Silica sol manufacturing method, polishing method, semiconductor wafer manufacturing method, and semiconductor device manufacturing method

Abstract

To provide a method for producing silica sol that enables low-viscosity silica sol to be produced with simple equipment.SOLUTION: A method for producing silica sol includes following steps (1)-(4) in order. Step (1): tetraalkoxysilane is subjected to hydrolysis and condensation to give a dispersion liquid of silica particles. Step (2): the dispersion liquid of silica particles obtained in the step (1) is concentrated. Step (3): the dispersion medium of the dispersion liquid of silica particles obtained in the step (2) is replaced. Step (4): the dispersion liquid of silica particles obtained in the step (3) is concentrated.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 technology]

[0002] Polishing methods using polishing solutions are known as methods for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in chemical mechanical polishing (CMP), such as the final polishing of prime silicon wafers for semiconductors and reclaimed silicon wafers, and in the planarization of interlayer insulating films during semiconductor device manufacturing, the formation of metal plugs, and the formation of buried wiring, the surface condition of these components has a significant impact on their semiconductor characteristics, so the surfaces and edge faces of these components must be polished with extremely high precision.

[0003] In such precision polishing, polishing compositions containing silica particles are employed, and silica sol is widely used as the abrasive grains that are the main component thereof. Silica sols are known to be produced by different methods, such as those produced by thermal decomposition of silicon tetrachloride (fumed silica, etc.), those produced by deionization of alkali silicate such as water glass, and those produced by hydrolysis and condensation reaction of alkoxysilane (generally referred to as the "sol-gel method").

[0004] Many studies have been conducted on silica sols and methods for producing silica sols. For example, Patent Document 1 discloses a method including a step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain silica particles, and a step of subjecting the silica particles to a pressure and heat treatment at 0.1 MPa to 2.3 MPa.

[0005] Patent Document 2 discloses silica-based particles for polishing, which are silica-based particles having a three-dimensional polycondensed structure containing alkoxy groups, and are characterized by an average particle diameter (d) of 5 to 300 nm, an aspect ratio of 1.00 or more and 1.20 or less, and a carbon content of 0.005% by mass or more and less than 0.50% by mass.

[0006] Patent Document 3 discloses a silica sol synthesized by an alkoxide method, which contains at least a dispersant and silica, the concentration of the dispersant being 10 to 3000 ppm relative to the silica, the dispersant being at least one selected from inorganic acids, inorganic acid salts, organic acids and organic acid salts, each having a decomposition temperature and boiling point of 60°C or higher, and the silica sol having a silica concentration of 20% by weight or higher. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2020-132478 [Patent Document 2] Japanese Patent Application Publication No. 2018-080331 [Patent Document 3] International Publication No. 2008 / 015943 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method for producing silica sol described in Patent Document 1, the detailed conditions for the step of replacing the dispersion medium are unknown, and it is unclear whether a silica sol with a sufficiently low viscosity is obtained.

[0009] Furthermore, when producing the silica sol described in Patent Document 2, the silica sol is purified with amphoteric ion exchange resins and concentrated with an ultrafiltration membrane, so that large facilities are required for producing the silica sol.

[0010] Furthermore, when producing the silica sol described in Patent Document 3, substitution is carried out after the concentration is completed, and therefore a silica sol with a sufficiently low viscosity cannot be obtained.

[0011] The present invention has been made in view of the above-mentioned conventional circumstances, and an object to be achieved is to provide a method for producing a silica sol that can produce a low-viscosity silica sol using simple equipment. [Means for solving the problem]

[0012] As a result of extensive research into achieving the above object, the present inventors have found that the above problems can be solved by the following production method, and have thus completed the present invention.

[0013] That is, the gist of the present invention is as follows. <1> A method for producing silica sol, comprising the following steps (1) to (4) in order: Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles. Step (2): Concentrating the dispersion of silica particles obtained in step (1). Step (3): A step of replacing the dispersion medium of the dispersion liquid of silica particles obtained in the step (2). Step (4): Concentrating the dispersion of silica particles obtained in step (3). <2> The concentration rate in the step (2) is 101% by mass to 220% by mass. <1> The method for producing silica sol according to claim 1. <3> The concentration rate in the step (4) is 101% by mass to 250% by mass. <1> or <2> The method for producing silica sol according to claim 1. <4> The step of replacing the dispersion medium in the step (3) includes a step of removing alcohol and adding water. <1> ~ <3> 10. The method for producing silica sol according to claim 9, wherein the silica sol is a silica sol. <5> In the step (3), the ratio of the volume of the dispersion medium distilled off per unit time to the volume of water added is maintained at 4:6 to 6:4. <1> ~ <3> 10. The method for producing silica sol according to claim 9, wherein the silica sol is a silica sol. <6> In the step (1), the tetraalkoxysilane is tetramethoxysilane. <1> ~ <5> 10. The method for producing silica sol according to claim 9, wherein the silica sol is a silica sol. <7> In the step (1), the hydrolysis reaction and condensation reaction of the tetraalkoxysilane are carried out by adding the solution (B) containing the tetraalkoxysilane and the solution (C) containing the alkali catalyst to the solution (A) containing the alkali catalyst. <1> ~ <6> 10. The method for producing silica sol according to claim 9, wherein the silica sol is a silica sol. <8> The content of silica particles in the silica sol is 3% by mass to 50% by mass. <1> ~ <7> 10. The method for producing silica sol according to claim 9, wherein the silica sol is a silica sol. <9> The metal content in the silica sol is 1 ppm by mass or less. <1> ~ <8> 10. The method for producing silica sol according to claim 9, wherein the silica sol is a silica sol. <10> <1> ~ <9> 10. A polishing method comprising the step of polishing with a polishing composition containing the silica sol obtained by the method for producing a silica sol according to any one of the above items. <11> <10> A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 1. <12> <10> A method for manufacturing a semiconductor device, comprising the polishing method described above. [Effects of the Invention]

[0014] According to the method for producing a silica sol of the present invention, a silica sol having a low viscosity can be produced using simple equipment. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be practiced with various modifications within the scope of the gist. In this specification, when the expression "to" is used, it is used as an expression including the numerical values ​​or physical property values ​​before and after it.

[0016] [Method of producing silica sol] The method for producing a silica sol of the present invention includes the following steps (1) to (4) in this order. Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles. Step (2): Concentrating the dispersion of silica particles obtained in step (1). Step (3): A step of replacing the dispersion medium of the dispersion liquid of silica particles obtained in the step (2). Step (4): Concentrating the dispersion of silica particles obtained in step (3).

[0017] (Process (1)) Step (1) is a step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles.

[0018] In step (1), for example, the hydrolysis reaction and condensation reaction of tetraalkoxysilane can be carried out by adding a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst to a solution (A) containing an alkali catalyst.

[0019] The solution (A) contains an alkali catalyst.

[0020] Examples of alkali catalysts in solution (A) 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 alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control the particle shape, can suppress metal contamination, is highly volatile, and is easily removable after the hydrolysis reaction and the condensation reaction.

[0021] Furthermore, the solution (A) preferably contains an alcohol.

[0022] Examples of alcohols 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 more preferred, and methanol is even more preferred, because they easily dissolve tetraalkoxysilane, the by-products used in the hydrolysis reaction and the condensation reaction are the same as those used in the hydrolysis reaction and the condensation reaction, and they are convenient for production.

[0023] The solution (A) preferably contains water, since this can promote the hydrolysis of the alkoxysilane.

[0024] The solution (A) may contain a solvent other than alcohol and water.

[0025] The concentration of the alkali catalyst in solution (A) is preferably 0.5% by mass to 2.0% by mass, and more preferably 0.6% by mass to 1.5% by mass, based on 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 silica particles in the silica sol is excellent. Furthermore, when the concentration of the alkali catalyst in solution (A) is 2.0% by mass or less, the reaction does not proceed excessively quickly, and the reaction controllability is excellent.

[0026] The concentration of alcohol in solution (A) is preferably 69% by mass to 96% by mass, more preferably 74% by mass to 94% by mass, based on 100% by mass of solution (A). When the concentration of alcohol in solution (A) is 69% by mass or more, the dispersibility of tetraalkoxysilane in the reaction liquid is excellent. Furthermore, when the concentration of alcohol in solution (A) is 96% by mass or less, the dispersibility of silicic acid produced by the hydrolysis reaction in the reaction liquid is excellent.

[0027] 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, based on 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 produced by the hydrolysis reaction in the reaction liquid is excellent. Furthermore, when the concentration of water in solution (A) is 30% by mass or less, the dispersibility of tetraalkoxysilane in the reaction liquid is excellent.

[0028] The concentration of the solvent other than the alcohol and water in the solution (A) is preferably the same as the concentration of the alkali catalyst, alcohol, and the balance of water.

[0029] The solution (B) contains a tetraalkoxysilane. Examples of tetraalkoxysilanes 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 preferred, and tetramethoxysilane is more preferred, because they undergo a fast hydrolysis reaction, are less likely to leave unreacted substances, are highly productive, and can easily produce a stable silica sol.

[0030] The solution (B) preferably contains a solvent, as this provides excellent dispersibility of the tetraalkoxysilane in the reaction liquid.

[0031] Examples of the solvent in solution (B) include alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; and esters such as ethyl acetate. These solvents may be used alone or in combination of two or more. Among these solvents, alcohols are preferred, more preferably methanol and ethanol, and even more preferably methanol, because the solvents used in the hydrolysis reaction and the condensation reaction are the same as the by-products, and therefore are convenient for production.

[0032] The concentration of tetraalkoxysilane in solution (B) is preferably 76% by mass to 89% by mass, and more preferably 77% by mass 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 solvent used can be reduced, resulting in excellent productivity of silica particles. Furthermore, when the concentration of tetraalkoxysilane in solution (B) is 89% by mass or less, the dispersibility of tetraalkoxysilane in the reaction liquid is excellent.

[0033] The concentration of the solvent in solution (B) is preferably 11% by mass to 24% by mass, and more preferably 12% by mass 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 the tetraalkoxysilane in the reaction liquid is excellent. Furthermore, when the concentration of the solvent in solution (B) is 24% by mass or less, the amount of solvent used can be reduced, resulting in excellent productivity of silica particles. The concentration of the solvent in solution (B) is preferably the concentration of the remainder of the tetraalkoxysilane in solution (B).

[0034] The solution (C) contains an alkali catalyst.

[0035] Examples of alkali catalysts in solution (C) 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 alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control particle shape, can suppress metal contamination, is highly volatile, and is easily removable after the hydrolysis reaction and condensation reaction.

[0036] The solution (C) may contain water and 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, ethylene glycol, etc. These solvents may be used alone or in combination of two or more.

[0038] The concentration of the alkali catalyst in solution (C) is preferably 0 to 5% by mass, more preferably 1 to 4% by mass, based on 100% by mass of solution (C). When the concentration of the alkali catalyst in solution (C) is 5% by mass or less, the reaction does not proceed excessively quickly, resulting in excellent reaction controllability.

[0039] The concentration of water in 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 solution (C). When the concentration of water in solution (C) is 95% by mass or more, the dispersibility of silicic acid produced by the hydrolysis reaction in the reaction liquid is excellent.

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

[0041] The water concentration in the hydrolysis and condensation reaction systems is preferably maintained at 3% to 30% by mass, more preferably 5% to 25% by mass, based on 100% by mass of the reaction solution in the reaction system. When the water concentration in the reaction system is 3% by mass or more, the dispersibility of the intermediate product, silicic acid, in the reaction solution is excellent. Furthermore, when the water concentration in the reaction system is 30% by mass or less, the dispersibility of the tetraalkoxysilane in the reaction solution is excellent.

[0042] The water concentration in the reaction system refers to the total amount of water in the total amount of liquid and substances dissolved in the liquid in the reaction system during hydrolysis and condensation reactions. The total amount of liquid and substances dissolved in the liquid in the reaction system is only solution (A) at the start of the reaction, and during the reaction it is the total amount of solution (A), solution (B), solution (C), and the alcohol produced in the reaction. The liquid and substances dissolved in the liquid in the reaction system do not include silica particles dispersed in the liquid.

[0043] The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and condensation reaction is preferably maintained at 0.5% to 2.0% by mass, and more preferably at 0.6% to 1.5% by mass, based on 100% by mass of the reaction solution in the reaction system. When the concentration of the alkali catalyst in the reaction system is equal to or greater than the lower limit, aggregation of silica particles is suppressed, resulting in excellent dispersion stability of the silica particles in the silica sol. Furthermore, when the concentration of the alkali catalyst in the reaction system is equal to or less than the upper limit, the reaction does not proceed excessively quickly, resulting in excellent reaction controllability.

[0044] 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.

[0045] The reaction temperature (temperature of the reaction solution in the reaction system) for the hydrolysis and condensation reactions of tetraalkoxysilane is preferably 15°C to 50°C, more preferably 20°C to 45°C. When the reaction temperature is 15°C or higher, the reaction does not proceed too slowly, resulting in excellent controllability. Furthermore, when the reaction temperature is 50°C or lower, an excellent balance between the hydrolysis reaction rate and the condensation reaction rate is achieved.

[0046] (Process (2)) Step (2) is a step of concentrating the dispersion of silica particles obtained in step (1).

[0047] Examples of methods for concentrating the dispersion of silica particles include heat concentration and vacuum concentration.

[0048] The concentration ratio in step (2) is preferably 101% by mass to 220% by mass, more preferably 102% by mass to 140% by mass. When the concentration ratio is 101% by mass or more, the polishing rate for a workpiece such as a silicon wafer is excellent. When the concentration ratio is 220% by mass or less, the variation in viscosity of the silica sol and the aggregation of silica particles can be suppressed.

[0049] The concentration rate can be calculated using the following formula. Concentration rate (mass%)=(x / y)×100 In the above formula, x represents the mass of the dispersion of silica particles obtained in step (1), and y represents the mass of the dispersion of silica particles after concentration.

[0050] (Step (3)) Step (3) is a step of substituting the dispersion medium of the dispersion liquid of silica particles obtained in step (2).

[0051] The step of substituting the dispersion medium in step (3) preferably includes a step of removing the alcohol and adding water, and more preferably includes a step of removing the alcohol and the alkali catalyst and adding water.

[0052] In step (3), for example, the dispersion of silica particles obtained in step (2) can be heated while adding water, thereby removing the alcohol-containing solution and adding water.

[0053] The heating temperature may be set to the boiling point of the dispersion medium of the silica particle dispersion, and is preferably 50°C to 100°C.

[0054] In step (3), the ratio of the volume of the dispersion medium distilled off per unit time to the volume of water added is preferably maintained at 4:6 to 6:4, and more preferably at 4.5:5.5 to 5.5:4.5. When the ratio is within the above range, variation in the viscosity of the silica sol and aggregation of the silica particles can be suppressed.

[0055] (Step (4)) Step (4) is a step of concentrating the dispersion of silica particles obtained in step (3).

[0056] Examples of methods for concentrating the dispersion of silica particles include pressure concentration and vacuum concentration.

[0057] The concentration ratio in step (4) is preferably 101% by mass to 250% by mass, more preferably 102% by mass to 200% by mass. When the concentration ratio is 101% by mass or more, the polishing rate for a workpiece such as a silicon wafer is excellent. When the concentration ratio is 250% by mass or less, aggregation of silica particles and generation of fine particles can be suppressed.

[0058] The concentration rate can be calculated using the following formula. Concentration rate (mass%) = (α / β) × 100 In the above formula, α represents the mass of the dispersion of silica particles obtained in step (3), and β represents the mass of the dispersion of silica particles after concentration.

[0059] [Silica sol] The content of silica particles in the silica sol obtained by the silica sol production method of the present invention (hereinafter sometimes referred to as "silica sol") is preferably 3% to 50% by mass, more preferably 4% to 40% by mass, and even more preferably 5% 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 a workpiece such as a silicon wafer is excellent. Furthermore, 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.

[0060] The content of metals mixed as impurities in the silica sol (metal impurity content) is preferably 1 ppm by mass or less, and more preferably 0.2 ppm by mass or less.

[0061] When polishing silicon wafers, metal impurities adhere to the surface of the object to be polished, contaminating the object and adversely affecting the properties of the object and the final product.

[0062] Furthermore, if metal impurities are present in the silica sol, coordination interactions occur between the acidic surface silanol groups and the metal impurities, which changes the chemical properties (acidity, etc.) of the surface silanol groups and the three-dimensional environment of the silica particle surfaces (e.g., the tendency of silica particles to aggregate), thereby affecting the polishing rate.

[0063] The metal content of silica sol is measured using inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, and the mixture is heated, dissolved, and evaporated. Pure water is added to the remaining sulfuric acid droplets to make a total of exactly 10 g to create a test solution, which is then measured using an 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 taken as the metal content.

[0064] The metal content of silica sol can be reduced to 1 ppm by mass or less, for example, by obtaining silica particles by carrying out a hydrolysis reaction and a condensation reaction using alkoxysilane as a main raw material. In the method of deionizing alkali silicate such as water glass, sodium and other elements derived from the raw materials remain, making it extremely difficult to reduce the metal content of silica particles to 1 ppm by mass or less.

[0065] 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 the silica sol (100% by mass). 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 or polishing composition can be suppressed, resulting in excellent storage stability of the silica sol or polishing composition. Furthermore, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for a workpiece, typically a silicon wafer, is excellent.

[0066] The content of silica particles and dispersion medium in the silica sol can be set within a desired range in step (3).

[0067] In addition to silica particles and a dispersion medium, the silica sol may contain other components such as an oxidizing agent, an antiseptic, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial / biocide, as needed, within a range that does not impair the performance of the silica sol.

[0068] In particular, it is preferable to include an antibacterial biocide in the silica sol, since this gives the silica sol excellent storage stability.

[0069] Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxides, 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 of its excellent affinity with silica sol. Antimicrobial biocides also include those commonly referred to as disinfectants.

[0070] 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 the total amount of the silica sol (100% by mass). 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 silica sol is not impaired.

[0071] 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, the dispersion stability is excellent and aggregation of the silica particles can be suppressed. Furthermore, when the pH of the silica sol is 8.0 or lower, dissolution of the silica particles is prevented and long-term storage stability is excellent.

[0072] The pH of the silica sol can be adjusted to a desired range by adding a pH adjuster.

[0073] [Physical properties of silica particles] Preferred physical properties of the silica particles in the silica sol produced by the method for producing a silica sol of the present invention will be described below.

[0074] 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. Furthermore, when the average primary particle diameter of the silica particles is 100 nm or less, the surface roughness and scratches on the polished object, such as a silicon wafer, can be reduced, and sedimentation of the silica particles can be suppressed.

[0075] 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 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)

[0076] The average primary particle size of the silica particles can be set within a desired range using known conditions and methods.

[0077] 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 removal of particles and the like during cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. Furthermore, when the average secondary particle diameter of the silica particles is 200 nm or less, the surface roughness and scratches on the polished object, typified by a silicon wafer, can be reduced during polishing, the removal of particles and the like during cleaning after polishing is excellent, and sedimentation of the silica particles can be suppressed.

[0078] The average secondary particle size of the silica particles is measured by the DLS method, specifically, using a dynamic light scattering particle size measuring device.

[0079] The average secondary particle size of the silica particles can be set within a desired range using known conditions and methods.

[0080] The cv value of the silica particles is preferably 10% to 50%, more preferably 15% to 40%, and even more preferably 20% to 35%. When the cv value of the silica particles is 10% or more, the polishing rate for a workpiece, such as a silicon wafer, is excellent, resulting in excellent silicon wafer productivity. Furthermore, when the cv value of the silica particles is 50% or less, the surface roughness and scratches on a workpiece, such as a silicon wafer, during polishing can be reduced, resulting in excellent particle removal efficiency during post-polishing cleaning.

[0081] The cv value of the silica particles is calculated using the following formula (2) after measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter measuring device. CV value (%) = (standard deviation (nm) / average secondary particle size (nm)) × 100 (%) (2)

[0082] 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 1.0 or more, the polishing rate for a workpiece, such as a silicon wafer, is excellent, resulting in excellent silicon wafer productivity. Furthermore, when the association ratio of silica particles is 4.0 or less, the surface roughness and scratches on a workpiece, such as a silicon wafer, during polishing can be reduced, and aggregation of silica particles can be suppressed.

[0083] 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)

[0084] The surface silanol group density of silica particles is 0.1 / nm 2 ~10 pieces / nm 2 is preferable, and 0.5 particles / nm 2 ~7.5 pieces / nm 2 More preferably, 2.0 particles / nm 2 ~7.0 pieces / nm 2 It is more preferable that the surface silanol group density of the silica particles is 0.1 / nm 2When the surface silanol group density of the silica particles is 10 / nm or more, the silica particles have a moderate surface repulsion, and the dispersion stability of the silica sol is excellent. 2 When the particle size is equal to or less than this, the silica particles have an appropriate surface repulsion, and aggregation of the silica particles can be suppressed.

[0085] The surface silanol group density of silica particles is measured by the Sears method, specifically, under the following conditions and calculated.

[0086] Take a 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 add pure water until the total volume of the test liquid is 150 mL to obtain the test liquid.

[0087] The obtained test solution is placed in an automatic titrator, and 0.1 mol / L aqueous sodium hydroxide solution is added dropwise to measure the titer A (mL) of 0.1 mol / L aqueous sodium hydroxide solution required to change the pH from 4.0 to 9.0.

[0088] The amount of 0.1 mol / L sodium hydroxide solution consumed per 1.5 g of silica particles, V (mL), required to change the pH from 4.0 to 9.0 was calculated using the following equation (4), and the surface silanol group density ρ (number / nm 2 ) is calculated.

[0089] V=(A×f×100×1.5) / (W×C)...(4) A: The amount (mL) of 0.1 mol / L sodium hydroxide solution required to change the pH from 4.0 to 9.0 per 1.5 g of silica particles f: Potency of the 0.1 mol / L sodium hydroxide solution used C: Concentration of silica particles in silica sol (mass%) W: Amount of silica sol collected (g)

[0090] ρ=(B×N A ) / (10 18 ×M×S BET )···(5) B: The amount of sodium hydroxide (mol) required to change the pH from 4.0 to 9.0 per 1.5 g of silica particles calculated from V N A : Avogadro's number (units / mol) M: Silica particle amount (1.5g) S BET : The specific surface area (m) of silica particles measured when calculating the average primary particle diameter 2 / g)

[0091] The method for measuring and calculating the surface silanol group density of the silica particles is based on "GW Sears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981-1983 (1956)," "Haba Shinichi, Development of Abrasives for Semiconductor Integrated Circuit Processing, Doctoral Dissertation, Kochi University of Technology, pp. 39-45, March 2004," "Patent Publication No. 5967118," and "Patent Publication No. 6047395."

[0092] The surface silanol group density of the silica particles can be set within a desired range by adjusting the conditions for the hydrolysis reaction and condensation reaction of the alkoxysilane.

[0093] Examples of the shape of silica particles include spherical, chain-like, cocoon-like (also called knob-like or peanut-like), irregular shapes (for example, wart-like, bent, branched, etc.), etc. Among these shapes of silica particles, spherical shapes are preferred when it is desired to reduce the surface roughness and scratches on a polished object, such as a silicon wafer, during polishing, and irregular shapes are preferred when it is desired to further increase the polishing rate for a polished object, such as a silicon wafer.

[0094] [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.

[0095] The water-soluble polymer enhances the wettability of the polishing composition to the object to be polished, such as a silicon wafer. The water-soluble polymer is preferably a polymer having a functional group with high water affinity, and this functional group with high water affinity has a high affinity with the surface silanol groups of the silica particles, so that the silica particles and the water-soluble polymer are stably dispersed in close proximity in the polishing composition. 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.

[0096] Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0097] Examples of cellulose derivatives include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose.

[0098] Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone.

[0099] Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0100] 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 high affinity with the surface silanol groups of silica particles and act synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0101] 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. Furthermore, when the weight-average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with silica sol is excellent and the polishing rate for a workpiece, such as a silicon wafer, is excellent.

[0102] The weight-average molecular weight of the water-soluble polymer is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, in terms of polyethylene oxide.

[0103] 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 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. 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.

[0104] 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, antifungal agents, pH adjusters, pH buffers, surfactants, chelating agents, and antibacterial and biocide agents, as needed, provided that the performance of the polishing composition is not impaired.

[0105] In particular, it is preferable to include a basic compound in the polishing composition, since it can exert a chemical action on the surface of the object to be polished, such as a silicon wafer, thereby performing chemical polishing (chemical etching), and the synergistic effect with the surface silanol groups of the silica particles can improve the polishing rate of the object to be polished, such as a silicon wafer.

[0106] Examples of basic compounds include organic basic compounds, alkali metal hydroxides, alkali metal hydrogencarbonates, 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 hydrogencarbonate, and ammonium carbonate are preferred because they have high water solubility and excellent affinity with silica particles and water-soluble polymers, with ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide being more preferred, and ammonia being even more preferred.

[0107] 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 amount of the polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of a polished object, typically a silicon wafer, can be improved. Furthermore, 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.

[0108] 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 polishing composition has excellent dispersion stability. When the pH of the polishing composition is 12.0 or lower, dissolution of silica particles can be suppressed, and the polishing composition has excellent stability.

[0109] The pH of the polishing composition can be adjusted to a desired range by adding a pH adjuster.

[0110] The polishing composition can be obtained by mixing the silica sol obtained by the silica sol manufacturing method of the present invention, the water-soluble polymer, and, if necessary, other components. However, in consideration of storage and transportation, the polishing composition can be prepared at a high concentration first and then diluted with water or the like immediately before polishing.

[0111] [Polishing method] The polishing method of the present invention is a polishing method using a polishing composition containing the silica sol obtained by the method for producing silica sol of the present invention. The polishing composition used is preferably the polishing composition described above.

[0112] A specific polishing method includes, for example, a method in which the surface of a silicon wafer is pressed against a polishing pad, the polishing composition of the present invention is dropped onto the polishing pad, and the surface of the silicon wafer is polished.

[0113] [Methods of manufacturing semiconductor wafers and semiconductor devices] The method for producing a semiconductor wafer of the present invention and the method for producing a semiconductor device of the present invention include the polishing method of the present invention.

[0114] [Application] The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, 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 for photomasks and liquid crystals, and polishing magnetic disk substrates, and among these, it can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing. [Example]

[0115] The present invention will be explained in more detail below using examples, but the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the invention.

[0116] (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 an automatic specific surface area measuring device "BELSORP-MR1" (model name, Microtrack BEL Co., Ltd.). The density was calculated to be 2.2 g / cm using the following formula (1). 3 The average primary particle size was calculated. Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 ))···(1)

[0117] (Measurement of average secondary particle size) The average secondary particle size of the silica particles in the silica sols obtained in the examples and comparative examples was measured using a dynamic light scattering particle size measuring device "Zetersizer Nano ZS" (model name, manufactured by Malvern Instruments).

[0118] (Calculation of association ratio) The association ratio was calculated from the measured average primary particle size and average secondary particle size using the following formula (3). Association ratio = average secondary particle diameter / average primary particle diameter...(3)

[0119] (Measurement of surface silanol group density) An amount of silica sol obtained in each of the Examples and Comparative Examples, equivalent to 1.5 g of silica particles, was placed in a 200 mL tall beaker, and purified water was added to make the liquid volume 90 mL. In a 25°C environment, a pH electrode was inserted into a tall beaker, and the test solution was stirred for 5 minutes using a magnetic stirrer. While continuing to stir using the magnetic stirrer, a 0.1 mol / L aqueous hydrochloric acid solution was added until the pH reached 3.6. The pH electrode was removed from the tall beaker, and while continuing to stir using the magnetic stirrer, 30 g of sodium chloride was added, and pure water was gradually added until the sodium chloride was completely dissolved. Finally, pure water was added until the total volume of the test solution reached 150 mL, and the test solution was stirred for 5 minutes using a magnetic stirrer to obtain the test solution.

[0120] The tall beaker containing the obtained test solution was placed in an automatic titrator "COM-1600" (manufactured by Hiranuma Sangyo Co., Ltd.), and the pH electrode and buret included with the device were inserted into the tall beaker. While stirring the test solution with a magnetic stirrer, 0.1 mol / L aqueous sodium hydroxide solution was added dropwise through the buret, and the titer A (mL) of 0.1 mol / L aqueous sodium hydroxide solution required to change the pH from 4.0 to 9.0 was measured. The amount of 0.1 mol / L sodium hydroxide solution consumed per 1.5 g of silica particles, V (mL), required to change the pH from 4.0 to 9.0 was calculated using the following equation (6), and the surface silanol group density ρ (number / nm 2 ) was calculated. V=(A×f×100×1.5) / (W×C)...(6) A: The amount (mL) of 0.1 mol / L sodium hydroxide solution required to change the pH from 4.0 to 9.0 per 1.5 g of silica particles f: Potency of the 0.1 mol / L sodium hydroxide solution used C: Concentration of silica particles in silica sol (mass%) W: Amount of silica sol collected (g) ρ=(B×N A ) / (10 18 ×M×S BET )···(7) B: The amount of sodium hydroxide (mol) required to change the pH from 4.0 to 9.0 per 1.5 g of silica particles calculated from V N A : Avogadro's number (units / mol) M: Silica particle amount (1.5g) S BET : The specific surface area (m) of silica particles measured when calculating the average primary particle diameter 2 / g)

[0121] (Viscosity measurement) The viscosity of the silica sol obtained in the examples and comparative examples was measured using an E-type viscometer "TVE-25L" (model name, manufactured by Toki Sangyo Co., Ltd.) at 25°C and a shear rate of 150 / sec.

[0122] [Example 1] Solution (B) was prepared by mixing 85% by mass of tetramethoxysilane and 15% by mass of methanol, and solution (C) was prepared by mixing 3% by mass of aqueous ammonia. Solution (A), which was prepared by mixing methanol, pure water, and ammonia, was charged into a reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line. The methanol concentration in solution (A) was 87.8% by mass, the water concentration in solution (A) was 11.5% by mass, and the ammonia concentration in solution (A) was 0.7% by mass.

[0123] While maintaining the temperature of the reaction solution at 22°C, 100% by volume of solution (B) and 33% by volume of solution (C) were added to 180% by volume of solution (A) at equal rates over a period of 210 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 12.5% ​​by mass.

[0124] The temperature of the obtained silica particle dispersion was increased and concentrated to a silica particle content of approximately 17.5% by mass. Next, methanol and ammonia were removed while adding pure water to maintain the volume of the silica particle dispersion constant. Next, the silica particle dispersion was concentrated to obtain a silica particle dispersion (silica sol) with a silica particle content of approximately 20% by mass.

[0125] [Comparative Example 1] Solution (B) was prepared by mixing 85% by mass of tetramethoxysilane and 15% by mass of methanol, and solution (C) was prepared by mixing 3% by mass of aqueous ammonia. Solution (A), which was prepared by mixing methanol, pure water, and ammonia, was charged into a reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line. The methanol concentration in solution (A) was 87.8% by mass, the water concentration in solution (A) was 11.5% by mass, and the ammonia concentration in solution (A) was 0.7% by mass.

[0126] While maintaining the temperature of the reaction solution at 22°C, 100% by volume of solution (B) and 33% by volume of solution (C) were added to 180% by volume of solution (A) at equal rates over a period of 210 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 12.5% ​​by mass.

[0127] The temperature of the obtained silica particle dispersion was raised and concentrated to a silica particle content of about 23.5% by mass. Next, while adding pure water to keep the volume of the silica particle dispersion constant, methanol and ammonia were removed to obtain a silica particle dispersion (silica sol) with a silica particle content of about 20% by mass.

[0128] The evaluation results of the obtained silica sol are shown in Table 1.

[0129] [Table 1]

[0130] From the above, it was found that the silica sol production method of the present invention can be carried out with simple equipment. Furthermore, from Table 1, it was found that the silica sol obtained by the silica sol production method of the present invention has a low viscosity. [Industrial Applicability]

[0131] The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used for polishing purposes, such as polishing semiconductor materials such as silicon wafers, 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 for photomasks and liquid crystals, and polishing magnetic disk substrates, and among these, 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 (4) in order: Step (1): A step of subjecting tetraalkoxysilane to hydrolysis and condensation reaction to obtain a dispersion of silica particles. Step (2): Concentrating the dispersion of silica particles obtained in step (1). Step (3): Substituting the dispersion medium of the dispersion of silica particles obtained in step (2). Step (4): Concentrating the dispersion of silica particles obtained in step (3). The method for producing a silica sol, wherein the concentration rate in the step (2) is 101% by mass to 220% by mass.

2. The method for producing a silica sol according to claim 1, wherein the concentration rate in the step (4) is 101% by mass to 250% by mass.

3. 3. The method for producing a silica sol according to claim 1, wherein the step of substituting the dispersion medium in the step (3) comprises the steps of removing alcohol and adding water.

4. 3. The method for producing a silica sol according to claim 1, wherein in the step (3), the ratio of the volume of the dispersion medium distilled off per unit time to the volume of water added is maintained at 4:6 to 6:

4.

5. The method for producing a silica sol according to any one of claims 1 to 4, wherein in the step (1), the tetraalkoxysilane is tetramethoxysilane.

6. 6. The method for producing a silica sol according to claim 1, wherein in the step (1), the hydrolysis reaction and condensation reaction of the tetraalkoxysilane are carried out by adding the solution (B) containing the tetraalkoxysilane and the solution (C) containing the alkali catalyst to the solution (A) containing the alkali catalyst.

7. The method for producing a silica sol according to any one of claims 1 to 6, wherein the content of silica particles in the silica sol is 3% by mass to 50% by mass.

8. The method for producing a silica sol according to any one of claims 1 to 7, wherein the metal content in the silica sol is 1 ppm by mass or less.

9. A polishing method comprising a step of polishing with a polishing composition containing the silica sol obtained by the method for producing a silica sol according to any one of claims 1 to 8.

10. A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 9.

11. A method for manufacturing a semiconductor device, comprising the polishing method according to claim 9.

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