Method for producing silica sol, polishing method, method for producing semiconductor wafer, and method for producing semiconductor device

Abstract

To provide a production method of silica sol, which, in a hydrolysis reaction and a condensation reaction of a tetraalkoxylsilane, reduces separation and purification amounts and waste amounts of an organic solvent and an alkaline catalyst used in the reaction and an alcohol generated in the reaction and decreases a load of separation and purification and an environmental load.SOLUTION: Provided is a production method of silica sol, comprising the following steps (1) to (3), where a solution containing an alkaline catalyst and an alcohol removed in the following Step (3) is used as at least a portion of a solution (A) in the following Step (1). Step (1): a step of preparing respectively a solution (A) containing an alkaline catalyst and an alcohol, a solution (B) containing a tetraalkoxysilane, and a solution (C) containing water. Step (2): a step of conducting a hydrolysis reaction and a condensation reaction of the tetraalkoxysilane by adding the solution (B) and the solution (C) to the solution (A). Step (3): a step of removing a solution containing the alkali catalyst and the alcohol and adding water.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a silica sol, a polishing method, a method for producing a semiconductor wafer, and a method for producing a semiconductor device.

Background Art

[0002] As a method for polishing the surface of materials such as metals and inorganic compounds, a polishing method using a polishing liquid is known. Among them, in the final finishing polishing of prime silicon wafers for semiconductors and these recycled silicon wafers, and in chemical mechanical polishing (CMP) such as planarization of interlayer insulating films, formation of metal plugs, and formation of embedded wirings during semiconductor device manufacturing, since the surface state greatly affects semiconductor characteristics, the surfaces and end faces of these components are required to be polished with extremely high precision.

[0003] In such precision polishing, a polishing composition containing silica particles is adopted, and colloidal silica is widely used as the abrasive grains that are the main component thereof. Depending on the manufacturing method, colloidal silica includes those obtained by thermal decomposition of silicon tetrachloride (such as fumed silica), those obtained by deionization of alkali silicates such as water glass, and those obtained by hydrolysis reaction and condensation reaction of alkoxysilane (generally referred to as the "sol-gel method").

[0004] Regarding the method for producing silica particles, many studies have been made so far. For example, Patent Document 1 discloses a method for producing a silica sol by hydrolysis reaction and condensation reaction of alkoxysilane.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, when producing an aqueous dispersion of silica sol by hydrolysis reaction and condensation reaction of tetraalkoxysilane, it is necessary to remove the organic solvent, alkali catalyst, alcohol, etc. generated in the reaction. The removed organic solvent, alkali catalyst and alcohol require a large amount of equipment and high cost for separation and purification. In addition, when these are discarded, the environmental load increases. In particular, when the organic solvent used in the reaction or the alcohol generated in the reaction is methanol, methanol, which is a highly toxic substance, will be discarded, and there is also concern about adverse effects on the human body.

[0007] The method for producing silica sol disclosed in Patent Document 1 does not mention anything about the treatment of methanol or ammonia after the hydrolysis reaction and condensation reaction of alkoxysilane.

[0008] The present invention has been made in view of such problems. An object of the present invention is to provide a method for producing silica sol that reduces the amount of separation and purification and the amount of waste of the organic solvent, alkali catalyst, and alcohol generated in the reaction in the hydrolysis reaction and condensation reaction of tetraalkoxysilane, and reduces the load of separation and purification and the environmental load.

Means for Solving the Problems

[0009] As described above, in the conventional hydrolysis reaction and condensation reaction of alkoxysilane, the organic solvent, alkali catalyst used in the reaction, and the alcohol generated in the reaction are all separated, purified, and discarded in their entirety, and there is a problem that the load of separation and purification and the environmental load are large. As a result of intensive studies, the present inventors have found that the organic solvent, alkali catalyst, and alcohol used in the reaction can be utilized in the hydrolysis reaction and condensation reaction of alkoxysilane, and have completed the present invention.

[0010] That is, the gist of the present invention is as follows. [1] Including the following steps (1) to (3), Use the solution containing the alkali catalyst and alcohol removed in the following step (3) as at least a part of the solution (A) in the following step (1). Method for producing silica sol. Step (1): A step of preparing a solution (A) containing an alkali catalyst and alcohol, a solution (B) containing tetraalkoxysilane, and a solution (C) containing water respectively. Step (2): A step of adding the solution (B) and the solution (C) to the solution (A) to carry out a hydrolysis reaction and a condensation reaction of tetraalkoxysilane. Step (3): A step of removing the solution containing an alkali catalyst and alcohol and adding water. [2] The method for producing silica sol according to [1], wherein the alkali catalyst is ammonia. [3] The method for producing silica sol according to [1] or [2], wherein the alcohol is methanol. [4] The method for producing silica sol according to any one of [1] to [3], wherein the tetraalkoxysilane is tetramethoxysilane. [5] The method for producing silica sol according to any one of [1] to [4], wherein the concentration of the alkali catalyst in the solution containing the alkali catalyst and alcohol removed in the step (3) is 0.2 mass% to 3 mass%. [6] The method for producing silica sol according to any one of [1] to [5], wherein the concentration of the alcohol in the solution containing the alkali catalyst and alcohol removed in the step (3) is 85 mass% to 99 mass%. [7] The method for producing silica sol according to any one of [1] to [6], further including the following step (4). Step (4): A step of subjecting the silica sol obtained in the step (3) to a pressure heat treatment. [8] The method for producing silica sol according to any one of [1] to [7], wherein the concentration of silica particles in the silica sol is 3 mass% to 50 mass%. [9] The method for producing silica sol according to any one of [1] to [8], wherein the metal content rate in the silica sol is 1 mass ppm or less. A polishing method comprising a step of polishing using a polishing composition containing a silica sol obtained by the method for producing a silica sol according to any one of [1] to [9].

[11] A method for manufacturing a semiconductor wafer, comprising the polishing method according to

[10] .

[12] A method for manufacturing a semiconductor device, comprising the polishing method according to

[10] . [Effect of the Invention]

[0011] According to the method for producing a silica sol of the present invention, in the hydrolysis reaction and condensation reaction of tetraalkoxysilane, the amount of separation and purification and the amount of waste of the organic solvent, alkali catalyst, and alcohol used in the reaction can be reduced, and the load of separation and purification and the load on the environment can be reduced. [Embodiments for Carrying Out the Invention]

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist. In the present specification, when the expression "~" is used, it is used as an expression including the numerical values or physical property values before and after it.

[0013] (Method for Producing Silica Sol) The method for producing a silica sol of the present invention includes the following steps (1) to (3), and a solution containing an alkali catalyst and alcohol removed in the following step (3) is used as at least a part of the solution (A) in step (1). Step (1): A step of preparing a solution (A) containing an alkali catalyst and alcohol, a solution (B) containing tetraalkoxysilane, and a solution (C) containing water Step (2): A step of adding the solution (B) containing tetraalkoxysilane and the solution (C) containing water to the solution (A) containing an alkali catalyst and alcohol to carry out a hydrolysis reaction and a condensation reaction of tetraalkoxysilane Step (3): A step of removing an alkali catalyst and alcohol and adding water

[0014] (Step (1)) Step (1) is a step of preparing a solution (A) containing an alkali catalyst and alcohol, a solution (B) containing tetraalkoxysilane, and a solution (C) containing water, respectively.

[0015] Solution (A) contains an alkali catalyst.

[0016] Examples of the alkali catalyst in solution (A) include ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, tetramethylammonium hydroxide, etc. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control the particle shape, can suppress the mixing of metals, has high volatility, and is excellent in removability after hydrolysis reaction and condensation reaction.

[0017] Solution (A) contains alcohol.

[0018] Examples of the alcohol in solution (A) include methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These alcohols may be used alone or in combination of two or more. Among these alcohols, methanol and ethanol are more preferred, and methanol is even more preferred because they are easy to dissolve tetraalkoxysilane, the ones used in the hydrolysis reaction and condensation reaction are the same as the by-products, and they are excellent in manufacturing convenience.

[0019] Since solution (A) can promote the hydrolysis of alkoxysilane, it preferably contains water.

[0020] Solution (A) may contain a solvent other than alcohol and water.

[0021] The concentration of the alkali catalyst in solution (A) is preferably 0.5% by mass to 2.0% by mass, more preferably 0.6% by mass to 1.5% by mass in 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the silica sol is excellent. Further, when the concentration of the alkali catalyst in solution (A) is 2.0% by mass or less, the reaction does not proceed too fast, and the reaction controllability is excellent.

[0022] The concentration of the alcohol in solution (A) is preferably 69% by mass to 96% by mass, more preferably 74% by mass to 94% by mass in 100% by mass of solution (A). When the concentration of the alcohol in solution (A) is 69% by mass or more, the dispersibility of tetraalkoxysilane in the reaction solution is excellent. Further, when the concentration of the alcohol in solution (A) is 96% by mass or less, the dispersibility of silicic acid generated by the hydrolysis reaction in the reaction solution is excellent.

[0023] The concentration of water in solution (A) is preferably 3% by mass to 30% by mass, more preferably 5% by mass to 25% by mass in 100% by mass of solution (A). When the concentration of water in solution (A) is 3% by mass or more, the dispersibility of silicic acid generated by the hydrolysis reaction in the reaction solution is excellent. Further, when the concentration of water in solution (A) is 30% by mass or less, the dispersibility of tetraalkoxysilane in the reaction solution is excellent.

[0024] The concentration of the solvent other than alcohol and water in solution (A) is preferably the remaining concentration of the alkali catalyst, alcohol and water.

[0025] In the present invention, since the load of separation and purification and the load on the environment can be reduced, a solution containing the alkali catalyst and alcohol removed in step (3) described later is used as at least a part of solution (A) in step (1).

[0026] The solution (A) in step (1) may use a part or the entire amount of the solution containing the alkali catalyst and alcohol removed in step (3) described later. However, since it is easy to adjust the concentration and amount of the solution (A), it is preferable to use a part. In particular, when ammonia and methanol are used as the alkali catalyst and alcohol, it is preferable to use the initial removal portion with high concentrations of ammonia and methanol as the solution (A).

[0027] For the solution (A) in step (1), by adding the necessary components to the solution containing the alkali catalyst and alcohol removed in step (3) described later, each component can be adjusted to a desired concentration.

[0028] The solution (B) contains tetraalkoxysilane. As the tetraalkoxysilane, it is preferable to use tetramethoxysilane.

[0029] Since the solution (B) has excellent dispersibility of tetraalkoxysilane in the reaction solution, it preferably contains a solvent.

[0030] Examples of the solvent in the solution (B) include alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate, etc. These solvents may be used alone or in combination of two or more. Among these solvents, since the ones used in the hydrolysis reaction and condensation reaction are the same as the by-products, and it has excellent convenience in production, alcohol is preferable, methanol and ethanol are more preferable, and methanol is even more preferable.

[0031] The concentration of tetraalkoxysilane in solution (B) is preferably 76% to 89% by mass, more preferably 77% to 88% by mass, based on 100% by mass of solution (B). When the concentration of tetraalkoxysilane in solution (B) is 76% by mass or more, the amount of the solvent used can be reduced, and the productivity of silica particles is excellent. Further, when the concentration of tetraalkoxysilane in solution (B) is 89% by mass or less, the dispersibility of tetraalkoxysilane in the reaction solution is excellent.

[0032] The concentration of the solvent in solution (B) is preferably 11% to 24% by mass, more preferably 12% to 23% by mass, based on 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 11% by mass or more, the dispersibility of tetraalkoxysilane in the reaction solution is excellent. Further, when the concentration of the solvent in solution (B) is 24% by mass or less, the amount of the solvent used can be reduced, and the productivity of silica particles is excellent. The concentration of the solvent in solution (B) is preferably the concentration of the remainder of tetraalkoxysilane in solution (B).

[0033] Solution (C) contains water.

[0034] Since solution (C) can efficiently proceed with the hydrolysis reaction and the condensation reaction, it may contain an alkali catalyst.

[0035] Examples of the alkali catalyst in solution (C) include ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic action, is easy to control the particle shape, can suppress the mixing of metals, has high volatility, and has excellent removability after the hydrolysis reaction and the condensation reaction.

[0036] Solution (C) may contain a solvent other than water.

[0037] Examples of the solvent other than water in the solution (C) include alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more.

[0038] The concentration of water in the solution (C) is preferably 95% by mass to 100% by mass, more preferably 96% by mass to 99% by mass, based on 100% by mass of the solution (C). When the concentration of water in the solution (C) is 95% by mass or more, the silicic acid produced by the hydrolysis reaction has excellent dispersibility in the reaction solution.

[0039] The concentration of the alkali catalyst in the solution (C) is preferably 0% by mass to 5% by mass, more preferably 1% by mass to 4% by mass, based on 100% by mass of the solution (C). When the concentration of the alkali catalyst in the solution (C) is 5% by mass or less, the reaction does not proceed too fast, and the reaction controllability is excellent.

[0040] The concentration of the solvent other than water in the solution (C) is preferably the remaining concentration of water and the alkali catalyst.

[0041] (Step (2)) Step (2) is a step of adding a solution (B) containing tetraalkoxysilane and a solution (C) containing water to a solution (A) containing an alkali catalyst and an alcohol, and performing a hydrolysis reaction and a condensation reaction of tetraalkoxysilane.

[0042] The concentration of water in the reaction system of the hydrolysis reaction and the condensation reaction is preferably maintained at 3% by mass to 30% by mass, more preferably 5% by mass to 25% by mass, based on 100% by mass of the reaction solution in the reaction system. When the concentration of water in the reaction system is 3% by mass or more, the intermediate product, silicic acid, has excellent dispersibility in the reaction solution. Also, when the concentration of water in the reaction system is 30% by mass or less, the tetraalkoxysilane has excellent dispersibility in the reaction solution.

[0043] The concentration of water in the reaction system refers to the total amount of water in the total amount of the liquid and the substances dissolved in the liquid in the reaction system in the hydrolysis reaction and the condensation reaction. The total amount of the liquid and the substances dissolved in the liquid in the reaction system is only the solution (A) at the start of the reaction, and during the reaction, it is the total amount of the solution (A), the solution (B), the solution (C), and the alcohol produced by the reaction. The silica particles dispersed in the liquid are not included in the liquid and the substances dissolved in the liquid in the reaction system.

[0044] The concentration of the alkali catalyst in the reaction system in the hydrolysis reaction and the condensation reaction is preferably maintained at 0.5% by mass to 2.0% by mass, and more preferably maintained at 0.6% by mass to 1.5% by mass in 100% by mass of the reaction solution in the reaction system. When the concentration of the alkali catalyst in the reaction system is at or above the above lower limit value, the aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the silica sol is excellent. In addition, when the concentration of the alkali catalyst in the reaction system is at or below the above upper limit value, the reaction does not proceed too fast, and the reaction controllability is excellent.

[0045] The concentration of the alkali catalyst in the reaction system refers to the total amount of the alkali catalyst in the total amount of the liquid and the substances dissolved in the liquid in the reaction system in the hydrolysis reaction and the condensation reaction.

[0046] The reaction temperature (the temperature of the reaction solution in the reaction system) in the hydrolysis reaction and the condensation reaction of tetraalkoxysilane is preferably 15°C to 50°C, and more preferably 20°C to 45°C. When the reaction temperature is 15°C or higher, the reaction does not proceed too slowly, and the controllability is excellent. In addition, when the reaction temperature is 50°C or lower, the balance between the hydrolysis reaction rate and the condensation reaction rate is excellent.

[0047] (Step (3)) Step (3) is a step of removing the solution containing the alkali catalyst and alcohol and adding water.

[0048] In step (3), the dispersion liquid of silica particles obtained in step (2) can be heated while adding water to remove the solution containing the alkali catalyst and add water.

[0049] The heating temperature may be the boiling point of the dispersion medium of the silica particle dispersion, and is preferably 50°C to 100°C.

[0050] The concentration of the alkali catalyst in the solution containing the removed alkali catalyst and alcohol, which is used as at least a part of solution (A) in step (1), is preferably 0.2% by mass to 3% by mass, and more preferably 0.5% by mass to 2.0% by mass, since the required amount for solution (A) can be ensured.

[0051] The concentration of the alcohol in the solution containing the removed alkali catalyst and alcohol, which is used as at least a part of solution (A) in step (1), is preferably 85% by mass to 99% by mass, and more preferably 86% by mass to 98% by mass, since the required amount for solution (A) can be ensured.

[0052] (Step (4)) Since the method for producing the silica sol of the present invention can increase the degree of condensation of silica particles, it preferably further has the following step (4). Step (4): A step of subjecting the silica sol obtained in step (3) to a pressure heat treatment

[0053] The pressure of the pressure heat treatment is preferably 0.10 MPa to 2.3 MPa, and more preferably 0.14 MPa to 1.0 MPa. When the pressure of the pressure heat treatment is 0.10 MPa or more, the degree of condensation of silica particles can be increased. Also, when the pressure of the pressure heat treatment is 2.3 MPa or less, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and aggregation ratio, and the dispersion stability of the silica sol is excellent.

[0054] When applying pressure, the silica sol may be heated to a temperature equal to or higher than the boiling point of the dispersion medium in a sealed state. When the aqueous dispersion of silica particles is heated to 100°C or higher in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0055] The temperature of the pressure heating treatment is preferably 100°C to 220°C, more preferably 110°C to 180°C. When the temperature of the pressure heating treatment is 100°C or higher, the degree of condensation of the silica particles can be increased. Also, when the temperature of the pressure heating treatment is 220°C or lower, silica particles can be produced without significantly changing the average primary particle size, average secondary particle size, cv value, and aggregation ratio, and the dispersion stability of the silica sol is excellent.

[0056] The time of the pressure heating treatment is preferably 0.25 hours to 10 hours, more preferably 0.5 hours to 8 hours. When the time of the pressure heating treatment is 0.25 hours or longer, the degree of condensation of the silica particles can be increased. Also, when the time of the pressure heating treatment is 10 hours or shorter, silica particles can be produced without significantly changing the average primary particle size, average secondary particle size, cv value, and aggregation ratio, and the dispersion stability of the silica sol is excellent.

[0057] The pH of the silica sol during the pressure heating treatment is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol during the pressure heating treatment is 6.0 or higher, gelation of the silica sol can be suppressed. Also, when the pH of the silica sol during the pressure heating treatment is 8.0 or lower, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, and aggregation ratio.

[0058] 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 still more preferably 5% by mass to 30% by mass in 100% by mass of the total amount of the silica sol. When the content of silica particles in the silica sol is 3% by mass or higher, the polishing rate for a workpiece typified by a silicon wafer is excellent. Also, when the content of silica particles in the silica sol is 50% by mass or lower, aggregation of the silica particles in the silica sol or the polishing composition can be suppressed, and the storage stability of the silica sol or the polishing composition is excellent.

[0059] The content rate 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 still more preferably 70% by mass to 95% by mass in 100% by mass of the total amount of the silica sol. When the content rate of the dispersion medium in the silica sol is 50% by mass or more, aggregation of silica particles in the silica sol or the polishing composition can be suppressed, and the storage stability of the silica sol or the polishing composition is excellent. Further, when the content rate of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate with respect to the object to be polished typified by a silicon wafer is excellent.

[0060] The content rates of the silica particles and the dispersion medium in the silica sol can be set within a desired range in step (3).

[0061] In addition to the silica particles and the dispersion medium, the silica sol may contain other components such as an oxidizing agent, a preservative, a fungicide, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial and biocidal agent, as long as its performance is not impaired.

[0062] In particular, since the silica sol has excellent storage stability, it is preferable to include an antibacterial and biocidal agent in the silica sol.

[0063] Examples of the antibacterial and biocidal agent include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, sodium chlorite, and the like. These antibacterial and biocidal agents may be used alone or in combination of two or more. Among these antibacterial and biocidal agents, hydrogen peroxide is preferable because of its excellent affinity with the silica sol. The antibacterial and biocidal agent generally includes those referred to as bactericides.

[0064] The content rate of the antibacterial and biocidal agent in the silica sol is preferably 0.0001 mass% to 10 mass%, more preferably 0.001 mass% to 1 mass% in 100 mass% of the total amount of the silica sol. When the content rate of the antibacterial and biocidal agent in the silica sol is 0.0001 mass% or more, the storage stability of the silica sol is excellent. When the content rate of the antibacterial and biocidal agent in the silica sol is 10 mass% or less, the original performance of the silica sol is not impaired.

[0065] 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 more, it has excellent dispersion stability and can suppress the aggregation of silica particles. Also, when the pH of the silica sol is 8.0 or less, it prevents the dissolution of silica particles and has excellent long-term storage stability.

[0066] The pH of the silica sol can be set within a desired range by adding a pH adjuster.

[0067] (Physical properties of silica particles) Regarding the suitable physical properties and the like of the silica particles in the silica sol produced by the method for producing the silica sol of the present invention, they will be described below.

[0068] 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. Also, when the average primary particle diameter of the silica particles is 100 nm or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer can be reduced, and the sedimentation of the silica particles can be suppressed.

[0069] The average primary particle diameter of the silica particles is measured by the BET method. Specifically, the specific surface area of the silica particles is measured using a specific surface area automatic 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) × density (g / cm 3 )) ··· (1)

[0070] The average primary particle diameter of the silica particles can be set within a desired range by known conditions and methods.

[0071] 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 in the cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. Further, when the average secondary particle diameter of the silica particles is 200 nm or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer during polishing can be reduced, the removability of particles and the like in the cleaning after polishing is excellent, and the sedimentation of the silica particles can be suppressed.

[0072] The average secondary particle diameter of the silica particles is measured by the DLS method. Specifically, it is measured using a dynamic light scattering particle size measuring device.

[0073] The average secondary particle diameter of the silica particles can be set within a desired range by known conditions and methods.

[0074] The cv value of the silica particles is preferably 10 to 50, more preferably 15 to 40, and still more preferably 20 to 35. When the cv value of the silica particles is 10 or more, the polishing rate with respect to the object to be polished typified by a silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Further, when the cv value of the silica particles is 50 or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer during polishing can be reduced, and the removability of particles and the like in the cleaning after polishing is excellent.

[0075] The cv value of the silica particles is measured by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle size measuring device, and calculated using the following formula (2). cv value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 ··· (2)

[0076] The aggregation ratio of the silica particles is preferably from 1.0 to 4.0, more preferably from 1.1 to 3.0. When the aggregation ratio of the silica particles is 1.0 or more, the polishing rate with respect to the object to be polished typified by a silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Further, when the aggregation ratio of the silica particles is 4.0 or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer during polishing can be reduced, and aggregation of the silica particles can be suppressed.

[0077] The aggregation ratio of the silica particles is calculated using the following formula (3) from the average primary particle diameter measured by the above-described measurement method and the average secondary particle diameter measured by the above-described measurement method. Aggregation ratio = average secondary particle diameter / average primary particle diameter ··· (3)

[0078] The surface silanol group density of the silica particles is 0.1 per nm 2 ~10 per nm 2 is preferable, and 0.5 per nm 2 ~7.5 per nm 2 is more preferable, and 2.0 per nm 2 ~7.0 per nm 2 is even more preferable. When the surface silanol group density of the silica particles is 0.1 per nm 2 or more, the silica particles have appropriate surface repulsion and are excellent in the dispersion stability of the silica sol. Further, when the surface silanol group density of the silica particles is 10 per nm 2 or less, the silica particles have appropriate surface repulsion and aggregation of the silica particles can be suppressed.

[0079] The surface silanol group density of the silica particles is measured by the shear method. Specifically, it is measured and calculated under the conditions shown below.

[0080] Collect a silica sol corresponding to 1.5 g of silica particles, add pure water to make the liquid volume 90 mL. In an environment at 25 ° C, add a 0.1 mol / L hydrochloric acid aqueous solution until the pH reaches 3.6, add 30 g of sodium chloride, and gradually add pure water while completely dissolving sodium chloride. Finally, add pure water until the total volume of the test solution reaches 150 mL to obtain a test solution.

[0081] Put the obtained test solution into an automatic titrator, dropwise add an aqueous sodium hydroxide solution with a concentration of 0.1 mol / L, and measure the titration volume A (mL) of the 0.1 mol / L aqueous sodium hydroxide solution required for the pH to change from 4.0 to 9.0.

[0082] Using the following formula (4), calculate the consumption volume V (mL) of the 0.1 mol / L aqueous sodium hydroxide solution required for the pH to change from 4.0 to 9.0 per 1.5 g of silica particles, and using the following formula (5), calculate the surface silanol group density ρ (pieces / nm 2 ) of the silica particles.

[0083] V=(A×f×100×1.5) / (W×C)···(4) A: Titration volume (mL) of the 0.1 mol / L aqueous sodium hydroxide solution required for the pH to change from 4.0 to 9.0 per 1.5 g of silica particles f: Normality of the 0.1 mol / L aqueous sodium hydroxide solution used C: Concentration (mass %) of silica particles in the silica sol W: Sampling amount (g) of the silica sol

[0084] ρ=(B×N A ) / (10 18 ×M×S BET )···(5) B: Amount of sodium hydroxide required for the pH to change from 4.0 to 9.0 per 1.5 g of silica particles calculated from V (mol) N A : Avogadro's number (pieces / mol) M: Amount of silica particles (1.5 g) S BET : Specific surface area (m 2 / g) of the silica particles measured when calculating the average primary particle diameter

[0085] For the measurement and calculation method of the surface silanol group density of the silica particles, refer to "G.W. Sears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981 - 1983 (1956).", "Shinichi Haba, Development of Abrasives for Semiconductor Integrated Circuit Processes, Doctoral Thesis of Kochi University of Technology, pp. 39 - 45, March 2004", "Japanese Patent Publication No. 5967118", and "Japanese Patent Publication No. 6047395".

[0086] The surface silanol group density of the silica particles can be set within a desired range by adjusting the conditions of the hydrolysis reaction and condensation reaction of the alkoxysilane.

[0087] Examples of the shape of the silica particles include spherical, chain - like, cocoon - like (also referred to as knob - like or peanut - like), and irregular shapes (e.g., wart - like, bent, branched, etc.). Among these shapes of silica particles, when it is desired to reduce the surface roughness and scratches of the workpiece represented by the silicon wafer during polishing, a spherical shape is preferred; when it is desired to increase the polishing rate for the workpiece represented by the silicon wafer, an irregular shape is preferred.

[0088] (Physical properties of silica sol) The metal content (metal impurity content) mixed as an impurity in the silica sol is preferably 1 mass ppm or less, and more preferably 0.2 mass ppm or less.

[0089] In the polishing of a silicon wafer, metal impurities adhere to the surface of the workpiece, contaminating the workpiece and adversely affecting the properties of the workpiece and the final product.

[0090] In addition, when metal impurities are present in the silica sol, a coordination interaction occurs between the surface silanol groups showing acidity and the metal impurities, changing the chemical properties (such as acidity) of the surface silanol groups, changing the three - dimensional environment on the surface of the silica particles (such as the ease of aggregation of the silica particles), and affecting the polishing rate.

[0091] The metal content of the silica sol is measured by high-frequency inductively coupled plasma mass spectrometry (ICP-MS). Specifically, an accurately weighed amount of silica sol containing 0.4 g of silica particles is added with sulfuric acid and hydrofluoric acid, heated, dissolved, evaporated, and pure water is added to the remaining sulfuric acid drops so that the total amount becomes exactly 10 g to prepare a test solution, which is then 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, nickel, and the sum of the contents of these metals is defined as the metal content.

[0092] The metal content of the silica sol can be made 1 ppm by mass or less by obtaining silica particles through hydrolysis reaction and condensation reaction using alkoxysilane as the main raw material. In the method of deionizing alkali silicates such as water glass, since sodium and the like derived from the raw materials remain, it is extremely difficult to make the metal content of the silica particles 1 ppm by mass or less.

[0093] (Polishing composition) The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used as a polishing composition. The polishing composition preferably contains a silica sol produced by the method for producing a silica sol of the present invention and a water-soluble polymer.

[0094] The water-soluble polymer enhances the wettability of the polishing composition with respect to the object to be polished typified by a silicon wafer. The water-soluble polymer is preferably a polymer having a highly water-affinity functional group, and the affinity between this highly water-affinity functional group and the surface silanol group of the silica particles is high, so that the silica particles and the water-soluble polymer are stably dispersed in the vicinity of each other in the polishing composition. Therefore, when polishing an object to be polished typified by a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0095] Examples of the water-soluble polymer include cellulose derivatives, polyvinyl alcohol, polyvinyl pyrrolidone, copolymers having a polyvinyl pyrrolidone skeleton, polymers having a polyoxyalkylene structure, and the like.

[0096] Examples of the cellulose derivative include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, and the like.

[0097] Examples of the copolymer having a polyvinyl pyrrolidone skeleton include a graft copolymer of polyvinyl alcohol and polyvinyl pyrrolidone, and the like.

[0098] Examples of the polymer having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, a copolymer of ethylene oxide and propylene oxide, and the like.

[0099] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethyl cellulose is more preferred because they have a high affinity for the surface silanol groups of the silica particles and act synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0100] The weight average molecular weight of the water-soluble polymer is preferably from 1,000 to 3,000,000, more preferably from 5,000 to 2,000,000, and still more preferably from 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. When the weight average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with the silica sol is excellent, and the polishing rate with respect to the object to be polished typified by a silicon wafer is excellent.

[0101] The weight average molecular weight of the water-soluble polymer is measured by size exclusion chromatography under the condition of using a 0.1 mol / L NaCl solution as the mobile phase, in terms of polyethylene oxide conversion.

[0102] 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, in 100% by mass of the total amount of the 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. Further, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, aggregation of silica particles during the preparation of the polishing composition can be suppressed.

[0103] In addition to the silica sol and the water-soluble polymer, the polishing composition may contain other components such as basic compounds, polishing accelerators, surfactants, hydrophilic compounds, preservatives, fungicides, pH adjusters, pH buffers, surfactants, chelating agents, antibacterial and biocidal agents, etc., as long as its performance is not impaired.

[0104] In particular, since it can chemically act on the surface of the object to be polished typified by a silicon wafer to perform chemical polishing (chemical etching), and the polishing rate of the object to be polished typified by a silicon wafer can be improved by the synergistic effect with the surface silanol groups of the silica particles, it is preferable to include a basic compound in the polishing composition.

[0105] Examples of the basic compound include organic basic compounds, alkali metal hydroxides, alkali metal hydrogen carbonates, alkali metal carbonates, ammonia, etc. 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 preferable, ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferable, and ammonia is even more preferable, because of their high water solubility and excellent affinity with silica particles and water-soluble polymers.

[0106] The content rate of the basic compound in the polishing composition is preferably 0.001 mass% to 5 mass%, more preferably 0.01 mass% to 3 mass% in 100 mass% of the total amount of the polishing composition. When the content rate of the basic compound in the polishing composition is 0.001 mass% or more, the polishing rate of the object to be polished typified by a silicon wafer can be improved. Further, when the content rate of the basic compound in the polishing composition is 5 mass% or less, the stability of the polishing composition is excellent.

[0107] 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 more, 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 the silica particles can be suppressed, and the stability of the polishing composition is excellent.

[0108] The pH of the polishing composition can be set to a desired range by adding a pH adjuster.

[0109] The polishing composition can be obtained by mixing the silica sol obtained by the method for producing the silica sol of the present invention, a water-soluble polymer, and, if necessary, other components. However, in consideration of storage and transportation, it may be prepared at a high concentration once and diluted with water or the like immediately before polishing.

[0110] (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 method for producing the silica sol of the present invention. It is preferable to use the polishing composition described above as the polishing composition.

[0111] As a specific polishing method, for example, there is 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.

[0112] (Method for manufacturing a semiconductor wafer, method for manufacturing a semiconductor device) The method for manufacturing a semiconductor wafer of the present invention and the method for manufacturing a semiconductor device of the present invention include the polishing method of the present invention.

[0113] (Use) The silica sol obtained by the method for manufacturing a silica sol of the present invention can be suitably used for polishing applications. For example, it can be used for polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for 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.

Examples

[0114] Hereinafter, the present invention will be described more specifically using examples, but the present invention is not limited to the description of the following examples as long as the gist thereof is not deviated from.

[0115] (Measurement of average primary particle size) The silica sols obtained in the examples and comparative examples were dried at 150 ° C., and the specific surface area of the silica particles was measured using a specific surface area automatic measurement device “BELSORP-MR1” (model name, Microtrac·BEL Co., Ltd.). Using the following formula (1), with a density of 2.2 g / cm 3 the average primary particle size was calculated. Average primary particle size (nm)=6000 / (specific surface area (m 2 / g)×density (g / cm 3 ))···(1)

[0116] (Measurement of average secondary particle size) The silica sols obtained in the examples and comparative examples were used to measure the average secondary particle size of the silica particles using a dynamic light scattering particle size measuring device “Zetasizer Nano ZS” (model name, manufactured by Malvern), and the cv value was calculated using the following formula (2). cv value=(standard deviation (nm) / average secondary particle size (nm))×100···(2)

[0117] (Calculation of aggregation ratio) From the measured average primary particle diameter and average secondary particle diameter, the aggregation ratio was calculated using the following formula (3). Aggregation ratio = average secondary particle diameter / average primary particle diameter ··· (3)

[0118] (Measurement of metal content) An exact amount of a silica sol containing 0.4 g of silica particles was 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 became exactly 10 g to prepare a test solution. Using a high-frequency inductively coupled plasma mass spectrometer "ELEMENT2" (model name, manufactured by Thermo Fisher Scientific), the contents of sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel were measured, and the total was taken as the metal content.

[0119] [Comparative Example 1] A solution (B) obtained by mixing tetramethoxysilane and methanol at a volume ratio of 2.3:1 and a solution (C) of a 3.5 mass% aqueous ammonia solution were each prepared. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with a solution (A) in which methanol, water, and ammonia were previously mixed. The concentration of methanol in solution (A) was 85.9 mass%, the concentration of water in solution (A) was 13 mass%, and the concentration of ammonia in solution (A) was 1.1 mass%.

[0120] While maintaining the temperature of the reaction solution at 31°C, 100 volume% of solution (B) and 32 volume% of solution (C) were added to 194 volume% of solution (A) at a constant rate over 109 minutes to obtain a dispersion of silica particles.

[0121] The obtained dispersion of silica particles was heated so that the content of silica particles became about 20 mass%, and a solution (X) containing ammonia and methanol in the dispersion of silica particles was removed. The concentration of ammonia in the removed solution was 1 mass%, the concentration of methanol in the removed solution was 93 mass%, and the concentration of water in the removed solution was 6 mass%.

[0122] Thereafter, the temperature was raised, and water was added while removing ammonia and methanol to obtain an aqueous dispersion (silica sol) of silica particles having a silica particle content of about 20% by mass. The evaluation results of the obtained silica sol are shown in Table 1.

[0123] [Example 1] Water and ammonia were added to the solution (X) containing ammonia and methanol removed in Comparative Example 1 (ammonia concentration 1% by mass, methanol concentration 93% by mass, water concentration 6% by mass), and the same operation as in Example 1 was performed except that a solution (A) with a methanol concentration of 85.9% by mass, a water concentration of 13% by mass, and an ammonia concentration of 1.1% by mass was prepared, to obtain an aqueous dispersion (silica sol) of silica particles having a silica particle content of about 20% by mass. The evaluation results of the obtained silica sol are shown in Table 1.

[0124]

Table 1

[0125] As can be seen from Table 1, an equivalent physical property silica sol was obtained between the example using, as the solution (A) in step (1), the solution containing the alkali catalyst and alcohol removed in step (3) and the comparative example not using it, and it was confirmed that there is no problem even when using, as the solution (A) in step (1), the solution containing the alkali catalyst and alcohol removed in step (3).

Industrial Applicability

[0126] The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used for polishing applications. For example, it can be used for polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for 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

1. A method for producing a silica sol, comprising the following steps (1) to (3), wherein a solution containing an alkali catalyst and an alcohol removed in the following step (3) is used as at least a part of the solution (A) in the following step (1), and the concentration of the alkali catalyst in the solution containing the alkali catalyst and the alcohol is 0.2% by mass or more. Step (1): A step of preparing a solution (A) containing an alkali catalyst and an alcohol, a solution (B) containing tetraalkoxysilane, and a solution (C) containing water Step (2): A step of adding the solution (B) and the solution (C) to the solution (A) to perform a hydrolysis reaction and a condensation reaction of tetraalkoxysilane Step (3): A step of removing a solution containing an alkali catalyst and an alcohol and adding water

2. The method for producing a silica sol according to claim 1, wherein the alkali catalyst is ammonia.

3. The method for producing a silica sol according to claim 1 or 2, wherein the alcohol is methanol.

4. The method for producing a silica sol according to any one of claims 1 to 3, wherein the tetraalkoxysilane is tetramethoxysilane.

5. The method for producing a silica sol according to any one of claims 1 to 4, wherein the concentration of the alkali catalyst in the solution containing the alkali catalyst and the alcohol removed in the step (3) is 0.2% by mass to 3% by mass.

6. The method for producing a silica sol according to any one of claims 1 to 5, wherein the concentration of the alcohol in the solution containing the alkali catalyst and the alcohol removed in the step (3) is 85% by mass to 99% by mass.

7. The method for producing a silica sol according to any one of claims 1 to 6, further comprising the following step (4). Step (4): A step of subjecting the silica sol obtained in the step (3) to a pressure heat treatment

8. The method for producing a silica sol according to any one of claims 1 to 7, wherein the concentration of silica particles in the silica sol is 3% by mass to 50% by mass.

9. The method for producing a silica sol according to any one of claims 1 to 8, wherein the metal content rate in the silica sol is 1 ppm by mass or less.

10. A polishing method having a step of polishing using a polishing composition containing a silica sol obtained by the method for producing a silica sol according to any one of claims 1 to 9.

11. A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 10.

12. A method for manufacturing a semiconductor device, comprising the polishing method according to claim 10.

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