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. [Solution] A sulfonic acid-modified colloidal silica characterized in that the sulfur content of the silica particles is 700 ppm by mass or more and less than 3000 ppm by mass per gram of silica particles, the sulfur content of the solvent is 250 ppm by mass or less per gram of solvent, and the average secondary particle diameter of the silica particles is 5 nm or more and 43 nm or less.

Description

[Technical Field]

[0001] This invention relates to sulfonic acid-modified colloidal silica. [Background technology]

[0002] In semiconductor manufacturing processes, silicon nitride films (Si3N4 films), which possess high density 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 investigated and found that when conventionally proposed sulfonic acid-modified colloidal silica was used as an abrasive for polishing semiconductor wafers having a silicon nitride film, (1) the level of modification of sulfo groups to the silica particles constituting the sulfonic acid-modified colloidal silica was insufficient, resulting in a low polishing rate against the silicon nitride film when used as an abrasive.

[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 is thought to be because silane coupling agents such as 3-mercaptopropyltrimethoxysilane, used, for example, when modifying sulfo groups in silica particles, 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.

[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 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] Under such circumstances, an object of the present invention is to provide a sulfonic acid-modified colloidal silica capable of forming 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

[0012] In order to solve the above technical problems, the inventors of the present invention conducted intensive studies and found that the above problems can be solved by a sulfonic acid-modified colloidal silica in which the sulfur content of silica particles is 700 mass ppm or more and less than 3000 mass ppm per 1 g of silica particles, the sulfur content in the solvent is 250 mass ppm or less per 1 g of the solvent, and the average secondary particle diameter of the silica particles is 5 nm or more and 43 nm or less. Based on this finding, the present invention has been completed.

[0013] That is, the present invention is a sulfonic acid-modified colloidal silica, wherein the sulfur content of silica particles is 700 mass ppm or more and less than 3000 mass ppm per 1 g of silica particles, the sulfur content in the solvent is 250 mass ppm or less per 1 g of the solvent, and the average secondary particle diameter of the silica particles is 5 nm or more and 43 nm or less characterized sulfonic acid-modified colloidal silica is provided.

Effects of the Invention

[0014] According to the present invention, it is possible to provide a sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at a high speed even when used for polishing a semiconductor wafer provided with a silicon nitride film.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, 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 The sulfur content of the silica particles is 700 ppm by mass or more and less than 3000 ppm by mass per gram of silica particles. The sulfur content in the solvent is 250 ppm by mass or less per gram of solvent. The average secondary particle diameter of the silica particles is between 5 nm and 43 nm. It is characterized by the following:

[0016] The sulfonic acid-modified colloidal silica according to the present invention is obtained by immobilizing sulfo groups (-SO3H) on the silica particles that constitute the colloidal silica.

[0017] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content of 700 ppm by mass or more and less than 3000 ppm by mass per gram of silica particles, preferably 705 ppm by mass or more and 2995 ppm by mass or less, more preferably 710 ppm by mass or more and 2990 ppm by mass or less, even more preferably 715 ppm by mass or more and 2985 ppm by mass or less, and particularly preferably 720 ppm by mass or more and 2980 ppm by mass or less.

[0018] In the present invention, the sulfur content of the silica particles constituting the sulfonic acid-modified colloidal silica serves as an indicator of the amount of sulfo groups (-SO3H) in the silica particles constituting the colloidal silica. The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the silica particles that is above the lower limit of each of the above ranges, thereby enabling a further improvement in polishing speed when used as an abrasive grain. Furthermore, because the sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the silica particles that is below the upper limit of each of the above ranges, it can easily exhibit sufficient polishability even when used to polish semiconductor wafers on which a silicon nitride film is provided.

[0019] In this application, the sulfur content of the silica particles constituting the sulfonic acid-modified colloidal silica refers to the value calculated by the following method.

[0020] (Procedure 1) Sulfonic acid-modified colloidal silica (solution) is centrifuged using an Eppendorf Hi-Mac Technologies centrifuge tube (model number: S303922A) at 260,000 G, 5°C, and for 150 minutes. The resulting 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) Add hydrofluoric acid to 1 g of silica solids obtained in Procedure 1 to dissolve the silica, and add ultrapure water to the solution to obtain a diluted solution of 100 mL. (Step 3) Using the diluted solution obtained in Step 2, the sulfur content (mass ppm) per gram of silica particles is measured using an inductively coupled plasma atomic emission spectrometry (ICP-AES) instrument (ICPS-8100, manufactured by Shimadzu Corporation) with an absolute calibration curve method.

[0021] 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.

[0022] As described above, the sulfonic acid-modified colloidal silica according to the present invention has sulfo groups (-SO3H) immobilized on the silica particles constituting colloidal silica, and therefore the sulfonic acid-modified colloidal silica according to the present invention has a basic structure derived from colloidal silica.

[0023] In this application, the presence of sulfonic acid-modified colloidal silica containing sulfonic acid-modified silica particles is confirmed by the following method. The colloidal silica solution was centrifuged at 77400G, 5°C, and for 90 minutes. The resulting precipitate was dried at 60°C for 12 hours, then the silica was pulverized and dried under reduced pressure at 60°C and a gauge pressure of -0.1 MPa or less 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 was 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

[0024] 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 undergoes polymerization (oligomerization), forming spherical silica primary particles in the solvent. Colloidal silica is obtained by dispersing these silica primary particles in the solvent. Furthermore, the colloidal silica may also consist of primary silica particles, along with 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 silica particles dispersed in the above colloidal silica with a sulfo group (-SO3H) immobilized on them.

[0025] 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.

[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 39 nm or less, more preferably 35 nm or less, even more preferably 30 nm or less, and particularly preferably 25 nm or less.

[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 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.

[0028] 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 10 nm or more, and even more preferably 15 nm or more.

[0029] Because the average primary particle diameter of the 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.

[0030] In this application, the average primary particle size of 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 a nearly spherical particle, the average primary particle diameter (nm) is given by the following formula: Average primary particle diameter (nm)=6000 / (BET specific surface area S(m 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 diameter (nm) of silica particles is given by the following formula Average primary particle diameter of silica particles (nm) = 2727 / specific surface area (m²) 2 / g) This can be determined by [method].

[0031] The sulfonic acid-modified colloidal silica according to the present invention contains 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 silica primary particles contained in the sulfonic acid-modified colloidal silica according to the present invention, constitute the main particles of the silica, and are distinct from the coarse particles (described later) that are formed by the aggregation of the above-mentioned silica secondary particles.

[0032] 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 and 200 nm or less.

[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 200 nm or less, more preferably 180 nm or less, even more preferably 150 nm or less, even more preferably 110 nm or less, and even more preferably 80 nm or less.

[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 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.

[0035] 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 7 nm or more, and even more preferably 9 nm or more.

[0036] Because the average secondary particle diameter of the 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.

[0037] 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% by mass aqueous solution of citric acid is added to colloidal silica to dilute it to a 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 the silica particles.

[0038] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the solvent of 250 ppm by mass or less per gram of solvent.

[0039] The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the solvent of 250 ppm by mass or less per gram of solvent, preferably 230 ppm by mass or less, more preferably 210 ppm by mass or less, and even more preferably 190 ppm by mass or less.

[0040] 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), which allows for the formation of a polished surface at high speed when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention.

[0041] 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 sulfonic acid content 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.

[0042] 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.

[0043] 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 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 method.

[0044] 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).

[0045] 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 9,000,000 particles / mL or less, and even 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.

[0046] 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, a highly flat polished surface can be easily formed.

[0047] 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 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 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).

[0048] 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.

[0049] 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 number count method described below.

[0050] <Method for measuring the content of coarse particles with a particle size of 0.2 μm or larger in 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 : 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

[0051] 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.

[0052] 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 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.

[0053] Furthermore, the pH of the sulfonic acid-modified colloidal silica according to the present invention is preferably 11.0 or less, more preferably 10.5 or less, and even more preferably 10.0 or less. 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.

[0054] 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.).

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 keeping the silica particle content 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.

[0059] 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. 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. Silica particle content (mass%) in sulfonic acid-modified colloidal silica = (W / 10.0) × 100 The silica particle content mentioned above corresponds to the total content of primary silica particles, secondary silica particles, and coarse particles in sulfonic acid-modified colloidal silica.

[0060] The sulfonic acid-modified colloidal silica according to the present invention may contain metal impurities.

[0061] 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.

[0062] 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.

[0063] In this application, the metal impurity content refers to the value measured using an atomic absorption spectrometer.

[0064] The sulfonic acid-modified colloidal silica according to the present invention can be suitably prepared by the manufacturing method described later in this application.

[0065] According to the present invention, even when used to polish semiconductor wafers provided with a silicon nitride film, a sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at high speed can be provided.

[0066] Next, a method for producing sulfonic acid-modified colloidal silica according to the present invention will be described. A method for producing sulfonic acid-modified colloidal silica according to the present invention is: (i) BET specific surface area is 70-500m 2 Silanol group density is 7.0-20.0 groups / nm per gram. 2 The process involves contacting a raw material 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 into sulfo groups. (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) When contacting the silane coupling agent containing the mercapto group with the colloidal silica raw material, the silane coupling agent is diluted with methanol by a mass ratio of 3 to 50 times. (iv) The amount of hydrogen peroxide in contact is 3.50 to 10.00 mol per 1 mol of silane coupling agent containing the mercapto group in contact. (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. A manufacturing method characterized by the above can be cited (hereinafter, this manufacturing method will be appropriately referred to as "the method for producing sulfonic acid-modified colloidal silica according to the present invention a").

[0067] (Colloidal silica as 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 7.0-20.0 groups / nm per gram. 2 The raw material used is colloidal silica containing silica particles.

[0068] 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 small amount of metal impurities that are diffusible into semiconductors and corrosive ions such as chloride ions.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Silicon compounds represented by general formula (1) or their derivatives undergo hydrolysis and condensation in the reaction solvent to form colloidal silica.

[0075] Examples of reaction solvents used when silicon compounds represented by general formula (1) or their derivatives undergo antihydrolysis 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).

[0076] 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.

[0077] 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.

[0078] 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. With the above adjustment, the reaction solvent is preferably controlled to a pH of 8.0 or higher and 11.0 or lower, more preferably 8.5 or higher and 10.5 or lower, and colloidal silica can be formed promptly.

[0079] From the perspective of preventing contamination by impurities, the basic catalyst preferably includes one or more selected from organic amines and ammonia, and more preferably one or more selected from ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide.

[0080] To hydrolyze and condense the silicon compound in the reaction solvent, the silicon compound represented by the general formula (1) or its derivative is added to an organic solvent, and stirring treatment is usually performed under temperature conditions of 0°C or higher and 100°C or lower, preferably 0°C or higher and 50°C or lower.

[0081] By stirring the silicon compound in a solvent containing water, the hydrolysis and dehydration condensation reactions of the silicon compound represented by the general formula (1) or its derivative proceed. First, the silicon compound represented by the general formula (1) or its derivative undergoes dehydration condensation to form a dimer, and this dimer polymerizes (oligomerizes) to form spherical silica primary particles in the solvent, whereby colloidal silica in which silica primary particles are dispersed in the solvent can be obtained. By hydrolyzing and condensing the silicon compound while stirring in a solvent containing water, colloidal silica with uniform silica particle diameters can be obtained.

[0082] The colloidal silica obtained by the above hydrolysis and condensation reaction (sol-gel method) can be used as the raw material colloidal silica according to the production method of the present invention by appropriately adjusting the concentration.

[0083] In the production method a of 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 m 2 / g, and 80 to 490 m 2It is preferable that the value be / g, and 90-480m 2 It is more preferable that the amount be / g, and 100-470m 2 It is even more preferable that it be / g.

[0084] 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).

[0085] 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 7.5 to 19.5 particles / nm. 2 Preferably, the density is 8.0 to 19.0 particles / nm. 2 It is preferable that it be so.

[0086] 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)

[0087] 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.

[0088] 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.

[0089] As silane coupling agents having a mercapto group, mercaptoalkylalkoxysilanes are preferred, and mercaptoalkyltrialkoxysilanes are more preferred. Examples of silane coupling agents having such mercapto groups include, for example, 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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 the 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.

[0094] 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)".

[0095] 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 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.

[0096] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the raw material colloidal silica and the 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 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.

[0097] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw colloidal silica is brought into contact with a silane coupling agent containing mercapto groups (-SH) to perform a modification treatment, and then hydrogen peroxide is brought into contact with it to oxidize the mercapto groups introduced on the surface of the silica particles and convert them to sulfo groups (-SO3H).

[0098] The amount of hydrogen peroxide in contact with the reaction product of colloidal silica as a raw material and a silane coupling agent containing a mercapto group (-SH) is 3.50 to 10.00 mol per 1 mol of silane coupling agent containing a mercapto group used in the preparation of the above reaction product, preferably 3.75 to 9.75 mol, and more preferably 4.00 to 9.50 mol.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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 converted to a sulfo group (-SO3H), thereby enabling the stable preparation of a silane coupling agent substituted with a sulfo group (-SO3H).

[0104] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, hydrogen peroxide is brought into contact with the reaction product of the raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH), and 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 obtained after contacting the reaction product of the raw colloidal silica and the silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide is heated is not particularly limited and may be 100.0°C or lower. By setting the heating temperature to 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.

[0105] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting the reaction product of the raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide, the heating time for heating the resulting mixture 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 the raw material 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. 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.

[0106] 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 substitution with water may be performed after adding a silane coupling agent containing a mercapto group, but before adding hydrogen peroxide.

[0107] 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.

[0108] 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.

[0109] Details of the sulfonic acid-modified colloidal silica obtained by the method a for producing sulfonic acid-modified colloidal silica according to the present invention are as described above.

[0110] 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]

[0111] 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.

[0112] (Example 1) Colloidal silica (BET specific surface area 135 m²) 2 / g, silanol group density 8.5 groups / nm 2 The silica particles (20% by mass) and 3-mercaptopropyltrimethoxysilane, diluted 10 times by mass with methanol, were subjected to a modification treatment by contacting them for 1 hour under pH 7.1 and a temperature of 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the raw material colloidal silica (silica particles in the raw material colloidal particles) was 28.00 μmol / g in terms of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution was added in an amount equivalent to 4.00 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane, and then the product was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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, for 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 set to 1 mass%, and the metal impurity content (mass ppm) were determined. 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.

[0113] (Example 2) Colloidal silica (BET specific surface area 200 m²) 2 / g, silanol group density 9.0 groups / nm 2 The silica particles were subjected to a modification treatment by contacting 3-mercaptopropyltrimethoxysilane, diluted 10 times by mass with methanol, with a silica particle concentration of 20% by mass, for 1 hour under pH 7.0 and a temperature of 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the silica was 90.00 μmol per gram of raw colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution in an amount equivalent to 4.00 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane was added, and the mixture was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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%, and the metal impurity content (mass ppm) were determined in the same manner as in Example 1. The results are shown in Table 2.

[0114] (Example 3) Colloidal silica (BET specific surface area 235 m²) 2 / g, silanol group density 8.1 groups / nm 2 The silica particles were subjected to a modification treatment by contacting 3-mercaptopropyltrimethoxysilane, diluted 10 times by mass with methanol, with a silica particle concentration of 20% by mass, under pH 7.2 and a temperature of 60.0°C for 1 hour, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the raw material colloidal silica (silica particles in the raw material colloidal particles) was 60.00 μmol per gram of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution in an amount equivalent to 4.00 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane was added, and the mixture was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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%, and the metal impurity content (mass ppm) 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 85 m²) 2 / g, silanol group density 5.8 groups / nm 2 The silica particles (20% by mass) and 3-mercaptopropyltrimethoxysilane (undiluted with methanol) were brought into contact for 1 hour under pH 7.1 and a temperature of 60.0°C, so that the amount of 3-mercaptopropyltrimethoxysilane in contact with the raw material colloidal silica (silica particles in the raw material colloidal particles) was 100.00 μmol per gram of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution in an amount equivalent to 4.00 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane was added, and the mixture was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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%, and the metal impurity content (mass ppm) 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 225 m²) 2 / g, silanol group density 5.3 groups / nm 2 The silica particles (20% by mass) and 3-mercaptopropyltrimethoxysilane (undiluted with methanol) were subjected to a modification treatment by contacting them for 1 hour under pH 7.1 and a temperature of 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the raw material colloidal silica (silica particles in the raw material colloidal particles) was 23.00 μmol per gram of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution in an amount equivalent to 4.00 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane was added, and the mixture was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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%, and the metal impurity content (mass ppm) were determined in the same manner as in Example 1. The results are shown in Table 2.

[0117] (Comparative Example 3) Colloidal silica (BET specific surface area 210 m²) 2 / g, silanol group density 2.4 / nm 2 The silica particles were subjected to a modification treatment by contacting 3-mercaptopropyltrimethoxysilane, diluted 20 times by mass with methanol, with a silica particle concentration of 20% by mass, for 1 hour under pH 6.9 and a temperature of 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the silica particles was 6.37 μmol per gram of raw colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution in an amount equivalent to 3.05 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane was added, and the mixture was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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%, and the metal impurity content (mass ppm) were determined in the same manner as in Example 1. The results are shown in Table 2.

[0118] (Comparative Example 4) Colloidal silica (BET specific surface area 210 m²) 2 / g, silanol group density 2.4 / nm 2 The silica particles were subjected to a modification treatment by contacting 3-mercaptopropyltrimethoxysilane, diluted 20 times by mass with methanol, with a silica particle concentration of 20% by mass, for 1 hour under pH 7.2 and a temperature of 60.0°C, such that the amount of 3-mercaptopropyltrimethoxysilane in contact with the silica particles was 50.93 μmol per gram of raw colloidal silica (silica particles in the raw colloidal particles) in terms of solid content. Next, to the contact and modification treatment product of the above raw materials colloidal silica and 3-mercaptopropyltrimethoxysilane, a 35% by mass hydrogen peroxide solution in an amount equivalent to 3.03 mol of hydrogen peroxide per 1 mol of contact amount of 3-mercaptopropyltrimethoxysilane was added, and the mixture was heated at 100.0°C for 20 hours. Subsequently, the desired sulfonic acid-modified colloidal silica was obtained by cooling it to room temperature. 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%, and the metal impurity content (mass ppm) were determined in the same manner as in Example 1. The results are shown in Table 2.

[0119] (Comparative Example 5) 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 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 silica. 220 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. 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%, and the metal impurity content (mass ppm) were determined in the same manner as in Example 1. The results are shown in Table 2.

[0120] 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.

[0121] <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

[0122] <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). JPEG0007887531000001.jpg37128 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.

[0123] [Table 1]

[0124] [Table 2]

[0125] Table 1 shows that in Examples 1 to 3, 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 7.0-20.0 groups / nm per gram. 2 The method involves a step of bringing a raw material 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 to sulfo groups, wherein (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 material colloidal silica in terms of solid content, (iii) when bringing the silane coupling agent containing mercapto groups into contact with the raw material colloidal silica, the silane coupling agent is diluted with methanol by mass ratio to a dilution ratio of 3 to 50 times, (iv) the amount of hydrogen peroxide added is 3.50 to 10.00 mol per 1 mol of the amount of silane coupling agent containing mercapto groups in contact, 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.

[0126] Therefore, as can be seen from Table 2, the sulfonic acid-modified colloidal silica obtained in Examples 1 to 3 has a sulfur content of 700 ppm or more and less than 3000 ppm per gram of silica particles, a sulfur content of 250 ppm or less per gram of solvent, and an average secondary particle diameter of 5 nm or more and 43 nm or less of silica particles. This indicates that even when used to polish semiconductor wafers with silicon nitride films, it is possible to form highly flat polished surfaces at high speed.

[0127] On the other hand, Table 1 shows that in Comparative Examples 1 to 5, the methods for producing sulfonic acid-modified colloidal silica involved (i) using colloidal silica raw materials with a silanol group density outside the specified range (Comparative Examples 1 to 5), (ii) contact amounts of silane coupling agent containing mercapto groups per gram of colloidal silica raw materials (based on solid content) outside the specified range (Comparative Examples 1 to 3), (iii) not diluting the silane coupling agent containing mercapto groups with methanol when contacting the colloidal silica raw materials (Comparative Examples 1, 2, and 5), and (iv) contact amounts of hydrogen peroxide per 1 mole of silane coupling agent containing mercapto groups outside the specified range (Comparative Examples 3 and 4).

[0128] Therefore, as can be seen from Table 2, the sulfonic acid-modified colloidal silica obtained in Comparative Examples 1 to 5 had sulfur content per gram of silica particles outside the predetermined range (Comparative Examples 2 and 3), sulfur content in the solvent per gram of solvent exceeding the predetermined value (Comparative Examples 1 and 4), or average secondary particle diameter of silica particles outside the predetermined range (Comparative Examples 1 and 5). Consequently, when a semiconductor wafer with a silicon nitride film provided as an abrasive was polished using these silica particles, the polishing speed was low (Comparative Examples 1 to 4), or a highly flat polished surface could not be obtained (Comparative Examples 3 to 5). [Industrial applicability]

[0129] According to the present invention, even when used to polish semiconductor wafers provided with a silicon nitride film, a sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at high speed can be provided.

Claims

[Claim 1] Sulfonic acid-modified colloidal silica, The sulfur content of the silica particles is 700 ppm by mass or more and less than 3000 ppm by mass per gram of silica particles. The sulfur content in the solvent is 250 ppm by mass or less per gram of solvent. The average secondary particle diameter of the silica particles is between 5 nm and 43 nm. A sulfonic acid-modified colloidal silica characterized by the following features.

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