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

Abstract

Even when used for polishing a semiconductor wafer provided with a silicon nitride film, there is provided sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at high speed. Sulfonic acid-modified colloidal silica, wherein the sulfur content of the silica particles is 700 mass ppm or more and less than 3000 mass ppm per 1 g of the silica particles, the sulfur content in the solvent is 250 mass ppm or less per 1 g of the solvent, and the content of coarse particles having a particle size of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1 mass%.

Description

Technical Field

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

Background Art

[0002] In semiconductor manufacturing processes, silicon nitride films (Si3N4 films) having high density and excellent insulation properties are used as semiconductor protective films, insulating films, etc.

[0003] In the above semiconductor manufacturing process, a semiconductor wafer is held by a member called a carrier, and the wafer and a polishing pad are brought into contact and rotated while flowing a slurry containing chemicals, abrasive grains, etc., thereby polishing the semiconductor wafer to make it flat and polished.

[0004] In the above polishing method, chemical mechanical polishing (CMP) that utilizes the chemical polishing action of chemicals and the mechanical polishing action of abrasive grains is also used.

[0005] By the way, since the above silicon nitride film has poor chemical reactivity, it is generally difficult to perform polishing at a high speed when polishing a semiconductor wafer provided with the above silicon nitride film.

[0006] Under such circumstances, as an abrasive grain for polishing a semiconductor wafer, one made of sulfonic acid-modified colloidal silica obtained by modifying colloidal silica (silica sol) with a sulfonic acid group (sulfonic group (-SO3H)) has been proposed (see Patent Document 1 (Japanese Patent Laid-Open No. 2012-040671)).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Disclosure of the Invention

Problems to be Solved by the Invention

[0008] However, as a result of investigations by the present inventors, when the conventionally proposed sulfonic acid-modified colloidal silica is used as an abrasive grain for polishing a semiconductor wafer having a silicon nitride film, (1) due to the insufficient modification level of the sulfonic acid group with respect to the silica particles constituting the sulfonic acid-modified colloidal silica, the polishing rate with respect to the silicon nitride film is low when used as an abrasive grain for polishing. It has been found.

[0009] Further, as a result of investigations by the present inventors, when the conventionally proposed sulfonic acid-modified colloidal silica is used as an abrasive grain for polishing a semiconductor wafer having a silicon nitride film, (2) it has been found that the unreacted silane coupling agent component used when modifying the sulfonic acid group remains in the solvent of the sulfonic acid-modified colloidal silica, and this silane coupling agent component reacts with the silicon nitride film to inhibit the above polishing treatment. This is presumably because a silane coupling agent such as 3-mercaptopropyltrimethoxysilane used when modifying a sulfonic acid group on silica particles has poor reactivity with silica particles as compared with other silane coupling agents such as 3-aminopropyltrimethoxysilane, and thus easily remains as an unreacted silane coupling agent in the solvent.

[0010] Furthermore, as a result of investigations by the present inventors, when attempting to remove the unreacted silane coupling agent component remaining in the solvent of the sulfonic acid-modified colloidal silica by ultrafiltration, although the unreacted silane coupling agent component can be removed, aggregation of the silica particles constituting the sulfonic acid-modified colloidal silica proceeds during ultrafiltration, increasing the content of coarse particles having a particle size of 0.2 μm or more. It has been found that when the sulfonic acid-modified colloidal silica obtained by the above ultrafiltration is used as an abrasive grain for polishing, the roughness of the polished surface increases due to the above 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, and a method for producing the sulfonic acid-modified colloidal silica.

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 a sulfonic acid-modified colloidal silica having a sulfur content in silica particles of 700 mass ppm or more and less than 3000 mass ppm per 1 g of silica particles, a sulfur content in the solvent of 250 mass ppm or less per 1 g of the solvent, and a content of coarse particles having a particle size of 0.2 μm or more in the silica particles of 10,000,000 particles / mL or less when the silica particle concentration is 1 mass% can solve the above problems, and that the above sulfonic acid-modified colloidal silica can be produced by a specific production method. Based on these findings, the present invention has been completed.

[0013] That is, the present invention is (1) A sulfonic acid-modified colloidal silica, wherein the sulfur content in the silica particles is 700 mass ppm or more and less than 3000 mass ppm per 1 g of the silica particles, the sulfur content in the solvent is 250 mass ppm or less per 1 g of the solvent, and the content of coarse particles having a particle size of 0.2 μm or more in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1 mass%. The sulfonic acid-modified colloidal silica characterized by the above, (2) A method for producing the sulfonic acid-modified colloidal silica according to (1) above, (i) The BET specific surface area is 70 to 500 m 2 / g and the silanol group density is 7.0 to 20.0 per nm 2After subjecting raw material colloidal silica containing silica particles to a modification treatment by contacting it with a silane coupling agent containing a mercapto group, hydrogen peroxide is further contacted to oxidize the mercapto group introduced on the surface of the silica particles and convert it to a sulfo group, and (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) when the silane coupling agent containing a mercapto group is contacted with the raw material colloidal silica, the silane coupling agent is diluted with methanol at a mass ratio dilution factor of 3 to 50 times, (iv) the contact amount of the hydrogen peroxide is 3.50 to 10.00 mol per 1 mol of the contact amount of the silane coupling agent containing a mercapto group, (v) after contacting the hydrogen peroxide, the resulting mixture is heated at a temperature of 80.0 °C or higher for 15 hours or more A method for producing sulfonic acid-modified colloidal silica, characterized by the above is provided.

Advantages of the Invention

[0014] 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 and a method for producing the sulfonic acid-modified colloidal silica.

Embodiments for Carrying Out the Invention

[0015] First, the sulfonic acid-modified colloidal silica according to the present invention will be described. The sulfonic acid-modified colloidal silica according to the present invention has a sulfur content in the silica particles of 700 mass ppm or more and less than 3000 mass ppm per 1 g of the silica particles, and a sulfur content in the solvent of 250 mass ppm or less per 1 g of the solvent, The content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. It is characterized by this.

[0016] The sulfonic acid-modified colloidal silica according to the present invention is obtained by fixing a sulfonic acid group (-SO3H) to the silica particles constituting the colloidal silica.

[0017] In the sulfonic acid-modified colloidal silica according to the present invention, the sulfur content of the silica particles is 700 ppm by mass or more and less than 3000 ppm by mass per 1 g of the 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, still 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 index of the amount of sulfonic acid groups (-SO3H) in the silica particles constituting the colloidal silica. In the sulfonic acid-modified colloidal silica according to the present invention, since the sulfur content of the silica particles is equal to or higher than the lower limit value of each of the above ranges, the polishing rate can be further improved when used as abrasive grains for polishing. Further, in the sulfonic acid-modified colloidal silica according to the present invention, since the sulfur content of the silica particles is equal to or lower than the upper limit value of each of the above ranges, sufficient abrasiveness can be easily exhibited even when used for polishing a semiconductor wafer provided with a silicon nitride film.

[0019] In the present application documents, the sulfur content of the silica particles constituting the sulfonic acid-modified colloidal silica means a value calculated by the following method.

[0020] (Step 1) Centrifuge the sulfonic acid-modified colloidal silica (solution) using an Eppendorf Highmark Technologies centrifuge tube (model number: S303922A) under the conditions of 260,000 G, 5 °C, and 150 minutes. After drying the obtained precipitate at 60 °C for 12 hours, pulverize the silica and then dry it at 60 °C under reduced pressure for 2 hours. (Step 2) Add hydrofluoric acid to 1 g of the silica solid content obtained in Step 1 to dissolve the silica, and add ultrapure water to the resulting solution to obtain a diluted solution diluted to 100 mL. (Step 3) Using the diluted solution obtained in Step 2, measure the sulfur content (mass ppm) per 1 g of silica particles by inductively coupled plasma atomic emission spectrometry (ICP-AES) using an absolute calibration curve method with an ICP-AES device (ICPS-8100 manufactured by Shimadzu Corporation).

[0021] Also, the fact that the sulfonic acid-modified colloidal silica according to the present invention contains sulfonic acid-modified silica particles can be confirmed by X-ray photoelectron spectroscopy (XPS).

[0022] As described above, since the sulfonic acid-modified colloidal silica according to the present invention is obtained by fixing a sulfonic acid group (-SO3H) to the silica particles constituting the colloidal silica, the sulfonic acid-modified colloidal silica according to the present invention has a basic structure derived from the colloidal silica.

[0023] In the present application documents, the fact that the sulfonic acid-modified colloidal silica contains sulfonic acid-modified silica particles is confirmed by the following method. Centrifuge the colloidal silica solution under the conditions of 77,400 G, 5 °C, and 90 minutes. After drying the obtained precipitate at 60 °C for 12 hours, pulverize the silica and then dry it under reduced pressure at 60 °C with a gauge pressure of -0.1 MPa or less for 2 hours to prepare a measurement sample. Using the measurement sample, confirm the presence or absence of sulfonic acid groups on the surface of the silica particles by X-ray photoelectron spectroscopy under the following conditions. Measuring instrument: AXIS-NOVA manufactured by Shimadzu Corporation Irradiating X-ray: Al-Kα (15 kV, 10 mA) Analysis of X-ray spot diameter: 300×700μm

[0024] As described below, as a method for preparing colloidal silica, for example, in an organic solvent containing water, by stirring tetramethoxysilane (Si(OCH3)4), hydrolysis and dehydration condensation are carried out to form a dimer, and this dimer polymerizes (oligomerizes) to form spherical silica primary particles in the solvent. The dispersion of these silica primary particles in the solvent corresponds to colloidal silica. In addition, as the colloidal silica, a dispersion in which silica secondary particles formed by the association of the silica primary particles are dispersed in the solvent together with the silica primary particles may be used. Therefore, the sulfonic acid-modified colloidal silica according to the present invention corresponds to a material in which a sulfonic acid group (-SO3H) is fixed to silica particles dispersed in the above colloidal silica.

[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, still more preferably 30 nm or less, and particularly preferably 25 nm or less.

[0027] When 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 less than the above value (upper limit value), when polishing is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polishing surface having better 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 still more preferably 15 nm or more.

[0029] When 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 value), 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 the present application documents, the average primary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica means the value measured by the BET method described below. That is, first, the sulfonic acid-modified colloidal silica is pre-dried on a hot plate at 150 ° C, and then heat-treated at 800 ° C for 1 hour to prepare a measurement sample. Using the obtained measurement sample, the specific surface area (BET specific surface area) S by the BET method is measured. In the case of substantially spherical particles, the average primary particle diameter (nm) is given by the following formula Average primary particle diameter (nm) = 6000 / (BET specific surface area S (m 2 / g) × true density (g / cm 3 )) Here, since the true density of the silica particles is 2.2 g / cm 3 , the average primary particle diameter (nm) of the silica particles is given by the following formula Average primary particle diameter of silica particles (nm) = 2727 / specific surface area (m 2 / g) and can be determined by

[0031] The sulfonic acid-modified colloidal silica according to the present invention may contain secondary particles (silica secondary particles) in which silica primary particles are aggregated. 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, form the main particles of the silica particles, and are distinguished from the coarse particles formed by aggregation of the above silica secondary particles (described later).

[0032] The average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but is preferably 5 nm or more and 200 nm or less.

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

[0034] When 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 less than the above value (upper limit value), when polishing treatment is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polishing surface having better 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 still more preferably 9 nm or more.

[0036] When 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 more than the above value (lower limit value), when polishing treatment is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polishing surface can be formed at a higher speed.

[0037] In the present application documents, the average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica means a value measured by the dynamic light scattering method described below. That is, first, an aqueous citric acid solution of 0.3 mass% is added to the colloidal silica and diluted so that the silica concentration becomes 0.8 mass%, and the resulting diluted solution is used as a measurement sample. Using the above measurement sample, the average particle diameter measured by the dynamic light scattering method using a 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 mass ppm or less per 1 g of the solvent.

[0039] In the sulfonic acid-modified colloidal silica according to the present invention, the sulfur content in the solvent is 250 mass ppm or less, preferably 230 mass ppm or less, more preferably 210 mass ppm or less, and even more preferably 190 mass ppm or less per 1 g of the solvent.

[0040] In the sulfonic acid-modified colloidal silica according to the present invention, the sulfur content in the solvent serves as an index for the amount of unreacted silane coupling agent component remaining in the solvent. In the sulfonic acid-modified colloidal silica according to the present invention, when the sulfur content in the solvent is equal to or less than the above value (upper limit value), a polished surface can be formed at a 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 the lower the better. However, the content of the sulfonic acid-modified colloidal silica according to the present invention may be, for example, 1 mass ppm or more, 5 mass ppm or more, or 10 mass ppm or more.

[0042] As described above, when the inventors studied, when polishing a semiconductor wafer provided with a silicon nitride film using sulfonic acid-modified colloidal silica, the unreacted silane coupling agent component used to modify the sulfonic acid group (-SO3H) remained in the solvent of the colloidal silica, and it was found that this silane coupling agent component reacted with the silicon nitride film provided on the surface of the semiconductor wafer and inhibited the above polishing process. On the other hand, in the sulfonic acid-modified colloidal silica according to the present invention, since the sulfur content in the solvent is limited to a predetermined amount or less, it is possible to perform the polishing process at a high speed even when polishing a semiconductor wafer provided with a silicon nitride film.

[0043] In the present application documents, the sulfur content in the solvent of the sulfonic acid-modified colloidal silica means the value calculated by the following method. (Step 1) The colloidal silica solution is subjected to centrifugal filtration treatment at 12,000 rpm for 10 minutes using a centrifugal ultrafiltration unit (model number: VN01H92, molecular weight cut-off 2000) manufactured by Sartorius AG, and the filtrate passing through the ultrafiltration membrane is collected. (Step 2) The sulfur concentration (mass ppm) in the filtrate obtained in Step 1 is measured using an inductively coupled plasma optical emission spectrometry (ICP-AES) apparatus (ICPS-8100 manufactured by Shimadzu Corporation) by the absolute calibration curve method.

[0044] The presence of the silane coupling agent remaining 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 by the method described above and comparing it with the amount of the 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 having a particle size of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less, 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.

[0046] In the sulfonic acid-modified colloidal silica according to the present invention, when the content of coarse particles having a particle size of 0.2 μm or more contained in the silica particles is below the above value (upper limit value) when the silica particle concentration in the sulfonic acid-modified colloidal silica is 1% by mass, a highly flat polishing surface can be easily formed when performing chemical mechanical polishing (CMP) using the sulfonic acid-modified colloidal silica according to the present invention.

[0047] In the sulfonic acid-modified colloidal silica according to the present invention, the lower limit of the content of coarse particles having a particle size of 0.2 μm or more contained in the silica particles is not particularly limited. However, in the sulfonic acid-modified colloidal silica according to the present invention, the content of coarse particles having a particle size of 0.2 μm or more contained in the silica particles can be 1,000 particles / mL or more when the silica particle concentration is 1% by mass, and preferably no coarse particles are contained at all (0 particles / mL).

[0048] As described above, according to the studies by the present inventors, in the conventionally known sulfonic acid-modified colloidal silica, an unreacted silane coupling agent component that reacts with the silicon nitride film during the polishing process remains. When this unreacted silane coupling agent is removed by ultrafiltration, the silica primary particles constituting the sulfonic acid-modified colloidal silica aggregate to generate a large amount of coarse particles having a particle size of 0.2 μm or more. It has been found that when the obtained sulfonic acid-modified colloidal silica is used as an abrasive grain for polishing, the roughness of the polished surface increases. As described above, the sulfonic acid-modified colloidal silica according to the present invention has a small remaining amount of the unreacted silane coupling agent (the sulfur content in the solvent is suppressed), and the content of coarse particles having a particle size of 0.2 μm or more is suppressed. Therefore, when chemical mechanical polishing (CMP) is performed using the sulfonic acid-modified colloidal silica according to the present invention, a polished surface with high flatness can be easily formed.

[0049] In the present application documents, the content of coarse particles having a particle size of 0.2 μm or more contained in the silica particles constituting the sulfonic acid-modified colloidal silica means the value measured by the particle number count method particle size distribution measurement method described below.

[0050] <Method for measuring the content of coarse particles having a particle size of 0.2 μm or more contained in silica particles> Add ultrapure water to the sulfonic acid-modified colloidal silica to be measured and dilute it so that the silica particle concentration becomes 1.0% by mass. Use the obtained dilution as a measurement sample, and use an Accusizer FX-nano manufactured by Particle sizing system Inc. to measure the number of coarse particles with a particle size of 0.2 μm or more 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 may be appropriately set according to its use and is not particularly limited, but is preferably 2.0 or more and 11.0 or less.

[0052] The pH of the sulfonic acid-modified colloidal silica according to the present invention is preferably 2.0 or more, more preferably 2.5 or more, and even more preferably 3.0 or more. When the pH of the sulfonic acid-modified colloidal silica according to the present invention is equal to or higher than the above value (lower limit value), 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] Also, 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. When the pH of the sulfonic acid-modified colloidal silica according to the present invention is equal to or lower than the above value (upper limit value), the long-term dispersion stability of the colloidal silica can be further improved.

[0054] In the present application documents, pH means a 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 content of silica particles in the sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but when the content of the sulfonic acid-modified colloidal silica is 100% by mass, it is preferably 1% by mass or more and 50% by mass or less.

[0056] The content of silica particles 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 still more preferably 5% by mass or more when the content of the sulfonic acid-modified colloidal silica is 100% by mass.

[0057] When the content of silica particles in the sulfonic acid-modified colloidal silica according to the present invention is equal to or higher than the above value (lower limit value), the polishing performance when the sulfonic acid-modified colloidal silica according to the present invention is used as abrasive grains for polishing is further improved.

[0058] The content of 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 still more preferably 30% by mass or less. When the content of silica particles in the sulfonic acid-modified colloidal silica according to the present invention is equal to or lower than the above value (upper limit value), the dispersion stability of the silica particles can be further improved.

[0059] In the present application documents, the content of silica particles in the sulfonic acid-modified colloidal silica according to the present invention means a value measured by the following measurement method. That is, 10.0 g of sulfonic acid-modified colloidal silica is dried on a hot plate at 150 °C and then heat-treated at 800 °C for 1 hour to remove moisture. The value calculated from the following formula represents the amount of the obtained solid content as W g. Content of silica particles in sulfonic acid-modified colloidal silica (mass %) = (W / 10.0) × 100 The content of the above silica particles corresponds to the total content of silica primary particles, silica secondary particles, and coarse particles in the 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, examples of the above metal impurities include 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 mass ppm or less. When the total content of metal impurities is 1 mass ppm or less, the sulfonic acid-modified colloidal silica according to the present invention can be suitably used as abrasive grains for polishing electronic materials such as semiconductor wafers.

[0063] In the present application documents, the content of metal impurities means 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 production method according to the present application described later.

[0065] 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.

[0066] Next, a method for producing sulfonic acid-modified colloidal silica according to the present invention will be described. The method for producing sulfonic acid-modified colloidal silica according to the present invention is as follows. (i) A step of contacting a raw material colloidal silica containing silica particles having a BET specific surface area of 70 to 500 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 for modification treatment, and then further contacting hydrogen peroxide to oxidize the mercapto group introduced on the surface of the silica particles to convert it into a sulfo group. (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) When the silane coupling agent containing a mercapto group is contacted with the raw material colloidal silica, the silane coupling agent is diluted with methanol at a mass ratio dilution factor of 3 to 50 times. (iv) The contact amount of the hydrogen peroxide is 3.50 to 10.00 mol per 1 mol of the contact amount of the silane coupling agent containing a mercapto group. (v) After contacting the hydrogen peroxide, the obtained mixture is heated at a temperature of 80.0 °C or higher for 15 hours or more. It is characterized by the above.

[0067] (Raw material colloidal silica) In the method for producing sulfonic acid-modified colloidal silica according to the present invention, a raw material colloidal silica containing silica particles having a BET specific surface area of 70 to 500 m 2 / g and a silanol group density of 7.0 to 20.0 per nm 2 is used.

[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 silicas having desired properties produced by known production methods. For example, colloidal silica having desired properties produced by the sol-gel method can be mentioned. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the raw material colloidal silica is colloidal silica produced by the sol-gel method, it can be preferably used because the contents of corrosive ions such as metal impurities having diffusibility into the semiconductor and chloride ions are low.

[0069] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when using colloidal silica produced by the sol-gel method as the raw material colloidal silica, examples of the method for producing the colloidal silica include conventionally known techniques. Specifically, it can be produced by using one or more hydrolyzable silicon compounds (for example, alkoxysilane or its derivative) as raw materials and performing a hydrolysis and condensation reaction.

[0070] Examples of the silicon compound include 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 thereof include tetraalkoxysilane represented by the formula or its derivative.

[0071] In the silicon compound represented by the general formula (1) or its derivative, 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 the silicon compound represented by the general formula (1) or its derivative, examples of the R group include one or more selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, etc., and one or more selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group are preferred.

[0073] As the silicon compound represented by the general formula (1), 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 is preferable. Moreover, as the derivative of the silicon compound represented by the general formula (1), a low condensate obtained by partially hydrolyzing the silicon compound (tetraalkoxysilane) represented by the general formula (1) can be mentioned. As the silicon compound represented by the general formula (1) or its derivative, tetramethoxysilane is preferable in terms of easy control of the hydrolysis rate, easy obtainment of fine silica particles, and low residue of unreacted substances.

[0074] The silicon compound represented by the general formula (1) or its derivative is hydrolyzed and condensed in a reaction solvent to become colloidal silica.

[0075] As the reaction solvent used when the silicon compound represented by the general formula (1) or its derivative undergoes reverse hydrolysis and condensation, water or an organic solvent containing water can be mentioned. Examples of the organic solvent include one or more selected from hydrophilic organic solvents such as alcohols such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, ethylene glycol, propylene glycol, 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, etc., it is more preferable to use alcohols having the same alkyl group as the alkyl group (R group) of the raw material silicon compound (for example, methanol for tetramethoxysilane).

[0076] The amount of the organic solvent used is not particularly limited, but it is preferably 5 mol or more and 50 mol or less per 1 mol of the silicon compound represented by the general formula (1) or its derivative. When the amount of the organic solvent used is less than 5 moles per mole of the silicon compound represented by the general formula (1) or its derivative, it may be difficult to exhibit compatibility with the silicon compound represented by the general formula (1). When it exceeds 50 moles per mole of the silicon compound represented by the general formula (1) or its derivative, the production efficiency may decrease.

[0077] The amount of water added to the silicon compound represented by the general formula (1) or its derivative is not particularly limited, and may be an amount required for hydrolysis of the silicon compound represented by the general formula (1). About 2 to 200 moles per mole of the silicon compound represented by the general formula (1) is preferable. In addition, when adding an organic solvent containing water to the silicon compound represented by the general formula (1) or its derivative, the amount of water mixed in the organic solvent greatly affects the particle size of the colloidal silica formed. If the amount of water added is relatively increased with respect to the amount of the organic solvent added, the particle size of the resulting colloidal silica can be relatively increased. If the amount of water added is relatively decreased with respect to the amount of the organic solvent added, the particle size of the resulting colloidal silica can be relatively decreased. Thus, by changing the mixing ratio of water and the organic solvent, the particle size of the resulting colloidal silica can be arbitrarily adjusted.

[0078] For the reaction solvent of the hydrolysis and condensation reaction of the silicon compound to obtain colloidal silica, it is preferable to adjust the reaction solvent to be alkaline in the presence of a basic catalyst. By the above adjustment, the reaction solvent is preferably controlled to a pH of 8.0 or more and 11.0 or less, more preferably a pH of 8.5 or more and 10.5 or less, and colloidal silica can be formed promptly.

[0079] From the viewpoint of preventing contamination of impurities, the basic catalyst is preferably at least one selected from organic amines and ammonia, and more preferably at least one selected from ethylenediamine, diethylenetriamine, triethylenetetramine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide.

[0080] In order to hydrolyze and condense a silicon compound in a reaction solvent, a silicon compound represented by the general formula (1) or a derivative thereof may be added to an organic solvent and stirred under temperature conditions usually of 0°C or higher and 100°C or lower, preferably 0°C or higher and 50°C or lower.

[0081] By stirring a silicon compound in a solvent containing water, the hydrolysis and dehydration condensation reactions of the silicon compound represented by the general formula (1) or a derivative thereof proceed. First, the silicon compound represented by the general formula (1) or a derivative thereof 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 can be obtained in the solvent. By hydrolyzing and condensing while stirring a silicon compound 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] Production method of 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 70 to 500 m 2 / g, preferably 80 to 490 m 2 / g, more preferably 90 to 480 m 2 / g, and even more preferably 100 to 470 m 2 / g.

[0084] In the present application documents, the BET specific surface area of the silica particles constituting the raw material colloidal silica means 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 per nm 2 and preferably 7.5 to 19.5 per nm 2 and more preferably 8.0 to 19.0 per nm 2 is even more preferred.

[0086] In the present application documents, the silanol group density (per nm 2 ) of the silica particles constituting the raw material colloidal silica means the value calculated by the following method. That is, based on the Sears method described in G.W. Sears, Jr., “Determination of Specific Surface Area of Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981(1956)., after adjusting the silica particle concentration of the raw material colloidal silica to be measured to 1% by mass, when titrating with a 0.1 mol / L aqueous sodium hydroxide solution, the silanol group density “ρ” (per nm 2 ) calculated based on the following formula is meant. ρ = (a × f × 6022) ÷ (c × S) ρ: Silanol group density (per nm 2 ) a: Drop volume (mL) of 0.1 mol / L aqueous sodium hydroxide solution at pH 4 to pH 9 f: Factor of 0.1 mol / L aqueous sodium hydroxide solution c: Mass (g) of silica particles S: BET specific surface area (m 2 / g)

[0087] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, since the BET specific surface area and silanol group density of the silica particles constituting the raw material colloidal silica are within the above ranges, the reaction points with the silane coupling agent containing a mercapto group (described later) formed on the surface of the silica particles can be easily controlled within a suitable range.

[0088] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the above raw material colloidal silica and a silane coupling agent containing a mercapto group are brought into contact with each other for modification treatment.

[0089] As the silane coupling agent having a mercapto group, mercaptoalkylalkoxysilane is preferable, and mercaptoalkyltrialkoxysilane is more preferable. Specific examples of such a silane coupling agent having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the like.

[0090] The contact amount of the above 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 (per 1 g of the silica particles contained in the raw material colloidal silica), preferably 26.0 μmol or more and 99.0 μmol or less, and more preferably 27.0 μmol or more and 98.0 μmol.

[0091] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, since the contact amount of the silane coupling agent containing a mercapto group is within the above range, the amount of the silane coupling agent remaining in the solvent of the obtained sulfonic acid-modified colloidal silica (sulfur content) can be easily controlled, and the surface of the silica particles can be sufficiently anionized, and sulfonic acid-modified colloidal silica exhibiting excellent performance when used as an abrasive grain for polishing can be easily prepared.

[0092] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, as the dispersion medium of the raw material colloidal silica, as described above, it may contain water as a main component and may also contain an organic solvent. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the raw material colloidal silica is brought into contact with a silane coupling agent containing a mercapto group, since the silane coupling agent is hardly soluble in water, for the purpose of dissolving the silane coupling agent, it is preferable to use the raw material colloidal silica containing a certain amount or more of an organic solvent (hydrophilic solvent) as the dispersion medium.

[0093] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when the silane coupling agent containing a mercapto group is brought into contact with the raw material colloidal silica, it is preferable to bring the silane coupling agent into contact with the raw material colloidal silica while diluting it with methanol at a mass ratio dilution factor of 3 to 50 times, more preferably while diluting it with methanol at a mass ratio dilution factor of 4 to 45 times, and even more preferably while diluting it with methanol at a mass ratio dilution factor of 5 to 40 times.

[0094] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the dilution factor of the silane coupling agent containing a mercapto group with methanol means a value calculated by mass ratio. Specifically, it means a value calculated by "the amount of methanol (g) used at the time of dilution / the amount of the 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 bringing a silane coupling agent containing a mercapto group into contact with raw material colloidal silica, the silane coupling agent is diluted to a predetermined dilution ratio with methanol and then brought into contact with the raw material colloidal silica, so that the silane coupling agent can be preferably mixed while suppressing local reactions during the addition of the coupling agent, and a desired amount of the silane coupling agent can be effectively fixed to the silica particles constituting the raw material colloidal silica. As a result, the residual amount of the silane coupling agent in the solvent constituting the finally obtained 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 a silane coupling agent containing a mercapto group are brought into contact for modification treatment, although not particularly limited, it is preferable to perform the contact treatment while appropriately performing heat treatment within the temperature range from normal 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 either, but it is preferably 10 minutes or more and 10 hours or less, more preferably 30 minutes or more and 5 hours or less, and even more preferably 30 minutes or more and 2 hours or less. The pH during the above contact treatment is not limited either, but a pH of 7 or more and 11 or less is preferable. By performing the contact treatment while performing heat treatment, the hydrolysis and condensation reactions are promoted, and the silane coupling agent containing a mercapto group can be preferably fixed (chemically bonded) to the surface of the silica particles constituting the colloidal silica.

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

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

[0099] By controlling the contact amount of hydrogen peroxide with respect to the contact reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH) within the above range, while preferably proceeding with the conversion of the mercapto group (-SH) to a sulfo group (-SO3H), the residual oxidant concentration in the resulting sulfonic acid-modified colloidal silica can be minimized.

[0100] The residual oxidant concentration in the sulfonic acid-modified colloidal silica obtained by the production method according to the present invention is not particularly limited, but is preferably 1000 mass ppm or less, more preferably 700 mass ppm or less, and even more preferably 500 mass ppm or less.

[0101] When the residual oxidant concentration in the sulfonic acid-modified colloidal silica obtained by the production method according to the present invention is equal to or less than the above value (upper limit value), wafer dishing can be effectively suppressed when the sulfonic acid-modified colloidal silica obtained by the production method according to the present invention is used as abrasive grains for polishing a semiconductor wafer.

[0102] As described above, by bringing hydrogen peroxide into contact with the contact reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH), while the mercapto group (-SH) of the above silane coupling agent can be converted to a sulfo group (-SO3H), the portion other than the above mercapto group of the above silane coupling agent and colloidal silica have a stable structure with respect to hydrogen peroxide, so by-products are hardly generated.

[0103] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after subjecting raw material colloidal silica to a modification treatment by contacting it with a silane coupling agent containing a mercapto group (-SH), the mercapto group (-SH) is converted to a sulfo group (-SO3H), whereby a silane coupling agent substituted with a sulfo group (-SO3H) can be stably prepared.

[0104] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting hydrogen peroxide with the contact reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH), the resulting mixture is heated at a temperature of 80.0°C or higher. It is preferably heated at a temperature of 85.0°C or higher, more preferably heated at a temperature of 90.0°C or higher, and even more preferably heated at a temperature of 95.0°C or higher. Further, in the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting hydrogen peroxide with the contact reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH), the upper limit of the temperature for heating the resulting mixture is not particularly limited and may be 100.0°C or lower. When the heating temperature is 80.0°C or higher, the amount of unreacted silane coupling agent remaining in the solvent can be effectively suppressed in the resulting sulfonic acid-modified colloidal silica.

[0105] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting hydrogen peroxide with the contact reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH), the heating time for heating the resulting mixture is 15 hours or longer, preferably 16 hours or longer, more preferably 18 hours or longer, and even more preferably 19 hours or longer. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting hydrogen peroxide with the contact reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH), the upper limit of the heating time for heating the obtained mixture is not particularly limited, and it may be 50 hours or less, 40 hours or less, or 30 hours or less. Also, when the heating time is 15 hours or more, the amount of unreacted silane coupling agent remaining in the solvent can be effectively suppressed in the obtained sulfonic acid-modified colloidal silica.

[0106] The reaction solution obtained by contacting the above hydrogen peroxide and heating the obtained mixture at a temperature of 80.0 °C or higher for 15 hours or more contains an organic solvent such as methanol in addition to water. Therefore, in order to enhance the long-term storage stability, if necessary, the dispersion medium of the obtained reaction solution may be replaced with water. The replacement with water may be performed after adding a silane coupling agent containing a mercapto group and before adding hydrogen peroxide.

[0107] The method for replacing the dispersion medium with water is not particularly limited. For example, there is a method of dropping a certain amount of water little by little while heating the reaction solution obtained by contacting the above hydrogen peroxide and heating the obtained mixture at a temperature of 80.0 °C or higher for 15 hours or more.

[0108] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, since the amount of the silane coupling agent remaining in the solvent of the obtained sulfonic acid-modified colloidal silica is suppressed, even without performing ultrafiltration, the remaining amount of the silane coupling agent in the above solvent can be easily controlled within a suitable range. 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] The details of the sulfonic acid-modified colloidal silica obtained by the production method according to the present invention are as described in the description of the sulfonic acid-modified colloidal silica according to the present invention.

[0110] According to the present invention, even when used for polishing a semiconductor wafer provided with a silicon nitride film, a method for effectively producing a novel sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at high speed can be provided.

Examples

[0111] Next, the present invention will be described more specifically 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 m 2 / g, silanol group density 8.5 per nm 2 , silica particle concentration 20% by mass) and 3-mercaptopropyltrimethoxysilane diluted 10-fold by mass with methanol were contacted at a temperature of pH 7.1 and 60.0 ° C for 1 hour so that the contact amount of the 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, thereby performing a modification treatment. Next, 35% by mass hydrogen peroxide water in an amount corresponding to 4.00 mol of hydrogen peroxide per 1 mol of the contact amount of the 3-mercaptopropyltrimethoxysilane was added to the contact and modification product of the raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and then heated at 100.0 ° C for 20 hours. Thereafter, by cooling to room temperature, the target sulfonic acid-modified colloidal silica was obtained. The above production conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles having sulfonic groups fixed thereto, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. In addition, in the obtained sulfonic acid-modified colloidal silica, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content (number / mL) of coarse particles having a particle diameter of 0.2 μm or more contained in the silica particles when the silica particle concentration was 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 contents of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the sulfonic acid-modified colloidal silica. The results are shown in Table 2.

[0113] (Example 2) Colloidal silica (BET specific surface area 200 m 2 / g, silanol group density 9.0 pieces / nm 2 , silica particle concentration 20 mass %) and 3-mercaptopropyltrimethoxysilane diluted 10-fold by mass with methanol were brought into contact at a temperature of pH 7.0 and 60.0 °C for 1 hour so that the contact amount of the 3-mercaptopropyltrimethoxysilane was 90.00 μmol per 1 g of the raw material colloidal silica in terms of solid content (silica particles in the raw material colloidal particles), thereby performing a modification treatment. Next, 35 mass % hydrogen peroxide water in an amount corresponding to 4.00 mol of hydrogen peroxide per 1 mol of the contact amount of the above 3-mercaptopropyltrimethoxysilane was added to the contact and modification treatment product of the above raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and the mixture was heated at 100.0 °C for 20 hours. Thereafter, by cooling to room temperature, the target sulfonic acid-modified colloidal silica was obtained. The above production conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles having sulfonic groups fixed thereto, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Also, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content (number / mL) of coarse particles having a particle diameter of 0.2 μm or more contained in silica particles when the silica particle concentration was 1 mass %, and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0114] (Example 3) Colloidal silica (BET specific surface area 235 m 2 / g, silanol group density 8.1 pieces / nm 2 , and colloidal silica with a silica particle concentration of 20 mass %) and 3-mercaptopropyltrimethoxysilane diluted 10-fold by mass with methanol were brought into contact at a temperature of pH 7.2 and 60.0 °C for 1 hour so that the contact amount of the 3-mercaptopropyltrimethoxysilane was 60.00 μmol per 1 g of the raw material colloidal silica (silica particles in the raw material colloidal particles) in terms of solid content, thereby performing a modification treatment. Next, 35 mass % hydrogen peroxide water in an amount corresponding to 4.00 mol of hydrogen peroxide per 1 mol of the contact amount of the 3-mercaptopropyltrimethoxysilane was added to the contact and modification product of the raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and the mixture was heated at 100.0 °C for 20 hours. Thereafter, by cooling to room temperature, the target sulfonic acid-modified colloidal silica was obtained. The above production conditions are shown in Table 1. It was confirmed that the obtained sulfonic acid-modified colloidal silica contained silica particles with sulfonic groups fixed, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Further, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content of coarse particles having a particle diameter of 0.2 μm or more contained in the silica particles (number / mL) when the silica particle concentration was 1 mass %, and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0115] (Comparative Example 1) Colloidal silica (BET specific surface area 85 m 2 / g, silanol group density 5.8 pieces / nm 2 , silica particle concentration 20 mass %) and 3-mercaptopropyltrimethoxysilane (without methanol dilution) were brought into contact with each other at a temperature of pH 7.1 and 60.0 °C for 1 hour so that the contact amount of the 3-mercaptopropyltrimethoxysilane was 100.00 μmol per 1 g of the raw material colloidal silica in terms of solid content (silica particles in the raw material colloidal particles), and a modification treatment was performed. Next, 35 mass % hydrogen peroxide water in an amount corresponding to 4.00 mol of hydrogen peroxide per 1 mol of the contact amount of the 3-mercaptopropyltrimethoxysilane was added to the contact and modification product of the above raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and the mixture was heated at 100.0 °C for 20 hours. Thereafter, the mixture was cooled to room temperature to obtain the target sulfonic acid-modified colloidal silica. The above production conditions are shown in Table 1. It was confirmed that the obtained sulfonic acid-modified colloidal silica contained silica particles with sulfonic groups fixed, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Also, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content of coarse particles having a particle diameter of 0.2 μm or more contained in silica particles (number / mL), and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0116] (Comparative Example 2) Colloidal silica (BET specific surface area 225 m 2 / g, silanol group density 5.3 pieces / nm 2 , colloidal silica concentration 20 mass %) and 3-mercaptopropyltrimethoxysilane (without methanol dilution) were brought into contact with each other at a temperature of pH 7.1 and 60.0 °C for 1 hour so that the contact amount of the 3-mercaptopropyltrimethoxysilane was 23.00 μmol per 1 g of the raw material colloidal silica (silica particles in the raw material colloidal particles) in terms of solid content, and a modification treatment was performed. Next, 35 mass% hydrogen peroxide water in an amount corresponding to 4.00 mol of hydrogen peroxide per 1 mol of the contact amount of the above 3-mercaptopropyltrimethoxysilane was added to the contact and modification-treated product of the above raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and the mixture was heated at 100.0 °C for 20 hours. Thereafter, by cooling to room temperature, the target sulfonic acid-modified colloidal silica was obtained. The above production conditions are shown in Table 1. It was confirmed that the obtained sulfonic acid-modified colloidal silica contained silica particles with sulfonic groups fixed, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Further, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content (number / mL) of coarse particles having a particle diameter of 0.2 μm or more contained in silica particles when the silica particle concentration was 1 mass %, and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0117] (Comparative Example 3) Colloidal silica (BET specific surface area 210 m 2 / g, silanol group density 2.4 pieces / nm 2 , and colloidal silica with a silica particle concentration of 20 mass %) and 3-mercaptopropyltrimethoxysilane diluted 20-fold by mass with methanol were brought into contact at a temperature of pH 6.9 and 60.0 °C for 1 hour so that the contact amount of the 3-mercaptopropyltrimethoxysilane was 6.37 μmol per 1 g of the raw material colloidal silica (silica particles in the raw material colloidal particles) in terms of solid content, thereby performing a modification treatment. Next, 35 mass % hydrogen peroxide water in an amount corresponding to 3.05 mol of hydrogen peroxide per 1 mol of the contact amount of the 3-mercaptopropyltrimethoxysilane was added to the contact and modification treatment product of the above raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and the mixture was heated at 100.0 °C for 20 hours. Thereafter, by cooling to room temperature, the target sulfonic acid-modified colloidal silica was obtained. The above production conditions are shown in Table 1. It was confirmed that the obtained sulfonic acid-modified colloidal silica contained silica particles with sulfonic groups fixed, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Also, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content (number / mL) of coarse particles having a particle diameter of 0.2 μm or more contained in silica particles when the silica particle concentration was 1 mass %, and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0118] (Comparative Example 4) Colloidal silica (BET specific surface area 210 m 2 / g, silanol group density 2.4 pieces / nm 2 , and colloidal silica with a silica particle concentration of 20 mass %) and 3-mercaptopropyltrimethoxysilane diluted 20-fold by mass with methanol were brought into contact at a temperature of pH 7.2 and 60.0 °C for 1 hour so that the contact amount of the 3-mercaptopropyltrimethoxysilane was 50.93 μmol per 1 g of the raw material colloidal silica (silica particles in the raw material colloidal particles) in terms of solid content, and a modification treatment was performed. Next, 35 mass % hydrogen peroxide water in an amount corresponding to 3.03 mol of hydrogen peroxide per 1 mol of the contact amount of the 3-mercaptopropyltrimethoxysilane was added to the contact and modification treatment product of the above raw material colloidal silica and 3-mercaptopropyltrimethoxysilane, and the mixture was heated at 100.0 °C for 20 hours. Thereafter, by cooling to room temperature, the target sulfonic acid-modified colloidal silica was obtained. The above production conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with sulfonic groups fixed, and unreacted 3-mercaptopropyltrimethoxysilane remained in the solvent. Further, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content (number / mL) of coarse particles having a particle diameter of 0.2 μm or more contained in silica particles when the silica particle concentration was 1 mass %, and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0119] (Comparative Example 5) Using an ultrafiltration treatment apparatus having the following configuration for 40 g of the sulfonic acid-modified colloidal silica obtained in Comparative Example 1, ultrafiltration treatment was performed to obtain the target sulfonic acid-modified colloidal silica. <Configuration of ultrafiltration treatment apparatus> · Filtration treatment apparatus: Tabletop filtration unit for Pencil type module manufactured by Asahi Kasei Corporation (PX-02001) · Ultrafiltration membrane: Ultrafiltration membrane with a molecular weight cut-off of 80,000 (Pencil type module (AOP-0013) manufactured by Asahi Kasei Corporation) · Pump: 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) · Tube: Silicon peroxide decomposition tube manufactured by Masterflex (99400-25) During the above ultrafiltration treatment, ultrapure water was added to the sulfonic acid-modified colloidal silica to keep the liquid volume of the sulfonic acid-modified colloidal silica constant. The liquid volume passing through the ultrafiltration membrane was 220 g, and the time required for ultrafiltration was 150 minutes. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with sulfonic groups fixed, and unreacted 3-mercaptopropyltrimethoxysilane remaining in the solvent. In addition, in the obtained sulfonic acid-modified colloidal silica, in the same manner as in Example 1, the sulfur content (mass ppm) per 1 g of silica particles, the sulfur content (mass ppm) in the solvent per 1 g of the solvent, the content (mass %) of silica particles, the average primary particle diameter of silica particles, the average secondary particle diameter of silica particles, the content of coarse particles having a particle diameter of 0.2 μm or more contained in silica particles (number / mL), and the metal impurity content (mass ppm) were determined. The results are shown in Table 2.

[0120] Using the sulfonic acid-modified colloidal silica obtained in each of the above Examples and Comparative Examples as abrasive grains for polishing, the polishing rate and the polished surface roughness were evaluated by the following method. The results are shown in Table 2.

[0121] <Evaluation method of polishing rate> Ultra-pure water was added to the colloidal silica produced in each Example and Comparative Example to dilute it so that the silica concentration became 3.0 mass%, and a polishing composition was prepared. Using the obtained polishing composition, a 3 cm square silicon wafer having a silicon nitride film formed on its surface was polished under the following conditions. The polishing rate was calculated from the difference in the film 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: IC1000TM Pad manufactured by Nitto Denko 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 film thickness measuring machine

[0122] <Evaluation method of polished surface roughness> Ultra-pure water was added to the sulfonic acid-modified colloidal silica obtained in each Example and Comparative Example and diluted so that the silica particle concentration became 3.0 mass%, and a polishing composition was prepared. Using the obtained polishing composition, a 3 cm square silicon wafer with a silicon oxide film formed on its surface was polished under the following conditions. (Polishing conditions) Polishing machine: Manufactured by Nanofactor Co., Ltd., NF-300CMP Polishing pad: Manufactured by Nitto Denko Corporation, 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) For the wafer after polishing, the surface roughness of the polished surface was measured using an atomic force microscope under the following conditions. Atomic force microscope: SPM-9700HT manufactured by Shimadzu Corporation Cantilever: Manufactured by OLYMPUS, MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: Five arbitrary fields per wafer after polishing were observed (observation range per field: 3 μm × 3 μm). At five observation fields (five fields) on the wafer polishing surface, the surface roughness x i (nm) was determined, and the root mean square of the surface roughness x i (nm) in the five fields obtained by the following formula was defined as the polishing surface roughness Rms (nm). When the polishing surface roughness was measured by the above method, if the polishing surface roughness was 10.0 nm or less, the polishability was judged to be good, and if the polishing surface roughness was more than 10.0 nm, the polishability was judged to be poor.

[0123]

Table 1

[0124]

Table 2

[0125] From Table 1, in Examples 1 to 3, as a method for producing sulfonic acid-modified colloidal silica, (i) a raw material colloidal silica containing silica particles with a BET specific surface area of 70 to 500 m 2 / g and a silanol group density of 7.0 to 20.0 per nm 2 is contacted with a silane coupling agent containing a mercapto group for modification treatment, and then further contacted with hydrogen peroxide to oxidize the mercapto group introduced on the surface of the silica particles to convert it into a sulfo group. (ii) The contact amount of the silane coupling agent containing the 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) When the silane coupling agent containing the mercapto group is contacted with the raw material colloidal silica, the silane coupling agent is diluted with methanol at a mass ratio dilution factor of 3 to 50 times. (iv) The addition amount of the hydrogen peroxide is 3.50 to 10.00 mol per 1 mol of the contact amount of the silane coupling agent containing the mercapto group. (v) After contacting with the hydrogen peroxide, the obtained mixture is heated at a temperature of 80.0 °C or higher for 15 hours or more. It can be seen that it is such a product.

[0126] Therefore, from Table 2, the sulfonic acid-modified colloidal silica obtained in Examples 1 to 3 has a sulfur content in the silica particles of 700 mass ppm or more and less than 3000 mass ppm per 1 g of the silica particles, a sulfur content in the solvent of 250 mass ppm or less per 1 g of the solvent, and a content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles of 10,000,000 particles / mL or less when the silica particle concentration is 1 mass%. It can be seen that even when used for polishing a semiconductor wafer provided with a silicon nitride film, a polishing surface with high flatness can be formed at a high speed.

[0127] On the one hand, from Table 1, in Comparative Examples 1 to 5, as methods for producing sulfonic acid-modified colloidal silica, (i) colloidal silica raw materials with a silanol group density outside the predetermined range were used (Comparative Examples 1 to 5), (ii) the contact amount of the silane coupling agent containing a mercapto group per 1 g of the raw material colloidal silica in terms of solid content was outside the predetermined range (Comparative Examples 1 to 3), (iii) when the silane coupling agent containing a mercapto group was brought into contact with the raw material colloidal silica, the silane coupling agent was not diluted with methanol (Comparative Examples 1, 2, and 5), and (iv) the contact amount of hydrogen peroxide per 1 mol of the contact amount of the silane coupling agent containing a mercapto group was outside the predetermined range (Comparative Examples 3 and 4).

[0128] Therefore, from Table 2, the sulfonic acid-modified colloidal silica obtained in Comparative Examples 1 to 5 had a sulfur content in the silica particles per 1 g of silica particles outside the predetermined range (Comparative Examples 2 and 3), a sulfur content in the solvent per 1 g of solvent exceeding the predetermined value (Comparative Examples 1 and 4), and a content of coarse particles with a particle size of 0.2 μm or more contained in the silica particles exceeding the predetermined value (Comparative Example 5). When polishing a semiconductor wafer provided with a silicon nitride film as abrasive grains for polishing, the polishing rate was low (Comparative Examples 1 to 4), and it can be seen that 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 for polishing a semiconductor wafer provided with a silicon nitride film, it is possible to provide a sulfonic acid-modified colloidal silica and a method for producing the sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface at a high speed.

Claims

1. A 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 1 g of the silica particles, The sulfur content in the solvent is 250 ppm by mass or less per 1 g of the solvent; The content of coarse particles having a particle diameter of 0.2 μm or more contained in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass.

1. A sulfonic acid-modified colloidal silica comprising:

2. A method for producing the sulfonic acid modified colloidal silica according to claim 1, comprising the steps of: (i) BET specific surface area is 70 to 500 m ２ / g and the silanol group density is 7.0 to 20.0 / nm ２ the step of contacting a raw material colloidal silica containing silica particles represented by the formula (I) with a silane coupling agent containing a mercapto group to carry out a modification treatment, and then contacting the raw material colloidal silica with hydrogen peroxide to oxidize the mercapto group introduced on the surface of the silica particles to convert it into a sulfo group, (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 calculated as a solid content, (iii) when the silane coupling agent containing a mercapto group is brought into contact with the raw material colloidal silica, the silane coupling agent is diluted with methanol to a dilution ratio of 3 to 50 times by mass; (iv) the amount of hydrogen peroxide added is 3.50 to 10.00 mol per 1 mol of the contact amount of the silane coupling agent containing a mercapto group, (v) after contacting the hydrogen peroxide, heating the resulting mixture at a temperature of 80.0° C. or greater for 15 hours or more; 1. A method for producing sulfonic acid-modified colloidal silica, comprising the steps of:

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