (A2), and (A3). Step (A1): Synthesis step for obtaining colloidal silica Step (A2): Surface treatment step using a trifunctional silane compound Step (A3): Dispersion medium replacement step Each step will be described in order below.

[0013] Step (A1): Synthesis step for obtaining colloidal silica This step is a step of obtaining colloidal silica by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), its partial hydrolysis and condensation product, or a mixture thereof, in the presence of a basic substance in a mixed liquid containing a hydrophilic organic solvent and water. Si(OR 1 ) 4 (I) (In the formula, R 1 each independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.

[0014] In the above formula (I), R 1 R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably having 1 to 4 carbon atoms, and particularly preferably having 1 or 2 carbon atoms. 1 Examples of the monovalent hydrocarbon group represented by the formula (I) include a methyl group, an ethyl group, a propyl group, a butyl group, and a phenyl group. Of these, a methyl group, an ethyl group, a propyl group, and a butyl group are preferred, and a methyl group and an ethyl group are particularly preferred.

[0015] Examples of the tetrafunctional silane compound represented by the above formula (I) include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and tetraphenoxysilane, and preferably tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and particularly preferably tetramethoxysilane and tetraethoxysilane. Examples of the hydrolysis condensation product of the tetrafunctional silane compound represented by the above formula (I) include methyl silicate, ethyl silicate, and the like.

[0016] Examples of the basic substance include ammonia, dimethylamine, diethylamine, etc., and preferably ammonia and diethylamine, and particularly preferably ammonia. These basic substances can be used after dissolving the required amount in water.

[0017] The hydrophilic organic solvent is not particularly limited as long as it dissolves the compound represented by the above formula (I) and / or its partial hydrolysis condensate and water, and examples thereof include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, t-butanol, etc.; ethers such as tetrahydrofuran, dioxane, etc.; glycols such as diethylene glycol, dipropylene glycol, etc., and alcohols are preferred. Since the particle size of the silica particles produced increases as the number of carbon atoms in the alcohol increases, the type of alcohol can be selected depending on the particle size of the desired silica particles.

[0018] The amount of water used in this step is preferably 0.5 to 5 moles, more preferably 0.6 to 2 moles, and particularly preferably 0.7 to 1 mole, per mole of the total of hydrocarbyloxy groups of the tetrafunctional silane compound represented by the above formula (I) and / or its partial hydrolysis condensate. When the above-mentioned basic substance is used by dissolving it in water, the water in which the basic substance is dissolved is also included in the "water" in this step. The ratio of the hydrophilic organic solvent to water is preferably 0.2 to 10, and more preferably 0.3 to 5, in terms of the affinity between the silica particles and the mixed solvent and ease of production. In terms of the size of the resulting silica particles, the amount of the basic substance is preferably 0.01 to 2 mol, and more preferably 0.03 to 0.5 mol, per 1 mol of the total of the hydrocarbyloxy groups of the tetrafunctional silane compound represented by the above formula (I) and / or its partial hydrolysis condensation product.

[0019] The reaction conditions for the hydrolysis and condensation in this step are preferably a reaction temperature of 20 to 120° C. and a reaction time of 1 to 8 hours, more preferably a reaction temperature of 20 to 100° C. and a reaction time of 1 to 6 hours.

[0020] The concentration of silica particles in the colloidal silica obtained in step (A1) is preferably from 2 to 20% by mass, and particularly preferably from 3 to 10% by mass.

[0021] Step (A2): Surface treatment step using a trifunctional silane compound In this step, a trifunctional silane compound represented by the following formula (II), a partial hydrolysis condensate thereof, or a mixture thereof is added to the colloidal silica obtained in step (A1), and R is formed on the surface of the colloidal silica. 2 SiO 3 / 2 This is the process of introducing the unit to obtain surface-treated colloidal silica. R 2 Si(OR 3 ) 3 (II) (In the formula, R 2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, R 3 each independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.

[0022] In the above formula (II), R 2 R is a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and particularly preferably 1 to 3 carbon atoms. 2 Examples of the monovalent hydrocarbon group represented by the formula (I) include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, and decyl, and particularly preferred are methyl, ethyl, and propyl. Some or all of the hydrogen atoms in these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine, chlorine, and bromine, preferably fluorine atoms.

[0023] In the above formula (II), R 3 R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably having 1 to 4 carbon atoms, and particularly preferably having 1 or 2 carbon atoms. 3 Examples of the monovalent hydrocarbon group represented by the formula (I) include a methyl group, an ethyl group, a propyl group, a butyl group, and a phenyl group. Of these, a methyl group, an ethyl group, a propyl group, and a butyl group are preferred, and a methyl group and an ethyl group are particularly preferred.

[0024] Specific examples of the trifunctional silane compound represented by the above formula (II) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane, and the like.

[0025] The amount of the trifunctional silane compound represented by the above formula (II) used is determined based on the SiO 2 The amount is preferably 0.001 to 1 mol, more preferably 0.01 to 0.1 mol, and particularly preferably 0.01 to 0.05 mol, relative to 1 mol of the unit (Si atom derived from the above formula (I)).

[0026] In this step (A2), the trifunctional silane compound represented by the above formula (II) is added to the colloidal silica obtained in step (A1), and a surface treatment reaction of the silica with the trifunctional silane compound is carried out under the following reaction conditions: The reaction conditions in this step (A2) are preferably a reaction temperature of 40 to 60°C and a reaction time of 1 to 10 hours, more preferably a reaction temperature of 50 to 60°C and a reaction time of 1 to 8 hours.

[0027] The surface-treated colloidal silica obtained in this step preferably has a median diameter (D50) in the volume-based particle size distribution of 5 to 300 nm, more preferably 10 to 150 nm.

[0028] Step (A3): Dispersion medium replacement step This step is a step of replacing the hydrophilic organic solvent in the dispersion medium of the surface-treated colloidal silica obtained in step (A2) with water. The hydrophilic organic solvent replaced in step (A3) includes the hydrophilic organic solvent used in step (A1) and volatile by-products such as alcohol generated by condensation. As a method for the replacement, a heat concentration method in which the surface-treated colloidal silica obtained in the step (A2) is heated and concentrated while adding water in an amount equal to or greater than the amount of the distillate obtained by heating, or ultrafiltration using a filter can be used to easily and economically obtain a water-dispersed surface-treated colloidal silica.

[0029] The amount of water added is preferably 0.5 to 4 times, and more preferably 1.8 to 3.0 times by weight the total amount of the hydrophilic organic solvent used and the alcohol produced, from the viewpoint of the stability of the water-dispersed surface-treated colloidal silica.

[0030] The concentration of the hydrophilic organic solvent in the water-dispersed surface-treated colloidal silica obtained in this step is preferably 0 to 1 mass%, more preferably 0 to 100 ppm, and particularly preferably 0 to 10 ppm. The solid content concentration in the water-dispersed surface-treated colloidal silica is preferably 15 to 50 mass%, more preferably 30 to 40 mass%.

[0031] The production method of the present invention provides a water-dispersed, surface-treated colloidal silica having a high purity and a low content of metal impurities such as sodium, potassium, iron, calcium, magnesium, titanium, nickel, chromium, copper, etc. The total concentration of these metal impurities is preferably 0 to 1 ppm by mass, and more preferably 0 to 0.5 ppm by mass, relative to the total mass of the water-dispersed, surface-treated colloidal silica.

[0032] Furthermore, the production method of the present invention makes it possible to obtain a water-dispersed surface-treated colloidal silica that exhibits little increase in viscosity during long-term storage and is excellent in stability, without using a dispersant such as sulfuric acid, nitric acid, ammonium sulfate, ammonium nitrate, citric acid, benzoic acid, ammonium benzoate, triammonium citrate, diammonium hydrogen citrate, or tetramethylammonium citrate. The water-dispersed surface-treated colloidal silica produced by the production method of the present invention has a kinetic viscosity at 25° C. of 1 to 100 mm 2 / s is preferably 5 to 20 mm 2Within this range, the powder is suitable for use as an abrasive. EXAMPLES

[0033] The present invention will be specifically described below using examples and comparative examples. Note that the following examples do not limit the present invention in any way. The water-dispersed colloidal silica obtained in each example and comparative example was evaluated as follows, and the results are shown in Table 1.

[0034] [Particle size distribution] Water-dispersed colloidal silica was diluted with methanol so that the silica particles were 0.5% by mass, and the particle size distribution when irradiated with ultrasound for 10 minutes was measured using a dynamic light scattering Nanotrac particle size distribution measuring device (NanotracWaveII-Ex150, manufactured by Microtrack Bell). Based on the obtained volume-based particle size distribution, the median diameter (D50) and cumulative 95% diameter (D95) were calculated. The monodispersity of the particles was evaluated based on the CV value calculated by the following formula: The smaller the CV value, the higher the monodispersity of the particles. CV[%]=(SD / MV)×100 (In the formula, SD is the standard deviation in the measurement, and MV is the volume mean diameter.)

[0035] [Solid content concentration] 1.5 g of water-dispersed colloidal silica was precisely weighed and placed in an aluminum petri dish, and the residue (X) g after drying at 105°C for 3 hours was precisely weighed, and the silica solids concentration was calculated using the following formula. Silica solid concentration (mass%) = (X / 1.5) x 100

[0036] [Measurement of remaining methanol amount] The amount of remaining methanol in the water-dispersed colloidal silica was measured by analyzing the gas phase of the vial while heating it at 60°C for 30 minutes using a headspace gas chromatography measuring device (HP6890 Series GC system, 5975 Mass Selective Detector, G1888 Network headspace Sampler, all manufactured by Agilent Technologies, Inc.).

[0037] [Measurement of metal impurity amount] Metal elements were measured using an ICP optical emission spectrometer (Agilent 5110 ICP-OES, manufactured by Agilent Technologies, Inc.), and the amount of metal impurities in the water-dispersed colloidal silica was calculated.

[0038] [Kinematic viscosity] The kinetic viscosity of the water-dispersed colloidal silica at 25°C was measured using a Cannon-Fenske viscometer. In addition, 80 g of water-dispersed colloidal silica was placed in a 100 ml polyethylene bottle, which was then sealed and stored at 60° C., and the kinetic viscosity at 25° C. was measured after 14 days, 30 days, and 60 days.

[0039] [Example 1] ·Process (A1) In a 3-liter glass reactor equipped with a stirrer, a dropping funnel and a thermometer, 793.0 g of methanol, 32.1 g of ion-exchanged water and 40.6 g of 28% aqueous ammonia were mixed. The solution was adjusted to 53°C, and while stirring, 646.5 g of tetramethoxysilane and 160.9 g of 5.5% aqueous ammonia were simultaneously added dropwise, the former over 6 hours and the latter over 4 hours. After the dropwise addition of tetramethoxysilane was completed, stirring was continued for another 0.5 hours to carry out hydrolysis and condensation, thereby obtaining colloidal silica. The concentration of silica particles in this colloidal silica was 15.5% by mass.

[0040] ·Process (A2): The colloidal silica obtained in the step (A1) was mixed with 6.5 g of methyltrimethoxysilane (SiO in the colloidal silica) at 25° C.2 After adding 0.01 mole equivalent per mole of unit, the mixture was stirred at 55°C for 1 hour to perform surface treatment of the colloidal silica.

[0041] ·Process (A3): 1000 g of ion-exchanged water was added to the surface-treated colloidal silica obtained in the above step (A2) at 25° C., and then methanol was distilled off. At this time, ion-exchanged water was added dropwise while distilling off methanol so as to keep the volume of the dispersion constant, and the dropwise addition of ion-exchanged water was terminated when the internal temperature reached 100° C. and the pH reached 7.5 or less, thereby obtaining 770 g of water-dispersed surface-treated colloidal silica (i).

[0042] [Example 2] In step (A2) of Example 1, the amount of methyltrimethoxysilane added was 32.5 g (SiO of colloidal silica). 2 The same procedure as in Example 1 was repeated except for changing the amount of the tertiary amine to 0.05 moles per mole of the unit, to obtain 805 g of water-dispersed surface-treated colloidal silica (ii).

[0043] [Example 3] In step (A2) of Example 1, 6.5 g of methyltrimethoxysilane was mixed with 32.5 g of propyltrimethoxysilane (SiO 2 The same procedure as in Example 1 was repeated except for changing the amount of the tertiary amine to 0.05 moles per mole of the unit, to obtain 783 g of water-dispersed surface-treated colloidal silica (iii).

[0044] [Example 4] In step (A2) of Example 1, 6.5 g of methyltrimethoxysilane was mixed with 10.5 g of 3,3,3-trifluoropropyltrimethoxysilane (SiO 2 The same procedure as in Example 1 was repeated except for changing the amount of the tertiary amine to 0.01 mole per mole of the unit, to obtain 795 g of water-dispersed surface-treated colloidal silica (iv).

[0045] [Example 5] The same procedure as in Example 1 was conducted except that in the step (A1) of Example 1, the reaction temperature was changed to 36° C., to obtain 775 g of water-dispersed surface-treated colloidal silica (v).

[0046] [Example 6] The same procedure as in Example 1 was conducted except that in the step (A1) of Example 1, the reaction temperature was changed to 20° C., to obtain 778 g of water-dispersed surface-treated colloidal silica (vi).

[0047] [Comparative Example 1] 771 g of water-dispersed colloidal silica (vii) was obtained in the same manner as in Example 1, except that the step (A2) was not performed.

[0048] [Comparative Example 2] 775 g of water-dispersed colloidal silica (viii) was obtained in the same manner as in Example 5, except that the step (A2) was not performed.

[0049] [Comparative Example 3] 780 g of water-dispersed colloidal silica was obtained in the same manner as in Example 1, except that the step (A2) was not performed. 0.17 g of ammonium benzoate (660 ppm relative to the mass of the colloidal silica solids) was added to the obtained water-dispersed colloidal silica, and the mixture was stirred at room temperature for 1 hour to obtain water-dispersed colloidal silica (ix).

[0050] [Comparative Example 4] Water-dispersed colloidal silica (x) was obtained in the same manner as in Comparative Example 3, except that the amount of ammonium benzoate added was changed to 0.084 g (330 ppm relative to the mass of the colloidal silica solid content).

[0051] [Table 1]

[0052] From the above results, it was found that the water-dispersed surface-treated colloidal silica obtained by the production method of the present invention does not contain metal impurities and dispersants, has a high concentration, and exhibits little increase in viscosity during long-term storage. [Industrial Applicability]

[0053] The water-dispersed surface-treated colloidal silica obtained by the production method of the present invention does not contain metal impurities or dispersants, and despite its high concentration, it exhibits little increase in viscosity during long-term storage, and therefore can be suitably used as abrasive grains in the polishing of silicon wafers, the CMP process of semiconductor devices, and the like.

Claims

1. A method for producing a water-dispersed surface-treated colloidal silica, comprising the following steps (A1), (A2), and (A3): Step (A1): A step of obtaining colloidal silica by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), a partial hydrolysis condensate thereof, or a mixture thereof in a mixed liquid containing a hydrophilic organic solvent and water in the presence of a basic substance: Si(OR 1 ) 4 (I) (In the formula, R 1 each independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms. Step (A2): A trifunctional silane compound represented by the following formula (II), a partial hydrolysis condensate thereof or a mixture thereof (not including any other silane coupling agent) is added to the colloidal silica obtained in step (A1) in an amount of 0.001 to 1 mol per mol of SiO 2 units in the colloidal silica obtained in step (A1), to form R 2 SiO 3 / 2 A step of introducing units to obtain surface-treated colloidal silica. R 2 Si (OR 3 ) 3 (II) (In the formula, R 2 represents a halogen-substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms; R 3 each independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms. Step (A3): A step of replacing the hydrophilic organic solvent in the dispersion medium of the surface-treated colloidal silica obtained in step (A2) with water.

2. 2. The method for producing a water-dispersed, surface-treated colloidal silica according to claim 1, wherein the produced water-dispersed, surface-treated colloidal silica has a concentration of metal impurities of 0 to 1 ppm by mass.

3. 3. The method for producing a water-dispersed, surface-treated colloidal silica according to claim 1, wherein the concentration of the hydrophilic organic solvent in the produced water-dispersed, surface-treated colloidal silica is 0 to 1 mass %.

4. The method for producing a water-dispersed, surface-treated colloidal silica according to any one of claims 1 to 3, wherein the produced water-dispersed, surface-treated colloidal silica has a solid content concentration of 15 to 50 mass %.

5. The produced water-dispersed surface-treated colloidal silica has a kinetic viscosity of 1 to 100 mm at 25°C. 2 The method for producing the water-dispersed surface-treated colloidal silica according to any one of claims 1 to 4, wherein

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