Silica particle and method for producing the same, silica sol, abrasive composition, abrasive method, method for producing semiconductor wafer, and method for producing semiconductor device

Abstract

To provide silica particles, a silica sol, and an abrasive composition excellent in mechanical strength, abrasive characteristics, and storage stability.SOLUTION: A silica particle has a refractive index of 1.390 or more and an average secondary particle diameter of 20 nm or more, and is amorphous.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] Japanese Patent Application Publication No. 2019-89692 Summary of the Invention [Problem to be solved by the invention]

[0006] However, generally, the silica particles obtained by hydrolysis and condensation of alkoxysilane do not have sufficient mechanical strength.And, if the silica particles with insufficient mechanical strength are used for polishing, the silica particles are broken during polishing, and the broken silica particles are attached to the object to be polished, which adversely affects the polishing.In addition, if the silica particles are broken during polishing, a sufficient polishing rate cannot be maintained.Furthermore, such silica particles have poor storage stability.

[0007] The silica particles obtained by the production methods disclosed in Patent Documents 1 and 2 are inferior in mechanical strength, polishing properties, and storage stability.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide silica particles, silica sol, and polishing composition having excellent mechanical strength, polishing properties, and storage stability. Another object of the present invention is to provide a polishing method for polishing an object, a method for manufacturing a semiconductor wafer, and a method for manufacturing a semiconductor device, which are excellent in productivity. [Means for solving the problem]

[0009] Conventional silica particles do not necessarily have sufficient mechanical strength, polishing properties, and storage stability. The present inventors have focused on the fact that silica particles are crushed as a cause of the reduction in the mechanical strength, polishing properties, and storage stability of silica particles, and have conducted intensive research into reducing this. As a result, the present inventors have discovered that nanoscale pores exist inside silica particles, and that when these are large, the nanoscale pores become the starting point of crushing, thereby reducing the mechanical strength. The present inventors have also found that silica particles having large nanoscale pores have poor storage stability, such as the alkoxy groups reacting during storage, because many alkoxy groups remain inside the particles. Furthermore, the present inventors have found that optimizing the nanoscale pores measured by positron annihilation spectroscopy can suppress the pores of silica particles from becoming the starting point of crushing, thereby improving the mechanical strength, polishing properties, and storage stability of silica particles, and have completed the present invention.

[0010] That is, the gist of the present invention is as follows. [1] The average pore volume of nanoscale pores measured by positron annihilation spectroscopy is 5.3 nm 3 Silica particles, which are: [2] The average pore volume of nanoscale pores measured by positron annihilation spectroscopy is 4.0 nm 3 The silica particles according to [1], [3] The average pore volume of nanoscale pores measured by positron annihilation spectroscopy is 1.5 nm 3 The silica particles according to [1] above. [4] The average pore volume of atomic-scale pores measured by positron annihilation spectroscopy is 0.33 nm 3 The silica particles according to [1] above. [5] The average pore volume of atomic-scale pores measured by positron annihilation spectroscopy is 0.80 nm 3 The silica particles according to [1], [6] The volume of pores with diameters of 2 nm or less measured by nitrogen gas adsorption is 0.0070 cm 3 / g or less. [7] The silica particles according to [1], having a refractive index of 1.390 or more. [8] The silica particles according to [1], having a metal impurity content of 5 ppm or less. [9] The silica particles according to [1], which are mainly composed of a tetraalkoxysilane condensate.

[0011]

[10] The method for producing silica particles according to any one of [1] to [9], comprising a step of carrying out a hydrolysis reaction and a condensation reaction of an alkoxysilane at 40° C. or higher.

[11] A silica sol comprising the silica particles according to any one of [1] to [9].

[12] A polishing composition comprising the silica sol according to

[11] .

[13] A polishing method comprising polishing using the polishing composition according to

[12] .

[14] A method for producing a semiconductor wafer, comprising the step of polishing the semiconductor wafer with the polishing composition according to

[12] .

[15] A method for producing a semiconductor device, comprising the step of polishing a semiconductor device with the polishing composition according to

[12] . Effect of the Invention

[0012] The silica particles of the present invention have improved mechanical strength, polishing properties and storage stability, and are less likely to be destroyed in the process of polishing a polished object using a polishing composition containing the silica particles. Therefore, the silica sol and polishing composition containing the silica particles of the present invention can be used to effectively polish an object to be polished without damaging it, and the silica particles can be easily removed after polishing. Therefore, high-quality polished products can be produced with high productivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and practiced in various ways within the scope of the gist. In addition, when the expression "~" is used in this specification, it is used as an expression including the numerical values ​​or physical property values ​​before and after it.

[0014] (Silica particles) The silica particles of the present invention have an average pore volume of nanoscale pores (hereinafter, also simply referred to as the "average pore volume of nanoscale pores") of 5.3 nm 3 Less than 4.0 nm, preferably 3 Less than 3.5 nm, more preferably 3 This reduces the starting points for crushing the silica particles, and improves the mechanical strength, polishing properties, and storage stability of the silica particles.

[0015] The reason why nanoscale pores are formed in silica particles is thought to be that the reaction rate of the hydrolysis reaction and condensation reaction of alkoxysilane is not fast enough, and particle growth proceeds before the four bonds of silicon atoms form siloxane bonds, and alkoxy groups and silanol groups remain inside the particles. Silica particles with large nanoscale pores have poor mechanical strength because the pores become the starting points for crushing. If silica particles with such large nanoscale pores are used for polishing, the silica particles are destroyed during polishing, and the destroyed silica particles adhere to the polished body, which has a negative effect on polishing. In addition, if the silica particles are destroyed during polishing, a sufficient polishing rate cannot be maintained. Furthermore, silica particles with large nanoscale pores have many alkoxy groups remaining inside the particles, and therefore have poor storage stability, such as the alkoxy groups reacting during storage.

[0016] By setting the average pore volume of the nanoscale pores in the silica particles of the present invention within the above range, the starting points for crushing the silica particles are reduced and the alkoxy groups remaining inside the particles are reduced, which is thought to improve the mechanical strength, polishing properties and storage stability of the silica particles.

[0017] Although there is no particular lower limit for the average pore volume of the nanoscale pores of the silica particles, from the viewpoint of maintaining the flexibility of the particles and preventing scratches during polishing, a lower limit of 1.5 nm 3 It is preferable that the thickness is 2.0 nm or more. 3 More preferably, it is 2.5 nm or more. 3 More preferably, it is equal to or greater than this.

[0018] The positron annihilation method is a method for measuring the lifetime of a positron by the time difference between the moment a positron is emitted and the moment the gamma ray generated when the positron is annihilated is observed. When a positron is incident on a material, the larger the vacancy defects in the material are, the longer the positron lifetime becomes. By utilizing this property, the average pore volume of nanoscale pores in silica particles and the average pore volume of atomic scale pores described later can be measured.

[0019] The average pore volume of nanoscale pores of silica particles in this specification is a value measured by positron annihilation. Specifically, the positron lifetime spectrum obtained by applying positron annihilation to dried silica particles is fitted with a linear sum of four exponential functions to obtain the average positron lifetime of each component. Of these four exponential function components, the two components with the shortest lifetimes are components that are not involved in the material. The component with the third shortest lifetime is a component that corresponds to atomic scale pores described below. The component with the fourth shortest lifetime is a component that corresponds to nanoscale pores, and the average pore volume is obtained by applying the average lifetime to the following formula and converting it into the volume of the pores. From the average pore volume of the nanoscale pores of the obtained silica particles, the pores surrounded by Si-O-Si structures, silanol groups and / or alkoxide groups, etc., mainly 1 nm in silica particles, are obtained. 3 It is possible to grasp the volume of pores exceeding a volume. The relationship between positron lifetime and pore volume was based on K. Wada et al., J. Phys.: Conf. Ser. 443, 012003 (2013).

[0020]

number

[0021] Where:

[0022]

number

[0023] where τ is the average positron lifetime, R is the average radius of the nanoscale pores, r0 is the correction value for the radius of the nanoscale pores, and λ T is the annihilation rate of ortho-positronium in vacuum, and V is the average pore volume of the nanoscale pores.

[0024] Other methods for measuring pore volume include gas adsorption and desorption methods such as nitrogen gas adsorption, but these have problems such as the inability to measure closed pores and the occurrence of errors in the measurement results due to chemical interactions between the measurement object and the probe gas. The positron annihilation method can measure the volume of closed pores and is not dependent on the chemical properties of the measurement object, making it possible to perform highly accurate measurements.

[0025] The average pore volume of the atomic-scale pores of the silica particles measured by a positron annihilation method (hereinafter, also simply referred to as the "average pore volume of the atomic-scale pores") is 0.33 nm from the viewpoint of further improving the mechanical strength, polishing properties, and storage stability of the silica particles. 3 It is preferable that the thickness is 0.35 nm or more. 3 More preferably, it is 0.37 nm or more. 3 From the viewpoint of maintaining the stability of the bond angle of the siloxane bond, it is more preferable that the bond angle is 0.80 nm or more. 3 Preferably, it is 0.60 nm or less. 3 More preferably, it is 0.45 nm or less. 3 It is even more preferable that:

[0026] The average pore volume of the atomic-scale pores of the silica particles in this specification is a value measured by positron annihilation. A positron lifetime spectrum is obtained in the same manner as in the measurement of the average pore volume of the nanoscale pores, and fitting is performed with four components. The average lifetime of the component with the third shortest lifetime is converted to the pore volume by applying the following formula to obtain the average pore volume of the atomic-scale pores. From the obtained average pore volume of the atomic-scale pores of the silica particles, the volume of the pores inside the ring structure of the siloxane network, etc., mainly in the silica particles, of 1 nm 3 The volume of the pores can be determined as follows:

[0027]

number

[0028] Where:

[0029]

number

[0030] where τ is the average positron lifetime, R is the average radius of the atomic-scale pores, ΔR is a correction value for the radius of the atomic-scale pores, and V is the average pore volume of the atomic-scale pores.

[0031] The mechanical strength of silica particles can be adjusted by the pore volume. From this perspective, the pore volume of pores with diameters of 2 nm or less measured by nitrogen gas adsorption method is 0.0070 cm 3 / g or less, and 3 / g or less is more preferable, and 0.0050 cm 3 From the viewpoint of maintaining the flexibility of the silica particle structure, the pore volume of pores with diameters of 2 nm or less as measured by nitrogen gas adsorption method is more preferably 0.0005 cm 3 / g or more, and 0.001 cm 3 / g or more is more preferable, and 0.0015 cm 3 It is more preferable that the molecular weight is 1 / g or more.

[0032] When the refractive index of the silica particles is large, the atomic density of the silica particles is high and the mechanical strength is easily maintained, so the refractive index is preferably 1.390 or more, more preferably 1.400 or more, and even more preferably 1.410 or more. In addition, since it is preferable for silica to maintain an amorphous structure, the refractive index is preferably 1.550 or less, more preferably 1.500 or less, and even more preferably 1.450 or less.

[0033] The refractive index of the silica particles is determined by adding different ratios of special grade 2-propanol and special grade toluene to a container containing the silica particles, measuring the supernatant when the silica particles in the container become transparent with an Abbe refractometer, and using the refractive index at that point as the refractive index of the silica particles.

[0034] The silica particles are preferably amorphous. In this case, a suitable amount of silanol groups are present on the surface of the silica particles, and in the step of polishing the object to be polished, chemical interaction occurs between the silica particles and the object to be polished via the silanol groups, and polishing proceeds smoothly. The fact that the silica particles are amorphous can be confirmed by a halo pattern observed in wide-angle X-ray scattering measurement.

[0035] The metal impurity content of the silica particles is preferably 5 ppm or less, and more preferably 2 ppm or less. When the metal impurity content of the silica particles is 5 ppm or less, it is preferable because it reduces contamination caused by metal impurities adhering to the surface of the object to be polished and the influence on the wafer characteristics caused by this during polishing of silicon wafers of semiconductor devices.It is also preferable because it reduces deterioration of quality caused by metal impurities adhering to the surface of the object to be polished diffusing into the wafer and deterioration of the performance of the semiconductor device manufactured by using such wafer.

[0036] Furthermore, when the metal impurity content of the silica particles is 5 ppm or less, the effects on the polishing rate of changes in the chemical properties (acidity, etc.) of the surface silanol groups due to the occurrence of coordinate interactions between the acidic surface silanol groups and the metal impurities, and changes in the three-dimensional environment of the silica particle surface (ease of aggregation of silica particles, etc.) are reduced, which is preferable.

[0037] The metal impurity content of silica particles in this specification is a value measured by inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, and the silica sol is heated, dissolved, and evaporated. Pure water is added to the remaining sulfuric acid droplets so that the total amount is exactly 10 g to prepare a test solution, which is then measured using an inductively coupled plasma mass spectrometry device. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver, and nickel, and the total content of these metals is the metal impurity content.

[0038] The metal impurity content of the silica particles can be reduced to 5 ppm or less by obtaining the silica particles through hydrolysis and condensation reactions using alkoxysilane as the main raw material. In the method of deionizing alkali silicate such as water glass, sodium and other impurities derived from the raw material remain, making it extremely difficult to reduce the metal impurity content of silica particles to 5 ppm or less.

[0039] The average primary particle diameter of the silica particles is preferably 10 nm to 100 nm, more preferably 15 nm to 60 nm, and even more preferably 30 nm to 50 nm. When the average primary particle diameter of the silica particles is 10 nm or more, the storage stability of the silica sol is excellent. In addition, when the average primary particle diameter of the silica particles is 100 nm or less, the surface roughness and scratches of the polished object, such as a silicon wafer, can be reduced, and the sedimentation of the silica particles can be suppressed.

[0040] 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 an automatic specific surface area 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) x density (g / cm 3 )) (2)

[0041] The average primary particle size of the silica particles can be set within a desired range by adjusting the production conditions of the silica particles.

[0042] The average secondary particle diameter of the silica particles is preferably 20 nm to 200 nm, more preferably 30 nm to 100 nm, and even more preferably 55 nm to 80 nm. When the average secondary particle diameter of the silica particles is 20 nm or more, the removability of particles and the like during cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. Furthermore, when the average secondary particle diameter of the silica particles is 200 nm or less, the surface roughness and scratches of the polished object, typified by a silicon wafer, during polishing can be reduced, the removability of particles and the like during cleaning after polishing can be excellent, and sedimentation of the silica particles can be suppressed.

[0043] The average secondary particle size of the silica particles is measured by a DLS method, specifically, using a dynamic light scattering particle size measuring device.

[0044] The average secondary particle size of the silica particles can be set within a desired range by adjusting the production conditions of the silica particles.

[0045] The cv value of the silica particles is preferably 10% to 50%, more preferably 15% to 40%, and even more preferably 20% to 35%. When the cv value of the silica particles is 10% or more, the polishing rate for the object to be polished, such as a silicon wafer, is excellent, and the productivity of the silicon wafer is excellent. When the cv value of the silica particles is 50% or less, the surface roughness and scratches of the object to be polished, such as a silicon wafer, during polishing can be reduced, and the removal of particles and the like during cleaning after polishing is excellent.

[0046] The cv value of the silica particles is calculated using the following formula (3) by measuring the average secondary particle size of the silica particles using a dynamic light scattering particle size measuring device. CV value = (standard deviation (nm) / average secondary particle size (nm)) x 100 ... (3)

[0047] The association ratio of the silica particles is preferably 1.0 to 4.0, more preferably 1.1 to 3.0. When the association ratio of the silica particles is 1.0 or more, the polishing rate for the polished object, typically a silicon wafer, is excellent, and the productivity of the silicon wafer is excellent. When the association ratio of the silica particles is 4.0 or less, the surface roughness and scratches of the polished object, typically a silicon wafer, during polishing can be reduced, and the aggregation of the silica particles can be suppressed.

[0048] The association ratio of silica particles is calculated using the following formula (4) from the average primary particle diameter measured by the above-mentioned measuring method and the average secondary particle diameter measured by the above-mentioned measuring method. Association ratio=average secondary particle diameter / average primary particle diameter... (4)

[0049] The silica particles of the present invention preferably contain an alkoxysilane condensate as the main component, more preferably a tetraalkoxysilane condensate as the main component, and even more preferably a tetramethoxysilane condensate as the main component, because they have a low content of metal impurities and are excellent in mechanical strength and storage stability. The main component refers to a component that is 50% by mass or more out of 100% by mass of all components constituting the silica particles. In order to obtain silica particles mainly composed of alkoxysilane condensates, it is preferable to use alkoxysilane as the main raw material. In order to obtain silica particles mainly composed of tetraalkoxysilane condensates, it is preferable to use tetraalkoxysilane as the main raw material. In order to obtain silica particles mainly composed of tetramethoxysilane condensates, it is preferable to use tetramethoxysilane as the main raw material. The main raw material refers to a raw material that is 50% by mass or more out of 100% by mass of all raw materials constituting the silica particles.

[0050] The surface silanol group density of the silica particles of the present invention is 1 / nm2 ~8 pieces / nm 2 is preferable, and 4 / nm 2 ~7 pieces / nm 2 It is more preferable that the surface silanol group density of the silica particle is 1 / nm 2 When the surface silanol group density of the silica particles is 8 / nm or more, the silica particles have a suitable surface repulsion, and the dispersion stability of the silica sol is excellent. 2 When the amount is equal to or less than this, the silica particles have an appropriate surface repulsion, and aggregation of the silica particles can be suppressed.

[0051] The surface silanol group density of the silica particles is measured by the Sears method, specifically, under the conditions shown below. Take a silica sol equivalent to 1.5 g of silica particles, add pure water to make the liquid volume 90 mL, add 0.1 mol / L hydrochloric acid aqueous solution until the pH becomes 3.6 in an environment of 25°C, add 30 g of sodium chloride, gradually add pure water to completely dissolve the sodium chloride, and finally add pure water until the total volume of the test liquid is 150 mL to obtain the test liquid. The obtained test liquid is placed in an automatic titrator, and 0.1 mol / L aqueous sodium hydroxide solution is added dropwise to measure the titer A (mL) of 0.1 mol / L aqueous sodium hydroxide solution required to change the pH from 4.0 to 9.0.

[0052] The consumption amount V (mL) of 0.1 mol / L sodium hydroxide solution required for the pH to change from 4.0 to 9.0 per 1.5 g of silica particles was calculated using the following formula (5), and the surface silanol group density ρ (particles / nm 2 ) is calculated. V=(A×f×100×1.5) / (W×C) ··· (5) A: The amount (mL) of 0.1 mol / L sodium hydroxide solution required to change the pH from 4.0 to 9.0 per 1.5 g of silica particles f: Potency of the 0.1 mol / L sodium hydroxide solution used C: Concentration of silica particles in silica sol (mass%) W: Amount of silica sol collected (g) ρ=(B×NA) / (1018×M×SBET) ··· (6) B: The amount of sodium hydroxide (mol) required to change the pH from 4.0 to 9.0 per 1.5 g of silica particles calculated from V NA: Avogadro's number (pieces / mol) M: Silica particle amount (1.5g) SBET: The specific surface area (m2) of silica particles measured when calculating the average primary particle size 2 / g)

[0053] (Method of producing silica particles) The silica particles of the present invention can be obtained by including a process of hydrolyzing and condensing tetraalkoxysilane at pH 8 to 14. The hydrolysis and condensation reactions are easily controlled, the reaction rate of the hydrolysis and condensation reactions can be increased, gelation of the silica particle dispersion can be prevented, and silica particles with a uniform particle size can be obtained. Therefore, a method of adding a solution (B) containing tetraalkoxysilane and, if necessary, a solution (C) to a solution (A) containing water and hydrolyzing and condensing tetraalkoxysilane is preferable. The average pore volume of the nanoscale pores of the silica particles and the average pore volume of the atomic scale pores can be set within a desired range by the production conditions of the silica particles such as pH, reaction temperature, reaction time, catalyst concentration, and raw material supply rate, and the pressurization pressure, heating temperature, and pressurization and heating time. For example, the higher the reaction temperature of the hydrolysis and condensation reactions of the tetraalkoxysilane, and the longer the time of the hydrolysis and condensation reactions of the tetraalkoxysilane, the smaller the average pore volume of the nanoscale pores of the silica particles tends to be. On the other hand, for example, the shorter the reaction time of the hydrolysis reaction and condensation reaction of tetraalkoxysilane, and the higher the temperature and pressure of the pressurized heat treatment, the larger the average pore volume of the atomic-scale pores in the silica particles tends to be.

[0054] The solution (A) contains water.

[0055] The solution (A) preferably contains a solvent other than water, since this provides excellent dispersibility of the tetraalkoxysilane in the reaction liquid. Examples of the solvent other than water in the solution (A) include methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because it is easy to dissolve tetraalkoxysilane, the by-product is the same as that used in the hydrolysis reaction and the condensation reaction, and it is convenient in production.

[0056] The solution (A) preferably contains an alkali catalyst, since this can increase the reaction rates of the hydrolysis reaction and condensation reaction of the tetraalkoxysilane.

[0057] Examples of the alkali catalyst in the solution (A) include ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide. These alkali catalysts may be used alone or in combination of two or more. Among these alkali catalysts, ammonia is preferred because it has excellent catalytic action, is easy to control the particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easy to remove after the hydrolysis reaction and the condensation reaction.

[0058] The concentration of water in solution (A) is preferably 3% by mass to 90% by mass, more preferably 5% by mass to 50% by mass, based on 100% by mass of solution (A). When the concentration of water in solution (A) is 3% by mass or more, the hydrolysis reaction rate of tetraalkoxysilane is easily controlled. Also, when the concentration of water in solution (A) is 90% by mass or less, the reaction balance between the hydrolysis reaction and the condensation reaction is good, and the particle shape is easily controlled.

[0059] The concentration of the alkali catalyst in solution (A) is preferably 0.5% by mass to 2.0% by mass, more preferably 0.6% by mass to 1.5% by mass, based on 100% by mass of solution (A). When the concentration of the alkali catalyst in solution (A) is 0.5% by mass or more, aggregation of silica particles is suppressed, and the dispersion stability of silica particles in the dispersion is excellent. In addition, when the concentration of the alkali catalyst in solution (A) is 2.0% by mass or less, the reaction does not proceed excessively fast, and the reaction controllability is excellent.

[0060] The concentration of the solvent other than water in the solution (A) is preferably the balance of water and the alkali catalyst.

[0061] The solution (B) contains a tetraalkoxysilane.

[0062] Examples of the tetraalkoxysilane in the solution (B) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferred, and tetramethoxysilane is more preferred, because they undergo a fast hydrolysis reaction, are less likely to leave unreacted substances, are highly productive, and can easily produce a stable silica sol.

[0063] The raw materials for the silica particles may be raw materials other than tetraalkoxysilane, such as low condensates of tetraalkoxysilane. However, due to their excellent reactivity, it is preferable that, out of 100 mass% of all raw materials constituting the silica particles, tetraalkoxysilane accounts for 50 mass% or more and raw materials other than tetraalkoxysilane accounts for 50 mass% or less, and it is more preferable that tetraalkoxysilane accounts for 90 mass% or more and raw materials other than tetraalkoxysilane accounts for 10 mass% or less.

[0064] The solution (B) may contain only tetraalkoxysilane without containing a solvent, but it is preferable that the solution (B) contains a solvent, since this improves the dispersibility of the tetraalkoxysilane in the reaction liquid. Examples of the solvent in the solution (B) include methanol, ethanol, propanol, isopropanol, and ethylene glycol. These solvents may be used alone or in combination of two or more. Among these solvents, alcohol is preferred, more preferably methanol or ethanol, and even more preferably methanol, because the solvent used in the hydrolysis reaction and the solvent by-produced in the condensation reaction are the same, and the convenience in production is excellent.

[0065] The concentration of the tetraalkoxysilane in solution (B) is preferably 60% by mass to 95% by mass, more preferably 70% by mass to 90% by mass, in 100% by mass of solution (B). When the concentration of the tetraalkoxysilane in solution (B) is 60% by mass or more, the reaction liquid tends to become homogeneous. In addition, when the concentration of the tetraalkoxysilane in solution (B) is 95% by mass or less, the formation of a gel-like substance can be suppressed.

[0066] The concentration of the solvent in solution (B) is preferably 5% by mass to 40% by mass, more preferably 10% by mass to 30% by mass, in 100% by mass of solution (B). When the concentration of the solvent in solution (B) is 5% by mass or more, the generation of a gel-like substance can be suppressed. Also, when the concentration of the solvent in solution (B) is 40% by mass or less, the reaction liquid tends to become homogenous.

[0067] The addition rate of solution (B) per hour relative to the volume of solution (A) is preferably 0.02 kg / hour / L to 1.3 kg / hour / L, and 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. Furthermore, 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.

[0068] The solution (C) is a solution containing water, and preferably further contains an alkali catalyst.

[0069] Examples of the alkali catalyst that can be contained in the solution (C) include ethylenediamine, diethylenetriamine, triethylenetetraamine, 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 action, is easy to control the particle shape, can suppress the inclusion of metal impurities, is highly volatile, and is easy to remove after the hydrolysis reaction and the condensation reaction.

[0070] Solution (C) contains water as a solvent, and examples of the solvent other than water include methanol, ethanol, propanol, isopropanol, and ethylene glycol. The solvent other than water may be used alone or in combination of two or more. Among the solvents of solution (C), water alone or a combination of water and alcohol is preferred, since the solvent used in the hydrolysis reaction and the solvent produced as a by-product are the same as those used in the condensation reaction, and this is convenient for production. Water alone is more preferred.

[0071] The concentration of the alkali catalyst in solution (C) is preferably 0% by mass to 10% by mass in 100% by mass of solution (C). The alkali catalyst in solution (C) may be 0% by mass, i.e., may not be contained, but when an alkali catalyst is contained, its concentration is preferably 0.5% by mass or more, more preferably 1% by mass or more. When the concentration of the alkali catalyst in solution (C) is 0.5% by mass or more, it is easy to adjust the concentration of the alkali catalyst in the reaction liquid from the start of the reaction to the end of the reaction. In addition, from the viewpoint of reducing the fluctuation of the concentration of the alkali catalyst in the reaction liquid, the concentration of the alkali catalyst in solution (C) is preferably 10% by mass or less, more preferably 6% by mass or less.

[0072] The water concentration in solution (C) is preferably 90% by mass to 100% by mass in 100% by mass of solution (C). The water concentration in solution (C) may be 100% by mass, that is, solution (C) may be composed of only water, but when other components are contained, the water concentration is preferably 99.5% by mass or less, more preferably 99% by mass or less. From the viewpoint of reducing the fluctuation of the concentration of the alkali catalyst in the reaction liquid, the water concentration in solution (C) is preferably 90% by mass or more, more preferably 94% by mass or more. In addition, when the water concentration in solution (C) is 99.5% by mass or less, it is easy to adjust the concentration of the alkali catalyst in the reaction liquid from the start of the reaction to the end of the reaction.

[0073] The concentration of the solvent other than water in the solution (C) is preferably the concentration of the balance of water and the alkali catalyst.

[0074] The addition of solution (B) and solution (C) is preferably performed into solution (A). By adding solution (B) and solution (C) into solution (A), when it is desired to use a highly volatile alkali catalyst such as ammonia and to proceed with hydrolysis and condensation reactions at a high reaction temperature, the mixing of each component in the reaction solution is improved, 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 level, and by making the supply outlet of solution (B) and the supply outlet of solution (C) below the liquid level of solution (A), solution (B) and solution (C) can be added into solution (A).

[0075] The timing of adding solution (B) and solution (C) to solution (A) may be the same or may be different, such as alternately. However, it is preferable that they are the same, since this reduces the fluctuation in the reaction composition and does not complicate the operation.

[0076] The pH in the step of hydrolyzing and condensing tetraalkoxysilane is 8.0 to 14, preferably 8.2 to 13, and more preferably 8.5 to 12. When the pH in the step is 8.0 or more, the reaction rates of the hydrolysis and condensation reactions are excellent and the aggregation of silica particles can be suppressed. In addition, when the pH in the step is 14 or less, the shape of the silica particles is easily controlled and the smoothness of the silica particle surface is excellent.

[0077] The method for producing silica particles of the present invention preferably includes a step of carrying out the hydrolysis reaction and condensation reaction of alkoxysilane at 40°C or higher, more preferably at 46°C or higher. When the reaction temperature is 40°C or higher, the reaction rate of the hydrolysis reaction and condensation reaction of alkoxysilane is moderately improved, and four bonds of silicon atoms can form siloxane bonds before particle growth progresses. This prevents alkoxy groups and silanol groups from remaining inside the silica particles and from forming nanoscale pores, and the average pore volume of the nanoscale pores of the silica particles can be adjusted to a suitable range, which is preferable. In addition, when the reaction temperature is 50°C or lower, the balance between the hydrolysis reaction rate and the condensation reaction rate is excellent.

[0078] The concentration of water in the reaction system for the hydrolysis and condensation reactions is preferably maintained at 3% to 90% by mass, more preferably at 5% to 30% by mass, and even more preferably at 6% to 25% by mass, based on the total amount of the reaction system (100% by mass). When the concentration of water in the reaction system is 3% by mass or more, it is easy to control the hydrolysis reaction rate of tetraalkoxysilane. Also, when the concentration of water in the reaction system is 90% 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.

[0079] The concentration of the alkali catalyst in the reaction system for the hydrolysis reaction and the condensation reaction is preferably maintained at 0.5% by mass to 2.0% by mass, more preferably at 0.6% by mass to 1.5% by mass, based on the total amount of the reaction system (100% by mass). When the concentration of the alkali catalyst in the reaction system is 0.5% by mass or more, the aggregation of the silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion liquid is excellent. In addition, when the concentration of the alkali catalyst in the reaction system is 2.0% by mass or less, the reaction does not proceed too quickly, and the reaction controllability is excellent.

[0080] The method for producing silica particles preferably further includes the following step (1) since it is possible to remove unnecessary components and add necessary components. Step (1): A step of concentrating the obtained dispersion liquid of silica particles and adding a dispersion medium

[0081] In the step (1), either the concentration of the dispersion of silica particles or the addition of the dispersion medium may be carried out first.

[0082] The method for concentrating the dispersion of silica particles is not particularly limited, and examples thereof include a heat concentration method and a membrane concentration method. In order to concentrate the dispersion of silica particles by the heat concentration method, the dispersion may be heated and concentrated under normal pressure or reduced pressure.

[0083] To concentrate the dispersion of silica particles by the membrane concentration method, membrane separation by ultrafiltration is preferred. Here, the main purpose of the ultrafiltration method is to remove unnecessary components such as intermediate products. The molecular weight cutoff of the ultrafiltration membrane used here is selected according to the intermediate products in the dispersion, so that the intermediate products can be filtered and removed. 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 a spiral type, a tubular type, a hollow fiber type, etc.

[0084] Examples of the dispersion medium to be added to the dispersion liquid of silica particles include water, methanol, ethanol, propanol, isopropanol, and ethylene glycol. 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 they have excellent affinity with silica particles.

[0085] The method for producing silica particles preferably further includes the following step (2) since the degree of condensation of the silica particles can be increased. Step (2): A step of subjecting the dispersion of silica particles obtained in step (1) to a pressurized and heated treatment.

[0086] The pressure of the pressurized 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 pressurized heat treatment is 0.10 MPa or more, the degree of condensation of the silica particles can be increased. When the pressure of the pressurized heat treatment is 2.3 MPa or less, the silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0087] Pressurization can be achieved by heating the silica particle dispersion in a sealed state to above the boiling point of the dispersion medium. When the silica particle aqueous dispersion is heated to 100°C or higher in a sealed state, the pressure becomes the saturated water vapor pressure at that temperature.

[0088] The temperature of the pressure and heat treatment is preferably 100° C. to 220° C., and more preferably 110° C. to 180° C. When the temperature of the pressure and heat treatment is 100° C. or higher, the degree of condensation of the silica particles can be increased. When the temperature of the pressure and heat treatment is 220° C. or lower, silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0089] The time of the pressurized heat treatment is preferably 0.25 hours to 10 hours, and more preferably 0.5 hours to 8 hours. When the time of the pressurized heat treatment is 0.25 hours or more, the degree of condensation of the silica particles can be increased. When the time of the pressurized heat treatment is 10 hours or less, the silica particles can be produced without significant changes in the average primary particle size, average secondary particle size, cv value, and association ratio, and the dispersion stability of the silica sol is excellent.

[0090] The pressurized heat treatment is preferably carried out in an aqueous dispersion because it can increase the degree of condensation of the silica particles without significantly changing the average primary particle size, the average secondary particle size, the cv value, or the association ratio.

[0091] The pH when the pressure heat treatment is carried out in the aqueous dispersion is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH when the pressure heat treatment is carried out in the aqueous dispersion is 6.0 or more, gelation of the silica sol can be suppressed. When the pH when the pressure heat treatment is carried out in the aqueous dispersion is 8.0 or less, the degree of condensation of the silica particles can be increased without significantly changing the average primary particle size, average secondary particle size, cv value, and association ratio.

[0092] (Silica sol) The silica sol of the present invention contains the silica particles of the present invention.

[0093] The silica sol may be produced by using the dispersion liquid of the silica particles of the present invention as it is, or by removing unnecessary components from the dispersion liquid of the silica particles of the present invention and adding necessary components.

[0094] The silica sol of the present invention preferably contains silica particles and a dispersion medium. Examples of the dispersion medium in silica sol include water, methanol, ethanol, propanol, isopropanol, ethylene glycol, etc. These dispersion mediums in silica sol may be used alone or in combination of two or more. Among these dispersion mediums in silica sol, water and alcohol are preferred, and water is more preferred, because they have excellent affinity with silica particles.

[0095] The content of silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and even more preferably 5% by mass to 30% by mass, based on the total amount of the silica sol (100% by mass). When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for a polished object such as a silicon wafer is excellent. When the content of silica particles in the silica sol is 50% by mass or less, the aggregation of silica particles in the silica sol or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent.

[0096] 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 even more preferably 70% by mass to 95% by mass, based on the total amount of the silica sol (100% by mass). When the content of the dispersion medium in the silica sol is 50% by mass or more, the aggregation of silica particles in the silica sol or polishing composition can be suppressed, and the storage stability of the silica sol or polishing composition is excellent. In addition, when the content of the dispersion medium in the silica sol is 97% by mass or less, the polishing rate for the polished object, typically a silicon wafer, is excellent.

[0097] The content of silica particles and dispersion medium in the silica sol can be set within a desired range by removing unnecessary components from the components in the obtained dispersion of silica particles and adding necessary components.

[0098] In addition to the silica particles and the dispersion medium, the silica sol may contain other components such as an oxidizing agent, a preservative, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial and biocide, as necessary, within the range that does not impair the performance of the silica sol. In particular, it is preferable to include an antibacterial biocide in the silica sol, since this provides excellent storage stability of the silica sol.

[0099] Examples of antibacterial biocides include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, methyl p-hydroxybenzoate, sodium chlorite, etc. These antibacterial biocides may be used alone or in combination of two or more. Among these antibacterial biocides, hydrogen peroxide is preferred because it has excellent affinity with silica sol. Antimicrobial biocides also include those commonly referred to as germicides.

[0100] The content of the antibacterial biocide in the silica sol is preferably 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 1% by mass, based on the total amount of the silica sol (100% by mass). When the content of the antibacterial biocide in the silica sol is 0.0001% by mass or more, the storage stability of the silica sol is excellent. When the content of the antibacterial biocide in the silica sol is 10% by mass or less, the inherent performance of the silica sol is not impaired.

[0101] The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or more, the dispersion stability is excellent and the aggregation of the silica particles can be suppressed. Also, when the pH of the silica sol is 8.0 or less, dissolution of the silica particles is prevented, and the long-term storage stability is excellent. The pH of the silica sol can be adjusted to a desired range by adding a pH adjuster.

[0102] (polishing composition) The polishing composition of the present invention comprises the silica sol of the present invention. The polishing composition of the present invention preferably contains a water-soluble polymer in addition to the silica sol of the present invention.

[0103] The water-soluble polymer enhances the wettability of the polishing composition to the object to be polished, such as a silicon wafer. The water-soluble polymer is preferably a polymer having a functional group with high water affinity, and the functional group with high water affinity has a high affinity with the surface silanol group of the silica particles, so that the silica particles and the water-soluble polymer are stably dispersed in the polishing composition in a closer vicinity. Therefore, when polishing the object to be polished, such as a silicon wafer, the effects of the silica particles and the water-soluble polymer function synergistically.

[0104] Examples of the water-soluble polymer include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

[0105] Examples of cellulose derivatives include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose.

[0106] An example of the copolymer having a polyvinylpyrrolidone skeleton is a graft copolymer of polyvinyl alcohol and polyvinylpyrrolidone.

[0107] Examples of polymers having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and copolymers of ethylene oxide and propylene oxide.

[0108] These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferred, and hydroxyethyl cellulose is more preferred, because they have high affinity with the surface silanol groups of silica particles and act synergistically to impart good hydrophilicity to the surface of the polished object.

[0109] The mass average molecular weight of the water-soluble polymer is preferably 1,000 to 3,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. When the mass average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. When the mass average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with silica sol is excellent, and the polishing rate for the object to be polished, typified by a silicon wafer, is excellent.

[0110] The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography using a 0.1 mol / L NaCl solution as the mobile phase, in terms of polyethylene oxide.

[0111] The content of the water-soluble polymer in the polishing composition is preferably 0.02% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, based on the total amount of the polishing composition (100% by mass). When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Furthermore, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, the aggregation of silica particles during preparation of the polishing composition can be suppressed.

[0112] In addition to the silica sol and the water-soluble polymer, the polishing composition of the present invention may contain other components, such as a basic compound, a polishing accelerator, a surfactant, a hydrophilic compound, a preservative, an antifungal agent, a pH adjuster, a pH buffer, a surfactant, a chelating agent, and an antibacterial and biocide, as necessary, within the range that does not impair the performance of the composition. In particular, it is preferable to include a basic compound in the polishing composition, since it is possible to perform chemical polishing (chemical etching) by applying a chemical action to the surface of an object to be polished, such as a silicon wafer, and because a synergistic effect with the surface silanol groups of the silica particles can improve the polishing speed of an object to be polished, such as a silicon wafer.

[0113] Examples of the basic compound include organic basic compounds, alkali metal hydroxides, alkali metal hydrogen carbonates, alkali metal carbonates, and ammonia. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogen carbonate, and ammonium carbonate are preferred because they are highly soluble in water and have excellent affinity with silica particles and water-soluble polymers, and ammonia, tetramethylammonium hydroxide, and tetraethylammonium hydroxide are more preferred, with ammonia being even more preferred.

[0114] The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on the total amount of the polishing composition (100% by mass). When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing speed of the object to be polished, such as a silicon wafer, can be improved. In addition, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

[0115] The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or more, the aggregation of silica particles in the polishing composition can be suppressed, and the dispersion stability of the polishing composition is excellent. When the pH of the polishing composition is 12.0 or less, the dissolution of silica particles can be suppressed, and the stability of the polishing composition is excellent. The pH of the polishing composition can be adjusted to a desired range by adding a pH adjuster.

[0116] The polishing composition can be obtained by mixing the silica sol of the present invention, the water-soluble polymer, and, if necessary, other components. However, taking into consideration storage and transportation, the composition may be prepared at a high concentration and then diluted with water or the like immediately before polishing.

[0117] (polishing method) The polishing method of the present invention is a method of polishing using a polishing composition containing the silica sol of the present invention. As the polishing composition, it is preferable to use the above-mentioned polishing composition. A specific example of the polishing method is a method in which the surface of a silicon wafer is pressed against a polishing pad, the polishing composition of the present invention is dropped onto the polishing pad, and the surface of the silicon wafer is polished.

[0118] (Method of manufacturing semiconductor wafers) The method for producing a semiconductor wafer of the present invention is a method comprising a step of polishing with the polishing composition of the present invention, and the specific polishing composition and polishing method are as described above. Examples of semiconductor wafers include silicon wafers and compound semiconductor wafers.

[0119] (Method of manufacturing semiconductor devices) The method for producing a semiconductor device of the present invention is a method comprising a step of polishing with the polishing composition of the present invention, and the specific polishing composition and polishing method are as described above.

[0120] (Application) The silica particles and silica sol of the present invention can be suitably used for polishing purposes, for example, polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the planarization process in manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for photomasks and liquid crystals, polishing magnetic disk substrates, and the like, and among these, they can be particularly suitably used for polishing silicon wafers and chemical mechanical polishing.

[0121] Other examples of the objects to be polished include metals such as Si, Cu, W, Ti, Cr, Co, Zr, Hf, Mo, Ta, Ru, Au, Pt, Ag, Ni, and Al; metal compounds such as oxides, nitrides, and silicides of the above metals; and intermetallic compounds. Among these objects to be polished, the present invention is suitable for use with metals and metal oxides, and is particularly suitable for use with metal oxides.

[0122] As described above, the present specification discloses the following: <1> The average pore volume of nanoscale pores measured by positron annihilation spectroscopy is 5.3 nm 3 Silica particles, which are: <2> The average pore volume of nanoscale pores measured by positron annihilation spectroscopy is 4.0 nm 3 Below is the <1> The silica particles according to claim 1. <3> The average pore volume of nanoscale pores measured by positron annihilation spectroscopy is 1.5 nm 3 That's all. <1> or <2> The silica particles according to claim 1. <4> The average pore volume of atomic-scale pores measured by positron annihilation spectroscopy is 0.33 nm 3 That's all. <1> ~ <3> 13. Silica particles according to any one of claims 1 to 12. <5> The average pore volume of atomic-scale pores measured by positron annihilation spectroscopy is 0.80 nm 3 Below is the <1> ~ <4> 13. Silica particles according to any one of claims 1 to 12. <6> The volume of pores with diameters of 2 nm or less measured by nitrogen gas adsorption is 0.0070 cm 3 / g or less, <1> ~ <5> 13. Silica particles according to any one of claims 1 to 12. <7> The refractive index is 1.390 or more. <1> ~ <6> 13. Silica particles according to any one of claims 1 to 12. <8> Metal impurity content is 5ppm or less. <1> ~ <7> 13. Silica particles according to any one of claims 1 to 12. <9> The main component is tetraalkoxysilane condensate. <1> ~ <8> 13. Silica particles according to any one of claims 1 to 12.

[0123] <10> The method includes a step of carrying out a hydrolysis reaction and a condensation reaction of an alkoxysilane at 40° C. or higher. <1> ~ <9> 13. A method for producing silica particles according to any one of the above. <11> <1> ~ <9> A silica sol comprising the silica particles according to any one of the above items. <12> <11> A polishing composition comprising the silica sol according to claim 1. <13> <12> A polishing method comprising polishing using the polishing composition according to claim 1. <14> <12> A method for producing a semiconductor wafer, comprising the step of polishing the semiconductor wafer with the polishing composition according to claim 1. <15> <12> A method for producing a semiconductor device, comprising the step of polishing a semiconductor device using the polishing composition according to claim 1. EXAMPLES

[0124] The present invention will be described in more detail below using examples. However, the present invention is not limited to the description of the following examples as long as it does not deviate from the gist of the present invention.

[0125] (Measurement of the average pore volume of nanoscale pores and the average pore volume of atomic scale pores) A positron lifetime spectrum was obtained using a positron beam type lifetime measurement device (National Institute of Advanced Industrial Science and Technology) according to the following procedure. A dry powder of silica particles was obtained from the dispersion liquid of silica particles obtained in the examples and comparative examples. The dry powder of silica particles was set on a sample holder. The vacuum degree was 4×10 ―4 A positron lifetime spectrum was obtained by irradiating a dry powder of silica particles with positrons at 20°C and measuring the time lag between the emission of a positron and the detection of a gamma ray accompanying the annihilation of the positron. The incident energy of the positrons was 10 keV. The positron lifetime spectrum was fitted with a linear sum of four exponential functions to obtain the average positron lifetime for each component. The two with the shortest lifetimes were determined to be components not originating from the sample, while the remaining two with the shortest lifetimes were determined to be components originating from atomic-scale pores and the other was determined to be a component originating from the nanoscale. The average positron lifetime was converted to average pore volume using the following formula:

[0126] (Atomic scale pores)

[0127]

number

[0128] Where:

[0129]

number

[0130] where τ is the average positron lifetime, R is the average radius of the atomic-scale pores, ΔR is a correction value for the radius of the atomic-scale pores, and V is the average pore volume of the atomic-scale pores.

[0131] (Nanoscale pores)

[0132]

number

[0133] Where:

[0134]

number

[0135] where τ is the average positron lifetime, R is the average radius of the nanoscale pores, r0 is the correction value for the radius of the nanoscale pores, and λ T is the annihilation rate of ortho-positronium in vacuum, and V is the average pore volume of the nanoscale pores.

[0136] (Refractive index measurement) Dry powder of silica particles was obtained from the dispersion of silica particles obtained in the examples and comparative examples. 0.1 g of dry powder of silica particles was placed in a 10 mL glass bottle, and special grade 2-propanol and special grade toluene were added in different 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.) and the refractive index of the silica particles was determined.

[0137] (Measurement of average primary particle size) The dispersions of 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 an automatic specific surface area measuring device "BELSORP-MR1" (model name, Microtrack BEL Co., Ltd.). The density was calculated to be 2.2 g / cm using the following formula (2). 3 The average primary particle size was calculated. Average primary particle diameter (nm) = 6000 / (specific surface area (m 2 / g) x density (g / cm 3 )) (2)

[0138] (Measurement of average secondary particle size) The average secondary particle size of the silica particles in the dispersions obtained in the examples and comparative examples was measured using a dynamic light scattering particle size measurement device "Zetersizer Nano ZS" (model name, Malvern Panalytical).

[0139] (Measurement of pore volume with diameters of 2 nm or less using nitrogen gas adsorption method) The dispersions of silica particles obtained in the examples and comparative examples were dried at 300°C, and the adsorption isotherm of nitrogen gas onto the silica particles was measured using a pore distribution measuring device "Nova-touch" (model name, Anton Paar K.K.), and analysis was performed using the BJH method to determine the volume of pores with a diameter of 2 nm or less.

[0140] (Mechanical strength) The silica particles obtained in the Examples and Comparative Examples were evaluated using the following indices to determine whether they had mechanical strength suitable for polishing a substrate having a metal oxide film on its surface. A: It is assumed that the mechanical strength is extremely suitable for polishing. B: The mechanical strength is assumed to be suitable for polishing. C: The mechanical strength is assumed to be not suitable for polishing.

[0141] (Storage stability) The storage stability of the silica particles obtained in the examples and comparative examples was evaluated using the following indices. A: It is expected that the storage stability is extremely excellent. B: It is assumed that the storage stability is excellent. C: Storage stability is assumed to be poor.

[0142] [Example 1] A solution (B) of tetramethoxysilane and methanol mixed at a ratio of 5.7:1 (mass ratio) and a solution (C) of 6.6 mass% aqueous ammonia solution were prepared. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with a solution (A) of methanol, pure water, and ammonia mixed in advance. The concentration of water in solution (A) was 15 mass%, and the concentration of ammonia in solution (A) was 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 added at equal rates to 100 parts by volume of solution (A) over a period of 153 minutes to obtain a dispersion of silica particles. The temperature of the obtained dispersion of silica particles was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the content of silica particles was about 20% by mass, and a dispersion of silica particles with a content of silica particles of about 20% by mass was obtained.

[0143] [Example 2] The dispersion of silica particles obtained in Example 1 was placed in an autoclave, heated and maintained at 140° C. for 2 hours, to obtain a dispersion of silica particles that had been subjected to a pressurized heat treatment.

[0144] [Comparative Example 1] A commercially available silica sol (product name "PL-3", manufactured by Fuso Chemical Co., Ltd.) was used as is.

[0145] [Comparative Example 2] A solution (B) of tetramethoxysilane and methanol mixed at a ratio of 5.7:1 (mass ratio) and a solution (C) of 2.9 mass% aqueous ammonia solution were prepared. A reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line was charged with a solution (A) of methanol, pure water, and ammonia mixed in advance. The concentration of water in solution (A) was 15 mass%, and the concentration of ammonia in solution (A) was 0.52 mass%. While maintaining the temperature of the reaction solution at 10°C, 75.5 parts by volume of solution (B) and 27.6 parts by volume of solution (C) were added at equal rates to 100 parts by volume of solution (A) over a period of 612 minutes to obtain a dispersion of silica particles. The temperature of the obtained dispersion of silica particles was raised to remove methanol and ammonia while adjusting the liquid volume by adding pure water so that the content of silica particles was about 20% by mass, and a dispersion of silica particles with a content of silica particles of about 20% by mass was obtained. The obtained dispersion of silica particles was placed in an autoclave and heated to 140° C. for 2 hours to obtain a dispersion of silica particles that had been subjected to a pressurized heat treatment.

[0146] The evaluation results of the silica particles of the above Examples and Comparative Examples are shown in Tables 1 and 2.

[0147] [Table 1]

[0148] [Table 2]

[0149] As can be seen from Table 1, the silica particles obtained in Examples 1 and 2 have a smaller average pore volume of nanoscale pores and a larger refractive index than the silica particles obtained in Comparative Examples 1 and 2, although the particle diameter is almost the same. Since the average pore volume of the nanoscale pores is within an appropriate range, it can be said that the silica particles obtained in Examples 1 and 2 have alkoxy groups and silanol groups remaining inside the silica particles and suppress the formation of nanoscale pores with a large volume. This improves the mechanical strength and storage stability of the silica particles obtained in Examples 1 and 2. In addition, the silica particles are less likely to be broken in the process of polishing a polished object using a polishing composition containing the silica particles obtained in Examples 1 and 2. Furthermore, as shown in Table 2, the pore volumes of pores with diameters of 2 nm or less measured by nitrogen gas adsorption for the silica obtained in Examples 1 and 2 are within an appropriate range. This also means that there are fewer pores inside the silica that can become the starting point of crushing, which improves the mechanical strength of the silica in Examples 1 and 2.

[0150] Therefore, the silica sol and polishing composition containing the silica particles of Examples 1 and 2 can be used to effectively polish an object to be polished without damaging it, and the silica particles can be easily removed after polishing, allowing high-quality polished products to be produced with high productivity.

[0151] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention. Furthermore, the components in the above-mentioned embodiments may be arbitrarily combined within the scope of the invention.

[0152] This application is based on a Japanese patent application (Patent Application No. 2022-099054) filed on June 20, 2022, the contents of which are incorporated by reference into this application. [Industrial Applicability]

[0153] The silica particles and silica sol of the present invention can be suitably used for polishing purposes. For example, they can be used for polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing (chemical mechanical polishing) in the flattening process when manufacturing integrated circuits, 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 chemical mechanical polishing of silicon wafers.

Claims

1. The average pore volume of nanoscale pores measured by positron annihilation was 5.3 nm. ３ The following: Silica particles with a cv value of 15% or higher and that are amorphous.

2. The average pore volume of nanoscale pores measured by positron annihilation was 4.0 nm. ３ The silica particles according to claim 1, which are as follows:

3. The average pore volume of nanoscale pores measured by positron annihilation was 1.5 nm. ３ The silica particles described in claim 1 are as described above.

4. The average pore volume of atomic-scale pores measured by positron annihilation is 0.33 nm. ３ The silica particles described in claim 1 are as described above.

5. The average pore volume of atomic-scale pores measured by positron annihilation was 0.80 nm. ３ The silica particles according to claim 1, which are as follows:

6. Pore ​​volume of pores with a diameter of 2 nm or less, as measured by nitrogen gas adsorption, was 0.0070 cm³. ３ Silica particles according to claim 1, wherein the amount is less than or equal to / g.

7. Silica particles according to claim 1, wherein the refractive index is 1.390 or higher.

8. Silica particles according to claim 1, wherein the metal impurity content is 5 ppm or less.

9. Silica particles according to claim 1, comprising a tetraalkoxysilane condensate as the main component.

10. A method for producing silica particles according to any one of claims 1 to 9, comprising the step of carrying out a hydrolysis reaction and a condensation reaction of an alkoxysilane at a pH of 8 to 14 and a temperature of 40°C or higher.

11. A silica sol comprising silica particles according to any one of claims 1 to 9.

12. An abrasive composition comprising the silica sol described in claim 11.

13. A polishing method comprising polishing using the polishing composition described in claim 12.

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

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