Method for producing colloidal silica

Abstract

This invention provides colloidal silica that, when used as an abrasive for polishing electronic materials such as semiconductor wafers, can exhibit excellent polishing speed, suppress the amount of abrasive residue on the polished surface, and form a polished surface with excellent flatness. Colloidal silica comprising silica particles dispersed in a solvent, wherein the average primary particle diameter of the silica particles is 55-200 nm, the average secondary particle diameter of the silica particles is 80-300 nm, the degree of association of the silica particles is 1.50-3.00, and the silanol group density of the silica particles, as measured by the Sears method, is 2.8 groups / nm. 2 The above describes colloidal silica characterized by having a silica fine particle content parameter of 15.0 or less.

Description

[Technical Field]

[0001] This invention relates to colloidal silica and a method for producing colloidal silica. [Background technology]

[0002] In the semiconductor manufacturing process, semiconductor wafers are held in place by a component called a carrier, and a slurry containing chemicals and abrasive particles is passed through them while the wafers are brought into contact with and rotated against a polishing pad. This process polishes the semiconductor wafers to a flat surface.

[0003] In the polishing methods described above, chemical mechanical polishing (CMP), which utilizes both chemical polishing action by chemicals and mechanical polishing action by abrasive grains, is also being used.

[0004] In the chemical mechanical polishing (CMP) of the above-mentioned semiconductor devices, nanoparticles such as silica are used as abrasive particles. Specifically, colloidal silica, in which the silica particles are dispersed in a medium such as water, is used.

[0005] As a method for producing the above-mentioned colloidal silica, a method is known in which high-purity colloidal silica with a low metal content is produced by hydrolysis and condensation using alkoxysilane as a raw material (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-164351 Public Relations [Patent Document 2] Japanese Patent Publication No. 2021-054684 [Patent Document 3] Japanese Patent Publication No. 2021-116208 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0007] Incidentally, in chemical mechanical polishing (CMP) of semiconductor devices, colloidal silica is required to exhibit a high polishing speed when used as an abrasive grain, form a highly flat polished surface, and leave minimal abrasive residue on the polished surface.

[0008] In other words, colloidal silica used in the above-mentioned CMP applications contains silica microparticles with a smaller particle size than the main particles, which consist of primary and secondary silica particles. When used in CMP applications, these silica microparticles tend to remain on the polished surface as abrasive residue. Therefore, there is a demand for colloidal silica with a reduced content of these silica microparticles.

[0009] In this regard, the manufacturing method described in Patent Document 1 states that in the hydrolysis and condensation reaction of alkoxysilane or its condensate, a silica sol with a small amount of fine particles can be obtained by adjusting the reaction conditions so that the value of electrical conductivity does not change by more than 90% from 5 minutes after the point in time when the electrical conductivity first reaches its maximum after the start of the reaction until the end of the reaction.

[0010] Furthermore, in the manufacturing method described in Patent Document 2, it is stated that in the hydrolysis and condensation reaction of alkoxysilane or its condensate, by first reducing the concentration of the alkaline catalyst in the reaction system and then adding an additional alkaline catalyst, the generation of unreacted products can be suppressed while obtaining a dispersion of silica particles with a high degree of association.

[0011] However, as a result of the inventors' investigations, it was found that when attempting to synthesize large-diameter silica particles with the aim of reducing fine particles by following the method described in Patent Document 1, the high temperature during particle synthesis accelerates the hydrolysis and condensation reactions of alkoxysilane, resulting in a low silanol group (Si-OH) density in the resulting silica particles. In addition, as a result of investigations by the present inventors, when an alkali catalyst is added during the reaction according to the method described in Patent Document 2, the hydrolysis and condensation reactions of alkoxysilane are promoted, and particle aggregation proceeds. At the same time, it has been found that the density of silanol groups (Si-OH) in the resulting silica particles decreases.

[0012] When the density of silanol groups (Si-OH) in the silica particles in colloidal silica decreases, the density of siloxane bonds (Si-O-Si bonds) becomes relatively high. As a result of investigations by the present inventors, when colloidal silica containing silica particles with a high density of siloxane bonds (Si-O-Si bonds) is used for abrasive grain applications for polishing semiconductor devices, scratches are likely to occur on the polished surface, and it has been found that it is difficult to obtain a flat (smooth) polished surface.

[0013] On the other hand, in the production method described in Patent Document 3, it is said that a silica sol with a reduced amount of intermediate products that cause fine particles can be obtained by including a step of ultrafiltrating a silica sol obtained by subjecting tetraalkoxysilane to hydrolysis and condensation reactions using an ultrafiltration membrane with a molecular weight cut-off of 5,000 to 80,000.

[0014] However, as a result of investigations by the present inventors, when ultrafiltration is performed for a long time in an attempt to reduce the amount of fine particles according to the method described in Patent Document 3, silica secondary particles are likely to aggregate due to the shear force generated during ultrafiltration, and coarse particles are easily formed. When such a silica sol is used as an abrasive grain for polishing semiconductor devices, it has been found that it is difficult to obtain a flat polished surface.

[0015] Under such circumstances, an object of the present invention is to provide colloidal silica that can exhibit an excellent polishing rate and form a polished surface with excellent flatness while suppressing the amount of abrasive grain residue on the polished surface when used as an abrasive grain for polishing electronic materials such as semiconductor wafers, and to provide a method for producing the colloidal silica.

Means for Solving the Problems

[0016] To solve the above technical problems, the present inventors conducted intensive studies and found that a colloidal silica in which silica particles are dispersed in a solvent, wherein the average primary particle diameter of the silica particles is 55 to 200 nm, the average secondary particle diameter of the silica particles is 80 to 300 nm, the degree of aggregation of the silica particles is 1.50 to 3.00, and the silanol group density of the silica particles measured by the shear method is 2.8 per nm 2 or more, and it was found that it can be solved by producing a colloidal silica having a silica fine particle content parameter of 15.0 or less by a specific method, and the present invention has been completed based on this finding.

[0017] That is, the present invention provides (1) A colloidal silica in which silica particles are dispersed in a solvent, wherein the average primary particle diameter of the silica particles is 55 to 200 nm, the average secondary particle diameter of the silica particles is 80 to 300 nm, the following formula Degree of aggregation of silica particles = average secondary particle diameter (nm) of the silica particles ÷ average primary particle diameter (nm) of the silica particles The degree of aggregation of the silica particles calculated by the above formula is 1.50 to 3.00, the silanol group density of the silica particles measured by the shear method is 2.8 per nm 2 or more, the following formula Silica fine particle content parameter = total number of detected silica particles with a particle diameter of 15 nm or less / total number of detected silica particles with a particle diameter of 25 nm or more (However, the total number of detected silica particles with a particle diameter of 15 nm or less and the total number of detected silica particles with a particle diameter of 25 nm or more are the detection numbers when measured with a particle size distribution measuring device based on the scanning electrical mobility diameter measurement method.) The silica fine particle content parameter calculated by the above formula is 15.0 or less A colloidal silica characterized by (2) With respect to a mother liquor containing a basic catalyst, water and alcohol, A method for producing colloidal silica by continuously or intermittently adding a solution containing at least alkoxysilane as an additive component and reacting it, The temperature of the mother liquor at the start of adding the aforementioned additive component is 4.0 to 21.0°C. While controlling the temperature so that the difference t0-t1 between the liquid temperature t0 of the mother liquor at the start of adding the additive component and the liquid temperature t1 of the mixture of the mother liquor and the additive component at the end of adding the additive component is 0.50 to 2.00°C, The alkoxysilane-containing solution shall be added at an addition rate of 1.50 mL / minute or less per liter of the total volume of mother liquor and the total amount of added components. A method for producing colloidal silica characterized by the following, This provides... [Effects of the Invention]

[0018] According to the present invention, when used as an abrasive grain for polishing electronic materials such as semiconductor wafers, it is possible to provide colloidal silica that can exhibit excellent polishing speed, suppress the amount of abrasive residue on the polished surface, and form a polished surface with excellent flatness, as well as a method for producing said colloidal silica. [Modes for carrying out the invention]

[0019] First, the colloidal silica according to the present invention will be described. The colloidal silica according to the present invention is a colloidal silica in which silica particles are dispersed in a solvent, The average primary particle diameter of the silica particles is 55-200 nm. The average secondary particle diameter of the silica particles is 80-300 nm. The following formula Degree of association of silica particles = Average secondary particle diameter of the silica particles (nm) ÷ Average primary particle diameter of the silica particles (nm) The degree of association of the silica particles calculated by this method is 1.50 to 3.00. The silanol group density of the aforementioned silica particles, measured by the Sears method, was 2.8 groups / nm. 2 That's all. The following formula Silica microparticle content parameter = Total number of silica particles with a particle size of 15 nm or less / Total number of silica particles with a particle size of 25 nm or more (However, the total number of silica particles with a particle size of 15 nm or less and the total number of silica particles with a particle size of 25 nm or more are the number of particles detected when measured using a particle size distribution analyzer based on the scanning electrical mobility diameter measurement method.) The silica fine particle content parameter calculated by this method is 15.0 or less. It is characterized by the following:

[0020] As will be described later, one method for preparing colloidal silica according to the present invention is to add an alkoxysilane such as tetramethoxysilane (Si(OCH3)4) to a mother liquor containing water, thereby hydrolyzing and dehydrating the alkoxysilane to form a dimer, and this dimer polymerizes (oligomerizes) to form spherical silica primary particles in a solvent. Colloidal silica is formed when these spherical silica primary particles are dispersed in a solvent. Furthermore, the colloidal silica described above includes not only primary silica particles but also secondary silica particles formed by the association of these primary silica particles, and these secondary silica particles are dispersed in the solvent together with the primary silica particles.

[0021] In the colloidal silica according to the present invention, the average primary particle diameter of the silica particles (average diameter of the silica primary particles) is 55 to 200 nm (55 nm or more and 200 nm or less).

[0022] The average primary particle diameter of the silica particles contained in the colloidal silica according to the present invention is preferably 200 nm or less, more preferably 199 nm or less, and even more preferably 198 nm or less.

[0023] Because the average primary particle diameter of the silica particles contained in the colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0024] The average primary particle diameter of the silica particles contained in the colloidal silica according to the present invention is preferably 55 nm or more, more preferably 56 nm or more, and even more preferably 57 nm or more.

[0025] Because the average primary particle diameter of the silica particles contained in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), a high polishing speed can be easily achieved when polishing using the colloidal silica according to the present invention.

[0026] In this application, the average primary particle size of the silica particles contained in colloidal silica refers to the value measured by the BET method described below. Specifically, first, colloidal silica is pre-dried on a hot plate at 150°C, then heat-treated at 800°C for 1 hour to prepare a sample for measurement. The specific surface area (BET specific surface area) S is then measured using the obtained sample by the BET method. For nearly perfectly spherical particles, the average primary particle diameter (nm) of silica particles is given by the following formula: Average primary particle diameter of silica particles (nm) = 6000 / (BET specific surface area S (m²) 2 / g) x true density (g / cm 3 )) This can be determined by the following formula, where the true density of silica particles is 2.2 g / cm³. 3 Based on this, the average primary particle diameter (nm) of silica particles is given by the following formula Average primary particle diameter of silica particles (nm) = 2727 / BET specific surface area S (m²) 2 / g) This can be determined by [method].

[0027] The colloidal silica according to the present invention includes secondary silica particles formed by the association of primary silica particles. The silica secondary particles contained in the colloidal silica according to the present invention, together with the silica primary particles contained in the colloidal silica according to the present invention, constitute the main particles of the silica, and are distinguishable from coarse particles formed by the aggregation of the above-mentioned silica secondary particles.

[0028] The average secondary particle diameter (average diameter of silica secondary particles) of the silica particles contained in the colloidal silica according to the present invention is 80 to 300 nm (80 nm or more and 300 nm or less).

[0029] The average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is preferably 300 nm or less, more preferably 295 nm or less, and even more preferably 290 nm or less.

[0030] Because the average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0031] The average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is preferably 80 nm or more, more preferably 85 nm or more, and even more preferably 90 nm or more.

[0032] Because the average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), a high polishing speed can be easily achieved when polishing using the colloidal silica according to the present invention.

[0033] In this application, the average secondary particle diameter of the silica particles contained in colloidal silica refers to the value measured by the dynamic light scattering method described below. Specifically, first, a 0.3% by mass citric acid aqueous solution is added to the colloidal silica sample to be measured, and the mixture is uniformly diluted to a silica particle concentration of 0.8% by mass. The resulting diluted solution is then used as the measurement sample. Using the above-mentioned sample for measurement, measurements were performed using the dynamic light scattering method with the zeta potential, particle size, and molecular weight measurement system "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd. The hydrodynamic diameter was determined by analyzing the autocorrelation function derived from the temporal change in scattered light intensity using the cumulant method, and the obtained hydrodynamic diameter was taken as the average secondary particle diameter of the silica particles.

[0034] The colloidal silica according to the present invention contains silica particles with a large particle size in which the average primary particle diameter and the average secondary particle diameter are each within the above-described predetermined ranges, and thus can easily exhibit a high polishing rate when used as abrasive grains for polishing.

[0035] In the colloidal silica according to the present invention, the following formula Degree of association of silica particles = average secondary particle diameter (nm) of silica particles ÷ average primary particle diameter (nm) of silica particles The degree of association of the silica particles calculated by the formula is 1.50 to 3.00.

[0036] In the colloidal silica according to the present invention, the degree of association of the silica particles is preferably 3.00 or less, more preferably 2.95 or less, and still more preferably 2.90 or less. In the colloidal silica according to the present invention, when the degree of association of the silica particles is below the above value (upper limit value), it becomes easier to improve the flatness of the polished surface when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0037] In the colloidal silica according to the present invention, the degree of association of the silica particles is preferably 1.50 or more, more preferably 1.55 or more, and still more preferably 1.60 or more. In the colloidal silica according to the present invention, when the degree of association of the silica particles is above the above value (lower limit value), a high polishing rate can be easily achieved when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0038] In the colloidal silica according to the present invention, the silanol group density of the silica particles measured by the shear method is 2.8 per nm 2 or more.

[0039] In the colloidal silica according to the present invention, the silanol group density (per nm 2 ) of the silica particles measured by the shear method is 2.8 per nm 2 or more, preferably 2.9 per nm 2 or more, and more preferably 3.0 per nm2 The above is preferable.

[0040] In the colloidal silica according to the present invention, the silanol group density of the silica particles measured by the Sears method is equal to or greater than the above value (lower limit), resulting in a relatively low density of siloxane bonds (Si-O-Si bonds). When the colloidal silica of the present invention is used as an abrasive grain for polishing, the flatness of the polished surface can be further improved.

[0041] In the colloidal silica according to the present invention, the silanol group density of silica particles (particles / nm) measured by the Sears method is 2 ) is not particularly limited, but is typically 20.0 pieces / nm 2 The following is true: 18.0 pieces / nm 2 The following may be true, and 16.0 pieces / nm 2 The following is also acceptable.

[0042] In addition, in this application document, the silanol group density (particles / nm) of silica particles measured by the Sears method is specified. 2 ) refers to the value calculated by the following method. Specifically, based on the Sears method described in GWSears, Jr., “Determination of Specific Surface Area of ​​Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981(1956), the silica particle concentration of the colloidal silica to be measured is adjusted to 1% by mass, and then titrated with a 0.1 mol / L aqueous sodium hydroxide solution. The silanol group density ρ (particles / nm) is calculated based on the following formula. 2 ) means. ρ = (a × f × 60²²) ÷ (c × S) ρ: Silanol group density (pieces / nm 2 ) a: Dropping volume (mL) of 0.1 mol / L sodium hydroxide aqueous solution with pH 4 to pH 9 f: Factor of 0.1 mol / L sodium hydroxide aqueous solution c: Mass of silica particles (g) S:BET specific surface area (m 2 / g)

[0043] The colloidal silica according to the present invention contains silica particles in which the degree of association of silica particles and the density of silanol groups are each within a predetermined range. Therefore, when used as an abrasive grain for polishing, it can form a polished surface with excellent flatness (smoothness).

[0044] The colloidal silica according to the present invention is of the following formula Silica microparticle content parameter = Total number of silica particles with a particle size of 15 nm or less / Total number of silica particles with a particle size of 25 nm or more (However, the total number of silica particles with a particle size of 15 nm or less and the total number of silica particles with a particle size of 25 nm or more are the number of particles detected when measured using a particle size distribution analyzer based on the scanning electrical mobility diameter measurement method.) The silica fine particle content parameter calculated by this method is 15.0 or less.

[0045] In the colloidal silica according to the present invention, the silica fine particle content parameter is 15.0 or less, preferably 14.5 or less, and more preferably 14.0 or less.

[0046] In the colloidal silica according to the present invention, by having the silica fine particle content parameter be less than or equal to the above value (upper limit), the amount of abrasive residue remaining on the polished surface when the colloidal silica of the present invention is used as an abrasive grain can be easily reduced.

[0047] In the colloidal silica according to the present invention, the silica fine particle content parameter is not particularly limited, but can be 1.0 or higher, and preferably 0.0.

[0048] In this application, the silica nanoparticle content parameter refers to the value calculated by the following method. (i) Add ultrapure water with an electrical resistivity of 18.2 MΩ or higher (hereinafter referred to as "ultrapure water") to the colloidal silica to be measured, and obtain a diluted solution by diluting it so that the silica particle concentration is 2% by mass. (ii)9.1g of the diluent obtained in (i) is placed in a centrifuge tube (model number: S303922A) and centrifuged using a centrifuge rotor S58A and a centrifuge CS100FNX at a centrifugal speed of 50,000 rpm, a centrifugal temperature of 5°C, and a centrifugal time of 60 minutes (Note that the above centrifuge tube, centrifuge rotor, and centrifuge are all manufactured by Eppendorf Highmac Technologies Co., Ltd.). (iii) After the centrifugation process in (ii) is complete, 2 mL of the supernatant is taken from the centrifuge tube, and this 2 mL of supernatant after centrifugation is mixed with a diluted solution of ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Industries, Ltd., diluted 10 times with ultrapure water, in the following mass ratio to obtain a mixed solution. Calcium supernatant after centrifugation: 10-fold dilution of PL-3 = 9:1 (mass ratio) (iv)(iii) The particle size distribution of the obtained mixture is measured using a particle size distribution analyzer based on the scanning electrical mobility diameter measurement method (Liquid Nanoparticle Sizer System Model 9310 (LNS) manufactured by KANOMAX). (v) The value calculated from the obtained particle size distribution using the following formula is defined as the silica fine particle content parameter of colloidal silica. Silica microparticle content parameter = Total number of particles with a particle size of 15 nm or less / Total number of silica particles with a particle size of 25 nm or more

[0049] As is clear from the method for calculating the silica fine particle content parameter described above, in this application, silica particles with a particle size of 15 nm or less when measured with a particle size distribution analyzer based on the scanning electrical mobility diameter measurement method described above are considered to be silica fine particles.

[0050] The colloidal silica according to the present invention preferably contains 10,000,000 or fewer coarse particles with a particle size of 0.2 μm or more when the silica particle concentration is 1% by mass.

[0051] In the colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or more is preferably 10,000,000 particles / mL or less, more preferably 9,800,000 particles / mL or less, and even more preferably 9,600,000 particles / mL or less, when the silica particle concentration is 1% by mass.

[0052] In the colloidal silica according to the present invention, coarse particles with a particle size of 0.2 μm or more are included as part of the silica particles. In the colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or more is less than or equal to the above value (upper limit) when the silica particle concentration is 1% by mass. Therefore, when performing chemical mechanical polishing (CMP) using the colloidal silica according to the present invention, surface roughness caused by the presence of coarse particles is suppressed, and a highly flat polished surface can be easily formed.

[0053] In the colloidal silica according to the present invention, there is no particular lower limit to the content of coarse particles with a particle size of 0.2 μm or larger. However, in the colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or larger contained in the silica particles can be 1,000 particles / mL or more when the silica particle concentration is 1% by mass, and it is preferable that there are no coarse particles at all (0 particles / mL).

[0054] In this application, the content of coarse particles with a particle size of 0.2 μm or larger refers to the value measured by the particle size distribution method using the particle counting method described below. <Method for measuring the content of coarse particles with a particle size of 0.2 μm or larger> The colloidal silica to be measured is diluted with ultrapure water until the silica particle concentration reaches 1% by mass. The resulting diluted solution was used as the measurement sample, and the number of coarse particles with a particle size of 0.2 μm or larger was measured using an Accusizer FX-nano manufactured by Particle Sizing System Inc. under the following measurement conditions. <System Setup> ·Stirred Vessel Volume: 13.22mL • Sample Loop Volume: 0.52mL ·Autodilution delay time: 3sec. ·Normal Speed ​​Flow Rate: 15mL / min <Sensor Setup Menu> ·FX-Nano HG Minimum Size: 0.15μm ·FX-Nano HG Maximum Size: 0.27μm ·FX-Nano HG Collection Time: 60sec. ·HG Starting Concentration : 8000♯ / mL

[0055] The silica particle content in the colloidal silica according to the present invention is not particularly limited, but it is preferably 2% by mass or more and 50% by mass or less, when the colloidal silica content is 100% by mass.

[0056] The silica particle content (silica particle concentration) in the colloidal silica according to the present invention is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, when the colloidal silica content is 100% by mass.

[0057] By ensuring that the silica particle content in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), the polishing performance when the colloidal silica according to the present invention is used as an abrasive grain can be further improved.

[0058] The silica particle content (concentration of silica particles) in the colloidal silica according to the present invention is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, when the colloidal silica content is 100% by mass. By keeping the silica particle content in the colloidal silica according to the present invention below the above value (upper limit), the long-term dispersion stability of the silica particles can be further improved.

[0059] In this application, the silica particle content (silica particle concentration) in the colloidal silica according to the present invention refers to the value measured by the following measurement method. In other words, it refers to the value calculated using the following formula, where 10.0 g of colloidal silica is dried on a hot plate at 150°C, then heated at 800°C for 1 hour to remove moisture, and the resulting amount of solids is denoted as Wg. Silica particle content (mass%) in colloidal silica = (W / 10.0) × 100

[0060] The silica particles in colloidal silica according to the present invention may include silica fine particles, primary silica particles, secondary silica particles formed by association of primary silica particles, and coarse particles formed by aggregation of secondary silica particles. Therefore, in this application, the silica particle content in colloidal silica refers to the total content of these particles.

[0061] The pH of the colloidal silica according to the present invention can be set appropriately according to its application and is not particularly limited, but it is preferably 2.0 to 11.0.

[0062] The pH of the colloidal silica according to the present invention is preferably 2.0 or higher, and more preferably 3.0 or higher. By having a pH of colloidal silica according to the present invention that is equal to or greater than the above value (lower limit), the long-term dispersion stability of the silica particles of the colloidal silica according to the present invention is more easily improved.

[0063] Furthermore, the pH of the colloidal silica according to the present invention is preferably 11.0 or lower, and more preferably 10.0 or lower. By ensuring that the pH of the colloidal silica according to the present invention is below the above value (upper limit), it becomes easier to improve the long-term dispersion stability of the colloidal silica.

[0064] In this application, pH refers to the value measured by a benchtop pH / water quality analyzer (F-2000PI, manufactured by Horiba, Ltd.).

[0065] The colloidal silica according to the present invention preferably has a true specific gravity of 1.0 or more and 3.0 or less, determined by liquid-phase displacement of the silica particles constituting the colloidal silica.

[0066] The colloidal silica according to the present invention preferably has a true specific gravity of 3.0 or less, more preferably 2.8 or less, and even more preferably 2.6 or less, obtained by liquid-phase displacement of the silica particles constituting the colloidal silica.

[0067] The colloidal silica according to the present invention has a true specific gravity of silica particles constituting the colloidal silica obtained by liquid-phase displacement method that is less than or equal to the above value (upper limit). Therefore, when the colloidal silica according to the present invention is used as an abrasive grain for polishing, it is less likely to cause scratches on the polished surface of the workpiece, and a polished surface with excellent flatness (smoothness) can be easily formed.

[0068] The colloidal silica according to the present invention preferably has a true specific gravity of 1.0 or higher, more preferably 1.2 or higher, and even more preferably 1.4 or higher, depending on the liquid-phase displacement method of the silica particles constituting the colloidal silica.

[0069] The colloidal silica according to the present invention has a true specific gravity of silica particles constituting the colloidal silica determined by liquid-phase displacement method that is equal to or greater than the above value (lower limit). Therefore, when the colloidal silica according to the present invention is used as an abrasive grain, a high polishing speed can be easily achieved.

[0070] In this application, true specific gravity measured by the liquid-phase displacement method refers to the value obtained by drying the sample on a hot plate at 150°C, heating it in a furnace at 300°C for 1 hour, and then measuring it using the liquid-phase displacement method with ethanol.

[0071] In the colloidal silica according to the present invention, the metal impurity content (total content of metal impurities) is preferably 1 ppm by mass or less (0 ppm by mass to 1 ppm by mass). Because the metal impurity content is 1 ppm by mass or less, the colloidal silica according to the present invention can be suitably used as an abrasive grain for polishing electronic materials such as semiconductor wafers.

[0072] In the colloidal silica according to the present invention, the metal impurity content refers to the total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt.

[0073] In this application, the metal impurity content refers to the value measured using an atomic absorption spectrometer.

[0074] According to the present invention, when used as an abrasive grain for polishing electronic materials such as semiconductor wafers, colloidal silica can be provided that exhibits excellent polishing speed, suppresses the amount of abrasive residue on the polished surface, and forms a polished surface with excellent flatness.

[0075] Next, a method for producing colloidal silica according to the present invention will be described. The method for producing colloidal silica according to the present invention is A mother liquor containing a basic catalyst, water, and alcohol, A method for producing colloidal silica by continuously or intermittently adding a solution containing at least alkoxysilane as an additive component and reacting it, The temperature of the mother liquor at the start of adding the aforementioned additive component is 4.0 to 21.0°C. While controlling the temperature so that the difference t0-t1 between the liquid temperature t0 of the mother liquor at the start of adding the additive component and the liquid temperature t1 of the mixture of the mother liquor and the additive component at the end of adding the additive component is 0.50 to 2.00°C, The alkoxysilane-containing solution shall be added at an addition rate of 1.50 mL / minute or less per liter of the total volume of mother liquor and the total amount of added components. It is characterized by the following:

[0076] In the method for producing colloidal silica according to the present invention, the basic catalyst constituting the mother liquor is preferably one or more selected from organic amines and ammonia, from the viewpoint of preventing the inclusion of impurities, and more preferably one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, 3-ethoxypropylamine (3-EOPOA), ammonia, urea, ethanolamine, and tetramethylammonium hydroxide, with ammonia being even more preferred. In the method for producing colloidal silica according to the present invention, when the basic catalyst constituting the mother liquor is the one described above, it exhibits excellent catalytic activity, high volatility, and can be easily removed in subsequent processes.

[0077] In the method for producing colloidal silica according to the present invention, the concentration of the basic catalyst in the mother liquor is preferably 0.2 to 3.0% by mass, more preferably 0.3 to 2.5% by mass, and even more preferably 0.4 to 1.8% by mass. In the method for producing colloidal silica according to the present invention, by keeping the concentration of the basic catalyst in the mother liquor within the above range, the particle size of the silica particles in the resulting colloidal silica can be easily controlled to a desired range.

[0078] In the method for producing colloidal silica according to the present invention, the water constituting the mother liquor is preferably pure water or ultrapure water in order to minimize the inclusion of metal impurities.

[0079] In the method for producing colloidal silica according to the present invention, the concentration of water constituting the mother liquor is preferably 3.0 to 30.0% by mass, more preferably 5.0 to 28.0% by mass, and even more preferably 7.0 to 26.0% by mass. In the method for producing colloidal silica according to the present invention, by adjusting the concentration of water in the mother liquor to the above range and controlling the mixing ratio of the mother liquor and the added components, the hydrolysis and dehydration condensation reactions of the alkoxysilane, described later, are more readily and effectively promoted.

[0080] In the method for producing colloidal silica according to the present invention, the alcohol constituting the mother liquor is preferably one or more selected from methanol, ethanol, isopropanol, etc.

[0081] In the method for producing colloidal silica according to the present invention, the alcohol constituting the mother liquor is more preferably the same alcohol as the alcohol produced by the hydrolysis of the alkoxysilane described later. For example, if the alkoxysilane described later is tetramethoxysilane (TMOS), methanol is preferred as the alcohol constituting the mother liquor. In the method for producing colloidal silica according to the present invention, by using the same alcohol as the alcohol produced by the hydrolysis of tetramethoxysilane described later as the alcohol constituting the mother liquor, the alcohol can be easily recovered and reused.

[0082] In the method for producing colloidal silica according to the present invention, the concentration of the alcohol constituting the mother liquor is preferably 65 to 95% by mass, more preferably 67 to 93% by mass, and even more preferably 69 to 91% by mass. In the method for producing colloidal silica according to the present invention, the concentration of alcohol in the mother liquor is within the above range, which allows for easy dispersion of the alkoxysilane described later and easy promotion of the hydrolysis reaction.

[0083] In the method for producing colloidal silica according to the present invention, a solution containing at least an alkoxysilane is continuously or intermittently added to the mother liquor as an additive component and reacted with it.

[0084] In the method for producing colloidal silica according to the present invention, the form in which the alkoxysilane-containing solution is added to the mother liquor includes (a) a form in which only liquid alkoxysilane is added to the mother liquor, and (b) a form in which an alcoholic solution of alkoxysilane is added.

[0085] In the method for producing colloidal silica according to the present invention, tetraalkoxysilane can be used as an alkoxysilane to be added to the mother liquor. The above tetraalkoxysilane is given by the following general formula (I) Si(OR)4(I) (In the above general formula (I), the R group is an alkyl group having 1 to 8 carbon atoms.) Examples of tetraalkoxysilanes represented by [formula] include [formula].

[0086] In a tetraalkoxysilane or derivative represented by general formula (I), the R group is an alkyl group having 1 to 8 carbon atoms, and preferably an alkyl group having 1 to 4 carbon atoms.

[0087] In a tetraalkoxysilane represented by general formula (I) or its derivatives, the R group can be one or more selected from, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group, with one or more selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group being preferred.

[0088] The tetraalkoxysilane represented by general formula (I) is preferably tetramethoxysilane, in which the R group is a methyl group; tetraethoxysilane, in which the R group is an ethyl group; or tetraisopropoxysilane, in which the R group is an isopropyl group. Furthermore, examples of derivatives of the tetraalkoxysilane represented by general formula (I) include low-condensation products obtained by partially hydrolyzing the tetraalkoxysilane represented by general formula (I). Among the tetraalkoxysilanes or derivatives represented by general formula (I), tetramethoxysilane (TMOS) is preferred because it is easy to control the hydrolysis rate, easy to obtain fine silica particles, and leaves little unreacted residue.

[0089] In the method for producing colloidal silica according to the present invention, when an alcohol solution of the above-mentioned (b) alkoxysilane is added to the mother liquor as an additive component, it is preferable that the alcohol constituting the alcohol solution be one or more selected from methanol, ethanol, isopropanol, etc.

[0090] In the method for producing colloidal silica according to the present invention, the alcohol constituting the alcohol solution is more preferably the same alcohol as the alcohol produced by the hydrolysis of the alkoxysilane described later. For example, if the alkoxysilane described later is tetramethoxysilane (TMOS), methanol is preferred as the alcohol constituting the alcohol solution. In the method for producing colloidal silica according to the present invention, by using the same alcohol as the alcohol produced by the hydrolysis of the alkoxysilane described later as the alcohol constituting the alcohol solution, the alcohol can be easily recovered and reused.

[0091] In the method for producing colloidal silica according to the present invention, the concentration of alkoxysilane in the alcohol solution is preferably 2.0 to 8.0 mol / L, more preferably 2.5 to 7.5 mol / L, and even more preferably 3.0 to 7.0 mol / L.

[0092] In the method for producing colloidal silica according to the present invention, the concentration of alkoxysilane in the alcohol solution is within the above range, which facilitates the hydrolysis and dehydration condensation reaction of the alkoxysilane.

[0093] In the method for producing colloidal silica according to the present invention, when adding an alkoxysilane-containing solution to the mother liquor, as described above, (a) only liquid alkoxysilane may be added to the mother liquor, or (b) an alcoholic solution of alkoxysilane may be added, and as an optional additive, (c) a mixture of a basic catalyst and water may also be added.

[0094] In the method for producing colloidal silica according to the present invention, the basic catalyst constituting the mixture of (c) basic catalyst and water, which is an optional additive to the mother liquor, is preferably one or more selected from organic amines and ammonia, from the viewpoint of preventing the inclusion of impurities, and is more preferably one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, 3-ethoxypropylamine (3-EOPOA), ammonia, urea, ethanolamine, and tetramethylammonium hydroxide, with ammonia being even more preferred. In the method for producing colloidal silica according to the present invention, if the basic catalyst constituting the mixture of (c) basic catalyst and water, which is an optional additive component, is the one described above, it exhibits excellent catalytic activity, high volatility, and can be easily removed in subsequent processes.

[0095] In the method for producing colloidal silica according to the present invention, the concentration of the basic catalyst in the mixture of the optional additive component (c) basic catalyst and water is preferably 0.1 to 10.0% by mass, more preferably 0.5 to 9.5% by mass, and even more preferably 1.0 to 9.0% by mass.

[0096] In the method for producing colloidal silica according to the present invention, by ensuring that the concentration of the basic catalyst in the mixture of (c) a basic catalyst and water, which is an optional additive component, is within the above range, the particle size of the silica particles in the resulting colloidal silica can be easily controlled to a desired range.

[0097] In the method for producing colloidal silica according to the present invention, the water in the mixture of (c) a basic catalyst and water, which is an optional additive, is preferably pure water or ultrapure water in order to minimize the inclusion of metal impurities.

[0098] In the method for producing colloidal silica according to the present invention, when adding an alkoxysilane-containing solution to the mother liquor, if a mixture of (c) a basic catalyst and water is added as an optional additive, it is preferable to start adding the mixture of (c) the basic catalyst and water at the same time as the start of adding the alkoxysilane-containing solution and stop adding it at the same time as the end of adding the alkoxysilane-containing solution.

[0099] In the method for producing colloidal silica according to the present invention, a reaction is carried out by continuously or intermittently adding a solution containing at least an alkoxysilane as an additive component to a mother liquor containing the above-mentioned basic catalyst, water, and alcohol.

[0100] In the method for producing colloidal silica according to the present invention, the liquid temperature of the mother liquor at the start of adding the additive component is 4.0 to 21.0°C.

[0101] In the method for producing colloidal silica according to the present invention, the liquid temperature of the mother liquor at the start of adding the additive component is preferably 4.0°C or higher, more preferably 4.5°C or higher, and even more preferably 5.0°C or higher.

[0102] In the method for producing colloidal silica according to the present invention, the generation of unreacted substances and gel-like substances can be suppressed by ensuring that the liquid temperature of the mother liquor at the start of the addition of the additive component is equal to or greater than the above value (lower limit).

[0103] In the method for producing colloidal silica according to the present invention, the liquid temperature of the mother liquor at the start of adding the additive component is preferably 21.0°C or lower, more preferably 20.5°C or lower, and even more preferably 20.0°C or lower.

[0104] In the method for producing colloidal silica according to the present invention, large-particle-sized silica particles can be easily produced if the liquid temperature of the mother liquor at the start of the addition of the additive component is below the above value (upper limit).

[0105] In the method for producing colloidal silica according to the present invention, the temperature is controlled so that the difference t0-t1 between the liquid temperature t0 of the mother liquor at the start of the addition of the additive component and the liquid temperature t1 of the mixed solution of the mother liquor and the additive component at the end of the addition of the additive component is 0.50 to 2.00°C.

[0106] In the method for producing colloidal silica according to the present invention, the temperature is controlled such that t0 > t1, as is clear from the fact that the difference t0-t1 between the liquid temperature t0 of the mother liquor at the start of the addition of the additive component and the liquid temperature t1 of the mixture of the mother liquor and the additive component at the end of the addition of the additive component takes a positive value.

[0107] In the method for producing colloidal silica according to the present invention, the difference t0-t1 between the liquid temperature t0 of the mother liquor at the start of the addition of the additive component and the liquid temperature t1 of the mixture of the mother liquor and the additive component at the end of the addition of the additive component is preferably 0.50°C or higher, more preferably 0.55°C or higher, and even more preferably 0.60°C or higher.

[0108] In the method for producing colloidal silica according to the present invention, if the difference t0-t1 between the liquid temperature t0 of the mother liquor at the start of the addition of the additive component and the liquid temperature t1 of the mixture of the mother liquor and the additive component at the end of the addition of the additive component is greater than or equal to the above value (lower limit), the rate of hydrolysis and dehydration condensation of alkoxysilane is reduced, thereby suppressing the generation of fine silica particles.

[0109] In the method for producing colloidal silica according to the present invention, the difference t0-t1(°C) between the liquid temperature t0(°C) of the mother liquor at the start of the addition of the additive component and the liquid temperature t1(°C) of the mixture of the mother liquor and the additive component at the end of the addition of the additive component is preferably 2.00°C or less, more preferably 1.95°C or less, and even more preferably 1.90°C or less.

[0110] In the method for producing colloidal silica according to the present invention, the difference t0-t1(°C) between the liquid temperature t0(°C) of the mother liquor at the start of adding the additive component and the liquid temperature t1(°C) of the mixed liquid of the mother liquor and the additive component at the end of adding the additive component is less than or equal to the above value (upper limit), thereby suppressing the aggregation of main particles (primary silica particles and secondary silica particles) due to rapid changes in liquid temperature.

[0111] Furthermore, in the method for producing colloidal silica according to the present invention, when a component other than the alkoxysilane-containing solution is added along with the alkoxysilane-containing solution as an additive component, the above-mentioned "start of addition of additive component" means the point in time when the addition of any of the additive components to the mother liquor begins, and the above-mentioned "end of addition of additive component" means the point in time when the total amount of all additive components has been added to the mother liquor.

[0112] In the method for producing colloidal silica according to the present invention, the ratio "t0-t1 / t0" of the difference t0-t1 (°C) between the liquid temperature t1 of the mixture of the mother liquor and the additive at the end of the addition of the additive and the liquid temperature t0 (°C) of the mother liquor at the start of the addition of the additive is preferably 0.05 to 0.15, more preferably 0.06 to 0.14, and even more preferably 0.07 to 0.13.

[0113] In the method for producing colloidal silica according to the present invention, the ratio of the difference t0-t1(°C) between the liquid temperature t0(°C) of the mother liquor at the start of the addition of the additive and the liquid temperature t1 of the mixed solution of the mother liquor and the additive at the end of the addition of the additive, "t0-t1 / t0", is within the above range, thereby effectively suppressing the generation of fine silica particles while suppressing the aggregation of main particles.

[0114] In the method for producing colloidal silica according to the present invention, it is desirable to add the additive component to the mother liquor while controlling the temperature so that the liquid temperature t0 of the mother liquor at the start of adding the additive component is the highest temperature, and the liquid temperature t1 of the mixture of the mother liquor and the additive component at the end of adding the additive component is the lowest temperature, throughout the entire time the additive component is added to the mother liquor. In other words, in the method for producing colloidal silica according to the present invention, it is desirable to add the additive component to the mother liquor while controlling the temperature so that the liquid temperature gradually decreases compared to the liquid temperature t0 of the mother liquor at the start of the addition of the additive component.

[0115] Thus, in the method for producing colloidal silica according to the present invention, by adding the additive component to the mother liquor while controlling the temperature so that the liquid temperature gradually decreases compared to the liquid temperature t0 of the mother liquor at the start of the addition of the additive component, it is possible to suppress the formation of silica fine particles while allowing the hydrolysis and dehydration condensation reaction of the alkoxysilane to proceed and producing silica particles suitably.

[0116] In the method for producing colloidal silica according to the present invention, the method of temperature control is not particularly limited. For example, the method may be performed by slowly cooling a container containing a mixture of the mother liquor and the additive components with a cooling device, or by gradually adding the additive components, which are at a lower temperature than the mother liquor, to the mother liquor.

[0117] In the method for producing colloidal silica according to the present invention, the mother liquor containing the basic catalyst, water, and alcohol is preferably added to and contacted with the additive component alkoxysilane in an amount of 0.5 to 75.0 parts by mass, more preferably 1.0 to 70.0 parts by mass, and even more preferably 1.5 to 65.0 parts by mass, per 100 parts by mass of the mother liquor.

[0118] In the method for producing colloidal silica according to the present invention, by controlling the amount of alkoxysilane in contact with 100 parts by mass of the mother liquor within the above range, the hydrolysis and dehydration condensation reaction of the alkoxysilane can be effectively facilitated.

[0119] In the method for producing colloidal silica according to the present invention, it is preferable to mix and react the mother liquor and the additive component such that the ratio of the water content in the mixture of the mother liquor and the additive component to the alkoxysilane content in the mixture of the mother liquor and the additive component ("water content in the mixture of mother liquor and additive component / alkoxysilane content in the mixture of mother liquor and additive component") is 3.0 to 20.0 in molar ratio, more preferably 3.5 to 19.5, and even more preferably 4.0 to 19.0.

[0120] In the method for producing colloidal silica according to the present invention, by mixing and reacting the materials so that the "water content in the mixture of mother liquor and additive components / alkoxysilane content in the mixture of mother liquor and additive components" is within the above range, the hydrolysis and dehydration condensation reaction of alkoxysilane can be easily carried out, while the particle size of the silica particles in the resulting colloidal silica can be easily controlled to a desired range.

[0121] In the method for producing colloidal silica according to the present invention, the alkoxysilane-containing solution is added at an addition rate of 1.50 mL / min or less (more than 0.0 mL / min and 1.50 mL / min or less) per 1 L of the total amount of the mother liquor and all added components.

[0122] In the method for producing colloidal silica according to the present invention, the alkoxysilane-containing solution is added at an addition rate of 1.50 mL / min or less per 1 L of the total amount of the mother liquor and all added components. It is preferable to add the substance at an addition rate of 1.49 mL / min or less, and more preferably at an addition rate of 1.48 mL / min or less.

[0123] In the method for producing colloidal silica according to the present invention, by adding the alkoxysilane-containing solution at an addition rate of no more than the above value (upper limit) per liter of the total amount of the mother liquor and all added components, the hydrolysis and dehydration condensation reaction of the alkoxysilane can be easily facilitated, suppressing the formation of silica fine particles, while easily controlling the particle size of the silica particles in the resulting colloidal silica to a desired range.

[0124] In the method for producing colloidal silica according to the present invention, the alkoxysilane-containing solution is usually added at an addition rate of more than 0.00 mL / min per 1 L of the total amount of the mother liquor and all added components, and can be added at an addition rate of 0.10 mL / min or more.

[0125] In the method for producing colloidal silica according to the present invention, an alkoxysilane-containing solution is added to the mother liquor continuously or intermittently as an additive component. In the method for producing colloidal silica according to the present invention, intermittently adding the alkoxysilane-containing solution to the mother liquor means dividing the total amount of the alkoxysilane-containing solution to be added to the mother liquor into multiple parts and adding them sequentially to the mother liquor.

[0126] In the method for producing colloidal silica according to the present invention, when an alkoxysilane-containing solution is continuously added to the mother liquor as an additive component, it is preferable to add the alkoxysilane-containing solution to the mother liquor at a constant rate.

[0127] In the method for producing colloidal silica according to the present invention, if the total amount of alkoxysilane-containing solution added to the mother liquor is w (g), and the total time of adding the alkoxysilane-containing solution to the mother liquor is t (minutes), and the added component is continuously added to the mother liquor in a constant amount over the entire addition time (added at a constant rate), then the theoretical addition rate s (g / minute) of the added component is s = w / t. On the other hand, in reality, the rate at which the alkoxysilane-containing solution is added to the mother liquor can vary to a certain extent over time depending on the method of addition. Therefore, in the method for producing colloidal silica according to the present invention, adding the alkoxysilane-containing solution to the mother liquor at a constant rate means continuously supplying the alkoxysilane-containing solution to the mother liquor at an addition rate of 0.9 s (g / min) or more and 1.1 s (g / min) over the entire addition time (where s (g / min) is the theoretical addition rate mentioned above).

[0128] In the method for producing colloidal silica according to the present invention, when adding the additive component to the mother liquor, it is preferable to complete the addition of the additive component within 100 to 600 minutes, and more preferably within 110 to 590 minutes.

[0129] Furthermore, in the method for producing colloidal silica according to the present invention, The time for adding additives to the mother liquor refers to the time from the start of adding any of the additives to the mother liquor until the entire amount of all additives has been added to the mother liquor.

[0130] In the method for producing colloidal silica according to the present invention, the step of adding additive components to the mother liquor can be carried out under any pressure conditions, such as reduced pressure, normal pressure, or pressurized pressure, but it is preferable to carry it out under normal pressure.

[0131] In the method for producing colloidal silica according to the present invention, a solution containing at least alkoxysilane is added to the mother liquor as an additive component and mixed, thereby initiating a hydrolysis and dehydration condensation reaction of alkoxysilane in the resulting mixture, and silica particles are synthesized.

[0132] In the method for producing colloidal silica according to the present invention, the colloidal silica obtained by adding additive components to the mother liquor contains organic solvents such as alcohol in addition to water. Therefore, in order to improve long-term storage stability, the dispersion medium of the obtained reaction solution may be replaced with water or the solution may be concentrated as needed.

[0133] The method for replacing the above organic solvent with water is not particularly limited; for example, one method is to add a fixed amount of water dropwise while heating the above mixture.

[0134] In the method for producing colloidal silica according to the present invention, the method for concentrating the colloidal silica obtained by adding additive components to the mother liquor is not particularly limited, and examples include heating concentration, membrane concentration, and reduced pressure method.

[0135] In the method for producing colloidal silica according to the present invention, it is preferable that the colloidal silica obtained by adding additive components to the mother liquor is not subjected to ultrafiltration.

[0136] Details of the colloidal silica obtained by the manufacturing method according to the present invention are as described in detail in the above-mentioned description of the colloidal silica according to the present invention.

[0137] According to the present invention, a colloidal silica can be produced in a simple manner that exhibits excellent polishing speed when used as an abrasive for polishing electronic materials such as semiconductor wafers, and can form a polished surface with excellent flatness while suppressing the amount of abrasive residue on the polished surface. [Examples]

[0138] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples.

[0139] (Example 1) (1) A mother liquor was prepared by mixing 1570.9 g of pure water, 316.3 g of 28% by mass aqueous ammonia, and 8363.2 g of methanol at a temperature of 20.0°C. Next, to the mother liquor, the entire amounts of additive solution a, consisting of 6088.0 g of tetramethoxysilane (TMOS) at a liquid temperature of 20.0°C, and additive solution b, a mixture of 1210.5 g of pure water and 316.3 g of 28% by mass aqueous ammonia, were added and mixed at a constant rate over 300 minutes to obtain a silica sol reaction solution using water and methanol as dispersion media. In this process, the temperature of the mother liquor was adjusted so that, from a temperature of 20.0°C at the start of adding the additive solutions a and b, the temperature of the mixture of the mother liquor, additive solutions a and b would gradually decrease to 18.3°C at the end of adding the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions in this embodiment are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this embodiment are shown in Table 2.

[0140] (Example 2) (1) A mother liquor was prepared by mixing 1570.9 g of pure water, 316.3 g of 28% by mass aqueous ammonia, and 8363.2 g of methanol at a temperature of 18.0°C. Next, to the mother liquor, the entire amounts of additive solution a, consisting of 6088.0 g of tetramethoxysilane (TMOS) at a liquid temperature of 18.0°C, and additive solution b, a mixture of 1210.5 g of pure water and 316.3 g of 28% by mass aqueous ammonia, were added and mixed at a liquid temperature of 18.0°C, respectively, at a constant rate for 240 minutes to obtain a silica sol reaction solution using water and methanol as dispersion media. In this process, the entire amounts of additive solutions a and b were added to the mother liquor while adjusting the temperature so that the temperature of the mixture of the mother liquor, additive solution a, and additive solution b gradually decreased from 18.0°C at the start of adding the mother liquor to 16.1°C at the end of adding the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions in this embodiment are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this embodiment are shown in Table 2.

[0141] (Example 3) (1) A mother liquor was prepared by mixing 440.0 g of pure water, 240.0 g of 28% by mass aqueous ammonia, and 4000.0 g of methanol at a temperature of 15.0°C. Next, to the mother liquor, an additive solution a, prepared by mixing 2000.0 g of tetramethoxysilane (TMOS) and 480.0 g of methanol at a temperature of 15.0°C, and an additive solution b, prepared by mixing 1360.0 g of pure water and 200.0 g of 28% by mass aqueous ammonia, were added in their entirety at a constant rate over 130 minutes to obtain a silica sol reaction solution using water and methanol as dispersion media. In this process, the entire contents of additive solutions a and b were added to the mother liquor while adjusting the temperature so that the temperature of the mixture of the mother liquor, additive solution a, and additive solution b gradually decreased from 15.0°C at the start of adding the mother liquor to 13.9°C at the end of adding the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions in this embodiment are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this embodiment are shown in Table 2.

[0142] (Example 4) (1) A mother liquor was prepared by mixing 729.2 g of pure water, 126.8 g of 28% by mass aqueous ammonia, and 7800.0 g of methanol at a temperature of 5.0°C. Next, to the mother liquor, an additive solution containing 1160.0 g of tetramethoxysilane (TMOS) and 913.0 g of methanol, at a liquid temperature of 5.0°C, was added in its entirety at a constant rate over 130 minutes and mixed to obtain a silica sol reaction solution with water and methanol as dispersion media. In this process, the entire amounts of additive solutions a and b were added to the mother liquor while adjusting the temperature so that the temperature of the mixture of the mother liquor, additive solution a, and additive solution b gradually decreased from 5.0°C at the start of the addition of the additive solutions a to 4.4°C at the end of the addition of the additive solutions b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions in this embodiment are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this embodiment are shown in Table 2.

[0143] (Comparative Example 1) (1) A mother liquor was prepared by mixing 427.2 g of pure water, 270.3 g of 28% by mass aqueous ammonia, and 4392.0 g of methanol at a temperature of 34.0°C. Next, to the mother liquor, the entire amounts of additive solution a, consisting of 2277.0 g of tetramethoxysilane (TMOS) and 855.0 g of methanol at a liquid temperature of 34.0°C, and additive solution b, consisting of 535.5 g of pure water at a liquid temperature of 34.0°C, were added and mixed at a constant rate over 75 minutes to obtain a silica sol reaction solution with water and methanol as dispersion media. In this process, the temperature of the mother liquor was adjusted so that the temperature of the mixture of the mother liquor, additive solution a, and additive solution b gradually decreased from 34.0°C at the start of adding the mother liquor to 24.5°C at the end of adding the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions for this comparative example are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this comparative example are shown in Table 2.

[0144] (Comparative Example 2) (1) A mother liquor was prepared by mixing 473.1 g of pure water, 63.1 g of 28% by mass aqueous ammonia, and 3302.2 g of methanol at a temperature of 20.0°C. Next, to the mother liquor, the entire volume of additive solution a, prepared by mixing 2761.1 g of tetramethoxysilane (TMOS) and 185.1 g of methanol at a liquid temperature of 20.0°C, was added and mixed at a constant rate over 120 minutes. At 30 minutes and 60 minutes after the start of adding additive solution a, 340.0 g each of additive solution b, prepared by mixing 176.1 g of pure water and 163.9 g of 28% by mass aqueous ammonia solution at a liquid temperature of 20.0°C, was added and mixed to allow the reaction to proceed, thereby obtaining a silica sol reaction solution with water and methanol as dispersion media. In this process, the temperature of the mother liquor was adjusted to a constant temperature while adding the additive solutions a and b to the mother liquor, so that the temperature of the mixture of the mother liquor, additive solution a, and additive solution b remained at 20.0°C when the addition of the additive solutions a and b was completed, relative to the mother liquor's temperature of 20.0°C at the start of the addition of the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions for this comparative example are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this comparative example are shown in Table 2.

[0145] (Comparative Example 3) (1) A mother liquor was prepared by mixing 109.0 g of pure water, 146.0 g of 28% by mass aqueous ammonia, and 3153.0 g of methanol at a temperature of 26.0°C. Next, to the mother liquor, an additive solution a, prepared by mixing 3000.0 g of tetramethoxysilane (TMOS) and 528.0 g of methanol at a temperature of 26.0°C, and an additive solution b, prepared by mixing 817.2 g of pure water and 139.8 g of 28% by mass aqueous ammonia, were added in their entirety at a constant rate over 208 minutes, and the mixtures were allowed to react to obtain a silica sol reaction solution using water and methanol as dispersion media. In this process, the temperature of the mother liquor was adjusted to a constant temperature while adding the mother liquor and adding solution b, so that the temperature of the mixture of the mother liquor, adding solution a, and adding solution b remained at 26.0°C when the addition of the mother liquor was completed, compared to the mother liquor's temperature of 26.0°C at the start of adding the mother liquor and adding solution b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions for this comparative example are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this comparative example are shown in Table 2.

[0146] (Comparative Example 4) (1) A mother liquor was prepared by mixing 1570.9 g of pure water, 316.3 g of 28% by mass aqueous ammonia, and 8363.2 g of methanol at a temperature of 20.0°C. Next, to the mother liquor, the entire contents of additive solution a, consisting of 6088.0 g of tetramethoxysilane (TMOS) at a combined temperature of 20.0°C, and additive solution b, a mixture of 1210.5 g of pure water and 316.3 g of 28% by mass aqueous ammonia, at a temperature of 20.0°C, were added and mixed at a constant rate over 100 minutes to obtain a silica sol reaction solution using water and methanol as dispersion media. In this process, the temperature of the mother liquor was adjusted to a constant temperature while adding the additive solutions a and b to the mother liquor, so that the temperature of the mixture of the mother liquor, additive solutions a and b was maintained at 20.0°C at the time the addition of the additive solutions a and b was completed, compared to the mother liquor's temperature of 20.0°C at the start of the addition of the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions for this comparative example are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this comparative example are shown in Table 2.

[0147] (Comparative Example 5) (1) A mother liquor was prepared by mixing 1570.9 g of pure water, 316.3 g of 28% by mass aqueous ammonia, and 8363.2 g of methanol at a temperature of 20.0°C. Next, to the mother liquor, the entire amounts of additive solution a, consisting of 6088.0 g of tetramethoxysilane (TMOS) at a combined temperature of 20.0°C, and additive solution b, a mixture of 1210.5 g of pure water and 316.3 g of 28% by mass aqueous ammonia, at a temperature of 20.0°C, were added and mixed at a constant rate over 200 minutes to obtain a silica sol reaction solution using water and methanol as dispersion media. In this process, the temperature of the mother liquor was adjusted to a constant temperature while adding the additive solutions a and b to the mother liquor, so that the temperature of the mixture of the mother liquor, additive solutions a and b was maintained at 20.0°C at the time the addition of the additive solutions a and b was completed, compared to the mother liquor's temperature of 20.0°C at the start of the addition of the additive solutions a and b. Next, the silica sol reaction solution was heated and concentrated under stirring conditions, and heated pure water was added to replace the solvent with water, thereby obtaining the desired colloidal silica. The manufacturing conditions for this comparative example are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this comparative example are shown in Table 2.

[0148] (Comparative Example 6) 120 g of the colloidal silica obtained in Comparative Example 4 was taken and subjected to ultrafiltration using an ultrafiltration apparatus having the following configuration to obtain the target colloidal silica. <Configuration of the ultrafiltration system> • Filtration treatment device: Pencil-type module (PX-02001) manufactured by Asahi Kasei Corporation • Ultrafiltration membrane: Ultrafiltration membrane with a molecular weight cutoff of 80,000 (Asahi Kasei Lab Module AOP-0013) • Pumps: Masterflex L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MF07514-10), and Masterflex L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) • Tubing: Masterflex tubing for peristaltic pumps (96400-25) The manufacturing conditions for this comparative example are shown in Table 1. Furthermore, the physical properties of the colloidal silica obtained in this comparative example are shown in Table 2.

[0149] The colloidal silica obtained in each of the above examples and comparative examples was used as abrasive grains, and the number of residual particles on the polished surface, the polishing speed, and the surface roughness were evaluated by the following method. The results are shown in Table 2.

[0150] <Method for evaluating polishing speed> The colloidal silica produced in each example and comparative example was diluted with ultrapure water to a silica concentration of 3.0% by mass to prepare a polishing composition. A 3 cm square silicon wafer with a silicon nitride film deposited on its surface was polished using the obtained polishing composition under the following conditions. The polishing speed was calculated from the difference in the thickness of the silicon nitride film before and after polishing and the polishing time. Polishing machine: NF-300CMP manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TMPad manufactured by Nitta DuPont Corporation. Slurry supply rate: 50 ml / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min Film thickness measuring machine: SiN film, optical interference type film thickness measuring machine When the polishing speed is measured using the method described above, a polishing speed of 25 nm / min or more is considered good, and a polishing speed of less than 25 nm / min is considered poor.

[0151] <Method for evaluating the number of remaining fine particles on a polished surface> First, a 3cm square silicon wafer polished under the polishing conditions described in the above <Method for Evaluating Polishing Speed> was subjected to scrubbing cleaning using a PVA roll brush in the scrubbing section built into the MAT ZAB-8S1M washing and drying apparatus under the following cleaning conditions. To secure the silicon wafers, a jig was used in which the frame was made of glass epoxy resin and the wafer-holding part was made of polyurethane. (Washing conditions) Brush: AION SCL BRUSH ROLLER 48 (40 / 26) x 224mm (manufactured by AION Corporation) Scrub cleansing time: 1 min Brush rotation speed: 200 rpm Spin rotation speed of the silicon wafer fixing part: 50 rpm After scrubbing, ultrapure water was flowed over the polished substrate at a flow rate of 750 mL / min for 1 minute, and then the substrate was further treated with a spin dryer built into the above apparatus at 1800 rpm for 20 seconds. (Measurement conditions for the number of remaining particulate matter) For silicon wafers treated under the above cleaning conditions and dried, the number of remaining fine particles on the polished surface was measured using an atomic force microscope. Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: OLYMPUS MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning area: 3.0 μm square Scanning speed: 1.00Hz Number of fields of view observed: Five arbitrary fields of view were observed per polished wafer (observation area per field of view: 3 μm × 3 μm). In five observation fields (5 fields) on the wafer polished surface, the number of particles remaining on the polished surface is counted, and the total count in the 5 fields is calculated over the area of ​​the 5 fields (45 μm). 2 The value obtained by dividing it by the number of remaining particles (particles / μm) on the polished surface 2 ) The number of remaining fine particles (particles / μm) on the polished surface using the above method 2 When the measurement was taken, the number of remaining fine particles on the polished surface was 3 (particles / μm). 2 If the number of remaining silica particles on the polished surface is 3 or less, it is determined that the amount of remaining silica particles on the polished surface is small, and the number of remaining fine particles on the polished surface is 3 (particles / μm). 2 If the value exceeds ), it is judged that there is a large amount of silica particles remaining on the polished surface.

[0152] <Method for evaluating polished surface roughness> According to the (measurement conditions for the number of remaining fine particles) in the above-mentioned <Method for evaluating the number of remaining fine particles on the polished surface>, the root mean square roughness x was measured in five observation fields (5 fields) on the wafer polished surface using an atomic force microscope. i (nm) was measured, and the root mean square roughness x in 5 fields of view was measured. i The arithmetic mean of (nm) was defined as the polished surface roughness Rms(nm). A polished surface is judged to have good surface roughness if the polished surface roughness Rms is 3.00 nm or less, and poor surface roughness is judged if the polished surface roughness Rms is greater than 3.00 nm.

[0153] [Table 1]

[0154] [Table 2]

[0155] Table 2 shows that the colloidal silica obtained by the specific manufacturing methods in Examples 1 to 4 had an average primary particle diameter of 55 to 200 nm, an average secondary particle diameter of 80 to 300 nm, a degree of association of 1.50 to 3.00, and a silanol group density of 2.8 groups / nm as measured by the Sears method. 2 The above conditions are met, and the silica fine particle content parameter calculated from the specific formula is 15.0 or less. Therefore, it can be seen that the colloidal silica obtained in Examples 1 to 4 can exhibit excellent polishing speed when used as abrasive grains for polishing electronic materials such as semiconductor wafers, and can form a polished surface with reduced surface roughness Rms while suppressing the amount of abrasive residue on the polished surface.

[0156] On the other hand, as shown in Table 2, the colloidal silica obtained in Comparative Examples 1 to 6 had the following characteristics: the average primary particle diameter of the silica particles was outside the specified range (Comparative Examples 1 and 3), the average secondary particle diameter of the silica particles was outside the specified range (Comparative Example 3), the degree of association of the silica particles was outside the specified range (Comparative Examples 2 and 6), the silanol group density measured by the Sears method of the silica particles was below the specified value (Comparative Examples 1 and 2), and the silica fine particle content parameter calculated from a specific formula was above the specified value (Comparative Examples 3 to 5). Therefore, it can be seen that when the colloidal silica obtained in Comparative Examples 1 to 6 is used as an abrasive for polishing electronic materials such as semiconductor wafers, it exhibits inferior polishing speed (Comparative Examples 1 and 3), fails to suppress the amount of abrasive residue on the polished surface (Comparative Examples 3 to 5), and fails to form a polished surface with reduced surface roughness Rms (Comparative Examples 1, 2, and 6). [Industrial applicability]

[0157] According to the present invention, when used as an abrasive grain, it is possible to provide colloidal silica and a method for producing colloidal silica that can form a polished surface with reduced surface roughness and less silica particle residue on the polished surface.

Claims

[Claim 1] A mother liquor containing a basic catalyst, water, and alcohol, A method for producing colloidal silica by continuously or intermittently adding a solution containing at least alkoxysilane as an additive component and reacting it, The temperature of the mother liquor at the start of adding the aforementioned additive component is 4.0 to 21.0°C. The liquid temperature t of the mother liquor at the start of adding the aforementioned additive component ０ The liquid temperature t of the mother liquor and the mixed solution of the additive components at the end of the addition of the additive components. １ The difference between t ０ -t １ While controlling the temperature so that it is between 0.50 and 2.00°C, The alkoxysilane-containing solution shall be added at an addition rate of 1.50 mL / min or less per liter of the total volume of mother liquor and the total amount of added components. A method for producing colloidal silica characterized by the following.

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