Sulfonic acid-modified colloidal silica and method for producing sulfonic acid-modified colloidal silica

Abstract

Provided is sulfonic acid-modified colloidal silica capable of forming a polished surface with highly reduced surface roughness.　This sulfonic acid-modified colloidal silica is characterized in that: the sulfur content of silica particles is 3000-9000 ppm by mass per 1 g of the silica particles; the sulfur content in a solvent is 750 ppm by mass or less per 1 g of the solvent; and the content of coarse particles with a particle size of 0.2 μm or more included in the silica particles is 10,000,000 particles or less per 1 mL when the silica particle concentration is 1 mass%.

Description

Sulfonic acid-modified colloidal silica and method for producing sulfonic acid-modified colloidal silica

[0001] The present invention relates to sulfonic acid-modified colloidal silica and a method for producing sulfonic acid-modified colloidal silica.

[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 by 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 chemical mechanical polishing (CMP), there is a growing demand for abrasive grains that can produce a polished surface with even lower surface roughness on the semiconductor wafer being polished.

[0005] Under these circumstances, colloidal silica (silica sol) is used as an abrasive for polishing semiconductor wafers, with sulfonic acid groups (sulfo groups (-SO)) added. ３ Sulfonic acid-modified colloidal silica with H)) has been proposed (see Patent Document 1 (Japanese Patent Application Publication No. 2010-269985)).

[0006] Japanese Patent Publication No. 2010-269985

[0007] However, the inventors have found that conventionally proposed sulfonic acid-modified colloidal silica has the following problems: (1) The level of modification of sulfo groups to the silica particles constituting the sulfonic acid-modified colloidal silica is insufficient, resulting in poor dispersion stability of the silica particles. When the above sulfonic acid-modified colloidal silica is used as an abrasive for polishing semiconductor wafers, the silica particles tend to aggregate during storage or polishing, making it difficult to obtain a polished surface with a highly reduced surface roughness. (2) Unreacted silane coupling agent components used when modifying the sulfo groups remain in the solvent of the sulfonic acid-modified colloidal silica. When the above sulfonic acid-modified colloidal silica is used as an abrasive for polishing semiconductor wafers, the silane coupling agent components remaining in the solvent tend to crosslink and aggregate the silica particles during storage or polishing, making it difficult to obtain a polished surface with a highly reduced surface roughness. This was thought to be because silane coupling agents such as 3-mercaptopropyltrimethoxysilane, used, for example, when modifying silica particles with sulfo groups, have poor reactivity with silica particles compared to other silane coupling agents such as 3-aminopropyltrimethoxysilane, and therefore tend to remain in the solvent as unreacted silane coupling agents.

[0008] Furthermore, the inventors found that conventionally proposed sulfonic acid-modified colloidal silica has the following problems: (3) When attempting to remove unreacted silane coupling agent components remaining in the solvent of the sulfonic acid-modified colloidal silica by ultrafiltration, although the unreacted silane coupling agent components can be removed, the aggregation of silica particles constituting the sulfonic acid-modified colloidal silica progresses during ultrafiltration, increasing the content of coarse particles with a particle size of 0.2 μm or more. When the sulfonic acid-modified colloidal silica obtained by ultrafiltration is used as an abrasive grain for polishing, the roughness of the polished surface increases due to the coarse particles.

[0009] Under these circumstances, the present invention aims to provide sulfonic acid-modified colloidal silica and a method for producing sulfonic acid-modified colloidal silica that can form a polished surface with a highly reduced surface roughness.

[0010] In order to solve the above technical problems, the present inventors conducted diligent studies and found that the above problems can be solved by sulfonic acid-modified colloidal silica, wherein the sulfur content of the silica particles is 3,000 ppm by mass or more and 9,000 ppm by mass or less per gram of silica particles, the sulfur content of the solvent is 750 ppm by mass or less per gram of solvent, and the content of coarse particles with a particle size of 0.2 μm or more in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Furthermore, they found that the above sulfonic acid-modified colloidal silica can be produced by a specific manufacturing method, and based on these findings, the present invention was completed.

[0011] In other words, the present invention provides: (1) Sulfonic acid-modified colloidal silica characterized in that the sulfur content of the silica particles is 3,000 ppm by mass or more and 9,000 ppm by mass or less per gram of silica particles, the sulfur content of the solvent is 750 ppm by mass or less per gram of solvent, and the content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass; (2) A method for producing the sulfonic acid-modified colloidal silica described in (1) above, wherein (i) the BET specific surface area is 70 to 500 m ２ Silanol group density is 7.0 to 20.0 groups / nm per gram. ２The present invention provides a method for producing sulfonic acid-modified colloidal silica, comprising the steps of: (ii) bringing a raw colloidal silica containing silica particles into contact with a silane coupling agent containing mercapto groups to perform a modification treatment, and then further contacting it with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles and convert them into sulfo groups; (ii) the amount of silane coupling agent containing mercapto groups in contact with the raw colloidal silica is 100.00 μmol or more and 400.00 μmol or less in terms of solid content; (iii) when bringing the silane coupling agent containing mercapto groups into contact with the raw colloidal silica, the silane coupling agent is diluted with methanol by a mass ratio to a dilution ratio of 3 to 50 times; (iv) the amount of hydrogen peroxide in contact is 3.50 to 10.00 mol per mol of the amount of silane coupling agent containing mercapto groups in contact; and (v) after contacting with hydrogen peroxide, heating the resulting mixture at a temperature of 80.0°C or higher for 15 hours or more.

[0012] According to the present invention, it is possible to provide sulfonic acid-modified colloidal silica and a method for producing sulfonic acid-modified colloidal silica that can form a polished surface with a highly reduced surface roughness.

[0013] First, the sulfonic acid-modified colloidal silica according to the present invention will be described. The sulfonic acid-modified colloidal silica according to the present invention is characterized in that the sulfur content of the silica particles is 3,000 ppm by mass or more and 9,000 ppm by mass or less per gram of silica particles, the sulfur content of the solvent is 750 ppm by mass or less per gram of solvent, and the content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass.

[0014] The sulfonic acid-modified colloidal silica according to the present invention has sulfonic groups (-SO) in the silica particles constituting the colloidal silica. ３ H) is fixed in place.

[0015] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the silica particles of 3000 ppm by mass or more and 9000 ppm by mass or less per 1 g of the silica particles, preferably 3050 ppm by mass or more and 8900 ppm by mass or less, more preferably 3100 ppm by mass or more and 8700 ppm by mass or less, still more preferably 3150 ppm by mass or more and 8600 ppm by mass or less, and particularly preferably 3200 ppm by mass or more and 8500 ppm by mass or less.

[0016] In the present invention, the sulfur content in the silica particles constituting the sulfonic acid-modified colloidal silica is an index of the amount of sulfonic acid groups (—SO ３ H) (the amount of modification of sulfonic acid groups to the silica particles) in the silica particles constituting the colloidal silica. The sulfonic acid-modified colloidal silica according to the present invention has a high absolute value of zeta potential and high dispersion stability of the silica particles because the sulfur content in the silica particles is within the above range, so that aggregation of the particles during storage or polishing of the sulfonic acid-modified colloidal silica is less likely to occur. Therefore, when the sulfonic acid-modified colloidal silica is used as abrasive grains for polishing, a highly flat polished surface can be obtained.

[0017] In the present application documents, the sulfur content in the silica particles constituting the sulfonic acid-modified colloidal silica means a value calculated by the following method.

[0018] (Procedure 1) The sulfonic acid-modified colloidal silica (solution) is centrifuged using an Eppendorf Highmark Technologies Co., Ltd. centrifuge tube (model number: S303922A) under the conditions of 260000 G, 5° C., and 150 minutes. The obtained precipitate is dried at 60° C. for 12 hours, then the silica is pulverized and dried at 60° C. under reduced pressure for 2 hours. (Procedure 2) Hydrofluoric acid is added to 1 g of the silica solid content obtained in Procedure 1 to dissolve the silica, and ultrapure water is added to the resulting solution to obtain a diluted solution diluted to 100 mL. (Procedure 3) Using the diluted solution obtained in Procedure 2, the sulfur content (ppm by mass) per 1 g of the silica particles is measured with an inductively coupled plasma atomic emission spectrometry (ICP-AES) apparatus (ICPS-8100 manufactured by Shimadzu Corporation) using the absolute calibration curve method.

[0019] In addition, the fact that the sulfonic acid-modified colloidal silica according to the present invention contains silica particles modified with sulfonic acid can be confirmed by X-ray photoelectron spectroscopy (XPS).

[0020] As described above, the sulfonic acid-modified colloidal silica according to the present invention is obtained by fixing a sulfo group (—SO ３ 3 H) to the silica particles constituting the colloidal silica. Therefore, the sulfonic acid-modified colloidal silica according to the present invention has a basic structure derived from colloidal silica.

[0021] In the present application documents, the fact that the sulfonic acid-modified colloidal silica contains silica particles modified with sulfonic acid is confirmed by the following method. A colloidal silica solution was centrifuged under the conditions of 77400 G, 5° C., and 90 minutes. The obtained precipitate was dried at 60° C. for 12 hours, then the silica was pulverized, and it was depressurized and dried for 2 hours under reduced pressure at 60° C. and a gauge pressure of 0.1 MPa or less to prepare a measurement sample. Using the measurement sample, the presence or absence of a sulfo group on the surface of the silica particles was confirmed by X-ray photoelectron spectroscopy under the following conditions. Measuring instrument: AXIS-NOVA manufactured by Shimadzu Corporation Irradiating X-ray: Al—Kα (15 kV, 10 mA) Analyzing X-ray spot diameter: 300×700 μm

[0022] As described later, as a method for preparing colloidal silica, in an organic solvent containing water, for example, by stirring tetramethoxysilane (Si(OCH ３ 3 ４ )), hydrolysis and dehydration condensation are performed to form a dimer, and this dimer polymerizes (oligomerizes) to form spherical silica primary particles in the solvent. A method in which the spherical silica primary particles are dispersed in the solvent corresponds to colloidal silica. In addition, as the colloidal silica, silica secondary particles in which the silica primary particles are associated may be dispersed in the solvent together with the silica primary particles. Therefore, the sulfonic acid-modified colloidal silica according to the present invention corresponds to a material in which a sulfo group (—SO ３ 3 H) is fixed to the silica particles dispersed in the colloidal silica.

[0023] The average primary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but is preferably 5 nm or more and 39 nm or less.

[0024] The average primary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 39 nm or less, more preferably 35 nm or less, and even more preferably 31 nm or less.

[0025] Because the average primary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0026] The average primary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 5 nm or more, more preferably 6 nm or more, and even more preferably 7 nm or more.

[0027] Because the average primary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is greater than or equal to the above value (lower limit), particle aggregation is less likely to occur when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, thereby enabling the formation of a polished surface with superior flatness.

[0028] In this application, the average primary particle diameter of silica particles contained in sulfonic acid-modified colloidal silica refers to the value measured by the BET method described below. Specifically, first, the sulfonic acid-modified 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 spherical particles, the average primary particle diameter (nm) is given by the following formula: Average primary particle diameter (nm) = 6000 / (BET specific surface area S (nm) 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. ３Therefore, the average primary particle diameter (nm) of silica particles is given by the following formula: Average primary particle diameter (nm) of silica particles = 2727 / specific surface area (m²) ２ It can be calculated by ( / g).

[0029] The sulfonic acid-modified colloidal silica according to the present invention may contain secondary particles (silica secondary particles) formed by the association of primary silica particles. The silica secondary particles contained in the sulfonic acid-modified colloidal silica according to the present invention, together with the primary silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention, constitute the main particles of the silica, and are distinguishable from coarse particles (described later) formed by the aggregation of the above-mentioned silica secondary particles.

[0030] The average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but is preferably 5 nm or more and 200 nm or less.

[0031] The average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 200 nm or less, more preferably 180 nm or less, even more preferably 160 nm or less, even more preferably 140 nm or less, and particularly preferably 120 nm or less.

[0032] Because the average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0033] The average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 5 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, and particularly preferably 20 nm or more.

[0034] Because the average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is greater than or equal to the above value (lower limit), when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, aggregation of silica particles is less likely to occur, making it possible to form a polished surface with superior flatness.

[0035] In this application, the average secondary particle diameter of silica particles contained in sulfonic acid-modified colloidal silica refers to the value measured by the dynamic light scattering method described below. Specifically, first, a 0.3 mass% aqueous citric acid solution is added to the colloidal silica to dilute it to a silica concentration of 0.8 mass%, and the resulting diluted solution is used as the measurement sample. Using the above measurement sample, the average particle diameter measured by the dynamic light scattering method using the zeta potential, particle size, and molecular weight measurement system "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd. is defined as the average secondary particle diameter of the silica particles.

[0036] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the solvent of 750 ppm by mass or less per gram of solvent.

[0037] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the solvent of 750 ppm by mass or less per gram of solvent, preferably 740 ppm by mass or less, more preferably 730 ppm by mass or less, and even more preferably 720 ppm by mass or less.

[0038] In the sulfonic acid-modified colloidal silica according to the present invention, the sulfur content in the solvent serves as an indicator of the amount of unreacted silane coupling agent components remaining in the solvent. The sulfonic acid-modified colloidal silica according to the present invention, having a sulfur content in the solvent below the above-mentioned value (upper limit), allows for the creation of a highly flat polished surface when the sulfonic acid-modified colloidal silica is used as an abrasive grain.

[0039] In the sulfonic acid-modified colloidal silica according to the present invention, the lower limit of the sulfur content in the solvent is not particularly limited, and a lower amount is preferable. However, the sulfur content in the solvent of the sulfonic acid-modified colloidal silica according to the present invention may be, for example, 1 ppm by mass or more, 5 ppm by mass or more, or 10 ppm by mass or more.

[0040] As described above, the inventors have found that when a semiconductor wafer is polished using conventionally known sulfonic acid-modified colloidal silica, the sulfo group (-SO ３Unreacted silane coupling agent components used to modify H) remain in the solvent of the sulfonic acid-modified colloidal silica. During storage or polishing, these remaining silane coupling agent components easily crosslink and aggregate the silica particles, making it difficult to obtain a polished surface with significantly reduced surface roughness. In contrast, the sulfonic acid-modified colloidal silica according to the present invention limits the sulfur content in the solvent to a predetermined amount or less. Since it is less likely to crosslink and aggregate the silica particles, when used as an abrasive grain for polishing semiconductor wafers, a highly flat polished surface can be easily obtained.

[0041] In this application, the sulfur content in the solvent of sulfonic acid-modified colloidal silica refers to the value calculated by the following method: (Procedure 1) The sulfonic acid-modified colloidal silica in solution is subjected to centrifugal filtration using a Sartorius AG centrifugal ultrafiltration unit (model number: VN01H92, molecular weight cutoff 2000) at 12000 rpm for 10 minutes, and the filtrate that has passed through the ultrafiltration membrane is collected. (Procedure 2) The sulfur concentration (mass ppm) in the filtrate obtained in Procedure 1 is measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES) (ICPS-8100, manufactured by Shimadzu Corporation) using the absolute calibration curve method.

[0042] The presence of residual silane coupling agent in the solvent of the sulfonic acid-modified colloidal silica according to the present invention can be confirmed by liquid chromatography-mass spectrometry (LC-MS) or by determining the sulfur content of the silica particles using the method described above and comparing it with the amount of silane coupling agent used in the reaction (contacted with the raw material colloidal silica).

[0043] In the sulfonic acid-modified colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles is preferably 10,000,000 particles / mL or less, more preferably 9,800,000 particles / mL or less, and more preferably 9,600,000 particles / mL or less, when the silica particle concentration (in the sulfonic acid-modified colloidal silica) is 1% by mass.

[0044] In the sulfonic acid-modified colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles is less than or equal to the above value (upper limit) when the silica particle concentration in the sulfonic acid-modified colloidal silica is 1% by mass. Therefore, when performing chemical mechanical polishing (CMP) using the sulfonic acid-modified 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.

[0045] In the sulfonic acid-modified 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 more contained in the silica particles. However, in the sulfonic acid-modified colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or more 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).

[0046] As described above, the inventors' studies have shown that conventionally known sulfonic acid-modified colloidal silica contains unreacted silane coupling agent components. When these unreacted silane coupling agents are removed by ultrafiltration, the silica primary particles constituting the sulfonic acid-modified colloidal silica tend to aggregate, easily generating a large amount of coarse particles with a particle size of 0.2 μm or larger. When the resulting sulfonic acid-modified colloidal silica is used as an abrasive, the roughness of the polished surface increases. The sulfonic acid-modified colloidal silica according to the present invention has a suppressed content of coarse particles with a particle size of 0.2 μm or larger. Therefore, when performing chemical mechanical polishing (CMP) using the sulfonic acid-modified colloidal silica according to the present invention, a highly flat polished surface can be easily formed.

[0047] In this application, the content of coarse particles with a particle size of 0.2 μm or larger in the silica particles constituting sulfonic acid-modified colloidal silica refers to the value measured by the particle size distribution measurement 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 in silica particles> Ultrapure water is added to the sulfonic acid-modified colloidal silica to be measured and diluted so that the silica particle concentration becomes 1.0 mass%. The resulting diluted solution is used as a measurement sample, and the number of coarse particles with a particle size of 0.2 μm or larger is measured using an Accusizer FX-nano manufactured by Particle sizing system Inc. under the following measurement conditions. <System Setup> ・Stirred Vessel Volume: 13.22 mL ・Sample Loop Volume: 0.52 mL ・Autodilution delay time: 3 sec. ・Normal Speed ​​Flow Rate: 15 mL / 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

[0048] The pH of the sulfonic acid-modified colloidal silica according to the present invention can be set appropriately according to its application and is not particularly limited, but is preferably 2.0 or more and 11.0 or less.

[0049] The pH of the sulfonic acid-modified colloidal silica according to the present invention is preferably 2.0 or higher, more preferably 2.5 or higher, and even more preferably 3.0 or higher. By having a pH of the sulfonic acid-modified colloidal silica according to the present invention that is above the above value (lower limit), the dispersion stability of the silica particles of the sulfonic acid-modified colloidal silica according to the present invention is easily improved, and particle aggregation is less likely to occur during storage or polishing of the sulfonic acid-modified colloidal silica according to the present invention, making it possible to easily form a highly flat polished surface when used as an abrasive grain.

[0050] Furthermore, the pH of the sulfonic acid-modified colloidal silica according to the present invention is preferably 11.0 or less, more preferably 10.8 or less, even more preferably 10.6 or less, and particularly preferably 10.4 or less. By having the pH of the sulfonic acid-modified colloidal silica according to the present invention be below the above value (upper limit), the long-term dispersion stability of the sulfonic acid-modified colloidal silica can be further improved, and when used as an abrasive grain for polishing, a highly flat polished surface can be easily formed.

[0051] In this application, pH refers to the value measured by a pH meter F-2000PI (manufactured by Horiba, Ltd.) equipped with a pH electrode 9615S-10D (manufactured by Horiba, Ltd.).

[0052] The silica particle content in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but it is preferably 1% by mass or more and 50% by mass or less, when the sulfonic acid-modified colloidal silica content is 100% by mass.

[0053] The silica particle content in the sulfonic acid-modified colloidal silica according to the present invention is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, when the sulfonic acid-modified colloidal silica content is 100% by mass.

[0054] By ensuring that the silica particle content in the sulfonic acid-modified colloidal silica according to the present invention is equal to or greater than the above value (lower limit), the polishing performance when the sulfonic acid-modified colloidal silica according to the present invention is used as an abrasive grain is further improved.

[0055] The silica particle content in the sulfonic acid-modified colloidal silica according to the present invention is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. By having the silica particle content in the sulfonic acid-modified colloidal silica according to the present invention be below the above value (upper limit), the dispersion stability of the silica particles can be further improved.

[0056] In this application, the silica particle content in the sulfonic acid-modified colloidal silica according to the present invention refers to the value measured by the following measurement method. Specifically, 10.0 g of sulfonic acid-modified colloidal silica is dried on a hot plate at 150°C, then heated at 800°C for 1 hour to remove moisture, and the amount of solid obtained is Wg, which is then calculated using the following formula: Silica particle content in sulfonic acid-modified colloidal silica (mass%) = (W / 10.0) × 100 The above silica particle content corresponds to the total content of primary silica particles, secondary silica particles, and coarse particles in the sulfonic acid-modified colloidal silica.

[0057] The sulfonic acid-modified colloidal silica according to the present invention may contain metal impurities.

[0058] In the sulfonic acid-modified colloidal silica according to the present invention, the above-mentioned metal impurities can be one or more selected from sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, cobalt, and the like.

[0059] In the sulfonic acid-modified colloidal silica according to the present invention, the total content of metal impurities is preferably 1 ppm by mass or less. Because the total content of metal impurities is 1 ppm by mass or less, the sulfonic acid-modified colloidal silica according to the present invention can be suitably used as an abrasive for polishing electronic materials such as semiconductor wafers.

[0060] In this application, the metal impurity content refers to the value measured using an atomic absorption spectrometer.

[0061] The sulfonic acid-modified colloidal silica according to the present invention can be suitably prepared by the manufacturing method described later in this application.

[0062] According to the present invention, it is possible to provide sulfonic acid-modified colloidal silica capable of forming a polished surface with a highly reduced surface roughness.

[0063] Next, the method for producing sulfonic acid-modified colloidal silica according to the present invention will be described. The method for producing sulfonic acid-modified colloidal silica according to the present invention is as follows: (i) BET specific surface area is 70 to 500 m ２ Silanol group density is 7.0 to 20.0 groups / nm per gram. ２ The process comprises the steps of: (ii) bringing a raw colloidal silica containing silica particles into contact with a silane coupling agent containing mercapto groups to perform a modification treatment, and then further contacting it with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles and convert them into sulfo groups; (iii) when bringing the silane coupling agent containing mercapto groups into contact with the raw colloidal silica, the silane coupling agent is diluted with methanol by a mass ratio of 3 to 50 times; (iv) the amount of hydrogen peroxide that comes into contact with the raw colloidal silica is 3.50 to 10.00 mol per mol of the silane coupling agent containing mercapto groups that comes into contact with the silica; and (v) after contacting the hydrogen peroxide, the resulting mixture is heated at a temperature of 80.0°C or higher for 15 hours or more.

[0064] (Colloidal silica raw material) In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the BET specific surface area is 70 to 500 m². ２ Silanol group density is 7.0 to 20.0 groups / nm per gram. ２ The raw material used is colloidal silica containing silica particles.

[0065] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw material colloidal silica can be appropriately selected from colloidal silica having desired properties produced by known production methods, for example, colloidal silica having desired properties produced by the sol-gel method. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the raw material colloidal silica is colloidal silica produced by the sol-gel method, it can be suitably used because it contains a small amount of metal impurities that are diffusible into semiconductors and corrosive ions such as chloride ions.

[0066] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when colloidal silica produced by the sol-gel method is used as the raw material colloidal silica, conventionally known methods can be used as the method for producing said colloidal silica. Specifically, it can be produced by using one or more hydrolyzable silicon compounds (for example, alkoxysilanes or their derivatives) as raw materials and carrying out a hydrolysis-condensation reaction.

[0067] The silicon compound mentioned above is the following general formula (1) Si(OR) ４ (1) Examples of tetraalkoxysilanes or derivatives thereof represented by the above general formula (1) (wherein the R group is an alkyl group having 1 to 8 carbon atoms) include:

[0068] In a silicon compound or derivative represented by general formula (1), the R group is an alkyl group having 1 to 8 carbon atoms, and preferably an alkyl group having 1 to 4 carbon atoms.

[0069] In a silicon compound or derivative represented by general formula (1), 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.

[0070] Preferred silicon compounds represented by general formula (1) include tetramethoxysilane, where the R group is a methyl group; tetraethoxysilane, where the R group is an ethyl group; or tetraisopropoxysilane, where the R group is an isopropyl group. Furthermore, derivatives of the silicon compound represented by general formula (1) include low-condensation products obtained by partially hydrolyzing the silicon compound represented by general formula (1) (tetraalkoxysilane). Among the silicon compound represented by general formula (1) or its derivatives, tetramethoxysilane is preferred because the hydrolysis rate is easily controlled, fine silica particles are easily obtained, and there is little residue of unreacted material.

[0071] Silicon compounds represented by general formula (1) or their derivatives undergo hydrolysis and condensation in the reaction solvent to form colloidal silica.

[0072] Examples of dispersion solvents (reaction solvents) used when a silicon compound represented by general formula (1) or its derivative undergoes hydrolysis and condensation include water or an organic solvent containing water. Examples of such organic solvents include one or more selected from hydrophilic organic solvents such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, ethylene glycol, propylene glycol, 1,4-butanediol, and other alcohols, as well as ketones such as acetone and methyl ethyl ketone. Among these organic solvents, it is particularly preferable to use alcohols such as methanol, ethanol, and isopropanol, and from the viewpoint of post-treatment of the reaction solvent, it is even more preferable to use alcohols having the same alkyl group as the alkyl group (R group) of the silicon compound used as a raw material (for example, methanol for tetramethoxysilane).

[0073] The amount of the above-mentioned organic solvent used is not particularly limited, but it is preferable to use 5 moles or more and 50 moles or less per mole of the silicon compound or derivative represented by general formula (1). If the amount of the above-mentioned organic solvent used is less than 5 moles per mole of the silicon compound or derivative represented by general formula (1), it may be difficult to exhibit compatibility with the silicon compound represented by general formula (1), and if it exceeds 50 moles per mole of the silicon compound or derivative represented by general formula (1), the manufacturing efficiency may decrease.

[0074] The amount of water added to the silicon compound or derivative represented by general formula (1) is not particularly limited and should be an amount required for the hydrolysis of the silicon compound represented by general formula (1), preferably about 2 to 200 moles per mole of the silicon compound represented by general formula (1). When an organic solvent containing water is added to the silicon compound or derivative represented by general formula (1), the amount of water mixed with the organic solvent greatly affects the particle size of the resulting colloidal silica. By relatively increasing the amount of water added relative to the amount of organic solvent added, the particle size of the resulting colloidal silica can be made relatively larger, and by relatively decreasing the amount of water added relative to the amount of organic solvent added, the particle size of the resulting colloidal silica can be made relatively smaller. In this way, the particle size of the resulting colloidal silica can be arbitrarily adjusted by changing the mixing ratio of water and organic solvent.

[0075] For the hydrolysis condensation reaction of silicon compounds to obtain colloidal silica, it is preferable to adjust the reaction solvent to be alkaline in the presence of a basic catalyst. Through this adjustment, the reaction solvent is preferably controlled to a pH of 8.0 to 11.0, more preferably 8.5 to 10.5, allowing for the rapid formation of colloidal silica.

[0076] As for the basic catalyst mentioned above, from the viewpoint of preventing contamination with impurities, one or more selected from organic amines and ammonia are preferred, and one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide are particularly preferred.

[0077] To hydrolyze and condense a silicon compound in a reaction solvent, the silicon compound represented by general formula (1) or a derivative thereof is added to a solvent containing water, and the mixture is stirred at a temperature of typically 0°C to 100°C, preferably 0°C to 50°C.

[0078] By stirring a silicon compound in a water-containing solvent, hydrolysis and dehydration condensation reactions proceed of the silicon compound or its derivative represented by general formula (1). First, the silicon compound or its derivative represented by general formula (1) undergoes dehydration condensation to form a dimer, and this dimer undergoes polymerization (oligomerization) to form spherical primary silica particles in the solvent, thereby obtaining colloidal silica in which primary silica particles are dispersed in the solvent. By hydrolyzing and condensing a silicon compound while stirring it in a water-containing solvent, colloidal silica with uniform silica particle sizes can be obtained.

[0079] The colloidal silica obtained by the above hydrolysis-condensation reaction (sol-gel method) can be used as a raw material colloidal silica in the production method of the present invention by adjusting its concentration as appropriate.

[0080] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the BET specific surface area of ​​the silica particles constituting the raw material colloidal silica is 70 to 500 m². ２ / g, 75-450m ２ It is preferable that the value be / g, and 80 to 400m ２ It is more preferable that it be / g.

[0081] In this application, the BET specific surface area of ​​the silica particles constituting the raw material colloidal silica refers to the specific surface area measured by the BET method using a BET specific surface area measuring device (AUTOSORB 6B manufactured by QUANTACHROME INSTRUMMENTS).

[0082] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the silanol group density of the silica particles constituting the raw material colloidal silica is 7.0 to 20.0 groups / nm. ２ The density is 7.1 to 19.0 particles / nm.２ Preferably, the density is 7.2 to 18.0 particles / nm. ２ It is preferable that it be so.

[0083] In this application, the silanol group density of silica particles constituting the raw material colloidal silica 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 raw material 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 ρ = (a × f × 60²²) ÷ (c × S) ρ: Silanol group density (groups / nm) ２ a: Droplet 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 (g) of silica particles S: BET specific surface area (m²) ２ / g)

[0084] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the reaction site with the silane coupling agent containing mercapto groups (described later) formed on the surface of the silica particles can be easily controlled to a suitable range because the BET specific surface area and silanol group density of the silica particles constituting the raw material colloidal silica are within the above range.

[0085] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the above-mentioned raw material colloidal silica is brought into contact with a silane coupling agent containing a mercapto group to perform a modification treatment.

[0086] As silane coupling agents having a mercapto group, mercaptoalkylalkoxysilanes are preferred, and mercaptoalkyltrialkoxysilanes are more preferred. Specific examples of such silane coupling agents having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0087] The amount of silane coupling agent containing the mercapto group in contact with the material is preferably 100.00 μmol or more and 400.00 μmol or less per gram of the raw material colloidal silica (per gram of silica particles contained in the raw material colloidal silica), calculated on a solid content basis, more preferably 110.00 μmol or more and 390.00 μmol or less, and more preferably 120.00 μmol or more and 380.00 μmol or more.

[0088] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, by ensuring that the amount of silane coupling agent containing mercapto groups in contact with the silica is within the above range, the amount of silane coupling agent remaining in the solvent of the obtained sulfonic acid-modified colloidal silica (sulfur content in the solvent) can be easily controlled, while the surface of the silica particles can be sufficiently anionized. This makes it possible to easily prepare sulfonic acid-modified colloidal silica that exhibits excellent performance when used as an abrasive grain.

[0089] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the dispersion medium for the raw material colloidal silica may be an organic solvent containing water, as described above. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the raw material colloidal silica is brought into contact with a silane coupling agent containing mercapto groups, since the silane coupling agent is poorly soluble in water, it is preferable to use raw material colloidal silica containing a certain amount or more of an organic solvent (hydrophilic solvent) as a dispersion medium for the purpose of dissolving the silane coupling agent.

[0090] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when contacting a silane coupling agent containing a mercapto group with a raw colloidal silica, it is preferable to contact the raw colloidal silica with the silane coupling agent while diluting it with methanol to a mass ratio of 3 to 50 times, and more preferably to contact the raw colloidal silica with the silane coupling agent while diluting it with methanol to a mass ratio of 4 to 45 times, and even more preferably to contact the raw colloidal silica with the silane coupling agent while diluting it with methanol to a mass ratio of 5 to 40 times.

[0091] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the dilution ratio of the silane coupling agent containing a mercapto group with methanol refers to a value calculated by mass ratio, specifically, the value calculated by "amount of methanol used during dilution (g) / amount of silane coupling agent containing a mercapto group (g)".

[0092] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when contacting a silane coupling agent containing mercapto groups with the raw colloidal silica, the silane coupling agent is diluted with methanol to a predetermined dilution ratio while contacting the raw colloidal silica. This allows for suitable mixing of the silane coupling agent, suppressing local reactions during the addition of the coupling agent, and effectively immobilizing a desired amount of the silane coupling agent onto the silica particles constituting the raw colloidal silica. As a result, the amount of residual silane coupling agent in the solvent constituting the final sulfonic acid-modified colloidal silica can be significantly reduced.

[0093] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the raw material colloidal silica and a silane coupling agent containing mercapto groups are brought into contact to perform the modification treatment, there are no particular limitations, but it is preferable to perform the contact treatment while appropriately applying heat treatment at a temperature range from room temperature (about 20°C) to the boiling point of the reaction solvent. The contact time (reaction time) during the above contact treatment is also not particularly limited, but it is preferably 10 minutes to 10 hours, more preferably 30 minutes to 5 hours, and even more preferably 30 minutes to 2 hours. The pH during the above contact treatment is also not limited, but it is preferably pH 7 to 11. By performing the contact treatment while applying heat treatment, hydrolysis and condensation reactions are promoted, and the silane coupling agent containing mercapto groups can be suitably fixed (chemically bonded) to the surface of the silica particles constituting the raw material colloidal silica.

[0094] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw colloidal silica is subjected to a modification treatment by contacting it with a silane coupling agent containing a mercapto group (-SH), and then hydrogen peroxide is brought into contact with it to oxidize the mercapto groups introduced on the surface of the silica particles to form sulfonic acid-modified groups (-SO ３ Convert to H).

[0095] The amount of hydrogen peroxide that comes into contact with the reaction product of the raw material colloidal silica and the silane coupling agent containing a mercapto group (-SH) is 3.50 to 10.00 mol per 1 mol of the silane coupling agent containing a mercapto group used in the preparation of the above reaction product, preferably 3.55 to 8.00 mol, and more preferably 3.60 to 6.00 mol.

[0096] By controlling the amount of hydrogen peroxide that comes into contact with the reaction product of colloidal silica (a raw material) and a silane coupling agent containing a mercapto group (-SH) within the above range, the sulfo group (-SO) is converted from the mercapto group (-SH). ３ This method allows for a favorable conversion to H while minimizing the residual oxidizing agent concentration in the resulting sulfonic acid-modified colloidal silica.

[0097] The residual oxidizing agent concentration in the sulfonic acid-modified colloidal silica obtained by the manufacturing method according to the present invention is not particularly limited, but is preferably 3000 ppm by mass or less, more preferably 2500 ppm by mass or less, and even more preferably 2000 ppm by mass or less.

[0098] By ensuring that the residual oxidizing agent concentration in the sulfonic acid-modified colloidal silica obtained by the manufacturing method according to the present invention is below the above value (upper limit), wafer dishing can be effectively suppressed when the sulfonic acid-modified colloidal silica obtained by the manufacturing method according to the present invention is used as an abrasive for polishing semiconductor wafers.

[0099] As described above, by contacting hydrogen peroxide with the reaction product of colloidal silica as a raw material and a silane coupling agent containing a mercapto group (-SH), the mercapto group (-SH) of the silane coupling agent is converted to a sulfo group (-SO ３ While it can be converted to H), the parts of the silane coupling agent other than the mercapto group and the colloidal silica raw material have a structure that is stable against hydrogen peroxide, so by-products are unlikely to be generated.

[0100] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw material colloidal silica is first subjected to a modification treatment by contacting it with a silane coupling agent containing a mercapto group (-SH), and then the mercapto group (-SH) is replaced with a sulfonate group (-SO ３ By converting to H, sulfo groups (-SO) are formed on the surface of silica particles. ３ A silane coupling agent having H can be stably modified.

[0101] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting the reaction product of raw colloidal silica and a silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide, the resulting mixture is heated at a temperature of 80.0°C or higher, preferably at 85.0°C or higher, more preferably at 90.0°C or higher, and even more preferably at 95.0°C or higher. Furthermore, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, the upper limit of the temperature at which the mixture is heated after contacting the reaction product of raw colloidal silica and a silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide is not particularly limited, and may be 100.0°C or lower. By heating at a temperature of 80.0°C or higher, the amount of unreacted silane coupling agent remaining in the solvent in the resulting sulfonic acid-modified colloidal silica can be effectively suppressed.

[0102] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the heating time for heating the mixture obtained after contacting the reaction product of raw colloidal silica and a silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide is 15 hours or more, preferably 16 hours or more, more preferably 18 hours or more, and even more preferably 19 hours or more. Furthermore, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, the upper limit of the heating time for heating the mixture obtained after contacting the reaction product of raw colloidal silica and a silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide is not particularly limited and may be 50 hours or less, 40 hours or less, or 30 hours or less. Even if the above heating time is 15 hours or more, the amount of unreacted silane coupling agent remaining in the solvent in the obtained sulfonic acid-modified colloidal silica can be effectively suppressed.

[0103] The reaction solution obtained by contacting the above-mentioned hydrogen peroxide and heating the resulting mixture at a temperature of 80.0°C or higher for 15 hours or more contains organic solvents such as methanol 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 as needed. The above water replacement may be performed after contacting the silane coupling agent containing mercapto groups with the colloidal silica raw material, and before further contacting the resulting contact reaction product with hydrogen peroxide.

[0104] The method of replacing the dispersion medium with water is not particularly limited. For example, one method involves contacting the hydrogen peroxide and heating the resulting mixture at a temperature of 80.0°C or higher for 15 hours or more, and then adding a fixed amount of water dropwise while heating the resulting reaction solution.

[0105] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the amount of silane coupling agent remaining in the solvent of the obtained sulfonic acid-modified colloidal silica is suppressed. Therefore, the amount of silane coupling agent remaining in the solvent can be easily controlled to a suitable range without ultrafiltration. For this reason, it is preferable not to perform ultrafiltration in the method for producing sulfonic acid-modified colloidal silica according to the present invention.

[0106] Details of the sulfonic acid-modified colloidal silica obtained by the manufacturing method according to the present invention are as described in the description of the sulfonic acid-modified colloidal silica according to the present invention.

[0107] According to the present invention, it is possible to provide a method for producing sulfonic acid-modified colloidal silica that can form a polished surface with a highly reduced surface roughness.

[0108] 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.

[0109] (Example 1) Colloidal silica (BET specific surface area 90 m²) as the raw material. ２ / g, silanol group density 7.5 groups / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 9.8 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the colloidal silica (silica particles in the raw colloidal particles) was 145.00 μmol / g in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per mol of 3-mercaptopropyltrimethoxysilane in contact with the colloidal silica and 3-mercaptopropyltrimethoxysilane, was added to the treated and modified product, and then heated at 100.0°C for 20 hours. After that, the product was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, the sulfur content per gram of silica particles (mass ppm), sulfur content in the solvent per gram of solvent (mass ppm), silica particle content (mass %), average primary particle diameter of silica particles, average secondary particle diameter of silica particles, content of coarse particles with a particle size of 0.2 μm or larger (particles / mL) when the silica particle concentration is 1% by mass, metal impurity content (mass ppm), and pH were determined for the obtained sulfonic acid-modified colloidal silica. The metal impurity content was measured and calculated as the sum of the content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the sulfonic acid-modified colloidal silica. The results are shown in Table 2.

[0110] (Example 2) Colloidal silica (BET specific surface area 147 m²) as the raw material. ２ / g, silanol group density 15.2 / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 9.7 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact was 180.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact, was added to the treated colloidal silica and 3-mercaptopropyltrimethoxysilane mixture, and the mixture was heated at 100.0°C for 20 hours. After that, it was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0111] (Example 3) Colloidal silica as the raw material (BET specific surface area 170 m²) ２ / g, silanol group density 9.6 groups / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 7.1 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact was 190.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact, was added to the treated colloidal silica and 3-mercaptopropyltrimethoxysilane mixture, and the mixture was heated at 100.0°C for 20 hours. After that, the mixture was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0112] (Example 4) Colloidal silica as a raw material (BET specific surface area 280 m²) ２ / g, silanol group density 8.1 / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 10.7 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact was 250.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact with the above colloidal silica and 3-mercaptopropyltrimethoxysilane, was added to the treated and modified product, and the mixture was heated at 100.0°C for 20 hours. After that, it was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0113] (Example 5) Colloidal silica as the raw material (BET specific surface area 330 m²) ２ / g, silanol group density 10.3 groups / nm ２A denaturing treatment was performed by contacting 20% ​​by mass silica particles with 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol for 1 hour under conditions of pH 8.8 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the colloidal silica (silica particles in the raw colloidal particles) was 340.00 μmol per gram of solid content colloidal silica. Next, to the treated and denatured product of colloidal silica and 3-mercaptopropyltrimethoxysilane, an amount equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact was added, and the product was heated at 100.0°C for 20 hours. After that, the product was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0114] (Example 6) Colloidal silica (BET specific surface area 384 m²) as the raw material. ２ / g, silanol group density 13.5 / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 9.5 and 60.0°C, so that the amount of 3-mercaptopropyltrimethoxysilane in contact with the silica was 370.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact with the colloidal silica and 3-mercaptopropyltrimethoxysilane, was added to the treated and modified product, and the mixture was heated at 100.0°C for 20 hours. After that, it was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0115] (Comparative Example 1) Colloidal silica (BET specific surface area 172 m²) as the raw material. ２ / g, silanol group density 5.5 groups / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 9.7 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact was 250.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact, was added to the treated colloidal silica and 3-mercaptopropyltrimethoxysilane mixture, and the mixture was heated at 100.0°C for 20 hours. After that, the mixture was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0116] (Comparative Example 2) Colloidal silica (BET specific surface area 47 m²) as the raw material. ２ / g, silanol group density 7.0 groups / nm ２A denaturing treatment was performed by contacting 20% ​​by mass silica particles with 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol for 1 hour under conditions of pH 8.5 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact was 250.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact with the denatured colloidal silica and 3-mercaptopropyltrimethoxysilane, was added and heated at 100.0°C for 20 hours. After that, the mixture was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0117] (Comparative Example 3) Colloidal silica as a raw material (BET specific surface area 170 m²) ２ / g, silanol group density 8.1 / nm ２A silica particle concentration of 20% by mass and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact for 1 hour under conditions of pH 10.8 and 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact was 95.00 μmol per gram of colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, 35% by mass hydrogen peroxide solution, equivalent to 4.00 mol of hydrogen peroxide per 1 mol of 3-mercaptopropyltrimethoxysilane in contact with the above colloidal silica and 3-mercaptopropyltrimethoxysilane, was added to the treated and modified product, and the mixture was heated at 100.0°C for 20 hours. After that, it was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0118] (Comparative Example 4) The target sulfonic acid-modified colloidal silica was obtained by further ultrafiltration treatment of 40 g of sulfonic acid-modified colloidal silica obtained in Comparative Example 1 using an ultrafiltration apparatus having the following configuration. <Configuration of the Ultrafiltration System> ・Filtration system: Benchtop filtration unit for pencil-type module manufactured by Asahi Kasei Corporation (PX-02001) ・Ultrafiltration membrane: Ultrafiltration membrane with molecular weight cutoff of 80,000 (pencil-type module manufactured by Asahi Kasei Corporation (AOP-0013)) ・Pump: L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MFLX07514-10) and L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) manufactured by Masterflex.・Tube: Masterflex silicon hydrolysis tube (99400-25) During the ultrafiltration process described above, ultrapure water was added to the sulfonic acid-modified colloidal silica to maintain a constant volume of the sulfonic acid-modified colloidal silica. The amount of liquid that passed through the ultrafiltration membrane was 220 g, and the ultrafiltration time was 150 minutes. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica contained silica particles with immobilized sulfo groups, and it was confirmed that unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Furthermore, in the obtained sulfonic acid-modified colloidal silica, the sulfur content per gram of silica particles (mass ppm), the sulfur content in the solvent per gram of solvent (mass ppm), the silica particle content (mass %), the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the content of coarse particles with a particle size of 0.2 μm or larger (particles / mL) when the silica particle concentration is 1 mass %, the metal impurity content (mass ppm), and the pH were determined in the same manner as in Example 1. The results are shown in Table 2.

[0119] The sulfonic acid-modified colloidal silica obtained in each of the above examples and comparative examples was used as abrasive grains, and the surface roughness of the polished surface was evaluated by the following method. The results are shown in Table 2.

[0120] <Method for Evaluating Polished Surface Roughness> To the sulfonic acid-modified colloidal silica obtained in each example and comparative example, ultrapure water was added to dilute it to a silica particle concentration of 3.0% by mass to prepare a polishing composition. Using the obtained polishing composition, a 3 cm square silicon wafer with a silicon oxide film deposited on its surface was polished under the following conditions. (Polishing conditions) Polishing machine: NF-300CMP, manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TM Pad, manufactured by Nitta DuPont Co., Ltd. Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min (Surface roughness measurement conditions) The surface roughness of the polished wafer was measured using an atomic force microscope under the following conditions. Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: OLYMPUS MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: Five arbitrary observation fields were observed per polished wafer (observation range per field: 3 μm × 3 μm). The root mean square roughness x was measured for each of the five observation fields (five fields) on the wafer polished surface. ｉ (nm) was measured, and the root mean square roughness x in 5 fields was calculated. ｉ The arithmetic mean of (nm) was defined as the polished surface roughness Rms (nm). When the surface roughness of the polished surface is measured using the method described above, the polishing performance is judged to be good if the surface roughness is 1.0 nm or less, and poor if the surface roughness is greater than 1.0 nm.

[0121]

[0122]

[0123] Table 1 shows that in Examples 1 to 6, the method for producing sulfonic acid-modified colloidal silica was (i) a BET specific surface area of ​​70 to 500 m². ２ Silanol group density is 7.0 to 20.0 groups / nm per gram. ２The process involves (ii) contacting a raw colloidal silica containing silica particles with a silane coupling agent containing mercapto groups to perform a modification treatment, and then further contacting it with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles and convert them to sulfo groups, and (iii) when contacting the raw colloidal silica containing mercapto groups with the raw colloidal silica, the silane coupling agent is diluted with methanol to a dilution ratio of 3 to 50 times, and (iv) the amount of hydrogen peroxide added is 3.50 to 10.00 mol per mol of the contact amount of the silane coupling agent containing mercapto groups, and (v) after contacting with hydrogen peroxide, the resulting mixture is heated at a temperature of 80.0°C or higher for 15 hours or more.

[0124] Therefore, as can be seen from Table 2, the sulfonic acid-modified colloidal silica obtained in Examples 1 to 6 has a sulfur content of 3,000 ppm by mass or more and 9,000 ppm by mass per gram of silica particles, a sulfur content of 750 ppm by mass or less per gram of solvent, and a coarse particle content of 0.2 μm or larger in the silica particles of 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Thus, even when used for polishing semiconductor wafers, it can form a polished surface with a highly reduced surface roughness.

[0125] On the other hand, Table 1 shows that in Comparative Examples 1 to 4, as a method for producing sulfonic acid-modified colloidal silica, (i) the raw material colloidal silica used had a BET specific surface area outside the specified range (Comparative Example 2) or a silanol group density outside the specified range (Comparative Examples 1 and 4), or the amount of silane coupling agent containing mercapto groups per gram of raw material colloidal silica, calculated on a solid content basis, was outside the specified range (Comparative Example 3).

[0126] Therefore, as can be seen from Table 2, the sulfonic acid-modified colloidal silica obtained in Comparative Examples 1 to 4 had sulfur content in silica particles per gram of silica particles outside the predetermined range (Comparative Example 3), sulfur content in solvent per gram of solvent exceeding the predetermined value (Comparative Examples 1 and 2), or content of coarse particles with a particle size of 0.2 μm or more in the silica particles exceeding the predetermined value (Comparative Example 4). As a result, when used as abrasive grains to polish semiconductor wafers, a polished surface with significantly reduced surface roughness cannot be obtained (Comparative Examples 1 to 4).

[0127] According to the present invention, it is possible to provide sulfonic acid-modified colloidal silica and a method for producing sulfonic acid-modified colloidal silica that can form a polished surface with a highly reduced surface roughness.

Claims

1. Sulfonic acid-modified colloidal silica, characterized in that the sulfur content of the silica particles is 3,000 ppm by mass or more and 9,000 ppm by mass or less per gram of silica particles, the sulfur content of the solvent is 750 ppm by mass or less per gram of solvent, and the content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass.

2. A method for producing sulfonic acid-modified colloidal silica according to claim 1, wherein (i) the BET specific surface area is 70 to 500 m² ２ Silanol group density is 7.0 to 20.0 groups / nm per gram. ２ A method for producing sulfonic acid-modified colloidal silica, comprising the steps of: (ii) bringing a raw colloidal silica containing silica particles into contact with a silane coupling agent containing mercapto groups to perform a modification treatment, and then further contacting it with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles and convert them into sulfo groups; (iii) when bringing the silane coupling agent containing mercapto groups into contact with the raw colloidal silica, the silane coupling agent is diluted with methanol to a dilution ratio of 3 to 50 times; (iv) the amount of hydrogen peroxide that comes into contact with the raw colloidal silica is 3.50 to 10.00 mol per mol of the silane coupling agent containing mercapto groups that comes into contact with the silica; and (v) after contacting the hydrogen peroxide, heating the resulting mixture at a temperature of 80.0°C or higher for 15 hours or more.

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