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

Abstract

The present invention provides a silica sol and polishing composition in which the amount of water confined to the surface of silica particles does not change even when the temperature is changed, thereby suppressing the decrease in dispersion stability due to the reduction of surface hydration water and the occurrence of scratches on the workpiece when used for polishing. [Solution] A silica sol containing silica particles in which the absolute value of the rate of change of the specific relaxation rate at 40°C relative to the specific relaxation rate at 25°C, as measured by the CPMG method using a pulsed NMR spectrometer, is 30% or less.

Description

[Technical Field]

[0001] This invention relates to silica sol, a method for producing the same, a polishing composition, a polishing method, a method for producing a semiconductor wafer, and a method for producing a semiconductor device. [Background technology]

[0002] Polishing methods using polishing solutions are known for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in the final finishing polishing of prime silicon wafers for semiconductors and recycled silicon wafers, as well as in chemical mechanical polishing (CMP) for planarization of interlayer insulating films, formation of metal plugs, and formation of embedded wiring during semiconductor device manufacturing, the surface condition greatly affects the semiconductor properties, and therefore, the surfaces and edges of these components are required to be polished with extremely high precision.

[0003] In such precision polishing, polishing compositions containing silica particles are employed, and silica sol, also known as colloidal silica, is widely used as the main abrasive component. Depending on the manufacturing method, colloidal silica is known to be produced by thermal decomposition of silicon tetrachloride (fumed silica, etc.), deionization of alkali silicates such as water glass, and hydrolysis and condensation reactions of alkoxysilanes (generally referred to as the "sol-gel method").

[0004] Many studies have been conducted on methods for producing silica sol. For example, Patent Documents 1 and 2 disclose a method for producing silica sol by hydrolysis and condensation reactions of alkoxysilanes. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-60232 [Patent Document 2] Japanese Patent Publication No. 2019-89692 [Overview of the project] [Problems that the invention aims to solve]

[0006] Conventionally, the amount of water confined to the silica surface of silica particles contained in silica sols changes with temperature, which has resulted in insufficient suppression of the decrease in dispersion stability due to the reduction of surface hydration water and inadequate stable scratch reduction during polishing.

[0007] The silica particles contained in the silica sol obtained by the manufacturing methods disclosed in Patent Documents 1 and 2 do not take into account the water confined to the surface of the silica particles, and therefore, the reduction in dispersion stability when the temperature changes during storage or polishing, and the stable reduction of scratches during polishing, are not sufficiently suppressed.

[0008] This invention has been made in view of the above problems, and the object of this invention is to provide a silica sol and polishing composition that can suppress the decrease in dispersion stability due to the decrease in surface hydration water and the occurrence of scratches on the workpiece when used for polishing, as the amount of water confined on the surface of silica particles does not change even when the temperature is changed. Another object of this invention is to provide a polishing method, a method for manufacturing a semiconductor wafer, and a method for manufacturing a semiconductor device that are excellent in reducing scratches even under high temperature conditions. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have found that the above problem can be solved by setting the absolute value of the rate of change of the specific relaxation rate at 40°C to the specific relaxation rate at 25°C of nuclide 1H, as measured by the CPMG method using a pulsed NMR spectrometer of silica sol, to a predetermined value or less. Furthermore, the inventors have found that the transverse relaxation time at each of the above temperatures can be controlled by adjusting the ammonia concentration, water content, temperature, etc., in the reaction step of the silica sol production method, and have completed the present invention. In other words, the gist of the present invention is as follows:

[0010] One aspect of the present invention is: Regarding a silica sol that contains silica particles and has an absolute value of the rate of change of the specific relaxation rate at 40°C with respect to the specific relaxation rate at 25°C, measured by the CPMG method using a pulsed NMR apparatus, of 30% or less.

[0011] Aspect 2 of the present invention is the silica sol of Aspect 1, wherein Regarding a silica sol in which the average primary particle diameter of the silica particles contained in the silica sol, measured by the BET method, is 3 nm to 200 nm.

[0012] Aspect 3 of the present invention is the silica sol of Aspect 1 or 2, wherein Regarding a silica sol in which the average secondary particle diameter of the silica particles contained in the silica sol, measured by the DLS method, is 5 nm to 300 nm.

[0013] Aspect 4 of the present invention is the silica sol of any one of Aspects 1 to 3, wherein Regarding a silica sol in which the silica particles contained in the silica sol are amorphous.

[0014] Aspect 5 of the present invention is Regarding a method for producing a silica sol of any one of Aspects 1 to 4, the method including a step of subjecting an alkoxysilane to a hydrolysis reaction and a condensation reaction.

[0015] Aspect 6 of the present invention is the method for producing a silica sol of Aspect 5, wherein The step of subjecting the alkoxysilane to a hydrolysis reaction and a condensation reaction is a step of adding a liquid (B) containing an alkoxysilane and a liquid (C) containing an alkali catalyst to a liquid (A) containing an alkali catalyst, and subjecting the alkoxysilane to a hydrolysis reaction and a condensation reaction. Regarding the method for producing a silica sol.

[0016] Aspect 7 of the present invention is the method for producing a silica sol of Aspect 5 or 6, wherein Regarding the method for producing a silica sol, in the step of subjecting the alkoxysilane to a hydrolysis and condensation reaction, the water content in the reaction system throughout the step is 3 mol or more and 20 mol or less per 1 mol of the alkoxysilane.

[0017] Aspect 8 of the present invention is a method for producing a silica sol according to any one of Aspects 5 to 7, in the step of subjecting the alkoxysilane to hydrolysis and condensation reactions, the method for producing a silica sol, wherein the concentration of the alkali catalyst in the reaction system throughout the step is less than 1.2% by mass in 100% by mass of the total amount in the reaction system.

[0018] Aspect 9 of the present invention relates to a polishing composition containing a silica sol according to any one of Aspects 1 to 4.

[0019] Aspect 10 of the present invention relates to a polishing method of polishing using the polishing composition of Aspect 9.

[0020] Aspect 11 of the present invention relates to a method for manufacturing a semiconductor wafer including a step of polishing using the polishing composition of Aspect 9.

[0021] Aspect 12 of the present invention relates to a method for manufacturing a semiconductor device including a step of polishing using the polishing composition of Aspect 9. [[Effect of the Invention]]

[0022] The silica sol and polishing composition of the present invention can suppress a decrease in dispersion stability due to a decrease in surface hydrated water and the occurrence of scratches on the polished object when used for polishing, because the amount of water constrained on the surface of the silica particles does not change even when the temperature is changed. [[Modes for Carrying Out the Invention]]

[0023] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be variously modified and implemented within the scope of the gist. In 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.

[0024] [[Silica Sol]] The silica sol according to an embodiment of the present invention is a silica sol comprising silica particles, wherein the absolute value of the rate of change of the specific relaxation rate at 40°C relative to the specific relaxation rate at 25°C, as measured by the CPMG method using a pulsed NMR spectrometer, is 30% or less.

[0025] The silica sol according to the embodiment of the present invention is one in which silica particles are dispersed in any dispersion medium. Furthermore, the absolute value of the rate of change of the specific relaxation rate at 40°C compared to the specific relaxation rate at 25°C, as measured by the CPMG method using a pulsed NMR spectrometer, is 30% or less, preferably 25% or less, more preferably 20% or less, and particularly preferably 10% or less. When the absolute value of the rate of change of the specific relaxation rate from 25°C to 40°C is below the upper limit, the amount of water constrained on the surface of the silica particles does not change even when the temperature is changed, resulting in excellent dispersion stability. Alternatively, the absolute value of the rate of change may be 0, meaning that the specific relaxation rate at 40°C and the specific relaxation rate at 25°C are exactly the same. The rate of change can be calculated using the following formula (1). Rate of change = (Specific relaxation rate at 40°C - Specific relaxation rate at 25°C) ÷ Specific relaxation rate at 25°C × 100 ... (1)

[0026] In this specification, the specific relaxation rate of silica sol at each temperature is calculated from the transverse relaxation time T2 measured by the CPMG method using a pulsed NMR spectrometer. Specifically, the measurement and calculation are performed under the conditions shown below.

[0027] Pulsed NMR is a technique for observing the resonance phenomenon of nuclear spins in atomic nuclei placed in a static magnetic field. Pulsed NMR is a method that observes the magnetization decay (or recovery) curve during the process when hydrogen nucleus spins, excited by electromagnetic pulses of several microseconds, return to a stable state. It is also called TD-NMR (Time Domain NMR). The relaxation time can be obtained by analyzing the magnetization decay curve.

[0028] The relaxation times that can be measured by pulsed NMR include longitudinal relaxation time (spin-lattice relaxation time, T1) and transverse relaxation time (spin-spin relaxation time, T2). In this invention, the transverse relaxation time is used.

[0029] Methods for measuring T2 include the solid echo method, which is suitable for measuring crystals and glassy states; the Hahn echo method, which is suitable for measuring elastomers; and the CPMG method (Carr-Purcell-Meiboom-Gill method), which is suitable for measuring liquids. In this invention, the CPMG method is used.

[0030] The CPMG method is a method in which the pulse sequence is described as "90° pulse - (τ - 180° pulse - τ - echo -)n". In this pulse sequence, a 90° pulse is applied, followed by a 180° pulse after τs, and the echo that appears after τs is observed. Then, the pulse sequence in parentheses is repeated n times. As a result, an echo is obtained every (2τs + 180° pulse width).

[0031] By analyzing the magnetization decay curve M(t), which plots the time immediately after applying a 90° pulse to the X-axis as 0, the time t at which the echo was obtained on the X-axis, and the echo intensity on the Y-axis, the transverse relaxation time can be obtained. Transverse relaxation time is related to molecular mobility; a smaller value indicates lower mobility.

[0032] The specific relaxation rate can be calculated from the lateral relaxation time T2 of the obtained sample and the lateral relaxation time T2 of ultrapure water using the following equation (2). The specific relaxation rate is an indicator of the water affinity of the silica particle surface; a larger value indicates a higher water affinity. Specific relaxation rate = {(1 / T2 of silica particle dispersion) / (1 / T2 of ultrapure water)} - 1 ... (2) Using the method described above, the specific relaxation rate at temperatures of 25°C and 40°C is calculated, and by applying equation (1), the rate of change and its absolute value from 25°C to 40°C can be obtained.

[0033] The average primary particle diameter of the silica particles contained in the silica sol according to the embodiment of the present invention is preferably 3 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more. When the average primary particle diameter of the silica particles is above the lower limit, the removal of particles and the like during cleaning after polishing is excellent, and the dispersion stability of the silica sol is excellent. Furthermore, the average primary particle diameter of the silica particles is preferably 200 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. When the average primary particle diameter of the silica particles is below the upper limit, the surface roughness and scratches of the object to be polished, such as a silicon wafer, during polishing can be reduced, and the sedimentation of silica particles can be suppressed. The average primary particle diameter of the silica particles contained in the silica sol according to the embodiment of the present invention is preferably, for example, 3 nm to 200 nm.

[0034] The average primary particle diameter of silica particles is measured by the BET method. Specifically, the specific surface area of ​​silica particles is measured using an automatic specific surface area measuring device, and the average primary particle diameter is calculated using the following formula (3). Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 )) ··· (3)

[0035] The average primary particle size of silica particles can be set to a desired range depending on the manufacturing conditions of the silica particles.

[0036] The average secondary particle diameter of the silica particles contained in the silica sol according to the embodiment of the present invention is preferably 5 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. When the average secondary particle diameter of the silica particles is above the lower limit, the removal of particles and the like during cleaning after polishing is excellent, and the dispersion stability of the silica sol is excellent. Furthermore, the average secondary particle diameter of the silica particles is preferably 300 nm or less, more preferably 250 nm or less, and even more preferably 200 nm or less. Furthermore, when the average secondary particle diameter of the silica particles is below the upper limit, the surface roughness and scratches of the workpiece, such as silicon wafers, during polishing can be reduced, the removal of particles and the like during cleaning after polishing is excellent, and the sedimentation of silica particles can be suppressed. The average secondary particle diameter of the silica particles contained in the silica sol according to the embodiment of the present invention is preferably, for example, 5 nm to 300 nm.

[0037] The average secondary particle size of silica particles is measured by the DLS method. Specifically, it is measured using a dynamic light scattering particle size analyzer.

[0038] The average secondary particle size of silica particles can be set to a desired range depending on the manufacturing conditions of the silica particles.

[0039] The CV value of the average secondary particle diameter of the silica particles contained in the silica sol according to the embodiment of the present invention is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. When the CV value of the silica particles is above the lower limit, the polishing rate for the workpiece, such as silicon wafers, is excellent, and the productivity of the workpiece, such as silicon wafers, is excellent. Furthermore, when the CV value of the average secondary particle diameter of the silica particles according to the embodiment of the present invention is preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less. When the CV value of the silica particles is below the upper limit, the surface roughness and scratches of the workpiece, such as silicon wafers, during polishing can be reduced, and the removal of particles, etc., during cleaning after polishing is excellent.

[0040] The cv value of silica particles is calculated by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle diameter analyzer and then using the following formula (4). cv value = (standard deviation (nm) / mean secondary particle diameter (nm)) × 100 ... (4)

[0041] In the embodiments of the present invention, the association ratio of silica particles is preferably 1.0 or higher, and more preferably 1.1 or higher. When the association ratio of silica particles is above the lower limit, the polishing rate for the workpiece, such as a silicon wafer, is excellent, and the productivity of the workpiece, such as a silicon wafer, is excellent. Furthermore, the association ratio of silica particles is preferably 4.0 or lower, and more preferably 3.0 or lower. When the association ratio of silica particles is below the upper limit, the surface roughness and scratches of the workpiece, such as a silicon wafer, during polishing can be reduced, and the aggregation of silica particles can be suppressed.

[0042] The association ratio of silica particles contained in the silica sol according to the embodiment of the present invention is calculated using the following formula (5) from the average primary particle diameter measured by the measurement method described above and the average secondary particle diameter measured by the measurement method described above. Association ratio = average secondary particle diameter / average primary particle diameter (5)

[0043] The silica particles contained in the silica sol according to the embodiment of the present invention preferably have a metal impurity content of 5 ppm by mass or less, and more preferably 1 ppm by mass or less. When the metal impurity content is below the upper limit, the influence on the polishing rate due to changes in the chemical properties (acidity, etc.) of the surface silanol groups and changes in the steric environment of the silica particle surface (ease of aggregation of silica particles, etc.) due to coordination interactions between the acidic surface silanol groups and the metal impurities is reduced.

[0044] In this specification, the metal impurity content of silica particles is a value measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, the mixture is heated, dissolved, and evaporated, and pure water is added to the remaining sulfuric acid droplets to create a test solution with a total volume of exactly 10 g. This test solution is then measured using an inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the sum of the content of these metals is defined as the metal impurity content.

[0045] The metal impurity content of silica particles can be reduced to 5 ppm by mass or less by performing hydrolysis and condensation reactions using alkoxysilane as the main raw material to obtain silica particles. In methods involving the deionization of alkali silicates such as water glass, residual sodium and other substances from the raw materials remain, making it extremely difficult to reduce the metal impurity content of silica particles to 5 ppm by mass or less.

[0046] The silica particles contained in the silica sol according to the embodiment of the present invention have a low content of metal impurities and excellent mechanical strength and storage stability, therefore it is preferable that the main component be an alkoxysilane condensate, more preferably a tetraalkoxysilane condensate, and even more preferably a tetramethoxysilane condensate. The main component refers to a component that accounts for 50% or more by mass of 100% by mass of all components constituting the silica particles. To obtain silica particles mainly composed of alkoxysilane condensates, it is preferable to use alkoxysilane as the main raw material. To obtain silica particles mainly composed of tetraalkoxysilane condensates, it is preferable to use tetraalkoxysilane as the main raw material. To obtain silica particles mainly composed of tetramethoxysilane condensates, it is preferable to use tetramethoxysilane as the main raw material.

[0047] In the embodiment of the present invention, the silica particles contained in the silica sol are preferably amorphous. Because the silica particles are amorphous, a suitable amount of silanol groups are present on the surface of the silica particles. During the polishing process, a chemical reaction occurs between the silica particles and the workpiece via the silanol groups, resulting in smooth polishing.

[0048] The amorphous nature of silica particles can be confirmed by the halo pattern observed in wide-angle X-ray scattering measurements.

[0049] The silica particles contained in the silica sol according to the embodiment of the present invention preferably have a surface silanol group concentration of 0.2% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1.0% by mass or more, as measured by the Sears method. When the surface silanol group concentration is above the lower limit, the silica particles have appropriate surface resilience, and the dispersion stability of the silica sol is excellent. Furthermore, there is no particular upper limit to the surface silanol group concentration of the silica particles, but it is preferably 4% by mass or less, more preferably 3% by mass or less, and particularly preferably 2% by mass or less. When the surface silanol group concentration of the silica particles is below the upper limit, the removal from the workpiece during cleaning when used for polishing is excellent.

[0050] The surface silanol group concentration of silica particles is measured by the Sears method. Specifically, it is measured and calculated under the conditions shown below. Take a silica sol equivalent to 1.5 g of silica particles and add pure water to make a volume of 90 mL. At 25°C, add 0.1 mol / L hydrochloric acid solution until the pH reaches 3.6, add 30 g of sodium chloride, and gradually add pure water to completely dissolve the sodium chloride. Finally, add pure water until the total volume of the test solution is 150 mL to obtain the test solution. The obtained test solution is placed in an automatic titrator, and a 0.1 mol / L sodium hydroxide solution is added dropwise to measure the titration volume A (mL) of the 0.1 mol / L sodium hydroxide solution required to change the pH from 4.0 to 9.0.

[0051] Using the following formula (6), calculate the amount of 0.1 mol / L sodium hydroxide solution (V) consumed to change the pH of 1.5 g of silica particles from 4.0 to 9.0, and use the following formula (7) to calculate the surface silanol group concentration C of the silica particles. OH Calculate (wt%). V = (A × f × 100 × 1.5) / (W × C) SiO2 ) ··· (6) A: The amount of 0.1 mol / L sodium hydroxide solution required to change the pH of 1.5 g of silica particles from 4.0 to 9.0 (mL) f: Titer of the 0.1 mol / L sodium hydroxide solution used C SiO2 Concentration of silica particles in silica sol (mass%) W: Amount of silica sol collected (g) C OH =(B×M OH ) / m×100 ··· (7) The amount of sodium hydroxide (mol) required to change the pH of 1.5g of silica particles from 4.0 to 9.0, calculated from B:V. M OH : Molar mass of OH (17g / mol) m: Silica particle quantity (1.5g)

[0052] Examples of dispersion media in silica sols according to embodiments of the present invention include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media in silica sols may be used individually or in combination of two or more. Among these dispersion media in silica sols, water and alcohol are preferred, and water is more preferred, due to their excellent affinity with silica particles.

[0053] In the embodiments of the present invention, the silica particle content in the silica sol is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the total amount of silica sol. When the silica particle content in the silica sol is above the lower limit, the polishing rate for the workpiece, such as silicon wafers, is excellent. Furthermore, the silica particle content in the silica sol is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the silica particle content in the silica sol is below the upper limit, aggregation of silica particles in the silica sol and polishing composition can be suppressed, and the dispersion stability of the silica sol and polishing composition is excellent.

[0054] In the embodiments of the present invention, the content of the dispersion medium in the silica sol is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the total amount of silica sol. When the content of the dispersion medium in the silica sol is above the lower limit, aggregation of silica particles in the silica sol and polishing composition can be suppressed, and the dispersion stability of the silica sol and polishing composition is excellent. Furthermore, the content of the dispersion medium in the silica sol is preferably 97% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less. When the content of the dispersion medium in the silica sol is below the upper limit, the polishing rate for the workpiece, such as silicon wafers, is excellent.

[0055] In addition to silica particles and a dispersion medium, the silica sol according to the embodiment of the present invention may optionally contain other components such as oxidizing agents, preservatives, fungicides, pH adjusters, pH buffers, surfactants, chelating agents, and antimicrobial biocides, to the extent that it does not impair its performance. In particular, since silica sol has excellent storage stability, it is preferable to include an antimicrobial biocide in the silica sol.

[0056] Examples of antimicrobial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, and sodium chlorite. These antimicrobial biocides may be used individually or in combination of two or more. Among these antimicrobial biocides, hydrogen peroxide is preferred due to its excellent affinity for silica sol. Antimicrobial biocides include what are commonly known as disinfectants.

[0057] The content of the antimicrobial biocide in the silica sol is preferably 0.0001% by mass or more, and more preferably 0.001% by mass or more, based on 100% by mass of the total silica sol. When the content of the antimicrobial biocide in the silica sol is above the lower limit, the silica sol exhibits excellent storage stability. Furthermore, the content of the antimicrobial biocide in the silica sol is preferably 10% by mass or less, and more preferably 1% by mass or less. When the content of the antimicrobial biocide in the silica sol is below the upper limit, the original performance of the silica sol is not impaired.

[0058] The pH of the silica sol according to the embodiment of the present invention is preferably 6.0 or higher, and more preferably 6.5 or higher. When the pH of the silica sol is above the lower limit, it exhibits excellent dispersion stability and can suppress the aggregation of silica particles. Furthermore, the pH of the silica sol is preferably 8.0 or lower, and more preferably 7.8 or lower. When the pH of the silica sol is below the upper limit, it prevents the dissolution of silica particles and exhibits excellent long-term storage stability. The pH of silica sol can be set to a desired range by adding a pH adjusting agent.

[0059] <Method for producing silica sol> A method for producing silica sol according to an embodiment of the present invention includes a step of hydrolyzing and condensing an alkoxysilane. In this production method, by controlling various production conditions, silica particles can be obtained in which the rate of change of relaxation time measured by the CPMG method using a pulsed NMR spectrometer is 30% or less at temperatures between 25°C and 40°C.

[0060] In the embodiment of the present invention, a preferred method for producing silica sol involves adding a liquid (B) containing alkoxysilane and a liquid (C) containing an alkaline catalyst to a liquid (A) containing an alkaline catalyst, and then hydrolyzing and condensing the alkoxysilane. This method is preferable because it allows for easy control of the hydrolysis and condensation reactions, increases the reaction rates of the hydrolysis and condensation reactions, prevents gelation of the silica particle dispersion, and yields silica particles of uniform size.

[0061] By adjusting the manufacturing conditions of the silica sol, such as pH, reaction temperature, reaction time, catalyst concentration, and raw material supply rate during the reaction, and by applying post-treatments such as pressurized heat treatment to the manufactured silica particles, the rate of change of the relaxation time measured by the CPMG method using a pulsed NMR spectrometer for silica particles, from 25°C to 40°C, can be set to a desired range.

[0062] Liquid (A) contains an alkaline catalyst because it can increase the reaction rates of the hydrolysis and condensation reactions of alkoxysilanes.

[0063] Examples of alkaline catalysts in liquid (A) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkaline catalysts may be used individually or in combination of two or more. Among these alkaline catalysts, ammonia is preferred because it exhibits excellent catalytic activity, allows for easy control of particle shape, suppresses the inclusion of metal impurities, and has high volatility, resulting in excellent removal after hydrolysis and condensation reactions.

[0064] Liquid (A) preferably contains water.

[0065] Since solution (A) exhibits excellent dispersibility in the reaction solution of alkoxysilane, it is preferable that it contains a solvent other than water. Other solvents in liquid (A) include, for example, alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used individually or in combination of two or more. Among these solvents, methanol and ethanol are preferred, and methanol is more preferred, because they readily dissolve alkoxysilanes, produce the same by-products as those used in the hydrolysis and condensation reactions, and offer excellent manufacturing convenience.

[0066] The concentration of the alkaline catalyst in liquid (A) is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, based on 100% by mass of liquid (A). When the concentration of the alkaline catalyst in liquid (A) is above the lower limit, the reaction on the particle surface proceeds appropriately, allowing for the formation of a stable surface state. Furthermore, the concentration of the alkaline catalyst in liquid (A) is preferably 2.0% by mass or less, and more preferably 1.5% by mass or less. When the concentration of the alkaline catalyst in liquid (A) is below the upper limit, the balance between hydrolysis and dehydration condensation is within an appropriate range, and the stability of water confined on the surface can be enhanced.

[0067] The concentration of water in liquid (A) is preferably 3% by mass or more, and more preferably 5% by mass or more, out of 100% by mass of liquid (A). When the concentration of water in liquid (A) is above the lower limit, it is easier to control the hydrolysis reaction rate of alkoxysilane. Furthermore, the concentration of water in liquid (A) is preferably 90% by mass or less, and more preferably 50% by mass or less. When the concentration of water in liquid (A) is below the upper limit, the reaction balance between the hydrolysis reaction and the condensation reaction is good, making it easier to control the particle shape, and the concentration of silicic acid produced by the hydrolysis of alkoxysilane increases, thus increasing the concentration of silanol groups contained in the silica particles.

[0068] The concentration of solvents other than water in solution (A) is preferably the remainder of the water and alkaline catalyst.

[0069] Liquid (B) contains alkoxysilane.

[0070] Among the alkoxysilanes in liquid (B), tetraalkoxysilanes are preferred, such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used individually or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred, and tetramethoxysilane is more preferred, because they undergo a rapid hydrolysis reaction, leave little unreacted residue, have excellent productivity, and allow for easy acquisition of a stable silica sol.

[0071] As raw materials for silica particles, raw materials other than alkoxysilane, such as low condensates of alkoxysilane, may be used. However, due to their excellent reactivity, it is preferable that alkoxysilane accounts for 50% or more by mass and other raw materials account for 50% or less by mass of the total raw materials constituting the silica particles, and it is more preferable that alkoxysilane accounts for 90% or more by mass and other raw materials account for 10% or less by mass.

[0072] Solution (B) may contain only alkoxysilane without a solvent, but it is preferable to include a solvent because it provides excellent dispersibility of the alkoxysilane in the reaction solution. Examples of solvents in liquid (B) include alcohols such as methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used individually or in combination of two or more. Among these solvents, monohydric alcohols are preferred, methanol and ethanol are more preferred, and methanol is even more preferred, because the by-products used in the hydrolysis and condensation reactions are the same and offer excellent manufacturing convenience.

[0073] The concentration of alkoxysilane in solution (B) is preferably 60% by mass or more, and more preferably 70% by mass or more, out of 100% by mass of solution (B). If the concentration of alkoxysilane in solution (B) is above the lower limit, the reaction solution tends to become more homogeneous. Furthermore, the concentration of alkoxysilane in solution (B) is preferably 95% by mass or less, and more preferably 90% by mass or less. If the concentration of alkoxysilane in solution (B) is below the upper limit, the formation of gel-like substances can be suppressed.

[0074] The concentration of the solvent in solution (B) is preferably 5% by mass or more, and more preferably 10% by mass or more, out of 100% by mass of solution (B). If the concentration of the solvent in solution (B) is above the lower limit, the formation of gel-like substances can be suppressed. Furthermore, the concentration of the solvent in solution (B) is preferably 40% by mass or less, and more preferably 30% by mass or less. If the concentration of the solvent in solution (B) is below the upper limit, the reaction solution tends to become more homogeneous.

[0075] The addition rate of solution (B) is preferably 15 g silica / hour / kg solution or higher, and more preferably 50 g silica / hour / kg solution or higher. If the addition rate of solution (B) is above the lower limit, the reaction time is shortened, productivity is excellent, and the generation of fine particles can be suppressed. Furthermore, the concentration of silicic acid produced by the hydrolysis of alkoxysilane increases, so the concentration of silanol groups contained in silica particles increases. In addition, the addition rate of solution (B) is preferably 150 g silica / hour / kg solution or lower, and more preferably 130 g silica / hour / kg solution or lower. If the addition rate of solution (B) is below the upper limit, the dispersibility of alkoxysilane in the reaction solution is excellent, and the generation of fine particles can be suppressed. Silica / hour / kg solution refers to the value obtained by converting the mass of alkoxysilane added per hour to 1 kg of solution (A) into the mass of silica.

[0076] Liquid (C) preferably contains an alkaline catalyst and further contains water.

[0077] Examples of alkaline catalysts contained in liquid (C) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkaline catalysts may be used individually or in combination of two or more. Among these alkaline catalysts, ammonia is preferred because it exhibits excellent catalytic activity, allows for easy control of particle shape, suppresses the inclusion of metal impurities, and has high volatility, resulting in excellent removal after hydrolysis and condensation reactions.

[0078] Examples of solvents other than water in liquid (C) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. The solvents other than water may be used individually or in combination of two or more. Among the solvents in liquid (C), water alone or a combination of water and alcohol is preferred, and water alone is more preferred, because the by-products used in the hydrolysis and condensation reactions are the same, offering excellent manufacturing convenience.

[0079] The concentration of the alkaline catalyst in liquid (C) is preferably 0.05% by mass or higher, and more preferably 0.1% by mass or higher. When the concentration of the alkaline catalyst in liquid (C) is above the lower limit, it is easy to adjust the concentration of the alkaline catalyst in the reaction solution from the start to the end of the reaction. Furthermore, the concentration of the alkaline catalyst in liquid (C) is preferably 10% by mass or less, and more preferably 6% by mass or less. From the viewpoint of minimizing fluctuations in the concentration of the alkaline catalyst in the reaction solution in liquid (C), the concentration of water in liquid (C) is preferably 99.5% by mass or less, and more preferably 99% by mass or less. When the concentration of water in liquid (C) is below the upper limit, it is easy to adjust the concentration of the alkaline catalyst in the reaction solution from the start to the end of the reaction. Furthermore, the concentration of water in liquid (C) is preferably 90% by mass or higher, and more preferably 94% by mass or higher. When the concentration of water in liquid (C) is above the lower limit, fluctuations in the concentration of the alkaline catalyst in the reaction solution can be minimized.

[0080] The concentration of solvents other than water in liquid (C) is preferably the same as the concentration of the remainder of the water and alkaline catalyst.

[0081] It is preferable to add liquid (B) and liquid (C) into liquid (A). Adding liquid (B) and liquid (C) into liquid (A) improves the mixability of each component in the reaction solution, suppresses abnormal reactions in the air, and makes it easier to control the particle shape, especially when using a highly volatile alkaline catalyst such as ammonia and when proceeding with hydrolysis and condensation reactions at high reaction temperatures. Adding into the liquid means adding below the liquid level, and by positioning the supply outlets for liquid (B) and liquid (C) below the liquid level of liquid (A), liquid (B) and liquid (C) can be added into liquid (A).

[0082] The timing of adding liquids (B) and (C) to liquid (A) may be the same or alternate, but it is preferable that the timing be the same because it minimizes variations in the reaction composition and avoids complicated procedures.

[0083] In the step of hydrolyzing and condensing the alkoxysilane, the pH is preferably 8.0 or higher, more preferably 8.2 or higher, and even more preferably 8.5 or higher. When the pH in the above step is above the lower limit, the reaction rate of the hydrolysis and condensation reactions is excellent, and the aggregation of silica particles can be suppressed. Furthermore, the pH in the above step is preferably 14 or lower, more preferably 13 or lower, and even more preferably 12 or lower. When the pH in the above step is below the upper limit, the shape of the silica particles is easier to control, and the smoothness of the silica particle surface is excellent.

[0084] The temperature in the step of hydrolyzing and condensing the alkoxysilane is preferably 0°C or higher, more preferably 20°C or higher, and even more preferably 40°C or higher. If the temperature in the above step is above the lower limit, the hydrolysis and condensation reactions are promoted, and a silica skeleton with high strength can be formed. Furthermore, the temperature in the above step is preferably 80°C or lower, more preferably 70°C or lower, and even more preferably 60°C or lower. If the temperature in the above step is below the upper limit, excessive condensation of silanol groups can be suppressed, and the stability of water confined on the silica particle surface can be increased.

[0085] In the process of hydrolyzing and condensing alkoxysilane, the water content in the reaction system throughout the entire process is preferably 3 moles or more per mole of alkoxysilane, more preferably 4 moles or more, and even more preferably 5 moles or more. When the water content per mole of alkoxysilane in the reaction system is above the lower limit, the hydrolysis of the alkoxysilane is promoted, and the reaction on the particle surface proceeds appropriately, so that a stable surface state can be formed. Furthermore, the water content in the reaction system throughout the entire process is preferably 20 moles or less per mole of alkoxysilane, more preferably 18 moles or less, and even more preferably 16 moles or less. When the water content per mole of alkoxysilane in the reaction system is below the upper limit, the balance between hydrolysis and dehydration condensation on the silica surface is within an appropriate range, and the stability of water confined on the surface can be increased. The water content in the reaction system for hydrolysis and condensation reactions includes the water consumed during the reaction, and can be adjusted to the desired range by adding water during the reaction. In the process of hydrolyzing and condensing alkoxysilane, the water content in the reaction system throughout the entire process is preferably, for example, 3 moles or more and 20 moles or less per mole of alkoxysilane.

[0086] In the process of hydrolyzing and condensing alkoxysilane, the concentration of the alkaline catalyst in the reaction system is preferably maintained at 0.05% by mass or more, and more preferably at 0.1% by mass or more, out of 100% by mass of the total amount in the reaction system throughout the entire process. When the concentration of the alkaline catalyst in the reaction system is above the lower limit, the hydrolysis of the alkoxysilane is promoted, and the reaction on the particle surface proceeds appropriately, allowing for the formation of a stable surface state. Furthermore, the concentration of the alkaline catalyst in the reaction system is preferably maintained at less than 1.2% by mass, and more preferably at less than 1.1% by mass. When the concentration of the alkaline catalyst in the reaction system is below the upper limit, the balance between hydrolysis and dehydration condensation is within an appropriate range, and the stability of water confined on the surface can be enhanced.

[0087] The method for producing silica sol according to the embodiment of the present invention can remove unnecessary components and add necessary components, and therefore, it is preferable to further include a step of concentrating the silica particle dispersion and replacing the dispersion medium by adding a dispersion medium.

[0088] In the above dispersion medium replacement step, the concentration of the silica sol and the addition of the dispersion medium may be performed in either order, or simultaneously. Furthermore, it is not necessary for all of the dispersion medium in the silica sol to be replaced; it is sufficient for a portion of the dispersion medium to be removed, the silica sol to be concentrated, and the liquid that will serve as the dispersion medium to be added.

[0089] The method for concentrating a dispersion of silica particles is not particularly limited and includes methods such as heat concentration and membrane concentration. Among these, heat concentration is preferred from the viewpoint of promoting surface condensation of silica particles. To concentrate a dispersion of silica particles by a heating concentration method, the silica sol can be heated and concentrated under normal pressure or under reduced pressure.

[0090] For concentrating silica sol by membrane concentration, membrane separation by ultrafiltration is preferred. Here, the primary purpose of ultrafiltration is to remove unwanted components, such as intermediate products. The molecular weight cutoff of the ultrafiltration membrane used here is selected to match the intermediate products in the dispersion, so that these intermediate products can be filtered and separated and removed. Materials for ultrafiltration membranes include polysulfone, polyacrylonitrile, sintered metal, ceramic, and carbon. Examples of ultrafiltration membrane shapes include spiral, tubular, and hollow fiber types.

[0091] Examples of dispersion media to be added to silica sol include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. These dispersion media may be used individually or in combination of two or more. Among these dispersion media, water and alcohol are preferred, with water being more preferred, due to their excellent affinity with silica particles.

[0092] <Polishing composition> The polishing composition according to an embodiment of the present invention includes a silica sol according to an embodiment of the present invention. The polishing composition according to the embodiment of the present invention preferably contains a water-soluble polymer in addition to the silica sol according to the embodiment of the present invention.

[0093] Water-soluble polymers enhance the wettability of the polishing composition to the workpiece, such as silicon wafers. Preferably, the water-soluble polymer has functional groups with high water affinity. These water-affinity functional groups have a high affinity for the surface silanol groups of silica particles, resulting in a more stable dispersion of silica particles and water-soluble polymers in close proximity within the polishing composition. Therefore, during polishing of workpieces such as silicon wafers, the effects of silica particles and water-soluble polymers function synergistically.

[0094] Examples of water-soluble polymers include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0095] Examples of cellulose derivatives include hydroxyethylcellulose, hydrolyzed hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, and carboxymethylcellulose.

[0096] Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone.

[0097] Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0098] These water-soluble polymers may be used individually or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethylcellulose is more preferred, because they have a high affinity for the silanol groups on the surface of silica particles and act synergistically to provide good hydrophilicity to the surface of the object to be polished.

[0099] The mass-average molecular weight of the water-soluble polymer is preferably 1,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more. When the mass-average molecular weight of the water-soluble polymer is above the lower limit, the hydrophilicity of the polishing composition is improved. Furthermore, the mass-average molecular weight of the water-soluble polymer is more preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,000,000 or less. When the mass-average molecular weight of the water-soluble polymer is below the upper limit, it exhibits excellent affinity with silica sol and provides excellent polishing rate for materials to be polished, such as silicon wafers.

[0100] The mass-average molecular weight of water-soluble polymers is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, based on polyethylene oxide.

[0101] The content of water-soluble polymers in the abrasive composition is preferably 0.02% by mass or more, and more preferably 0.05% by mass or more, based on 100% by mass of the total amount of the abrasive composition. When the content of water-soluble polymers in the abrasive composition is above the lower limit, the hydrophilicity of the abrasive composition is improved. Furthermore, the content of water-soluble polymers in the abrasive composition is preferably 10% by mass or less, and more preferably 5% by mass or less. When the content of water-soluble polymers in the abrasive composition is below the upper limit, aggregation of silica particles during the preparation of the abrasive composition can be suppressed.

[0102] In addition to silica sol and water-soluble polymer, the polishing composition according to the embodiment of the present invention may optionally contain other components such as basic compounds, polishing accelerators, surfactants, hydrophilic compounds, preservatives, fungicides, pH adjusters, pH buffers, surfactants, chelating agents, and antimicrobial biocides, to the extent that it does not impair its performance. In particular, it is preferable to include a basic compound in the polishing composition because it allows for chemical polishing (chemical etching) by applying a chemical action to the surface of the workpiece, such as a silicon wafer, and the polishing speed of the workpiece, such as a silicon wafer, can be improved due to the synergistic effect with the silanol groups on the surface of the silica particles.

[0103] Examples of basic compounds include organic basic compounds, alkali metal hydroxides, alkali metal bicarbonates, alkali metal carbonates, and ammonia. These basic compounds may be used individually or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium bicarbonate, and ammonium carbonate are preferred due to their high water solubility and excellent affinity with silica particles and water-soluble polymers. Ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferred, and ammonia is even more preferred.

[0104] The content of basic compounds in the polishing composition is preferably 0.001% by mass or more, and more preferably 0.01% by mass or more, based on 100% by mass of the total amount of the polishing composition. When the content of basic compounds in the polishing composition is 0.001% by mass or more, the polishing speed of the workpiece, such as silicon wafers, can be improved. Furthermore, the content of basic compounds in the polishing composition is preferably 5% by mass or less, and more preferably 3% by mass or less. When the content of basic compounds in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0105] The pH of the abrasive composition is preferably 8.0 or higher, and more preferably 9.0 or higher. When the pH of the abrasive composition is above the lower limit, aggregation of silica particles in the abrasive composition can be suppressed, and the dispersion stability of the abrasive composition is excellent. Furthermore, the pH of the abrasive composition is preferably 12.0 or lower, and more preferably 11.0 or lower. When the pH of the abrasive composition is below the upper limit, dissolution of silica particles can be suppressed, and the stability of the abrasive composition is excellent. The pH of the abrasive composition can be set to a desired range by adding a pH adjusting agent.

[0106] The polishing composition can be obtained by mixing silica sol, a water-soluble polymer, and other components as needed according to the present invention. However, considering storage and transportation, it may be prepared at a high concentration first and then diluted with water or the like immediately before polishing.

[0107] <Polishing method> A polishing method according to an embodiment of the present invention is a method of polishing using a polishing composition containing a silica sol according to an embodiment of the present invention. It is preferable to use the polishing composition described above. Specific polishing methods include, for example, pressing the surface of a silicon wafer against a polishing pad, dropping a polishing composition according to the embodiment of the present invention onto the polishing pad, and polishing the surface of the silicon wafer.

[0108] <Manufacturing method for semiconductor wafers> A method for manufacturing a semiconductor wafer according to an embodiment of the present invention includes a step of polishing using a polishing composition according to an embodiment of the present invention. The specific polishing composition and polishing method are as described above. Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

[0109] <Manufacturing methods for semiconductor devices> A method for manufacturing a semiconductor device according to an embodiment of the present invention includes a step of polishing using a polishing composition according to an embodiment of the present invention. The specific polishing composition and polishing method are as described above.

[0110] Other materials that can be polished include metals such as Si, Cu, W, Ti, Cr, Co, Zr, Hf, Mo, Ta, Ru, Au, Pt, Ag, Al, and Ni; metal compounds such as oxides, nitrides, and silicides of the aforementioned metals; and intermetallic compounds. Among these materials that can be polished, this product can be suitably used for metals and metal oxides, and is particularly suitably used for metal oxides.

[0111] <Uses of silica sol> The silica sol according to the embodiment of the present invention can be suitably used for polishing applications, for example, polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used in photomasks and liquid crystals, polishing magnetic disk substrates, etc., and can be used particularly suitably for polishing silicon wafers and chemical mechanical polishing. [Examples]

[0112] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples without departing from its essence.

[0113] <Measurement method> (Specific relaxation rates of nuclide 1H at each temperature) Dispersions of silica particles and ultrapure water obtained in the examples and comparative examples were measured using a pulsed NMR spectrometer (Bruker, minispec mq20) to obtain magnetization decay curves. The CPMG method was used for measurement. Measurements were performed at temperatures of 25°C and 40°C. Other measurement conditions are shown below. • 90°-180° pulse interval: 0.5ms • Repeat waiting time: 10s • Total number of times: 8 • Number of data points: 6400 Analysis method: The relaxation time T2 was calculated using analysis software (TDNMR-A, Bruker). The specific relaxation rate was calculated from the obtained relaxation time T2 value using the following equation (2). Specific relaxation rate = {(1 / T2 of silica particle dispersion) / (1 / T2 of ultrapure water)} - 1 ... (2)

[0114] (Average primary particle size) The silica sols obtained in the examples and comparative examples were dried at 150°C, and the specific surface area of ​​the silica particles was measured using the automatic specific surface area analyzer "BELSORP-MR1" (model name, Microtrac-Bel Corporation). The density was then calculated to be 2.2 g / cm³ using the following formula (3).3 and the average primary particle diameter was calculated. Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) × density (g / cm 3 )) ··· (3)

[0115] (Average secondary particle diameter) The average secondary particle diameter of the silica particles in the silica sols obtained in the examples and comparative examples was measured using a dynamic light scattering particle size measuring device "Zetasizer Nano ZS" (model name, manufactured by Malvern).

[0116] (Concentration of surface silanol groups (SiOH groups)) An amount corresponding to 1.5 g of silica particles in the silica sols obtained in the examples and comparative examples was collected in a 200 mL tall beaker, and pure water was added to make the liquid volume 90 mL. In an environment at 25 °C, a pH electrode was inserted into the tall beaker, and the test solution was stirred for 5 minutes using a magnetic stirrer. While continuing to stir with the magnetic stirrer, a 0.1 mol / L hydrochloric acid aqueous solution was added until the pH reached 3.6. The pH electrode was removed from the tall beaker, and while continuing to stir with the magnetic stirrer, 30 g of sodium chloride was added, and sodium chloride was completely dissolved while gradually adding pure water. Finally, pure water was added until the total volume of the test solution reached 150 mL, and the test solution was stirred for 5 minutes using a magnetic stirrer to obtain a test solution.

[0117] The tall beaker containing the obtained test solution was set in an automatic titrator "COM-1600" (manufactured by Hiranuma Sangyo Co., Ltd.), and the pH electrode and burette attached to the device were inserted into the tall beaker. While stirring the test solution with a magnetic stirrer, a 0.1 mol / L sodium hydroxide aqueous solution was dropped through the burette, and the titration volume A (mL) of the 0.1 mol / L sodium hydroxide aqueous solution required for the pH to change from 4.0 to 9.0 was measured. Using the following formula (6), calculate the amount of 0.1 mol / L sodium hydroxide solution (V) consumed to change the pH of 1.5 g of silica particles from 4.0 to 9.0, and use the following formula (7) to calculate the surface silanol group concentration C of the silica particles. OH (wt%) was calculated. V = (A × f × 100 × 1.5) / (W × C) SiO2 )···(6) A: The amount of 0.1 mol / L sodium hydroxide solution required to change the pH of 1.5 g of silica particles from 4.0 to 9.0 (mL) f: Titer of the 0.1 mol / L sodium hydroxide solution used C SiO2 Concentration of silica particles in silica sol (mass%) W: Amount of silica sol collected (g) C OH =(B×M OH ) / m×100···(7) The amount of sodium hydroxide (mol) required to change the pH of 1.5g of silica particles from 4.0 to 9.0, calculated from B:V. M OH : Molar mass of OH (17g / mol) m: Silica particle quantity (1.5g)

[0118] [Example 1] Solution (B) was prepared by mixing 75% by mass of tetramethoxysilane and 25% by mass of methanol, and solution (C) was prepared by mixing a 2.3% by mass aqueous solution of ammonia. A reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line was charged with a pre-mixed solution (A) containing methanol, pure water, and ammonia. The methanol concentration in solution (A) was 81.7% by mass, the water concentration in solution (A) was 17.5% by mass, and the ammonia concentration in solution (A) was 0.8% by mass. The water content of solution (A) was 11.9 mol per 1 mol of tetramethoxysilane injected.

[0119] The reaction solution was heated to 70°C, and 100% by mass of solution (B) and 37% by mass of solution (C) were added to 603% by mass of solution (A) at a constant rate over 180 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 4% by mass. After adding solutions (B) and (C), the water content of the solution was 14.0 mol per 1 mol of tetramethoxysilane injected, and the ammonia concentration was 0.8% by mass. The resulting silica particle dispersion was heated to remove methanol and ammonia while adjusting the liquid volume by adding pure water, thereby obtaining a silica sol with water as the dispersion medium.

[0120] [Example 2] Solution (B) was prepared by mixing 85% by mass of tetramethoxysilane and 15% by mass of methanol, and solution (C) was prepared by mixing a 0.4% by mass aqueous solution of ammonia. A reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line was charged with a pre-mixed solution (A) containing methanol, pure water, and ammonia. The methanol concentration in solution (A) was 59.8% by mass, the water concentration in solution (A) was 40% by mass, and the ammonia concentration in solution (A) was 0.2% by mass. The water content of solution (A) was 6.2 moles per mole of tetramethoxysilane injected.

[0121] The reaction solution was heated to 40°C, and 157% by mass of solution (A) was mixed with 100% by mass of solution (B) and 78% by mass of solution (C) at a constant rate over 256 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 10% by mass. After adding solutions (B) and (C), the water content of the solution was 12.0 mol per 1 mol of tetramethoxysilane injected, and the ammonia concentration was 0.2% by mass. The resulting silica particle dispersion was diluted to a silica particle content of approximately 5% by mass. Then, while adjusting the volume by adding pure water, the temperature was raised to remove methanol and ammonia, thereby obtaining a silica sol with water as the dispersion medium.

[0122] [Example 3] Solution (B) was prepared by mixing 75% by mass of tetramethoxysilane and 25% by mass of methanol, and solution (C) was prepared by mixing a 2.2% by mass aqueous solution of ammonia. A reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line was charged with a pre-mixed solution (A) containing methanol, pure water, and ammonia. The methanol concentration in solution (A) was 81.4% by mass, the water concentration in solution (A) was 17.5% by mass, and the ammonia concentration in solution (A) was 1.1% by mass. The water content of solution (A) was 3.4 moles per mole of tetramethoxysilane injected.

[0123] The reaction solution was heated to 70°C, and 100% by mass of solution (B) and 37% by mass of solution (C) were added to 603% by mass of solution (A) at a constant rate over 180 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 4% by mass. After adding solutions (B) and (C), the water content of the solution was 3.9 mol per 1 mol of tetramethoxysilane injected, and the ammonia concentration was 0.8% by mass. The resulting silica particle dispersion was heated to remove methanol and ammonia while adjusting the liquid volume by adding pure water, thereby obtaining a silica sol with water as the dispersion medium.

[0124] [Comparative Example 1] Solution (B) was prepared by mixing 85% by mass of tetramethoxysilane and 15% by mass of methanol, and solution (C) was prepared by mixing a 6.2% by mass aqueous solution of ammonia. A reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line was charged with a pre-mixed solution (A) containing methanol, pure water, and ammonia. The methanol concentration in solution (A) was 85.9% by mass, the water concentration in solution (A) was 12% by mass, and the ammonia concentration in solution (A) was 2.1% by mass. The water content of solution (A) was 1.1 moles per mole of tetramethoxysilane injected.

[0125] The reaction solution was heated to 38°C, and 100% by mass of solution (B) and 34% by mass of solution (C) were added to 89% by mass of solution (A) at a constant rate over 225 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 15% by mass. After adding solutions (B) and (C), the water content of the solution was 2.3 mol per 1 mol of tetramethoxysilane injected, and the ammonia concentration was 1.8% by mass. The resulting silica particle dispersion was heated to remove methanol and ammonia while adjusting the liquid volume by adding pure water, thereby obtaining a silica sol with water as the dispersion medium.

[0126] [Comparative Example 2] Solution (B) was prepared by mixing 85% by mass of tetramethoxysilane and 15% by mass of methanol, and solution (C) was prepared by mixing a 4.3% by mass aqueous solution of ammonia. A reaction vessel equipped with a thermometer, stirrer, feed pipe, and distillation line was charged with a pre-mixed solution (A) containing methanol, pure water, and ammonia. The methanol concentration in solution (A) was 93.8% by mass, the water concentration in solution (A) was 5% by mass, and the ammonia concentration in solution (A) was 1.2% by mass. The water content of solution (A) was 0.7 mol per 1 mol of tetramethoxysilane injected.

[0127] The reaction solution was heated to 24°C, and 100% by mass of solution (B) and 26% by mass of solution (C) were added to 143% by mass of solution (A) at a constant rate over 610 minutes to obtain a dispersion of silica particles with a silica particle content of approximately 12.5% ​​by mass. After adding solutions (B) and (C), the water content of the solution was 1.2 mol per 1 mol of tetramethoxysilane injected, and the ammonia concentration was 1.1% by mass. The resulting silica particle dispersion was heated to remove methanol and ammonia while adjusting the liquid volume by adding pure water, thereby obtaining a silica sol with water as the dispersion medium.

[0128] [Comparative Example 3] A commercially available silica sol (product name "PL-1," manufactured by Fuso Chemical Industry Co., Ltd.) was used as is.

[0129] [Comparative Example 4] A commercially available silica sol (product name "PL-2", manufactured by Fuso Chemical Industry Co., Ltd.) was used as is.

[0130] [Comparative Example 5] A commercially available silica sol (product name "PL-7," manufactured by Fuso Chemical Industry Co., Ltd.) was used as is.

[0131] Table 1 shows the manufacturing conditions for each example and comparative example, and Table 2 shows the evaluation results of the obtained aqueous dispersions of silica particles.

[0132] [Table 1]

[0133] [Table 2]

[0134] As can be seen from Tables 1 and 2, the silica sols obtained in the examples achieved a reduction in the absolute value of the rate of change in the specific relaxation rate by adjusting the component ratio of each solution, the temperature during hydrolysis and condensation reactions, the ammonia concentration of solution (A), and the water content. Compared to the silica sols obtained in the comparative examples, these silica sols show less change in the amount of water confined to the silica particle surface even when the temperature is changed, and can suppress the decrease in dispersion stability due to the decrease in surface hydration water and the occurrence of scratches during polishing. [Industrial applicability]

[0135] The silica sol of the present invention can be used, for example, for polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used in photomasks and liquid crystals, and polishing magnetic disk substrates.

Claims

1. A silica sol containing silica particles, wherein the absolute value of the rate of change of the specific relaxation rate at 40°C relative to the specific relaxation rate at 25°C, as measured by the CPMG method using a pulsed NMR device, is 30% or less.

2. The silica sol according to claim 1, wherein the average primary particle diameter of the silica particles contained in the silica sol, as measured by the BET method, is 3 nm to 200 nm.

3. The silica sol according to claim 1, wherein the average secondary particle diameter of the silica particles contained in the silica sol, as measured by DLS method, is 5 nm to 300 nm.

4. The silica sol according to claim 1, wherein the silica particles contained in the silica sol are amorphous.

5. A method for producing silica sol according to any one of claims 1 to 4, comprising the step of hydrolyzing and condensing an alkoxysilane.

6. The method for producing silica sol according to claim 5, wherein the step of hydrolyzing and condensing the alkoxysilane is to add a liquid (B) containing an alkoxysilane and a liquid (C) containing an alkaline catalyst to a liquid (A) containing an alkaline catalyst, and then hydrolyze and condense the alkoxysilane.

7. The method for producing silica sol according to claim 5, wherein, in the step of hydrolyzing and condensing the alkoxysilane, the water content in the reaction system throughout the entire process is 3 mol or more and 20 mol or less per mol of alkoxysilane.

8. The method for producing silica sol according to claim 5, wherein, in the step of hydrolyzing and condensing the alkoxysilane, the concentration of the alkaline catalyst in the reaction system throughout the entire process is less than 1.2% by mass of the total amount in the reaction system (100% by mass).

9. An abrasive composition comprising the silica sol described in any one of claims 1 to 4.

10. A polishing method comprising polishing using the polishing composition described in claim 9.

11. A method for manufacturing a semiconductor wafer, comprising the step of polishing using the polishing composition described in claim 9.

12. A method for manufacturing a semiconductor device, comprising the step of polishing using the polishing composition described in claim 9.

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