Colloidal silica and method for producing same

Abstract

Provided are: colloidal silica which has a small average secondary particle diameter of silica particles and is capable of maintaining the dispersion stability of the silica particles for a long period of time even under strongly acidic conditions at pH 3; and a method for producing the colloidal silica. The present invention provides colloidal silica containing silica particles, which 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 method and a Zeta potential of-20 mV or less as measured under pH 3 conditions, and the surfaces of the silica particles are modified with sulfonic acid groups.

Description

Technical Field

[0001] This invention relates to colloidal silica and its manufacturing method. Background Technology

[0002] Colloidal silica is formed by dispersing silica particles in a medium such as water. In addition to being used as a property modifier in the fields of paper, fiber, steel, etc., it can also be used as an abrasive in CMP (concrete polishing) of electronic materials such as semiconductor wafers.

[0003] With the miniaturization of semiconductor linewidths, electronic materials in CMP processes require high flatness and low defect rates. To meet these requirements, silica particles with small average secondary particle size and good dispersion stability are needed. Generally, the smaller the particle size of silica, the more prone it is to aggregation. Since the zeta potential (ξ-potential) is close to the isoelectric point under acidic conditions, it becomes more unstable.

[0004] Colloidal silica containing small-diameter silica particles with an average particle size of less than 20 nm has been proposed (see Patent Document 1). However, the silica gel disclosed in Patent Document 1 has the problem that it cannot maintain good dispersion stability under strongly acidic conditions below pH 3, and the particles agglomerate over time.

[0005] To improve dispersion stability under acidic conditions, a method for surface modification of silica particles using sulfonic acid groups was proposed (see Patent Document 2). In the method described in Patent Document 2, small-particle-size sulfonic acid-modified colloidal silica with an average particle size of less than 20 nm is prepared by sulfonic acid modification of small-particle-size colloidal silica.

[0006] However, the small-particle-size sulfonic acid modified colloidal silica described in Patent Document 2 has a low absolute value of Zeta potential in the acidic region due to insufficient surface modification of the sulfonic acid groups. Under strongly acidic conditions of around pH 3, it cannot maintain long-term dispersion stability.

[0007] Therefore, there is a need to develop colloidal silica with a small average secondary particle size and a long-term ability to maintain the dispersion stability of silica particles even under strongly acidic conditions of pH 3, as well as a method for manufacturing the same.

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2004-315300 Patent Document 2: International Publication No. 2023-007938 Summary of the Invention

[0009] The problem that the invention aims to solve In view of the above-mentioned problems, the present invention aims to provide colloidal silica with small average secondary particle size and the ability to maintain the dispersion stability of silica particles for a long time under strongly acidic conditions of pH 3, and a method for manufacturing the same.

[0010] Technical solutions for solving the problem In order to achieve the above objectives, the inventors of this invention have conducted repeated and in-depth research and found that by preparing colloidal silica containing silica particles, wherein the average secondary particle size of the silica particles, as measured by dynamic light scattering, is less than 20 nm, the Zeta potential, as measured under pH 3 conditions, is less than -20 mV, and the surface is modified with sulfonic acid groups, the above objectives can be achieved, thus completing this invention.

[0011] That is, the present invention relates to the following colloidal silica and its manufacturing method.

[0012] 1. A colloidal silica comprising silica particles, characterized in that, The average secondary particle size of the silica particles measured by dynamic light scattering method is less than 20 nm, and the zeta potential measured under pH 3 conditions is less than -20 mV. The surface of the silica particles is modified with sulfonic acid groups.

[0013] 2. The colloidal silica as described in item 1, wherein the sulfonic acid content of the silica particles is 0.02 atm% or more.

[0014] 3. Colloidal silica as described in item 1 or 2, wherein the average primary particle size of the silica particles, calculated from the BET specific surface area, is less than 18 nm.

[0015] 4. A method for manufacturing colloidal silica, comprising the steps of adding a silane coupling agent having a mercapto group and an oxidant to the colloidal silica. The temperature of the colloidal silica in the above process is above 65°C.

[0016] 5. The manufacturing method as described in item 4, wherein the silane coupling agent having a mercapto group is selected from at least one of 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane and 2-mercaptoethyltriethoxysilane.

[0017] 6. The manufacturing method as described in item 4 or 5, wherein the oxidant is selected from at least one of nitric acid, hydrogen peroxide, oxygen, ozone, organic peroxyacid, bromine, hypochlorite, potassium permanganate and chromic acid.

[0018] Invention Effects In view of the above, the present invention aims to provide colloidal silica with small average secondary particle size and the ability to maintain dispersion stability of silica particles for a long time under strongly acidic conditions below pH 3, and a method for manufacturing the same. Detailed Implementation

[0019] The colloidal silica of the present invention is a colloidal silica containing silica particles. The average secondary particle size of these silica particles, as determined by dynamic light scattering, is less than 20 nm, and the Zeta potential measured at pH 3 is less than -20 mV. The surface of this colloidal silica is modified with sulfonic acid groups. In the colloidal silica of the present invention, the average secondary particle size of the silica particles, as determined by dynamic light scattering, is less than 20 nm, and the Zeta potential measured at pH 3 is less than -20 mV. Therefore, even under acidic conditions with a pH less than 3, the silica particles have a small average secondary particle size of less than 20 nm, resulting in a smaller surface roughness when used as an abrasive. Furthermore, the surface of the colloidal silica of the present invention is modified with sulfonic acid groups, thus maintaining the average secondary particle size of the silica particles at less than 20 nm and maintaining the Zeta potential measured at pH 3 at less than -20 mV. Colloidal silica exhibiting the above properties demonstrates high dispersion stability under acidic conditions below pH 3, enabling high flatness when used as an abrasive.

[0020] Furthermore, the manufacturing method of the present invention includes a step of adding a silane coupling agent with a mercapto group and an oxidant to colloidal silica, wherein the temperature of the colloidal silica in the above step is 65°C or higher. By adding a silane coupling agent with a mercapto group and an oxidant to colloidal silica at a specific temperature range of 65°C or higher, the manufacturing method of the present invention can suppress the aggregation of silica particles when modified with sulfonic acid groups, suppress the increase in average secondary particle size to more than 20 nm, and improve the dispersion stability of silica particles through sulfonic acid group modification, enabling the suppression of aggregation to be maintained for a longer period of time.

[0021] The colloidal silica and its manufacturing method of the present invention will be described in detail below.

[0022] 1. Colloidal silica The colloidal silica of the present invention contains silica particles. When the colloidal silica is 100% by mass, 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. Furthermore, when the colloidal silica is 100% by mass, 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. By ensuring that the lower limit of the silica particle content in the colloidal silica is within the above-mentioned range, the grinding performance is further improved when the colloidal silica is used as an abrasive. Furthermore, by ensuring that the upper limit of the silica particle content in the colloidal silica is within the above-mentioned range, the dispersion stability of the silica particles is further improved.

[0023] In this specification, the content of silica particles in colloidal silica can be calculated by drying and curing 10.0g of colloidal silica with a heating plate at 150°C, then heating it at 800°C for 1 hour to remove moisture, and setting the amount of the obtained solid component as Wg.

[0024] The content of silica particles in colloidal silica [%] = (W ÷ 10.0) × 100 The colloidal silica of the present invention contains silica particles with an average secondary particle size of 20 nm or less, as determined by dynamic light scattering. The average secondary particle size is preferably 18 nm or less, more preferably 16 nm or less, further preferably 14 nm or less, and particularly preferably 13.5 nm or less. Furthermore, the lower limit of the average secondary particle size is not particularly limited, but is preferably 2 nm or more, more preferably 4 nm or more, further preferably 6 nm or more, and particularly preferably 8 nm or more. By ensuring the lower limit of the average secondary particle size is within the above range, the grinding performance is further improved when the colloidal silica is used as an abrasive.

[0025] In this specification, the method for determining the average secondary particle size of the silica particles contained in colloidal silica is a dynamic light scattering method, specifically the method described in the examples below.

[0026] The average primary particle size of the aforementioned silica particles is preferably 20 nm or less, more preferably 18 nm or less, and even more preferably 10 nm or less. If the upper limit of the average primary particle size is within the above range, the flatness during grinding using the colloidal silica of the present invention is further improved. Furthermore, the average primary particle size of the aforementioned silica particles is preferably 3 nm or more, more preferably 5 nm or more, and even more preferably 7 nm or more. If the lower limit of the average primary particle size of the silica particles is within the above range, the storage stability of the colloidal silica is further improved.

[0027] In this specification, the method for determining the average primary particle size of the silica particles contained in colloidal silica is the method described in the examples below.

[0028] In this specification, the Zeta potential of colloidal silica is determined by electrophoretic light scattering using an ELS-Z manufactured by Otsuka Electronics Co., Ltd.

[0029] The colloidal silica of the present invention exhibits a zeta potential of -20 mV or less when measured at pH 3. If the zeta potential measured at pH 3 exceeds -20 mV, the dispersion stability of the silica particles cannot be maintained for a long period under strongly acidic conditions. Preferably, the zeta potential measured at pH 3 is -22 mV or less, more preferably -24 mV or less, and even more preferably -26 mV or less. If the lower limit of the zeta potential is within the above range, higher dispersion stability can be maintained under strongly acidic conditions. Furthermore, the lower limit of the zeta potential measured at pH 3 is not particularly limited and can be -120 mV or more, -100 mV or more, etc.

[0030] In this specification, the method for measuring the Zeta potential obtained under pH 3 conditions is the method described in the examples below.

[0031] The colloidal silica of this invention contains silica particles whose surface is modified with sulfonic acid groups. If the surface of the silica particles is not modified with sulfonic acid groups, the colloidal silica cannot maintain the dispersion stability of the silica particles for a long time under strongly acidic conditions of pH 3.

[0032] In this specification, the surface of the silica particles contained in the colloidal silica is modified with sulfonic acid groups, which can be confirmed by the amount of sulfonic acid groups in the silica particles, as described later, showing a value of 0.02 atm% or more.

[0033] The amount of sulfonic acid groups in the colloidal silica particles of the present invention is preferably 0.02 atm% or more, more preferably 0.05 atm% or more, further preferably 0.08 atm% or more, particularly preferably 0.10 atm% or more, and most preferably 0.15 atm% or more. By keeping the lower limit of the sulfonic acid group amount 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 can be 2.00 atm% or less, 1.50 atm% or less, 1.00 atm% or less, etc.

[0034] In this specification, the method for determining the amount of sulfonic acid groups in the silica particles contained in colloidal silica is the method described in the examples described later.

[0035] 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. Furthermore, 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. If the lower limit of the association ratio of silica particles is within the above range, the grinding speed when using colloidal silica for grinding is further increased. If the upper limit of the association ratio of silica particles is within the above range, the flatness when using colloidal silica for grinding is further improved.

[0036] 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 the silica particles in the colloidal silica.

[0037] The pH of the colloidal silica of the present invention can be appropriately set according to the application of the colloidal silica, and is not particularly limited, but is preferably 2.0 or higher, more preferably 3.0 or higher. Furthermore, the pH is preferably 11.0 or lower, more preferably 10.0 or lower. By keeping the lower limit of the pH within the above range, the long-term dispersion stability of the silica particles in the colloidal silica is further improved. Furthermore, by keeping the upper limit of the pH within the above range, the long-term dispersion stability of the colloidal silica is further improved.

[0038] The colloidal silica of the present invention preferably has a true specific gravity of 1.50 or more, more preferably 1.65 or more, and even more preferably 1.80 or more. If the lower limit of the true specific gravity is within the above range, the abrasiveness of the colloidal silica of the present invention is 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. If the upper limit of the true specific gravity is within the above range, the occurrence of scratches on the workpiece is further reduced.

[0039] In this specification, true specific gravity can be determined by drying and curing colloidal silica on a heating plate at 150°C, holding it in an oven at 300°C for 1 hour, and then using a liquid-phase displacement method with ethanol.

[0040] In the colloidal silica of the present invention, the content of metallic impurities such as sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is preferably less than 1 ppm. With a metallic impurity content of less than 1 ppm, it is suitable for grinding electronic materials and the like.

[0041] The colloidal silica of the present invention can be used, for example, as a property modifier in the fields of paper, fiber, steel, etc., and as an abrasive for electronic materials such as semiconductor wafers. Furthermore, by drying it and forming it into a powder, it can be used as a filler additive, a colorant additive, etc.

[0042] 2. Method for manufacturing colloidal silica The method for manufacturing colloidal silica of the present invention includes a step of adding a silane coupling agent with a mercapto group and an oxidant to colloidal silica, wherein the temperature of the colloidal silica in the above step is 65°C or higher. By adding a silane coupling agent with a mercapto group and an oxidant to colloidal silica at a specific temperature range of 65°C or higher, the method of the present invention, when modified with sulfonic acid groups, suppresses the aggregation of silica particles, inhibits the increase in average secondary particle size to more than 20 nm, and improves the dispersion stability of silica particles through sulfonic acid group modification, enabling the state of suppressed aggregation to be maintained for a long time.

[0043] In the above process, 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 agglomerate during sulfonic acid modification, and silica particles with an average secondary particle size of less than 20 nm will not be obtained. The upper limit of the above temperature is not particularly limited as long as it can suppress the boiling of the reaction solvent, but it is preferably below 100°C, and more preferably below 90°C.

[0044] In the manufacturing method of the present invention, after adding a silane coupling agent with a mercapto group to colloidal silica, the above functional group is converted into a sulfonic acid group.

[0045] The colloidal silica used as raw material is not limited as long as it has silanol groups on its surface. However, if the absence of diffusing metallic impurities and corrosive ions such as chlorine in the semiconductor is considered, it is preferable to use a hydrolyzable silicon compound (e.g., alkoxysilane or its derivative) as raw material, and obtain colloidal silica through hydrolysis and condensation. One type of silicon compound or a mixture of two or more types can be used.

[0046] In this invention, the silicon compound is preferably an alkoxysilane or a derivative thereof represented by the following general formula (1).

[0047] Si(OR)4 (1) [In the formula, 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.] Examples of R can be methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, etc., with tetramethoxysilanes where R is methyl, tetraethoxysilanes where R is ethyl, and tetraisopropoxysilanes where R is isopropyl being preferred. Additionally, low-condensity derivatives obtained by partially hydrolyzing alkoxysilanes can also be used as derivatives. In this invention, tetramethoxysilane is preferred from the perspectives of easy control of the hydrolysis rate, easy acquisition of tiny silica particles of 1 nm, and minimal residue of unreacted matter.

[0048] The aforementioned silicon compounds are hydrolyzed and condensed in the reaction solvent to form colloidal silica. Water or an aqueous organic solvent can be used as the reaction solvent.

[0049] Examples of organic solvents include: alcohols such as methanol, ethanol, isopropanol, n-butanol, tert-butanol, pentanol, ethylene glycol, propylene glycol, and 1,4-butanediol; and ketones such as acetone and methyl ethyl ketone.

[0050] There is no particular limit to the amount of water added to the organic solvent, as long as the amount required for the hydrolysis of the silicon compound is present. Preferably, 1 mole of silicon compound is about 2 to 200 moles.

[0051] It is preferable to add an alkaline catalyst to the reaction solvent to adjust the solvent to be alkaline. Therefore, the reaction solvent is preferably adjusted to pH 8-11, more preferably to pH 8.5-10.5, which enables rapid formation of colloidal silica. The type of alkaline catalyst is not particularly limited. Considering the avoidance of metal impurities, metal-free organic alkaline catalysts are preferred, with nitrogen-containing organic alkaline catalysts being the most preferred. Examples of such organic alkaline catalysts include ethylenediamine, diethylenetriamine, triethylenetetramine, 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. From the viewpoint of excellent catalytic performance and high volatility for easy removal in subsequent processes, ammonia is preferred. From the viewpoint of increasing the true specific gravity of silica particles, in order to prevent volatilization even when the reaction temperature is increased, it is preferable to select an organic base catalyst with a boiling point of 90°C or higher, and more preferably at least one selected from tetramethylammonium hydroxide and 3-ethoxypropylamine.

[0052] In this invention, a silane coupling agent having a thiol group that can be chemically converted into a sulfonic acid group is added to colloidal silica, thereby converting the thiol group into a sulfonic acid group, thus enabling sulfonic acid modification of the colloidal silica. This is because the high acidity of the sulfonic acid group leads to hydrolysis, making it difficult to obtain a silane coupling agent with a sulfonic acid group.

[0053] Examples of silane coupling agents containing thiol groups include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0054] The aforementioned silane coupling agents with thiol groups can be used alone or in combination of two or more.

[0055] When adding a coupling agent to colloidal silica, considering the solubility of the coupling agent, it is preferable to include a hydrophilic organic solvent in the colloidal silica. In this regard, when colloidal silica is obtained by the Stover method, which involves the hydrolysis and condensation of alkoxysilanes in an alcohol-water solvent using a basic catalyst, the reaction solution already contains alcohol, thus eliminating the need for further addition of a hydrophilic organic solvent. In this case, the hydrophilic organic solvent is more preferably 5% by mass or more relative to the water in the colloidal silica, and this can be adjusted by concentrating the reaction solution as needed.

[0056] On the other hand, when adding a silane coupling agent to water-dispersed colloidal silica, a hydrophilic solvent is added to a degree that the silane coupling agent can dissolve. Examples of hydrophilic organic solvents include alcohols such as isopropanol, ethanol, and methanol; among these, an alcohol of the same type as the alcohol produced by the hydrolysis of the silicon compound is preferred. This is because using an alcohol of the same type as the alcohol produced by the hydrolysis of the silicon compound facilitates solvent recovery and reuse.

[0057] The amount of the coupling agent added is preferably about 0.1 to 10% by mass relative to silica. If the amount added is within this range, the zeta potential under acidic conditions is more stable. Furthermore, by keeping the upper limit of the added amount within the above range, the gelation of colloidal silica over time is further suppressed.

[0058] The reaction time for adding the coupling agent is not limited, but is preferably 10 minutes to 10 hours, 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 or higher and 11 or lower. By setting the upper limit of the pH to the above range, the silane coupling agent reacts more easily with the silica surface, further inhibiting the self-condensation of the silane coupling agents.

[0059] In the above process, an oxidizing agent is added together with a silane coupling agent containing a thiol group. The modified thiol group is oxidized by using the oxidizing agent.

[0060] Examples of oxidizing agents include: nitric acid, hydrogen peroxide, oxygen, ozone, organic peroxyacids (peroxycarboxylic acids), bromine, hypochlorite, potassium permanganate, and chromic acid. Among these oxidizing agents, hydrogen peroxide and organic peroxyacids (peracetic acid, perbenzoic acid derivatives) are preferred due to their ease of operation and good oxidation yield. Furthermore, if the substances generated as byproducts during the reaction are taken into account, hydrogen peroxide is the most preferred choice.

[0061] The above-mentioned oxidants can be used alone or in combination of two or more.

[0062] The amount of oxidant 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 preferred. Furthermore, regarding colloidal silica and silane coupling agents, since they have structures that are stable in oxidation reactions except for functional groups that can be oxidized (converted) to sulfonic acid groups, the generation of byproducts is suppressed.

[0063] Colloidal silica with sulfonic acid group modification obtained by the above method sometimes contains solvents other than water. Therefore, to further improve the long-term storage stability of this colloidal silica, the dispersion medium, which is mainly composed of the reaction solvent, can be replaced with water as needed. Furthermore, this water replacement can be performed after the addition of the coupling agent and before the addition of the oxidant.

[0064] There are no particular limitations on the method of replacing the dispersion medium, which is mainly composed of the reaction solvent, with water. For example, one method is to heat the colloidal silica while adding water dropwise in small increments. Another method is to precipitate and separate the colloidal silica, separate it from the dispersion medium, which is mainly composed of the reaction solvent, through centrifugation, and then redisperse it in water.

[0065] The colloidal silica of the present invention described above can be manufactured by the manufacturing method having the processes described above.

[0066] Example The present invention will now be described in detail with reference to embodiments and other specific examples, but the present invention is not limited to these embodiments.

[0067] Example 1 (The synthesis process of colloidal silica) In a flask, 8836 g of pure water was added as a solvent, and 13.968 g of 3-ethoxypropylamine was added as a base catalyst to prepare a mother liquor. The mother liquor was heated to an internal temperature of 85°C, and while maintaining a constant internal temperature, 1534 g of tetramethyl orthosilicate was injected into the mother liquor at a constant rate over 15 minutes. After the injection was completed, the mixture was stirred for 30 minutes to obtain a reaction solution with a solid content of approximately 6% by mass.

[0068] (Sulfonic acid group modification process) 900 g of the reaction solution obtained in the above-mentioned synthesis step of colloidal silica was extracted and heated to 80°C under normal pressure. 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% hydrogen peroxide aqueous solution were added to the heated reaction solution. Then, to maintain a constant volume, methanol was added while simultaneously replacing the methanol with pure water to produce colloidal silica. The resulting colloidal silica contained 6% silica particles by mass.

[0069] Example 2 900 g of the reaction solution obtained in the synthesis process of colloidal silica in Example 1 was heated to 80°C under normal pressure. 0.628 g of 3-mercaptopropyltrimethoxysilane and 2.901 g of a 30% hydrogen peroxide aqueous solution were added to the heated reaction solution. Then, to maintain a constant volume, methanol was added while simultaneously replacing the methanol with pure water to produce colloidal silica. The resulting colloidal silica contained 6% silica particles by mass.

[0070] Example 3 900 g of the reaction solution obtained in the synthesis process of colloidal silica in Example 1 was heated to 65°C under normal pressure. 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% hydrogen peroxide aqueous solution were added to the heated reaction solution. Then, to maintain a constant volume, methanol was added while simultaneously replacing the methanol with pure water to produce colloidal silica. The resulting colloidal silica contained 6% silica particles by mass.

[0071] Example 4 The reaction solution obtained in the synthesis process of colloidal silica in Example 1 was concentrated by heating to obtain a concentrated solution with a solid content of 10% by mass. 930 g of the concentrated solution was extracted and heated to 80°C under normal pressure. 1.116 g of 3-mercaptopropyltrimethoxysilane and 5.154 g of a 30% hydrogen peroxide aqueous solution were added to the heated concentrated solution. Then, to maintain a constant volume, pure water was added while replacing methanol to produce colloidal silica. The resulting colloidal silica had a silica particle content of 10% by mass.

[0072] Example 5 The reaction solution obtained in the synthesis process of colloidal silica in Example 1 was concentrated by heating to obtain a concentrated solution with a solid content of 17% by mass. 980 g of the concentrated solution was extracted and heated to 80°C under normal pressure. 1.999 g of 3-mercaptopropyltrimethoxysilane and 9.232 g of a 30% hydrogen peroxide aqueous solution were added to the heated concentrated solution. Then, to maintain a constant volume, pure water was added while replacing methanol to produce colloidal silica. The resulting colloidal silica had a silica particle content of 17% by mass.

[0073] Example 6 7500 g of pure water was added to a flask as a solvent, and 11.640 g of 3-ethoxypropylamine was added as a base catalyst to prepare a mother liquor. The mother liquor was heated to an internal temperature of 85°C, and while maintaining a constant internal temperature, 2740 g of tetraorthosilicate was injected into the mother liquor at a constant rate over 120 minutes. After the injection was completed and the mixture was stirred for 15 minutes, 7.00 g of 3-ethoxypropylamine was added, yielding a reaction solution with a solid content of approximately 11% by mass. The reaction solution was then concentrated under normal pressure to obtain a concentrated solution with a silica concentration of 20% by mass.

[0074] 1000g of the above concentrate was extracted and heated to 65°C under normal pressure. 2.400g of 3-mercaptopropyltrimethoxysilane and 11.083g of a 30% hydrogen peroxide aqueous solution were added to the heated concentrate. Then, to maintain a constant volume, pure water was added while replacing methanol to produce colloidal silica. The resulting colloidal silica contained 20% silica particles by mass.

[0075] Comparative Example 1 900g of the reaction solution obtained in the synthesis process of colloidal silica in Example 1 was extracted. To maintain a constant volume, pure water was added while methanol was being replaced with water to produce colloidal silica. The colloidal silica produced had a silica particle content of 6% by mass.

[0076] Comparative Example 2 A mother liquor was prepared by mixing 6588 g of methanol, 323 g of pure water, and 89 g of 28% ammonia in a flask. The mother liquor was heated to an internal temperature of 60°C, and while maintaining this internal temperature, 782 g of tetramethoxysilane was injected at a constant rate over 87 minutes. After the injection was completed, the mixture was stirred for 60 minutes to obtain a reaction solution with a solid content of approximately 4% by mass.

[0077] 740g of the reaction solution obtained in the above steps was extracted. To maintain a constant volume, pure water was added while methanol was being replaced with water to produce colloidal silica. The colloidal silica produced contained 4% silica particles by mass.

[0078] Comparative Example 3 A mother liquor was prepared by mixing 5000g of methanol, 2050g of pure water, and 300g of 28% ammonia in a flask. The temperature of the mother liquor was maintained at 35°C, and while adjusting the temperature by keeping the internal temperature constant, a mixture of 1400g of tetramethoxysilane and 750g of methanol was injected at a constant rate over 300 minutes. After the injection was completed, the mixture was stirred for 60 minutes to obtain a reaction solution with a solid content of approximately 6% by mass.

[0079] 740g of the reaction solution obtained in the above steps was extracted. To maintain a constant volume, pure water was added while methanol was being replaced with water to produce colloidal silica. The colloidal silica produced contained 6% silica particles by mass.

[0080] Comparative Example 4 A mother liquor was prepared by mixing 2945 g of methanol, 1459 g of pure water, and 381 g of 28% ammonia in a flask. The mother liquor was heated to an internal temperature of 45°C, and while maintaining this internal temperature, 3497 g of tetramethoxysilane was injected at a constant rate over 377 minutes. After the injection was completed, the mixture was stirred for 60 minutes to obtain a reaction solution with a solid content of approximately 17% by mass.

[0081] 740g of the reaction solution obtained in the above steps was extracted, and 1.232g of 3-mercaptopropyltrimethoxysilane and 5.691g of 30% hydrogen peroxide aqueous solution were added at 25°C and atmospheric pressure. Then, to maintain a constant volume, methanol was added while simultaneously replacing the methanol with pure water to produce colloidal silica. The content of silica particles in the obtained colloidal silica was 17% by mass.

[0082] Comparative Example 5 A mother liquor was prepared by mixing 5925 g of methanol, 304 g of pure water, and 59 g of 28% ammonia in a flask. The mother liquor was heated to an internal temperature of 60°C, and while maintaining this internal temperature, 726 g of tetramethoxysilane and 344 g of methanol were injected at a constant rate over 127 minutes. After the injection was completed, the mixture was stirred for 60 minutes to obtain a reaction solution with a solid content of approximately 4% by mass.

[0083] 740g of the reaction solution obtained in the above steps was extracted, and 0.288g of 3-mercaptopropyltrimethoxysilane and 1.330g of 30% hydrogen peroxide aqueous solution were added at 25°C and atmospheric pressure. Then, to maintain a constant volume, pure water was added while methanol was being replaced with water to produce colloidal silica. The content of silica particles in the produced colloidal silica was 4% by mass.

[0084] Comparative Example 6 900 g of the reaction solution obtained in the synthesis process of colloidal silica in Example 1 was extracted, and 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of 30% hydrogen peroxide aqueous solution were added at 25°C and atmospheric pressure. Then, to maintain a constant volume, methanol was added while simultaneously replacing the methanol with pure water to produce colloidal silica. The resulting colloidal silica contained 6% silica particles by mass.

[0085] Comparative Example 7 900 g of the reaction solution obtained in the synthesis process of colloidal silica in Example 1 was heated to 40°C under normal pressure. 2.530 g of 3-mercaptopropyltrimethoxysilane and 11.684 g of a 30% hydrogen peroxide aqueous solution were added to the heated reaction solution. Then, to maintain a constant volume, methanol was added while simultaneously replacing the methanol with pure water to produce colloidal silica. The resulting colloidal silica contained 6% silica particles by mass.

[0086] Comparative Example 8 740 g of the reaction solution obtained in the step of obtaining the reaction solution of Comparative Example 2 was extracted, and 0.352 g of 3-mercaptopropyltrimethoxysilane and 1.626 g of 30% hydrogen peroxide aqueous solution were added at 25°C and atmospheric pressure. Then, to maintain a constant volume, methanol was replaced with pure water while adding pure water to produce colloidal silica. The silica particles in the produced colloidal silica had a content of 4% by mass.

[0087] Comparative Example 9 740 g of the reaction solution obtained in the step of obtaining the reaction solution of Comparative Example 3 was extracted, and 0.517 g of 3-mercaptopropyltrimethoxysilane and 2.385 g of 30% hydrogen peroxide aqueous solution were added at 25°C and atmospheric pressure. Then, to maintain a constant volume, methanol was added while water replacement was performed to produce colloidal silica. The silica particles content of the produced colloidal silica was 6% by mass.

[0088] The colloidal silica of the examples and comparative examples obtained as described above was evaluated using the following methods.

[0089] (Average primary particle size) Colloidal silica was pre-dried on a hot plate and then heat-treated at 800°C for 1 hour to prepare a sample for measurement. The BET specific surface area was measured using the prepared sample. The true specific gravity of silica was set to 2.2, which was converted to 2727 / BET specific surface area (m²). 2 The value of ( / g) is used as the average primary particle size (nm) of silica particles in colloidal silica.

[0090] (Average secondary particle size) As a sample for dynamic light scattering, colloidal silica was added to a 0.3% (w / w) citric acid aqueous solution to prepare a sample with a silica concentration homogenized to 0.8% (w / w). Using this sample, the average secondary particle size (nm) was determined by dynamic light scattering (ELSZ-2000S, manufactured by Otsuka Electronics Co., Ltd.).

[0091] (Association ratio) The association ratio is calculated from the average secondary particle size / average primary particle size.

[0092] (Zeta potential) The pH of the colloidal silica was adjusted to 3.0 by adding hydrochloric acid. The zeta potential was determined by electrophoretic light scattering using an ELS-Z manufactured by Otsuka Electronics Co., Ltd.

[0093] (Sulfonic acid content) Colloidal silica was subjected to ultracentrifugation (5°C, 50,000 rpm) for 1 hour to obtain solid silica. The solid silica was then suspended in ultrapure water and ultrasonically cleaned. The water used in the cleaning was removed, yielding silica powder. The silica powder was analyzed using an X-ray photoelectron spectrometer (model 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 originating from sulfonic acid groups (S atoms) was identified in the S 2s region (binding energy 230 eV), and the sulfonic acid group content (atomic%) was calculated from the ratio of S atoms originating from sulfonic acid groups to the total number of detected atoms.

[0094] (True specific gravity) After the colloidal silica was dried and cured on a heating plate at 150°C, it was kept in an oven at 300°C for 1 hour. The true specific gravity of the silica particles was then determined by liquid-phase displacement with ethanol.

[0095] (Dispersion stability under acidic conditions (pH 3.0)) Samples were prepared by adding ultrapure water and 1 mol / L hydrochloric acid to the colloidal silica produced in the various examples and comparative examples to adjust the silica concentration to 3 wt% and pH 3.0. The obtained samples were placed in fluoropolymer containers, sealed, and stored at 25°C for one month. The average secondary particle size before and after storage was measured, and the increase in average secondary particle size was calculated. Furthermore, if the increase in average secondary particle size exceeded 3.0 nm, it was determined that the silica particles were agglomerating, indicating poor dispersion stability. Conversely, if the increase in average secondary particle size was less than 3.0 nm, the silica particles were considered to have good dispersion stability.

[0096] (Surface roughness RMS of the ground surface) Ultrapure water was added to the colloidal silica produced in the various examples and comparative examples to dilute the silica concentration to 3.0% by mass, thus preparing a polishing composition. Using the obtained polishing composition, a 3 cm square silicon wafer with a silica film formed on its surface was polished under the following conditions.

[0097] Grinding machine: NF-300CMP manufactured by Nano Factor Co., Ltd. Grinding pad: IC1000TMPad manufactured by Nitta DuPont Co., Ltd. Slurry feed rate: 50 mL / min Grinding head rotation speed: 32 rpm Pressure plate rotation speed: 32 rpm Grinding pressure: 4 psi Grinding time: 2 min The surface roughness of the polished silicon wafer was evaluated using an atomic force microscope under the following conditions.

[0098] Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: OLYMPUS Micro Cantilever OMCL-AC240TS-R3 Observation Mode: Dynamic Scan range: 3.0 μm square Scan speed: 1.00Hz Number of fields of view: Five fields of view are observed for each polished wafer.

[0099] Surface roughness calculation method: Calculate the average value of the root mean square roughness (RMS) of 5 fields of view, and use it as the surface roughness of the surface being ground.

[0100] (Metal impurity content) The content of metallic impurities was determined using an atomic absorption spectrometer. The sum of the contents of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in colloidal silica was taken as the content of metallic impurities.

[0101] The content of silica particles in colloidal silica was determined by drying and curing 10.0g of colloidal silica on a heating plate at 150°C, followed by heating at 800°C for 1 hour to remove moisture, and taking the amount of the resulting solid component as Wg, using the following formula.

[0102] The content of silica particles in colloidal silica [%] = (W ÷ 10.0) × 100 The results are shown in Table 1.

[0103] [Table 1]

Claims

1. Colloidal silica containing silica particles, the colloidal silica being characterized in that: the average secondary particle diameter of the silica particles is 20 nm or less as measured by a dynamic light scattering method, the Zeta potential as measured at pH 3 is -20 mV or less, and the surface of the silica particles is modified with sulfonic acid groups.

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

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

4. A method for producing colloidal silica, characterized by: 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 the step is 65°C or higher.

5. The production method according to claim 4, characterized in that: 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 production method according to claim 4 or 5, characterized in that: the oxidizing agent is at least one selected from the group consisting of nitric acid, hydrogen peroxide, oxygen, ozone, organic peroxy acid, bromine, hypochlorite, potassium permanganate, and chromic acid. ​ ​ ​ ​ ​ ​ ​

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