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

Abstract

To provide a method for producing silica particles that resist secondary aggregation, have excellent dispersion stability, and are suitable for polishing, a method for producing a silica sol containing the silica particles obtained by the production method, a polishing method suitable for polishing, a method for producing a semiconductor wafer, including the polishing method, and a method for producing a semiconductor device, including the polishing method.SOLUTION: A method for producing silica particles includes step (1) of adding, into a solution (A) containing an alkali catalyst, a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst, and subjecting the tetraalkoxysilane to hydrolysis and condensation reactions.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing silica particles, 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, the surface state greatly affects semiconductor characteristics. Therefore, the surfaces and end faces of these parts are required to be polished with extremely high precision.

[0003] In such precision polishing, a polishing composition containing silica particles is employed, and colloidal silica is widely used as the abrasive grains that are the main component thereof. Depending on the manufacturing method, colloidal silica can be obtained by thermal decomposition of silicon tetrachloride (such as fumed silica), by deionization of alkali silicates such as water glass, or by hydrolysis and condensation reactions of alkoxysilanes (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 Documents 1 to 4 and Non-Patent Documents 1 to 2 disclose methods for producing silica particles by hydrolysis and condensation reactions of alkoxysilanes.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

[0006] [Non-Patent Document 1] "Technology and Characteristics of High-Purity Colloidal Silica", Shinichi Sugita, JETI, Vol. 61, No. 3, pp58-61, (2013). [Non-Patent Document 2] "Controlled growth of monodisperse silica spheres in the micron size range", Stöber, Journal of Colloid and Interface Science, Vol. 26, pp62-69, (1968). [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] Incidentally, generally, as disclosed in Non-Patent Document 1, the silica particles in the silica sol obtained by the hydrolysis reaction and condensation reaction of alkoxysilane exhibit various shapes such as spherical, cocoon-shaped, and irregular shapes immediately after synthesis.

[0008] Patent Document 1 discloses cocoon-shaped silica particles. Patent Document 2 discloses irregular-shaped (elongated shape) silica particles. However, when using cocoon-shaped or irregular-shaped silica particles such as those disclosed in Patent Document 1 and Patent Document 2 as a polishing composition, while the polishing composition has excellent polishing power, it becomes a factor for scratching the object to be polished, and thus there is a problem that an object to be polished with a smooth surface cannot be obtained. In addition, when using cocoon-shaped or irregular-shaped silica particles as a polishing composition, during storage or use of the silica particles, physical properties such as secondary aggregation of the silica particles are likely to change, and there is a problem of poor stability of the polishing performance. In order to solve these problems, more spherical silica particles are required.

[0009] Even when silica particles with a large particle diameter are used as a polishing composition, while they have excellent polishing power, they become a factor in scratching the workpiece, so there is a problem that a workpiece with a smooth surface cannot be obtained. In addition, during storage or use of the silica particles, physical properties such as secondary aggregation of the silica particles and sedimentation of the silica particles are likely to change, and there is a problem of poor stability of the polishing performance. To solve these problems, silica particles with a smaller particle diameter are required.

[0010] Patent Documents 3 to 4 and Non-Patent Document 2 disclose particles close to a true sphere or silica particles with a small particle diameter, but do not disclose silica particles that are close to a true sphere and have a small particle diameter, and it cannot be said that they are sufficient to solve the problems of not being able to obtain a workpiece with a smooth surface and poor stability of polishing performance described above.

[0011] The present invention has been made in view of such problems, and an object of the present invention is to provide a method for producing silica particles that suppresses secondary aggregation, has excellent dispersion stability, and is suitable for polishing, and a method for producing a silica sol containing the silica particles obtained by the production method. Another object of the present invention is to provide a polishing method suitable for polishing, a method for producing a semiconductor wafer including the polishing method, and a method for producing a semiconductor device including the polishing method.

Means for Solving the Problems

[0012] Conventional silica particles, particularly non-spherical silica particles such as cocoon-shaped and irregular-shaped particles and silica particles with a large particle diameter, have problems that when used as a polishing composition, a workpiece with a smooth surface cannot be obtained and the stability of polishing performance is poor. However, as a result of intensive studies by the present inventors, it has been found that by optimizing the method of adding a solution during the hydrolysis reaction and condensation reaction of tetraalkoxysilane, silica particles with a large circularity coefficient and a small particle diameter can be obtained, and the present invention has been completed.

[0013] That is, the gist of the present invention is as follows. [1] A method for producing silica particles, comprising the following step (1). Step (1): A step of adding a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst into a solution (A) containing an alkali catalyst, and subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction [2] The method for producing silica particles according to [1], wherein the alkali catalyst in the solution (A) is ammonia. [3] The method for producing silica particles according to [1] or [2], wherein the alkali catalyst in the solution (C) is ammonia. [4] The method for producing silica particles according to any one of [1] to [3], wherein the reaction temperature of the hydrolysis reaction and the condensation reaction is 40 °C or higher. [5] The method for producing silica particles according to any one of [1] to [4], wherein the average value of the Heywood diameter of the silica particles measured by a field emission scanning electron microscope is 20 nm or less. [6] The method for producing silica particles according to any one of [1] to [5], further comprising the following step (2). Step (2): A step of concentrating the dispersion of the silica particles obtained in step (1) and adding a dispersion medium [7] The method for producing silica particles according to [6], further comprising the following step (3). Step (3): A step of subjecting the dispersion of the silica particles obtained in step (2) to a pressure heat treatment [8] A method for producing a silica sol, comprising the method for producing silica particles according to any one of [1] to [7]. [9] The method for producing a silica sol according to [8], wherein the concentration of the silica particles in the silica sol is 10% by mass to 25% by mass.

[10] A polishing method using a polishing composition containing the silica sol obtained by the method for producing a silica sol according to [8] or [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]

[0014] The method for producing silica particles of the present invention can obtain silica particles having a large circularity coefficient and a small particle diameter. The obtained silica particles suppress secondary aggregation, are excellent in dispersion stability, and when used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of polishing performance is excellent. Further, the method for producing a silica sol of the present invention can obtain a polished object with a smooth surface and is excellent in the stability of polishing performance when used as a polishing composition. The polishing method of the present invention is suitable for polishing. Further, since the method for manufacturing a semiconductor wafer and the method for manufacturing a semiconductor device of the present invention include the polishing method of the present invention, the production stability of the object to be polished is excellent.

Embodiments for Carrying Out the Invention

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

[0016] (Method for Producing Silica Particles) The method for producing silica particles of the present invention includes the following step (1). Step (1): A step of adding a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst into a solution (A) containing an alkali catalyst in a liquid, and subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction

[0017] Step (1) is a step of adding a solution (B) containing tetraalkoxysilane and a solution (C) containing an alkali catalyst into a solution (A) containing an alkali catalyst in a liquid, and subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction.

[0018] Since the solution (A) can cause the hydrolysis reaction and the condensation reaction of tetraalkoxysilane to proceed, it preferably contains water.

[0019] Since the solution (A) is excellent in the dispersibility of tetraalkoxysilane in the reaction solution, it preferably contains a solvent other than water. Examples of solvents other than water in solution (A) include methanol, ethanol, propanol, isopropanol, ethylene glycol, and the like. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred because it easily dissolves tetraalkoxysilane, the solvent used in the hydrolysis reaction and the condensation reaction is the same as the by-product, and it has excellent convenience in production. Methanol and ethanol are more preferred, and methanol is even more preferred.

[0020] Solution (A) contains an alkali catalyst. Examples of the alkali catalyst in solution (A) include ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, tetramethylammonium hydroxide, and the like. 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 incorporation of metal impurities, has high volatility, and has excellent removability after the hydrolysis reaction and the condensation reaction.

[0021] 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, it is easy to control the hydrolysis reaction rate of tetraalkoxysilane. When the concentration of water in solution (A) is 30% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and it is easy to control the particle shape.

[0022] 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 silica particles in the dispersion liquid is excellent. 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.

[0023] The concentration of the solvent other than water in the solution (A) is preferably the balance of water and the alkali catalyst.

[0024] The solution (B) contains tetraalkoxysilane. Examples of the tetraalkoxysilane in the solution (B) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, and the like. 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 have a fast hydrolysis reaction, are less likely to leave unreacted substances, are excellent in productivity, and can easily obtain a stable silica sol.

[0025] As the raw material of the silica particles, raw materials other than tetraalkoxysilane such as low condensates of tetraalkoxysilane may be used, but since they are excellent in reactivity, it is preferable that the tetraalkoxysilane is 50% by mass or more and the raw materials other than tetraalkoxysilane are 50% by mass or less in 100% by mass of all the raw materials constituting the silica particles, and more preferably the tetraalkoxysilane is 90% by mass or more and the raw materials other than tetraalkoxysilane are 10% by mass or less.

[0026] The solution (B) may contain only tetraalkoxysilane without a solvent, but it is preferably contains a solvent because it is excellent in the dispersibility of tetraalkoxysilane in the reaction solution. Examples of the solvent in the solution (B) include methanol, ethanol, propanol, isopropanol, ethylene glycol, and the like. These solvents may be used alone or in combination of two or more. Among these solvents, alcohols are preferred, methanol and ethanol are more preferred, and methanol is even more preferred because the ones used in the hydrolysis reaction and the condensation reaction are the same as the ones by-produced, and it is excellent in production convenience.

[0027] The concentration of the tetraalkoxysilane in solution (B) is preferably 60% to 95% by mass, more preferably 70% to 90% by mass in 100% by mass of solution (B). When the concentration of the tetraalkoxysilane in solution (B) is 60% by mass or more, the reaction solution tends to be uniform. Further, when the concentration of the tetraalkoxysilane in solution (B) is 95% by mass or less, the formation of a gel-like substance can be suppressed.

[0028] The concentration of the solvent in solution (B) is preferably 5% to 40% by mass, more preferably 10% to 30% by mass in 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 5% by mass or more, the formation of a gel-like substance can be suppressed. Further, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction solution tends to be uniform.

[0029] The addition rate of solution (B) per hour with respect to the volume of solution (A) is preferably 0.05 kg / hour / L to 1.3 kg / hour / L, more preferably 0.1 kg / hour / L to 0.8 kg / hour / L. When the addition rate of solution (B) is 0.05 kg / hour / L or more, the productivity of silica particles is excellent. Further, when the addition rate of solution (B) is 1.3 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0030] Solution (C) contains an alkali catalyst. Examples of the alkali catalyst in solution (C) include ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, tetramethylammonium hydroxide, and the like. 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 metal impurities, has high volatility, and is excellent in removability after hydrolysis reaction and condensation reaction.

[0031] Since solution (C) can reduce the fluctuation of the concentration of the alkali catalyst in the reaction solution, it preferably contains a solvent. Examples of the solvent in solution (C) include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, and the like. These solvents may be used alone or in combination of two or more. Among these solvents, water and alcohol are preferred, and water is more preferred because the solvent used in the hydrolysis reaction and the condensation reaction is the same as the by-product, and it is excellent in production convenience.

[0032] The concentration of the alkali catalyst in solution (C) is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 6% by mass in 100% by mass of solution (C). When the concentration of the alkali catalyst in solution (C) is 0.5% by mass or more, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction. Further, when the concentration of the alkali catalyst in solution (C) is 10% by mass or less, the variation in the concentration of the alkali catalyst in the reaction solution can be reduced.

[0033] The concentration of the solvent in solution (C) is preferably 90% by mass to 99.5% by mass, more preferably 94% by mass to 99% by mass in 100% by mass of solution (C). When the concentration of the solvent in solution (C) is 90% by mass or more, the variation in the concentration of the alkali catalyst in the reaction solution can be reduced. Further, when the concentration of the solvent in solution (C) is 99.5% by mass or less, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction.

[0034] The addition rate of solution (C) per hour with respect to the volume of solution (A) is preferably 0.02 kg / hour / L to 0.5 kg / hour / L, more preferably 0.04 kg / hour / L to 0.3 kg / hour / L. When the addition rate of solution (C) is 0.02 kg / hour / L or more, the productivity of silica particles is excellent. Further, when the addition rate of solution (C) is 0.5 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0035] The addition of solution (B) and solution (C) is carried out into the liquid of solution (A). By adding solution (B) and solution (C) into the liquid of solution (A), when it is desired to use a highly volatile alkali catalyst typified by ammonia and to proceed with the hydrolysis reaction and the condensation reaction at a high reaction temperature, the miscibility of each component in the reaction solution is enhanced, abnormal reactions in the air can be suppressed, and the circularity coefficient and particle size can be easily controlled. Adding into the liquid means adding below the liquid surface. By setting the supply outlet of solution (B) and the supply outlet of solution (C) below the liquid surface of solution (A), solution (B) and solution (C) can be added into the liquid of solution (A).

[0036] The timing of the addition of solution (B) and solution (C) may be the same or may be different alternately. However, since the variation in the reaction composition is small and the operation does not become complicated, it is preferably the same.

[0037] The reaction temperature of the hydrolysis reaction and the condensation reaction is preferably 50°C to 80°C, more preferably 55°C to 75°C. When the reaction temperature is 50°C or higher, it becomes easy to control the particle shape such as the Heywood diameter and the circularity coefficient. Also, when the reaction temperature is 80°C or lower, bumping and volatilization of the solvent can be suppressed, and the variation in the reaction solution composition can be reduced.

[0038] 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, in 100% by mass of the total amount in the reaction system. When the concentration of water in the reaction system is 3% by mass or more, it is easy to control the hydrolysis reaction rate of tetraalkoxysilane. Also, when the concentration of water in the reaction system is 30% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape is easy to control.

[0039] The concentration of the alkali catalyst in the reaction system of the hydrolysis reaction and the condensation reaction is preferably maintained at 0.5% by mass to 2.0% by mass, more preferably 0.6% by mass to 1.5% by mass, based on 100% by mass of the total amount in the reaction system. When the concentration of the alkali catalyst in the reaction system is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion liquid is excellent. Further, when the concentration of the alkali catalyst in the reaction system is 2.0% by mass or less, the reaction does not proceed too rapidly, and the reaction controllability is excellent.

[0040] Since the method for producing silica particles of the present invention can remove unnecessary components and add necessary components, it preferably further includes the following step (2). Step (2): A step of concentrating the dispersion liquid of silica particles obtained in step (1) and adding a dispersion medium

[0041] Examples of the dispersion medium include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, and the like. These dispersion media may be used alone or in combination of two or more. Among these dispersion media, water and alcohol are preferred, and water is more preferred because of its excellent affinity with silica particles.

[0042] Since the method for producing silica particles of the present invention can increase the degree of condensation of silica particles, it preferably further includes the following step (3). Step (3): A step of subjecting the dispersion liquid of silica particles obtained in step (2) to a pressure heat treatment

[0043] The pressure of the pressure heat treatment is preferably 0.10 MPa to 2.3 MPa, 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. Further, 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. Pressurization can be achieved by heating the dispersion of silica particles above 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 will be the saturated water vapor pressure at that temperature.

[0044] The temperature of the pressure-heat treatment is preferably 100°C to 220°C, more preferably 110°C to 180°C. When the temperature of the pressure-heat treatment is 100°C or higher, the degree of condensation of the silica particles can be increased. When the temperature of the pressure-heat 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.

[0045] The time of the pressure-heat treatment is preferably 0.25 hours to 10 hours, more preferably 0.5 hours to 8 hours. When the time of the pressure-heat treatment is 0.25 hours or longer, the degree of condensation of the silica particles can be increased. When the time of the pressure-heat 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.

[0046] Since the pressure-heat treatment can increase the degree of condensation of silica particles without significantly changing the average primary particle size, average secondary particle size, cv value, and aggregation ratio, it is more preferably carried out in an aqueous dispersion.

[0047] The pH when the pressure-heat treatment is carried out in an aqueous dispersion is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH when the pressure-heat treatment is carried out in an aqueous dispersion is 6.0 or higher, the gelation of the silica sol can be suppressed. Also, when the pH when the pressure-heat treatment is carried out in an aqueous dispersion is 8.0 or lower, the degree of condensation of silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, and aggregation ratio.

[0048] (Physical properties of silica particles) The average value of the Heywood diameter of the silica particles is preferably 30 nm or less, more preferably 5 nm to 25 nm, and even more preferably 6 nm to 20 nm. When the average value of the Heywood diameter of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Further, when the average value of the Heywood diameter of the silica particles is 30 nm or less, when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0049] The standard deviation of the Heywood diameter of the silica particles is preferably 0.10 nm to 4.00 nm, more preferably 0.50 nm to 3.00 nm. When the standard deviation of the Heywood diameter of the silica particles is 0.10 nm or more, the silica particles can be easily produced. Further, when the standard deviation of the Heywood diameter of the silica particles is 4.00 nm or less, secondary aggregation of the silica particles is suppressed, the dispersion stability of the silica particles in the dispersion liquid is excellent, and when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0050] The average value of the major axis of the silica particles is preferably 32 nm or less, more preferably 6 nm to 27 nm, and even more preferably 7 nm to 22 nm. When the average value of the major axis of the silica particles is 6 nm or more, the storage stability of the silica sol is excellent. Further, when the average value of the major axis of the silica particles is 32 nm or less, when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0051] The average value of the minor axis of the silica particles is preferably 28 nm or less, more preferably 4 nm to 23 nm, and even more preferably 5 nm to 18 nm. When the average value of the minor axis of the silica particles is 4 nm or more, the storage stability of the silica sol is excellent. Further, when the average value of the minor axis of the silica particles is 28 nm or less, when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0052] The average value of the circularity coefficient of the silica particles is preferably from 0.87 to 0.99, more preferably from 0.90 to 0.98. When the average value of the circularity coefficient of the silica particles is 0.87 or more, secondary aggregation of the silica particles is suppressed, the dispersion stability of the silica particles in the dispersion liquid is excellent, and when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent. Further, when the average value of the circularity coefficient of the silica particles is 0.99 or less, the silica particles can be easily produced.

[0053] The standard deviation of the circularity coefficient of the silica particles is preferably from 0.01 to 0.08, more preferably from 0.02 to 0.05. When the standard deviation of the circularity coefficient of the silica particles is 0.01 or more, the silica particles can be easily produced. Further, when the standard deviation of the circularity coefficient of the silica particles is 0.08 or less, secondary aggregation is suppressed, the dispersion stability is excellent, and when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0054] The average value of the aspect ratio of the silica particles is preferably from 1.01 to 1.30, more preferably from 1.02 to 1.20. When the average value of the aspect ratio of the silica particles is 1.01 or more, the silica particles can be easily produced. Further, when the average value of the aspect ratio of the silica particles is 1.30 or less, secondary aggregation of the silica particles is suppressed, the dispersion stability of the silica particles in the dispersion liquid is excellent, and when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0055] The standard deviation of the aspect ratio of the silica particles is preferably from 0.01 to 0.20, more preferably from 0.02 to 0.15. When the standard deviation of the aspect ratio of the silica particles is 0.01 or more, the silica particles can be easily produced. Further, when the standard deviation of the aspect ratio of the silica particles is 0.20 or less, secondary aggregation of the silica particles is suppressed, the dispersion stability of the silica particles in the dispersion liquid is excellent, and when the silica particles are used as a polishing composition, a polished object with a smooth surface can be obtained, and the stability of the polishing performance is excellent.

[0056] The average values and standard deviations of the circularity coefficient, Heywood diameter, major axis, minor axis, and aspect ratio of the silica particles are measured using a field emission scanning electron microscope. Specifically, they are measured and calculated under the conditions shown below.

[0057] A dispersion of silica particles is dropped onto a silicon substrate and dried. Using a field emission scanning electron microscope, the silicon substrate is irradiated with an electron beam at an acceleration voltage of 5 kV. Then, a secondary electron image is taken at a magnification of 50,000 to 200,000 times so that the total number of silica particles is 80 or more. The Heywood diameter, major axis, minor axis, circularity coefficient, and aspect ratio of all the silica particles are measured, and their average values and standard deviations are calculated. At that time, the concentration of the silica particles in the dispersion may be appropriately adjusted.

[0058] The determination of the shape of the silica particles is performed as described below. Whether or not two or more silica particles are joined is determined as follows: If a black line is visible between the silica particles, they are judged as individual non-joined silica particles; if no black line is visible between the silica particles, they are judged as one joined silica particle. Also, when three or more silica particles are aggregated, the determination is difficult, so they are excluded from the measurement targets.

[0059] The reason for setting the magnification of the field emission scanning electron microscope to 50,000 to 200,000 times is to enable the identification of the shape of individual silica particles of 30 nm or less.

[0060] The circularity coefficient is 4πS / L, where S is the area of the secondary electron image of the silica particles taken with the above-mentioned field emission scanning electron microscope, and L is the perimeter of the secondary electron image. 2 The numerical value calculated in this way is used. The Heywood diameter is the diameter of a circle having the same area as the secondary electron image. The major axis is the long side of the rectangle circumscribing the secondary electron image with the minimum area. The minor axis is the short side of the rectangle circumscribing the secondary electron image with the minimum area. The aspect ratio is the long side D of the rectangle circumscribing the secondary electron image with the minimum area. L The short side D of the rectangle circumscribing the secondary electron image with the minimum area.S When it is set to D L / D S shall be the calculated value.

[0061] The metal impurity content of the silica particles is preferably 5 ppm or less, more preferably 2 ppm or less.

[0062] In the polishing of a silicon wafer for a semiconductor device, when metal impurities adhere to and contaminate the surface of the object to be polished, it not only adversely affects the wafer characteristics but also diffuses into the wafer interior, deteriorating the quality. Therefore, the performance of a semiconductor device manufactured using such a wafer is significantly reduced. In addition, when metal impurities are present in the silica particles, a coordination interaction occurs between the surface silanol groups exhibiting acidity and the metal impurities, changing the chemical properties (such as acidity) of the surface silanol groups, changing the three-dimensional environment on the silica particle surface (such as the ease of aggregation of the silica particles), and affecting the polishing rate.

[0063] The metal impurity content of the silica particles is measured by high-frequency inductively coupled plasma mass spectrometry (ICP-MS). Specifically, an exact amount of a silica sol containing 0.4 g of silica particles is weighed, sulfuric acid and hydrofluoric acid are added, heated, dissolved, and evaporated, and pure water is added to the remaining sulfuric acid droplets 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, and nickel, and the total of the contents of these metals is taken as the metal impurity content.

[0064] The metal impurity content of the silica particles can be made 5 ppm or less by obtaining the silica particles by performing a hydrolysis reaction and a condensation reaction using an alkoxysilane as the main raw material. In the method by deionization of an alkali silicate such as water glass, since sodium or the like derived from the raw material remains, it is extremely difficult to make the metal impurity content of the silica particles 5 ppm or less.

[0065] Since the silica particles are excellent in mechanical strength and storage stability, it is preferable that they have no pores. The presence or absence of pores in the silica particles is confirmed by BET multipoint method analysis using an adsorption isotherm with nitrogen as the adsorption gas.

[0066] (Method for producing silica sol) The method for producing the silica sol of the present invention includes the method for producing the silica particles of the present invention.

[0067] As the silica sol, the dispersion of the silica particles obtained by the method for producing the silica particles of the present invention may be used as it is, or it may be produced by removing unnecessary components and adding necessary components among the components in the obtained dispersion of the silica particles.

[0068] The silica sol preferably contains silica particles and a dispersion medium. Examples of the dispersion medium in the silica sol include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These dispersion media in the silica sol may be used alone or in combination of two or more. Among these dispersion media in the silica sol, water and alcohol are preferable and water is more preferable because of their excellent affinity with the silica particles.

[0069] The content of the 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 the silica particles in the silica sol is 3% by mass or more, the polishing rate with respect to the workpiece typified by a silicon wafer is excellent. Further, when the content of the silica particles in the silica sol is 50% by mass or less, 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.

[0070] 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 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. 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 a workpiece typified by a silicon wafer is excellent.

[0071] The content rates of the silica particles and the dispersion medium in the silica sol can be set to a desired range by removing unnecessary components and adding necessary components among the components in the obtained dispersion liquid of the silica particles.

[0072] In addition to the silica particles and the dispersion medium, the silica sol may contain other components such as an oxidizing agent, a preservative, an antifungal agent, 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. In particular, since the silica sol has excellent storage stability, it is preferable to include an antibacterial and biocidal agent in the silica sol.

[0073] Examples of the antibacterial and biocidal agent include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, hydrogen peroxide, 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 biocidal agent generally includes those called bactericides.

[0074] The content rate of the antibacterial and biocidal agent in the silica sol is preferably 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 1% by mass in 100% by 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% by 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% by mass or less, the original performance of the silica sol is not impaired.

[0075] 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, the dispersion stability is excellent and aggregation of silica particles can be suppressed. Further, when the pH of the silica sol is 8.0 or less, dissolution of silica particles is prevented and the long-term storage stability is excellent. The pH of the silica sol can be set to a desired range by adding a pH adjuster.

[0076] (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 the above-described silica sol and a water-soluble polymer.

[0077] The water-soluble polymer enhances the wettability of the polishing composition with respect to a polished object typified by a silicon wafer. The water-soluble polymer is preferably a polymer having a highly hydrophilic functional group, and the affinity between this highly hydrophilic functional group and the surface silanol group of the silica particles is high, and the silica particles and the water-soluble polymer are stably dispersed in the vicinity of each other in the polishing composition. Therefore, when polishing a polished object typified by a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0078] 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.

[0079] Examples of the cellulose derivatives 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. Examples of the copolymer having a polyvinylpyrrolidone skeleton include a graft copolymer of polyvinyl alcohol and polyvinylpyrrolidone. Examples of the polymer having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and a copolymer of ethylene oxide and propylene oxide.

[0080] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, a cellulose derivative is preferable and hydroxyethyl cellulose is more preferable because it has a high affinity for the surface silanol groups of the silica particles and acts synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0081] The mass 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 mass average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. When the mass average molecular weight of the water-soluble polymer is 3,000,000 or less, it has excellent affinity for the silica sol and excellent polishing rate for the object to be polished typified by a silicon wafer.

[0082] The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography under the conditions using a 0.1 mol / L NaCl solution as a mobile phase in terms of polyethylene oxide.

[0083] The content rate of the water-soluble polymer in the polishing composition is preferably 0.02 mass% to 10 mass%, more preferably 0.05 mass% to 5 mass% in 100 mass% of the total amount of the polishing composition. When the content rate of the water-soluble polymer in the polishing composition is 0.02 mass% or more, the hydrophilicity of the polishing composition is improved. Also, when the content rate of the water-soluble polymer in the polishing composition is 10 mass% or less, aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0084] 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. 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 synergistic effect with the surface silanol groups of the silica particles can improve the polishing rate of the object to be polished typified by a silicon wafer, it is preferable to include a basic compound in the polishing composition.

[0085] 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.

[0086] 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.

[0087] 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. The pH of the polishing composition can be set to a desired range by adding a pH adjuster.

[0088] The polishing composition can be obtained by mixing the silica sol obtained by the method for producing a 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.

[0089] (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 a silica sol of the present invention. It is preferable to use the polishing composition described above as the polishing composition. As a specific polishing method, for example, a method of pressing the surface of a silicon wafer against a polishing pad, dropping the polishing composition of the present invention onto the polishing pad, and polishing the surface of the silicon wafer can be mentioned.

[0090] (Method for manufacturing a semiconductor wafer) The method for manufacturing a semiconductor wafer of the present invention is a method including the polishing method of the present invention, and the specific polishing method is as described above. Examples of the semiconductor wafer include a silicon wafer, a compound semiconductor wafer, and the like.

[0091] (Method for manufacturing a semiconductor device) The method for manufacturing a semiconductor device of the present invention is a method including the polishing method of the present invention, and the specific polishing method is as described above.

[0092] (Use) The silica particles obtained by the method for manufacturing silica particles of the present invention and 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, polishing of semiconductor materials such as silicon wafers, polishing of electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in a planarization process when manufacturing integrated circuits, polishing of synthetic quartz glass substrates used for photomasks and liquid crystals, polishing of magnetic disk substrates, etc. can be used, and among them, it can be particularly suitably used for polishing of silicon wafers and chemical mechanical polishing.

[0093] Since the silica particles obtained by the method for manufacturing silica particles of the present invention are silica particles having a large circularity coefficient and a small particle diameter, when used as a composite material with resins, they impart transparency and water repellency to the resins, and at the same time, improve dispersibility and miscibility and improve the processability of the composite material. Therefore, the silica particles obtained by the method for manufacturing silica particles of the present invention can also be suitably used as a hard coat agent, a paint, and a binder for ceramics.

Examples

[0094] 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.

[0095] (Measurement of the shape of silica particles) The dispersion liquids of silica particles obtained in the examples and comparative examples were diluted 5000-fold with ultrapure water, and 5 μL of the diluted dispersion liquid of silica particles was dropped onto a silicon substrate and dried. Next, using a field emission scanning electron microscope (model name "S-5200 type", manufactured by Hitachi High-Technologies Corporation, FE-SEM), the silicon substrate was irradiated with an electron beam at an acceleration voltage of 5 kV, and a secondary electron image was taken at a magnification of 50,000 to 200,000 times so that the total number of silica particles was 80 or more. The Heywood diameter, major axis, minor axis, circularity coefficient, and aspect ratio of all silica particles were measured, and their average values and standard deviations were measured. In the measurement of the shape of silica particles, the taken field emission scanning electron microscope photographs were imported into image analysis type particle size distribution measurement software (software name "Mac-View Ver.4", manufactured by Mountech Co., Ltd.). The determination of the shape of silica particles was performed as described below. Whether two or more silica particles were joined or not was determined as individual silica particles that were not joined when a black line was visible between the silica particles, and as one joined silica particle when a black line was not visible between the silica particles. Also, when three or more silica particles were aggregated, the determination was difficult, so they were excluded from the measurement targets.

[0096] [Example 1] Into the liquid of solution (A) obtained by mixing 34.2 parts by mass of pure water, 188.3 parts by mass of methanol, and 8.8 parts by mass of 29% by mass ammonia water, solution (B) obtained by mixing 100 parts by mass of tetramethoxysilane and 33.3 parts by mass of methanol, and solution (C) obtained by mixing 25.0 parts by mass of pure water and 2.2 parts by mass of 29% by mass ammonia water were added at a constant speed over 103 minutes, respectively. During the addition, the stirring of the reaction liquid was continued while maintaining the temperature of the reaction liquid at 70°C. After the addition was completed, the reaction liquid was further stirred for 30 minutes while maintaining the temperature of the reaction liquid at 70°C. The obtained dispersion liquid of silica particles was adjusted in liquid volume by adding pure water while raising the temperature to remove methanol and ammonia so that the content rate of silica particles became about 20% by mass, and a dispersion liquid of silica particles with a silica particle content rate of about 20% by mass was obtained. The evaluation results of the obtained silica particles are shown in Table 1.

[0097] [Example 2] The operation was carried out in the same manner as in Example 1 except that the reaction temperature and the holding temperature were set to 60°C, and a dispersion of silica particles with a silica particle content of about 20% by mass was obtained. The evaluation results of the obtained silica particles are shown in Table 1.

[0098] [Example 3] Into the solution (A) obtained by mixing 40.6 parts by mass of pure water, 207.6 parts by mass of methanol, and 5.2 parts by mass of 29% aqueous ammonia, the solution (B) obtained by mixing 100 parts by mass of tetramethoxysilane and 17.6 parts by mass of methanol and the solution (C) obtained by mixing 21.5 parts by mass of pure water and 2.1 parts by mass of 29% aqueous ammonia were added at a constant rate over 93 minutes, respectively. During the addition, the stirring of the reaction solution was continued while maintaining the temperature of the reaction solution at 50°C. After the addition was completed, the reaction solution was further stirred for 30 minutes while maintaining the temperature of the reaction solution at 50°C. The obtained dispersion of silica particles was adjusted to have a silica particle content of about 20% by mass by adjusting the liquid volume with additional pure water while raising the temperature to remove methanol and ammonia, thereby obtaining a dispersion of silica particles with a silica particle content of about 20% by mass. The evaluation results of the obtained silica particles are shown in Table 1.

[0099] [Example 4] Into the solution (A) obtained by mixing 34.9 parts by mass of pure water, 204.4 parts by mass of methanol, and 13.1 parts by mass of 29% aqueous ammonia, the solution (B) obtained by mixing 100 parts by mass of tetramethoxysilane and 17.6 parts by mass of methanol and the solution (C) obtained by mixing 19.4 parts by mass of pure water and 5.3 parts by mass of 29% aqueous ammonia were added at a constant rate over 94 minutes, respectively. During the addition, the stirring of the reaction solution was continued while maintaining the temperature of the reaction solution at 70°C. After the addition was completed, the reaction solution was further stirred for 30 minutes while maintaining the temperature of the reaction solution at 70°C. The obtained dispersion of silica particles was adjusted to have a silica particle content of about 20% by mass by adjusting the liquid volume with additional pure water while raising the temperature to remove methanol and ammonia, thereby obtaining a dispersion of silica particles with a silica particle content of about 20% by mass. The evaluation results of the obtained silica particles are shown in Table 1.

[0100] [Comparative Example 1] The operation was carried out in the same manner as in Example 1, except that the addition of Solution (B) and Solution (C) was dropped from above the liquid surface of Solution (A) instead of in the liquid of Solution (A). However, a large amount of silica particles adhered to the inner wall of the reaction tank and the stirring blades, etc., making it difficult to continue the subsequent operation.

[0101]

Table 1

[0102] As can be seen from Table 1, the silica particles obtained by the production methods of Examples 1 to 4 have a large average value of the circularity coefficient, small average values of the Heywood diameter, major axis, minor axis, and aspect ratio, and small standard deviations thereof. Therefore, it can be seen that they are silica particles with small variations in particle shape and particle size. Since the silica particles obtained in Examples 1 to 4 have small variations in particle shape and particle size, when used as a polishing composition, a polished object with a smooth surface can be obtained, and it is expected to have excellent stability in polishing performance. In addition, regarding the dispersion of the silica particles obtained in Example 1, the same evaluation was carried out 9 months after production, and there was almost no change, and secondary aggregation was also hardly confirmed, showing excellent dispersion stability.

Industrial Applicability

[0103] The silica particles obtained by the production method of the silica particles of the present invention and the silica sol obtained by the production method of the silica sol of the present invention can be suitably used for polishing applications. For example, polishing of semiconductor materials such as silicon wafers, polishing of electronic materials such as hard disk substrates, polishing in the planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing of synthetic quartz glass substrates used for photomasks and liquid crystals, polishing of 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) and (2). Step (1): The supply outlets of the solution (B) containing tetraalkoxysilane and the solution (C) containing an alkali catalyst are placed below the liquid level of the solution (A) containing an alkali catalyst, and the solution (B) containing tetraalkoxysilane and the solution (C) containing an alkali catalyst are added into the solution (A) containing an alkali catalyst to subject tetraalkoxysilane to a hydrolysis reaction and a condensation reaction. Step (2): A step of concentrating the dispersion of silica particles obtained in step (1) and adding a dispersion medium.

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

3. The method for producing a silica sol according to claim 1 or 2, wherein the alkali catalyst in the solution (C) is ammonia.

4. The method for producing a silica sol according to any one of claims 1 to 3, wherein the reaction temperature of the hydrolysis reaction and the condensation reaction is 50 °C or higher.

5. The method for producing a silica sol according to any one of claims 1 to 4, wherein the average value of the Heywood diameter of the silica particles measured by a field emission scanning electron microscope is 20 nm or less.

6. The method for producing a silica sol according to any one of claims 1 to 5, further comprising the following step (3). Step (3): A step of subjecting the dispersion of silica particles obtained in step (2) to a pressure heat treatment.

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

8. A polishing method 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 7.

9. A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 8.

10. A method for manufacturing a semiconductor device, comprising the polishing method according to claim 8.

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