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

Abstract

To provide a method for producing silica sol in which a production time of silica sol can be shortened.SOLUTION: Provided are: a method for producing silica sol that includes the following steps (1) and (2); a polishing method that includes polishing using a polishing composition containing the silica sol obtained by the method for producing silica sol; a method for producing semiconductor wafer that includes the polishing method; and a method for producing semiconductor device that includes the polishing method. Step (1): a step in which tetraalkoxysilane is subjected to hydrolyzation and condensation to yield a fluid dispersion of silica particles. Step (2): a step in which water at 50°C to 150°C is added to the fluid dispersion of silica particles obtained in step (1) to yield a silica sol.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 liquids are known as methods for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in the final polishing of prime silicon wafers for semiconductors and reclaimed silicon wafers, and in chemical mechanical polishing (CMP) for planarizing interlayer insulating films during semiconductor device manufacturing, forming metal plugs, forming buried wiring, and the like, the surface condition has a significant effect on the semiconductor characteristics, so the surfaces and end faces of these components are required to be polished with extremely high precision.

[0003] In such precision polishing, a polishing composition containing silica particles is adopted, and colloidal silica is widely used as the abrasive grains, which are the main component. Depending on the manufacturing method, colloidal silica is known to be produced by pyrolysis of silicon tetrachloride (fumed silica, etc.), by deionization of alkali silicate such as water glass, and by hydrolysis and condensation reaction of alkoxysilane (generally called the "sol-gel method").

[0004] Many studies have been conducted on methods for producing silica particles. For example, Patent Document 1 discloses a method for producing a silica sol by producing a dispersion of silica particles by hydrolysis and condensation reaction of alkoxysilane, and then replacing the liquid containing an organic solvent in the dispersion of silica particles with water. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-60217 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, after producing a dispersion of silica particles by hydrolysis and condensation of alkoxysilane, the process of replacing the liquid containing an organic solvent in the dispersion of silica particles with water has a problem that the process time is long.Generally, in the process of replacing the liquid containing an organic solvent in the dispersion of silica particles with water, the dispersion of silica particles is heated from the outside to distill off the liquid containing an organic solvent, while water is added.At that time, if the heating temperature is raised too much, the evaporation rate at the interface between the heater and the dispersion of silica particles becomes too fast, and the drying and agglomeration of the silica particles at the interface is promoted, so that the yield of the production of silica sol is deteriorated.Therefore, in order to reduce the drying and agglomeration of the silica particles, the heating temperature from the outside must be lowered, so that it is difficult to shorten the process time of the process of replacing the liquid containing an organic solvent in the dispersion of silica particles with water.

[0007] In addition, it is desirable that the silica sol used in precision polishing does not contain metal as an impurity. In order to avoid the elution of metal components into the silica sol, it is desirable to produce the silica sol in a container whose inner wall is covered with a resin. Since the heat transfer coefficient of resin is lower than that of metal, covering the inner wall of a metal container with resin has a problem that the thermal efficiency when heating from the outside is poor, and it takes a long time to distill off the liquid containing the organic solvent. Furthermore, since the heat resistance of resin is poor compared to metal, the heating temperature must be set low, so there is a problem that it is difficult to shorten the process time of the process of replacing the liquid containing the organic solvent in the dispersion liquid of silica particles with water.

[0008] For the above reasons, there is an issue that it is difficult to shorten the process time in the process of replacing the liquid containing an organic solvent in the silica particle dispersion with water after producing the silica particle dispersion by the hydrolysis reaction and condensation reaction of alkoxysilane.

[0009] The method for producing a silica sol disclosed in Patent Document 1 does not incorporate any effort to shorten the process time in the step of replacing the organic solvent in the dispersion of silica particles with water.

[0010] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a silica sol that can shorten the production time of the silica sol. [Means for solving the problem]

[0011] As described above, in the conventional method for producing silica sol by sol-gel method, it is difficult to shorten the process time of the step of replacing the liquid containing organic solvent in the dispersion liquid of silica particles with water.As a result of intensive research, the present inventors have found that the production time of silica sol can be shortened by controlling the temperature of the water added in the step of replacing the liquid containing organic solvent in the dispersion liquid of silica particles with water, and have completed the present invention.

[0012] That is, the gist of the present invention is as follows. [1] A method for producing a silica sol, comprising the following steps (1) and (2): Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles. Step (2): Adding water at 50°C to 150°C to the dispersion of silica particles obtained in step (1) to obtain a silica sol. [2] The method for producing a silica sol according to [1], wherein in the step (2), the temperature of the water added is 70°C to 120°C. [3] The method for producing a silica sol according to [1], wherein in the step (2), the temperature of the water added is 90°C to 110°C. [4] The method for producing a silica sol according to any one of [1] to [3], further comprising the step of heating the dispersion of silica particles and distilling off the liquid containing the organic solvent in the step (2). [5] The method for producing a silica sol according to [4], wherein in the step (2), the dispersion of silica particles is heated using a heat medium. [6] The method for producing a silica sol according to [5], wherein in the step (2), the temperature of the heat transfer medium is 130°C or lower. [7] The method for producing a silica sol according to [4], wherein in the step (2), the ratio of the mass of the liquid distilled off per unit time to the mass of the water added is maintained at 4:6 to 6:4. [8] The method for producing a silica sol according to any one of [1] to [7], wherein the mass of water added in step (2) is 0.5 to 5 times the mass of the liquid component of the dispersion of silica particles obtained in step (1). [9] The method for producing a silica sol according to any one of [1] to [8], wherein the step (2) is carried out in a container the inner wall of which is covered with a resin.

[10] The method for producing a silica sol according to any one of [1] to [9], wherein in the step (1), the tetraalkoxysilane is tetramethoxysilane.

[11] The method for producing a silica sol according to any one of [1] to

[10] , wherein in step (1), the hydrolysis reaction and condensation reaction of the tetraalkoxysilane are carried out by adding a solution (B) containing a tetraalkoxysilane and a solution (C) containing an alkali catalyst to a solution (A) containing an alkali catalyst.

[12] A method for producing a silica sol according to any one of [1] to

[11] , further comprising the following step (3): Step (3): A step of subjecting the silica sol obtained in step (2) to a pressurized heat treatment.

[13] The method for producing a silica sol according to any one of [1] to

[12] , wherein a concentration of silica particles in the silica sol is 3% by mass to 50% by mass.

[14] The method for producing a silica sol according to any one of [1] to

[12] , wherein the metal content in the silica sol is 1 ppm or less.

[15] A polishing method, comprising the steps of: polishing with a polishing composition containing the silica sol obtained by the method for producing a silica sol according to any one of [1] to

[14] .

[16] A method for producing a semiconductor wafer, comprising the polishing method according to

[15] .

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

[15] . Effect of the Invention

[0013] According to the method for producing a silica sol of the present invention, the production time of the silica sol can be shortened by shortening the process time of the step of replacing the liquid containing an organic solvent in the dispersion liquid of silica particles with water. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be modified and practiced in various ways within the scope of the gist. In addition, when the expression "~" is used in this specification, it is used as an expression including the numerical value or physical property value before and after it.

[0015] (Method of producing silica sol) The method for producing a silica sol of the present invention includes the following steps (1) and (2). Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles. Step (2): Adding water at 50°C to 150°C to the dispersion of silica particles obtained in step (1) to obtain a silica sol.

[0016] (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.

[0017] Examples of tetraalkoxysilanes include tetraalkoxysilanes having an alkoxy group with 1 to 12 carbon atoms, such as 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, since they undergo a fast hydrolysis reaction, are less likely to leave unreacted substances, are highly productive, and can easily produce a stable silica sol.

[0018] The method of obtaining a dispersion of silica particles by subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction is preferably 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, because the hydrolysis reaction and the condensation reaction are easily controlled, the reaction rates of the hydrolysis reaction and the condensation reaction can be increased, gelation of the dispersion of silica particles can be prevented, and silica particles having a uniform particle size can be obtained.

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

[0020] Examples of the alkali catalyst in the 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 action, is easy to control the particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easy to remove after the hydrolysis reaction and the condensation reaction.

[0021] The solution (A) preferably contains water, since this can promote the hydrolysis of the alkoxysilane.

[0022] It is preferable that the solution (A) contains a solvent other than water, since this provides excellent dispersibility of the tetraalkoxysilane in the reaction liquid.

[0023] Examples of the solvent other than water in the solution (A) 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 they are easy to dissolve tetraalkoxysilane, the by-products are the same as those used in the hydrolysis reaction and the condensation reaction, and they are convenient to manufacture.

[0024] 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, based on 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is equal to or higher than the lower limit, aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the resulting dispersion is excellent. When the concentration of the alkali catalyst in solution (A) is equal to or lower than the upper limit, the reaction does not proceed excessively fast, and the reaction controllability is excellent.

[0025] 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 equal to or higher than the lower limit, the dispersibility of silicic acid produced by hydrolysis in the reaction liquid is excellent. When the concentration of water in solution (A) is equal to or lower than the upper limit, the dispersibility of tetraalkoxysilane in the reaction liquid is excellent.

[0026] The concentration of the solvent other than water in the solution (A) is preferably the balance of the alkali catalyst and water.

[0027] The solution (B) contains a tetraalkoxysilane.

[0028] It is preferable that the solution (B) contains a solvent, since this provides excellent dispersibility of the tetraalkoxysilane in the reaction liquid.

[0029] Examples of the solvent in the solution (B) include alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol, ketones such as acetone and methyl ethyl ketone, 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 by-products are the same and are convenient to manufacture.

[0030] The concentration of tetraalkoxysilane in solution (B) is preferably 76% by mass to 89% by mass, 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 equal to or higher than the lower limit, the amount of solvent used can be reduced, and the productivity of silica particles is excellent. When the concentration of tetraalkoxysilane in solution (B) is equal to or lower than the upper limit, the dispersibility of tetraalkoxysilane in the reaction liquid is excellent.

[0031] The concentration of the solvent in solution (B) is preferably 11% by mass to 24% by mass, 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 equal to or higher than the lower limit, the dispersibility of the tetraalkoxysilane in the reaction liquid is excellent. When the concentration of the solvent in solution (B) is equal to or lower than the upper limit, the amount of the solvent used can be reduced, and the productivity of the silica particles is excellent. In addition, the concentration of the solvent in solution (B) is usually preferably the remainder of the tetraalkoxysilane in solution (B).

[0032] The solution (C) contains an alkali catalyst.

[0033] Examples of the alkali catalyst in the 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 action, is easy to control the particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easy to remove after the hydrolysis reaction and the condensation reaction.

[0034] It is preferable that the solution (C) contains a solvent, since this can reduce fluctuations in the composition of the reaction liquid.

[0035] Examples of the solvent in the solution (C) include water, methanol, ethanol, propanol, isopropanol, and alcohols such as ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, water and alcohols are preferred, and water is more preferred, because the solvents used in the hydrolysis reaction and the condensation reaction are the same as the by-products, and they are convenient to manufacture.

[0036] The concentration of the alkali catalyst in solution (C) is preferably 2% by mass to 5% by mass, more preferably 3% by mass to 4% by mass, based on 100% by mass of solution (C). When the concentration of the alkali catalyst in solution (C) is equal to or higher than the lower limit, the aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the resulting dispersion is excellent. When the concentration of the alkali catalyst in solution (C) is equal to or lower than the upper limit, the reaction does not proceed too quickly, and the reaction controllability is excellent.

[0037] The concentration of water in solution (C) is preferably 95% by mass to 98% by mass, more preferably 96% by mass to 97% by mass, based on 100% by mass of solution (C). When the concentration of water in solution (C) is equal to or higher than the lower limit, the dispersibility of silicic acid produced by hydrolysis in the reaction liquid is excellent. When the concentration of water in solution (C) is equal to or lower than the upper limit, the dispersibility of tetraalkoxysilane in the reaction liquid is excellent.

[0038] The reaction temperature (temperature of the reaction solution) of the hydrolysis reaction and condensation reaction of the tetraalkoxysilane is preferably 20° C. to 50° C., more preferably 25° C. to 45° C. When the reaction temperature is equal to or higher than the lower limit, the reaction does not proceed too slowly, and controllability is excellent. On the other hand, when the reaction temperature is equal to or lower than the upper limit, a good balance between the hydrolysis reaction rate and the condensation reaction rate is obtained. Here, the reaction liquid in the reaction system corresponds to a mixture of solution (A), solution (B) and solution (C).

[0039] The concentration of water in the reaction system of the hydrolysis reaction and the condensation reaction is preferably maintained at 3% by mass to 30% by mass, more preferably 5% by mass to 25% by mass, based on 100% by mass of the reaction solution in the reaction system. When the concentration of water in the reaction system is equal to or higher than the lower limit, the dispersibility of the intermediate product, silicic acid, in the reaction solution is excellent. When the concentration of water in the reaction system is equal to or lower than the upper limit, the dispersibility of the tetraalkoxysilane in the reaction solution is excellent. Here, the reaction liquid in the reaction system corresponds to a mixture of solution (A), solution (B) and solution (C).

[0040] 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 at 0.6% by mass 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 higher than the lower limit, the aggregation of the silica particles is suppressed, and the dispersion stability of the silica particles in the resulting dispersion is excellent. When the concentration of the alkali catalyst in the reaction system is equal to or lower than the upper limit, the reaction does not proceed too quickly, and the reaction controllability is excellent.

[0041] (Process (2)) Step (2) is a step of adding water at 50° C. to 150° C. to the dispersion liquid of silica particles obtained in step (1) to obtain a silica sol.

[0042] The temperature of the water added to the dispersion of silica particles in step (2) is 50°C to 150°C, preferably 70°C to 130°C, and more preferably 90°C to 110°C. When the temperature of the water added is 50°C or higher, the amount of heat added to the dispersion of silica particles increases, so that the production time of the silica sol can be shortened. When the temperature of the water added to the dispersion of silica particles is 150°C or lower, the amount of water that escapes from the dispersion of silica particles as steam can be reduced, so that the production time of the silica sol can be shortened.

[0043] Examples of the method for adding water at 50° C. to 150° C. include a method of adding preheated water by pump, a method of adding water while heating by providing a heat exchanger in the water flow path, etc. Among these methods, the method of adding water while heating by providing a heat exchanger in the water flow path is preferred because it has excellent temperature controllability and is easy to handle steam.

[0044] In step (2), it is preferable to heat the dispersion liquid of silica particles and evaporate off the liquid containing the organic solvent, since this allows efficient replacement of the liquid containing the organic solvent with water. The liquid containing the organic solvent may be removed by distillation before, simultaneously with, or after the addition of water.

[0045] When the addition of water and the distillation of the liquid containing the organic solvent are carried out simultaneously, it is preferable to maintain the ratio of the mass of the liquid distilled off per unit time to the mass of the water added at 4:6 to 6:4, since this can prevent the liquid level of the silica particle dispersion from rising or falling and can prevent the silica particles from agglomerating on the inner wall of the container.

[0046] Examples of the method for heating the dispersion liquid of silica particles include a method for heating by direct flame, a method for heating by an electric heater, a method for heating by using a heat medium, etc. Among these methods for heating the dispersion liquid of silica particles, the method for heating by using a heat medium is preferred because of its excellent temperature controllability.

[0047] Examples of the method of heating using a heat medium include a method of heating the dispersion of silica particles by putting a heat medium circulating type immersion heater into the dispersion, a method of heating by circulating a heat medium on the wall surface of a container having a multi-wall structure, etc. Among these methods of heating using a heat medium, the method of heating by circulating a heat medium on the wall surface of a container having a multi-wall structure is preferred because it allows the production equipment to be simplified.

[0048] The temperature of the heat medium used here is preferably 65° C. to 140° C. or less, more preferably 100° C. to 130° C. When the temperature of the heat medium is 65° C. or more, it is excellent in distilling off the organic solvent. In addition, when the temperature of the heat medium is 140° C. or less, particularly 130° C. or less, it is possible to reduce the evaporation rate of the dispersion of silica particles at the three-phase interface between the dispersion of silica particles, the heating device such as the heat medium or heater, and the gas phase, and it is possible to prevent aggregation of the silica particles.

[0049] In step (2), the mass of water added is preferably 0.5 to 5 times the mass of the liquid component of the silica particle dispersion. When the mass of water added is 0.5 times or more, the liquid containing the organic solvent in the silica particle dispersion can be sufficiently replaced. When the mass of water added is 5 times or less, the silica particles can be prevented from being dissolved and gelled by being exposed to high temperatures for a long time.

[0050] Step (2) is preferably carried out in a vessel the inner wall of which is covered with a resin, since this can prevent elution of metal impurities.

[0051] (Step (3)) The method for producing a silica sol of the present invention preferably further includes the following step (3) since this can increase the degree of condensation of the silica particles. Step (3): A step of subjecting the dispersion of silica particles obtained in step (2) to a pressurized and heated treatment.

[0052] The pressure of the pressurized 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 pressurized heat treatment is 0.10 MPa or more, the degree of condensation of the silica particles can be increased. When the pressure of the pressurized heat treatment is 2.3 MPa or less, the silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent. Pressurization can be achieved by heating the silica particle dispersion in a sealed state to above the boiling point of the dispersion medium. When the silica particle aqueous dispersion is heated to 100°C or higher in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0053] The temperature of the pressure and heat treatment is preferably 100° C. to 220° C., and more preferably 110° C. to 180° C. When the temperature of the pressure and heat treatment is 100° C. or higher, the degree of condensation of the silica particles can be increased. When the temperature of the pressure and heat treatment is 220° C. or lower, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0054] The time of the pressurized heat treatment is preferably 0.25 hours to 10 hours, more preferably 0.5 hours to 8 hours. When the time of the pressurized heat treatment is 0.25 hours or more, the degree of condensation of the silica particles can be increased. When the time of the pressurized heat treatment is 10 hours or less, the silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0055] The pressurized heat treatment is preferably carried out in an aqueous dispersion because it can increase the degree of condensation of the silica particles without significantly changing the average primary particle size, the average secondary particle size, the cv value, or the association ratio.

[0056] The pH when the pressure heat treatment is carried out in the 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 the aqueous dispersion is 6.0 or more, gelation of the silica sol can be suppressed. When the pH when the pressure heat treatment is carried out in the aqueous dispersion is 8.0 or less, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, and association ratio.

[0057] (Physical properties of silica sol) Preferred physical properties of the silica sol produced by the method for producing a silica sol of the present invention will be described below.

[0058] The average primary particle diameter of the silica particles in the silica sol 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. In addition, when the average primary particle diameter of the silica particles is 100 nm or less, the surface roughness and scratches of the polished object, such as a silicon wafer, can be reduced, and the sedimentation of the silica particles can be suppressed.

[0059] The average primary particle size of the silica particles in the silica sol 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 size 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)

[0060] The average primary particle size of the silica particles in the silica sol can be set within a desired range by known conditions and methods.

[0061] The average secondary particle diameter of the silica particles in the silica sol is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm. When the average secondary particle diameter of the silica particles is 10 nm or more, the removability of particles and the like during cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. When the average secondary particle diameter of the silica particles is 200 nm or less, the surface roughness and scratches of the polished object, typically a silicon wafer, during polishing can be reduced, the removability of particles and the like during cleaning after polishing can be excellent, and sedimentation of the silica particles can be suppressed.

[0062] The average secondary particle size of the silica particles in the silica sol is measured by the DLS method, specifically, by using a dynamic light scattering particle size measuring device.

[0063] The average secondary particle size of the silica particles in the silica sol can be set within a desired range by known conditions and methods.

[0064] The cv value of the silica particles in the silica sol 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 polished object such as a silicon wafer is excellent, and the productivity of the silicon wafer is excellent. When the cv value of the silica particles is 50 or less, the surface roughness and scratches of a polished object such as a silicon wafer during polishing can be reduced, and the removal of particles and the like during cleaning after polishing is excellent.

[0065] The cv value of the silica particles in the silica sol is calculated using the following formula (2) by measuring the average secondary particle size of the silica particles using a dynamic light scattering particle size measuring device. cv value = (standard deviation (nm) / average secondary particle size (nm)) × 100 (2)

[0066] The association ratio of silica particles in the silica sol 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 the polished object, such as a silicon wafer, is excellent, and the productivity of the silicon wafer is excellent. When the association ratio of silica particles is 4.0 or less, the surface roughness and scratches of the polished object, such as a silicon wafer, during polishing can be reduced, and the aggregation of silica particles can be suppressed.

[0067] The association ratio of silica particles in a silica sol is calculated using the following formula (3) from the average primary particle diameter measured by the above-mentioned measuring method and the average secondary particle diameter measured by the above-mentioned measuring method. Association ratio=average secondary particle diameter / average primary particle diameter... (3)

[0068] The surface silanol group density of silica particles in silica sol 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 More preferably, the surface silanol group density of the silica particles is 0.1 / nm 2 When the surface silanol group density of the silica particles is 10 / nm or more, the silica particles have a suitable surface repulsion, and the dispersion stability of the silica sol is excellent. 2 When the amount is equal to or less than this, the silica particles have an appropriate surface repulsion, and aggregation of the silica particles can be suppressed.

[0069] The surface silanol group density of the silica particles in the silica sol is measured by the Sears method, specifically, under the following conditions. Take a silica sol equivalent to 1.5 g of silica particles, add pure water to make the liquid volume 90 mL, add 0.1 mol / L hydrochloric acid aqueous solution until the pH becomes 3.6 in an environment of 25°C, 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. The obtained test liquid 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. 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 formula (4), and the surface silanol group density ρ (particles / nm 2 ) is calculated. 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) 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 (pieces / mol) M: Silica particle amount (1.5g) S BET : The specific surface area (m2) of silica particles measured when calculating the average primary particle size 2 / g)

[0070] The method for measuring and calculating the surface silanol group density of the silica particles was based on "GW Ears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981-1983 (1956)," "Haba Shinichi, Development of Abrasives for Semiconductor Integrated Circuit Processes, Doctoral Dissertation, Kochi University of Technology, pp. 39-45, March 2004," "Patent No. 5967118," and "Patent No. 6047395."

[0071] The surface silanol group density of the silica particles in the silica sol can be set within a desired range by adjusting the conditions for the hydrolysis reaction and condensation reaction of the alkoxysilane.

[0072] The content of silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass, based on the total amount of the silica sol (100% by mass). When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for a polished object such as a silicon wafer is excellent. When the content of silica particles in the silica sol is 50% by mass or less, the 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.

[0073] The content of water 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, the 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. In addition, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for the polished object, typically a silicon wafer, is excellent.

[0074] The content of silica particles and water in the silica sol can be set within a desired range by distilling off unnecessary components from the obtained dispersion of silica particles and adding necessary components.

[0075] Silica sol may contain a dispersion medium other than water because it has excellent dispersion stability of silica particles. Examples of the dispersion medium include alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media may be used alone or in combination of two or more, but it is preferable to use water, which has excellent affinity with silica particles, as the dispersion medium.

[0076] In addition to silica particles and water, 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 biocide, as necessary, within the range that does not impair the performance of the silica sol. In particular, it is preferable to include an antibacterial biocide in the silica sol, since this provides excellent storage stability of the silica sol.

[0077] Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, sodium chlorite, etc. These antibacterial biocides may be used alone or in combination of two or more. Among these antibacterial biocides, hydrogen peroxide is preferred because it has excellent affinity with silica sol. Antimicrobial biocides also include those commonly referred to as germicides.

[0078] 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. Furthermore, when the content of the antibacterial biocide in the silica sol is 10% by mass or less, the inherent performance of the silica sol is not impaired.

[0079] 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 the aggregation of the silica particles can be suppressed. Also, when the pH of the silica sol is 8.0 or less, dissolution of the silica particles is prevented, and the long-term storage stability is excellent. The pH of the silica sol can be adjusted to a desired range by adding a pH adjuster.

[0080] The content of metals mixed as impurities in the silica sol (metal impurity content) is preferably 1 ppm or less, and more preferably 0.2 ppm or less.

[0081] When polishing silicon wafers for semiconductor devices, metallic impurities adhere to and contaminate the surface of the workpiece to be polished, adversely affecting the characteristics of the wafer and diffusing into the interior of the wafer, degrading its quality, resulting in a significant decrease in the performance of semiconductor devices manufactured from such wafers. Furthermore, when metal impurities are present in the silica sol, coordination interactions occur between the acidic surface silanol groups and the metal impurities, changing the chemical properties (acidity, etc.) of the surface silanol groups and the three-dimensional environment of the silica particle surfaces (e.g. the ease of aggregation of silica particles), thereby affecting the polishing rate.

[0082] The metal impurity content of silica sol is measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, 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 so that the total amount is exactly 10 g to create a test solution, which is then measured using an inductively coupled plasma mass spectrometry device. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the sum of the contents of these metals is the metal impurity content.

[0083] The metal impurity content of the silica sol can be reduced to 1 ppm or less by obtaining silica particles through hydrolysis and condensation reactions using alkoxysilane as the main raw material. In the method of deionizing alkali silicate such as water glass, sodium and other impurities derived from the raw material remain, making it extremely difficult to reduce the metal impurity content of silica particles to 1 ppm or less.

[0084] Examples of the shape of silica particles in silica sol include spherical, chain-like, cocoon-like (also called lump-like or peanut-like), irregular shapes (for example, wart-like, bent, branched, etc.) etc. Among these shapes of silica particles, when it is desired to reduce the surface roughness or scratches of a polished object, such as a silicon wafer, during polishing, a spherical shape is preferred, and when it is desired to increase the polishing rate for a polished object, such as a silicon wafer, an irregular shape is preferred.

[0085] The silica particles in the silica sol preferably have no pores, since this provides excellent mechanical strength and storage stability. The presence or absence of pores in the silica particles in the silica sol is confirmed by a multipoint BET analysis using an adsorption isotherm with nitrogen as the adsorption gas.

[0086] (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.

[0087] 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 the functional group with high water affinity has a high affinity with the surface silanol group of the silica particles, so that the silica particles and the water-soluble polymer are stably dispersed in the polishing composition in a closer vicinity. Therefore, when polishing the object to be polished, such as a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0088] Examples of the water-soluble polymer include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0089] 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. An example of the copolymer having a polyvinylpyrrolidone skeleton is a graft copolymer of polyvinyl alcohol and polyvinylpyrrolidone. Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0090] 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 polished object.

[0091] The mass 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 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, the affinity with silica sol is excellent, and the polishing rate for the object to be polished, typified by a silicon wafer, is excellent.

[0092] The mass 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.

[0093] 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 the total amount of the polishing composition (100% by mass). 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, the aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0094] In addition to the silica sol and the water-soluble polymer, the polishing composition may contain other components, such as a basic compound, a polishing accelerator, a surfactant, a hydrophilic compound, a preservative, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial and biocide, as necessary, within the range that does not impair the performance of the polishing composition. In particular, it is preferable to include a basic compound in the polishing composition, since it is possible to perform chemical polishing (chemical etching) by applying a chemical action to the surface of an object to be polished, such as a silicon wafer, and because a synergistic effect with the surface silanol groups of the silica particles can improve the polishing speed of an object to be polished, such as a silicon wafer.

[0095] Examples of the basic compound include organic basic compounds, alkali metal hydroxides, alkali metal hydrogen carbonates, alkali metal carbonates, and ammonia. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogen carbonate, and ammonium carbonate are preferred because they are highly soluble in water and have excellent affinity with silica particles and water-soluble polymers, and ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferred, with ammonia being even more preferred.

[0096] 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 the total amount of the polishing composition (100% by mass). When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing speed of the object to be polished, such as a silicon wafer, can be improved. In addition, 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.

[0097] 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, the aggregation of silica particles in the polishing composition can be suppressed, and the dispersion stability of the polishing composition is excellent. When the pH of the polishing composition is 12.0 or less, the dissolution of silica particles can be suppressed, and the stability of the polishing composition is excellent. The pH of the polishing composition can be adjusted to a desired range by adding a pH adjuster.

[0098] The polishing composition can be obtained by mixing the silica sol obtained by the silica sol manufacturing method of the present invention, a water-soluble polymer, and, as necessary, other components. However, taking into consideration storage and transportation, the composition may be prepared at a high concentration and then diluted with water or the like immediately before polishing.

[0099] (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. As the polishing composition, it is preferable to use the above-mentioned polishing composition. A specific example of the polishing method is 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.

[0100] (Method of manufacturing semiconductor wafers) The method for producing a semiconductor wafer of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above. Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

[0101] (Method of manufacturing semiconductor devices) The method for producing a semiconductor device of the present invention includes the polishing method of the present invention, and the specific polishing method is as described above.

[0102] (Application) The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used for polishing purposes, for example, polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process in manufacturing integrated circuits, polishing synthetic quartz glass substrates used for photomasks and liquid crystals, polishing magnetic disk substrates, and the like, and among these, it can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing. EXAMPLES

[0103] The present invention will be described in more detail below using examples. However, 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 present invention.

[0104] (Measurement of average primary particle size) The silica sol obtained in the examples and comparative examples was 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)

[0105] (Measurement of average secondary particle size and cv value) The average secondary particle diameter of the silica particles in the dispersions of silica particles obtained in the examples and comparative examples was measured using a dynamic light scattering particle size measurement device "Zetersizer Nano ZS" (model name, manufactured by Malvern Instruments), and the cv value was calculated using the following formula (2). cv value = (standard deviation (nm) / average secondary particle size (nm)) × 100 (2)

[0106] (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)

[0107] [Example 1] A solution (B) of tetramethoxysilane and 15.0 parts by mass of methanol and a solution (C) of 97.9 parts by mass of pure water and 2.1 parts by mass of ammonia were added at equal speeds to a solution (A) of 17.5 parts by mass of pure water, 81.4 parts by mass of methanol and 1.1 parts by mass of ammonia over 142 minutes. During the addition, the reaction solution was stirred while maintaining the temperature at 33°C. After the dropwise addition, the reaction solution was stirred for another 30 minutes while maintaining the temperature at 33°C to obtain a dispersion of silica particles. While continuing to stir the obtained dispersion of silica particles, the temperature of the heat medium in the jacket of the reaction vessel was raised and heated to boiling, and the liquid equivalent to 28.5% by mass of the 100% by mass dispersion of silica particles was distilled off. Then, while distilling off the liquid of the dispersion of silica particles, water at 80°C was added to the dispersion of silica particles, and the liquid containing the organic solvent in the dispersion of silica particles was replaced with water, and a silica sol with a silica particle content of about 20% by mass was obtained. At that time, the ratio of the mass of the liquid distilled off per unit time to the mass of the water added was maintained at 4:6 to 5:5 so as to keep the height of the liquid level constant. The point at which the mass of the water added reached 1.6 times the mass of the liquid component of the dispersion of silica particles before adding water was determined as the end point of the process of replacing the liquid containing the organic solvent in the dispersion of silica particles with water. The temperature of the heat transfer medium in the jacket of the reaction vessel was raised from 33°C to 65°C over 25 minutes, then raised to 110°C over 300 minutes, and then raised to 125°C over 75 minutes, and then kept constant at 125°C. The time taken to replace the liquid containing the organic solvent in the dispersion of silica particles with water is shown in Table 1. The evaluation results of the obtained silica sol are shown in Table 2.

[0108] [Example 2] The same procedure as in Example 1 was carried out except that the temperature of the water added to the dispersion of silica particles was 100° C., to obtain a silica sol having a silica particle content of about 20 mass %. The time taken to replace the liquid containing the organic solvent in the dispersion of silica particles with water is shown in Table 1. The evaluation results of the obtained silica sol are shown in Table 2.

[0109] [Example 3] The same procedure as in Example 1 was carried out except that the temperature of the water added to the dispersion of silica particles was 130° C., to obtain a silica sol having a silica particle content of about 20 mass %. The time taken to replace the liquid containing the organic solvent in the dispersion of silica particles with water is shown in Table 1. The evaluation results of the obtained silica sol are shown in Table 2.

[0110] [Comparative Example 1] The same procedure as in Example 1 was carried out except that the temperature of the water added to the dispersion of silica particles was 25° C., to obtain a silica sol having a silica particle content of about 20 mass %. The time taken to replace the liquid containing the organic solvent in the dispersion of silica particles with water is shown in Table 1. The evaluation results of the obtained silica sol are shown in Table 2.

[0111] [Table 1]

[0112] [Table 2]

[0113] As shown in Tables 1 and 2, in Examples 1 to 3 and Comparative Example 1, silica sols having almost the same primary particle size, secondary particle size, cv value, and association ratio were obtained. However, in Comparative Example 1, in which 25°C water was added, Examples 1 to 3, in which heated water was added, were able to shorten the production time. This is believed to be because the liquid containing the organic solvent was efficiently distilled off due to the heat of the added water. In particular, in Example 2, in which 100°C water was added, the production time was significantly shortened. This is believed to be because the temperature of the added water was optimal, which increased the heat added to the dispersion of silica particles and prevented water from escaping as steam outside the container. [Industrial Applicability]

[0114] The silica sol obtained by the method for producing a silica sol of the present invention can be suitably used for polishing purposes, for example, polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the planarization process in manufacturing integrated circuits, polishing synthetic quartz glass substrates used for photomasks and liquid crystals, polishing magnetic disk substrates, etc. Among them, it can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

Claims

1. A method for producing a silica sol, comprising the following steps (1) and (2): Step (1): A step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction to obtain a dispersion of silica particles. Step (2): A step of adding water at 50° C. to 150° C. to the dispersion of silica particles obtained in step (1) to obtain a silica sol.

2. The method for producing a silica sol according to claim 1, wherein in the step (2), the temperature of the water added is 70°C to 120°C.

3. The method for producing a silica sol according to claim 1, wherein in the step (2), the temperature of the water added is 90°C to 110°C.

4. The method for producing a silica sol according to any one of claims 1 to 3, further comprising the step of heating the dispersion of silica particles and distilling off the liquid containing the organic solvent in the step (2).

5. The method for producing a silica sol according to claim 4, wherein in the step (2), the dispersion of silica particles is heated using a heat medium.

6. The method for producing a silica sol according to claim 5, wherein in the step (2), the temperature of the heat medium is 130°C or lower.

7. The method for producing a silica sol according to claim 4, wherein in the step (2), the ratio of the mass of the liquid distilled off per unit time to the mass of the water added is maintained at 4:6 to 6:

4.

8. The method for producing a silica sol according to any one of claims 1 to 7, wherein the mass of the water added in the step (2) is 0.5 to 5 times the mass of the liquid component of the dispersion of silica particles obtained in the step (1).

9. The method for producing a silica sol according to any one of claims 1 to 8, wherein the step (2) is carried out in a container whose inner wall is covered with a resin.

10. The method for producing a silica sol according to any one of claims 1 to 9, wherein in the step (1), the tetraalkoxysilane is tetramethoxysilane.

11. The method for producing a silica sol according to any one of claims 1 to 10, wherein in the step (1), the hydrolysis reaction and the 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.

12. The method for producing a silica sol according to any one of claims 1 to 11, further comprising the following step (3): Step (3): A step of subjecting the silica sol obtained in step (2) to a pressurized heat treatment.

13. The method for producing a silica sol according to any one of claims 1 to 12, wherein a concentration of silica particles in the silica sol is 3% by mass to 50% by mass.

14. The method for producing a silica sol according to any one of claims 1 to 12, wherein the metal content in the silica sol is 1 ppm or less.

15. A polishing method, comprising 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 14.

16. A method for manufacturing a semiconductor wafer, comprising the polishing method according to claim 15.

17. A method for manufacturing a semiconductor device, comprising the polishing method according to claim 15.

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