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

Abstract

This invention provides a silica sol and polishing composition that has a large amount of water trapped on the surface of silica particles, can maintain this state of trapped water even under high-temperature conditions, and exhibits high dispersion stability even when the temperature is increased. [Solution] A silica sol containing silica particles, wherein the transverse relaxation time of nuclide 1H at a temperature of 25°C, as measured by the CPMG method using a pulsed NMR spectrometer, is 400 ms or less, and the temperature dependence of the transverse relaxation time obtained by subtracting the transverse relaxation time at 25°C from the transverse relaxation time at 40°C is less than 100 ms.

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, silica particles contained in silica sol lose water trapped on their surface at high temperatures, potentially leading to a loss of dispersion stability when stored at high temperatures. Furthermore, when used for polishing, frictional heat and the temperature applied by the equipment reduce the amount of water trapped on the silica surface, preventing sufficient reduction of scratches.

[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 water confined to the surface of the silica particles, and therefore their dispersion stability and scratch reduction when the temperature rises during storage or polishing are not always sufficient.

[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 has a large amount of water confined on the surface of silica particles, can maintain this state of having a large amount of confined water even under high temperature conditions, and has high dispersion stability even when the temperature is raised. Another object of this invention is to provide a polishing method, a semiconductor wafer manufacturing method, and a semiconductor device manufacturing method 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 value obtained by subtracting the transverse relaxation time at 25°C from the transverse relaxation time at 40°C of nuclide 1H, measured by the CPMG method using a pulsed NMR spectrometer for silica sol, to a predetermined range. Furthermore, the inventors have found that the transverse relaxation times at each of the above temperatures can be controlled by adjusting the water content in the reaction step in the silica sol manufacturing method, and have completed the present invention. In other words, the gist of the present invention is as follows:

[0010] Aspect 1 of the present invention is relates to a silica sol containing silica particles, having a transverse relaxation time of nuclide 1H measured by the CPMG method using a pulsed NMR apparatus at a temperature of 25°C of 400 ms or less, and a temperature change of the transverse relaxation time obtained by subtracting the transverse relaxation time at 25°C from the transverse relaxation time at 40°C of less than 100 ms.

[0011] Aspect 2 of the present invention is, in the silica sol of Aspect 1, relates to a silica sol having an average primary particle diameter measured by the BET method of the silica particles contained in the silica sol of 5 nm or more.

[0012] Aspect 3 of the present invention is, in the silica sol of Aspect 1 or 2, relates to a silica sol having an average secondary particle diameter measured by the DLS method of the silica particles contained in the silica sol of 10 nm or more.

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

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

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

[0016] Aspect 7 of the present invention is, in the method for producing a silica sol of Aspect 5 or 6, This invention relates to a method for producing silica sol, wherein, in the step of hydrolyzing and condensing the tetraalkoxysilane, the water content in the reaction system throughout the entire process is 0.2 mol or more and 3 mol or less per mol of tetraalkoxysilane.

[0017] Aspect 8 of the present invention is This invention relates to an abrasive composition comprising one of the silica sols described in any of embodiments 1 to 4.

[0018] Aspect 9 of the present invention is This invention relates to a polishing method using the polishing composition of Embodiment 8.

[0019] Aspect 10 of the present invention is The present invention relates to a method for manufacturing a semiconductor wafer, which includes a step of polishing using the polishing composition of Embodiment 8.

[0020] Aspect 11 of the present invention is The present invention relates to a method for manufacturing a semiconductor device, which includes a step of polishing using the polishing composition of embodiment 8. [Effects of the Invention]

[0021] The silica sol and polishing composition of the present invention have a large amount of water confined on the surface of the silica particles, and can maintain this state of high water content even under high-temperature conditions, exhibiting excellent dispersion stability even at high temperatures. Furthermore, the polishing method, semiconductor wafer manufacturing method, and semiconductor device manufacturing method of the present invention exhibit excellent scratch reduction even under high-temperature conditions. [Modes for carrying out the invention]

[0022] The present invention will be described in detail below, but the present invention is not limited to the embodiments described below and can be implemented with various modifications within the scope of its gist. In this specification, when the expression "~" is used, it is used to include the numerical value or physical property value before and after it.

[0023] <Silica sol> The silica sol according to the embodiment of the present invention is a silica sol that contains silica particles and has a transverse relaxation time of 400 ms or less at a temperature of 25°C, as measured by the CPMG method using a pulsed NMR spectrometer, and a temperature dependence of the transverse relaxation time obtained by subtracting the transverse relaxation time at 25°C from the transverse relaxation time at 40°C is less than 100 ms.

[0024] 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 transverse relaxation time of nuclide 1H at a temperature of 25°C, as measured by the CPMG method using a pulsed NMR spectrometer, is 400 ms or less, preferably 380 ms or less, and more preferably 350 ms or less. When the transverse relaxation time at 25°C is below the upper limit, a large amount of water is confined to the surface of the silica particles, resulting in excellent dispersion stability and reduced scratching during polishing. There is no particular lower limit for the transverse relaxation time at 25°C, but it is preferably 10 ms or more, more preferably 30 ms or more, and particularly preferably 50 ms or more. When the transverse relaxation time at 25°C is above the lower limit, there is no excess water confined to the surface of the silica particles, and a decrease in the polishing rate can be suppressed.

[0025] In the silica sol according to the embodiment of the present invention, the temperature change of the lateral relaxation time obtained by subtracting the lateral relaxation time at 25°C from the lateral relaxation time at 40°C is more preferably less than 100 ms, less than 80 ms, and more preferably less than 50 ms. When the temperature change of the lateral relaxation time obtained by subtracting the lateral relaxation time at 25°C from the lateral relaxation time at 40°C is below the upper limit, even when the temperature rises, a state in which a large amount of water is confined on the surface of the silica particles is maintained, resulting in excellent dispersion stability under high-temperature conditions and reduction of scratches during polishing. Furthermore, there is no particular limit to the lower limit of the temperature change of the lateral relaxation time obtained by subtracting the lateral relaxation time at 25°C from the lateral relaxation time at 40°C, but it is more preferably -200 ms or more, more preferably -150 ms or more, and particularly preferably -100 ms or more. When the temperature change of the lateral relaxation time obtained by subtracting the lateral relaxation time at 25°C from the lateral relaxation time at 40°C is above the lower limit, when the temperature rises, there is not an excess of water confined on the surface of the silica particles, and a decrease in the polishing rate can be suppressed.

[0026] In this specification, the transverse relaxation time of nuclide 1H at each temperature of silica sol is 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 lateral relaxation time measured by pulsed NMR is related to the proportion of water bound to silica particles. A smaller lateral relaxation time indicates a higher proportion of water bound to the silica particle surface, while a larger lateral relaxation time indicates a lower proportion of water bound to the silica particle surface. This lateral relaxation time can be set to a desired range depending on the manufacturing conditions of the silica particles. For example, by controlling the water content during silica particle synthesis within an appropriate range, a high proportion of water bound to the silica particle surface can be maintained, and this high proportion of bound water can be maintained even when the temperature is increased.

[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 5 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 workpiece, such as silicon wafers, during polishing can be reduced, and the sedimentation of silica particles can be suppressed.

[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 automated specific surface area measuring device, and the average primary particle diameter is calculated using the following formula (1). Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 )) ··· (1)

[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 10 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 500 nm or less, more preferably 400 nm or less, and even more preferably 300 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.

[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 silicon wafers is excellent. Furthermore, the CV value of the average secondary particle diameter of the silica particles 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 and other debris 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 (2). cv value = (standard deviation (nm) / mean secondary particle diameter (nm)) × 100 ... (2)

[0041] In the embodiment of the present invention, the association ratio of silica particles contained in the silica sol 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 silicon wafers 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 is calculated using the following formula (3) from the average primary particle diameter and the average secondary particle diameter measured using the aforementioned measurement method. Association ratio = average secondary particle diameter / average primary particle diameter (3)

[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 have a surface silanol group density of 0.2 particles / nm, as measured by the Sears method. 2 Preferably, the value is 0.5 particles / nm. 2 More preferably, the above is true, 1 particle / nm 2 The above is particularly preferable. When the surface silanol group density is above the lower limit, the silica particles have appropriate surface resilience and excellent dispersion stability of the silica sol. Furthermore, the hydration layer present on the silica surface becomes thicker, resulting in excellent scratch reduction. There is no particular upper limit to the surface silanol group density of silica particles, but it should be 20 groups / nm. 2It is preferably as follows, 15 pieces / nm 2 More preferably, it is as follows, 10 pieces / nm 2 It is particularly preferable that the surface silanol group density of the silica particles is below the upper limit value. When used for polishing, the removability from the polished object during cleaning is excellent.

[0050] The surface silanol group density of the silica particles is measured by the shear method. Specifically, it is measured and calculated under the conditions shown below. Collect a silica sol corresponding to 1.5 g of silica particles, add pure water to make the liquid volume 90 mL. In an environment of 25°C, add a 0.1 mol / L hydrochloric acid aqueous solution until the pH reaches 3.6, add 30 g of sodium chloride, and gradually add pure water while completely dissolving sodium chloride, and finally add pure water until the total volume of the test solution reaches 150 mL to obtain a test solution. Put the obtained test solution into an automatic titrator, drop a 0.1 mol / L sodium hydroxide aqueous solution, and measure the titration amount A (mL) of the 0.1 mol / L sodium hydroxide aqueous solution required for the pH to change from 4.0 to 9.0.

[0051] Using the following formula (4), calculate the consumption volume V (mL) of the 0.1 mol / L sodium hydroxide aqueous solution required for the pH of 1.5 g of silica particles to change from 4.0 to 9.0, and use the following formula (5) to calculate the surface silanol group density ρ (pieces / nm 2 ). V=(A×f×100×1.5) / (W×C SiO2 ) ··· (4) A: Titration amount (mL) of the 0.1 mol / L sodium hydroxide aqueous solution required for the pH of 1.5 g of silica particles to change from 4.0 to 9.0 f: Valence of the 0.1 mol / L sodium hydroxide aqueous solution used C SiO2 : Concentration (mass%) of silica particles in the silica sol W: Sampling amount (g) of the silica sol ρ=(B×N A ) / (10 18 ×m×S BET ) ··· (5) 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. N A Avogadro's number (particles / mol) m: Silica particle quantity (1.5g) S BET :Specific surface area (m²) of silica particles measured when calculating the average primary particle diameter 2 / g)

[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 a tetraalkoxysilane. In this production method, by controlling various production conditions, silica particles can be obtained in which the transverse relaxation time of nuclide 1H at a temperature of 25°C is 400 ms or less, as measured by the CPMG method using a pulsed NMR spectrometer, and the temperature dependence of the transverse relaxation time obtained by subtracting the transverse relaxation time at 25°C from the transverse relaxation time at 40°C is less than 100 ms.

[0060] In the embodiment of the present invention, the method for producing silica sol preferably includes a step of hydrolyzing and condensing tetraalkoxysilane, which involves adding a liquid (B) containing tetraalkoxysilane and a liquid (C) containing an alkaline catalyst to a liquid (A) containing an alkaline catalyst, and then hydrolyzing and condensing the tetraalkoxysilane. This production 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 particle 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 transverse relaxation time at each temperature, measured by the CPMG method using a pulsed NMR spectrometer for the nuclide 1H of the silica particles, 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 tetraalkoxysilanes.

[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 tetraalkoxysilane, 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 tetraalkoxysilane, 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 0.5% by mass or more, and more preferably 0.6% 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, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. 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 reaction does not proceed excessively quickly, and the reaction controllability is excellent.

[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 tetraalkoxysilane. 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 tetraalkoxysilane 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 tetraalkoxysilane.

[0070] Examples of tetraalkoxysilanes in liquid (B) include 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 rapid hydrolysis, leave little unreacted residue, have excellent productivity, and allow for easy acquisition of a stable silica sol.

[0071] While raw materials other than tetraalkoxysilane, such as low-level condensates of tetraalkoxysilane, may be used as raw materials for silica particles, it is preferable that, due to their excellent reactivity, the silica particles consist of 100% by mass of tetraalkoxysilane at 50% or more by mass and raw materials other than tetraalkoxysilane at 50% or less, and more preferably 90% by mass or more of tetraalkoxysilane and raw materials other than tetraalkoxysilane at 10% by mass or less.

[0072] Solution (B) may contain only tetraalkoxysilane without a solvent, but it is preferable to include a solvent because it provides excellent dispersibility of the tetraalkoxysilane 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 tetraalkoxysilane 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 tetraalkoxysilane in solution (B) is above the lower limit, the reaction solution tends to become more homogeneous. Furthermore, the concentration of tetraalkoxysilane in solution (B) is preferably 95% by mass or less, and more preferably 90% by mass or less. If the concentration of tetraalkoxysilane 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 tetramethoxysilane increases, so the concentration of silanol groups contained in the 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 tetraalkoxysilane 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 tetraalkoxysilane 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 0.5% by mass or more, and more preferably 1% by mass or more. 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 7% 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 more, and more preferably 94% by mass or more. This is preferable. If the concentration of water in solution (C) is above the lower limit, fluctuations in the concentration of the alkaline catalyst in the reaction solution can be reduced.

[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 tetraalkoxysilane, 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 tetraalkoxysilane is preferably 0°C or higher, more preferably 5°C or higher, and even more preferably 10°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 less than 70°C, more preferably less than 60°C, and even more preferably less than 50°C. If the temperature in the above step is below the upper limit, excessive condensation of silanol groups can be suppressed, and the proportion of water confined to the silica particle surface can be increased.

[0085] The water content in the reaction system for hydrolysis and condensation reactions is preferably 0.2 mol or more, more preferably 0.3 mol or more, and even more preferably 0.4 mol or more per mole of alkoxysilane throughout the entire reaction process. 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, allowing for the formation of a stable surface state. Furthermore, the water content is preferably 3 mol or less, more preferably 2.8 mol or less, and even more preferably 2.5 mol or less per mole of alkoxysilane throughout the entire reaction process. For example, in the process of hydrolyzing and condensing tetraalkoxysilane, the water content in the reaction system throughout the entire process can be 0.2 mol or more and 3 mol or less per mole of tetraalkoxysilane. 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 proportion of water confined to 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.

[0086] The concentration of the alkaline catalyst in the reaction system for hydrolysis and condensation reactions is preferably maintained at 0.5% by mass or higher, and more preferably at 0.6% by mass or higher, out of 100% by mass of the total amount in the reaction system. When the concentration of the alkaline catalyst in the reaction system is above the lower limit, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Furthermore, the concentration of the alkaline catalyst in the reaction system is preferably maintained at 2.0% by mass or lower, and more preferably at 1.5% by mass or lower. When the concentration of the alkaline catalyst in the reaction system is below the upper limit, the reaction does not proceed excessively quickly, and the reaction is well controllable.

[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] The dispersion medium concentration or substitution step of the silica particle dispersion by the heating concentration method is preferably carried out for 3 hours or more, and more preferably for 5 hours or more. If the time of the dispersion medium concentration or substitution step is above the lower limit, the silanols on the surface of the silica particles condense, resulting in excellent removal from the object to be polished during cleaning when used for polishing. Furthermore, the dispersion medium concentration or substitution step of the silica particle dispersion is preferably carried out within 20 hours, and more preferably within 15 hours. If the time of the dispersion medium concentration or substitution step is below the upper limit, the amount of residual silanol groups increases, so the silica particles have appropriate surface resilience and excellent dispersion stability of the silica sol. In addition, the proportion of water confined to the silica surface increases, resulting in excellent scratch reduction.

[0091] 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.

[0092] 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.

[0093] <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.

[0094] 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.

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

[0096] Examples of cellulose derivatives include hydroxyethylcellulose, hydrolyzed hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, and carboxymethylcellulose.

[0097] Examples of copolymers having a polyvinylpyrrolidone skeleton include graft copolymers of polyvinyl alcohol and polyvinylpyrrolidone.

[0098] Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] <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.

[0109] <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.

[0110] <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.

[0111] 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.

[0112] <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]

[0113] 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.

[0114] <Measurement method> (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 (1). 3 The average primary particle size was then calculated. Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 )) ··· (1)

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

[0116] (Surface silanol group (SiOH group) density) An amount of silica sol equivalent to 1.5 g of silica particles obtained in the examples and comparative examples was taken into a 200 mL tall beaker, and pure water was added to make a total volume of 90 mL. Under conditions of 25°C, a pH electrode was inserted into a tall beaker, and the test solution was stirred with a magnetic stirrer for 5 minutes. While continuing to stir with the magnetic stirrer, 0.1 mol / L hydrochloric acid solution was added until the pH reached 3.6. The pH electrode was removed from the tall beaker, and while continuing to stir with the magnetic stirrer, 30 g of sodium chloride was added, and pure water was gradually added to completely dissolve the sodium chloride. Finally, pure water was added until the total volume of the test solution reached 150 mL, and the test solution was stirred with a magnetic stirrer for 5 minutes to obtain the final test solution.

[0117] The tall beaker containing the obtained test solution was placed in the automatic titrator "COM-1600" (manufactured by Hiranuma Sangyo Co., Ltd.), and the pH electrode and burette attached to the apparatus were inserted into the tall beaker. While stirring the test solution with a magnetic stirrer, a 0.1 mol / L sodium hydroxide solution was added dropwise through the burette, and the titration volume A (mL) of 0.1 mol / L sodium hydroxide solution required to raise the pH from 4.0 to 9.0 was measured. Using the following formula (4), 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. Using the following formula (5), calculate the surface silanol group density ρ (particles / nm) of the silica particles. 2 ) was calculated. V = (A × f × 100 × 1.5) / (W × C) SiO2 )···(4) 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) ρ = (B × N) A ) / (10 18 ×M×S BET )···(5) 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. N A Avogadro's number (particles / mol) M: Silica particle amount (1.5g) S BET :Specific surface area (m²) of silica particles measured when calculating the average primary particle diameter 2 / g)

[0118] (Transverse relaxation time T2 at each temperature for nuclide 1H) The silica sols 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: 0.04ms • Repeat waiting time: 10s • Total number of times: 8 • Number of data points: 1600 Analysis method: Transverse relaxation times were calculated using analysis software (Bruker TDNMR-A).

[0119] [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.

[0120] 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. The water content of the solution after the addition of solution (B) and solution (C) was 2.3 mol per 1 mol of tetramethoxysilane injected. 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.

[0121] [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.

[0122] 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. The water content of the solution after the addition of solution (B) and solution (C) was 1.2 mol per 1 mol of tetramethoxysilane injected. 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.

[0123] [Comparative 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.

[0124] 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. The water content of the solution after the addition of solutions (B) and (C) was 14.0 mol per 1 mol of tetramethoxysilane injected. 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.

[0125] [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 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.

[0126] 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. The water content of the solution after the addition of solution (B) and solution (C) was 12.0 mol per 1 mol of tetramethoxysilane injected. 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.

[0127] [Comparative 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.

[0128] 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. The water content of the solution after adding solutions (B) and (C) was 3.9 mol per 1 mol of tetramethoxysilane injected. 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.

[0129] [Comparative Example 4] A commercially available silica sol (product name "PL-1," manufactured by Fuso Chemical Industry Co., Ltd.) was used as is.

[0130] [Comparative Example 5] A commercially available silica sol (product name "PL-2", manufactured by Fuso Chemical Industry Co., Ltd.) was used as is.

[0131] [Comparative Example 6] A commercially available silica sol (product name "PL-7," manufactured by Fuso Chemical Industry Co., Ltd.) was used as is.

[0132] The evaluation results of the obtained silica sol are shown in Table 1.

[0133] [Table 1]

[0134] As can be seen from Table 1, by adjusting various reaction conditions, silica sols with short lateral relaxation times and minimal temperature changes at 40°C and 25°C can be obtained. The silica particles contained in such silica sols have a large amount of surface hydration water and do not lose hydration water even at high temperatures, thus exhibiting stable dispersibility even under high-temperature conditions and further reducing 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 transverse relaxation time of nuclide 1H at a temperature of 25°C, as measured by the CPMG method using a pulsed NMR device, is 400 ms or less, and the temperature dependence of the transverse relaxation time (the difference between the transverse relaxation time at 40°C and the transverse relaxation time at 25°C) is less than 100 ms.

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 5 nm or more.

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 10 nm or more.

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 a tetraalkoxysilane.

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

7. The method for producing silica sol according to claim 5, wherein, in the step of hydrolyzing and condensing the tetraalkoxysilane, the water content in the reaction system throughout the entire process is 0.2 mol or more and 3 mol or less per mol of tetraalkoxysilane.

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

9. A polishing method comprising polishing using the polishing composition described in claim 8.

10. A method for manufacturing a semiconductor wafer, comprising the step of polishing using the polishing composition described in claim 8.

11. A method for manufacturing a semiconductor device, comprising the step of polishing using the polishing composition described in claim 8.

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