JP7443857B2 - Silica particle manufacturing method, silica sol manufacturing method, polishing method, semiconductor wafer manufacturing method, and semiconductor device manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing silica particles, a method for manufacturing silica sol, a method for polishing, a method for manufacturing semiconductor wafers, and a method for manufacturing semiconductor devices.

A polishing method using a polishing liquid is known as a method for polishing the surface of materials such as metals and inorganic compounds. Among these, chemical mechanical polishing (CMP) is used for final polishing of prime silicon wafers for semiconductors and recycled silicon wafers, as well as for flattening interlayer insulating films, forming metal plugs, and forming embedded wiring during semiconductor device manufacturing. ), the surface condition of these parts greatly affects the semiconductor properties, so the surfaces and end faces of these parts are required to be polished with extremely high precision.

In such precision polishing, a polishing composition containing silica particles is employed, and colloidal silica is widely used as the abrasive grain that is the main component. Depending on the manufacturing method, colloidal silica is produced by thermal decomposition of silicon tetrachloride (fumed silica, etc.), by deionization of alkali silicate such as water glass, and by hydrolysis reaction and condensation reaction of alkoxysilane (generally known as sol-gel method) is known.

Many studies have been made regarding methods for producing silica particles. For example, Patent Document 1 and Non-Patent Document 1 disclose methods for producing silica particles by hydrolysis reaction and condensation reaction of alkoxysilane.

Japanese Patent Application Publication No. 11-60232 Japanese Patent Application Publication No. 2009-224767 Japanese Patent Application Publication No. 2003-165718 "Controlled growth of monodisperse silica spheres in the micron size range" Staber, Journal of Colloid and Interface Science Vol. 26, Nos. 62-69, (1968).

Silica particles obtained by hydrolysis and condensation reactions of alkoxysilanes have a lower metal impurity content than silica particles obtained by thermal decomposition of silicon tetrachloride or silica particles obtained by deionization of alkali silicate. It can be suitably used in applications requiring precise polishing. However, the methods for producing silica particles disclosed in Patent Document 1 and Non-Patent Document 1 use alcohol as a reaction liquid in the hydrolysis reaction and condensation reaction of alkoxysilane, so the formation rate of silica particles is fast and the structure is undeveloped portions occur, and unreacted alkoxy groups tend to remain in the silica particles. Therefore, the silica particles obtained by the production methods disclosed in Patent Document 1 and Non-Patent Document 1 are compared to silica particles obtained by thermal decomposition of silicon tetrachloride and silica particles obtained by deionization of alkali silicate. , the problem is that the surface silanol group density becomes high.

Examples of methods for lowering the surface silanol group density of silica particles include methods such as autoclave treatment as disclosed in Patent Document 2 and surface modification treatment as disclosed in Patent Document 3. However, these methods require additional steps after the production of silica particles, require a large amount of production equipment, and have the problem of poor productivity.

The present invention was made in view of these problems, and an object of the present invention is to provide a method for producing silica particles that does not require a large amount of production equipment and can adjust the surface silanol group density, and a method for producing silica particles that can be obtained by the method. An object of the present invention is to provide a method for producing a silica sol containing silica particles. Another object of the present invention is to provide a polishing method suitable for polishing, a semiconductor wafer manufacturing method including the polishing method, and a semiconductor device manufacturing method including the polishing method.

Conventionally, silica particles obtained by hydrolysis and condensation reactions of alkoxysilanes have a higher surface silanol group density than silica particles obtained by thermal decomposition of silicon tetrachloride or silica particles obtained by deionization of alkali silicate. It has the problem of becoming expensive. In addition, in order to lower the surface silanol group density of silica particles, it is necessary to add additional processes such as autoclave treatment and surface modification treatment, which requires a lot of manufacturing equipment and has poor productivity. have challenges. However, as a result of extensive studies, the present inventors discovered that by optimizing the manufacturing conditions of silica particles, it was possible to adjust the surface silanol group density without requiring a large amount of manufacturing equipment, and completed the present invention. I ended up doing it.

That is, the gist of the present invention is as follows.
[1] A method for producing silica particles, which sequentially includes the following steps (1) and (2).
Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction in a liquid (A1) having an alcohol concentration of 70% by mass or more.
Step (2): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction in a liquid (A2) having a water concentration of 40% by mass or more.
[2] The method for producing silica particles according to [1], wherein the reaction temperature in step (1) is 60°C or lower.
[3] The method for producing silica particles according to [1] or [2], wherein the reaction temperature in step (2) is 65° C. or higher.
[4] The method of the hydrolysis reaction and condensation reaction in step (1) is a method of adding a solution (B1) containing a tetraalkoxysilane and a solution (C1) containing an alkali catalyst to the liquid (A1), The method for producing silica particles according to any one of [1] to [3].
[5] The method of the hydrolysis reaction and condensation reaction in step (2) is to add a solution (B2) containing a tetraalkoxysilane and a solution (C2) containing water or an alkali catalyst to the liquid (A2). The method for producing silica particles according to any one of [1] to [4], which is a method.
[6] The method for producing silica particles according to any one of [1] to [5], comprising the following step (1') between step (1) and step (2).
Step (1'): Step of removing alcohol and adding water.
[7] The method for producing silica particles according to any one of [1] to [6], wherein the pH within the reaction system in step (2) is maintained at 8.0 to 12.0.
[8] The method for producing silica particles according to any one of [1] to [7], further comprising the following step (3).
Step (3): A step of concentrating the silica particle dispersion obtained in step (2) and adding a dispersion medium.
[9] A method for producing a silica sol, including the method for producing silica particles according to any one of [1] to [8].
[10] The method for producing a silica sol according to [9], wherein the concentration of silica particles in the silica sol is 3% by mass to 50% by mass.
[11] A polishing method comprising polishing using a polishing composition containing a silica sol obtained by the silica sol manufacturing method according to [9] or [10].
[12] A method for manufacturing a semiconductor wafer, including the polishing method according to [11].
[13] A method for manufacturing a semiconductor device, including the polishing method according to [11].

The method for producing silica particles of the present invention and the method for producing silica sol of the present invention do not require a large amount of production equipment, and the surface silanol group density of silica particles can be adjusted. In addition, the method for producing silica particles of the present invention and the method for producing silica sol of the present invention can adjust the surface silanol group density of the silica particles, so it is possible to obtain silica particles with a desired surface silanol group density suitable for polishing. . Therefore, the polishing method of the present invention is suitable for polishing.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be implemented with various changes within the scope of the gist. Note that when the expression "~" is used in this specification, it is used as an expression that includes numerical values or physical property values before and after it.

(Method for manufacturing silica particles)
The method for producing silica particles of the present invention sequentially includes the following steps (1) and (2).
Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction in a liquid (A1) having an alcohol concentration of 70% by mass or more.
Step (2): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction in a liquid (A2) having a water concentration of 40% by mass or more.

(Step (1))
Step (1) is a step in which tetraalkoxysilane is subjected to a hydrolysis reaction and a condensation reaction in a liquid (A1) having an alcohol concentration of 70% by mass or more.

The liquid (A1) refers to the liquid medium in the initially charged reaction liquid and the alcohol generated in the hydrolysis reaction, excluding the tetraalkoxysilane, its reactant, and the alkali catalyst.

Liquid (A1) contains alcohol because it has excellent dispersibility in the reaction solution of tetraalkoxysilane.
Examples of the alcohol include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These alcohols may be used alone or in combination of two or more. Among these alcohols, methanol and ethanol are preferred because they easily dissolve tetraalkoxysilane, the by-products used in hydrolysis and condensation reactions are the same, and they are convenient for production. is more preferable.

It is preferable that the liquid (A1) contains water in addition to alcohol, since this allows the hydrolysis reaction and condensation reaction of the tetraalkoxysilane to proceed.

The liquid (A1) may contain other liquids than alcohol and water. Examples of other liquids include acetonitrile, tetrahydrofuran, and sulfolane.

The concentration of alcohol in the liquid (A1) is 70% by weight or more based on 100% by weight of the liquid (A1), preferably 70% to 95% by weight, more preferably 75% to 90% by weight. When the concentration of alcohol in the liquid (A1) is at least the lower limit, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape can be easily controlled. When the alcohol concentration in the liquid (A1) is below the upper limit, it is easy to control the hydrolysis reaction rate of the tetraalkoxysilane.

The concentration of water in the liquid (A1) is 30% by mass or less based on 100% by mass of the liquid (A1), preferably 5% by mass to 30% by mass, and more preferably 10% to 25% by mass. When the concentration of water in the liquid (A1) is at least the lower limit, it is easy to control the hydrolysis reaction rate of the tetraalkoxysilane. When the concentration of water in the liquid (A1) is below the upper limit, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape can be easily controlled.

The concentration of other liquids in the liquid (A1) is preferably 10% by mass or less, more preferably 5% by mass or less based on 100% by mass of the liquid (A1), since it has excellent hydrolysis reactivity of tetraalkoxysilane.

Since the reaction rate of the hydrolysis reaction and condensation reaction of tetraalkoxysilane can be increased, it is preferable to dissolve an alkali catalyst in the liquid (A1).
Examples of the alkali catalyst to be dissolved in the liquid (A1) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkaline catalysts, ammonia has excellent catalytic action, easy control of particle shape, can suppress the contamination of metal impurities, and has high volatility and excellent removability after hydrolysis and condensation reactions. is preferred.

The concentration of the alkali catalyst to be dissolved in the liquid (A1) is preferably 0.5% by mass to 2.0% by mass, and 0.6% by mass to 1.0% by mass, based on the total 100% by mass of the liquid (A1) and the alkali catalyst. 5% by mass is more preferred. When the concentration of the alkali catalyst is at least the lower limit, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. In addition, when the concentration of the alkali catalyst is below the upper limit, the reaction does not proceed excessively quickly and the reaction controllability is excellent.

Since the hydrolysis reaction and condensation reaction of tetraalkoxysilane in step (1) have excellent controllability of the concentrations of tetraalkoxysilane and alkali catalyst during the reaction process, a solution containing tetraalkoxysilane is used in the liquid (A1). A method of adding a solution (C1) containing (B1) and an alkali catalyst is preferred.

Examples of the tetraalkoxysilane in the solution (B1) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferable because they have a fast hydrolysis reaction, are difficult to leave unreacted substances, have excellent productivity, and can easily obtain a stable silica sol. Methoxysilane is more preferred.

As the raw material for the silica particles, raw materials other than tetraalkoxysilane such as low condensates of tetraalkoxysilane may be used, but due to their excellent reactivity, tetraalkoxysilane is is 50% by mass or more, raw materials other than tetraalkoxysilane are preferably 50% by mass or less, and more preferably tetraalkoxysilane is 90% by mass or more and raw materials other than tetraalkoxysilane are 10% by mass or less. preferable.

The solution (B1) may contain only tetraalkoxysilane without containing a solvent, but preferably contains a solvent because the dispersibility of tetraalkoxysilane in the reaction solution is excellent.
Examples of the solvent in the solution (B1) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferable, methanol and ethanol are more preferable, and methanol is even more preferable because the solvent used in the hydrolysis reaction and condensation reaction and the by-product are the same and are excellent in manufacturing convenience. .

The concentration of tetraalkoxysilane in solution (B1) is preferably 60% by mass to 95% by mass, more preferably 70% by mass to 90% by mass, based on 100% by mass of solution (B). When the concentration of tetraalkoxysilane in the solution (B1) is at least the lower limit, the reaction solution tends to become uniform. Moreover, when the concentration of tetraalkoxysilane in the solution (B1) is below the upper limit, generation of a gel-like substance can be suppressed.

The concentration of the solvent in the solution (B1) is preferably 5% to 40% by weight, more preferably 10% to 30% by weight based on 100% by weight of the solution (B1). When the concentration of the solvent in the solution (B1) is equal to or higher than the lower limit, generation of a gel-like substance can be suppressed. Furthermore, when the concentration of the solvent in the solution (B1) is below the upper limit, the reaction solution tends to become uniform.

The addition rate of the solution (B1) is preferably 0.05 kg/hour/L to 1.3 kg/hour/L, more preferably 0.1 kg/hour/L to 0.8 kg/hour/L. When the addition rate of the solution (B1) is equal to or higher than the lower limit, the productivity of silica particles is excellent. Moreover, when the addition rate of the solution (B1) is below the upper limit, generation of gel-like substances can be suppressed.
The addition rate of the solution (B1) is the addition rate of the solution (B1) per hour to the volume of the solution in which the alkali catalyst is dissolved in the liquid (A1).

The addition time of solution (B1) is preferably 0.2 hours to 10 hours, preferably 0.5 hours to 5 hours. When the addition time of the solution (B1) is equal to or longer than the lower limit, generation of a gel-like substance can be suppressed. Moreover, when the addition time of the solution (B1) is below the upper limit, the productivity of silica particles is excellent.

Examples of the alkali catalyst in the solution (C1) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkaline catalysts, ammonia has excellent catalytic action, easy control of particle shape, can suppress the contamination of metal impurities, and has high volatility and excellent removability after hydrolysis and condensation reactions. is preferred.

The solution (C1) preferably contains a solvent, since this can reduce fluctuations in the concentration of the alkali catalyst in the reaction solution.
Examples of the solvent in the solution (C1) include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, water and alcohol are preferred, and water is more preferred, since those used in the hydrolysis reaction and condensation reaction and those produced as by-products are the same and are excellent in manufacturing convenience.

The concentration of the alkali catalyst in the solution (C1) is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass based on 100% by mass of the solution (C1). When the concentration of the alkali catalyst in the solution (C1) is at least the lower limit, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start of the reaction to the end of the reaction. Further, when the concentration of the alkali catalyst in the solution (C1) is below the upper limit, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced.

The concentration of the solvent in the solution (C1) is preferably 90% by mass to 99.5% by mass, more preferably 94% by mass to 99% by mass based on 100% by mass of the solution (C1). When the concentration of the solvent in the solution (C1) is at least the lower limit, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced. Moreover, when the concentration of the solvent in the solution (C1) is below the upper limit value, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start of the reaction to the end of the reaction.

The addition rate of the solution (C1) is preferably 0.02 kg/hour/L to 0.5 kg/hour/L, more preferably 0.04 kg/hour/L to 0.3 kg/hour/L. When the addition rate of the solution (C1) is equal to or higher than the lower limit, the productivity of silica particles is excellent. Moreover, when the addition rate of the solution (C1) is below the upper limit value, formation of a gel-like substance can be suppressed.
The addition rate of the solution (C1) is the addition rate of the solution (C1) per hour to the volume of the solution in which the alkali catalyst is dissolved in the liquid (A1).

The addition time of the solution (C1) is preferably from 0.2 hours to 10 hours, preferably from 0.5 hours to 5 hours. When the addition time of the solution (C1) is equal to or longer than the lower limit, generation of a gel-like substance can be suppressed. Moreover, when the addition time of the solution (C1) is below the upper limit, the productivity of silica particles is excellent.

The solution (B1) and the solution (C1) are preferably added to a solution prepared by dissolving an alkali catalyst in the solution (A1). By adding solution (B1) and solution (C1) to the solution in which an alkali catalyst is dissolved in solution (A1), when you want to use a highly volatile alkali catalyst such as ammonia, and When it is desired to proceed with the hydrolysis reaction and the condensation reaction at the reaction temperature, the miscibility of each component in the reaction liquid increases, it is possible to suppress abnormal reactions in air, and it becomes easier to control the particle size. Adding into the liquid means adding below the liquid level, and the supply outlet of the solution (B1) and the supply outlet of the solution (C1) are below the liquid level of the solution in which the alkali catalyst is dissolved in the liquid (A1). By doing so, the solution (B1) and the solution (C1) can be added to the solution in which the alkali catalyst is dissolved in the solution (A1).

The timing of addition of the solution (B1) and the solution (C1) may be the same or may be different, such as alternating, but the timing of addition may be the same or different, since there is little variation in the reaction composition and the operation is not complicated. It is preferable that there be.

The reaction temperature of the hydrolysis reaction and condensation reaction in step (1) is preferably 60°C or lower, preferably 10°C to 60°C, and more preferably 20°C to 50°C. When the reaction temperature is equal to or higher than the lower limit, the particle shape can be easily controlled. Furthermore, when the reaction temperature is below the upper limit, bumping and solvent volatilization can be suppressed, and fluctuations in the reaction liquid composition can be reduced.

The concentration of water in the reaction system for the hydrolysis reaction and condensation reaction in step (1) is preferably maintained at 5% by mass to 30% by mass, and 10% by mass to 25% by mass, based on the total amount of 100% by mass in the reaction system. It is more preferable to maintain it at % by mass. When the concentration of water in the reaction system is at least the lower limit, it is easy to control the hydrolysis reaction rate of tetraalkoxysilane. Moreover, when the concentration of water in the reaction system is below the upper limit value, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape can be easily controlled.

The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and condensation reaction in step (1) is preferably maintained at 0.5% by mass to 2.0% by mass based on the total amount of 100% by mass in the reaction system, More preferably, it is maintained at 0.6% by mass to 1.5% by mass. When the concentration of the alkali catalyst in the reaction system is at least the lower limit, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion liquid is excellent. Furthermore, when the concentration of the alkali catalyst in the reaction system is below the upper limit, the reaction does not proceed excessively quickly and the reaction controllability is excellent.

The pH within the reaction system for the hydrolysis reaction and condensation reaction in step (1) is preferably maintained at 8.0 to 12.0, more preferably 8.2 to 11.8. When the pH within the reaction system is at least the lower limit, the reaction rates of the hydrolysis reaction and condensation reaction are excellent, and aggregation of silica particles can be suppressed. Furthermore, when the pH within the reaction system is below the upper limit, the particle shape can be easily controlled and the surface smoothness of the silica particles is excellent.

(Step (2))
Step (2) is a step in which tetraalkoxysilane is subjected to a hydrolysis reaction and a condensation reaction in a liquid (A2) having a water concentration of 40% by mass or more.

The liquid (A2) refers to the liquid medium in the reaction liquid and the alcohol generated in the hydrolysis reaction, excluding the tetraalkoxysilane, its reactant, and the alkali catalyst.

The liquid (A2) contains water because it allows the hydrolysis reaction and condensation reaction of the tetraalkoxysilane to proceed.

In addition to water, the liquid (A2) preferably contains alcohol because it has excellent dispersibility in the reaction solution of tetraalkoxysilane.
Examples of the alcohol include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These alcohols may be used alone or in combination of two or more. Among these alcohols, methanol and ethanol are preferred because they easily dissolve tetraalkoxysilane, the by-products used in hydrolysis and condensation reactions are the same, and they are convenient for production. is more preferable.

The liquid (A2) may contain a liquid other than water and alcohol. Examples of other liquids include acetonitrile, tetrahydrofuran, and sulfolane.

The concentration of water in the liquid (A2) is 40% by mass or more based on 100% by mass of the liquid (A2), preferably 40% to 98% by mass, more preferably 65% to 95% by mass. When the concentration of water in the liquid (A2) is at least the lower limit, it is easy to control the hydrolysis reaction rate of the tetraalkoxysilane, it is easy to increase the reaction temperature, and it is easy to adjust the surface silanol group density of the silica particles. When the concentration of water in the liquid (A2) is below the upper limit, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape can be easily controlled.

The concentration of alcohol in the liquid (A2) is 60% by mass or less based on 100% by mass of the liquid (A2), preferably 2% by mass to 60% by mass, and more preferably 5% to 35% by mass. When the concentration of alcohol in the liquid (A2) is at least the lower limit, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape can be easily controlled. When the alcohol concentration in the liquid (A2) is below the upper limit, it is easy to control the hydrolysis reaction rate of the tetraalkoxysilane, it is easy to increase the reaction temperature, and it is easy to adjust the surface silanol group density of the silica particles.

The concentration of the other liquids in the liquid (A2) is preferably 10% by mass or less, more preferably 5% by mass or less based on 100% by mass of the liquid (A2), since it has excellent hydrolysis reactivity of tetraalkoxysilane.

Since the reaction rate of the hydrolysis reaction and condensation reaction of tetraalkoxysilane can be increased, it is preferable to dissolve an alkali catalyst in the liquid (A2).
Examples of the alkali catalyst to be dissolved in the liquid (A2) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkaline catalysts, ammonia has excellent catalytic action, easy control of particle shape, can suppress the contamination of metal impurities, and has high volatility and excellent removability after hydrolysis and condensation reactions. is preferred.

The concentration of the alkali catalyst dissolved in the liquid (A2) is preferably 0.5% by mass to 2.0% by mass, and 0.6% by mass to 1.0% by mass, based on the total 100% by mass of the liquid (A2) and the alkali catalyst. 5% by mass is more preferred. When the concentration of the alkali catalyst is at least the lower limit, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, when the concentration of the alkali catalyst is below the upper limit, the reaction does not proceed excessively quickly and the reaction controllability is excellent.

The hydrolysis reaction and condensation reaction of tetraalkoxysilane in step (2) have excellent controllability of the concentrations of tetraalkoxysilane and alkali catalyst during the reaction process, so a solution containing tetraalkoxysilane is used in the liquid (A2). A method of adding (B2) and a solution containing an alkali catalyst or water (C2) is preferred.

Examples of the tetraalkoxysilane in the solution (B2) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferable because they have a fast hydrolysis reaction, are difficult to leave unreacted substances, have excellent productivity, and can easily obtain a stable silica sol. Methoxysilane is more preferred.

As the raw material for the silica particles, raw materials other than tetraalkoxysilane such as low condensates of tetraalkoxysilane may be used, but due to their excellent reactivity, tetraalkoxysilane is is 50% by mass or more, raw materials other than tetraalkoxysilane are preferably 50% by mass or less, and more preferably tetraalkoxysilane is 90% by mass or more and raw materials other than tetraalkoxysilane are 10% by mass or less. preferable.

The solution (B2) may contain only tetraalkoxysilane without a solvent, but preferably contains a solvent because the dispersibility of tetraalkoxysilane in the reaction solution is excellent.
Examples of the solvent in the solution (B2) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferable, methanol and ethanol are more preferable, and methanol is even more preferable because the solvent used in the hydrolysis reaction and condensation reaction and the by-product are the same and are excellent in manufacturing convenience. .

The concentration of tetraalkoxysilane in solution (B2) is preferably 60% by mass to 95% by mass, more preferably 70% by mass to 90% by mass, based on 100% by mass of solution (B). When the concentration of tetraalkoxysilane in the solution (B2) is at least the lower limit, the reaction solution tends to become uniform. Moreover, when the concentration of tetraalkoxysilane in the solution (B2) is below the upper limit, generation of a gel-like substance can be suppressed.

The concentration of the solvent in solution (B2) is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass based on 100% by mass of solution (B2). When the concentration of the solvent in the solution (B2) is equal to or higher than the lower limit, generation of a gel-like substance can be suppressed. Furthermore, when the concentration of the solvent in the solution (B2) is below the upper limit, the reaction solution tends to become uniform.

The addition rate of the solution (B2) is preferably 0.01 kg/hour/L to 1.3 kg/hour/L, more preferably 0.03 kg/hour/L to 0.8 kg/hour/L. When the addition rate of the solution (B2) is equal to or higher than the lower limit, the productivity of silica particles is excellent. Moreover, when the addition rate of the solution (B2) is below the upper limit value, formation of a gel-like substance can be suppressed.
The addition rate of the solution (B2) is the addition rate of the solution (B2) per hour to the volume of the solution in which the alkali catalyst is dissolved in the liquid (A2).

The addition time of solution (B2) is preferably 0.7 hours to 10 hours, preferably 1.5 hours to 5 hours. When the addition time of the solution (B2) is at least the lower limit, it is easy to adjust the surface silanol group density of the silica particles. Moreover, when the addition time of the solution (B2) is below the upper limit, the productivity of silica particles is excellent.

The solution (C2) is a solution containing water or an alkali catalyst, but in order to adjust the pH in the reaction system of the hydrolysis reaction and condensation reaction in step (2) described later to a desired value, water or an alkali catalyst is added. What is necessary is just to select the solution containing it suitably.

When the solution (C2) is a solution containing an alkali catalyst, examples of the alkali catalyst in the solution (C2) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. Can be mentioned. These alkali catalysts may be used alone or in combination of two or more. Among these alkaline catalysts, ammonia has excellent catalytic action, easy control of particle shape, can suppress the contamination of metal impurities, and has high volatility and excellent removability after hydrolysis and condensation reactions. is preferred.

When the solution (C2) is a solution containing an alkali catalyst, it is preferable that the solution (C2) contains a solvent, since this can reduce fluctuations in the concentration of the alkali catalyst in the reaction solution.
When the solution (C2) is a solution containing an alkali catalyst, examples of the solvent in the solution (C2) include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, water and alcohol are preferred, and water is more preferred, since those used in the hydrolysis reaction and condensation reaction and those produced as by-products are the same and are excellent in manufacturing convenience.

When the solution (C2) is a solution containing an alkali catalyst, the concentration of the alkali catalyst in the solution (C2) is preferably 0.01% by mass to 10% by mass, and 0.05% by mass based on 100% by mass of the solution (C2). More preferably, the amount is from % by mass to 6% by mass. When the concentration of the alkali catalyst in the solution (C2) is at least the lower limit, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start of the reaction to the end of the reaction. Furthermore, when the concentration of the alkali catalyst in the solution (C2) is below the upper limit, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced.

When the solution (C2) is a solution containing an alkali catalyst, the concentration of the solvent in the solution (C2) is preferably 90% by mass to 99.99% by mass, and preferably 94% by mass to 99.99% by mass based on 100% by mass of the solution (C2). 99.95% by mass is more preferred. When the concentration of the solvent in the solution (C2) is at least the lower limit, fluctuations in the concentration of the alkali catalyst in the reaction solution can be reduced. Moreover, when the concentration of the solvent in the solution (C2) is below the upper limit value, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start of the reaction to the end of the reaction.

The addition rate of the solution (C2) is preferably 0.01 kg/hour/L to 1.5 kg/hour/L, more preferably 0.03 kg/hour/L to 1.3 kg/hour/L. When the addition rate of the solution (C2) is at least the lower limit, the productivity of silica particles is excellent. Moreover, when the addition rate of the solution (C2) is below the upper limit value, generation of a gel-like substance can be suppressed.
The addition rate of the solution (C2) is the addition rate of the solution (C2) per hour to the volume of the solution in which the alkali catalyst is dissolved in the liquid (A2).

The addition time of the solution (C2) is preferably 0.7 hours to 10 hours, preferably 1.5 hours to 5 hours. When the addition time of the solution (C2) is at least the lower limit, it is easy to adjust the surface silanol group density of the silica particles. Moreover, when the addition time of the solution (C2) is below the upper limit, the productivity of silica particles is excellent.

It is preferable that the solution (B2) and the solution (C2) be added to a solution prepared by dissolving an alkali catalyst in the solution (A2). By adding solution (B2) and solution (C2) to the solution in which an alkali catalyst is dissolved in solution (A2), when you want to use a highly volatile alkali catalyst such as ammonia, and When it is desired to proceed with the hydrolysis reaction and the condensation reaction at the reaction temperature, the miscibility of each component in the reaction liquid increases, it is possible to suppress abnormal reactions in air, and it becomes easier to control the particle size. Adding into the liquid means adding below the liquid level, and the supply outlet of the solution (B2) and the supply outlet of the solution (C2) are below the liquid level of the solution in which the alkali catalyst is dissolved in the liquid (A2). By doing so, the solution (B2) and the solution (C2) can be added to the solution in which the alkali catalyst is dissolved in the solution (A2).

The timing of addition of solution (B2) and solution (C2) may be the same or may be different, such as alternating, but the timing of addition may be the same or different, since the reaction composition will not fluctuate and the operation will not be complicated. It is preferable that there be.

The reaction temperature of the hydrolysis reaction and condensation reaction in step (2) is preferably 65°C or higher, preferably 65°C to 100°C, and more preferably 75°C to 90°C. When the reaction temperature is equal to or higher than the lower limit, the surface silanol group density of the silica particles can be easily adjusted, and the particle shape can be easily controlled. Furthermore, when the reaction temperature is below the upper limit, bumping and solvent volatilization can be suppressed, and fluctuations in the reaction liquid composition can be reduced.

The concentration of water in the reaction system for the hydrolysis reaction and condensation reaction in step (2) is preferably maintained at 40% by mass to 98% by mass, and 65% by mass to 95% by mass, based on the total amount of 100% by mass in the reaction system. It is more preferable to maintain it at % by mass. When the concentration of water in the reaction system is at least the lower limit, it is easy to control the hydrolysis reaction rate of tetraalkoxysilane. Moreover, when the concentration of water in the reaction system is below the upper limit value, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape can be easily controlled.

The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and condensation reaction in step (2) is preferably maintained at 0.5% by mass to 2.0% by mass based on the total amount of 100% by mass in the reaction system, More preferably, it is maintained at 0.6% by mass to 1.5% by mass. When the concentration of the alkali catalyst in the reaction system is at least the lower limit, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion liquid is excellent. Furthermore, when the concentration of the alkali catalyst in the reaction system is below the upper limit, the reaction does not proceed excessively quickly and the reaction controllability is excellent.

The pH within the reaction system for the hydrolysis reaction and condensation reaction in step (2) is preferably maintained at 8.0 to 12.0, more preferably 8.2 to 10.5. When the pH within the reaction system is at least the lower limit, the reaction rates of the hydrolysis reaction and condensation reaction are excellent, and aggregation of silica particles can be suppressed. Furthermore, when the pH within the reaction system is below the upper limit, the particle shape can be easily controlled and the surface smoothness of the silica particles is excellent.

In step (2), the hydrolysis reaction and condensation reaction of the tetraalkoxysilane may be performed while removing low-boiling components such as alcohol. In step (2), by performing the hydrolysis reaction and condensation reaction of the tetraalkoxysilane while removing low-boiling components such as alcohol, it is easy to maintain the concentration of each component in the reaction system within the above-mentioned range. becomes.

The mass of the tetraalkoxysilane used in step (1) is 10% by mass to 90% by mass out of the total 100% by mass of the mass of tetraalkoxysilane used in step (1) and the mass of tetraalkoxysilane used in step (2). % is preferred, and 20% by mass to 80% by mass is more preferred. When the mass of the tetraalkoxysilane used in step (1) is at least the lower limit, the particle shape can be easily controlled. Moreover, when the mass of the tetraalkoxysilane used in step (1) is below the upper limit, it is easy to adjust the surface silanol group density of the silica particles.

The mass of the tetraalkoxysilane used in step (2) is 10% by mass to 90% by mass out of the total 100% by mass of the mass of tetraalkoxysilane used in step (2) and the mass of tetraalkoxysilane used in step (2). % is preferred, and 20% by mass to 80% by mass is more preferred. When the mass of the tetraalkoxysilane used in step (2) is at least the lower limit, it is easy to adjust the surface silanol group density of the silica particles. Moreover, when the mass of the tetraalkoxysilane used in step (2) is below the upper limit, it is easy to control the particle shape.

(Step (1'))
The method for producing silica particles of the present invention includes the following step (1') between step (1) and step (2) in order to change the composition of the liquid from liquid (A1) to liquid (A2). It is preferable to have.
Step (1'): Step of removing alcohol and adding water.

The amount of alcohol removed and the amount of water added in step (1') may be appropriately set according to the desired composition of the liquid (A2).

In order to adjust the pH within the reaction system to a desired value in step (2), it is preferable to add an alkali catalyst in step (1').
Examples of the alkali catalyst include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkaline catalysts, ammonia has excellent catalytic action, easy control of particle shape, can suppress the contamination of metal impurities, and has high volatility and excellent removability after hydrolysis and condensation reactions. is preferred.

(Step (3))
The method for producing silica particles of the present invention preferably further includes the following step (3), since unnecessary components can be removed and necessary components can be added.
Step (3): A step of concentrating the silica particle dispersion obtained in step (2) and adding a dispersion medium.

Examples of the dispersion medium include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media may be used alone or in combination of two or more. Among these dispersion media, water and alcohol are preferred, and water is more preferred, since they have excellent affinity with silica particles.

In the method for producing silica particles of the present invention, the silica particle dispersion obtained in step (3) may be subjected to pressure and heat treatment because the surface silanol group density can be lowered. Since equipment is required, it is preferable not to perform pressure and heat treatment on the silica particle dispersion obtained in step (3).

(Physical properties of silica particles)
The average primary particle diameter of the silica particles is preferably 5 nm to 100 nm, more preferably 10 nm to 60 nm. When the average primary particle diameter of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Further, when the average primary particle diameter of the silica particles is 100 nm or less, surface roughness and scratches on the object to be polished, such as a silicon wafer, can be reduced, and sedimentation of the silica particles can be suppressed.

The average primary particle diameter of silica particles is measured by the BET method. Specifically, the specific surface area of the silica particles is measured using an automatic specific surface area measuring device, and the average primary particle diameter is calculated using the following formula (1).
Average primary particle diameter (nm) = 6000/(specific surface area (m ² /g) x density (g/cm ³ )) ... (1)

The average primary particle diameter of the silica particles can be set within a desired range using known conditions and methods.

The average secondary particle diameter of the silica particles is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm. When the average secondary particle diameter of the silica particles is 10 nm or more, the removability of particles and the like during cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. When the average secondary particle diameter of the silica particles is 200 nm or less, surface roughness and scratches on the object to be polished, such as silicon wafers, can be reduced during polishing, and particles can be easily removed during post-polishing cleaning. Particle sedimentation can be suppressed.

The average secondary particle diameter of silica particles is measured by the DLS method. Specifically, it is measured using a dynamic light scattering particle size measuring device.

The average secondary particle diameter of the silica particles can be set within a desired range using known conditions and methods.

The cv value of the silica particles is preferably 10 to 50, more preferably 15 to 40, even more preferably 20 to 35. When the CV value of the silica particles is at least the lower limit value, the polishing rate for objects to be polished such as silicon wafers is excellent, and the productivity of silicon wafers is excellent. Furthermore, when the CV value of the silica particles is below the upper limit, surface roughness and scratches on the object to be polished, typified by silicon wafers, can be reduced during polishing, and particles and the like can be easily removed during cleaning after polishing.

The CV value of the silica particles is calculated by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter measuring device, and using the following formula (2).
cv value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 (2)

The association ratio of silica particles is preferably 1.0 to 4.0, more preferably 1.1 to 3.0. When the association ratio of silica particles is equal to or higher than the lower limit value, the polishing rate for objects to be polished such as silicon wafers is excellent, and the productivity of silicon wafers is excellent. Furthermore, when the association ratio of silica particles is below the upper limit, surface roughness and scratches on the object to be polished, typified by silicon wafers, can be reduced during polishing, and aggregation of silica particles can be suppressed.

The association ratio of silica particles is calculated using the following formula (3) from the average primary particle diameter measured by the above-mentioned measurement method and the average secondary particle diameter measured by the above-mentioned measurement method. .
Association ratio = average secondary particle diameter / average primary particle diameter ... (3)

Since the surface silanol group density of silica particles affects the polishing properties, it is necessary to produce silica particles having a desired surface silanol group density suitable for polishing. The method for producing silica particles of the present invention does not require a lot of production equipment, and the surface silanol group density of the silica particles can be easily adjusted, and is therefore a suitable production method.

The surface silanol group density of silica particles is measured by the Sears method. Specifically, it is measured and calculated under the conditions shown below.
Collect silica sol equivalent to 1.5 g of silica particles, and add pure water to make the liquid volume 90 mL. In an environment of 25°C, add 0.1 mol/L hydrochloric acid aqueous solution until the pH reaches 3.6, add 30 g of sodium chloride, gradually add pure water to completely dissolve the sodium chloride, and finally test. Add pure water until the total amount of liquid becomes 150 mL to obtain a test liquid.
The obtained test solution was put into an automatic titrator, and 0.1 mol/L of sodium hydroxide aqueous solution was added dropwise to obtain the 0.1 mol/L of sodium hydroxide required for the pH to change from 4.0 to 9.0. Measure the titer A (mL) of the aqueous solution.
Using the following formula (4), calculate the consumption amount V (mL) of 0.1 mol/L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to go from 4.0 to 9.0. Then, the surface silanol group density ρ (numbers/nm ² ) of the silica particles is calculated using the following formula (5).
V=(A×f×100×1.5)/(W×C)... (4)
A: Titration amount (mL) of 0.1 mol/L sodium hydroxide aqueous solution required for pH to change from 4.0 to 9.0 per 1.5 g of silica particles
f: Titer of the 0.1 mol/L sodium hydroxide aqueous solution used C: Concentration of silica particles in silica sol (mass%)
W: Amount of silica sol collected (g)
ρ=(B× _NA )/(10 ¹⁸ ×M×S _BET )...(5)
B: Amount of sodium hydroxide (mol) required for pH to change from 4.0 to 9.0 per 1.5 g of silica particles calculated from V
N _A : Avogadro's number (pieces/mol)
M: Silica particle amount (1.5g)
S _BET : Specific surface area of silica particles (m ² /g) measured when calculating the average primary particle diameter

The method for measuring and calculating the surface silanol group density of the silica particles is described in "G. W. Sears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981-1983 (1956).", "Shinichi Haba. , Development of Polishing Agent for Semiconductor Integrated Circuit Processing, Kochi University of Technology Ph.D. Thesis, pp. 39-45, March 2004," "Patent No. 5967118," and "Patent No. 6047395."

The metal impurity content of the silica particles is preferably 5 ppm or less, more preferably 2 ppm or less.

When polishing silicon wafers for semiconductor devices, metal impurities adhere to and contaminate the surface of the object to be polished, which not only adversely affects the wafer properties but also diffuses inside the wafer and degrades the quality. The performance of the manufactured semiconductor devices is significantly degraded.
In addition, if metal impurities exist in silica particles, coordination interactions occur between the acidic surface silanol groups and the metal impurities, which may change the chemical properties (acidity, etc.) of the surface silanol groups, or It changes the three-dimensional environment of the particle surface (ease of agglomeration of silica particles, etc.) and affects the polishing rate.

The metal impurity content of silica particles is measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, silica sol containing 0.4 g of silica particles was accurately weighed, sulfuric acid and hydrofluoric acid were added, heated, dissolved, and evaporated, and pure water was added to the remaining sulfuric acid droplets so that the total amount was exactly 10 g. A test solution is prepared and measured using a high frequency inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the total content of these metals is the metal impurity content. do.

The metal impurity content of the silica particles can be made 5 ppm or less by performing a hydrolysis reaction and a condensation reaction using alkoxysilane as a main raw material to obtain silica particles.
In the method of deionizing an alkali silicate such as water glass, it is extremely difficult to reduce the metal impurity content of silica particles to 5 ppm or less because sodium etc. derived from the raw material remain.

Examples of the shape of the silica particles include spherical, chain-like, cocoon-like (also referred to as knob-like or peanut-like), irregular shapes (for example, wart-like, bent-like, branched-like, etc.). Among these shapes of silica particles, if you want to reduce surface roughness and scratches on the object to be polished, such as a silicon wafer, during polishing, a spherical shape is preferable, and it will reduce the polishing rate for the object to be polished, such as a silicon wafer. If you want to increase the height even more, an irregular shape is preferable.

Silica particles preferably have no pores because they have excellent mechanical strength and storage stability.
The presence or absence of pores in the silica particles is confirmed by BET multipoint analysis using an adsorption isotherm using nitrogen as an adsorbent gas.

(Method for manufacturing silica sol)
The method for producing silica sol of the present invention includes the method for producing silica particles of the present invention.

As the silica sol, the dispersion of silica particles obtained by the method for producing silica particles of the present invention may be used as it is, and unnecessary components may be removed or necessary components may be removed from the dispersion of silica particles obtained. It may also be manufactured by adding other components.

The silica sol preferably contains silica particles and a dispersion medium.
Examples of the dispersion medium in the silica sol include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media in silica sol may be used alone or in combination of two or more. Among these dispersion media in silica sol, water and alcohol are preferred, and water is more preferred, since they have excellent affinity with silica particles.

The content of silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass, based on 100% by mass of the total amount of silica sol. When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for objects to be polished, such as silicon wafers, is excellent. Further, when the content of silica particles in the silica sol is 50% by mass or less, aggregation of silica particles in the silica sol or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent.

The content of the dispersion medium in the silica sol is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, and even more preferably 70% by mass to 95% by mass, based on the total amount of 100% by mass of the silica sol. When the content of the dispersion medium in the silica sol is 50% by mass or more, aggregation of silica particles in the silica sol and polishing composition can be suppressed, and the storage stability of the silica sol and polishing composition is excellent. Furthermore, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for objects to be polished, such as silicon wafers, is excellent.

The content of silica particles and dispersion medium in the silica sol is set within the desired range by removing unnecessary components and adding necessary components from among the components in the obtained dispersion of silica particles. be able to.

In addition to silica particles and a dispersion medium, silica sol may contain oxidizing agents, preservatives, antifungal agents, pH adjusting agents, pH buffering agents, surfactants, chelating agents, antibacterial agents, etc., as necessary, to the extent that does not impair its performance. Other ingredients such as biocides may also be included.
In particular, since the silica sol has excellent storage stability, it is preferable to include an antibacterial biocide in the silica sol.

Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salts, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, and sodium chlorite. These antibacterial biocides may be used alone or in combination of two or more. Among these antibacterial biocides, hydrogen peroxide is preferred because it has excellent affinity with silica sol.
Biocides also include what are commonly referred to as fungicides.

The content of the antibacterial biocide in the silica sol is preferably 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 1% by mass, based on 100% by mass of the total amount of silica sol. When the content of the antibacterial biocide in the silica sol is 0.0001% by mass or more, the storage stability of the silica sol is excellent. When the content of the antibacterial biocide in the silica sol is 10% by mass or less, the original performance of the silica sol is not impaired.

The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or higher, dispersion stability is excellent and aggregation of silica particles can be suppressed. Moreover, when the pH of the silica sol is 8.0 or less, dissolution of silica particles is prevented and long-term storage stability is excellent.
The pH of the silica sol can be set within a desired range by adding a pH adjuster.

(polishing composition)
The silica sol obtained by the method for producing silica sol of the present invention can be suitably used as a polishing composition.
The polishing composition preferably contains the silica sol and water-soluble polymer described above.

The water-soluble polymer increases the wettability of the polishing composition to the object to be polished, typified by a silicon wafer. The water-soluble polymer is preferably a polymer that has a functional group with high water affinity, and this functional group with high water affinity has a high affinity with the surface silanol group of the silica particles, so that it can be used in the polishing composition. The silica particles and the water-soluble polymer are more stably dispersed in the vicinity. Therefore, when polishing an object to be polished, such as a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

Examples of cellulose derivatives include hydroxyethylcellulose, hydrolyzed hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, and the like.
Examples of the copolymer having a polyvinylpyrrolidone skeleton include a graft copolymer of polyvinyl alcohol and polyvinylpyrrolidone.
Examples of the polymer having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and a copolymer of ethylene oxide and propylene oxide.

These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred because they have a high affinity with the surface silanol groups of silica particles and act synergistically to provide good hydrophilicity to the surface of the object to be polished, and hydroxyethyl cellulose is preferred. is more preferable.

The weight average molecular weight of the water-soluble polymer is preferably 1,000 to 3,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. When the weight average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. Moreover, when the mass average molecular weight of the water-soluble polymer is 3,000,000 or less, it has excellent affinity with silica sol and has an excellent polishing rate for objects to be polished, such as silicon wafers.

The mass average molecular weight of the water-soluble polymer is measured in terms of polyethylene oxide by size exclusion chromatography using a 0.1 mol/L NaCl solution as the mobile phase.

The content of the water-soluble polymer in the polishing composition is preferably 0.02% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, based on 100% by mass of the total polishing composition. When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, aggregation of silica particles during preparation of the polishing composition can be suppressed.

In addition to the silica sol and the water-soluble polymer, the polishing composition may optionally contain a basic compound, a polishing accelerator, a surfactant, a hydrophilic compound, a preservative, an antifungal agent, as long as it does not impair its performance. Other ingredients such as pH adjusters, pH buffers, surfactants, chelating agents, antibacterial biocides, etc. may also be included.
In particular, chemical polishing (chemical etching) can be performed by applying a chemical action to the surface of objects to be polished, such as silicon wafers. Since the polishing rate of the polishing body can be improved, it is preferable to include a basic compound in the polishing composition.

Examples of the basic compound include organic basic compounds, alkali metal hydroxides, alkali metal hydrogen carbonates, alkali metal carbonates, and ammonia. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogen carbonate, and ammonium carbonate are preferred because they have high water solubility and excellent affinity with silica particles and water-soluble polymers. , ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferred, and ammonia is even more preferred.

The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on 100% by mass of the total polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of objects to be polished, such as silicon wafers, can be improved. Moreover, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or higher, aggregation of silica particles in the polishing composition can be suppressed, and the dispersion stability of the polishing composition is excellent. Further, when the pH of the polishing composition is 12.0 or less, dissolution of silica particles can be suppressed, and the stability of the polishing composition is excellent.
The pH of the polishing composition can be set within a desired range by adding a pH adjuster.

The polishing composition can be obtained by mixing the silica sol obtained by the silica sol production method of the present invention, a water-soluble polymer, and other components as necessary. It may be prepared at a high concentration and diluted with water etc. immediately before polishing.

(polishing method)
The polishing method of the present invention is a method of polishing using a polishing composition containing the silica sol obtained by the silica sol manufacturing method of the present invention.
As the polishing composition, it is preferable to use the polishing composition described above.
A specific polishing method includes, for example, a method of pressing the surface of a silicon wafer against a polishing pad, dropping the polishing composition of the present invention onto the polishing pad, and polishing the surface of the silicon wafer.

(Method for manufacturing semiconductor wafers)
The semiconductor wafer manufacturing method of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above.
Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

(Method for manufacturing semiconductor devices)
The method for manufacturing a semiconductor device of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above.

(Application)
The silica particles obtained by the silica particle production method of the present invention and the silica sol obtained by the silica sol production method of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, Used for polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process when manufacturing integrated circuits, polishing synthetic quartz glass substrates used in photomasks and liquid crystals, polishing magnetic disk substrates, etc. Among them, it can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

Hereinafter, the present invention will be explained in more detail using examples, but the present invention is not limited to the description of the following examples unless it departs from the gist thereof.

(Measurement of average primary particle diameter)
The silica particle dispersions obtained in Examples and Comparative Examples were dried at 150°C, and the silica particle ratio was The surface area was measured, and the density was set to 2.2 g/cm ³ using the following formula (1), and the average primary particle diameter was calculated.
Average primary particle diameter (nm) = 6000/(specific surface area (m ² /g) x density (g/cm ³ )) ... (1)

(Measurement of average secondary particle diameter and cv value)
The average secondary particle diameter of the silica particles was measured using a dynamic light scattering particle diameter measuring device "Zetersizer Nano ZS" (model name, manufactured by Malvern) for the dispersion liquid of silica particles obtained in Examples and Comparative Examples. was measured, and the cv value was calculated using the following formula (2).
cv value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 (2)

(Calculation of association ratio)
The association ratio was calculated from the measured average primary particle diameter and average secondary particle diameter using the following formula (3).
Association ratio = average secondary particle diameter / average primary particle diameter ... (3)

(Measurement of surface silanol group density)
An amount of the silica particle dispersion obtained in Examples and Comparative Examples, equivalent to 1.5 g of silica particles, was collected in a 200 mL tall beaker, and pure water was added to make the liquid volume 90 mL.
A pH electrode was inserted into a tall beaker under an environment of 25° C., and the test solution was stirred for 5 minutes using a magnetic stirrer. While stirring with a magnetic stirrer, 0.1 mol/L aqueous hydrochloric acid solution was added until the pH reached 3.6. Remove the pH electrode from the tall beaker, continue stirring with a magnetic stirrer, add 30g of sodium chloride, and gradually add pure water until the sodium chloride is completely dissolved.Finally, the total volume of the test solution will be 150mL. Pure water was added to the solution up to 100%, and the test solution was stirred for 5 minutes using a magnetic stirrer to obtain a test solution.

Set the tall beaker containing the obtained test liquid in the automatic titration device "COM-1600" (manufactured by Hiranuma Sangyo Co., Ltd.), insert the pH electrode and burette attached to the device into the tall beaker, and test with a magnetic stirrer. Titration amount of 0.1 mol/L sodium hydroxide aqueous solution required to bring the pH from 4.0 to 9.0 by dropping 0.1 mol/L aqueous sodium hydroxide solution through a buret while stirring the liquid. A (mL) was measured.
Using the following formula (4), calculate the consumption amount V (mL) of 0.1 mol/L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to go from 4.0 to 9.0. Then, the surface silanol group density ρ (numbers/nm ² ) of the silica particles was calculated using the following formula (5).
V=(A×f×100×1.5)/(W×C)... (4)
A: Titration amount (mL) of 0.1 mol/L sodium hydroxide aqueous solution required for pH to change from 4.0 to 9.0 per 1.5 g of silica particles
f: Titer of the 0.1 mol/L sodium hydroxide aqueous solution used C: Concentration of silica particles in silica sol (mass%)
W: Amount of silica sol collected (g)
ρ=(B× _NA )/(10 ¹⁸ ×M×S _BET )...(5)
B: Amount of sodium hydroxide (mol) required for pH to change from 4.0 to 9.0 per 1.5 g of silica particles calculated from V
N _A : Avogadro's number (pieces/mol)
M: Silica particle amount (1.5g)
S _BET : Specific surface area of silica particles (m ² /g) measured when calculating the average primary particle diameter

[Example 1]
(Step (1))
81.5 parts of tetramethoxysilane and A solution (B1) containing 27.2 parts by mass of methanol and a solution (C1) containing 2.6 parts by mass of 29% ammonia water and 32.3 parts by mass of pure water were each heated at a constant rate over 1.2 hours. Added with. During the dropwise addition, stirring in the reaction system was continued while maintaining the reaction temperature at 31°C. After completion of the dropwise addition, the reaction system was further stirred for 10 minutes while maintaining the temperature inside the reaction system at 31° C. to obtain a dispersion of silica particles. The pH in the reaction system was maintained at 11 from the start of the reaction to the end of the reaction, and the concentration of methanol in the liquid (A1) at the end of the reaction was 86% by mass.

(Step (1'))
The dispersion of silica particles obtained in step (1) is heated while adding pure water, methanol and ammonia are removed, and a dispersion of silica particles with a silica particle content of about 10% by mass is obtained. Obtained.

(Step (2))
Silica particles were dispersed in a liquid (A2) in which 313.1 parts by mass of the silica particle dispersion obtained in step (1') and 32.0 parts by mass of methanol were mixed, and 89% by mass of water and 11% by mass of methanol were mixed. A dispersion of silica particles was obtained.
A solution (B2) in which 345.1 parts by mass of the obtained dispersion of silica particles was heated to 85° C. and 34.95 parts by mass of tetramethoxysilane and 11.64 parts by mass of methanol were mixed, and 108 parts by mass of pure water (C2) were prepared. 0.02 parts by mass were each added at a constant rate over 2.1 hours. During the dropwise addition, stirring in the reaction system was continued while maintaining the reaction temperature at 85°C. After completion of the dropwise addition, the reaction system was further stirred for 60 minutes while maintaining the temperature inside the reaction system at 85° C. to obtain a dispersion of silica particles. The pH in the reaction system was maintained at 8 from the start of the reaction to the end of the reaction, and the concentration of methanol in the liquid (A1) at the end of the reaction was 84% by mass.

(Step (3))
The dispersion of silica particles obtained in step (2) is heated while adding pure water, methanol and ammonia are removed, and a dispersion of silica particles with a silica particle content of about 20% by mass is obtained. Obtained.
Table 3 shows the evaluation results of the obtained silica particles.

[Examples 2 to 16]
A dispersion of silica particles having a silica particle content of about 20% by mass was obtained by operating in the same manner as in Example 1, except that the reaction conditions of step (2) were changed as shown in Table 2.
Table 3 shows the evaluation results of the obtained silica particles.

[Examples 17 to 20]
The procedure was carried out in the same manner as in Example 1, except that the reaction conditions of step (1) were changed as shown in Table 1, and the reaction conditions of step (2) were changed as shown in Table 2. A 20% by mass dispersion of silica particles was obtained.
Table 3 shows the evaluation results of the obtained silica particles.

[Comparative example 1]
Step (1) was operated in the same manner as in Example 1, and the dispersion of silica particles obtained in step (1) was heated while adding pure water, methanol and ammonia were removed, and the silica particles were heated. A dispersion of silica particles having a content of about 20% by mass was obtained. Step (2) and step (3) were not performed.
Table 3 shows the evaluation results of the obtained silica particles.

[Comparative example 2]
A dispersion of silica particles having a silica particle content of about 20% by mass was obtained by operating in the same manner as in Comparative Example 1, except that the reaction conditions in step (1) were changed as shown in Table 1.
Table 3 shows the evaluation results of the obtained silica particles.

As can be seen from Table 3, Examples 1 to 20, which have step (1) and step (2), have an average The surface silanol group density could be adjusted to be low without significantly changing the primary particle size, average secondary particle size, cv value, and association ratio.
By growing the core particles obtained in step (1) in step (2), the reactivity of the surface silanol groups of the growing silica particles can be gradually improved, and the surface silanol group density can be lowered. It seems possible that the adjustment could be made.
From these results, it was confirmed that the method for producing silica particles of the present invention can produce silica particles with a surface silanol group density in the range of 2.0 pieces/nm ² to 7.0 pieces/nm ² . . It was also confirmed that the method for producing silica particles of the present invention can be produced using the same production equipment in step (1) and step (2).

The silica particles obtained by the silica particle production method of the present invention and the silica sol obtained by the silica sol production method of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, Used for polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process when manufacturing integrated circuits, polishing synthetic quartz glass substrates used in photomasks and liquid crystals, polishing magnetic disk substrates, etc. Among them, it can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

Claims (13)

A method for producing silica particles, which sequentially includes the following steps (1) and (2).
Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction in a liquid (A1) having an alcohol concentration of 70% by mass or more to obtain silica particles .
Step (2): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction in a liquid (A2) containing the silica particles obtained in step (1) and having a water concentration of 40% by mass or more. The method for producing silica particles according to claim 1, wherein the reaction temperature in step (1) is 60°C or lower. The method for producing silica particles according to claim 1 or 2, wherein the reaction temperature in step (2) is 65°C or higher. Claim 1, wherein the method of the hydrolysis reaction and condensation reaction in step (1) is a method of adding a solution (B1) containing a tetraalkoxysilane and a solution (C1) containing an alkali catalyst to the liquid (A1). 3. The method for producing silica particles according to any one of items 3 to 3. The method of the hydrolysis reaction and condensation reaction in step (2) is a method of adding a solution (B2) containing a tetraalkoxysilane and a solution (C2) containing water or an alkali catalyst to the liquid (A2). A method for producing silica particles according to any one of claims 1 to 4. The method for producing silica particles according to any one of claims 1 to 5, comprising the following step (1') between step (1) and step (2).
Step (1'): Step of removing alcohol and adding water. The method for producing silica particles according to any one of claims 1 to 6, wherein the pH within the reaction system in step (2) is maintained at 8.0 to 12.0. The method for producing silica particles according to any one of claims 1 to 7, further comprising the following step (3).
Step (3): A step of concentrating the silica particle dispersion obtained in step (2) and adding a dispersion medium. A method for producing a silica sol, comprising the method for producing silica particles according to any one of claims 1 to 8. The method for producing a silica sol according to claim 9, wherein the concentration of silica particles in the silica sol is 3% by mass to 50% by mass. A polishing method comprising polishing using a polishing composition containing a silica sol obtained by the silica sol manufacturing method according to claim 9 or 10. A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 11. A method for manufacturing a semiconductor device, comprising the polishing method according to claim 11.