Colloidal silica and production method therefor

Abstract

The present invention provides a colloidal silica in which the average secondary particle diameter of silica particles is small, and the dispersion stability of silica particles can be maintained over a long period even under strongly acidic conditions of pH 3. The present invention also provides a method for producing the colloidal silica.　The present invention provides a colloidal silica containing silica particles, wherein the colloidal silica is characterized in that: the silica particles have an average secondary particle diameter of 20 nm or less as measured by a dynamic light scattering; the zeta potential measured under conditions of pH 3 is -20 mV or less; and the surface of the silica particles is modified with a sulfonic acid group.

Description

Colloidal silica and its manufacturing method

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

[0002] Colloidal silica is silica particles dispersed in a medium such as water, and is used as a property improver in fields such as paper, textiles, and steel, as well as an abrasive for polishing electronic materials such as semiconductor wafers (CMP).

[0003] As semiconductor line widths become finer, electronic materials are required to have high flatness and low defects in CMP processes. To meet these requirements, silica particles with a small average secondary particle size and good dispersion stability are needed. In general, the smaller the particle size of silica particles, the more likely they are to aggregate, and under acidic conditions, the zeta potential approaches the isoelectric point, making them even more unstable.

[0004] Colloidal silica containing small silica particles having an average particle size of 20 nm or less has been proposed (see Patent Document 1). However, the silica colloid disclosed in Patent Document 1 cannot maintain good dispersion stability under strongly acidic conditions of pH 3 or less, and there is a problem in that particle aggregation progresses over time.

[0005] In order to improve dispersion stability under acidic conditions, a method of modifying the surfaces of silica particles with sulfonic acid groups has been proposed (see Patent Document 2). In the method described in Patent Document 2, small particle size colloidal silica having an average particle size of 20 nm or less is modified with sulfonic acid to prepare small particle size sulfonic acid-modified colloidal silica having an average particle size of 20 nm or less.

[0006] However, the small particle size sulfonic acid-modified colloidal silica described in Patent Document 2 has a problem in that the surface modification with sulfonic acid groups is insufficient, and therefore the absolute value of the zeta potential in the acidic region is low, making it impossible to maintain long-term dispersion stability under strongly acidic conditions of about pH 3.

[0007] Therefore, there is a need for the development of colloidal silica in which the average secondary particle diameter of the silica particles is small and the dispersion stability of the silica particles can be maintained for a long period of time even under strongly acidic conditions of pH 3, and a method for producing the same.

[0008] JP 2004-315300 A International Publication No. 2023-007938

[0009] The present invention has been made in view of the above, and an object of the present invention is to provide colloidal silica in which the average secondary particle diameter of silica particles is small and the dispersion stability of the silica particles can be maintained for a long period of time even under a strongly acidic condition of pH 3, and a method for producing the same.

[0010] As a result of extensive research into achieving the above object, the present inventors have found that the above object can be achieved by using colloidal silica containing silica particles, the silica particles having an average secondary particle diameter of 20 nm or less as measured by dynamic light scattering, a zeta potential of −20 mV or less as measured under pH 3 conditions, and having surfaces modified with sulfonic acid groups, thereby completing the present invention.

[0011] That is, the present invention relates to the following colloidal silica and a method for producing the same: 1. Colloidal silica containing silica particles, wherein the silica particles have an average secondary particle diameter of 20 nm or less as measured by dynamic light scattering, a zeta potential of -20 mV or less as measured under pH 3 conditions, and are surface-modified with sulfonic acid groups. 2. Colloidal silica according to Item 1, wherein the amount of sulfonic acid groups in the silica particles is 0.02 atm% or more. 3. Colloidal silica according to Item 1 or 2, wherein the average primary particle diameter calculated from the BET specific surface area of ​​the silica particles is 18 nm or less. 4. A method for producing colloidal silica, comprising the step of adding a silane coupling agent having a mercapto group and an oxidizing agent to colloidal silica, wherein the temperature of the colloidal silica in the step is 65°C or higher. 5. Item 4. The manufacturing method according to Item 4, wherein the silane coupling agent having a mercapto group is at least one selected from the group consisting of 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane. Item 5. The manufacturing method according to Item 4 or 5, wherein the oxidizing agent is at least one selected from the group consisting of nitric acid, hydrogen peroxide, oxygen, ozone, organic peracid, bromine, hypochlorite, potassium permanganate, and chromic acid.

[0012] The present invention has been made in view of the above, and an object of the present invention is to provide colloidal silica in which the average secondary particle diameter of silica particles is small and the dispersion stability of the silica particles can be maintained for a long period of time even under strongly acidic conditions of pH 3 or less, and a method for producing the same.

[0013] The colloidal silica of the present invention is a colloidal silica containing silica particles, the silica particles having an average secondary particle diameter of 20 nm or less as measured by dynamic light scattering, a zeta potential of -20 mV or less as measured under pH 3 conditions, and surface-modified with sulfonic acid groups. Because the colloidal silica of the present invention has an average secondary particle diameter of 20 nm or less as measured by dynamic light scattering, and a zeta potential of -20 mV or less as measured under pH 3 conditions, the average secondary particle diameter of the silica particles remains small, 20 nm or less, even under acidic conditions of pH 3 or less, thereby reducing the surface roughness of the surface to be polished when used as an abrasive. Furthermore, because the colloidal silica of the present invention is surface-modified with sulfonic acid groups, the average secondary particle diameter of the silica particles can be maintained at a small particle diameter of 20 nm or less, and the zeta potential measured under pH 3 conditions can be maintained at -20 mV or less. Colloidal silica exhibiting the above characteristics has high dispersion stability under acidic conditions of pH 3 or less, and can achieve high flatness when used as an abrasive.

[0014] The production method of the present invention also includes a step of adding a silane coupling agent having a mercapto group and an oxidizing agent to colloidal silica, and the temperature of the colloidal silica in this step is 65° C. or higher. By adding the silane coupling agent having a mercapto group and the oxidizing agent to colloidal silica at a temperature in a specific range of 65° C. or higher, the production method of the present invention suppresses aggregation of silica particles when modified with sulfonic acid groups, suppresses an increase in the average secondary particle size to a size exceeding 20 nm, and improves the dispersion stability of the silica particles by modification with sulfonic acid groups, making it possible to maintain the suppressed aggregation state for a long period of time.

[0015] The colloidal silica of the present invention and its production method will be described in detail below.

[0016] 1. Colloidal Silica The colloidal silica of the present invention contains silica particles. The content of silica particles in the colloidal silica is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the colloidal silica. The content of silica in the colloidal silica is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass of the colloidal silica. When the lower limit of the content of silica particles in the colloidal silica is within the above range, the polishing performance when the colloidal silica is used as an abrasive is further improved. When the upper limit of the content of silica particles in the colloidal silica is within the above range, the dispersion stability of the silica particles is further improved.

[0017] In this specification, the content of silica particles in colloidal silica can be calculated by the following formula, where 10.0 g of colloidal silica is dried on a hot plate at 150°C, and then heated at 800°C for 1 hour to remove moisture, and the amount of solids obtained is defined as Wg: Content of silica particles in colloidal silica [%] = (W ÷ 10.0) × 100

[0018] The silica particles contained in the colloidal silica of the present invention have an average secondary particle diameter of 20 nm or less, as measured by dynamic light scattering. The average secondary particle diameter is preferably 18 nm or less, more preferably 16 nm or less, even more preferably 14 nm or less, and particularly preferably 13.5 nm or less. The lower limit of the average secondary particle diameter is not particularly limited, and is preferably 2 nm or more, more preferably 4 nm or more, even more preferably 6 nm or more, and particularly preferably 8 nm or more. When the lower limit of the average secondary particle diameter is within the above range, the polishing performance when the colloidal silica is used as an abrasive is further improved.

[0019] In this specification, the average secondary particle size of silica particles contained in colloidal silica is measured by dynamic light scattering, and more specifically, the method is described in the Examples below.

[0020] The average primary particle diameter of the silica particles is preferably 20 nm or less, more preferably 18 nm or less, and even more preferably 10 nm or less. When the upper limit of the average primary particle diameter is within the above range, the flatness when polished using the colloidal silica of the present invention is further improved. Furthermore, the average primary particle diameter of the silica particles is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 7 nm or more. When the lower limit of the average primary particle diameter of the silica particles is within the above range, the storage stability of the colloidal silica is further improved.

[0021] In this specification, the average primary particle diameter of silica particles contained in colloidal silica is measured by the measurement method described in the Examples below.

[0022] In this specification, the zeta potential of colloidal silica is measured by electrophoretic light scattering using an ELS-Z manufactured by Otsuka Electronics Co., Ltd.

[0023] The colloidal silica of the present invention has a zeta potential of -20 mV or less when measured under pH 3 conditions. If the zeta potential measured under pH 3 conditions exceeds -20 mV, the dispersion stability of the silica particles cannot be maintained over a long period of time under strongly acidic conditions. The zeta potential measured under pH 3 conditions is preferably -22 mV or less, more preferably -24 mV or less, and even more preferably -26 mV or less. When the lower limit of the zeta potential is within the above range, even higher dispersion stability can be maintained under strongly acidic conditions. Furthermore, the lower limit of the zeta potential measured under pH 3 conditions is not particularly limited, and may be -120 mV or more, -100 mV or more, etc.

[0024] In this specification, the method for measuring the zeta potential measured under the condition of pH 3 is the measurement method described in the Examples below.

[0025] The silica particles contained in the colloidal silica of the present invention have their surfaces modified with sulfonic acid groups. If the silica particles are not surface-modified with sulfonic acid groups, the colloidal silica will not be able to maintain dispersion stability of the silica particles for a long period of time under strongly acidic conditions of pH 3.

[0026] In this specification, whether the silica particles contained in the colloidal silica have their surfaces modified with sulfonic acid groups can be confirmed by the amount of sulfonic acid groups in the silica particles, which will be described later, being 0.02 atm % or more.

[0027] The amount of sulfonic acid groups in the silica particles contained in the colloidal silica of the present invention is preferably 0.02 atm% or more, more preferably 0.05 atm% or more, even more preferably 0.08 atm% or more, particularly preferably 0.10 atm% or more, and most preferably 0.15 atm% or more. When the lower limit of the sulfonic acid group amount is within the above range, the long-term dispersion stability of the silica particles in the colloidal silica of the present invention is further improved. Furthermore, the upper limit of the sulfonic acid group amount is not particularly limited, and may be 2.00 atm% or less, 1.50 atm% or less, 1.00 atm% or less, etc.

[0028] In this specification, the method for measuring the amount of sulfonic acid groups in silica particles contained in colloidal silica is the measurement method described in the Examples below.

[0029] The association ratio of silica particles in colloidal silica is preferably 1.00 or more, more preferably 1.05 or more, and even more preferably 1.10 or more. The association ratio of silica particles is preferably 4.00 or less, more preferably 3.00 or less, even more preferably 2.00 or less, and particularly preferably 1.50 or less. When the lower limit of the association ratio of silica particles is within the above range, the polishing rate when polishing with colloidal silica is further improved. When the upper limit of the association ratio of silica particles is within the above range, the flatness when polishing with colloidal silica is further improved.

[0030] In this specification, the association ratio of silica particles in the colloidal silica is a value obtained by calculating the average secondary particle size / average primary particle size of silica particles in the colloidal silica.

[0031] The pH of the colloidal silica of the present invention may be appropriately set depending on the application of the colloidal silica, and is not particularly limited, but is preferably 2.0 or higher, more preferably 3.0 or higher. The pH is preferably 11.0 or lower, more preferably 10.0 or lower. When the lower limit of the pH is within the above range, the long-term dispersion stability of the silica particles in the colloidal silica is further improved. When the upper limit of the pH is within the above range, the long-term dispersion stability of the colloidal silica is further improved.

[0032] The true specific gravity of the silica particles contained in the colloidal silica of the present invention is preferably 1.50 or more, more preferably 1.65 or more, and even more preferably 1.80 or more. When the lower limit of the true specific gravity is within the above range, the polishing properties of the colloidal silica of the present invention are further improved. Furthermore, the true specific gravity is preferably 2.30 or less, more preferably 2.20 or less, and even more preferably 2.16 or less. When the upper limit of the true specific gravity is within the above range, the occurrence of scratches on the object to be polished is further reduced.

[0033] In this specification, the true specific gravity can be measured by drying colloidal silica on a hot plate at 150°C, then holding it in a furnace at 300°C for 1 hour, and then subjecting it to a liquid phase substitution method using ethanol.

[0034] The colloidal silica of the present invention preferably has a content of metal impurities such as sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt of 1 ppm or less. By having a content of metal impurities of 1 ppm or less, the colloidal silica can be suitably used for polishing electronic materials and the like.

[0035] The colloidal silica of the present invention can be used as a property improver in the fields of paper, textiles, steel, etc., as well as an abrasive for electronic materials such as semiconductor wafers. Furthermore, when dried into powder, it can be used as an additive for fillers, an external toner additive, etc.

[0036] 2. Method for Producing Colloidal Silica The method for producing colloidal silica of the present invention comprises the step of adding a silane coupling agent having a mercapto group and an oxidizing agent to colloidal silica, wherein the temperature of the colloidal silica in the step is 65° C. or higher. In the production method of the present invention, by adding the silane coupling agent having a mercapto group and the oxidizing agent to colloidal silica at a temperature in a specific range of 65° C. or higher, aggregation of silica particles is suppressed when modified with sulfonic acid groups, and an increase in the average secondary particle size to a size exceeding 20 nm is suppressed. Furthermore, modification with sulfonic acid groups improves the dispersion stability of the silica particles, allowing the suppressed aggregation state to be maintained for a long period of time.

[0037] In the above step, the temperature of the colloidal silica is 65° C. or higher. If the temperature of the colloidal silica is lower than 65° C., the silica particles will aggregate when modified with sulfonic acid groups, making it impossible to obtain silica particles having an average secondary particle size of 20 nm or less. The upper limit of the temperature is not particularly limited as long as it can prevent the reaction solvent from boiling, and is preferably 100° C. or lower, more preferably 90° C. or lower.

[0038] In the production method of the present invention, a silane coupling agent having a mercapto group is added to colloidal silica, and then the functional group is converted to a sulfonic acid group.

[0039] The colloidal silica raw material is not limited as long as it has silanol groups on its surface, but considering that it does not contain metal impurities that are diffusible in semiconductors or corrosive ions such as chlorine, colloidal silica obtained by hydrolysis and condensation of a hydrolyzable silicon compound (e.g., alkoxysilane or its derivative) is preferred. This silicon compound can be used alone or in combination of two or more.

[0040] In the present invention, the silicon compound is preferably an alkoxysilane represented by the following general formula (1) or a derivative thereof: Si(OR) ４ (1) (wherein R is an alkyl group, preferably a lower alkyl group having 1 to 8 carbon atoms, more preferably a lower alkyl group having 1 to 4 carbon atoms.)

[0041] Examples of the R include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl groups, and preferred are tetramethoxysilane where R is a methyl group, tetraethoxysilane where R is an ethyl group, and tetraisopropoxysilane where R is an isopropyl group.Also, examples of the alkoxysilane derivative include low condensates obtained by partially hydrolyzing alkoxysilane.In the present invention, it is preferable to use tetramethoxysilane because it is easy to control the hydrolysis rate, it is easy to obtain single-nm fine silica particles, and there is little residual unreacted material.

[0042] The silicon compound is hydrolyzed and condensed in a reaction solvent to form colloidal silica, which is water or an organic solvent containing water.

[0043] Examples of the organic solvent include hydrophilic organic solvents such as alcohols such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, ethylene glycol, propylene glycol, and 1,4-butanediol, and ketones such as acetone and methyl ethyl ketone.

[0044] The amount of water added to the organic solvent is not particularly limited as long as it is an amount required for the hydrolysis of the silicon compound, and is preferably about 2 to 200 moles per mole of the silicon compound.

[0045] It is preferable to add a basic catalyst to the reaction solvent to adjust the reaction solvent to alkaline. This adjusts the reaction solvent to a pH of preferably 8 to 11, more preferably 8.5 to 10.5, allowing for rapid formation of colloidal silica. The type of basic catalyst is not particularly limited. As the basic catalyst, organic basic catalysts that do not contain metal components are preferred in order to avoid the inclusion of metal impurities, and nitrogen-containing organic basic catalysts are particularly preferred. Examples of such organic basic catalysts include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, 3-ethoxypropylamine, dipropylamine, and triethylamine. These can be used alone or in combination of two or more. Ammonia is preferred because of its excellent catalytic activity and high volatility, allowing for easy removal in a subsequent process. From the viewpoint of increasing the true specific gravity of the silica particles, it is preferable to select an organic base catalyst having a boiling point of 90°C or higher so that the catalyst is less likely to volatilize even at high reaction temperatures, and more preferable is at least one selected from tetramethylammonium hydroxide and 3-ethoxypropylamine.

[0046] In the present invention, colloidal silica is modified with sulfonic acid by adding a silane coupling agent having a mercapto group that can be chemically converted to a sulfonic acid group to colloidal silica, and then converting the mercapto group to a sulfonic acid group. This is because it is difficult to obtain a silane coupling agent having a sulfonic acid group because the sulfonic acid group has high acidity and is prone to hydrolysis.

[0047] Examples of silane coupling agents having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0048] The silane coupling agents having a mercapto group can be used alone or in combination of two or more.

[0049] When adding a coupling agent to colloidal silica, it is preferable for the colloidal silica to contain a hydrophilic organic solvent, taking into consideration the solubility of the coupling agent. In this regard, when colloidal silica is obtained by the Stöber method, in which an alkoxysilane is hydrolyzed and condensed in an alcohol-water solvent using a basic catalyst, the alcohol is contained in the reaction solution, so there is no need to add a hydrophilic organic solvent. In this case, the amount of the hydrophilic organic solvent relative to the water in the colloidal silica is more preferably 5% by mass or more, and this can be adjusted by concentrating the reaction solution as necessary.

[0050] On the other hand, when adding silane coupling agent to water-dispersed colloidal silica, add hydrophilic solvent to the extent that silane coupling agent dissolves.As hydrophilic organic solvent, for example, alcohol such as isopropyl alcohol, ethanol and methanol can be listed.Among these, it is preferable to use the same alcohol as that produced by hydrolysis of silicon compound.This is because by using the same alcohol as that produced by hydrolysis of silicon compound, solvent recovery and reuse can be facilitated.

[0051] The amount of the coupling agent added is preferably about 0.1 to 10% by mass relative to the silica. When the amount added is within this range, the zeta potential in acidic conditions becomes more stable. Furthermore, by setting the upper limit of the amount added within this range, gelation of the colloidal silica over time is further suppressed.

[0052] The reaction time when adding the coupling agent is not limited, but is preferably 10 minutes to 10 hours, and more preferably 30 minutes to 2 hours. The pH of the colloidal silica when adding the coupling agent is also not limited, but is preferably 7 to 11. By setting the upper limit of the pH within the above range, the silane coupling agent becomes more likely to react with the silica surface, and self-condensation between silane coupling agents is further suppressed.

[0053] In the above step, an oxidizing agent is added together with the silane coupling agent having a mercapto group, and the modified mercapto group is oxidized by using the oxidizing agent.

[0054] Examples of oxidizing agents include nitric acid, hydrogen peroxide, oxygen, ozone, organic peracids (percarboxylic acids), bromine, hypochlorite, potassium permanganate, and chromic acid. Among these oxidizing agents, hydrogen peroxide and organic peracids (peracetic acid, perbenzoic acids) are preferred because they are relatively easy to handle and have a good oxidation yield. Considering the by-products produced in the reaction, it is most preferred to use hydrogen peroxide.

[0055] The above oxidizing agents can be used alone or in combination of two or more.

[0056] The amount of oxidizing agent added is preferably 3 to 100 times the molar amount of the silane coupling agent. There is no particular upper limit to the amount added, but about 50 times the molar amount is more preferable. Note that the colloidal silica and the silane coupling agent have stable structures in the oxidation reaction except for the functional groups that are oxidized (converted) to sulfonic acid groups, so the generation of by-products is suppressed.

[0057] Since the colloidal silica having a surface modified with sulfonic acid groups obtained according to the above method may contain a solvent other than water, the dispersion medium mainly consisting of the reaction solvent may be replaced with water, if necessary, in order to further improve the long-term storage stability of the colloidal silica. This water replacement may be carried out after the addition of the coupling agent and before the addition of the oxidizing agent.

[0058] The method for replacing the dispersion medium mainly composed of the reaction solvent with water is not particularly limited, and examples thereof include a method in which a fixed amount of water is added dropwise to the colloidal silica while heating it.Another example is a method in which the colloidal silica is separated from the dispersion medium mainly composed of the reaction solvent by precipitation, separation, centrifugation, or the like, and then redispersed in water.

[0059] The colloidal silica of the present invention can be produced by the production method having the steps described above.

[0060] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

[0061] Example 1 (Colloidal Silica Synthesis Process) A mother liquor was prepared by adding 8,836 g of pure water as a solvent to a flask and adding 13.968 g of 3-ethoxypropylamine as an alkaline catalyst. The mother liquor was heated to an internal temperature of 85°C, and then 1,534 g of tetramethyl orthosilicate was added to the mother liquor at a constant rate over 15 minutes while controlling the temperature so as not to fluctuate the internal temperature. After the addition was completed, the mixture was stirred for 30 minutes, yielding a reaction liquid with a solids concentration of approximately 6% by mass.

[0062] (Sulfonic Acid Group Modification Step) 900 g of the reaction solution obtained in the above colloidal silica synthesis step was collected and heated to 80°C under normal pressure. 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% aqueous hydrogen peroxide solution were added to the heated reaction solution. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 6% by mass.

[0063] Example 2 900 g of the reaction solution obtained in the colloidal silica synthesis step of Example 1 was collected and heated to 80°C under normal pressure. 0.628 g of 3-mercaptopropyltrimethoxysilane and 2.901 g of a 30% aqueous hydrogen peroxide solution were added to the heated reaction solution. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 6% by mass.

[0064] Example 3: 900 g of the reaction solution obtained in the colloidal silica synthesis step of Example 1 was collected and heated to 65°C under normal pressure. 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% aqueous hydrogen peroxide solution were added to the heated reaction solution. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 6% by mass.

[0065] Example 4 The reaction solution obtained in the colloidal silica synthesis step of Example 1 was heated and concentrated to obtain a concentrated solution with a solids concentration of 10% by mass. 930 g of the concentrated solution was collected and heated to 80°C under normal pressure. 1.116 g of 3-mercaptopropyltrimethoxysilane and 5.154 g of a 30% aqueous hydrogen peroxide solution were added to the heated concentrated solution. Next, pure water was added to maintain a constant volume while replacing the methanol, thereby producing colloidal silica. The silica particle content of the produced colloidal silica was 10% by mass.

[0066] Example 5 The reaction solution obtained in the colloidal silica synthesis step of Example 1 was heated and concentrated to obtain a concentrated solution with a solids concentration of 17% by mass. 980 g of the concentrated solution was collected and heated to 80°C under normal pressure. 1.999 g of 3-mercaptopropyltrimethoxysilane and 9.232 g of a 30% aqueous hydrogen peroxide solution were added to the heated concentrated solution. Next, pure water was added to maintain a constant volume while replacing the methanol, thereby producing colloidal silica. The silica particle content of the produced colloidal silica was 17% by mass.

[0067] Example 6: A mother liquor was prepared by adding 7,500 g of purified water as a solvent to a flask and adding 11.640 g of 3-ethoxypropylamine as an alkaline catalyst. The mother liquor was heated to an internal temperature of 85°C, and then 2,740 g of tetraorthosilicate was added to the mother liquor at a constant rate over 120 minutes while controlling the temperature to prevent fluctuations in the internal temperature. After the addition, the mixture was stirred for 15 minutes, and then 7.00 g of 3-ethoxypropylamine was added, yielding a reaction liquid with a solids concentration of approximately 11% by mass. The reaction liquid was then heated and concentrated under normal pressure to yield a concentrated liquid with a silica concentration of 20% by mass.

[0068] 1000 g of the above concentrated liquid was collected and heated to 65°C under normal pressure. 2.400 g of 3-mercaptopropyltrimethoxysilane and 11.083 g of a 30% aqueous hydrogen peroxide solution were added to the heated concentrated liquid. Next, pure water was added to maintain a constant volume while replacing the methanol, producing colloidal silica. The silica particle content of the produced colloidal silica was 20% by mass.

[0069] Comparative Example 1: 900 g of the reaction solution obtained in the colloidal silica synthesis step of Example 1 was sampled, and the methanol was replaced with water while adding pure water to maintain a constant volume, thereby producing colloidal silica. The silica particle content of the produced colloidal silica was 6 mass%.

[0070] Comparative Example 2: A mother liquor was prepared by mixing 6,588 g of methanol, 323 g of pure water, and 89 g of 28% aqueous ammonia in a flask. After the mother liquor was heated to an internal temperature of 60°C, 782 g of tetramethoxysilane was added at a constant rate over 87 minutes while controlling the temperature to prevent fluctuations in the internal temperature. After the addition, the mixture was stirred for 60 minutes, yielding a reaction liquid with a solids concentration of approximately 4% by mass.

[0071] 740 g of the reaction solution obtained in the above step was sampled, and the methanol was replaced with water while adding pure water to keep the volume constant, to produce colloidal silica. The silica particle content of the produced colloidal silica was 4 mass%.

[0072] Comparative Example 3: A mother liquor was prepared in a flask by mixing 5,000 g of methanol, 2,050 g of pure water, and 300 g of 28% aqueous ammonia. The temperature of the mother liquor was maintained at 35°C, and a mixture of 1,400 g of tetramethoxysilane and 750 g of methanol was added at a constant rate over 300 minutes while controlling the temperature to prevent fluctuations in the internal temperature. After the addition, the mixture was stirred for 60 minutes, yielding a reaction liquid with a solids concentration of approximately 6% by mass.

[0073] 740 g of the reaction solution obtained in the above step was sampled, and the methanol was replaced with water while adding pure water to maintain a constant volume, to produce colloidal silica. The silica particle content of the produced colloidal silica was 6 mass%.

[0074] Comparative Example 4: A mother liquor was prepared by mixing 2,945 g of methanol, 1,459 g of pure water, and 381 g of 28% aqueous ammonia in a flask. After heating the mother liquor to an internal temperature of 45°C, 3,497 g of tetramethoxysilane was added at a constant rate over 377 minutes while controlling the temperature to prevent fluctuations in the internal temperature. After the addition, the mixture was stirred for 60 minutes, yielding a reaction liquid with a solids concentration of approximately 17% by mass.

[0075] 740 g of the reaction solution obtained in the above step was sampled, and 1.232 g of 3-mercaptopropyltrimethoxysilane and 5.691 g of a 30% aqueous hydrogen peroxide solution were added at 25°C and atmospheric pressure. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 17% by mass.

[0076] Comparative Example 5: A mother liquor was prepared by mixing 5,925 g of methanol, 304 g of pure water, and 59 g of 28% aqueous ammonia in a flask. After heating the mother liquor to an internal temperature of 60°C, 726 g of tetramethoxysilane and 344 g of methanol were added at a constant rate over 127 minutes while controlling the temperature to prevent fluctuations in the internal temperature. After the addition, the mixture was stirred for 60 minutes, yielding a reaction liquid with a solids concentration of approximately 4% by mass.

[0077] 740 g of the reaction solution obtained in the above step was sampled, and 0.288 g of 3-mercaptopropyltrimethoxysilane and 1.330 g of a 30% aqueous hydrogen peroxide solution were added at 25°C and atmospheric pressure. Subsequently, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 4% by mass.

[0078] Comparative Example 6: 900 g of the reaction solution obtained in the colloidal silica synthesis step of Example 1 was sampled, and 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% aqueous hydrogen peroxide solution were added at 25°C and atmospheric pressure. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, thereby producing colloidal silica. The silica particle content of the produced colloidal silica was 6% by mass.

[0079] Comparative Example 7 900 g of the reaction solution obtained in the colloidal silica synthesis step of Example 1 was sampled and heated to 40°C under normal pressure. 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% aqueous hydrogen peroxide solution were added to the heated reaction solution. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 6% by mass.

[0080] Comparative Example 8: 740 g of the reaction solution obtained in the step of obtaining the reaction solution in Comparative Example 2 was sampled, and 0.352 g of 3-mercaptopropyltrimethoxysilane and 1.626 g of a 30% aqueous hydrogen peroxide solution were added at 25°C and atmospheric pressure. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, thereby producing colloidal silica. The silica particle content of the produced colloidal silica was 4% by mass.

[0081] Comparative Example 9: 740 g of the reaction solution obtained in the step of obtaining the reaction solution in Comparative Example 3 was sampled, and 0.517 g of 3-mercaptopropyltrimethoxysilane and 2.385 g of a 30% aqueous hydrogen peroxide solution were added at 25°C under normal pressure. Next, the methanol was replaced with water while adding pure water to maintain a constant volume, producing colloidal silica. The silica particle content of the produced colloidal silica was 6% by mass.

[0082] The colloidal silica of the Examples and Comparative Examples obtained as described above was evaluated by the following methods.

[0083] (Average primary particle diameter) Colloidal silica was pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a measurement sample. The BET specific surface area was measured using the prepared measurement sample. The true specific gravity of silica was 2.2, and the BET specific surface area (m ２ / g) was converted to the average primary particle diameter (nm) of silica particles in the colloidal silica.

[0084] (Average secondary particle diameter) A measurement sample for dynamic light scattering was prepared by adding colloidal silica to a 0.3 mass% aqueous citric acid solution and homogenizing it to a silica concentration of 0.8 mass%. Using this measurement sample, the average secondary particle diameter (nm) was measured by dynamic light scattering ("ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd.).

[0085] (Association Ratio) The value calculated from the average secondary particle size / average primary particle size was taken as the association ratio.

[0086] (Zeta Potential) Hydrochloric acid was added to colloidal silica to adjust the pH to 3.0. The zeta potential was measured by electrophoretic light scattering using an ELS-Z manufactured by Otsuka Electronics Co., Ltd.

[0087] (Sulfonic Acid Group Amount) Colloidal silica was subjected to ultracentrifugation (5°C, 50,000 rpm) for 1 hour to obtain silica solids. The silica solids were suspended in ultrapure water and ultrasonically cleaned. The water used for cleaning was removed to obtain silica powder. The silica powder was analyzed using an X-ray photoelectron spectrometer (product name: AXIS NOVA, manufactured by Shimadzu Corporation). An Al-Kα X-ray source (15 kV, 10 mA) was used, and analysis was performed in the O 1s, C 1s, S 2s, and Si 2p regions. The peak of sulfur atoms derived from sulfonic acid groups was identified in the S 2s (binding energy 230 eV) region, and the sulfonic acid group amount (atomic %) was calculated from the ratio of the number of sulfur atoms derived from sulfonic acid groups to the number of all detected atoms.

[0088] (True Specific Gravity) Colloidal silica was dried on a hot plate at 150° C. and then held in a furnace at 300° C. for 1 hour, and the true specific gravity of the silica particles was measured by a liquid phase substitution method using ethanol.

[0089] (Dispersion Stability Under Acidic Conditions (pH 3.0)) Ultrapure water and 1 mol / L hydrochloric acid were added to the colloidal silica produced in each Example and Comparative Example to adjust the silica concentration to 3 wt % and the pH to 3.0 to prepare a sample. The obtained sample was placed in a fluororesin container, sealed, and stored at 25°C for 1 month. The average secondary particle diameter was measured before and after storage, and the increase in the average secondary particle diameter was calculated. If the increase in the average secondary particle diameter exceeds 3.0 nm, aggregation of the silica particles has progressed, and the dispersion stability is deemed to be poor. Conversely, if the increase in the average secondary particle diameter is less than 3.0 nm, the dispersion stability of the silica particles is deemed to be good.

[0090] (Surface roughness RMS of polished surface) The colloidal silica produced in each Example and Comparative Example was diluted with ultrapure water to a silica concentration of 3.0 mass % to prepare a polishing composition. A 3 cm square silicon wafer having a silicon oxide film formed on its surface was polished using the polishing composition under the following conditions: Polishing machine: NF-300CMP manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000T MPad manufactured by Nitta DuPont Co., Ltd. Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min

[0091] The surface roughness of the polished silicon wafers was evaluated using an atomic force microscope under the following conditions: Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: Olympus MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: Five fields were observed per polished wafer. Surface roughness calculation method: The average root mean square roughness (RMS) of the five fields was calculated and used as the surface roughness of the polished surface.

[0092] (Metal Impurity Content) The metal impurity content was measured using an atomic absorption spectrometer. The metal impurity content was defined as the sum of the contents of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the colloidal silica.

[0093] The content of silica particles in colloidal silica was calculated using the following formula: Content of silica particles in colloidal silica [%] = (W ÷ 10.0) × 100. 10.0 g of colloidal silica was dried on a hot plate at 150°C, then heated at 800°C for 1 hour to remove moisture, and the resulting solid content was defined as Wg.

[0094] The results are shown in Table 1.

[0095]

Claims

1. A colloidal silica containing silica particles, characterized in that the silica particles have an average secondary particle diameter of 20 nm or less as measured by a dynamic light scattering method, a zeta potential of -20 mV or less as measured under a pH 3 condition, and are surface-modified with sulfonic acid groups.

2. The colloidal silica according to claim 1, wherein the amount of sulfonic acid groups in the silica particles is 0.02 atm % or more.

3. The colloidal silica according to claim 1 or 2, wherein the average primary particle diameter calculated from the BET specific surface area of ​​the silica particles is 18 nm or less.

4. A method for producing colloidal silica, comprising the step of adding a silane coupling agent having a mercapto group and an oxidizing agent to colloidal silica, wherein the temperature of the colloidal silica in the step is 65° C. or higher.

5. The method according to claim 4, wherein the silane coupling agent having a mercapto group is at least one selected from the group consisting of 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

6. The manufacturing method according to claim 4 or 5, wherein the oxidizing agent is at least one selected from the group consisting of nitric acid, hydrogen peroxide, oxygen, ozone, organic peracid, bromine, hypochlorite, potassium permanganate, and chromic acid.

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