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

Abstract

The present invention provides sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface even when used for polishing semiconductor wafers. This sulfonic acid-modified colloidal silica is characterized in that, in the following formula A = width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / absolute value of the arithmetic mean of the zeta potential in each silica particle, parameter A and parameter B = width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / weight-average particle diameter of silica particles, A / B is 35.0 or less.

Description

[Technical Field]

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

[0002] In semiconductor manufacturing processes, silicon nitride films (Si3N4 films), which possess high density 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 grains 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 Documents 1 to 3). The above-mentioned sulfonic acid-modified colloidal silica is said to have excellent dispersion stability of silica particles due to sulfonic acid modification, and also exhibits superior polishing speed when used as an abrasive for polishing semiconductor wafers. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-146033 [Patent Document 2] Patent No. 7697162 [Patent Document 3] Patent No. 7731017 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0008] However, in recent years, semiconductor device development has required miniaturization and increased speed, necessitating the miniaturization and stacking of wiring to achieve higher density and integration. Consequently, there is a growing demand for abrasive grains for polishing semiconductor wafers that can produce a more flat polished surface.

[0009] On the other hand, the inventors found that when sulfonic acid-modified colloidal silica described in Patent Documents 1 to 3 is used as an abrasive for polishing semiconductor wafers having a silicon nitride film, it is difficult to obtain a highly flat polished surface.

[0010] Further investigation by the inventors revealed that conventionally known sulfonic acid-modified colloidal silica described in Patent Documents 1 to 3, etc., has variations in the amount of sulfonic acid group (sulfo group (-SO3H)) modification on individual silica particles, and therefore, when used as abrasive grains for polishing semiconductor wafers, it is difficult to obtain a highly flat polished surface.

[0011] Under these circumstances, the present invention aims to provide sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface even when used for polishing semiconductor wafers, and to provide a simple method for producing said sulfonic acid-modified colloidal silica. [Means for solving the problem]

[0012] In order to solve the above technical problems, the inventors of the present invention have conducted intensive studies. As a result, it has been found that sulfonic acid-modified colloidal silica, wherein the ratio A / B (half-value width of the zeta potential distribution at pH 3 measured by electrophoresis / absolute value of the arithmetic mean of the zeta potential of each silica particle) and parameter B (half-value width of the cumulative number particle size distribution of silica particles measured by centrifugal sedimentation method / weight average particle diameter of silica particles) defined by the following can solve the above problems, and 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 provides: (1) Sulfonic acid-modified colloidal silica, wherein the parameter A calculated by the following formula (I) A = half-value width of the zeta potential distribution at pH 3 measured by electrophoresis / absolute value of the arithmetic mean of the zeta potential of each silica particle (I) and the parameter B calculated by the following formula (II) B = half-value width of the cumulative number particle size distribution of silica particles measured by centrifugal sedimentation method / weight average particle diameter of silica particles (II) satisfy the following condition: A / B ≤ 35.0 Sulfonic acid-modified colloidal silica characterized by the above. (2) The sulfonic acid-modified colloidal silica according to (1) above, wherein D90 / D50 calculated by the following formula (III) D90 / D50 = particle diameter D90 at 90% of the integrated particle size from the small particle side in the cumulative number particle size distribution of silica particles / particle diameter D50 at 50% of the integrated particle size from the small particle side in the cumulative number particle size distribution of silica particles (III) is 1.1 to 3.0. (3) The sulfonic acid-modified colloidal silica according to (1) above, wherein the content of coarse particles having a particle diameter of 0.2 μm or more in the silica particles is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. (4) The sulfonic acid-modified colloidal silica according to (1) above, wherein the total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese and cobalt is 1 ppm by mass or less. (5) A method for producing the sulfonic acid-modified colloidal silica according to (1) above, (i) with respect to raw material colloidal silica having a pH of 6.0 to 10.0, (ii) at a liquid temperature of 20 to 80°C, a silane coupling agent containing a mercapto group is added at a flow rate of 10 to 300 mol / h / cm so that the pH fluctuation range with respect to the pH of the raw material colloidal silica is ±0.5 or less, and after performing a modification treatment, 2 (iii) further contacting with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles constituting the raw material colloidal silica and convert them into sulfonic groups. (iii) further contacting with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles constituting the raw material colloidal silica and convert them into sulfonic groups. A method for producing sulfonic acid-modified colloidal silica, characterized by the above. It is provided.

Advantages of the Invention

[0014] According to the present invention, even when used for polishing a semiconductor wafer, it is possible to provide sulfonic acid-modified colloidal silica capable of forming a highly flat polished surface, and a method for easily producing the sulfonic acid-modified colloidal silica can be provided.

Brief Description of the Drawings

[0015] [Figure 1] It is a diagram showing a zeta potential distribution spectrum in an example of the sulfonic acid-modified colloidal silica according to the present invention.

Embodiments for Carrying Out the Invention

[0016] First, the sulfonic acid-modified colloidal silica according to the present invention will be described. The sulfonic acid-modified colloidal silica according to the present invention is, Sulfonic acid-modified colloidal silica, wherein the following formula (I) A = Full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / Absolute value of the arithmetic mean of the zeta potential in each silica particle (I) The parameter A calculated by the following formula (II) B = Full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / Weight-average particle diameter of silica particles (II) In parameter B calculated by, A / B is 35.0 or less. It is characterized by the following:

[0017] The sulfonic acid-modified colloidal silica according to the present invention is obtained by dispersing silica particles constituting colloidal silica, to which sulfo groups (-SO3H) are immobilized, in a solvent.

[0018] The presence of sulfonic acid-modified colloidal silica according to the present invention, which contains sulfonic acid-modified silica particles, can be confirmed by X-ray photoelectron spectroscopy (XPS).

[0019] The sulfonic acid-modified colloidal silica according to the present invention preferably has a sulfur content of 700 ppm by mass or more and less than 3000 ppm by mass per gram of silica particles, more preferably 705 ppm by mass or more and 2995 ppm by mass or less, and even more preferably 710 ppm by mass or more and 2990 ppm by mass or less.

[0020] 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 polishing properties even when used for polishing semiconductor wafers.

[0021] 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.

[0022] (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.

[0023] In the sulfonic acid-modified colloidal silica according to the present invention, parameter A is given by the following formula (I) A = Full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / Absolute value of the arithmetic mean of the zeta potential in each silica particle (I) It is calculated by [this method].

[0024] Here, the zeta potential mentioned above refers to the potential of the liquid surface (slip surface) that moves in conjunction with the surface of particles dispersed in the liquid. The surfaces of particles dispersed in a liquid are usually positively or negatively charged. However, directly measuring the surface potential of particles is difficult, so the zeta potential is used as a potential with properties that can substitute for the surface potential.

[0025] In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis," which defines parameter A, is preferably 150 mV or less, and more preferably 130 mV or less. In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis," which defines parameter A, is suppressed to a value below the above upper limit. This makes it easy to homogenize the amount of sulfonic acid group (sulfo group (-SO3H)) modification to each silica particle, improving the dispersion stability of the silica particles, reducing the amount of aggregated particles (amount of coarse particles), and improving the flatness of the polished surface when used for polishing semiconductor wafers.

[0026] In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis," which defines parameter A, is not particularly limited, but is preferably 10 mV or greater. The half-width of the zeta potential distribution described above is preferable to a smaller value, as a smaller value indicates a more uniform amount of sulfonic acid group (sulfo group (-SO3H)) modification to each silica particle.

[0027] In this application, the full width at half maximum of the zeta potential distribution at pH 3, as measured by electrophoresis, which defines parameter A, refers to the value measured by the following method. <Method for measuring the full width at half maximum of the zeta potential distribution> (1) Dilute the sulfonic acid-modified colloidal silica to be measured with a 10 mM NaCl aqueous solution so that the silica concentration is 1.0% by mass. (2) Add 0.1 M hydrochloric acid or 0.1 M sodium hydroxide aqueous solution to the diluted solution obtained in (1) to obtain a measurement solution adjusted to pH 3. (3) The zeta potential of the measurement solution adjusted to pH 3 obtained in (2) is measured by electrophoresis using the zeta potential, particle size, and molecular weight measurement system "ELS-Z2" manufactured by Otsuka Electronics Co., Ltd. (4) Based on the measurement results in (3), a zeta potential distribution spectrum is obtained with the horizontal axis representing the zeta potential and the vertical axis representing the intensity (frequency of silica particles constituting sulfonic acid-modified colloidal silica). (5) In the zeta potential distribution spectrum obtained in (4), the spectral width at half the intensity value of the maximum intensity value is determined as the full width at half maximum of the zeta potential.

[0028] Figure 1 shows the zeta potential distribution spectrum obtained by the method described above for an example of sulfonic acid-modified colloidal silica according to the present invention. As shown in Figure 1, in this application, the maximum intensity value I in the zeta potential distribution spectrum M Half the intensity value I 1 / 2M The spectral width at this point is determined as the full width at half maximum of the zeta potential.

[0029] In the sulfonic acid-modified colloidal silica according to the present invention, the absolute value of the arithmetic mean of the zeta potential in each silica particle constituting the sulfonic acid-modified colloidal silica, which defines parameter A, is preferably 100 mV or less, and more preferably 90 mV or less.

[0030] In the sulfonic acid-modified colloidal silica according to the present invention, the absolute value of the arithmetic mean of the zeta potential in each silica particle constituting the sulfonic acid-modified colloidal silica, which defines parameter A, is less than or equal to the above upper limit. As a result, even when used for polishing semiconductor wafers, the polished surface is not over-removed, and a polished surface with improved flatness can be easily formed.

[0031] In the sulfonic acid-modified colloidal silica according to the present invention, the absolute value of the arithmetic mean of the zeta potential in each silica particle constituting the sulfonic acid-modified colloidal silica, which defines parameter A, is preferably 10 mV or more, and more preferably 15 mV or more.

[0032] In the sulfonic acid-modified colloidal silica according to the present invention, the absolute value of the arithmetic mean of the zeta potential in each silica particle constituting the sulfonic acid-modified colloidal silica, which defines parameter A, is greater than or equal to the above lower limit. This enhances the dispersion stability of each silica particle constituting the sulfonic acid-modified colloidal silica, making it less likely for aggregated particles (coarse particles) to form, and also makes it easy to improve the flatness of the polished surface.

[0033] In this application, the zeta potential and its arithmetic mean in each silica particle constituting the sulfonic acid-modified colloidal silica, which define parameter A, can be measured and calculated simultaneously when measuring the "full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis" as described above.

[0034] As illustrated in Figure 1, each silica particle constituting sulfonic acid-modified colloidal silica can have either a negative or positive zeta potential. In this application, the zeta potential values ​​of each silica particle, which define parameter A, are summed up, the arithmetic mean value is obtained by dividing the resulting sum by the number of particles, and the absolute value of this arithmetic mean value is calculated to determine the "absolute value of the arithmetic mean value of the zeta potential in each silica particle."

[0035] The sulfonic acid-modified colloidal silica according to the present invention is of the following formula (I) A = Full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / Absolute value of the arithmetic mean of the zeta potential in each silica particle (I) The parameter A calculated by this method is preferably 7.0 or less, and more preferably 6.5 or less.

[0036] In the sulfonic acid-modified colloidal silica according to the present invention, by setting parameter A to a value less than or equal to the above upper limit, the amount of sulfonic acid group (sulfo group (-SO3H)) modification to each silica particle can be easily made uniform, improving the dispersion stability of the silica particles, reducing the amount of aggregated particles (amount of coarse particles), and improving the flatness of the polished surface when used for polishing semiconductor wafers.

[0037] The sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but it is suitable if the above parameter A is 0.1 or higher. A smaller value for parameter A means that the amount of sulfonic acid group (sulfo group (-SO3H)) modification on each silica particle is uniform, so a smaller value is preferable.

[0038] In the sulfonic acid-modified colloidal silica according to the present invention, parameter A is defined as described above by "the full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / the absolute value of the arithmetic mean of the zeta potential in each silica particle constituting the sulfonic acid-modified colloidal silica," and serves as an indicator of the extent of modification of sulfonic acid groups (sulfo groups (-SO3H)) per silica particle (to determine whether the modification amount is uniform or not). For example, even if the "full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis" is the same 50mV, comparing the case where the "absolute value of the arithmetic mean of the zeta potential in each silica particle constituting sulfonic acid-modified colloidal silica" is small (10mV) and the case where it is large (100mV), generally, the degree of spread of the zeta potential distribution relative to the center of the zeta potential is wider when the "absolute value of the arithmetic mean of the zeta potential in each silica particle constituting sulfonic acid-modified colloidal silica" is small (10mV). Therefore, the full width at half maximum of the zeta potential distribution is insufficient as an indicator of the extent of modification of sulfonic acid groups (sulfo groups (-SO3H)) per silica particle. In this invention, a parameter A is introduced, which is obtained by dividing the full width at half maximum of the zeta potential distribution by the absolute value of the arithmetic mean of the zeta potential.

[0039] The sulfonic acid-modified colloidal silica according to the present invention preferably has a ratio (absolute value of Z90 / absolute value of Z50) of the absolute value of the zeta potential Z90 of silica particles at the cumulative 90% from the positive potential side in the cumulative particle size distribution of the zeta potential distribution to the absolute value of the zeta potential Z50 of silica particles at the cumulative 50% from the positive potential side in the cumulative particle size distribution of the cumulative particle size distribution of the zeta potential distribution of 50% of the cumulative particle size distribution of 50% from the positive potential side, of 50 or less, more preferably 45 or less, and even more preferably 40 or less.

[0040] In the sulfonic acid-modified colloidal silica according to the present invention, the absolute value of Z90 / the absolute value of Z50 is less than or equal to the upper limit, which reduces the proportion of silica particles with excessively high zeta potentials. When used for polishing semiconductor wafers, this makes it easy to suppress deterioration of the flatness of the polished surface due to over-polishing.

[0041] In the sulfonic acid-modified colloidal silica according to the present invention, the absolute value of Z90 / the absolute value of Z50 is not particularly limited, but it is appropriate that it be 5 or more. In the sulfonic acid-modified colloidal silica according to the present invention, the closer the absolute value of Z90 / Z50 is to 1, the less silica particles have an excessive amount of sulfonic acid group (sulfo group (-SO3H)) modification. Therefore, a value closer to 1 is preferable.

[0042] In this application, "Z90" and "Z50" can be measured simultaneously when measuring the "full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis."

[0043] As illustrated in Figure 1, each silica particle constituting sulfonic acid-modified colloidal silica can have either a negative or positive zeta potential. In this application, as illustrated in Figure 1, by determining the absolute value of the zeta potential Z90 of silica particles at 90% of the cumulative number-particle-size distribution from the positive potential side and the absolute value of the zeta potential Z50 of silica particles at 50% of the cumulative number-particle-size distribution from the positive potential side, The above calculation will be performed by dividing the absolute value of Z90 by the absolute value of Z50.

[0044] In the sulfonic acid-modified colloidal silica according to the present invention, parameter B is given by the following formula (II) B = Full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / Weight-average particle diameter of silica particles (II) It is calculated by [this method].

[0045] In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation," which defines parameter B, is preferably 120 nm or less, more preferably 110 nm or less, and even more preferably 100 nm or less.

[0046] In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation," which defines parameter B, is less than or equal to the above upper limit, thereby enabling the easy formation of a highly flat polished surface when used for polishing semiconductor wafers.

[0047] In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation," which defines parameter B, is preferably 3 nm or more, and more preferably 6 nm or more. In the sulfonic acid-modified colloidal silica according to the present invention, the "full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation," which defines parameter B, is greater than or equal to the above lower limit. This allows for an improvement in polishing speed while maintaining the flatness of the polished surface when used for polishing semiconductor wafers.

[0048] In this application, the parameter B, defined as "the full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation," refers to the value measured by the following method. <Method for measuring the half-width of the cumulative particle size distribution of silica particles constituting sulfonic acid-modified colloidal silica> (1) Dilute the sulfonic acid-modified colloidal silica solution to be measured with ultrapure water to a concentration of 0.8% by mass. (2) The diluted solution obtained in (1) is used as the measurement sample, and the cumulative particle size distribution of silica particles in the measurement sample is measured using a disk centrifugal particle size analyzer (DC24000UHR). (3) This can be measured by determining the width of the particle size distribution when it is half the value of the peak frequency of the particle size distribution in the cumulative particle size distribution of silica particles described above. If there are multiple peaks in the particle size distribution, the full width at half maximum of the largest peak is determined.

[0049] In the sulfonic acid-modified colloidal silica according to the present invention, the weight-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is preferably 150 nm or less, more preferably 145 nm or less, and even more preferably 140 nm or less.

[0050] In the sulfonic acid-modified colloidal silica according to the present invention, the weight-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is less than or equal to the above upper limit, so that when used for polishing semiconductor wafers, the flatness of the polished surface can be easily improved.

[0051] In the sulfonic acid-modified colloidal silica according to the present invention, the weight-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is preferably 8 nm or more, and more preferably 10 nm or more. Because the weight-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is greater than or equal to the above lower limit, when used for polishing semiconductor wafers, the polishing speed can be easily increased while maintaining the flatness of the polished surface.

[0052] In this application, the weight-average particle size of the silica particles constituting the sulfonic acid-modified colloidal silica refers to the value measured using a disk centrifugal particle size analyzer (DC24000UHR, manufactured by CPS Instruments).

[0053] The sulfonic acid-modified colloidal silica according to the present invention is of the following formula (II) B = Full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / Weight-average particle diameter of silica particles (II) The parameter B calculated by this method is preferably 1.0 or less, and more preferably 0.8 or less.

[0054] In the sulfonic acid-modified colloidal silica according to the present invention, by taking a value of parameter B that is less than or equal to the above upper limit, the flatness of the polished surface can be easily improved when used for polishing semiconductor wafers.

[0055] The sulfonic acid-modified colloidal silica according to the present invention is not particularly limited, but one in which the above parameter B is 0.1 or higher is suitable. In the sulfonic acid-modified colloidal silica according to the present invention, by taking a value of parameter B equal to or greater than the above lower limit, when used for polishing semiconductor wafers, the polishing speed can be easily increased while maintaining the flatness of the polished surface.

[0056] In the sulfonic acid-modified colloidal silica according to the present invention, parameter B is defined as "the half-width of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / the weight-average particle diameter of the silica particles," as described above, and serves as an indicator of the extent of the particle size distribution of colloidal silica. For example, even if the "full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation" is the same 50 nm, when comparing the case where the "weight-average particle diameter of silica particles" is small (10 nm) and the case where it is large (100 nm), generally, the degree of spread of the particle size distribution relative to the average particle diameter is wider when the "weight-average particle diameter of silica particles" is small (10 nm). Therefore, the full width at half maximum of the particle size distribution is insufficient as an indicator of the extent of the particle size distribution of colloidal silica. In this invention, a parameter B is introduced, which is obtained by dividing the full width at half maximum of the particle size distribution by the weight-average particle diameter of the silica particles.

[0057] In the sulfonic acid-modified colloidal silica according to the present invention, the number-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is preferably 150 nm or less, more preferably 140 nm or less, and even more preferably 130 nm or less.

[0058] In the sulfonic acid-modified colloidal silica according to the present invention, the number-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is less than or equal to the above upper limit, so that when used for polishing semiconductor wafers, the flatness of the polished surface can be easily improved.

[0059] In the sulfonic acid-modified colloidal silica according to the present invention, the number-average particle diameter of the silica particles constituting the sulfonic acid-modified colloidal silica is preferably 8 nm or more, and more preferably 10 nm or more. Because the number-average particle size of the silica particles constituting sulfonic acid-modified colloidal silica is greater than or equal to the above lower limit, when used for polishing semiconductor wafers, the polishing speed can be easily increased while maintaining the flatness of the polished surface.

[0060] In this application, the number-average particle size of the silica particles constituting sulfonic acid-modified colloidal silica refers to the value measured using a disk centrifugal particle size analyzer (DC24000UHR, manufactured by CPS Instruments).

[0061] In the sulfonic acid-modified colloidal silica according to the present invention, the ratio of the weight-average particle diameter to the number-average particle diameter (weight-average particle diameter / number-average particle diameter) of the silica particles constituting the sulfonic acid-modified colloidal silica is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.6 or less.

[0062] In the sulfonic acid-modified colloidal silica according to the present invention, the ratio of the weight-average particle diameter to the number-average particle diameter (weight-average particle diameter / number-average particle diameter) of the silica particles constituting the sulfonic acid-modified colloidal silica is less than or equal to the above upper limit, thereby easily improving the flatness of the polished surface when used for polishing semiconductor wafers.

[0063] In the sulfonic acid-modified colloidal silica according to the present invention, the ratio of the weight-average particle diameter to the number-average particle diameter (weight-average particle diameter / number-average particle diameter) of the silica particles constituting the sulfonic acid-modified colloidal silica is preferably 1.0 or higher.

[0064] In the sulfonic acid-modified colloidal silica according to the present invention, the ratio of the weight-average particle diameter to the number-average particle diameter (weight-average particle diameter / number-average particle diameter) of the silica particles constituting the sulfonic acid-modified colloidal silica is greater than or equal to the above lower limit. Therefore, when used for polishing semiconductor wafers, the polishing speed can be easily increased while maintaining the flatness of the polished surface.

[0065] The sulfonic acid-modified colloidal silica according to the present invention has an A / B ratio defined by the above parameter A (full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / absolute value of the arithmetic mean of the zeta potential in each silica particle) and the above parameter B (full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / weight-average particle diameter of silica particles) of 35.0 or less, preferably 33.0 or less, and more preferably 31.0 or less.

[0066] The sulfonic acid-modified colloidal silica according to the present invention has a ratio of A / B defined by the above-mentioned parameters A and B that is below the above-mentioned upper limit. This allows for easy homogenization of the amount of sulfonic acid group (sulfo group (-SO3H)) modification to each silica particle, improving the dispersion stability of the silica particles, reducing the amount of aggregated particles (amount of coarse particles), and improving the flatness of the polished surface when used for polishing semiconductor wafers.

[0067] The sulfonic acid-modified colloidal silica according to the present invention is preferably one in which the A / B ratio, defined by the above-mentioned parameters A and B, is 1.0 or greater. The half-width of the zeta potential distribution described above is preferable to a smaller value, as a smaller value indicates a more uniform amount of sulfonic acid group (sulfo group (-SO3H)) modification to each silica particle.

[0068] In the sulfonic acid-modified colloidal silica according to the present invention, parameter A itself corresponds to an index for determining whether the amount of sulfonic acid group (sulfo group (-SO3H)) modification is uniform for each silica particle. However, since parameter A is determined by the zeta potential measured by electrophoresis, the electrophoretic velocity at the time of measurement will fluctuate depending on the spread of the particle size distribution of the silica particles. Therefore, in this invention, "A / B" is introduced as a variable obtained by dividing parameter A by parameter B, and by controlling "A / B" within a predetermined range, the influence of the particle size distribution of silica particles on the electrophoretic speed is suppressed.

[0069] The sulfonic acid-modified colloidal silica according to the present invention has a ratio of "A / B" (parameter A divided by parameter B) of less than or equal to a predetermined value, which allows for uniform modification of sulfonic acid groups (sulfo groups (-SO3H)) to individual silica particles. As a result, when used as an abrasive for polishing semiconductor wafers, it provides a uniform effect on the polished surface, making it easier to polish flat. Furthermore, it suppresses the formation of coarse particles (described later) formed by the aggregation of silica secondary particles, making it easy to form a flat polished surface.

[0070] The sulfonic acid-modified colloidal silica according to the present invention is of the following formula (III) In the cumulative particle size distribution of silica particles, the particle size D90 represents 90% of the cumulative particle size distribution from the smallest particle side / the particle size D50 represents 50% of the cumulative particle size distribution of silica particles from the smallest particle side (III) The D90 / D50 calculated by this method is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.5 or less.

[0071] The sulfonic acid-modified colloidal silica according to the present invention has a D90 / D50 ratio calculated by formula (III) above that is below the upper limit, which allows for easy improvement of the polishing speed while maintaining the flatness of the polished surface when used for polishing semiconductor wafers.

[0072] The sulfonic acid-modified colloidal silica according to the present invention is of the following formula (III) In the cumulative particle size distribution of silica particles, the particle size D90 represents 90% of the cumulative particle size distribution from the smallest particle side / the particle size D50 represents 50% of the cumulative particle size distribution of silica particles from the smallest particle side (III) The D90 / D50 calculated by this method is preferably 1.0 or greater, more preferably 1.1 or greater, and even more preferably 1.2 or greater.

[0073] The sulfonic acid-modified colloidal silica according to the present invention has a D90 / D50 ratio calculated by formula (III) above that is equal to or greater than the lower limit, which allows for easy improvement of the polishing speed while maintaining the flatness of the polished surface when used for polishing semiconductor wafers.

[0074] In this application, the particle size D90 representing 90% of the cumulative particle size distribution from the smallest particle side in the cumulative particle size distribution of silica particles constituting sulfonic acid-modified colloidal silica, and the particle size D50 representing 50% of the cumulative particle size distribution from the smallest particle side in the cumulative particle size distribution of silica particles, refer to values ​​measured by the following method. <Method for measuring particle size D90 (90% of the cumulative particle size distribution from the smallest particle side) and particle size D50 (50% of the cumulative particle size distribution) in the cumulative particle size distribution of silica particles constituting sulfonic acid-modified colloidal silica> (1) Dilute the sulfonic acid-modified colloidal silica solution to be measured with ultrapure water to a concentration of 0.8% by mass. (2) The diluted solution obtained in (1) is used as the measurement sample, and the particle size distribution of silica particles in the measurement sample is measured using a disk centrifugal particle size analyzer (DC24000UHR). (3) In the particle size distribution of the silica particles described above, D90 is determined as the cumulative 90% value from the smallest particle side in the cumulative particle size distribution, and D50 is determined as the cumulative 50% value.

[0075] 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.

[0076] 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

[0077] 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 and secondary silica particles formed by association of these primary silica particles dispersed in a solvent. Therefore, the sulfonic acid-modified colloidal silica according to the present invention corresponds to silica particles dispersed in the above colloidal silica with a sulfo group (-SO3H) immobilized on them.

[0078] 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 200 nm or less.

[0079] The average primary 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 150 nm or less, and even more preferably 100 nm or less.

[0080] 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.

[0081] 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, and more preferably 10 nm or more.

[0082] 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 while maintaining flatness.

[0083] 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].

[0084] The sulfonic acid-modified colloidal silica according to the present invention may contain secondary particles (silica secondary particles) formed by the association of primary silica particles. The silica secondary particles contained in the sulfonic acid-modified colloidal silica according to the present invention, together with the 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.

[0085] 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 300 nm or less.

[0086] The average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica according to the present invention is preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 150 nm or less.

[0087] 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.

[0088] 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 10 nm or more.

[0089] 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 while maintaining flatness.

[0090] 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.

[0091] In the sulfonic acid-modified colloidal silica according to the present invention, the following formula Degree of association of silica particles = Average secondary particle diameter (nm) of silica particles contained in sulfonic acid-modified colloidal silica ÷ Average primary particle diameter (nm) of silica particles contained in sulfonic acid-modified colloidal silica The degree of association of silica particles calculated by this method is preferably between 1.2 and 3.0.

[0092] In the sulfonic acid-modified colloidal silica according to the present invention, the degree of association of silica particles contained in the sulfonic acid-modified colloidal silica is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.2 or less. In the sulfonic acid-modified colloidal silica according to the present invention, the degree of association of silica particles contained in the sulfonic acid-modified colloidal silica is less than or equal to the above value (upper limit), which makes it easier to improve the flatness of the polished surface when the sulfonic acid-modified colloidal silica according to the present invention is used as an abrasive grain for polishing.

[0093] In the sulfonic acid-modified colloidal silica according to the present invention, the degree of association of silica particles contained in the sulfonic acid-modified colloidal silica is preferably 1.2 or higher, more preferably 1.3 or higher, and even more preferably 1.5 or higher. In the sulfonic acid-modified colloidal silica according to the present invention, the degree of association of silica particles contained in the sulfonic acid-modified colloidal silica is equal to or greater than the above value (lower limit), so when the sulfonic acid-modified colloidal silica according to the present invention is used as an abrasive grain for polishing, a high polishing speed can be easily achieved while maintaining the flatness of the polished surface.

[0094] In the sulfonic acid-modified colloidal silica according to the present invention, the following formula The average secondary particle diameter D2 (nm) of silica particles contained in sulfonic acid-modified colloidal silica ÷ the number-average particle diameter Dn (nm) of silica particles contained in sulfonic acid-modified colloidal silica The value calculated by (D2 / Dn) is preferably 2.2 or less, and more preferably 2.0 or less. In the sulfonic acid-modified colloidal silica according to the present invention, the ratio of the average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica to the number-average particle diameter (D2 / Dn) is less than or equal to the above value (upper limit), which makes it easier to improve the flatness of the polished surface when the sulfonic acid-modified colloidal silica according to the present invention is used as an abrasive grain for polishing.

[0095] In the sulfonic acid-modified colloidal silica according to the present invention, the average secondary particle diameter ÷ number-average particle diameter (D2 / Dn) of the silica particles contained in the sulfonic acid-modified colloidal silica is preferably 1.0 or higher, and more preferably 1.1 or higher. In the sulfonic acid-modified colloidal silica according to the present invention, the ratio of the average secondary particle diameter of the silica particles contained in the sulfonic acid-modified colloidal silica to the number-average particle diameter (D2 / Dn) is equal to or greater than the above value (lower limit). Therefore, when the sulfonic acid-modified colloidal silica according to the present invention is used as an abrasive grain for polishing, a high polishing speed can be easily achieved while maintaining the flatness of the polished surface.

[0096] 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 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.

[0097] 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.

[0098] 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).

[0099] 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 method using the particle counting method described below.

[0100] <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

[0101] 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.

[0102] 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 the pH of the sulfonic acid-modified colloidal silica according to the present invention be 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.

[0103] 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.

[0104] 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.).

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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 35% 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.

[0109] 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.

[0110] The sulfonic acid-modified colloidal silica according to the present invention may contain metal impurities.

[0111] 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, and cobalt.

[0112] 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.

[0113] In this application, the content of each metal component constituting the metal impurity and the total content refer to values ​​obtained by measuring the content of each metal component using an atomic absorption spectrometer.

[0114] The sulfonic acid-modified colloidal silica according to the present invention can be suitably prepared by the production method according to the present invention, which will be described later.

[0115] According to the present invention, it is possible to provide sulfonic acid-modified colloidal silica that can form a highly flat polished surface even when used for polishing semiconductor wafers provided with a silicon nitride film.

[0116] 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: (i) For colloidal silica raw material with a pH of 6.0 to 10.0, (ii) At a liquid temperature of 20 to 80°C, the flow rate is 10 to 300 mol / h / cm such that the pH fluctuation range relative to the pH of the raw material colloidal silica is ±0.5 or less. 2 After adding a silane coupling agent containing a mercapto group and performing a modification treatment, (iii) Further contact with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles constituting the raw material colloidal silica and convert them into sulfo groups. It is characterized by the following:

[0117] (Colloidal silica as raw material) In the method for producing sulfonic acid-modified colloidal silica according to the present invention, a raw material colloidal silica having a pH of 6.0 to 10.0 is used.

[0118] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw material colloidal silica can be appropriately selected from colloidal silica having desired properties produced by known production methods, for example, colloidal silica having desired properties produced by the sol-gel method. In the method for producing sulfonic acid-modified colloidal silica according to the present invention, if the raw material colloidal silica is colloidal silica produced by the sol-gel method, it can be suitably used because it contains a low amount of metal impurities that are diffusible into semiconductors and corrosive ions such as chloride ions.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] Silicon compounds represented by general formula (1) or their derivatives undergo hydrolysis and condensation in the reaction solvent to form colloidal silica.

[0125] Examples of reaction solvents used when silicon compounds represented by general formula (1) or their derivatives undergo hydrolysis and condensation reactions 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).

[0126] The amount of the above organic solvent used is not particularly limited, but it is preferable to use 5 moles or more and 50 moles or less per mole of the silicon compound or its 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.

[0127] 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 into 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.

[0128] For the hydrolysis condensation reaction of silicon compounds to obtain colloidal silica, it is preferable to adjust the reaction solvent to be alkaline in the presence of a basic catalyst. Through the above adjustments, the reaction solvent is preferably controlled to a pH of 8.0 to 11.0, more preferably 8.5 to 10.5, allowing for the rapid formation of colloidal silica.

[0129] To hydrolyze and condense a silicon compound in a reaction solvent, the silicon compound represented by general formula (1) or a derivative thereof should be added to an organic solvent and stirred at a temperature of typically 0°C to 100°C, preferably 0°C to 50°C.

[0130] By stirring a silicon compound in a water-containing solvent, hydrolysis and dehydration condensation reactions proceed of the silicon compound or its derivative represented by general formula (1). First, the silicon compound or its derivative represented by general formula (1) undergoes dehydration condensation to form a dimer, and this dimer undergoes polymerization (oligomerization) to form spherical silica primary particles in the solvent, thereby obtaining colloidal silica in which silica primary particles are dispersed in the solvent. Colloidal silica with uniform silica particle size can be obtained by hydrolyzing and condensing a silicon compound while stirring it in a water-containing solvent.

[0131] The colloidal silica obtained by the above hydrolysis-condensation reaction (sol-gel method) can be used as a raw material colloidal silica in the production method of the present invention by adjusting its concentration as appropriate.

[0132] Method for producing sulfonic acid-modified colloidal silica according to the present invention In this process, the pH of the raw material colloidal silica is 6.0 to 10.0, preferably 6.3 to 9.9, and more preferably 6.5 to 9.8.

[0133] Method for producing sulfonic acid-modified colloidal silica according to the present invention By using colloidal silica as the raw material with a pH within the above range, the reaction rate of the silane coupling agent having a mercapto group described later can be controlled, whereby sulfonic acid groups (sulfonic groups (-SO3H)) can be uniformly modified on individual silica particles.

[0134] (Modification treatment with a silane coupling agent containing a mercapto group) In the method for producing sulfonic acid-modified colloidal silica according to the present invention, a silane coupling agent containing a mercapto group is added to the above raw material colloidal silica for modification treatment.

[0135] 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, for example, 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the like.

[0136] The addition rate of the silane coupling agent containing a mercapto group to the above raw material colloidal silica is preferably a flow rate of 10 to 300 mol / h / cm 2 more preferably a flow rate of 15 to 280 mol / h / cm 2 even more preferably a flow rate of 20 to 260 mol / h / cm 2 and even more preferably.

[0137] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, by controlling the rate of addition of the silane coupling agent containing the mercapto group to the raw material colloidal silica within the above range, the diffusivity of the silane coupling agent containing the mercapto group to the raw material colloidal silica can be controlled, thereby enabling the uniform modification of individual silica particles with sulfonic acid groups (sulfo groups (-SO3H)) regardless of the amount of silica particles to be reacted. If the addition rate of the silane coupling agent containing mercapto groups to the colloidal silica raw material is below the lower limit of the above range, the silane coupling agent containing mercapto groups tends to accumulate in the injection site and react locally with the silica particles. On the other hand, if the addition rate of the silane coupling agent containing mercapto groups exceeds the upper limit of the above range, it tends to react without being uniformly mixed with the individual silica particles.

[0138] The amount of silane coupling agent containing the above-mentioned mercapto group added is preferably 25.00 μmol or more and less than 100.00 μmol per 1 g of the raw material colloidal silica (per 1 g of silica particles contained in the raw material colloidal silica), calculated on a solid content basis, preferably 26.0 μmol or more and 99.0 μmol or less, and more preferably 27.0 μmol or more and 98.0 μmol.

[0139] 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.

[0140] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when adding a silane coupling agent containing a mercapto group to the raw colloidal silica, it is preferable to add the silane coupling agent containing a mercapto group so that the pH fluctuation range relative to the pH of the raw colloidal silica is ±0.5 or less, and to add the silane coupling agent containing a mercapto group so that the pH fluctuation range relative to the pH of the raw colloidal silica is ±0.4 or less.

[0141] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, by adding a silane coupling agent containing a mercapto group such that the pH fluctuation range relative to the pH of the raw material colloidal silica falls within the above range, the reaction rate when the silane coupling agent containing a mercapto group is added can be controlled to be constant.

[0142] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when adding a silane coupling agent containing a mercapto group to the raw colloidal silica, it is preferable to add the silane coupling agent containing a mercapto group to the raw colloidal silica while adding a pH adjusting agent in order to control the range of pH fluctuation relative to the pH of the raw colloidal silica within the above range.

[0143] As for the pH adjusting agent, from the viewpoint of preventing contamination with impurities, one or more selected from organic amines and ammonia are preferred, and one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, and tetramethylammonium hydroxide are particularly preferred.

[0144] 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 adding and contacting a silane coupling agent containing a mercapto group with the raw colloidal silica, it is preferable to use a raw 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.

[0145] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when contacting a silane coupling agent containing a mercapto group with a raw colloidal silica, it is preferable to contact the raw colloidal silica with the silane coupling agent while diluting it with methanol to a mass ratio of 3 to 50 times, more preferably to contact the raw colloidal silica with the silane coupling agent while diluting it with methanol to a mass ratio of 4 to 45 times, and even more preferably to contact the raw colloidal silica with the silane coupling agent while diluting it with methanol to a mass ratio of 5 to 40 times.

[0146] 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)".

[0147] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when contacting a silane coupling agent containing mercapto groups with 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 the silane coupling agent onto the silica particles constituting the raw colloidal silica.

[0148] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when a silane coupling agent containing a mercapto group is added to and brought into contact with the raw material colloidal silica to perform a modification treatment, it is preferable to add and bring into contact at a liquid temperature of 20 to 80°C, more preferably at a liquid temperature of 25 to 78°C, and even more preferably at a liquid temperature of 30 to 75°C.

[0149] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when a silane coupling agent containing a mercapto group is added to and brought into contact with the raw material colloidal silica to perform a modification treatment, the reaction rate of the coupling agent can be easily controlled by controlling the liquid temperature within the above range. If the liquid temperature exceeds the upper limit of the above range, the reaction rate of the coupling agent becomes too fast, making it difficult to uniformly modify the silica particles. If the liquid temperature is below the lower limit of the above range, the reaction of the coupling agent will not proceed easily, and it will be difficult to uniformly modify the silica particles.

[0150] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when a silane coupling agent containing a mercapto group is added to and brought into contact with the raw material colloidal silica to perform a modification treatment, the contact time (reaction time) during the above contact treatment is not particularly limited, but 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.

[0151] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, when a silane coupling agent containing mercapto groups is added to and brought into contact with the raw material colloidal silica to perform a modification treatment, the addition and contact may be performed while heat treatment is being carried out. By adding and contacting the agent while heat treatment is being carried out, hydrolysis and condensation reactions are promoted, and the silane coupling agent containing mercapto groups can be suitably fixed (chemically bonded) to the surface of the silica particles constituting the colloidal silica.

[0152] (Conversion of mercapto groups introduced to the surface of silica particles to sulfo groups) In the method for producing sulfonic acid-modified colloidal silica according to the present invention, the raw colloidal silica is subjected to a modification treatment by contacting it with a silane coupling agent containing mercapto groups (-SH), 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).

[0153] 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.

[0154] 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 a mercapto group (-SH) within the above range, the conversion from mercapto group (-SH) to sulfo group (-SO3H) can be suitably carried out.

[0155] 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.

[0156] 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).

[0157] 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 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. It is preferable to heat to a temperature of 85.0°C or higher, more preferably to a temperature of 90.0°C or higher, and even more preferably to a temperature of 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 a 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 heating the above 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.

[0158] In the method for producing sulfonic acid-modified colloidal silica according to the present invention, after contacting the reaction product of raw material colloidal silica and a silane coupling agent containing a mercapto group (-SH) with hydrogen peroxide, the heating time for 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 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.

[0159] The reaction solution obtained by contacting the above-mentioned hydrogen peroxide and heating the resulting mixture at a temperature of, for example, 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.

[0160] 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.

[0161] Details of the sulfonic acid-modified colloidal silica obtained by the manufacturing method according to the present invention are as described in the description of the sulfonic acid-modified colloidal silica according to the present invention.

[0162] According to the present invention, it is possible to provide a method for effectively producing a novel sulfonic acid-modified colloidal silica that can form a highly flat polished surface even when used for polishing semiconductor wafers. [Examples]

[0163] 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.

[0164] (Example 1) To 1000 parts by mass of colloidal silica A (pH 7.0, average secondary particle diameter 80 nm, full width at half maximum of the cumulative particle size distribution measured by centrifugal sedimentation method 20 nm, and silica particle concentration 20% by mass), 2 parts by mass of 3-mercaptopropyltrimethoxysilane (3-MPTMS) and 0.001 parts by mass of 0.01 M NH3 aqueous solution were added while maintaining the liquid temperature at 30°C. At this time, the addition rate of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was 30 mol / h / cm². 2 That's what I decided. At this time, 3-mercaptopropyltrimethoxysilane (3-MPTMS) was added so that the pH fluctuation range relative to the pH of colloidal silica A (pH 7.0) was -0.4, and the pH of the mixture after the addition of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was 6.6. Next, 35% by mass hydrogen peroxide solution was added in an amount equivalent to 4 parts by mass per 1000 parts by mass of colloidal silica A. After heating at 60°C for 5 hours, the resulting mixture was allowed to stand until it reached room temperature. Next, a water displacement procedure was performed by adding a fixed amount of water dropwise while heating the resulting mixture. When the liquid temperature reached 100°C, the water substitution was terminated, and the mixture was cooled to room temperature to obtain the desired sulfonic acid-modified colloidal silica. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the following physical properties were measured and calculated from the obtained sulfonic acid-modified colloidal silica. The results are shown in Table 3. Parameter A Parameter B A / B (Parameter A / Parameter B) • The full width at half maximum (FWHM) of the zeta potential distribution at pH 3, as measured by electrophoresis (FWHM of the zeta potential (mV)). • The absolute value of the arithmetic mean of the zeta potential in each silica particle (absolute value of the mean zeta potential (mV)) • The full width at half maximum (FWHM) of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation (FWHM of particle size distribution (nm)). • Weight-average particle diameter of silica particles (Dw (nm)) • Number-average particle size of silica particles (Dn (nm)) The ratio of the absolute value of the zeta potential Z90 of silica particles at 90% cumulatively from the positive potential side in the cumulative particle size distribution of the zeta potential distribution to the absolute value of the zeta potential Z50 of silica particles at 50% cumulatively from the positive potential side in the same cumulative particle size distribution (absolute value of Z90 / absolute value of Z50). • Particle size D90 represents 90% of the cumulative particle size distribution from the smallest particle side in the cumulative particle size distribution of silica particles / Particle size D50 represents 50% of the cumulative particle size distribution from the smallest particle side in the cumulative particle size distribution of silica particles (D90 / D50) • Content of coarse particles with a particle size of 0.2 μm or larger (LPC (≧0.20 μm), particles / mL) when the silica particle concentration is set to 1% by mass. • Weight-average particle diameter of silica particles / Number-average particle diameter of silica particles (Dw / Dn) The value (D2 / Dn) is calculated by dividing the average secondary particle diameter (nm) of the silica particles contained in sulfonic acid-modified colloidal silica by the number-average particle diameter (nm) of the silica particles contained in sulfonic acid-modified colloidal silica. • Average primary particle diameter of silica particles (D1 (nm)) • Average secondary particle diameter of silica particles (D2 (nm)) • Degree of association of silica particles (D2 / D1) • Metal impurity content (total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt (mass ppm)) • Silica particle content (mass%)

[0165] (Example 2) The addition rate of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was set to 250 mol / h / cm². 2 Except for the change, the target sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 3.

[0166] (Example 3) The desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1, except that the liquid temperature during the addition of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was changed to 70°C. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 3.

[0167] (Example 4) The desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1, except that colloidal silica A, prepared by adding a 30% by mass aqueous solution of NH3 to colloidal silica A as described in Example 1 to adjust the pH to 9.0. In this case, 3-mercaptopropyltrimethoxysilane (3-MPTMS) was added so that the pH fluctuation range relative to the pH of colloidal silica A (pH 9.0) after pH adjustment was -0.4, and the pH of the mixture after the addition of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was 8.6. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 3.

[0168] (Example 5) The desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1, except that colloidal silica B (pH 7.0, average secondary particle diameter 20 nm, full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation method 10 nm, silica particle concentration 20% by mass) was used instead of colloidal silica A. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 3.

[0169] (Example 6) The desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1, except that colloidal silica C (pH 7.0, average secondary particle diameter 140 nm, full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation method 100 nm, silica particle concentration 20% by mass) was used instead of colloidal silica A. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 3.

[0170] (Example 7) Except for changing the amount of 3-mercaptopropyltrimethoxysilane (3-MPTMS) added to 1000 parts by mass of colloidal silica A from 2 parts by mass to 10 parts by mass, the desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1. The above manufacturing conditions are shown in Table 1. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 3.

[0171] (Comparative Example 1) The addition rate of 3-mercaptopropyltrimethoxysilane (3-MPTMS) to colloidal silica A was set to 30 mol / h / cm². 2 From 400 mol / h / cm² 2Except for the change, the target sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1. The above manufacturing conditions are shown in Table 2. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 4.

[0172] (Comparative Example 2) The desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1, except that colloidal silica A, prepared by adding a 30% by mass aqueous solution of NH3 to colloidal silica A as described in Example 1 to adjust the pH to 12.0. In this case, 3-mercaptopropyltrimethoxysilane (3-MPTMS) was added so that the pH fluctuation range relative to the pH of colloidal silica A (pH 12.0) after pH adjustment was -0.4, and the pH of the mixture after the addition of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was 11.6. The above manufacturing conditions are shown in Table 2. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 4.

[0173] (Comparative Example 3) The desired sulfonic acid-modified colloidal silica was obtained by treating colloidal silica A under the same conditions as in Example 1, except that 0.1 parts by mass of a 0.01 M aqueous NH3 solution was not added, and only 3-mercaptopropyltrimethoxysilane (3-MPTMS) was added so that the pH fluctuation range relative to the pH of colloidal silica A was -0.7. The pH of the mixture obtained after adding 3-mercaptopropyltrimethoxysilane (3-MPTMS) to the above colloidal silica A (pH 7.0) was 6.3. The above manufacturing conditions are shown in Table 2. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 4.

[0174] (Comparative Example 4) The desired sulfonic acid-modified colloidal silica was obtained by processing under the same conditions as in Example 1, except that the liquid temperature during the addition of 3-mercaptopropyltrimethoxysilane (3-MPTMS) was changed to 85°C. The above manufacturing conditions are shown in Table 2. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 4.

[0175] (Comparative Example 5) Using colloidal silica A prepared by adding a 30% by mass aqueous solution of NH3 to the colloidal silica A described in Example 1 to adjust the pH to 12.0, and without adding 0.1 parts by mass of a 0.01 M aqueous solution of NH3 to the pH-adjusted colloidal silica A, only 3-mercaptopropyltrimethoxysilane (3-MPTMS) was added so that the pH fluctuation range relative to the pH of colloidal silica A was -1.0, the liquid temperature at the time of adding the 3-mercaptopropyltrimethoxysilane (3-MPTMS) was changed to 85°C, and the addition rate of the 3-mercaptopropyltrimethoxysilane (3-MPTMS) was 400 mol / h / cm². 2 Except for adding the desired compound, the material was processed under the same conditions as in Example 1 to obtain the desired sulfonic acid-modified colloidal silica. The pH of the mixture obtained after adding 3-mercaptopropyltrimethoxysilane (3-MPTMS) to the above colloidal silica A (pH 12.0) was 11.0. The above manufacturing conditions are shown in Table 2. The obtained sulfonic acid-modified colloidal silica was confirmed to contain silica particles with immobilized sulfo groups. Furthermore, the physical properties of the obtained sulfonic acid-modified colloidal silica were measured and calculated in the same manner as in Example 1. The results are shown in Table 4.

[0176] The sulfonic acid-modified colloidal silica obtained in each of the above examples and comparative examples was used as abrasive grains, and the surface roughness of the polished surface was evaluated by the following method. The results are shown in Tables 2 and 4.

[0177] <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 nitride (Si3N4) 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 Film thickness measuring instrument: Si3N4 film, optical interference type film thickness measuring instrument (Measurement conditions for surface roughness) The surface roughness of the polished wafer was measured using an atomic force microscope under the following conditions. Atomic force microscope: Shimadzu Corporation SPM-9700HT Cantilever: OLYMPUS MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning 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). JPEG0007911190000001.jpg35170 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 2.0 nm or less, and poor if the surface roughness is greater than 10.0 nm.

[0178] [Table 1]

[0179] [Table 2]

[0180] [Table 3]

[0181] [Table 4]

[0182] As shown in Table 1, in Examples 1 to 7, (i) a raw material colloidal silica with a pH of 6.0 to 10.0 was used, and (ii) under a liquid temperature of 20 to 80°C, the pH fluctuation range relative to the pH of the raw material colloidal silica was ±0.5 or less, with a flow rate of 10 to 300 mol / h / cm². 2It can be seen that sulfonic acid-modified colloidal silica is produced by (iii) first adding a silane coupling agent containing mercapto groups and performing a modification treatment, and then further contacting it with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles constituting the raw material colloidal silica and convert them into sulfo groups.

[0183] Therefore, as can be seen from Table 3, the sulfonic acid-modified colloidal silica obtained in Examples 1 to 7 has an "A / B" ratio of 35.0 or less, defined by parameters A and B, and can form a highly flat polished surface even when used to polish semiconductor wafers with silicon nitride films.

[0184] On the other hand, Table 2 shows that in Comparative Examples 1 to 5, sulfonic acid-modified colloidal silica was produced by employing manufacturing methods in which colloidal silica with a pH outside the specified range was used (Comparative Examples 2 and 5), the liquid temperature when adding the silane coupling agent containing a mercapto group to the colloidal silica was outside the specified range (Comparative Examples 4 and 5), the silane coupling agent containing a mercapto group was added in such a way that the range of pH fluctuation relative to the pH of the colloidal silica was outside the specified range (Comparative Examples 3 and 5), or the addition rate when adding the silane coupling agent containing a mercapto group to the colloidal silica was outside the specified range (Comparative Examples 1 and 5).

[0185] Therefore, as can be seen from Table 4, the sulfonic acid-modified colloidal silica obtained in Comparative Examples 1 to 5 has an "A / B" ratio greater than 35.0, defined by parameters A and B. When used to polish semiconductor wafers with silicon nitride films, it results in a high polished surface roughness (RMS) of 14.2 to 25.6, making it difficult to form a highly flat polished surface. [Industrial applicability]

[0186] According to the present invention, it is possible to provide sulfonic acid-modified colloidal silica and a method for producing sulfonic acid-modified colloidal silica that can form a highly flat polished surface even when used for polishing semiconductor wafers.

Claims

1. Sulfonic acid-modified colloidal silica, wherein the following formula (I) A = Full width at half maximum of the zeta potential distribution at pH 3 measured by electrophoresis / Absolute value of the arithmetic mean of the zeta potential in each silica particle (I) The parameter A calculated by the following formula (II) B = Full width at half maximum of the cumulative particle size distribution of silica particles measured by centrifugal sedimentation / Weight-average particle diameter of silica particles (II) In parameter B calculated by, A / B is 35.0 or less. A sulfonic acid-modified colloidal silica characterized by the following features.

2. The following formula (III) In the cumulative particle size distribution of silica particles, the particle size D90 represents 90% of the cumulative particle size distribution from the smallest particle side / the particle size D50 represents 50% of the cumulative particle size distribution of silica particles from the smallest particle side (III) The sulfonic acid-modified colloidal silica according to claim 1, wherein the D90 / D50 calculated by is 1.1 to 3.

0.

3. The sulfonic acid-modified colloidal silica according to claim 1, wherein 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.

4. The sulfonic acid-modified colloidal silica according to claim 1, wherein the total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is 1 ppm by mass or less.

5. A method for producing sulfonic acid-modified colloidal silica as described in claim 1, (i) For colloidal silica raw material with a pH of 6.0 to 10.0, (ii) At a liquid temperature of 20 to 80°C, the flow rate of 10 to 300 mol / h / cm is set such that the pH fluctuation range relative to the pH of the raw material colloidal silica is ±0.5 or less. ２ After adding a silane coupling agent containing a mercapto group and performing a modification treatment, (iii) Further contact with hydrogen peroxide to oxidize the mercapto groups introduced on the surface of the silica particles constituting the colloidal silica raw material and convert them into sulfo groups. A method for producing sulfonic acid-modified colloidal silica, characterized by the following features.

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