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

Abstract

The present invention provides sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at high speed, even when used for polishing semiconductor wafers coated with a silicon nitride film. This is a sulfonic acid-modified colloidal silica in which sulfonic acid-modified silica particles are dispersed in a solvent, wherein the sulfur content of the sulfonic acid-modified silica particles is 700 ppm to 3000 ppm per gram of sulfonic acid-modified silica particles, the sulfur content of the solvent is 400 ppm or less per gram of solvent, the average primary particle diameter of the sulfonic acid-modified silica particles is 30 to 101 nm, and the content of coarse particles with a particle size of 0.2 μm or more contained in the sulfonic acid-modified silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass.

Description

[Technical Field]

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

[0002] In semiconductor manufacturing processes, silicon nitride films (Si3N4 films), which possess high density, high dielectric constant, and excellent insulating properties, are used as protective films and insulating films for semiconductors.

[0003] In the semiconductor manufacturing process described above, the semiconductor wafer is held in place by a component called a carrier, and the wafer is brought into contact with and rotated by flowing a slurry containing chemicals and abrasive particles through it, thereby polishing the semiconductor wafer to a flat surface.

[0004] 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.

[0005] Incidentally, because the silicon nitride film described above has poor chemical reactivity, it is generally difficult to polish semiconductor wafers on which the silicon nitride film is applied at high speed.

[0006] Under these circumstances, abrasive particles for polishing semiconductor wafers have been proposed that consist of sulfonic acid-modified colloidal silica, which is colloidal silica (silica sol) modified with sulfonic acid groups (sulfo groups (-SO3H)) (see Patent Document 1 (Japanese Patent Application Publication No. 2012-040671)). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-040671 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0008] However, the inventors have found that when conventionally proposed sulfonic acid-modified colloidal silica is used as an abrasive for polishing semiconductor wafers having a silicon nitride film, (1) the level of sulfo group modification on the silica particles constituting the sulfonic acid-modified colloidal silica is insufficient, resulting in a low polishing rate on the silicon nitride film when used as an abrasive. It was revealed that...

[0009] Furthermore, the inventors found that when conventionally proposed sulfonic acid-modified colloidal silica is used as an abrasive for polishing semiconductor wafers having a silicon nitride film, (2) unreacted silane coupling agent components used when modifying the sulfo groups remain in the solvent of the sulfonic acid-modified colloidal silica, and these silane coupling agent components react with the silicon nitride film, inhibiting the polishing process. This phenomenon is thought to be particularly likely to occur when using silane coupling agents such as 3-mercaptopropyltrimethoxysilane, which have relatively poor reactivity with silica particles, to modify the sulfo group of silica particles.

[0010] Furthermore, the inventors investigated and found that (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 sulfonic acid-modified 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 larger. It was also found that when the sulfonic acid-modified colloidal silica obtained by ultrafiltration is used as an abrasive, the roughness of the polished surface increases due to the coarse particles.

[0011] In addition, as a result of investigations by the present inventors, it has been found that the conventionally proposed sulfonic acid-modified colloidal silica has a tendency for the polishing rate to be low because (4) the average primary particle diameter of the sulfonic acid-modified silica particles is small.

[0012] Under such circumstances, an object of the present invention is to provide a sulfonic acid-modified colloidal silica and a method for producing the same, which can form a highly flat polished surface at a high speed even when used for polishing a semiconductor wafer provided with a silicon nitride film.

Means for Solving the Problems

[0013] In order to solve the above technical problems, the present inventors conducted intensive studies. As a result, they found that a sulfonic acid-modified colloidal silica in which sulfonic acid-modified silica particles are dispersed in a solvent, wherein the sulfur content of the sulfonic acid-modified silica particles is 700 mass ppm to 3000 mass ppm per 1 g of the sulfonic acid-modified silica particles, the sulfur content in the solvent is 400 mass ppm or less per 1 g of the solvent, the average primary particle diameter of the sulfonic acid-modified silica particles is 30 to 101 nm, and the content of coarse particles having a particle diameter of 0.2 μm or more contained in the sulfonic acid-modified silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1 mass%. The present invention has been completed based on these findings.

[0014] That is, the present invention is (1) A sulfonic acid-modified colloidal silica in which sulfonic acid-modified silica particles are dispersed in a solvent, wherein the sulfur content of the sulfonic acid-modified silica particles is 700 mass ppm to 3000 mass ppm per 1 g of the sulfonic acid-modified silica particles, the sulfur content in the solvent is 400 mass ppm or less per 1 g of the solvent, the average primary particle diameter of the sulfonic acid-modified silica particles is 30 to 101 nm, The amount of coarse particles with a particle size of 0.2 μm or larger contained in the sulfonic acid-modified silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Sulfonic acid-modified colloidal silica characterized by, (2) A method for producing sulfonic acid-modified colloidal silica as described in (1) above, (i) BET specific surface area is 27-91m 2 Silanol group density is 7.0-20.0 groups / nm per gram. 2 The process involves a modification step in which a sulfo group is introduced to the surface of the silica particles by contacting a raw material colloidal silica containing 25.0 to 40.0% by mass of silica particles with a silane coupling agent containing mercapto groups and hydrogen peroxide. (ii) The amount of contact with the silane coupling agent containing the mercapto group is 25.00 μmol or more and less than 100.00 μmol per gram of the raw material colloidal silica, calculated on a solid content basis. (iii) A method for producing sulfonic acid-modified colloidal silica, characterized by contacting the raw material colloidal silica with a silane coupling agent containing a mercapto group and hydrogen peroxide, and then heating the resulting mixture. This provides... [Effects of the Invention]

[0015] 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 highly flat polished surface at high speed even when used for polishing semiconductor wafers provided with a silicon nitride film. [Modes for carrying out the invention]

[0016] First, let me explain the sulfonic acid-modified colloidal silica according to the present invention. The sulfonic acid-modified colloidal silica according to the present invention is Sulfonic acid-modified colloidal silica, wherein sulfonic acid-modified silica particles are dispersed in a solvent, The sulfur content of the sulfonic acid-modified silica particles is 700 ppm by mass or more and less than 3000 ppm by mass per gram of sulfonic acid-modified silica particles. The sulfur content in the solvent is 400 ppm by mass or less per gram of solvent. The average primary particle diameter of the sulfonic acid-modified silica particles is 30 to 101 nm. The amount of coarse particles with a particle size of 0.2 μm or larger contained in the sulfonic acid-modified silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. It is characterized by the following:

[0017] The sulfonic acid-modified colloidal silica according to the present invention includes sulfonic acid-modified silica particles in which a sulfo group (-SO3H) is immobilized on the silica particles constituting the colloidal silica. The sulfonic acid-modified colloidal silica according to the present invention is suitable in which sulfonic acid-modified silica particles are formed in which a silane compound having a sulfo group (-SO3H) is chemically bonded to the silica particles constituting the colloidal silica.

[0018] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content of 700 ppm to 3000 ppm per gram of sulfonic acid-modified silica particles, preferably 705 ppm to 2995 ppm, and more preferably 710 ppm to 2990 ppm.

[0019] In the present invention, the sulfur content of the sulfonic acid-modified silica particles constituting the sulfonic acid-modified colloidal silica serves as an indicator of the amount of sulfo groups (-SO3H) in the sulfonic acid-modified silica particles constituting the colloidal silica. The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content of sulfonic acid-modified silica particles that is above the lower limit of each of the above ranges, and as such, the sulfonic acid modification is sufficiently performed, which allows for a further improvement in polishing speed when used as an abrasive grain. Furthermore, the sulfonic acid-modified colloidal silica according to the present invention can easily exhibit sufficient polishability even when used to polish semiconductor wafers with silicon nitride films, because the sulfur content of the sulfonic acid-modified silica particles is below the upper limit of each of the above ranges.

[0020] In this application, the sulfur content of the sulfonic acid-modified silica particles constituting the sulfonic acid-modified colloidal silica refers to the value calculated by the following method.

[0021] (Procedure 1) Sulfonic acid-modified colloidal silica (solution) is centrifuged using an Eppendorf Hi-Mac Technologies centrifuge tube (model number: S303922A) at 77400G, 5°C, and for 90 minutes. The resulting precipitate is dried at 60°C for 12 hours, then the dried material is pulverized and further dried under reduced pressure at 60°C for 2 hours to obtain sulfonic acid-modified silica solids. (Procedure 2) Add hydrofluoric acid to 1 g of sulfonic acid-modified silica solids obtained in Procedure 1 to dissolve the sulfonic acid-modified silica, and add ultrapure water to the solution to obtain a diluted solution of 100 mL. (Step 3) Using the diluent obtained in Step 2, the sulfur content (mass ppm) per gram of sulfonic acid-modified silica particles is measured using an inductively coupled plasma atomic emission spectrometry (ICP-AES) instrument (ICPS-8100, Shimadzu Corporation) with an absolute calibration curve.

[0022] Furthermore, it can be confirmed by X-ray photoelectron spectroscopy (XPS) that the sulfonic acid-modified colloidal silica according to the present invention contains sulfonic acid-modified silica particles (sulfonic acid-modified silica particles).

[0023] As described above, the sulfonic acid-modified colloidal silica according to the present invention contains sulfonic acid-modified silica particles in which a sulfo group (-SO3H) is immobilized on 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.

[0024] In this application, the presence of sulfonic acid-modified colloidal silica containing sulfonic acid-modified silica particles is confirmed by the following method. The sulfonic acid-modified colloidal silica solution is centrifuged at 77400 G, 5°C, and for 90 minutes. The resulting precipitate is dried at 60°C for 12 hours, then the dried material is pulverized, and further dried under reduced pressure of -0.1 MPa or less at 60°C for 2 hours to prepare a sample for measurement. Using this sample, the presence or absence of sulfo groups on the surface of the silica particles is confirmed by X-ray photoelectron spectroscopy under the following conditions. Measuring instrument: Shimadzu Corporation AXIS-NOVA Irradiation X-ray: Al-Kα (15kV, 10mA) Analytical X-ray spot diameter: 300 × 700 μm

[0025] As will be described later, a method for preparing colloidal silica involves stirring, for example, tetramethoxysilane (Si(OCH3)4) in an organic solvent containing water, which undergoes hydrolysis and dehydration condensation to form a dimer. This dimer then polymerizes (oligomerizes) to form spherical silica primary particles in the solvent, and the resulting dispersion of these silica primary particles in the solvent constitutes colloidal silica. Furthermore, the colloidal silica may also consist of primary silica particles and secondary silica particles formed by association of these primary silica particles dispersed in a solvent. Therefore, the sulfonic acid-modified colloidal silica according to the present invention corresponds to a material containing sulfonic acid-modified silica particles in which a sulfo group (-SO3H) is immobilized on silica particles dispersed in the colloidal silica.

[0026] The average primary particle size of the sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is 30 nm to 101 nm.

[0027] The average primary particle diameter of the sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 30 nm or more, more preferably 35 nm or more, even more preferably 39 nm or more, and even more preferably greater than 39 nm.

[0028] The sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention have a large particle size with an average primary particle diameter equal to or greater than the above value (lower limit). Therefore, when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface can be formed at a higher speed.

[0029] The average primary particle diameter of the sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 101 nm or less, more preferably 98 nm or less, even more preferably 95 nm or less, and particularly preferably 92 nm or less.

[0030] Because the average primary particle diameter of the sulfonic acid-modified 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.

[0031] In this application, the average primary particle size of sulfonic acid-modified silica particles contained in sulfonic acid-modified colloidal silica refers to the value measured by the BET method described below. Specifically, first, 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) of sulfonic acid-modified silica particles is given by the following formula: Average primary particle diameter (nm) of sulfonic acid-modified silica particles = 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 Therefore, the average primary particle size (nm) of sulfonic acid-modified silica particles is given by the following formula: Average primary particle diameter (nm) of sulfonic acid-modified silica particles = 2727 / BET specific surface area S (m²) 2 / g) This can be determined by [method].

[0032] The sulfonic acid-modified colloidal silica according to the present invention may contain secondary particles (sulfonic acid-modified silica secondary particles) formed by the association of primary sulfonic acid-modified silica particles. The sulfonic acid-modified silica secondary particles contained in the sulfonic acid-modified colloidal silica according to the present invention, together with the sulfonic acid-modified silica primary particles contained in the sulfonic acid-modified colloidal silica according to the present invention, constitute the main particles of the sulfonic acid-modified silica, and are distinguishable from the coarse particles (described later) that are formed by the aggregation of the above sulfonic acid-modified silica secondary particles.

[0033] The average secondary particle diameter of the sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but is preferably 30 nm or more and 200 nm or less.

[0034] The average secondary particle diameter of the sulfonic acid-modified 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 150 nm or less, and even more preferably 130 nm or less.

[0035] Because the average secondary particle diameter of the sulfonic acid-modified 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.

[0036] The average secondary particle diameter of the sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 30 nm or more, more preferably 40 nm or more, and even more preferably 50 nm or more.

[0037] Because the average secondary particle diameter of the sulfonic acid-modified silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is equal to or greater than the above value (lower limit), when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface can be formed at a higher speed.

[0038] In this application, the average secondary particle diameter of sulfonic acid-modified 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% by mass aqueous solution of citric acid is added to sulfonic acid-modified colloidal silica to dilute it to a sulfonic acid-modified silica concentration of 0.8% by mass, and the resulting diluted solution is used as the sample for measurement. Using the above-mentioned sample for measurement, the average particle diameter measured by dynamic light scattering 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 sulfonic acid-modified silica particles.

[0039] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the solvent of 400 ppm by mass or less per gram of solvent.

[0040] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the solvent of 400 ppm by mass or less per gram of solvent, preferably 350 ppm by mass or less, and more preferably 300 ppm by mass or less.

[0041] 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 has a sulfur content in the solvent that is below the above value (upper limit), thereby sufficiently suppressing the amount of unreacted silane coupling agent components in the solvent. When polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface can be formed at high speed.

[0042] 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 limit is preferable. However, in the sulfonic acid-modified colloidal silica according to the present invention, the sulfur content in the solvent is, for example, usually 1 ppm by mass or more, may be 5 ppm by mass or more, or may be 10 ppm by mass or more.

[0043] As described above, the inventors have investigated and found that when a semiconductor wafer having a silicon nitride film prepared using sulfonic acid-modified colloidal silica is polished, unreacted silane coupling agent components used to modify the sulfo groups (-SO3H) remain in the colloidal silica solvent, and these silane coupling agent components react with the silicon nitride film prepared on the surface of the semiconductor wafer, thereby inhibiting the polishing process. 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, making it possible to polish semiconductor wafers with silicon nitride films at high speed.

[0044] 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 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 spectrometry (ICP-AES) instrument (ICPS-8100, manufactured by Shimadzu Corporation) with an absolute calibration curve.

[0045] 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).

[0046] In the sulfonic acid-modified colloidal silica according to the present invention, the Si content in the solvent is preferably 400 ppm by mass or less per gram of solvent.

[0047] In the sulfonic acid-modified colloidal silica according to the present invention, the Si content in the solvent is preferably 400 ppm by mass or less per gram of solvent, more preferably 375 ppm by mass or less, and even more preferably 350 ppm by mass or less.

[0048] In the sulfonic acid-modified colloidal silica according to the present invention, the Si content in the solvent serves as an indicator of the unreacted silane coupling agent remaining in the solvent. The sulfonic acid-modified colloidal silica according to the present invention has a Si content in the solvent that is below the above value (upper limit), thereby sufficiently suppressing the amount of unreacted silane coupling agent components in the solvent. When polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface can be formed at high speed.

[0049] In the sulfonic acid-modified colloidal silica according to the present invention, the lower limit of the Si content in the solvent is not particularly limited, and a lower limit is preferable. However, in the sulfonic acid-modified colloidal silica according to the present invention, the Si content in the solvent is, for example, usually 1 ppm by mass or more per gram of solvent, but may be 5 ppm by mass or more, or 10 ppm by mass or more.

[0050] In this application, the Si content in the solvent constituting the sulfonic acid-modified colloidal silica refers to the value calculated by the following method. (Procedure 1) The sulfonic acid-modified colloidal silica solution is centrifuged at 77400G, 5°C, for 90 minutes. (Procedure 2) The Si concentration (silicon atom concentration) in the supernatant obtained in Procedure 1 is measured using an inductively coupled plasma atomic emission spectroscopy (ICP-AES) instrument (ICPS-8100, manufactured by Shimadzu Corporation) with an absolute calibration curve method.

[0051] 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 sulfonic acid-modified silica particles is preferably 10,000,000 particles / mL or less, more preferably 9,000,000 particles / mL or less, and more preferably 8,000,000 particles / mL or less, when the silica particle concentration (in the sulfonic acid-modified colloidal silica) is 1% by mass.

[0052] 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 sulfonic acid-modified 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, a highly flat polished surface can be easily formed.

[0053] 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 larger contained in the sulfonic acid-modified 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 larger contained in the sulfonic acid-modified 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] As described above, the inventors' studies have shown that conventionally known sulfonic acid-modified colloidal silica contains unreacted silane coupling agent components that react with the silicon nitride film during polishing. When these unreacted silane coupling agents are removed by ultrafiltration, the silica primary particles constituting the sulfonic acid-modified colloidal silica aggregate, generating a large amount of coarse particles with a particle size of 0.2 μm or larger. As a result, when the obtained sulfonic acid-modified colloidal silica is used as an abrasive, the roughness of the polished surface increases. As described above, the sulfonic acid-modified colloidal silica according to the present invention has a low residual amount of unreacted silane coupling agent (the sulfur content in the solvent is suppressed), and the content of coarse particles with a particle size of 0.2 μm or larger is suppressed. 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.

[0055] In this application, the content of coarse particles with a particle size of 0.2 μm or larger in the sulfonic acid-modified silica particles constituting the sulfonic acid-modified colloidal silica refers to the value measured by the particle size distribution method using the number count method described below.

[0056] <Method for measuring the content of coarse particles with a particle size of 0.2 μm or larger in sulfonic acid-modified silica particles> The sulfonic acid-modified colloidal silica to be measured is diluted with ultrapure water until the silica particle concentration reaches 1.0% 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: 13.22 mL ·Sample Loop Volume: 0.52 mL ·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

[0057] 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 to 11.0.

[0058] The pH of the sulfonic acid-modified 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 the sulfonic acid-modified colloidal silica according to the present invention equal to or greater than the above value (lower limit), the long-term dispersion stability of the silica particles of the sulfonic acid-modified colloidal silica according to the present invention can be further improved.

[0059] Furthermore, the pH of the sulfonic acid-modified colloidal silica according to the present invention is preferably 11.0 or lower, and more preferably 10.0 or lower. By keeping the pH of the sulfonic acid-modified colloidal silica according to the present invention below the above value (upper limit), the long-term dispersion stability of the colloidal silica can be further improved.

[0060] 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.).

[0061] The content of sulfonic acid-modified silica particles in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but it is preferably 2% to 50% by mass when the content of sulfonic acid-modified colloidal silica is taken as 100% by mass.

[0062] The content of sulfonic acid-modified silica particles in the sulfonic acid-modified 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 content of sulfonic acid-modified colloidal silica is 100% by mass.

[0063] By ensuring that the content of sulfonic acid-modified silica particles 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 can be further improved when the sulfonic acid-modified colloidal silica according to the present invention is used as an abrasive grain.

[0064] The content of sulfonic acid-modified silica particles 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 keeping the content of sulfonic acid-modified silica particles in the sulfonic acid-modified colloidal silica according to the present invention below the above value (upper limit), the dispersion stability of the silica particles can be further improved.

[0065] In this application, the content of sulfonic acid-modified silica particles in the sulfonic acid-modified 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 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 resulting amount of solids is denoted as Wg. Content (mass%) of sulfonic acid-modified silica particles in sulfonic acid-modified colloidal silica = (W / 10.0) × 100 The content of sulfonic acid-modified silica particles mentioned above corresponds to the total content of primary sulfonic acid-modified silica particles, secondary sulfonic acid-modified silica particles, and coarse particles in the sulfonic acid-modified colloidal silica.

[0066] The sulfonic acid-modified colloidal silica according to the present invention may contain metal impurities.

[0067] 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.

[0068] 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 grain for polishing electronic materials such as semiconductor wafers.

[0069] In this application, the metal impurity content refers to the value measured using an atomic absorption spectrometer.

[0070] In the sulfonic acid-modified colloidal silica according to the present invention, the solvent for dispersing the sulfonic acid-modified silica particles is water or an organic solvent containing water. The above organic solvents include one or more selected from hydrophilic organic solvents such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, alcohols such as ethylene glycol, propylene glycol, and 1,4-butanediol, and ketones such as acetone and methyl ethyl ketone. Among these organic solvents, it is preferable to use one or more alcohols selected from methanol, ethanol, isopropanol, and the like.

[0071] The sulfonic acid-modified colloidal silica according to the present invention can be preferably prepared by the production method according to the present application described below.

[0072] According to the present invention, even when used for polishing a semiconductor wafer provided with a silicon nitride film, it is possible to provide a sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at a high speed.

[0073] Next, the production method of the sulfonic acid-modified colloidal silica according to the present invention will be described. The production method of the sulfonic acid-modified colloidal silica according to the present invention (i) has a modification step of introducing a sulfo group onto the surface of the silica particles by contacting a raw material colloidal silica containing 25.0 to 40.0% by mass of silica particles having a BET specific surface area of 27 to 91 m 2 / g and a silanol group density of 7.0 to 20.0 per nm 2 with a silane coupling agent containing a mercapto group and hydrogen peroxide, (ii) the contact amount of the silane coupling agent containing a mercapto group is 25.00 μmol or more and less than 100.00 μmol per 1 g of the raw material colloidal silica in terms of solid content, (iii) after contacting the raw material colloidal silica, the silane coupling agent containing a mercapto group, and hydrogen peroxide, the resulting mixture is heated and is characterized by the above.

[0074] (Raw material colloidal silica) In the production method of the sulfonic acid-modified colloidal silica according to the present invention, a raw material colloidal silica containing 25.0 to 40.0% by mass of silica particles having a BET specific surface area of 27 to 91 m 2 / g and a silanol group density of 7.0 to 20.0 per nm 2 is used.

[0075] 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, if the raw material colloidal silica is colloidal silica produced by the sol-gel method, it can be suitably used because it contains a low amount of metal impurities that are diffusible into semiconductors and corrosive ions such as chloride ions.

[0076] 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 to produce the 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.

[0077] The silicon compound mentioned above is the one shown in the following general formula (1) Si(OR)4(1) (In the above general formula (1), the R group is an alkyl group having 1 to 8 carbon atoms.) Examples of tetraalkoxysilanes or their derivatives can be given.

[0078] 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.

[0079] In silicon compounds or derivatives 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.

[0080] Preferred silicon compounds represented by general formula (1) are 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 silicon compounds represented by general formula (1) include low-condensation products obtained by partially hydrolyzing the silicon compound (tetraalkoxysilane) represented by general formula (1). As the silicon compound or derivative represented by general formula (1), tetramethoxysilane is preferred because it is easy to control the hydrolysis rate, easy to obtain fine silica particles, and leaves little unreacted residue.

[0081] Silicon compounds represented by general formula (1) or their derivatives undergo hydrolysis and condensation in the reaction solvent to form colloidal silica.

[0082] Examples of reaction solvents used when silicon compounds represented by general formula (1) or their derivatives undergo hydrolysis and condensation include water or organic solvents containing water. The above organic solvents include one or more selected from hydrophilic organic solvents such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, alcohols such as ethylene glycol, propylene glycol, and 1,4-butanediol, and 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. 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 starting material (for example, methanol for tetramethoxysilane).

[0083] The amount of 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 silicon compound or derivative represented by general formula (1). If the amount of organic solvent used is less than 5 moles per mole of the silicon compound or its derivative represented by general formula (1), compatibility with the silicon compound represented by general formula (1) may be poor. If the amount used exceeds 50 moles per mole of the silicon compound or its derivative represented by general formula (1), the manufacturing efficiency may decrease.

[0084] The amount of water added to the silicon compound or its derivative represented by general formula (1) is not particularly limited and should be any 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). Furthermore, when an organic solvent containing water is added to a silicon compound or its derivative represented by general formula (1), the amount of water mixed in the organic solvent greatly affects the particle size of the colloidal silica formed. 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.

[0085] 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 the above adjustments, 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.

[0086] 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.

[0087] 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 an organic solvent and stirred at a temperature of typically 0°C to 100°C, preferably 0°C to 50°C.

[0088] 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 silica primary particles in the solvent, thereby obtaining colloidal silica in which silica primary particles are dispersed in the solvent. Colloidal silica with uniform silica particle size can be obtained by hydrolyzing and condensing a silicon compound while stirring it in a water-containing solvent.

[0089] 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.

[0090] Method for producing sulfonic acid-modified colloidal silica according to the present invention In this case, the BET specific surface area of ​​the silica particles constituting the raw material colloidal silica is 27-91 m². 2 It is / g, and 28~80m 2 It is preferable that the amount be / g, which is 29-70m 2 It is more preferable that it be / g, which is 30m 2 / g or more 70m 2 It is even more preferable that the amount be less than / g.

[0091] Generally, when the BET specific surface area of ​​the silica particles constituting the raw material colloidal silica exceeds the upper limit of the above range, the number of silanol groups, which are reaction sites, becomes larger, making it easy to reduce the amount of unreacted silane coupling agent relative to the raw material colloidal silica.

[0092] On the other hand, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, by deliberately limiting the BET specific surface area of ​​the silica particles constituting the raw colloidal silica to the above range, large-particle-sized sulfonic acid-modified silica particles with a large average primary particle diameter can be easily formed, and when the sulfonic acid-modified colloidal silica obtained for this purpose is used as an abrasive grain, the polishing speed can be easily improved.

[0093] Furthermore, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, as will be described later, by controlling the silica particle concentration in the raw colloidal silica to a higher concentration range than usual, the total surface area of ​​the silica particles constituting the raw colloidal silica can be increased, thereby increasing the total number of silanol groups, which are reaction sites. To this end, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, while limiting the BET specific surface area of ​​the silica particles constituting the raw colloidal silica to the above-mentioned predetermined range, the amount of contact between the silane coupling agent containing mercapto groups and the silica particles can be increased, thereby easily reducing the amount of unreacted silane coupling agent containing mercapto groups.

[0094] 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 INSTRUMENTS).

[0095] 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 19.5 particles / nm. 2 Preferably, the density is 7.2 to 19.0 particles / nm. 2 It is preferable that it be so.

[0096] In this application, the silanol group density (particles / nm) of the silica particles constituting the raw material colloidal silica 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)

[0097] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the silanol group density constituting the raw material colloidal silica is within the above range, which allows for easy control of the reaction site with the silane coupling agent containing mercapto groups (described later) formed on the silica particle surface to a suitable range.

[0098] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw material colloidal silica has a silica particle concentration of 25.0 to 40.0% by mass, preferably 25.5 to 39.5% by mass, and more preferably 26.0 to 39.0% by mass.

[0099] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, by controlling the silica particle concentration in the raw colloidal silica to within the above-mentioned higher-than-usual concentration range, the total surface area of ​​the silica particles constituting the raw colloidal silica can be increased, and the total amount of silanol groups, which are reaction sites, can be easily increased. To this end, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, while limiting the BET specific surface area of ​​the silica particles constituting the raw colloidal silica to the above-mentioned predetermined range, the amount of contact between the silane coupling agent containing mercapto groups and the silica particles can be increased, thereby easily reducing the amount of unreacted silane coupling agent containing mercapto groups.

[0100] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the silica particle concentration in the raw material colloidal silica refers to the value measured by the following method.

[0101] (Method for measuring the silica particle concentration in colloidal silica raw material) This value is calculated using the following formula, after drying 10.0 g of colloidal silica raw material on a hot plate at 150°C, and then removing moisture by heating at 800°C for 1 hour, with the resulting solid content being defined as wg. Silica particle content (mass%) in raw material colloidal silica = (w / 10.0) × 100

[0102] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the above-mentioned raw material colloidal silica is subjected to a modification treatment by contacting it with a silane coupling agent containing a mercapto group and hydrogen peroxide.

[0103] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the modification treatment may be carried out in one step by simultaneously contacting the above-mentioned raw material colloidal silica with a silane coupling agent containing a mercapto group and hydrogen peroxide, or the modification treatment may be carried out in two steps by first contacting the above-mentioned raw material colloidal silica with a silane coupling agent containing a mercapto group and then further contacting it with hydrogen peroxide.

[0104] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, mercapto groups can be introduced to the surface of silica particles by contacting and reacting raw material colloidal silica with a silane coupling agent containing mercapto groups, and further contact with hydrogen peroxide can oxidize the mercapto groups introduced to the surface of the silica particles and convert them to sulfo groups.

[0105] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, mercaptoalkylalkoxysilane is preferred as the silane coupling agent having a mercapto group, and mercaptoalkyltrialkoxysilane is more preferred. Examples of silane coupling agents having such mercapto groups include, for example, 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0106] The amount of silane coupling agent containing the mercapto group in contact with the raw material colloidal silica is preferably 25.00 μmol or more and less than 100.00 μmol per gram of the raw material colloidal silica (per gram of silica particles contained in the raw material colloidal silica), more preferably 26.0 μmol or more and 99.0 μmol or less, and more preferably 27.0 μmol or more and 98.0 μmol, based on solid content.

[0107] 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 (sulfur content) remaining in the solvent of the obtained sulfonic acid-modified colloidal silica 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.

[0108] 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 contain water as the main component and also contain an organic solvent, as described above. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when contacting the raw material colloidal silica with a silane coupling agent containing mercapto groups, it is preferable to use a 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, since the silane coupling agent is poorly soluble in water.

[0109] 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, 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.

[0110] 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)".

[0111] 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 being contacted with the raw colloidal silica. This allows for suitable mixing of the silane coupling agent, suppression of local reactions during the addition of the coupling agent, and effective immobilization of a desired amount of silane coupling agent onto the silica particles constituting the raw colloidal silica. Furthermore, 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.

[0112] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when a treatment (modification treatment) is performed to introduce mercapto groups to the surface of silica particles constituting the raw colloidal silica by contacting the raw colloidal silica with a silane coupling agent containing mercapto groups, there are no particular limitations, but it is preferable to perform the contact treatment while appropriately applying heat treatment in 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 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 not limited, but a pH of 7 to 11 is preferred. By applying heat treatment and contact treatment simultaneously, hydrolysis and condensation reactions are promoted, allowing a silane coupling agent containing mercapto groups to be suitably immobilized (chemically bonded) to the surface of the silica particles constituting colloidal silica.

[0113] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, by contacting the raw material colloidal silica with a silane coupling agent containing mercapto groups (-SH) and further with hydrogen peroxide, the mercapto groups introduced on the surface of the silica particles can be oxidized and converted to sulfo groups (-SO3H).

[0114] The amount of hydrogen peroxide in contact with the reaction product of the raw material colloidal silica and the silane coupling agent containing a mercapto group (-SH) is preferably 3.50 to 10.00 mol, more preferably 3.75 to 9.75 mol, and even more preferably 4.00 to 9.50 mol, per 1 mol of the silane coupling agent containing a mercapto group used in the preparation of the above reaction product.

[0115] By controlling 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 mercapto groups (-SH) within the above range, the conversion from mercapto groups (-SH) to sulfo groups (-SO3H) can be suitably promoted while minimizing the residual oxidizing agent concentration in the resulting sulfonic acid-modified colloidal silica.

[0116] 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 1000 ppm by mass or less, more preferably 700 ppm by mass or less, and even more preferably 500 ppm by mass or less.

[0117] 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.

[0118] As described above, by contacting hydrogen peroxide with the reaction product of colloidal silica as a raw material and a silane coupling agent containing mercapto groups (-SH), the mercapto groups (-SH) of the silane coupling agent can be converted to sulfo groups (-SO3H). On the other hand, the parts of the silane coupling agent other than the mercapto groups and the colloidal silica have a structure that is stable with respect to hydrogen peroxide, so by-products are unlikely to be produced.

[0119] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, a silane coupling agent substituted with sulfonate groups (-SO3H) can be stably prepared by contacting the raw material colloidal silica with a silane coupling agent containing mercapto groups (-SH) and subjecting it to a modification treatment, thereby converting the mercapto groups (-SH) to sulfonate groups (-SO3H).

[0120] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw material colloidal silica is brought into contact with a silane coupling agent containing a mercapto group (-SH) and hydrogen peroxide, and the resulting mixture is then heated.

[0121] The above heat treatment is preferably carried out at a temperature of 80.0°C or higher, more preferably at a temperature of 85.0°C or higher, even more preferably at a temperature of 90.0°C or higher, and even more preferably at a temperature of 94.0°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 during the heat treatment is not particularly limited and may be 100.0°C or lower. By maintaining a temperature of 80.0°C or higher during the above-mentioned heat treatment, the amount of unreacted silane coupling agent remaining in the solvent in the resulting sulfonic acid-modified colloidal silica can be effectively suppressed.

[0122] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the time during the heat treatment (heating time) is preferably 15 hours or more, more preferably 16 hours or more, even 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 (heating time) is not particularly limited and may be 50 hours or less, 40 hours or less, or 30 hours or less. By heating for 15 hours or more, the amount of unreacted silane coupling agent remaining in the solvent in the resulting sulfonic acid-modified colloidal silica can be effectively suppressed.

[0123] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the process of contacting the raw material colloidal silica with a silane coupling agent containing mercapto groups and hydrogen peroxide, followed by heating the resulting mixture, may be carried out while replacing the dispersion medium of the mixture with water. Since the above mixture usually contains an organic solvent such as methanol in addition to water, its long-term storage stability can be easily improved by replacing the dispersion medium with water.

[0124] The method for replacing the above dispersion medium with water is not particularly limited; for example, one method is to add a fixed amount of water dropwise while heating the above mixture.

[0125] 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, so the amount of silane coupling agent remaining in the solvent can be easily controlled to a suitable range without ultrafiltration. Therefore, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, it is preferable not to perform ultrafiltration treatment.

[0126] 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.

[0127] According to the present invention, it is possible to provide a novel method for effectively producing sulfonic acid-modified colloidal silica that can form a highly flat polished surface at high speed, even when used for polishing semiconductor wafers provided with a silicon nitride film. [Examples]

[0128] 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.

[0129] (Example 1) Raw material colloidal silica (BET specific surface area is 68 m²) 2 / g, silanol group density of 8.5 groups / nm 2 1000 parts by mass of silica particles (containing 29.0% by mass) and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact and mixed so that the contact amount of 3-mercaptopropyltrimethoxysilane was 30.00 μmol / g per 1 g of the raw material colloidal silica (silica particles in the raw material colloidal particles) in terms of solid content. Then, a 35% by mass hydrogen peroxide solution equivalent to 4.0 mol of hydrogen peroxide per 1 mol of the contact amount of 3-mercaptopropyltrimethoxysilane was added and mixed to obtain a mixture. After that, the obtained mixture was heated and water was added dropwise in a fixed amount over 35 hours to perform water replacement. The temperature of the mixed solution at the start of the water displacement was 98.0°C, and the temperature of the mixed solution at the end of the water displacement was 100.0°C. After the water displacement was completed, the mixed solution 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. For the obtained sulfonic acid-modified colloidal silica, the following parameters were determined: sulfur content per gram of sulfonic acid-modified silica particles (mass ppm), sulfur content in the solvent per gram of solvent (mass ppm), Si content in the solvent per gram of solvent (mass ppm), sulfonic acid-modified silica particle content (mass %), average primary particle diameter of sulfonic acid-modified silica particles, average secondary particle diameter of sulfonic acid-modified 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 mass%, metal impurity content (mass ppm), and pH. The above 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 sulfonic acid-modified colloidal silica. The results are shown in Table 2.

[0130] (Example 2) The target sulfonic acid-modified colloidal silica was obtained by contacting and mixing raw colloidal silica with 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol, such that the contact amount of 3-mercaptopropyltrimethoxysilane was 95.00 μmol / g per gram of the raw colloidal silica (silica particles in the raw colloidal particles) in terms of solid content, and then adding hydrogen peroxide and setting the temperature of the mixture at the start of water displacement to 94.0°C, in the same manner as in Example 1. 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0131] (Example 3) As a raw material, colloidal silica has a BET specific surface area of ​​30 m². 2 / g, silanol group density of 7.2 groups / nm 2 Except for using silica particles containing 29.0% by mass, the desired sulfonic acid-modified colloidal silica was obtained by processing in the same manner as in Example 1. 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0132] (Example 4) As a raw material, colloidal silica has a BET specific surface area of ​​68 m². 2 / g, silanol group density of 8.5 groups / nm 2 Using a material containing 26.0% by mass of silica particles, the material was contacted and mixed with 3-mercaptopropyltrimethoxysilane such that the contact amount with the above-mentioned raw material colloidal silica (silica particles in the raw material colloidal particles) was 95.00 μmol / g in terms of solid content. Further hydrogen peroxide was added, and the liquid temperature of the mixture at the start of water displacement was set to 94.0°C. The process was carried out in the same manner as in Example 1 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0133] (Example 5) The desired sulfonic acid-modified colloidal silica was obtained by processing in the same manner as in Example 1, except that undiluted 3-mercaptopropyltrimethoxysilane was used instead of 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol. 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0134] (Comparative Example 1) Raw material colloidal silica (BET specific surface area of ​​135 m²) 2 / g, silanol group density of 8.5 groups / nm 2 1000 parts by mass of silica particles (containing 20.0% by mass) and 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol were brought into contact and mixed so that the contact amount of 3-mercaptopropyltrimethoxysilane was 28.00 μmol / g per 1 g of the raw material colloidal silica (silica particles in the raw material colloidal particles) in terms of solid content. Then, 35% by mass hydrogen peroxide solution in an amount equivalent to 4.0 mol of hydrogen peroxide per 1 mol of the contact amount of 3-mercaptopropyltrimethoxysilane was added and mixed to obtain a mixture. After that, the obtained mixture was heated and water was added dropwise in a fixed amount over 20 hours to perform water replacement. The temperature of the mixed solution at the start of the water displacement was 100.0°C, and the temperature of the mixed solution at the end of the water displacement was also 100.0°C. After the water displacement was completed, the mixed solution 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0135] (Comparative Example 2) As a raw material, colloidal silica has a BET specific surface area of ​​200 m². 2 / g, silanol group density of 9.0 groups / nm 2 A material containing 20.0% by mass of silica particles was used, and the material was contacted and mixed with 3-mercaptopropyltrimethoxysilane so that the amount of 3-mercaptopropyltrimethoxysilane in contact with the material was 90.00 μmol / g per gram of the above-mentioned raw material colloidal silica (silica particles in the raw material colloidal particles) on a solid content basis. The same procedure as in Comparative Example 1 was followed 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0136] (Comparative Example 3) As a raw material, colloidal silica has a BET specific surface area of ​​225 m². 2 / g, silanol group density of 5.3 groups / nm 2 A material containing 20.0% by mass of silica particles was used, and undiluted 3-mercaptopropyltrimethoxysilane was used instead of 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol. The amount of 3-mercaptopropyltrimethoxysilane in contact with and mixed was set to 23.00 μmol / g per 1 g of the above raw material colloidal silica (silica particles in the raw material colloidal particles) on a solid content basis. The process was carried out in the same manner as in Comparative Example 1 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0137] (Comparative Example 4) As a raw material, colloidal silica has a BET specific surface area of ​​30 m². 2 / g, silanol group density of 7.6 groups / nm 2 A material containing 20.0% by mass of silica particles was used, and undiluted 3-mercaptopropyltrimethoxysilane was used instead of 3-mercaptopropyltrimethoxysilane diluted 10 times by mass with methanol. The amount of 3-mercaptopropyltrimethoxysilane in contact with and mixed was set to 90.00 μmol / g per 1 g of the above raw material colloidal silica (silica particles in the raw material colloidal particles) on a solid content basis. The process was carried out in the same manner as in Comparative Example 1 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0138] (Comparative Example 5) The sulfonic acid-modified colloidal silica obtained in Comparative Example 4 was further subjected to ultrafiltration using an ultrafiltration apparatus having the following configuration to obtain the desired sulfonic acid-modified colloidal silica. <Configuration of the ultrafiltration system> • Filtration treatment device: Tabletop filtration unit for pencil-type module manufactured by Asahi Kasei Corporation (PX-02001) • Ultrafiltration membrane: Ultrafiltration membrane with a molecular weight cutoff of 80,000 (pencil-type module (AOP-0013) manufactured by Asahi Kasei Corporation) • Pumps: Masterflex L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MFLX07514-10) and Masterflex L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) • Tubing: Masterflex silicone hydrochloride tubing (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. 40 g of liquid passed through the ultrafiltration membrane, and the ultrafiltration process took 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. Various physical properties were measured in the obtained sulfonic acid-modified colloidal silica in the same manner as in Example 1. The results are shown in Table 2.

[0139] The sulfonic acid-modified colloidal silica obtained in each of the above examples and comparative examples was used as abrasive grains, and the polishing speed and polished surface roughness were evaluated by the following method. The results are shown in Table 2.

[0140] <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 40 nm / min or more is considered good, and a polishing speed of less than 40 nm / min is considered poor.

[0141] <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, and an abrasive composition was prepared. 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: Manufactured by Nitta DuPont, IC1000TMPad Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min (Measurement conditions for surface roughness) The surface roughness of the polished wafer was measured using an atomic force microscope under the following conditions after polishing. 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 surface roughness x was measured for each field. i Determine the (nm) and calculate the surface roughness x in the 5 fields of view using the following formula. i The root mean square of (nm) was defined as the polished surface roughness Rms(nm). JPEG0007900633000001.jpg37170 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 10.0 nm or less, and poor if the surface roughness is greater than 10.0 nm.

[0142] [Table 1]

[0143] [Table 2]

[0144] Table 1 shows that Examples 1 to 5 are methods for producing sulfonic acid-modified colloidal silica, with (i) a BET specific surface area of ​​27 to 91 m². 2 Silanol group density is 7.0-20.0 groups / nm per gram. 2 It can be seen that the process involves contacting a raw colloidal silica containing 25.0 to 40.0% by mass of silica particles with a silane coupling agent containing mercapto groups and hydrogen peroxide to introduce mercapto groups to the surface of the silica particles while oxidizing the mercapto groups to introduce sulfo groups, (ii) the amount of silane coupling agent containing mercapto groups in contact is 25.00 μmol or more and less than 100.00 μmol per gram of raw colloidal silica in terms of solid content, and (iii) the mixture obtained after contacting the raw colloidal silica, the silane coupling agent containing mercapto groups and hydrogen peroxide is heated.

[0145] Therefore, as can be seen from Table 2, the sulfonic acid-modified colloidal silica obtained in Examples 1 to 5 has a sulfur content of 700 ppm to 3000 ppm per gram of sulfonic acid-modified silica particles, a sulfur content of 400 ppm or less per gram of solvent, an average primary particle diameter of 30 to 101 nm, and a coarse particle content of 0.2 μm or larger in the sulfonic acid-modified silica particles of 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Thus, even when used to polish semiconductor wafers with silicon nitride films, it is possible to form highly flat polished surfaces at high speed.

[0146] On the other hand, as shown in Table 1, in Comparative Examples 1 to 5, the method for producing sulfonic acid-modified colloidal silica was: It can be seen that (i) colloidal silica raw materials with a BET specific surface area outside the specified range were used (Comparative Examples 1 to 3), (ii) colloidal silica raw materials with a silanol group density outside the specified range were used (Comparative Example 3), (iii) colloidal silica raw materials with a silica particle concentration outside the specified range were used (Comparative Examples 1 to 5), and (iv) the amount of silane coupling agent containing mercapto groups per gram of colloidal silica raw materials, calculated on a solid content basis, was outside the specified range (Comparative Example 3).

[0147] Therefore, as can be seen from Table 2, the sulfonic acid-modified colloidal silica obtained in Comparative Examples 1 to 5 had sulfonic acid-modified silica particles with a sulfur content outside the predetermined range per gram of sulfonic acid-modified silica particles (Comparative Example 3), a sulfur content in the solvent exceeding the predetermined value per gram of solvent (Comparative Example 4), an average primary particle diameter outside the predetermined range (Comparative Examples 1 to 3), or an amount of coarse particles with a particle size of 0.2 μm or larger exceeding the predetermined value (Comparative Example 5). Consequently, when a semiconductor wafer with a silicon nitride film provided as an abrasive grain was polished using these materials, the polishing speed was low (Comparative Examples 1 to 5), or a highly flat polished surface could not be obtained (Comparative Example 5). [Industrial applicability]

[0148] 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 highly flat polished surface at high speed even when used for polishing semiconductor wafers provided with a silicon nitride film.

Claims

1. Sulfonic acid-modified colloidal silica, wherein sulfonic acid-modified silica particles are dispersed in a solvent, The sulfur content of the sulfonic acid-modified silica particles is 700 ppm to 3000 ppm per gram of sulfonic acid-modified silica particles. The sulfur content in the solvent is 400 ppm by mass or less per gram of solvent. The Si content in the solvent is 400 ppm by mass or less per gram of solvent. The average primary particle diameter of the sulfonic acid-modified silica particles is greater than 39 nm and less than or equal to 101 nm. The amount of coarse particles with a particle size of 0.2 μm or larger contained in the sulfonic acid-modified silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. A sulfonic acid-modified colloidal silica characterized by the following features.

2. A method for producing sulfonic acid-modified colloidal silica as described in claim 1, (i) BET specific surface area is 27 m² ２ / g or more 70m ２ Silanol group density of 7.0 to 20.0 groups / nm at less than 1g ２ The process involves a modification step in which a sulfo group is introduced to the surface of a silica particle by contacting a raw material colloidal silica containing 26.0 to 29.0% by mass of silica particles with a silane coupling agent containing mercapto groups and hydrogen peroxide. (ii) The amount of contact with the silane coupling agent containing the mercapto group is 25.00 μmol or more and less than 100.00 μmol per gram of the raw material colloidal silica, calculated on a solid content basis. (iii) After contacting the colloidal silica raw material with a silane coupling agent containing mercapto groups and hydrogen peroxide, the resulting mixture is heated. A method for producing sulfonic acid-modified colloidal silica, characterized by the following features.

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