Silica particles and manufacturing method thereof, silica sol, polishing composition, polishing method, method for manufacturing semiconductor wafer, and method for manufacturing semiconductor device

Abstract

To provide silica particles, silica sol, and polishing compositions with high polishing speed and excellent polishing characteristics, and to provide polishing methods, semiconductor wafer manufacturing methods, and semiconductor device manufacturing methods with excellent productivity for work pieces.SOLUTION: Silica particles according to the present invention satisfy the following equation (1), where x (nm) is the average secondary particle diameter of the silica particles and y (%) is the percentage of water bound to the silica particles as measured by pulse NMR. y<0.02*x+0.3...(1)SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to silica particles and a method for producing the same, a silica sol, 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 liquids are known as methods for polishing the surfaces of materials such as metals and inorganic compounds. In particular, in the final polishing of prime silicon wafers for semiconductors and reclaimed silicon wafers, and in chemical mechanical polishing (CMP) for planarizing interlayer insulating films during semiconductor device manufacturing, forming metal plugs, forming buried wiring, and the like, the surface condition has a significant effect on the semiconductor characteristics, so the surfaces and end faces of these components are required to be polished with extremely high precision.

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

[0004] Many studies have been conducted on methods for producing silica particles. For example, Patent Documents 1 and 2 disclose methods for producing silica particles 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] JP 2019-89692 A Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the interaction between the silica particles and water as the dispersion medium has not been optimized. Generally, in an aqueous dispersion of silica particles, water molecules are adsorbed on the surface of the silica particles, and these water molecules are called hydration water. When silica particles with a large amount of hydration water are used for polishing, when the silica particles approach the object to be polished, a repulsive force is generated by the hydration water, and the silica particles cannot come into sufficient contact with the object to be polished, and sufficient polishing characteristics cannot be obtained. Also, although it is generally known that improving the proximity of silica particles to the object to be polished can be achieved by increasing the particle size of the silica particles, the inventors have found that increasing the particle size of the silica particles increases the amount of hydration water. That is, it has been found that it is difficult to simultaneously optimize the interaction between the silica particles and the water of the dispersion medium and the particle size of the silica particles by conventional methods.

[0007] The silica particles obtained by the production methods disclosed in Patent Documents 1 and 2 do not take into account the hydration water, and the polishing characteristics are not always sufficient.

[0008] The present invention has been made in view of such problems, and an object of the present invention is to provide silica particles, a silica sol, and a polishing composition having a high polishing rate and excellent polishing characteristics. Another object of the present invention is to provide a polishing method excellent in the productivity of the object to be polished, a method for manufacturing a semiconductor wafer, and a method for manufacturing a semiconductor device.

Means for Solving the Problems

[0009] As a result of intensive studies, the inventors have found that the above problems can be solved by setting the ratio of water bound to the silica particles and the particle size of the silica particles within a predetermined range. More specifically, the inventors have found that when silica particles with a small ratio of water bound to the silica particles, that is, silica particles with little hydration water, are used for polishing, the silica particles and the object to be polished are likely to come into contact, and the polishing proceeds well, and thus the present invention has been completed.

[0010] That is, the gist of the present invention is as follows.

[0011] Aspect 1 of the present invention relates to silica particles that satisfy the following formula (1) when the average secondary particle diameter of the silica particles is x (nm) and the proportion of water bound to the silica particles measured by pulsed NMR is y (%). y < 0.02x + 0.3 ··· (1) y < 0.02x ··· (1a)

[0012] Aspect 2 of the present invention relates to silica particles in the silica particles of Aspect 1 that satisfy the following formula (1a). y < 0.02x ··· (1a) y < 0.02x ··· (1a)

[0013] Aspect 3 of the present invention relates to silica particles in the silica particles of Aspect 1 or 2, wherein the average primary particle diameter is 5 nm to 500 nm. The average primary particle diameter is 5 nm to 500 nm.

[0014] Aspect 4 of the present invention relates to silica particles in any one of Aspects 1 to 3, wherein the average secondary particle diameter is 10 nm to 1000 nm. The average secondary particle diameter is 10 nm to 1000 nm.

[0015] Aspect 5 of the present invention relates to silica particles in any one of Aspects 1 to 4, wherein the metal impurity content is 5 mass ppm or less. The metal impurity content is 5 mass ppm or less.

[0016] Aspect 6 of the present invention relates to a method for producing silica particles in any one of Aspects 1 to 5, which includes a step of adding a solution (B) containing tetraalkoxysilane to a solution (A) containing an alkali catalyst. The method for producing silica particles includes a step of adding a solution (B) containing tetraalkoxysilane to a solution (A) containing an alkali catalyst.

[0017] Aspect 7 of the present invention relates to a method for producing silica particles in the method for producing silica particles of Aspect 6, which further includes a step of hydrolyzing and condensing alkoxysilane in a solution containing a salt. The method for producing silica particles further includes a step of hydrolyzing and condensing alkoxysilane in a solution containing a salt.

[0018] Aspect 8 of the present invention relates to a method for producing silica particles according to the method for producing silica particles of Aspect 7, wherein the salt is a salt that decomposes or volatilizes when heated to 100 °C.

[0019] Aspect 9 of the present invention relates to a method for producing silica particles according to the method for producing silica particles of Aspect 7 or 8, wherein, in the step of hydrolyzing and condensing an alkoxysilane in a solution containing a salt, the molar ratio of the amount of the salt used to the amount of the alkali catalyst used is 0.0001 to 0.045.

[0020] Aspect 10 of the present invention relates to a silica sol containing silica particles according to any one of Aspects 1 to 5.

[0021] Aspect 11 of the present invention relates to the silica sol of Aspect 10, wherein the content of silica particles in 100% by mass of the total amount of the silica sol is 3% to 50% by mass.

[0022] Aspect 12 of the present invention relates to the silica sol of Aspect 10 or 11, wherein the pH is 6.0 to 8.0.

[0023] Aspect 13 of the present invention relates to a polishing composition containing the silica sol according to any one of Aspects 10 to 12.

[0024] Aspect 14 of the present invention relates to a polishing method for polishing using the polishing composition of Aspect 13.

[0025] Aspect 15 of the present invention relates to a method for manufacturing a semiconductor wafer including a step of polishing using the polishing composition of Aspect 13.

[0026] Aspect 16 of the present invention relates to Relates to a method for manufacturing a semiconductor device, including a step of polishing using the polishing composition of Embodiment 13.

Effects of the Invention

[0027] The silica particles of the present invention have excellent polishing characteristics with a high polishing rate. Also, the polishing method, the method for manufacturing a semiconductor wafer, and the method for manufacturing a semiconductor device of the present invention are excellent in the productivity of the object to be polished.

Embodiments for Carrying Out the Invention

[0028] The present invention will be described in detail below. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the invention. 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.

[0029] [Silica Particles] The silica particles according to this embodiment satisfy the following formula (1), where the average secondary particle diameter of the silica particles is x (nm) and the ratio of water bound to the silica particles measured by pulsed NMR is y (%). y < 0.02x + 0.3 ··· (1)

[0030] By the silica particles satisfying the above formula (1), the ratio of water bound to the silica particles becomes small, that is, the hydration water of the silica particles becomes less, and the silica particles and the object to be polished are likely to come into contact. As a result, the polishing rate of the silica particles is high and the polishing characteristics are excellent. When the silica particles do not satisfy the above formula (1), the hydration water of the silica particles becomes excessive, so the contact with the object becomes poor. As a result, the polishing rate of the silica particles becomes slow and the polishing characteristics deteriorate.

[0031] The average secondary particle diameter of the silica particles can be set within a desired range according to the production conditions of the silica particles. For example, when the reaction temperature during the synthesis of the silica particles is low, the average secondary particle diameter of the silica particles tends to be large. On the other hand, when the reaction temperature during the synthesis of the silica particles is high, the average secondary particle diameter of the silica particles tends to be small.

[0032] Also, in this specification, the ratio of water bound to the silica particles measured by pulsed NMR means the percentage (%) of Ps of the pulsed NMR described below.

[0033] The pulsed NMR method is a technique for observing the resonance phenomenon of the nuclear spin of atomic nuclei placed in a static magnetic field. The pulsed NMR method is a method for observing the magnetization decay (or recovery) curve of the hydrogen atomic nucleus spin excited by applying an electromagnetic wave pulse of several μs as it returns to the stable state, and is also called the TD-NMR (Time Domain NMR) method. The relaxation time can be obtained by analyzing the magnetization decay curve.

[0034] The relaxation times that can be measured by the pulsed NMR method include the spin-lattice relaxation time (T1), the spin-spin relaxation time (T2), and the spin-lattice relaxation time (T1ρ) in the rotating coordinate system. In the present invention, T2 is used.

[0035] The measurement methods of T2 include the solid echo method suitable for measuring crystals and glass states, the Hahn echo method suitable for measuring elastomers, and the CPMG method (Carr-Purcell-Meiboom-Gill method) suitable for measuring liquids. In the present invention, the CPMG method is used.

[0036] 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, after applying a 90° pulse, a 180° pulse is applied after τ s, and the echo that appears after τ s is observed. Then, the pulse sequence in () is repeated n times. Then, an echo is obtained every (2τ s + 180° pulse width).

[0037] By analyzing the magnetization decay curve M(t) which plots the time t at which an echo is obtained on the X-axis and the echo intensity on the Y-axis, with the time immediately after applying a 90° pulse to the X-axis set as 0, T2 can be obtained. T2 is related to the molecular mobility, and the smaller the value, the lower the mobility.

[0038] The magnetization decay curve M(t) can be analyzed using the software attached to the pulsed NMR apparatus. Also, the data can be imported into a spreadsheet software such as Excel (registered trademark) for approximate calculation and analysis.

[0039] When measuring colloidal silica containing water and silica under the condition of τ = 0.5 ms or more, M(t) can be approximated by the following equation. M(t)=M0×exp(-t / T2)

[0040] On the other hand, since T2 is related to the molecular mobility, when there are components with different mobilities to a certain extent and the molecules can be distinguished by mobility, the T2 of multiple components can be observed. When T2 is represented by two components T2s and T2l (where T2s < T2l), M(t) is also represented by two components Ms and Ml and can be approximated by the following equation. M(t)=Ms×exp(-t / T2s)+Ml×exp(-t / T2l) ··Equation (※)

[0041] When T2 is represented by three or more components T2i (i = 1, 2, 3, ···), it can be approximated by the sum of three or more exponential functions as in the following equation. M(t)=Σ(Mi×exp(-t / T2i)) (i = 1, 2, 3, ···) Note that when the measurement object is colloidal silica, T2 of three or more components was not observed even when the measurement conditions were changed, such as by shortening the pulse interval.

[0042] When colloidal silica containing water and silica is measured under the condition that the interval between a 90° pulse and a 180° pulse is short, such as τ = 0.04 ms, as shown in formula (※), M(t) can be approximated by two exponential functions. And the relationship between Ps and Ms and Ml included in formula (※) is represented by the following formula. Ps = Ms / (Ms + Ml)

[0043] In this way, the ratio Ps of water bound to silica can be obtained. Also, the ratio y(%) of water bound to silica particles measured by the pulse NMR method is Ps expressed as a percentage and can be obtained by the following formula. y(%) = Ps × 100

[0044] Note that in this specification, the ratio of water bound to silica particles measured by the pulse NMR method is the value when the silica particles are dispersed in water at a concentration of 20% by mass. It is preferable to accurately adjust the concentration of the silica particles to 20% by mass for measurement, but if it is difficult to adjust, measure at that concentration and the obtained Ps can be corrected by the following formula. However, from the viewpoint of maintaining the measurement accuracy, it is preferable to measure with the concentration of the silica particles being 10% by mass or more. Also, from the viewpoint of ensuring the dispersibility of the silica particles and the fluidity of the dispersion liquid, it is preferable to measure with the concentration of the silica particles being 30% by mass or less. Ps = (Ps obtained by measurement) × 20 / (mass concentration of the aqueous dispersion of silica particles used for measurement)

[0045] The ratio of water bound to silica particles measured by the pulse NMR method can be set within a desired range depending on the production conditions of the silica particles. For example, when the reaction temperature during the synthesis of the silica particles is low, the ratio of water bound to the silica particles tends to be large, while when the reaction temperature during the synthesis of the silica particles is high, the ratio of water bound to the silica particles tends to be small. Also, when the concentration of water during the synthesis of the silica particles is low, the ratio of water bound to the silica particles tends to be small.

[0046] The average secondary particle diameter x (nm) of the silica particles according to this embodiment and the proportion y (%) of water bound to the silica particles measured by pulsed NMR are not particularly limited as long as they satisfy the above formula (1). However, y is preferably 0.1% or more, more preferably 0.5% or more, and even more preferably 1.0% or more. Also, y is preferably 3.5% or less, more preferably 2.8% or less, and even more preferably 2.4% or less. The preferred range of the average secondary particle diameter x (nm) of the silica particles and the reason therefor will be described later.

[0047] When y is 0.1% or more, it is preferable because contact between silicas is avoided and the dispersibility is excellent. Also, when y is 3.5% or less, it is preferable because contact between the silica and the object to be polished becomes easy and the polishing rate is excellent.

[0048] Since contact between the silica and the object to be polished becomes easy and the polishing rate is improved, the silica particles according to this embodiment preferably satisfy the following formula (1a). y < 0.02x ··· (1a) The definitions of x and y in the above formula (1a) are as described for the above formula (1).

[0049] When the refractive index of the silica particles is large, the atomic density of the silica particles is high and it becomes easy to maintain the mechanical strength. Therefore, the refractive index of the silica particles according to this embodiment is preferably 1.390 or more, more preferably 1.400 or more, and even more preferably 1.410 or more. Also, since it is preferable for the silica to maintain an amorphous structure, it is preferably 1.550 or less, more preferably 1.500 or less, and even more preferably 1.450 or less. As a method for controlling the refractive index of the silica particles, various methods can be considered. For example, the refractive index of the silica particles can be increased by raising the reaction temperature.

[0050] The refractive index of the silica particles is measured with an Abbe refractometer for the supernatant when the silica particles in the container become transparent by adding the silica particles to a container with varying ratios of special grade 2-propanol and special grade toluene, and the refractive index at that time is taken as the refractive index of the silica particles.

[0051] The silica particles according to this embodiment are preferably amorphous. In this case, silanol groups are appropriately present on the surface of the silica particles, and in the process of polishing the object to be polished, a chemical interaction occurs between the silica particles and the object to be polished via the silanol groups, and polishing proceeds well. The fact that the silica particles are amorphous can be confirmed by the halo pattern in wide-angle X-ray scattering measurement.

[0052] The metal impurity content of the silica particles according to this embodiment is preferably 5 mass ppm or less, and more preferably 1 mass ppm or less. When the metal impurity content of the silica particles is 5 mass ppm or less, in the polishing of the silicon wafer of the semiconductor device, it is preferable because contamination due to the adhesion of metal impurities to the surface of the object to be polished and the influence on the wafer characteristics are reduced. Further, it is preferable because deterioration of quality due to diffusion of the metal impurities attached to the surface of the object to be polished into the wafer and a decrease in the performance of the semiconductor device manufactured using such a wafer are reduced.

[0053] Furthermore, when the metal impurity content of the silica particles is 5 mass ppm or less, it is preferable because the influence on the polishing rate due to a change in the chemical properties (acidity, etc.) of the surface silanol groups and a change in the three-dimensional environment (ease of aggregation of the silica particles, etc.) on the silica particle surface due to the occurrence of a coordination interaction between the acidic surface silanol groups and the metal impurities is reduced.

[0054] The metal impurity content rate of the silica particles in this specification is a value measured by high-frequency inductively coupled plasma mass spectrometry (ICP-MS). Specifically, accurately weigh 0.4 g of silica particles-containing silica sol, add sulfuric acid and hydrofluoric acid, heat, dissolve, and evaporate, add pure water to the remaining sulfuric acid droplets so that the total amount is exactly 10 g to prepare a test solution, and measure using a high-frequency inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, nickel, and the sum of the content rates of these metals is defined as the metal impurity content rate.

[0055] The metal impurity content rate of the silica particles can be made 5 mass ppm or less by obtaining silica particles through a hydrolysis reaction and a condensation reaction using alkoxysilane as the main raw material. In the method of deionizing alkali silicates such as water glass, since sodium and the like derived from the raw materials remain, it is extremely difficult to make the metal impurity content rate of the silica particles 5 mass ppm or less.

[0056] The average primary particle diameter of the silica particles according to this embodiment is preferably 5 nm to 500 nm, more preferably 35 nm to 400 nm, and even more preferably 45 nm to 300 nm. When the average primary particle diameter of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Further, when the average primary particle diameter of the silica particles is 500 nm or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer can be reduced, and the sedimentation of the silica particles can be suppressed.

[0057] The average primary particle diameter of the silica particles is measured by the BET method. Specifically, the specific surface area of the silica particles is measured using a specific surface area automatic measuring device, and the average primary particle diameter is calculated using the following formula (2). Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) × density (g / cm 3 )) ··· (2)

[0058] The average primary particle diameter of the silica particles can be set within a desired range according to the production conditions of the silica particles.

[0059] The average secondary particle diameter x (nm) of the silica particles according to the present embodiment is preferably 10 nm or more, more preferably 60 nm or more, even more preferably 75 nm or more, and particularly preferably 135 nm or more. Also, it is preferably 1000 nm or less, more preferably 700 nm or less, and even more preferably 400 nm or less. When the average secondary particle diameter of the silica particles is 10 nm or more, the removability of particles and the like in the cleaning after polishing are excellent, and the storage stability of the silica sol is excellent. Also, when the average secondary particle diameter of the silica particles is 1000 nm or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer during polishing can be reduced, the removability of particles and the like in the cleaning after polishing is excellent, and the sedimentation of the silica particles can be suppressed. For example, the average secondary particle diameter of the silica particles according to the present embodiment can be 10 nm to 1000 nm.

[0060] The average secondary particle diameter of the silica particles is measured by the DLS method. Specifically, it is measured using a dynamic light scattering particle size measuring device.

[0061] The average secondary particle diameter of the silica particles can be set within a desired range according to the production conditions of the silica particles.

[0062] The cv value of the silica particles according to the present embodiment is preferably 10% to 50%, more preferably 15% to 40%, and even more preferably 20% to 30%. When the cv value of the silica particles is 10% or more, the polishing rate with respect to the object to be polished typified by a silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Also, when the cv value of the silica particles is 50% or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer during polishing can be reduced, and the removability of particles and the like in the cleaning after polishing is excellent.

[0063] The cv value of the silica particles is measured by measuring the average secondary particle diameter of the silica particles using a dynamic light scattering particle size measuring device and calculated using the following formula (3). cv value = (standard deviation (nm) / average secondary particle diameter (nm)) × 100 ··· (3)

[0064] The aggregation ratio of the silica particles according to this embodiment is preferably from 1.0 to 4.0, more preferably from 1.3 to 2.0, and even more preferably from 1.5 to 1.8. When the aggregation ratio of the silica particles is 1.0 or more, the polishing rate with respect to the object to be polished typified by a silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Further, when the aggregation ratio of the silica particles is 4.0 or less, the surface roughness and scratches of the object to be polished typified by a silicon wafer during polishing can be reduced, and aggregation of the silica particles can be suppressed.

[0065] The aggregation ratio of the silica particles is calculated using the following formula (4) from the average primary particle diameter measured by the above-described measurement method and the average secondary particle diameter measured by the above-described measurement method. Aggregation ratio = average secondary particle diameter / average primary particle diameter ··· (4)

[0066] The silica particles according to this embodiment have a low content of metal impurities and have appropriate mechanical strength and flexibility due to trace residual alkoxy groups inside the particles. Therefore, it is preferable that the main component is an alkoxysilane condensate, more preferably a tetraalkoxysilane condensate, and even more preferably a tetramethoxysilane condensate. The main component means a component that is 50% by mass or more in 100% by mass of all components constituting the silica particles. In order to obtain silica particles having an alkoxysilane condensate as the main component, it is preferable to use alkoxysilane as the main raw material. In order to obtain silica particles having a tetraalkoxysilane condensate as the main component, it is preferable to use tetraalkoxysilane as the main raw material. In order to obtain silica particles having a tetramethoxysilane condensate as the main component, it is preferable to use tetramethoxysilane as the main raw material. The main raw material means a raw material that is 50% by mass or more in 100% by mass of all raw materials constituting the silica particles.

[0067] That the alkoxysilane condensate is the main component can be confirmed by examining the presence of alkoxysilyl groups in the silica particles. The method for examining the presence of alkoxy groups is not particularly limited, and for example, methods such as measuring 13C solid NMR for the silica particles and measuring the alcohol content in the alkaline solution in which the silica particles are dissolved can be used.

[0068] The surface silanol group density of the silica particles according to this embodiment is 1 piece / nm 2 ~20 pieces / nm 2 is preferable, and 7 pieces / nm 2 ~19 pieces / nm 2 is more preferable, and 16 pieces / nm 2 ~18 pieces / nm 2 is even more preferable. When the surface silanol group density of the silica particles is 1 piece / nm 2 or more, the silica particles have appropriate surface repulsion and are excellent in the dispersion stability of the silica sol. Further, when the surface silanol group density of the silica particles is 20 pieces / nm 2 or less, the formation of chemical bonds between the silica particles and the object to be polished can be suppressed, so that it is excellent in suppressing the adhesion of particles after polishing.

[0069] 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 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.

[0070] Using the following formula (5), calculate the consumption V (mL) of 0.1 mol / L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to reach 4.0 to 9.0, and using the following formula (6), calculate the surface silanol group density ρ (number / nm 2 ). V=(A×f×100×1.5) / (W×C) ··· (5) A: Titration volume (mL) of 0.1 mol / L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to reach 4.0 to 9.0 f: Titer of 0.1 mol / L sodium hydroxide aqueous solution used C: Concentration (mass %) of silica particles in silica sol W: Sampling amount (g) of silica sol ρ=(B×NA) / (10 18 ×M×SBET) ··· (6) B: Amount of sodium hydroxide required for the pH per 1.5 g of silica particles calculated from V to reach 4.0 to 9.0 (mol) NA: Avogadro's number (number / mol) M: Amount of silica particles (1.5 g) SBET: Specific surface area (m 2 / g) of silica particles measured when calculating the average primary particle diameter

[0071] The ratio of the major axis / minor axis of the silica particles according to this embodiment is preferably 1.01 to 1.39, more preferably 1.06 to 1.25, and even more preferably 1.09 to 1.18. When the ratio of the major axis / minor axis is 1.01 or more, a frictional force is applied between the silica particles and the object to be polished due to the rotation of the silica particles during polishing, so the polishing speed is excellent. In addition, when the ratio of the major axis / minor axis is 1.39 or less, it is possible to suppress the excessive contact between the silica particles and the object to be polished periodically due to the rotation of the silica particles during polishing, so it is excellent in terms of smooth polishing progress. The ratio of the major axis to the minor axis of the silica particles is calculated by observing the silica particles with a scanning electron microscope to calculate the average major axis and the average minor axis of the silica particles, respectively, and dividing the average major axis by the average minor axis. The average major axis and the average minor axis are the average values obtained by determining the major axis and the minor axis of 100 or more silica particles, respectively. Here, the major axis is the long side of the rectangle circumscribing the electron microscope image of the particle with the minimum area, and the minor axis is the short side of the rectangle circumscribing the electron microscope image of the particle with the minimum area.

[0072] The number of fine particles contained in the silica particles according to this embodiment is preferably 10 or less, more preferably 5 or less, still more preferably 1 or less, and quite preferably not detected, per 100 main particles. The fine particles refer to particles having a major axis of less than 10 nm, and the main particles refer to particles having a major axis within the range of the average major axis ± 50%. The number of fine particles and main particles can be counted by observing the silica particles with a scanning electron microscope. When the number of fine particles contained in the silica particles is 10 or less per 100 main particles, it is preferable from the viewpoint of easily washing and removing the silica particles adhering to the object to be polished after polishing. The number of fine particles contained in the silica particles can be set within a desired range depending on the production conditions of the silica particles. For example, when the reaction temperature of the hydrolysis and condensation reaction of tetraalkoxysilane is high, the number of fine particles decreases.

[0073] The amine content of the silica particles according to this embodiment is preferably less than 5 μmol / g, more preferably less than 3 μmol / g, and still more preferably less than 1 μmol / g. When the amine content of the silica particles is less than 5 μmol / g, it is preferable because corrosion of the object to be polished and the equipment used for polishing can be avoided when the silica particles are used for polishing. There is no particular limitation on the lower limit value of the amine content of the silica particles, but for example, it can be 0.001 μmol / g or more. Alternatively, the content can be made zero by not using an amine in the production of the silica particles. Amine refers to primary amine, secondary amine, and tertiary amine, and specifically, it is represented by the following general formula (X). NRaRbRc(X) (In the formula, Ra, Rb, and Rc each represent an optionally substituted alkyl group having 1 to 12 carbon atoms or a hydrogen atom. However, not all of Ra, Rb, and Rc can be hydrogen atoms, that is, ammonia is excluded from the amines represented by the general formula (X). Ra, Rb, and Rc may be the same as or different from each other. When Ra, Rb, and Rc are alkyl groups, they may be linear, branched, or cyclic alkyl groups. Further, when Ra, Rb, and Rc are substituted alkyl groups, examples of the substituents include an alkoxy group, an amino group, a primary amino group substituted with an alkyl group, an amino group disubstituted with an alkyl group, a hydroxy group, and the like.)

[0074] The amine content of the silica particles is measured by ion chromatography analysis. Specifically, after separating the silica particles from other components by centrifugation or the like, the silica is dissolved with an aqueous sodium hydroxide solution or the like, and the amine in the solution is quantified by ion chromatography.

[0075] [Method for producing silica particles] The silica particles according to this embodiment can be obtained by a production method including a step of adding a solution (B) containing tetraalkoxysilane to a solution (A) containing an alkali catalyst. Including such a step makes it easy to control the hydrolysis reaction and the condensation reaction, can increase the reaction rates of the hydrolysis reaction and the condensation reaction, prevent gelation of the dispersion of the silica particles, and makes it easy to obtain silica particles with a uniform particle size, so it is preferable. Further, including such a step makes it possible to adjust the average secondary particle diameter x (nm) of the silica particles contained in the above formula (1) and the ratio y (%) of the water bound to the silica particles measured by pulsed NMR by appropriately adjusting the conditions for producing the silica particles, so it is preferable.

[0076] In the method for producing silica particles according to the present embodiment, the average secondary particle diameter x (nm) of the silica particles and the ratio y (%) of the water bound to the silica particles measured by pulsed NMR can be set within a desired range according to the production conditions of the silica particles, such as pH, reaction temperature, reaction time, catalyst concentration, concentration of water as a reaction substrate, raw material supply rate, additives into the reaction system, etc. For example, the lower the reaction temperature, the larger x becomes, and the higher the reaction temperature, the smaller x tends to be. Alternatively, as will be described later, when a salt is added to the reaction system, x tends to increase. Also, for example, the higher the reaction temperature, the smaller y becomes, and the lower the reaction temperature, the larger y tends to be. Thus, by appropriately adjusting the conditions for producing silica particles, silica particles satisfying the above formula (1) can be obtained.

[0077] The method for producing silica particles according to the present embodiment may include, for example, a step of hydrolyzing and condensing an alkoxysilane in a solution containing a salt, and preferably may include a step of hydrolyzing and condensing an alkoxysilane in a solution containing a salt that decomposes or volatilizes when heated to 100°C. Regarding the preferred type and amount of the salt used, etc. in the above step of hydrolyzing and condensing an alkoxysilane in a solution containing a salt, it is the same as the range described for the salt that can be contained in the solution (A) described later.

[0078] Solution (A) contains an alkali catalyst.

[0079] Since solution (A) has excellent dispersibility in the reaction solution of tetraalkoxysilane, it preferably contains water, and more preferably contains water and a solvent other than water. Examples of the solvent other than water in the solution (A) include methanol, ethanol, propanol, isopropanol, ethylene glycol, and the like. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferable, methanol and ethanol are more preferable, and methanol is even more preferable because it easily dissolves tetraalkoxysilane, the product by-produced in the hydrolysis reaction and condensation reaction is the same as that used in the reactions, and it has excellent convenience in production.

[0080] When the solution (A) contains an alkali catalyst, the reaction rates of the hydrolysis reaction and condensation reaction of tetraalkoxysilane can be increased.

[0081] Examples of the alkali catalyst in the solution (A) include ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, tetramethylammonium hydroxide, and the like. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferable because it has excellent catalytic action, is easy to control the particle shape, can suppress the mixing of metal impurities, has high volatility, and has excellent removability after the hydrolysis reaction and condensation reaction.

[0082] When the solution (A) contains water, the concentration of water is preferably 3% by mass to 80% by mass, more preferably 5% by mass to 50% by mass, and even more preferably 12.3% by mass to 17% by mass in 100% by mass of the solution (A). When the concentration of water in the solution (A) is 3% by mass or more, the hydrolysis reaction rate of tetraalkoxysilane is easy to control. When the concentration of water in the solution (A) is 80% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape is easy to control.

[0083] The concentration of the alkali catalyst in solution (A) is preferably maintained at 0.5% by mass to 4.0% by mass, more preferably maintained at 1.5% by mass to 3.5% by mass, and even more preferably maintained at 2.2% by mass to 3.0% by mass in 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. Further, when the concentration of the alkali catalyst in solution (A) is 4.0% by mass or less, the reaction does not proceed too rapidly, and the reaction controllability is excellent.

[0084] Solution (A) can contain salts. The salts in solution (A) are not particularly limited. For example, ammonium acetate, ammonium tartrate, ammonium citrate, ammonium acetate, ammonium benzoate, ammonium malate, ammonium butyrate, ammonium propionate, ammonium oxalate, ammonium maleate, ammonium succinate, ammonium glutarate, ammonium fumarate, ammonium adipate, ammonium sorbate, ammonium palmitate, ammonium laurate, ammonium sebacate, ammonium pimarate, ammonium stearate, sodium acetate, ammonium acetate, sodium carbonate, disodium hydrogen phosphate, ammonium hydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium citrate, ammonium citrate, ammonium nitrate, ammonium chloride, sodium sulfate, ammonium sulfate, sodium borate, ammonium borate, sodium butyrate, ammonium butyrate, sodium propionate, ammonium carbamate, ammonium sulfamate, ammonium lactate, ammonium oxalate, tetramethoxyammonium acetate, tetraethoxyammonium acetate, tetrapropoxyammonium acetate, tetrabutoxyammonium acetate, tetramethoxyammonium benzoate, tetraethoxyammonium benzoate, tetrapropoxyammonium benzoate, tetrabutoxyammonium benzoate, tetraethylammonium hydrogen carbonate, ammonium carbonate, sodium hydrogen carbonate, etc. can be mentioned. These salts may be used alone or in combination of two or more. As the salt, a neutral salt, that is, a salt of a weak acid and a weak base or a salt of a strong acid and a strong base is preferable because it suppresses the change in the pH of the reaction solution due to the addition and does not change the reaction rate of tetraalkoxysilane.

[0085] In addition, as the salt, a salt that can avoid contamination of the finally obtained silica particles and silica sol and expand the industrial application range of the silica particles and silica sol is preferable, and a salt that decomposes or volatilizes when heated is more preferable, and a salt that decomposes or volatilizes when heated to 100 °C is even more preferable. These salts do not need to be completely decomposed or volatilized when reaching 100 °C, and it is sufficient that decomposition or volatilization starts at 100 °C. Specifically, ammonium nitrate, ammonium carbamate, ammonium carbonate, and ammonium bicarbonate are preferable, and ammonium bicarbonate is more preferable.

[0086] By including a salt in solution (A), aggregation of silica particles is promoted, and the average secondary particle diameter x of the silica particles can be increased without significantly changing the ratio y (%) of the water bound to the silica particles measured by pulsed NMR.

[0087] When solution (A) contains a salt, the amount of the salt used is not particularly limited. However, the molar ratio of the amount of the salt used to the amount of the alkali catalyst used in the step of hydrolyzing and condensing the alkoxysilane in the solution containing the salt is preferably 0.0001 to 0.045, more preferably 0.001 to 0.03, still more preferably 0.003 to 0.02, and particularly preferably 0.0045 to 0.01. Specifically, the molar ratio is determined by the following formula. (Molar ratio) = (Amount of salt used (mol)) / (Amount of alkali catalyst used (mol)) When the molar ratio of the amount used is 0.0001 or more, the particle diameter can be effectively adjusted. When it is 0.045 or less, aggregation and precipitation of the silica particles can be suppressed.

[0088] When solution (A) contains a solvent other than water, the concentration of the solvent other than water is preferably the balance of water, the alkali catalyst, and the above-mentioned salt.

[0089] Solution (B) contains tetraalkoxysilane.

[0090] Examples of the tetraalkoxysilane in the solution (B) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, etc. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred because they have a fast hydrolysis reaction, are difficult for unreacted substances to remain, are excellent in productivity, and can easily obtain a stable silica sol, and tetramethoxysilane is more preferred.

[0091] As the raw material of the silica particles, raw materials other than tetraalkoxysilane such as low condensates of tetraalkoxysilane may be used, but since it has excellent reactivity, in 100% by mass of all raw materials constituting the silica particles, the tetraalkoxysilane is preferably 50% by mass or more and the raw material other than tetraalkoxysilane is 50% by mass or less, and more preferably the tetraalkoxysilane is 90% by mass or more and the raw material other than tetraalkoxysilane is 10% by mass or less.

[0092] The solution (B) may contain only tetraalkoxysilane without a solvent, but it is preferably contained because it has excellent dispersibility of tetraalkoxysilane in the reaction solution. Examples of the solvent in the solution (B) include methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These solvents may be used alone or in combination of two or more. Among these solvents, those used in the hydrolysis reaction and the condensation reaction are the same as those by-produced, and since they are excellent in production convenience, alcohol is preferred, methanol and ethanol are more preferred, and methanol is even more preferred.

[0093] The concentration of tetraalkoxysilane in solution (B) is preferably 60% to 95% by mass, more preferably 70% to 90% by mass, based on 100% by mass of solution (B). When the concentration of tetraalkoxysilane in solution (B) is 60% by mass or more, the reaction solution tends to be uniform. Further, when the concentration of tetraalkoxysilane in solution (B) is 95% by mass or less, the formation of a gel-like substance can be suppressed.

[0094] The concentration of the solvent in solution (B) is preferably 5% to 40% by mass, more preferably 10% to 30% by mass, based on 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 5% by mass or more, the formation of a gel-like substance can be suppressed. Further, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction solution tends to be uniform.

[0095] The addition rate of solution (B) per hour with respect to the volume of solution (A) is preferably 0.02 kg / hour / L to 1.3 kg / hour / L, more preferably 0.05 kg / hour / L to 0.8 kg / hour / L. When the addition rate of solution (B) is 0.02 kg / hour / L or more, the productivity of silica particles is excellent. Further, when the addition rate of solution (B) is 1.3 kg / hour / L or less, the formation of a gel-like substance can be suppressed.

[0096] As another embodiment, the silica particles according to the present embodiment can also be obtained by a production method including a step of adding solution (B) containing tetraalkoxysilane and solution (C) containing water to solution (A) containing an alkali catalyst. Solution (C) is a solution containing water, and preferably further contains an alkali catalyst.

[0097] Examples of the alkali catalyst that the solution (C) can contain include ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, tetramethylammonium hydroxide, etc. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic activity, is easy to control the particle shape, can suppress the mixing of metal impurities, has high volatility, and is excellent in removability after hydrolysis reaction and condensation reaction.

[0098] The solution (C) contains water as a solvent. Examples of solvents other than water include methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These solvents other than water may be used alone or in combination of two or more. Among the solvents of the solution (C), the one used in the hydrolysis reaction and the one by-produced are the same, and it is excellent in production convenience. Therefore, only water or a combination of water and alcohol is preferred, and only water is more preferred.

[0099] The concentration of the alkali catalyst in the solution (C) is preferably 0 mass% to 10 mass% in 100 mass% of the solution (C). The alkali catalyst in the solution (C) may be 0 mass%, that is, it may not be contained. However, when the alkali catalyst is contained, its concentration is preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 1.5 mass% or more. When the concentration of the alkali catalyst in the solution (C) is 0.5 mass% or more, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction. Also, from the viewpoint of reducing the fluctuation of the concentration of the alkali catalyst in the reaction solution, the concentration of the alkali catalyst in the solution (C) is preferably 10 mass% or less, more preferably 6 mass% or less.

[0100] The concentration of water in solution (C) is preferably 90% by mass to 100% by mass in 100% by mass of solution (C). The concentration of water in solution (C) may be 100% by mass, that is, solution (C) may be composed only of water. However, when other components are included, the concentration of water is preferably 99.5% by mass or less, more preferably 99% by mass or less. From the viewpoint of reducing the variation in the concentration of the alkali catalyst in the reaction solution, the concentration of water in solution (C) is preferably 90% by mass or more, more preferably 94% by mass or more. Further, when the concentration of water in solution (C) is 99.5% by mass or less, it is easy to adjust the concentration of the alkali catalyst in the reaction solution from the start to the end of the reaction.

[0101] The concentration of the solvent other than water in solution (C) is preferably the balance of water, or the balance of water and the alkali catalyst.

[0102] The addition of solution (B), or solutions (B) and (C) is preferably carried out into the liquid of solution (A). By adding solution (B), or solutions (B) and (C) into the liquid of solution (A), when it is desired to use an alkali catalyst with high volatility typified by ammonia and to proceed with the hydrolysis reaction and the condensation reaction at a high reaction temperature, the miscibility of each component in the reaction solution is enhanced, abnormal reactions in the air can be suppressed, and the particle shape can be easily controlled. Adding into the liquid means adding below the liquid surface. By setting the supply outlet of solution (B), or the supply outlets of solutions (B) and (C) below the liquid surface of solution (A), solution (B), or solutions (B) and (C) can be added into the liquid of solution (A).

[0103] When adding solutions (B) and (C), the timing of adding solutions (B) and (C) to solution (A) may be the same or different alternately. However, from the viewpoint of less variation in the reaction composition and no complication in the operation, it is preferably the same.

[0104] In the step of subjecting tetraalkoxysilane to a hydrolysis reaction and a condensation reaction, the pH is 8.0 to 14, preferably 8.2 to 13, and more preferably 8.5 to 12. When the pH in the above step is 8.0 or higher, the reaction rates of the hydrolysis reaction and the condensation reaction are excellent, and aggregation of silica particles can be suppressed. Further, when the pH in the above step is 14 or lower, it is easy to control the shape of the silica particles, and the smoothness of the silica particle surface is excellent.

[0105] The method for producing silica particles according to the present embodiment preferably includes a step of performing a hydrolysis reaction and a condensation reaction of alkoxysilane at 40°C or higher, and more preferably includes a step of performing the reaction at 46°C or higher. When the reaction temperature is 40°C or higher, the reaction rates of the hydrolysis reaction and the condensation reaction of alkoxysilane are moderately improved, and the four bonds of silicon atoms can form siloxane bonds before particle growth proceeds. Thereby, the silanol groups inside the fine pores existing in the particles can be reduced. As a result, when the particles are dispersed in water, the charge of the particles is reduced, so that the proportion of water bound to the particles can be reduced, which is preferable. Further, when the reaction temperature is 50°C or lower, the balance between the hydrolysis reaction rate and the condensation reaction rate is excellent.

[0106] The concentration of water in the reaction system of the hydrolysis reaction and the condensation reaction is preferably maintained at 3% by mass to 80% by mass, more preferably 5% by mass to 50% by mass, and even more preferably 12.3% by mass to 17% by mass in 100% by mass of the total amount in the reaction system. When the concentration of water in the reaction system is 3% by mass or higher, it is easy to control the hydrolysis reaction rate of tetraalkoxysilane. Further, when the concentration of water in the reaction system is 80% by mass or lower, the condensation reaction proceeds rapidly, so that the silanol groups inside the fine pores existing in the particles can be reduced. As a result, when the particles are dispersed in water, the charge of the particles is reduced, so that the proportion of water bound to the particles can be reduced, which is preferable.

[0107] The concentration of the alkali catalyst in the reaction system of the hydrolysis reaction and the condensation reaction is preferably maintained at 0.5% by mass to 4.0% by mass, more preferably maintained at 1.5% by mass to 3.5% by mass, and even more preferably maintained at 2.2% by mass to 3.0% by mass in 100% by mass of the total amount in the reaction system. When the concentration of the alkali catalyst in the reaction system is 0.5% by mass or more, the hydrolysis reaction and the condensation reaction proceed rapidly, so that the silanol groups inside the fine pores existing in the particles can be reduced. As a result, when the particles are dispersed in water, the charge carried by the particles decreases, and the proportion of water bound to the particles can be reduced, which is preferable. Further, when the concentration of the alkali catalyst in the reaction system is 4.0% by mass or less, the reaction does not proceed too rapidly, and the reaction controllability is excellent.

[0108] Since the method for producing silica particles according to the present embodiment can remove unnecessary components and add necessary components, it preferably further includes the following step (1). Step (1): A step of concentrating the obtained dispersion of silica particles and adding a dispersion medium

[0109] Either the concentration of the dispersion of silica particles or the addition of the dispersion medium in step (1) may be performed first.

[0110] The method for concentrating the dispersion of silica particles is not particularly limited, and examples thereof include a heating concentration method and a membrane concentration method. To concentrate the dispersion of silica particles by the heating concentration method, the dispersion may be heated and concentrated under normal pressure or reduced pressure.

[0111] To concentrate the dispersion of silica particles by the membrane concentration method, membrane separation by ultrafiltration is preferable. Here, the main purpose of the ultrafiltration method is to remove unnecessary components such as intermediate products. The molecular weight cut-off of the ultrafiltration membrane used here is selected to be able to filter and separate the intermediate product according to the intermediate product in the dispersion. Examples of the material of the ultrafiltration membrane include polysulfone, polyacrylonitrile, sintered metal, ceramic, carbon, etc. Examples of the form of the ultrafiltration membrane include spiral type, tubular type, hollow fiber type, etc.

[0112] Examples of the dispersion medium added to the dispersion of silica particles include, for example, water, methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These dispersion media may be used alone or in combination of two or more. Among these dispersion media, water and alcohol are preferred and water is more preferred because of their excellent affinity with silica particles.

[0113] Since the method for producing silica particles according to this embodiment can increase the degree of condensation of silica particles, it is further preferable to include the following step (2). Step (2): A step of subjecting the dispersion of silica particles obtained in step (1) to a pressure heat treatment

[0114] The pressure of the pressure heat treatment is preferably 0.10 MPa to 2.3 MPa, and more preferably 0.12 MPa to 2.0 MPa. When the pressure of the pressure heat treatment is 0.10 MPa or more, the degree of condensation of silica particles can be increased. Also, when the pressure of the pressure heat treatment is 2.3 MPa or less, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and aggregation ratio, and the dispersion stability of the silica sol is excellent.

[0115] Pressurization may be performed by heating the dispersion of silica particles above the boiling point of the dispersion medium in a sealed state. When the aqueous dispersion of silica particles is heated to 100 °C or more in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0116] The temperature of the pressure heating treatment is preferably 100°C to 220°C, more preferably 110°C to 180°C. When the temperature of the pressure heating treatment is 100°C or higher, the degree of condensation of the silica particles can be increased. When the temperature of the pressure heating treatment is 220°C or lower, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and aggregation ratio, and the dispersion stability of the silica sol is excellent.

[0117] The time of the pressure heating treatment is preferably 0.25 hours to 10 hours, more preferably 0.5 hours to 8 hours. When the time of the pressure heating treatment is 0.25 hours or longer, the degree of condensation of the silica particles can be increased. When the time of the pressure heating treatment is 10 hours or shorter, silica particles can be produced without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and aggregation ratio, and the dispersion stability of the silica sol is excellent.

[0118] Since the pressure heating treatment can increase the degree of condensation of the silica particles without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and aggregation ratio, it is more preferably carried out in an aqueous dispersion.

[0119] The pH when the pressure heating treatment is carried out in an aqueous dispersion is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH when the pressure heating treatment is carried out in an aqueous dispersion is 6.0 or higher, gelation of the silica sol can be suppressed. Also, when the pH when the pressure heating treatment is carried out in an aqueous dispersion is 8.0 or lower, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle diameter, average secondary particle diameter, cv value, and aggregation ratio.

[0120] [Silica sol] The silica sol according to this embodiment contains the silica particles according to this embodiment.

[0121] As the silica sol, the dispersion of the silica particles according to this embodiment may be used as it is, or it may be produced by removing unnecessary components and adding necessary components among the components in the dispersion of the silica particles according to this embodiment.

[0122] The silica sol according to this embodiment preferably contains silica particles and a dispersion medium. Examples of the dispersion medium in the silica sol include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, and the like. These dispersion media in the silica sol may be used alone or in combination of two or more. Among these dispersion media in the silica sol, water and alcohol are preferable and water is more preferable because of their excellent affinity with the silica particles.

[0123] The content of the silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and still more preferably 5% by mass to 30% by mass in 100% by mass of the total amount of the silica sol. When the content of the silica particles in the silica sol is 3% by mass or more, the polishing rate with respect to the workpiece represented by the silicon wafer is excellent. Further, when the content of the silica particles in the silica sol is 50% by mass or less, aggregation of the silica particles in the silica sol or the polishing composition can be suppressed, and the storage stability of the silica sol or the polishing composition is excellent.

[0124] The content of the dispersion medium in the silica sol is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, and still more preferably 70% by mass to 95% by mass in 100% by mass of the total amount of the silica sol. When the content of the dispersion medium in the silica sol is 50% by mass or more, aggregation of the silica particles in the silica sol or the polishing composition can be suppressed, and the storage stability of the silica sol or the polishing composition is excellent. Further, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate with respect to the workpiece represented by the silicon wafer is excellent.

[0125] The content of the silica particles and the dispersion medium in the silica sol can be set within a desired range by removing unnecessary components and adding necessary components among the components in the obtained dispersion liquid of the silica particles.

[0126] The content rate of the basic substance in the silica sol is preferably 1 mass ppm to 1000 mass ppm, more preferably 10 mass ppm to 500 mass ppm, still more preferably 45 mass ppm to 150 mass ppm, and quite preferably 50 mass ppm to 100 mass ppm in 100 mass% of the total amount of the silica sol. When the content rate of the basic substance in the silica sol is 1 mass ppm or more, the pH of the silica sol can be appropriately maintained near neutrality, so that the storage stability is excellent. Further, when the content rate of the basic substance in the silica sol is 1000 mass ppm or less, it is preferable in that corrosion of the object to be polished and the equipment used for polishing can be avoided when the silica sol is used for polishing. Also, it is preferable in that pH adjustment becomes easy when adjusting the polishing composition using the silica sol. Here, the basic substance is a general term for substances showing basicity, such as nitrogenous basic substances such as ammonia and amines, and inorganic hydroxides.

[0127] The content rate of the basic substance in the silica sol can be adjusted by appropriately selecting the type of the alkali catalyst used in the process of manufacturing the silica particles and then appropriately removing it. When ammonia is used as the alkali catalyst, the ammonia content rate in the silica sol can be appropriately decreased by performing the removal of the dispersion medium in the above-mentioned step (1) for an appropriate length of time. At this time, it is preferable to heat the dispersion liquid of the silica particles to remove the dispersion medium in order to improve the efficiency of ammonia removal.

[0128] The measurement method of the content rate of the basic substance in the silica sol may be selected according to the type of the target basic substance. For example, in the case of an amine, the amine can be quantified by adding sodium hydroxide to the silica sol to dissolve the silica particles and then measuring the obtained liquid by ion chromatography. Also, in the case of ammonia, the content rate of ammonia in the silica sol can be quantified by adding sodium hydroxide to the silica sol to desorb all ammonia in the form of ammonia molecules (NH3) from the silica particles and then measuring with an ammonia electrode.

[0129] In addition to silica particles and a dispersion medium, silica sol may contain other components such as an oxidizing agent, a preservative, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, an antibacterial and biocidal agent, etc., as long as its performance is not impaired. In particular, since the silica sol has excellent storage stability, it is preferable to include an antibacterial and biocidal agent in the silica sol.

[0130] Examples of the antibacterial and biocidal agent include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, sodium chlorite, etc. These antibacterial and biocidal agents may be used alone or in combination of two or more. Among these antibacterial and biocidal agents, hydrogen peroxide is preferable because of its excellent affinity with the silica sol. The antibacterial and biocidal agent includes those generally referred to as bactericides.

[0131] The content of the antibacterial and biocidal agent in the silica sol is preferably 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 1% by mass in 100% by mass of the total amount of the silica sol. When the content of the antibacterial and biocidal agent in the silica sol is 0.0001% by mass or more, the silica sol has excellent storage stability. When the content of the antibacterial and biocidal agent in the silica sol is 10% by mass or less, the original performance of the silica sol is not impaired.

[0132] The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or more, it has excellent dispersion stability and can suppress the aggregation of silica particles. Also, when the pH of the silica sol is 8.0 or less, it prevents the dissolution of silica particles and has excellent long-term storage stability. The pH of the silica sol can be set within a desired range by adding a pH adjuster.

[0133] [Polishing composition] The polishing composition according to this embodiment contains the silica sol according to this embodiment. The polishing composition according to this embodiment preferably contains a water-soluble polymer in addition to the silica sol according to this embodiment.

[0134] The water-soluble polymer enhances the wettability of the polishing composition with respect to the object to be polished typified by a silicon wafer. The water-soluble polymer is preferably a polymer having a highly hydrophilic functional group. The affinity between this highly hydrophilic functional group and the surface silanol group of the silica particles is high, and the silica particles and the water-soluble polymer are stably dispersed in closer proximity in the polishing composition. Therefore, when polishing an object to be polished typified by a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0135] Examples of the water-soluble polymer include cellulose derivatives, polyvinyl alcohol, polyvinyl pyrrolidone, copolymers having a polyvinyl pyrrolidone skeleton, polymers having a polyoxyalkylene structure, and the like.

[0136] Examples of the cellulose derivative include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, and the like.

[0137] Examples of the copolymer having a polyvinyl pyrrolidone skeleton include a graft copolymer of polyvinyl alcohol and polyvinyl pyrrolidone.

[0138] Examples of the polymer having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, a copolymer of ethylene oxide and propylene oxide, and the like.

[0139] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred and hydroxyethyl cellulose is more preferred because they have a high affinity for the surface silanol groups of silica particles and act synergistically to impart good hydrophilicity to the surface of the object to be polished.

[0140] The mass average molecular weight of the water-soluble polymer is preferably from 1,000 to 3,000,000, more preferably from 5,000 to 2,000,000, and even more preferably from 10,000 to 1,000,000. When the mass average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. Also, when the mass average molecular weight of the water-soluble polymer is 3,000,000 or less, it has excellent affinity with the silica sol and excellent polishing rate with respect to the object to be polished typified by a silicon wafer.

[0141] The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography under the condition that a 0.1 mol / L NaCl solution is used as the mobile phase in terms of polyethylene oxide.

[0142] The content of the water-soluble polymer in the polishing composition is preferably from 0.02% by mass to 10% by mass, more preferably from 0.05% by mass to 5% by mass in 100% by mass of the total amount of the polishing composition. When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Also, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0143] In addition to the silica sol and the water-soluble polymer, the polishing composition according to the present embodiment may contain other components such as basic compounds, polishing accelerators, surfactants, hydrophilic compounds, preservatives, fungicides, pH adjusters, pH buffers, surfactants, chelating agents, antibacterial and biocidal agents, etc., as long as their performance is not impaired. In particular, it is possible to perform chemical polishing (chemical etching) by applying a chemical action to the surface of the object to be polished typified by a silicon wafer, and the polishing rate of the object to be polished typified by a silicon wafer can be improved by the synergistic effect with the surface silanol groups of the silica particles. Therefore, it is preferable to include a basic compound in the polishing composition.

[0144] Examples of the basic compound include organic basic compounds, alkali metal hydroxides, alkali metal hydrogen carbonates, alkali metal carbonates, ammonia, and the like. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogen carbonate, and ammonium carbonate are preferable because they have high water solubility and excellent affinity with silica particles and water-soluble polymers. Ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferable, and ammonia is even more preferable.

[0145] The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass in 100% by mass of the total amount of the polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of the object to be polished typified by a silicon wafer can be improved. Also, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0146] The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or more, aggregation of silica particles in the polishing composition can be suppressed, and the dispersion stability of the polishing composition is excellent. Also, when the pH of the polishing composition is 12.0 or less, dissolution of silica particles can be suppressed, and the stability of the polishing composition is excellent. The pH of the polishing composition can be set within a desired range by adding a pH adjuster.

[0147] The polishing composition can be obtained by mixing the silica sol, water-soluble polymer, and, if necessary, other components according to this embodiment. However, considering storage and transportation, it may be prepared at a high concentration once and diluted with water or the like immediately before polishing.

[0148] [Polishing Method] The polishing method according to this embodiment is a method of polishing using a polishing composition containing the silica sol according to this embodiment. It is preferable to use the polishing composition described above as the polishing composition. As a specific polishing method, for example, there is a method of pressing the surface of a silicon wafer against a polishing pad, dropping the polishing composition according to this embodiment onto the polishing pad, and polishing the surface of the silicon wafer.

[0149] [Method for Manufacturing Semiconductor Wafer] The method for manufacturing a semiconductor wafer according to this embodiment is a method including a step of polishing using the polishing composition according to this embodiment. The specific polishing composition and polishing method are as described above. Examples of the semiconductor wafer include a silicon wafer, a compound semiconductor wafer, and the like.

[0150] [Method for Manufacturing Semiconductor Device] The method for manufacturing a semiconductor device according to this embodiment is a method including a step of polishing using the polishing composition according to this embodiment. The specific polishing composition and polishing method are as described above.

[0151] [Applications] The silica particles and silica sol according to this embodiment can be suitably used for polishing applications. For example, they can be used 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 for photomasks and liquid crystals, polishing magnetic disk substrates, etc. Among them, they can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

[0152] As the object to be polished, there are also other materials such as metals like Si, Cu, W, Ti, Cr, Co, Zr, Hf, Mo, Ta, Ru, Au, Pt, Ag, Ni, Al; metal compounds such as oxides, nitrides, silicides of the above metals, intermetallic compounds, etc., glass, resin, etc. Among these objects to be polished, it can be preferably used for metals and metal oxides, and can be particularly preferably used for metal oxides.

Examples

[0153] Hereinafter, the present invention will be described more specifically using examples. However, the present invention is not limited to the description of the following examples as long as the gist thereof is not deviated.

[0154] [Pulse NMR method] Regarding 1 mL of the dispersion of silica particles obtained in the examples and comparative examples, measurement was performed using a pulse NMR measuring device (manufactured by Bruker, minispec mq20) to obtain a magnetization decay curve. The CPMG method was used as the measurement method. The measurement was carried out at a temperature of 25 °C using a 10 mmΦ probe. Other measurement conditions are shown below. · 90°-180° pulse interval: 0.04 ms · Repetition waiting time: 10 s · Number of accumulations: 16 times · Number of data points: 800

[0155] The obtained magnetization decay curve data was analyzed using analysis software (manufactured by Bruker, TDNMR-A) with a two-component exponential function. That is, the observed M(t) was approximated by the following formula (※) to obtain Mi and T2i (where T2s < T2l). Hereinafter, the method for obtaining Mi and T2i will be specifically shown. M(t) = Ms × exp(-t / T2s) + Ml × exp(-t / T2l) ·· Formula (※)

[0156] First, 200 to 800 data points were used for analysis to obtain Ml and T2l. Next, the difference between the approximate curve obtained using the obtained Ml and T2l and the initial data was taken. Using 1 to 199 data points of the difference data for analysis, Ms and T2s were obtained. Then, the percentage of water bound to the silica particles was determined from [Ms / (Ms + Ml)]×100.

[0157] (Measurement of average secondary particle size) The dispersion liquids of the silica particles obtained in the examples and comparative examples were used to measure the average secondary particle size of the silica particles using a dynamic light scattering particle size measuring device (Zetasizer Nano ZS manufactured by Malvern Panalytical).

[0158] (Measurement of average primary particle size) The dispersion liquids of the silica particles obtained in the examples and comparative examples were dried at 150°C, and the specific surface area of the silica particles was measured using a specific surface area automatic measuring device "BELSORP-MR1" (model name, Microtrac BEL Corporation). Using the following formula (2), with a density of 2.2 g / cm 3 the average primary particle size was calculated. Average primary particle size (nm) = 6000 / (specific surface area (m 2 / g) × density (g / cm 3 )) ··· (2)

[0159] (Calculation of aggregation ratio) The aggregation ratios of the silica particles obtained in the examples and comparative examples were calculated using the following formula (4) from the average primary particle size measured by the aforementioned measurement method and the average secondary particle size measured by the aforementioned measurement method. Aggregation ratio = average secondary particle size / average primary particle size ··· (4)

[0160] (Measurement of refractive index) From the dispersion liquids of the silica particles obtained in the examples and comparative examples, dry powders of the silica particles were obtained. 0.1 g of the dry powder of the silica particles was placed in a 10 mL glass bottle, and special grade 2-propanol and special grade toluene were added while changing their ratios. When the powder in the glass bottle became transparent, the supernatant was measured with an Abbe refractometer "RX-7000α" (model name, Atago Co., Ltd.) to obtain the refractive index of the silica particles.

[0161] (Average major axis and average minor axis of the silica particles, and ratio of major axis / minor axis) After diluting the silica sol about 10,000 times with 1-propanol, the droplets were dried on a substrate with a flat surface. More than 100 silica particles remaining on the substrate surface were observed with a scanning electron microscope. After determining the major axis and minor axis for each particle, the average value of all the observed particles for each of the major axis and minor axis was determined. The obtained average major axis was divided by the average minor axis to obtain the ratio of major axis / minor axis of the silica particles. Here, the major axis and minor axis were the long side and short side of the rectangle circumscribing the particle with the minimum area, respectively. The magnification for observation with the scanning electron microscope was set such that 10 to 30 particles were included in one field of view.

[0162] (Number of fine particles in the silica sol) In the observation of the silica particles with the above scanning electron microscope, the presence or absence of particles with a major axis less than 10 nm was confirmed.

[0163] (Silica concentration in the silica sol) Approximately 3 g of the silica sol was precisely weighed into a glass container, which was heated to 150 °C in an oven to evaporate the moisture and dried. The mass of the silica particles obtained after drying was accurately measured, and the silica concentration in the silica sol was determined from the difference from the weight before drying.

[0164] [Example 1] A solution (B) obtained by mixing tetramethoxysilane and methanol at a mass ratio of 5.7:1 and a solution (C) of a 6.6 mass% aqueous ammonia solution were each prepared. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged in advance with a solution (A) obtained by mixing methanol, pure water, and aqueous ammonia at a mass ratio of 10.0:1.1:1. The concentration of ammonia in solution (A) was set to 2.4 mass%. While maintaining the temperature of the reaction solution at 50°C, 63.6 parts by volume of solution (B) and 24.6 parts by volume of solution (C) were each added to 100 parts by volume of solution (A) at a constant rate over 153 minutes to obtain a dispersion of silica particles. The obtained dispersion of silica particles was heated while adjusting the liquid volume by adding pure water so that the silica particle content became approximately 20 mass%, to remove methanol and ammonia, thereby obtaining a dispersion of silica particles with a silica particle content of approximately 20 mass%. The refractive index of the obtained silica particles was 1.413. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0165] [Example 2] A dispersion of silica particles was obtained in the same manner as in Example 1, except that ammonium bicarbonate was added to solution (A). In solution (A), the molar ratio of ammonium bicarbonate to ammonia was 0.125:100. The aspect ratio (major axis / minor axis) of the obtained silica particles was 1.12.

[0166] [Example 3] A dispersion of silica particles was obtained in the same manner as in Example 1, except that ammonium bicarbonate was added to solution (A). In solution (A), the molar ratio of ammonium bicarbonate to ammonia was 0.25:100. The aspect ratio (major axis / minor axis) of the obtained silica particles was 1.10. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0167] [Example 4] A silica particle dispersion was obtained in the same manner as in Example 1, except that ammonium bicarbonate was added to Solution (A). In Solution (A), the molar ratio of ammonium bicarbonate to ammonia was 0.375:100. The ratio of the major axis to the minor axis of the obtained silica particles was 1.15. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0168] [Example 5] A silica particle dispersion was obtained in the same manner as in Example 1, except that ammonium bicarbonate was added to Solution (A). In Solution (A), the molar ratio of ammonium bicarbonate to ammonia was 0.50:100. The ratio of the major axis to the minor axis of the obtained silica particles was 1.10. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0169] [Example 6] A silica particle dispersion was obtained in the same manner as in Example 1, except that ammonium bicarbonate was added to Solution (A). In Solution (A), the molar ratio of ammonium bicarbonate to ammonia was 0.876:100. The ratio of the major axis to the minor axis of the obtained silica particles was 1.09. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0170] [Comparative Example 1] Solution (B) in which tetramethoxysilane and methanol were mixed at a mass ratio of 5.7:1 and Solution (C) of a 2.2 mass% aqueous ammonia solution were each prepared. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with Solution (A) in which methanol, pure water, and aqueous ammonia had been previously mixed at a mass ratio of 20.3:5.1:1. The concentration of ammonia in Solution (A) was 1.1 mass%. While maintaining the temperature of the reaction solution at 35°C, 58.0 parts by volume of solution (B) and 13.5 parts by volume of solution (C) were added to 100 parts by volume of solution (A) at a constant rate over 139 minutes to obtain a dispersion of silica particles. The obtained dispersion of silica particles was adjusted in liquid volume by adding pure water while raising the temperature to remove methanol and ammonia so that the content rate of silica particles became about 20% by mass, and a dispersion of silica particles with a silica particle content rate of about 20% by mass was obtained. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0171] [Comparative Example 2] Solution (B) obtained by mixing tetramethoxysilane and methanol at a mass ratio of 5.7:1 and solution (C) of 6.2% by mass aqueous ammonia solution were each prepared. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged in advance with solution (A) obtained by mixing methanol, pure water, and aqueous ammonia at a mass ratio of 11.9:0.95:1. The concentration of ammonia in solution (A) was 2.1% by mass. While maintaining the temperature of the reaction solution at 38°C, 89.3 parts by volume of solution (B) and 34.3 parts by volume of solution (C) were added to 100 parts by volume of solution (A) at a constant rate over 225 minutes to obtain a dispersion of silica particles. The obtained dispersion of silica particles was adjusted in liquid volume by adding pure water while raising the temperature to remove methanol and ammonia so that the content rate of silica particles became about 20% by mass, and a dispersion of silica particles with a silica particle content rate of about 20% by mass was obtained. When the obtained silica particles were observed with a scanning electron microscope, no fine particles were detected.

[0172] [Comparative Example 3] As the silica particle dispersion of Comparative Example 3, the silica particle dispersion "PL-2" manufactured by Fuso Chemical Industry Co., Ltd. was used. The refractive index of these silica particles was 1.400, and the ratio of the major axis to the minor axis was 1.24.

[0173] [Comparative Example 4] As the silica particle dispersion of Comparative Example 4, the silica particle dispersion "PL-3" manufactured by Fuso Chemical Industry Co., Ltd. was used. The refractive index of this silica particle was 1.383, and the ratio of the major axis / minor axis was 1.19.

[0174] [Comparative Example 5] As the silica particle dispersion of Comparative Example 5, the silica particle dispersion "PL-7" manufactured by Fuso Chemical Industry Co., Ltd. was used. The refractive index of this silica particle was smaller than the refractive index of 2-propanol, 1.377, and could not be accurately measured. Further, the ratio of the major axis / minor axis of this silica particle was 1.05.

[0175] [Comparative Example 6] Silica particle production was attempted in the same manner as in Example 1, except that ammonium bicarbonate was added to Solution (A). In Solution (A), the molar ratio of ammonium bicarbonate to ammonia was 5:100. However, during the hydrolysis and condensation reaction of tetramethoxysilane, the silica particles significantly aggregated and production could not be continued.

[0176] (Evaluation of Polishing Rate) Regarding the silica particle dispersions obtained in the examples and comparative examples, the polishing rate with respect to a substrate having a metal oxide film on the surface was evaluated using the following criteria. A: It is assumed that the polishing rate is extremely excellent. B: It is assumed that the polishing rate is excellent. C: It is assumed that the polishing rate is inferior.

[0177] As can be seen from Table 1, the silica particles of Examples 1 to 6 satisfied the above formula (1), and the silica particles of Comparative Examples 1 to 5 did not satisfy the above formula (1). Further, the silica particles of Example 1 had a smaller proportion of water bound to the particles compared to the silica particles of Comparative Examples 1, 3, and 4 having the same particle size. Since both the average secondary particle size and the proportion of water bound to the particles were within the desired ranges, it is considered that excellent polishing rates are exhibited when the silica particles of Example 1 are used for polishing. Furthermore, the silica particles of Examples 2 to 6 correspond to the silica particles obtained by adding salt to Solution (A) in the production method of Example 1. While the average secondary particle diameter became larger compared to the silica particles of Example 1, the ratio of water bound to the silica particles was maintained at a small value. Since the ratio of water bound to the particles of the silica particles of Examples 2 and 3 is smaller than that of the silica particles of Comparative Examples 2 and 5 having a comparable average secondary particle diameter, it is considered that excellent polishing rates are exhibited when the silica particles of Examples 2 and 3 are used for polishing. Also, for the silica particles of Examples 4 to 6, although the average secondary particle diameter is larger than that of the silica particles of Comparative Examples 2, 4, and 5, the ratio of water bound to the silica particles was maintained at a value comparable to or smaller than that of the silica particles of the comparative examples. Therefore, it is considered that more excellent polishing rates are exhibited when the silica particles of Examples 4 to 6 are used for polishing.

[0178]

Table 1

Industrial Applicability

[0179] The silica particles 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 a planarization process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for photomasks and liquid crystals, polishing magnetic disk substrates, and the like.

Claims

1. Silica particles which satisfy the following formula (1), where the average secondary particle diameter of the silica particles is x (nm) and the proportion of water bound to the silica particles as measured by pulse NMR is y (%): y<0.02x + 0.3... (1)

2. The silica particles according to claim 1 , which satisfy the following formula (1a): y<0.02x... (1a)

3. 2. The silica particles according to claim 1, having an average primary particle size of 5 nm to 500 nm.

4. 2. The silica particles according to claim 1, having an average secondary particle diameter of 10 nm to 1000 nm.

5. 2. The silica particles according to claim 1, having a metal impurity content of 5 ppm by mass or less.

6. The method for producing silica particles according to any one of claims 1 to 5, comprising the step of adding a solution (B) containing a tetraalkoxysilane to a solution (A) containing an alkali catalyst.

7. The method for producing silica particles according to claim 6 , further comprising the step of subjecting alkoxysilane to hydrolysis and condensation reaction in a solution containing a salt.

8. The method for producing silica particles according to claim 7 , wherein the salt is a salt that decomposes or volatilizes when heated up to 100° C.

9. 8. The method for producing silica particles according to claim 7, wherein in the step of subjecting alkoxysilane to hydrolysis and condensation reaction in a solution containing a salt, a molar ratio of the amount of the salt used to the amount of the alkali catalyst used is 0.0001 to 0.

045.

10. A silica sol comprising the silica particles according to any one of claims 1 to 5.

11. The silica sol according to claim 10, wherein the content of silica particles in the total amount of the silica sol (100% by mass) is 3% by mass to 50% by mass.

12. The silica sol according to claim 10, having a pH of 6.0 to 8.

0.

13. A polishing composition comprising the silica sol according to claim 10.

14. A polishing method, comprising polishing with the polishing composition according to claim 13.

15. A method for producing a semiconductor wafer, comprising a step of polishing the wafer with the polishing composition according to claim 13.

16. A method for producing a semiconductor device, comprising a step of polishing with the polishing composition according to claim 13.

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