Colloidal silica and method for producing the same

Abstract

To provide colloidal silica with few fine particles.SOLUTION: Provided is a method for producing colloidal silica.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to colloidal silica with few fine particles.

Background Art

[0002] In the CMP (Chemical Mechanical Polishing) process in semiconductor manufacturing, the remaining fine particles on the polishing surface often become a problem. The remaining fine particles on the polishing surface lead to a deterioration in the yield in semiconductor manufacturing.

[0003] As semiconductor miniaturization progresses, it is required to further reduce the amount of fine particles remaining on the polishing surface, and accordingly, it is also required to reduce the amount of fine particles contained in the CMP slurry.

[0004] Colloidal silica is used as an abrasive raw material for CMP slurry. Usually, colloidal silica contains slightly fine particles smaller than the main particles, and these fine particles cause the problem of remaining on the polishing surface.

[0005] Conventionally, methods for producing colloidal silica with few fine particles have been disclosed (Patent Documents 1 and 2). Patent Document 1 discloses that in the hydrolysis and condensation reaction of alkoxysilane or its condensate, by adjusting the reaction conditions so that the value of the electrical conductivity does not change by more than 90% from 5 minutes after the point when the electrical conductivity first reaches a maximum after the start of the reaction until the end of the reaction, a silica sol with few fine particles can be obtained. Patent Document 2 discloses that in the hydrolysis and condensation reaction of tetraalkoxysilane, by making the change in the concentration of water in the reaction system within 3% by mass from the start to the end of the hydrolysis reaction and the condensation reaction, a silica sol with few fine particles can be obtained.

[0006] In addition, methods for subjecting the produced colloidal silica to solvent replacement treatment so that the organic solvent concentration becomes less than 1% by mass by means of heating and distillation (Patent Document 3), methods for adding a neutral oxidizing agent (Patent Document 4), and methods for reducing fine particles by performing ultrafiltration using an ultrafiltration membrane (Patent Document 5) have been disclosed. Patent Document 3 discloses that by distilling off the organic solvent coexisting with the colloidal silica so that the residual organic solvent concentration in the colloidal silica produced by the sol-gel method becomes less than 1% by mass, a colloidal silica having a number distribution ratio of fine particles having a particle size of 40% or less of the volume average particle size of 10% or less can be obtained. Patent Document 4 discloses that by adding a neutral oxidizing agent (including hydrogen peroxide) to the silica sol of the sol-gel method, a silica sol with fewer intermediate products (unreacted substances) can be obtained. Patent Document 5 discloses that the intermediate products are removed by subjecting the silica sol obtained by hydrolyzing and condensing tetraalkoxysilane to ultrafiltration using an ultrafiltration membrane with a fractional molecular weight of 5,000 to 80,000.

[0007] Even when using these conventional techniques, colloidal silica with a reduced amount of fine particles to a level that sufficiently meets the requirements of the semiconductor CMP process for advanced technology nodes has not been obtained.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention provides colloidal silica with few fine particles.

Means for Solving the Problems

[0010] As a result of intensive studies, the inventors of the present invention have developed a technique for producing colloidal silica with a low content of fine particles by including a specific heat treatment during the production process of colloidal silica.

[0011] The present invention includes the following colloidal silica and a method for producing colloidal silica.

[0012] Item 1. A method for producing colloidal silica, comprising: a step of heat-treating a silica sol composed of water and silica particles at the boiling point of water under normal pressure The method for producing colloidal silica according to claim 1, comprising:

[0013] Item 2. The pH of the silica sol during the heat treatment is pH 9.0 to pH 10.5, the time of the heat treatment is 11 hours to 35 hours, the heat treatment stirs the silica sol under the condition that the stirring power per 1 m 3 of the silica sol is 0.01 kW / m 3 to 0.40 kW / m 3 The method for producing colloidal silica according to claim 1, comprising: The method for producing colloidal silica according to claim 1, comprising:

[0014] Item 3. The silica sol is (a) A solution B containing alkoxysilane is added to a solution A containing water and an alkali catalyst, (b) A silica sol obtained by hydrolyzing and dehydrating and condensing alkoxysilane under the condition that the addition rate of alkoxysilane contained in the solution B to 1 kg of the solution A is 0.8 mol / h / kg to 2.50 mol / h / kg. The method for producing colloidal silica according to claim 1 or 2, comprising:

[0015] Item 4. The silica sol is (a) A solution B containing an alkoxysilane is added to a solution A containing water and an alkali catalyst, (b) It is a silica sol obtained by hydrolyzing and dehydrating and condensing an alkoxysilane under the condition that the alkoxysilane concentration contained in the solution B is 60% by mass to 98% by mass. The method for producing colloidal silica according to item 1 or 2 above.

[0016] Item 5. Colloidal silica, Colloidal silica in which the particulate content parameter 1 defined as follows is 15.0 or less.

[0017] Definition of particulate content parameter 1 (i) Ultra-pure water with an electrical resistivity of 18.2 MΩ or more (hereinafter referred to as "ultra-pure water") is added to the colloidal silica and diluted to a silica concentration of 2% by mass (wt%) (diluted solution).

[0018] (ii) 9.1 g of the diluted solution is placed separately in an Eppendorf high-mag technology Co., Ltd. centrifuge tube (model number: S303922A), and centrifuged under the conditions of a centrifugal rotation speed of 50,000 rpm, a centrifugal temperature of 5 °C, and a centrifugal time of 60 minutes using a centrifugal rotor S58A and a centrifuge CS100FNX (all manufactured by Eppendorf high-mag technology Co., Ltd.).

[0019] (iii) After centrifugation, 2 mL of the supernatant is collected from the centrifuge tube, and this 2 mL of the post-centrifugation supernatant and a silica sol obtained by diluting the ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Industry Co., Ltd. 10-fold with ultra-pure water are mixed at the following mass ratio (mixed solution).

[0020] Post-centrifugation supernatant: 10-fold diluted solution of PL-3 = 9:1 (mass ratio) (iv) The particle size distribution of the obtained mixed solution is measured using a particle size distribution measuring device based on the scanning type electrical mobility diameter measurement method.

[0021] (v) From the measured values of the obtained particle size distribution, the value calculated using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica.

[0022] Formula (1) Fine particle content parameter 1 = (Total number of detected particles of 15 nm or less) ÷ (Total number of detected particles of 25 nm or more) The colloidal silica of the present invention has a low content of fine particles. When CMP is carried out using the colloidal silica of the present invention as an abrasive grain, the amount of residual fine particles on the polished surface is significantly reduced compared to the case where conventional colloidal silica is used as an abrasive grain, and it is possible to reduce the surface roughness of the polished surface.

Advantages of the Invention

[0023] The present invention can provide colloidal silica with a low content of fine particles.

Modes for Carrying Out the Invention

[0024] The present invention will be described in detail below.

[0025] The embodiments representing the present invention are explanations for better understanding of the gist of the invention, and do not limit the invention content unless otherwise specified.

[0026] In this specification, “including” and “containing” are concepts that include any of “comprise”, “consist essentially of”, and “consist of”.

[0027] In this specification, when a numerical range is indicated as “A to B”, it means “A or more and B or less”.

[0028] In this specification, generally, expressions such as parts and % are used.

[0029] In this specification, unless otherwise specified, parts by mass or mass % (wt%) are represented.

[0030] [1] Method for manufacturing colloidal silica The present invention includes a method for producing colloidal silica.

[0031] The method for producing colloidal silica of the present invention includes a step of heat-treating a silica sol composed of water and silica particles at the boiling point of water under normal pressure.

[0032] The pH of the silica sol during the heat treatment is preferably pH 9.0 to pH 10.5.

[0033] The heat treatment time is preferably 11 hours to 35 hours.

[0034] The heat treatment is preferably carried out with a stirring power of 0.01 kW / m 3 per 1 m of silica sol to 0.40 kW / m 3 under the condition of ~0.40 kW / m 3 while stirring the silica sol.

[0035] The silica sol (a silica sol composed of water and silica particles) is preferably (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst, (b) a silica sol obtained by hydrolyzing and dehydrating and condensing an alkoxysilane under the condition that the addition rate of the alkoxysilane contained in the solution B is 0.8 mol / h / kg to 2.50 mol / h / kg with respect to 1 kg of the solution A.

[0036] mol / h / kg indicates a value obtained by converting the mass of the alkoxysilane added per hour to 1 kg of the solution A into the amount of substance of silica.

[0037] The silica sol (a silica sol composed of water and silica particles) is preferably (a) adding a solution B containing an alkoxysilane to a solution A containing water and an alkali catalyst, (b) It is a silica sol obtained by hydrolyzing and dehydrating and condensing an alkoxysilane under the condition that the concentration of the alkoxysilane contained in the solution B is 60% by mass to 98% by mass.

[0038] The colloidal silica of the present invention has a low content of fine particles. When CMP is carried out using the colloidal silica obtained by the production method of the present invention as abrasive grains, the amount of residual fine particles on the polished surface is significantly reduced, and it is possible to reduce the surface roughness of the polished surface.

[0039] In the method for producing colloidal silica of the present invention, preferably, (i) silica particles are synthesized by the alkoxide method (particle synthesis), (ii) the particle concentration is concentrated by heating and distillation (heating concentration), (iii) the solvent is replaced with water by heating and distillation (heating water replacement), and (iv) the fine particles are reduced by heat treatment (heat treatment). By going through a series of operations, it is possible to produce colloidal silica with few fine particles.

[0040] (1) Synthesis step of silica particles In the method for producing colloidal silica of the present invention, the silica particles are preferably obtained by hydrolyzing and dehydrating and condensing an alkoxysilane to obtain a silica sol (particle synthesis step according to the alkoxide method).

[0041] Three - liquid method (method for synthesizing silica particles) The synthesis of silica particles is preferably a three-liquid method. A solution B containing an alkoxysilane (tetraalkoxysilane) and a solution C containing water are added to a solution A containing water, an alkali catalyst, and alcohol, and the alkoxysilane (tetraalkoxysilane) is subjected to a hydrolysis reaction and a condensation reaction to synthesize silica particles. By preferably adopting the three-liquid method for the synthesis of silica particles, the controllability of the hydrolysis reaction and the condensation reaction is excellent.

[0042] Solution A (three - liquid method) In the synthesis of silica particles, the three - liquid method is adopted. The water concentration (mass%, wt%) of solution A is preferably 3 wt% to 25 wt%, more preferably 3 wt% to 23 wt%, still more preferably 3 wt% to 20 wt%, and most preferably 3 wt% to 18 wt%. By preferably adjusting the water concentration of solution A to 3 wt% to 25 wt%, the solubility of the silicic acid generated by the hydrolysis reaction in the reaction solution is excellent.

[0043] In the synthesis of silica particles, the three - liquid method is adopted. The alkali catalyst concentration (mass%, wt%) of solution A is preferably 0.1 wt% to 3.0 wt%, more preferably 0.2 wt% to 2.5 wt%, still more preferably 0.3 wt% to 2.0 wt%, and most preferably 0.5 wt% to 1.6 wt%. By preferably adjusting the alkali catalyst concentration of solution A to 0.1 wt% to 3.0 wt%, the aggregation of silica particles is suppressed, and the dispersion stability of the silica particles in the dispersion is excellent.

[0044] The alkali catalyst is preferably an organic base catalyst containing no metal component in terms of avoiding the mixing of metal impurities, and more preferably an organic base catalyst containing nitrogen.

[0045] The alkali catalyst is preferably ammonia.

[0046] The organic base catalyst is preferably ethylenediamine, diethylenetriamine, triethylenetetramine, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, 3 - ethoxypropylamine (3 - EOPA), dipropylamine, triethylamine, etc.

[0047] From the points of excellent catalytic action, high volatility, and easy removal in the subsequent process, ammonia is preferably used.

[0048] From the perspective of increasing the true specific gravity of the silica particles, it is preferable to select an organic base catalyst with a boiling point of 90 °C or higher so that it is difficult to volatilize even when the reaction temperature is increased. Preferably, tetramethylammonium hydroxide, 3-ethoxypropylamine, etc. are used.

[0049] As for the alkali catalyst, these alkali catalysts may be used alone, or two or more of them may be mixed (blended) and used.

[0050] The alcohol is preferably methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1,4-butanediol, etc.

[0051] As for the alcohol, these alcohols may be used alone, or two or more of them may be mixed (blended) and used.

[0052] Solution B (three - liquid method) The silica sol is preferably (a) Solution B containing alkoxysilane is added to solution A containing water and an alkali catalyst, (b) It is a silica sol obtained by hydrolyzing and dehydrating and condensing alkoxysilane under the condition that the alkoxysilane concentration (mass%, wt%) contained in the solution B is 60 mass% to 98 mass%.

[0053] In the synthesis of silica particles, the three-liquid method is adopted, and the alkoxysilane concentration of solution B is preferably 60 wt% to 98 wt%, more preferably 65 wt% to 98 wt%, still more preferably 68 wt% to 98 wt%, and most preferably 70 wt% to 95 wt%. By adjusting the alkoxysilane concentration of solution B to preferably 60 wt% to 98 wt%, the amount of solvent used can be reduced, and the productivity of silica particles is excellent.

[0054] The silica sol is preferably (a) Solution B containing alkoxysilane is added to solution A containing water and an alkali catalyst, (b) It is a silica sol obtained by hydrolyzing and dehydrating and condensing an alkoxysilane under the condition that the addition rate of the alkoxysilane contained in the solution B is 0.8 mol / h / kg to 2.50 mol / h / kg with respect to 1 kg of the solution A.

[0055] In the synthesis of silica particles, the three-liquid method is adopted. The addition rate (mol / h / kg) of the alkoxysilane in the solution B is preferably 0.8 mol / h / kg to 2.5 mol / h / kg, and more preferably 1.1 mol / h / kg to 2.4 mol / h / kg. By adjusting the addition rate of the alkoxysilane in the solution B to preferably 0.8 mol / h / kg to 2.5 mol / h / kg, the reaction time is shortened and the productivity is excellent.

[0056] mol / h / kg indicates the value obtained by converting the mass of the alkoxysilane added per hour with respect to 1 kg of the solution A into the amount of substance of silica.

[0057] The alkoxysilane is preferably tetraC such as tetramethoxysilane (TMOS), tetraethoxysilane, tetraisopropoxysilane, etc. 1-8 An alkoxysilane is used. The alkoxysilane is more preferably tetraC 1-4 An alkoxysilane is used, and more preferably, tetramethoxysilane (TMOS), tetraethoxysilane, etc. are used.

[0058] The alkoxysilane may be used alone or in a mixture (blend) of two or more thereof.

[0059] The alcohol is preferably methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, 1,4-butanediol, etc.

[0060] The alcohol may be used alone or in a mixture (blend) of two or more thereof.

[0061] Solution C (three - liquid method) In the synthesis of silica particles, the three-liquid method is adopted. The alkali catalyst concentration (mass%, wt%) of solution C is preferably 0 wt% to 9 wt%, more preferably 0 wt% to 8 wt%, still more preferably 0 wt% to 7 wt%, and most preferably 0 wt% to 6 wt%. By adjusting the alkali catalyst concentration of solution C to preferably 0 wt% to 9 wt%, the reaction does not proceed too slowly and has excellent controllability.

[0062] The alkali catalyst is preferably ammonia.

[0063] The organic base catalyst is preferably ethylenediamine, diethylenetriamine, triethylenetetramine, urea, monoethanolamine, diethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetramethylguanidine, 3-ethoxypropylamine, dipropylamine, triethylamine, etc.

[0064] From the viewpoint of excellent catalytic action, high volatility, and easy removal in the subsequent process, ammonia is preferably used.

[0065] From the viewpoint of increasing the true specific gravity of silica particles, it is preferable to select an organic base catalyst with a boiling point of 90 °C or higher so that it is difficult to volatilize even when the reaction temperature is increased. Preferably, tetramethylammonium hydroxide, 3-ethoxypropylamine, etc. are used.

[0066] These alkali catalysts may be used alone or in combination (blended) of two or more.

[0067] Hydrolysis reaction and condensation reaction In the synthesis of silica particles, the three - liquid method is adopted. The maximum value of the water concentration (mass%, wt%) in the reaction system from the start to the end of the hydrolysis reaction and the condensation reaction is preferably 28 wt% or less, more preferably 25 wt% or less, still more preferably 20 wt% or less, and most preferably 18 wt% or less. By preferably adjusting the maximum value of the water concentration in the reaction system from the start to the end of the hydrolysis reaction and the condensation reaction to 28 wt% or less, the solubility of alkoxysilane (such as tetraalkoxysilane) in the reaction solution becomes good, and the generation of fine silica particles can be suppressed.

[0068] In the synthesis of silica particles, the three - liquid method is adopted. The change in the water concentration (mass%, wt%) in the reaction system from the start to the end of the hydrolysis reaction and the condensation reaction is preferably 15 wt% or less, more preferably 13 wt% or less, still more preferably 11 wt% or less, and most preferably 8 wt% or less. By preferably adjusting the change in the water concentration in the reaction system from the start to the end of the hydrolysis reaction and the condensation reaction to 15 wt% or less, the solubility of silicic acid generated by the reaction is maintained, and the generation of fine silica particles can be suppressed.

[0069] In the synthesis of silica particles, the three - liquid method is adopted. The reaction temperature (°C) is preferably 10°C to 80°C, more preferably 12°C to 70°C, still more preferably 15°C to 60°C, and most preferably 18°C to 55°C. By preferably adjusting the reaction temperature for the synthesis of silica particles to 10°C to 80°C, the reaction does not proceed too slowly and has excellent controllability.

[0070] In the method for producing colloidal silica of the present invention, in addition to the production method of hydrolyzing and dehydrating - condensing alkoxysilane to obtain a silica sol (the method for synthesizing silica particles according to the alkoxide method), a production method may be used in which sodium silicate is ion - exchanged, active silicic acid is prepared, and then the silicic acid species are condensed under basic conditions to obtain a silica sol.

[0071] (2) Heating and concentration step In the method for producing colloidal silica of the present invention, preferably, a heat concentration step is included, and the particle concentration is concentrated by heat distillation. By including the heat concentration step in the method for producing colloidal silica, it is possible to reduce the fine particles of silica particles contained in the colloidal silica.

[0072] In the heat concentration step, the Pv value (stirring power per unit volume) is preferably 0.01 kW / m 3 ~0.40 kW / m 3 and more preferably 0.01 kW / m 3 ~0.30 kW / m 3 and still more preferably 0.01 kW / m 3 ~0.20 kW / m 3 and most preferably 0.01 kW / m 3 ~0.10 kW / m 3 is. By adjusting the Pv value of the heat concentration treatment to preferably 0.40 kW / m 3 or less, the concentration temperature of the silica particles is made uniform, and by making the Pv value below a certain value, aggregation of the silica particles can be suppressed.

[0073] The heat concentration time (minutes, min) of the heat concentration step is preferably 60 minutes to 600 minutes. By adjusting the heat concentration time of the heat concentration step to preferably 60 minutes to 600 minutes, it is possible to reduce the fine particles of silica particles without significantly changing the average secondary particle diameter and the degree of association of the silica particles.

[0074] (3) Heating and water replacement step (manufacture of silica sol composed of water and silica particles) The colloidal silica to be subjected to the heat treatment is preferably one in which the concentration of silica particles is concentrated by heat distillation and the solvent is replaced with water. By performing heat concentration and heat water replacement under the following conditions, the content of fine particles of 15 nm or less can be reduced from the time point before the heat treatment. By subjecting the colloidal silica with a low fine particle content obtained by performing heat concentration and heat water replacement under the following conditions to the heat treatment under the above conditions, colloidal silica with an even lower fine particle content can be obtained.

[0075] In the method for producing colloidal silica of the present invention, preferably, a hot water replacement step is included, and the solvent is replaced with water by heating and distillation. In the method for producing colloidal silica, by including the hot water replacement step, it is possible to reduce the fine particles of silica particles contained in the colloidal silica.

[0076] In the hot water replacement step, the Pv value (stirring power per unit volume) is preferably 0.01 kW / m 3 ~0.40 kW / m 3 and more preferably 0.01 kW / m 3 ~0.30 kW / m 3 and still more preferably 0.01 kW / m 3 ~0.20 kW / m 3 and most preferably 0.01 kW / m 3 ~0.10 kW / m 3 is. By preferably adjusting the Pv value of the hot water replacement treatment to 0.40 kW / m 3 or less, the concentration temperature of the silica sol can be made uniform, and by setting the Pv value to a certain value or less, aggregation of silica particles can be suppressed.

[0077] The hot water replacement time (minutes, min) in the hot water replacement step is preferably 60 minutes to 600 minutes. By preferably adjusting the hot water replacement time in the hot water replacement step to 60 minutes to 600 minutes, it is possible to reduce the fine particles of silica particles without significantly changing the average secondary particle diameter and the degree of association of the silica particles.

[0078] In the hot water replacement step, the methanol concentration (ppm) after hot water replacement is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, still more preferably 1,000 ppm or less, and most preferably 500 ppm or less. By preferably adjusting the methanol concentration after hot water replacement to 10,000 ppm or less, it is possible to reduce the fine particles of silica particles contained in the colloidal silica.

[0079] (4) Heat treatment step (method for manufacturing colloidal silica) The colloidal silica to be subjected to heat treatment is preferably obtained by heating and distilling to concentrate the concentration of silica particles and replace the solvent with water. By heating and concentrating and heating with water replacement, the content of fine particles of silica particles with a size of 15 nm or less can be reduced from the time before the heat treatment. By subjecting the colloidal silica with a low content of fine particles of silica particles obtained by heating and concentrating and heating with water replacement to heat treatment, colloidal silica with an even lower content of fine particles can be obtained.

[0080] The method for producing colloidal silica of the present invention includes a step of heat-treating a silica sol composed of water and silica particles under normal pressure at the boiling point of water. In the method for producing colloidal silica of the present invention, by performing heat treatment, the fine particles of silica particles contained in the colloidal silica can be reduced.

[0081] In the heat treatment step, the heating temperature is heated to reflux at the boiling point of water. By heating the temperature to reflux at the boiling point of water, the fine particles of silica particles can be reduced without significantly changing the average secondary particle diameter and the degree of aggregation of the silica particles.

[0082] In the heat treatment step, the pressure during heating is carried out under normal pressure. By carrying out the pressure during heating under normal pressure, the fine particles of silica particles can be reduced without significantly changing the average secondary particle diameter and the degree of aggregation of the silica particles.

[0083] The pH of the silica sol during heat treatment is preferably pH 9.0 to pH 10.5.

[0084] The pH of the silica sol is preferably adjusted to pH 9.0 to pH 10.5 using 3-ethoxypropylamine (3-EOPA), ammonia, ethylenediamine, diethylenetriamine, etc.

[0085] The minimum pH value of the silica sol during the heat treatment is preferably 9.0 or higher, more preferably 9.2 or higher, still more preferably 9.4 or higher, and most preferably 9.5 or higher. By preferably adjusting the minimum pH value of the silica sol during the heat treatment to 9.0 or higher, it is possible to reduce the fine particles of the silica particles contained in the colloidal silica.

[0086] The maximum pH value of the silica sol during the heat treatment is preferably 10.5 or lower, more preferably 10.3 or lower, still more preferably 10.1 or lower, and most preferably 10.0 or lower. By preferably adjusting the maximum pH value of the silica sol during the heat treatment to 10.5 or lower, it is possible to suppress the aggregation of the silica particles.

[0087] The heat treatment is preferably carried out by stirring the silica sol under the condition that the stirring power (Pv value) per 1 m 3 of the silica sol is 0.01 kW / m 3 ~0.40 kW / m 3

[0088] In the heat treatment step, the Pv value (stirring power per unit volume) is preferably 0.01 kW / m 3 ~0.40 kW / m 3 and more preferably 0.01 kW / m 3 ~0.30 kW / m 3 and still more preferably 0.01 kW / m 3 ~0.20 kW / m 3 and most preferably 0.01 kW / m 3 ~0.10 kW / m 3 3 By preferably adjusting the Pv value during the heat treatment to 0.40 kW / m

[0089] ​​The heat treatment time is preferably 11 hours to 35 hours. In the heat treatment step, the heating time (in hours, hr) is preferably 11 hr to 35 hr, more preferably 12 hr to 30 hr, still more preferably 14 hr to 28 hr, and most preferably 15 hr to 25 hr. By preferably adjusting the heat treatment time to 11 hours to 35 hours, it is possible to reduce the fine particles of silica particles without significantly changing the average secondary particle diameter and the degree of aggregation of the silica particles.

[0090] In the heat treatment step, the concentration of the silica sol during heating (in mass%, wt%) is preferably 2 wt% to 50 wt%, more preferably 4 wt% to 45 wt%, still more preferably 6 wt% to 40 wt%, and most preferably 8 wt% to 35 wt%. By preferably adjusting the concentration of the silica sol during heat treatment to 2 wt% to 50 wt%, it is possible to reduce the fine particles of silica particles without significantly changing the average secondary particle diameter and the degree of aggregation of the silica particles.

[0091] [2] Colloidal silica The present invention includes colloidal silica.

[0092] The colloidal silica of the present invention has a particulate content parameter 1 defined as follows of 15.0 or less.

[0093] Definition of fine particle content parameter 1 (i) Ultra-pure water with an electrical resistivity of 18.2 MΩ or more (hereinafter referred to as "ultra-pure water") is added to the colloidal silica and diluted to a silica concentration of 2 mass% (wt%) (diluted solution).

[0094] (ii) 9.1 g of the diluted solution is separately placed in an Eppendorf Highmark Technologies Co., Ltd. centrifuge tube (model number: S303922A), and centrifuged under the conditions of a centrifugal rotation speed of 50,000 rpm, a centrifugal temperature of 5°C, and a centrifugal time of 60 minutes using a centrifuge rotor S58A and a centrifuge CS100FNX (all manufactured by Eppendorf Highmark Technologies Co., Ltd.).

[0095] (iii) After centrifugation, 2 mL of the supernatant is collected from the centrifuge tube, and 2 mL of this post - centrifugation supernatant and a silica sol obtained by diluting the ultra - high - purity colloidal silica PL - 3 manufactured by Fuso Chemical Industry Co., Ltd. 10 - fold with ultrapure water are mixed at the following mass ratio (mixed solution).

[0096] Post - centrifugation supernatant: 10 - fold diluted solution of PL - 3 = 9:1 (mass ratio)

[0097] (iv) Measure the particle size distribution of the obtained mixed solution using a particle size distribution measuring device based on the scanning electro - mobility diameter measurement method.

[0098] (v) From the measured values of the obtained particle size distribution, the value calculated using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica.

[0099] Formula (1) Fine particle content parameter 1 = (Total number of detected particles with a size of 15 nm or less)÷(Total number of detected particles with a size of 25 nm or more) The colloidal silica of the present invention has (i) an average secondary particle size of 20 nm to 250 nm and (ii) a fine particle content parameter 1 of 15.0 or less.

[0100] The colloidal silica of the present invention has a low content of fine particles. When CMP is carried out using the colloidal silica obtained by the production method of the present invention as abrasive grains, the amount of residual fine particles on the polished surface is significantly reduced, and it is possible to reduce the surface roughness of the polished surface.

[0101] The silica concentration (mass%, wt%) of the colloidal silica is preferably 2 wt% to 55 wt%, more preferably 2 wt% to 50 wt%, still more preferably 2 wt% to 45 wt%, and most preferably 3 wt% to 40 wt%. By preferably adjusting the silica concentration of the colloidal silica to 2 wt% to 55 wt%, excellent polishing rate can be obtained.

[0102] [3] Method for evaluating physical properties of colloidal silica In the present invention, each physical property of the silica particles is evaluated as follows.

[0103] (1 - 1) Measurement method of fine particle content parameter 1 (i) Add ultrapure water with an electrical resistivity of 18.2 MΩ or more (hereinafter referred to as "ultrapure water") to the colloidal silica sample to be measured, and dilute it to a silica concentration of 2% by mass (wt%) (diluted solution).

[0104] (ii) Take 9.1 g of the diluted solution and dispense it into a centrifuge tube (model number: S303922A) manufactured by Eppendorf Highmark Technologies Co., Ltd. Use a centrifuge rotor S58A and a centrifuge CS100FNX to centrifuge under the conditions of a centrifugal rotation speed of 50,000 rpm, a centrifugal temperature of 5 °C, and a centrifugal time of 60 minutes (all manufactured by Eppendorf Highmark Technologies Co., Ltd.).

[0105] (iii) After centrifugation, collect 2 mL of the supernatant from the centrifuge tube, and mix this 2 mL of the post - centrifugation supernatant with a silica sol obtained by diluting ultra - high - purity colloidal silica PL - 3 manufactured by Fuso Chemical Industry Co., Ltd. 10 - fold with ultra - pure water at the following mass ratio.

[0106] Post - centrifugation supernatant: 10 - fold diluted solution of PL - 3 = 9:1 (mass ratio) Use the obtained mixed solution as measurement sample 1.

[0107] (iv) Measure the particle size distribution of measurement sample 1 using a particle size distribution measuring device based on the scanning electrical mobility diameter measurement method. A particle size distribution measuring device based on the scanning electrical mobility diameter measurement method is, for example, the Liquid Nanoparticle Sizer System Model9310 (LNS) manufactured by KANOMAX. Measure under the following (1 - 2) particle size distribution measurement conditions using the LNS.

[0108] (v) From the measured values of the obtained particle size distribution, use the following formula to calculate the fine particle content parameter 1 of the colloidal silica sample.

[0109] Formula (1) Fine particle content parameter 1 = (Total number of detected particles of 15 nm or less)÷(Total number of detected particles of 25 nm or more)

[0110] (1 - 2) Particle size distribution measurement conditions (i) The air used for measurement is purified dry air generated by a compressor and purified by an air filter (manufactured by CKD, FCS500-88-P90).

[0111] (ii) Before measurement, a pre-operation is carried out for more than 24 hours with ultrapure water and the above-mentioned dry air supplied into the LNS device.

[0112] (iii) The inside of the measuring device is cleaned with ultrapure water. When the particle concentration of the ultrapure water is measured under the conditions shown in Table 1 and the total number of detected particles is less than 5.0E+11 (# / mL), the cleaning is completed.

[0113] (iv) Under the measurement conditions shown in Table 1, as a standard particle, measurement is carried out on the LNS Volumetric Standard manufactured by KANOMAX.

[0114] (v) The inside of the measuring device is cleaned with ultrapure water. When the particle concentration of the ultrapure water is measured under the conditions shown in Table 1 and the total number of detected particles is less than 1.0E+11 (# / mL), the cleaning is completed.

[0115] (vi) Measurement of the measurement sample 1 is carried out under the measurement conditions shown in Table 1.

[0116] The colloidal silica has a particulate content parameter 1 measured according to the above-mentioned measurement method of 15.0 or less.

[0117] The colloidal silica has a particulate content parameter 1 measured according to the above-mentioned measurement method of 15.0 or less, preferably 12.0 or less, more preferably 10.0 or less, and still more preferably 8.0 or less. By adjusting the particulate content parameter 1 to 15.0 or less, the amount of residual fine particles on the polished surface can be reduced.

[0118] (2 - 1) Measurement method of fine particle content parameter 2 (%) (i) Add ultrapure water with an electrical resistivity of 18.2 MΩ or more (hereinafter referred to as "ultrapure water") to the colloidal silica sample to be measured, and dilute it so that the silica concentration after dilution is 0.1 mass% (wt%). The obtained diluted solution is used as measurement sample 2.

[0119] (ii) Measure the particle size distribution of measurement sample 2 using a particle size distribution measuring device based on the scanning electrical mobility diameter measurement method. Examples of the particle size distribution measuring device based on the scanning electrical mobility diameter measurement method include Liquid Nanoparticle Sizer System Model 9310 (LNS) manufactured by KANOMAX. Measure under the following (2-2) particle size distribution measurement conditions using LNS.

[0120] (iii) From the measured values of the obtained particle size distribution, use the following formula to calculate the fine particle content parameter 2 of the colloidal silica sample.

[0121] Formula (3) Fine particle content parameter 2 = (Total number of detected particles of 15 nm or less) ÷ (Total number of detected all particles) × 100 [%]

[0122] (2 - 2) Particle size distribution measurement conditions (i) As the air used for measurement, use the compressed air generated by a compressor and purified and dried air using an air filter (manufactured by CKD, FCS500-88-P90).

[0123] (ii) Perform a pre-measurement pre-operation for 24 hours or more with ultrapure water and the above-mentioned dried air supplied into the LNS device.

[0124] (iii) Wash the inside of the measuring device with ultrapure water. Measure the particle concentration of the ultrapure water under the conditions shown in Table 1, and end the washing when the total number of detected particles is less than 5.0E+11 (# / mL).

[0125] (iv) Under the measurement conditions shown in Table 1 (LNS measurement conditions), perform the measurement of LNS Volumetric Standard manufactured by KANOMAX as a standard particle.

[0126] (v) Wash the inside of the measuring device using ultrapure water. Measure the particle concentration of the ultrapure water under the conditions shown in Table 1, and end the washing when the total number of detected particles becomes less than 1.0E+11 (# / mL).

[0127] (vi) Measure the measurement sample 2 under the measurement conditions shown in Table 1.

[0128] The colloidal silica has a particulate content parameter 2 measured by the above-described measurement method of 8.0% or less.

[0129] The colloidal silica has a particulate content parameter 2 measured by the above-described measurement method of 8.0% or less, preferably 7.0% or less, more preferably 6.0% or less, and still more preferably 5.0% or less. By adjusting the particulate content parameter 2 to 8.0% or less, the amount of residual fine particles on the polished surface can be reduced.

[0130]

Table 1

[0131] (3) Ratio of the amount of fine particles evaluated by SEM (%) (i) Drop a dispersion obtained by mixing 7.5 mL of methanol, 1.5 mL of water, 1 mL of 0.01 M HCl, and 5 μL of 20% colloidal silica onto a sample stage and dry it. Set this sample stage in a scanning electron microscope (SEM) and take an SEM image.

[0132] (ii) For the images of 1,000 silica particles taken with a scanning electron microscope, approximate each to an ellipse using image analysis software (「WinRoof2018」 by Mitani Shouji Co., Ltd.) and measure the minor axis of the ellipse.

[0133] (iii) In the number frequency distribution of the minor axes of the ellipses by the above-described SEM image analysis, define particles with a minor axis of the ellipse of 25% or less of its average value as fine particles and calculate the percentage of the number of fine particles.

[0134] The proportion of the amount of fine particles evaluated by SEM of colloidal silica is preferably 0.1% or less. By adjusting the proportion of the amount of fine particles evaluated by SEM of colloidal silica to 0.1% or less, the amount of residual fine particles on the polishing surface can be reduced.

[0135] (4) Average primary particle diameter (nm) After pre-drying colloidal silica on a hot plate, it is heat-treated at 800 °C for 1 hour to prepare a measurement sample. Using the prepared measurement sample, the BET specific surface area is measured. Assuming the true specific gravity of silica is 2.2, the value of 2727 / BET specific surface area (m 2 / g) is converted to obtain the average primary particle diameter (nm) of silica particles in colloidal silica.

[0136] The average primary particle diameter of colloidal silica is preferably 5 nm to 130 nm, more preferably 10 nm to 120 nm, still more preferably 12 nm to 110 nm, and most preferably 14 nm to 100 nm. By adjusting the average primary particle diameter of colloidal silica to preferably 5 nm to 130 nm, the roughness of the polishing surface during polishing can be reduced.

[0137] (5) Average secondary particle diameter (nm) To colloidal silica, an aqueous citric acid solution of 0.3 mass% is added and diluted to a silica concentration of 1.0 mass% (wt%) (diluted solution).

[0138] The diluted solution is used as a measurement sample. Using the measurement sample, the average secondary particle diameter is measured by the dynamic light scattering method (manufactured by Otsuka Electronics Co., Ltd., ELSZ-2000).

[0139] The average secondary particle diameter (nm) of colloidal silica is preferably 20 nm to 250 nm, more preferably 24 nm to 200 nm, still more preferably 27 nm to 170 nm, and most preferably 30 nm to 140 nm. By preferably adjusting the average secondary particle diameter of colloidal silica to 20 nm to 250 nm, the roughness of the polished surface can be reduced.

[0140] (6) Aggregation ratio The aggregation ratio of silica particles in colloidal silica is a value obtained by calculating the average secondary particle diameter / average primary particle diameter of silica particles in colloidal silica.

[0141] The aggregation ratio of silica particles in colloidal silica is preferably 1.0 or more, more preferably 1.1 or more, still more preferably 1.2 or more, and most preferably 1.3 or more. By adjusting the lower limit of the aggregation ratio of colloidal silica to 1.0 or more, the polishing rate when polishing with colloidal silica is further improved.

[0142] Also, the aggregation ratio of colloidal silica is preferably 4.0 or less, more preferably 3.5 or less, still more preferably 3.0 or less, and most preferably 2.9 or less. By adjusting the upper limit of the aggregation ratio of colloidal silica to 4.0 or less, the roughness of the polished surface when polishing with colloidal silica can be reduced.

[0143] (7) Silica concentration (mass% (wt%)) Colloidal silica was pre-dried on a hot plate and then heat-treated at 800 °C for 1 hour, and calculated from its remaining amount.

[0144] The silica concentration of colloidal silica is preferably 2 wt% to 55 wt%, more preferably 2 wt% to 50 wt%, still more preferably 2 wt% to 45 wt%, and most preferably 3 wt% to 40 wt%. By adjusting the silica concentration of colloidal silica to 2 wt% to 55 wt%, the polishing rate when polishing colloidal silica is further improved.

[0145] (8) Silanol group density (number / nm 2 ) The silanol group density of colloidal silica can be determined by the Sears method. The Sears method was carried out with reference to the description in G.W. Sears, Jr., “Determination of Specific Surface Area of Colloidal Silica by Titration with Sodium Hydroxide”, Analytical Chemistry, 28(12), 1981(1956). For the measurement, a 1 mass% (wt%) silica dispersion was used, titrated with a 0.1 mol / L aqueous sodium hydroxide solution, and the silanol group density was calculated based on the following formula.

[0146] ρ = (a × f × 6022) ÷ (c × S) In the above formula, ρ: silanol group density (number / nm 2 ), a: the volume of the 0.1 mol / L aqueous sodium hydroxide solution dropped at pH 4 - 9 (mL), f: the factor of the 0.1 mol / L aqueous sodium hydroxide solution, c: the mass of silica particles (g), S: BET specific surface area (m 2 / g) respectively represent.

[0147] The silanol group density of silica particles in colloidal silica is preferably 1.5 number / nm 2 or more, more preferably 1.6 number / nm 2 or more, still more preferably 1.8 number / nm 2 or more, and most preferably 2.0 number / nm 2 or more. By adjusting the lower limit of the silanol group density to 1.5 number / nm 2 or more, the generation of scratches on the workpiece to be polished is further reduced.

[0148] Also, the silanol group density is preferably 10.0 number / nm 2 or less, more preferably 9.5 number / nm 2 or less, still more preferably 9.0 number / nm 2is as follows, and most preferably, 8.8 pieces / nm 2 is as follows. The upper limit of the silanol group density is adjusted to 10.0 pieces / nm 2 By adjusting it as described below, the polishing performance of the colloidal silica is further improved.

[0149] (9) True specific gravity In this specification, the true specific gravity can be measured by the liquid phase replacement method using ethanol after drying the colloidal silica on a hot plate at 150 °C and then holding it in a furnace at 300 °C for 1 hour.

[0150] The true specific gravity of the silica particles contained in the colloidal silica is preferably 1.0 or more, more preferably 1.2 or more, still more preferably 1.4 or more, and most preferably 1.5 or more. By adjusting the lower limit of the true specific gravity to 1.0 or more, the polishing performance of the colloidal silica of the present invention is further improved.

[0151] Also, the true specific gravity is preferably 3.0 or less, more preferably 2.8 or less, still more preferably 2.5 or less, and most preferably 2.3 or less. By adjusting the upper limit of the true specific gravity to 3.0 or less, the occurrence of scratches on the object to be polished is further reduced.

[0152] (10) Metal impurity content (ppm) The content of metal impurities was measured using an atomic absorption spectrometer. The sum of the contents of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt in the colloidal silica was defined as the content of metal impurities.

[0153] The content of metal impurities contained in the colloidal silica is preferably 1 ppm or less. By adjusting the content of metal impurities contained in the colloidal silica to 1 ppm or less, it is more suitable for CMP slurry applications.

[0154] (11) RMS roughness of polished surface (nm) Add ultrapure water to colloidal silica and dilute it to a silica concentration of 3.0 mass% (wt%) to obtain a polishing composition.

[0155] Using the obtained polishing composition, polish a 3 cm square silicon wafer with a silicon oxide film formed on its surface under the following conditions.

[0156] Polishing machine: NF-300CMP manufactured by Nanofactor Co., Ltd. Polishing pad: IC1000TM Pad manufactured by Nitto DuPont Co., Ltd. Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Polishing pressure: 4 psi Polishing time: 2 min Regarding the wafer after polishing, use an atomic force microscope to evaluate the surface roughness of the polished surface under the following conditions.

[0157] Atomic force microscope: SPM-9700HT manufactured by Shimadzu Corporation Cantilever: MICRO CANTILEVER OMCL-AC240TS-R3 manufactured by OLYMPUS Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: Observe 5 fields per wafer after polishing.

[0158] Calculation method for surface roughness: The average value of the root mean square roughness of 5 fields was defined as the polished surface roughness RMS.

[0159] The polished surface roughness RMS (nm) is preferably 3.00 nm or less.

[0160] (12) Number of residual fine particles on polished surface (number / μm 2 ) Add ultrapure water to colloidal silica and dilute it to a silica concentration of 3.0 mass% (wt%) to obtain a polishing composition.

[0161] Using the obtained polishing composition, a 3 cm square silicon wafer with a silicon oxide film formed on its surface is polished under the following conditions.

[0162] Polisher: Manufactured by Nanofactor Co., Ltd., NF-300CMP Polishing pad: Manufactured by Nitto DuPont Co., Ltd., 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 The polished silicon wafer is cleaned by performing scrub cleaning in which a PVA roll brush is brought into contact with the scrubbing section built into the cleaning and drying apparatus MAT ZAB-8S1M under the following conditions. A jig made of glass epoxy resin for the frame and polyurethane for the wafer fixing part is used to fix the silicon wafer.

[0163] Brush: Manufactured by AION, AION SCL BRUSH ROLLER 48(40 / 26)×224 mm Scrub cleaning time: 1 min Brush rotation speed: 200 rpm Spin rotation speed of the silicon wafer fixing section: 50 rpm After scrub cleaning, it is flushed with ultrapure water at 750 mL / min for 1 minute on the upper side of the polishing substrate, and further processed at 1800 rpm for 20 seconds using the spin drying apparatus built into the above apparatus.

[0164] Regarding the dried silicon wafer, the number of residual fine particles on the polished surface is measured using SPM-9700HT manufactured by Shimadzu Corporation.

[0165] Number of residual fine particles on the polished surface (particles / μm 2 ) is preferably 3 particles / μm 2 or less.

[0166] [4] Polishing composition The present invention includes a polishing composition containing the colloidal silica of the present invention.

[0167] The polishing composition is useful for CMP applications.

[0168] The polishing composition contains colloidal silica and may further contain additives. Examples of the additives include diluents, oxidizing agents, pH adjusters, corrosion inhibitors, stabilizers, surfactants, and the like.

[0169] The content (mass%, wt%, silica concentration) of colloidal silica in the polishing composition is preferably 0.01 wt% to 20 wt%, more preferably 0.1 wt% to 15 wt%, still more preferably 1 wt% to 10 wt%, and particularly preferably 2 wt% to 5 wt%.

[0170] As described above, the embodiments of the present invention have been described, but the present invention is not limited to such examples. Needless to say, the present invention can be implemented in various forms without departing from the gist of the present invention.

Examples

[0171] The present invention will be specifically described with reference to examples.

[0172] However, the present invention is not limited to the examples.

[0173] [1] Manufacture of colloidal silica (1) Example 1 (with heat treatment) Preparation of silica sol after heating and water replacement To a solution A obtained by mixing 976 g of methanol, 97 g of water, and 58 g of 29% by mass aqueous ammonia, a solution B obtained by mixing 190 g of methanol and 506 g of tetramethoxysilane (TMOS), and a solution C (pH = 7.85) of 119 g of pure water were added at a constant rate over 75 minutes.

[0174] In the adjustment of the reaction solution, the temperature of each solution before mixing was maintained at 35°C, and the temperature of the reaction solution was adjusted while adding the total amounts of the solution B and the solution C to the solution A at a constant rate so that the temperature decreased from the initial reaction temperature of 35°C at the start of the addition of the solution B to the solution A (start of synthesis) to the final reaction temperature of 24.5°C at the end of the addition (end of synthesis).

[0175] The reaction solution was heated and concentrated and heated water was replaced under stirring conditions. The methanol concentration after the replacement with heated water was 301 ppm.

[0176] Manufacture of colloidal silica (heat treatment) To 100 parts by mass of the silica sol replaced with heated water obtained above, 0.65 part by mass of 3-ethoxypropylamine (3-EOPA) was added, the pH was adjusted to 9.9, and the silica sol was heated at 100°C under normal pressure conditions while being stirred. Sampling was performed every 0.5 hours starting from the time when the silica sol reached 100°C, and pH measurement was performed.

[0177] After 0.5 hours had elapsed since the start of the heat treatment, since the pH had become 9.6, 0.2 part by mass of 3-EOPA was added again and the pH was adjusted to 9.9. The above operation was performed every 1.5 hours from the start of the heat treatment to the end of the heat treatment. A total of 2.2 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0178] The above heat treatment was performed for 16 hours to obtain colloidal silica.

[0179] Measurement of methanol concentration A gas chromatograph (FocusGC manufactured by Thermo), an autosampler (AS3000 manufactured by Thermo, or an apparatus with equivalent or higher performance), and an air compressor (capable of supplying compressed air of 0.4 MPa or higher) were used. 1 μL of the sample was extracted with a 10 μL syringe, the syringe was set in the autosampler, and measurement was performed.

[0180] (2) Example 2 (with heat treatment) Preparation of silica sol after heating and water replacement To solution A, which was a mixture of 7.7 g of pure water, 96.8 g of methanol, and 4.5 g of 29% by mass aqueous ammonia, solution B, which was a mixture of 100 g of TMOS and 17.7 g of methanol, and solution C, which was a mixture of 31.7 g of pure water and 4.7 g of 29% by mass aqueous ammonia, were added at a constant rate over 217 minutes while maintaining the liquid temperature at 36°C.

[0181] After the addition was completed, the reaction solution was further stirred for 30 minutes while maintaining the temperature of the reaction solution at 36°C.

[0182] The reaction solution was heated and concentrated and heated with water substitution under stirring conditions. The methanol concentration after the water substitution by heating was 212 ppm.

[0183] Manufacture of colloidal silica (heat treatment) To 100 parts by mass of the silica sol that had been subjected to water substitution by heating obtained above, 0.6 part by mass of 3-EOPA was added, the pH was adjusted to 9.8, and the silica sol was heated at 100°C under normal pressure conditions while being stirred. Sampling was carried out every 0.5 hours starting from the time when the silica sol reached 100°C, and pH measurement was performed.

[0184] After 0.5 hours had elapsed since the start of the heat treatment, since the pH had become 9.6, 0.12 part by mass of 3-EOPA was re-added and the pH was adjusted to 9.8. The above operations were carried out every 1.0 hour from the start of the heat treatment until the end of the heat treatment. A total of 2.76 parts by mass of 3-EOPA was added from the start of the heat treatment until the end of the heat treatment.

[0185] The above heat treatment was carried out for 23.0 hours to obtain colloidal silica.

[0186] (3) Example 3 (with heat treatment, example with small average particle size) Preparation of silica sol after heating and water replacement To solution A, which was a mixture of 463.1 g of pure water, 104.8 g of 26% by mass aqueous ammonia, and 4255.0 g of methanol, solution B, which was a mixture of 3044.4 g of TMOS and 229.4 g of methanol, and solution C, which was a mixture of 643.2 g of pure water and 104.8 g of 26% by mass aqueous ammonia, were added at a constant rate over 150 minutes while maintaining the liquid temperature at 50°C.

[0187] The reaction solution was heated and concentrated and heated for water replacement under stirring conditions. The methanol concentration after the water replacement by heating was 198 ppm.

[0188] Manufacture of colloidal silica (heat treatment) To 100 parts by mass of the silica sol that had been subjected to water replacement by heating obtained above, 0.65 part by mass of 3-EOPA was added, the pH was adjusted to 9.9, and the silica sol was heated at 100°C under normal pressure conditions while being stirred. Sampling was performed every 0.5 hours starting from the time when the silica sol reached 100°C, and pH measurement was carried out.

[0189] After 0.5 hours had elapsed since the start of the heat treatment, since the pH had become 9.6, 0.2 part by mass of 3-EOPA was re-added and the pH was adjusted to 9.9. The above operations were carried out every 1.0 hour from the start of the heat treatment until the end of the heat treatment. A total of 3.2 parts by mass of 3-EOPA was added from the start of the heat treatment until the end of the heat treatment.

[0190] The above heat treatment was carried out for 24.5 hours to obtain colloidal silica.

[0191] (4) Example 4 (with heat treatment, example with large average particle size) Preparation of silica sol after heating and water replacement To solution A, which was a mixture of 1546.6 g of pure water, 340.6 g of 26% by mass aqueous ammonia, and 8363.2 g of methanol, solution B, which was a mixture of 6088.0 g of TMOS and 350.0 g of methanol, and solution C, which was a mixture of 1186.2 g of pure water and 340.6 g of 26% by mass aqueous ammonia, were added at a constant rate over 100 minutes while maintaining the liquid temperature at 20°C.

[0192] The reaction solution was heated and concentrated and heated water was replaced under stirring conditions. The methanol concentration after heating water replacement was 196 ppm.

[0193] Manufacture of colloidal silica (heat treatment) To 100 parts by mass of the silica sol replaced with heated water obtained above, 0.65 part by mass of 3-EOPA was added, the pH was adjusted to 9.9, and it was heated at 100 °C under normal pressure conditions under stirring conditions of the silica sol. Sampling was carried out every 0.25 hours from the time when the silica sol reached 100 °C, and pH measurement was carried out.

[0194] After 0.25 hours from the start of the heat treatment, since the pH had become 9.7, 0.15 part by mass of 3-EOPA was re-added and the pH was adjusted to 9.9. The above operation was carried out every 1.0 hour from the start of the heat treatment to the end of the heat treatment. A total of 3.0 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0195] The above heat treatment was carried out for 20.0 hours to obtain colloidal silica.

[0196] (5) Example 5 (with heat treatment, example with low silica concentration during heating) Preparation of silica sol after heating and water replacement The reaction solution obtained in Example 1 was replaced with heated water under stirring conditions. The methanol concentration after heating water replacement was 387 ppm.

[0197] Manufacture of colloidal silica (heat treatment) To 100 parts by mass of the silica sol replaced with heated water obtained above, 0.65 part by mass of 3-EOPA was added, the pH was adjusted to 9.9, and it was heated at 100 °C under normal pressure conditions under stirring conditions of the silica sol. Sampling was carried out every 0.5 hours from the time when the silica sol reached 100 °C, and pH measurement was carried out.

[0198] After 0.5 hours had elapsed since the start of the heat treatment, since the pH had reached 9.6, 0.2 parts by mass of 3-EOPA was added again, and the pH was adjusted to 9.9. The above operations were carried out every 1.5 hours from the start of the heat treatment to the end of the heat treatment. A total of 2.4 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0199] The above heat treatment was carried out for 18.0 hours to obtain colloidal silica.

[0200] (6) Example 6 (with heat treatment, example with high silica concentration during heating) Preparation of silica sol after heating and water replacement The reaction solution obtained in Example 1 was heated and concentrated and heated water substitution was carried out under stirring conditions. The methanol concentration after the heated water substitution was 184 ppm.

[0201] Manufacture of colloidal silica (heat treatment) To 100 parts by mass of the silica sol that had been subjected to heated water substitution obtained above, 0.65 parts by mass of 3-EOPA was added, the pH was adjusted to 9.9, and the silica sol was heated at 100 °C under normal pressure conditions while stirring. The time when the silica sol reached 100 °C was taken as the start of the heat treatment, and sampling was carried out every 0.5 hours from the start of the heat treatment, and pH measurement was carried out.

[0202] After 0.5 hours had elapsed since the start of the heating, since the pH had reached 9.6, 0.2 parts by mass of 3-EOPA was added again, and the pH was adjusted to 9.9. The above operations were carried out every 1.5 hours from the start of the heat treatment to the end of the heat treatment. A total of 2.0 parts by mass of 3-EOPA was added from the start of the heat treatment to the end of the heat treatment.

[0203] The above heat treatment was carried out for 15.5 hours to obtain colloidal silica.

[0204] (7) Comparative Example 1 (without heat treatment) This is an example that simulates the prior art (Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-164351, and Patent Document 3: International Publication No. WO2016 / 117560A1).

[0205] To a solution A prepared by mixing 976 g of methanol, 97 g of water, and 58 g of 29% by mass aqueous ammonia, a solution B prepared by mixing 190 g of methanol and 506 g of tetramethoxysilane (TMOS), and a solution C (pH = 7.85) of 119 g of pure water were added at a constant rate over 75 minutes.

[0206] In the preparation of the reaction solution, the temperature of each solution before mixing was maintained at 35 °C, and the temperature of the reaction solution was adjusted so as to decrease from the initial reaction temperature of 35 °C at the start of the addition of solution B to solution A (start of synthesis) to the final reaction temperature of 24.5 °C at the end of the addition (end of synthesis). While adjusting the temperature, the total amounts of solution B and solution C were added to solution A at a constant rate.

[0207] The reaction solution was heated and concentrated and heated with water substitution under stirring conditions to obtain colloidal silica.

[0208] (8) Comparative Example 2 (without heat treatment) This is an example that simulates the prior art (Patent Document 2: JP-A-2022-109711, and Patent Document 3).

[0209] To a solution A prepared by mixing 7.7 g of pure water, 96.8 g of methanol, and 4.5 g of 29% by mass aqueous ammonia, a solution B prepared by mixing 100 g of tetramethoxysilane and 17.7 g of methanol, and a solution C prepared by mixing 31.7 g of pure water and 4.7 g of 29% by mass aqueous ammonia were added at a constant rate over 217 minutes while maintaining the liquid temperature at 36 °C.

[0210] After the addition was completed, the reaction solution was further stirred for 30 minutes while maintaining the temperature of the reaction solution at 36 °C.

[0211] The reaction solution was heated and concentrated and heated with water substitution under stirring conditions to obtain colloidal silica.

[0212] (9) Comparative Example 3 (without heat treatment) This is an example that simulates the prior art (Patent Documents 2 to 3, and Patent Document 4: JP-A-2020-75830).

[0213] To the colloidal silica obtained in Comparative Example 2, 35% by mass hydrogen peroxide was added so that the hydrogen peroxide content was 0.5 g per 100 g of silica in terms of tetraalkoxysilane, and colloidal silica was obtained.

[0214] (10) Comparative Example 4 (without heat treatment) This is an example simulating the prior art (Patent Documents 2 to 4 and Patent Document 5: JP-A-2021-116208).

[0215] 120 g of the colloidal silica obtained in Comparative Example 3 was subjected to ultrafiltration using an ultrafiltration membrane with a molecular weight cut-off of 80,000 (Asahi Kasei's Lab Module AOP-0013) in Asahi Kasei's Pensil type module (PX-02001), Masterflex's L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MFLX07514-10) and Masterflex's L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) for the pump, and Masterflex's silicone perhydrolysis tube (96400-25) for the tube, to obtain colloidal silica.

[0216] The amount of the liquid permeated through the ultrafiltration membrane was 63.6 g, and the permeation rate was 53%.

[0217] (11) Comparative Example 5 (without heat treatment, example of long - time ultrafiltration) This is an example simulating the prior art (Patent Documents 2 to 5).

[0218] 40 g of the colloidal silica obtained in Comparative Example 4 was subjected to ultrafiltration using an ultrafiltration membrane with a fractional molecular weight of 80,000 (Lab Module AOP-0013 manufactured by Asahi Kasei Corporation) in a pencil-type module (PX-02001 manufactured by Asahi Kasei Corporation), a Masterflex L / S Easy-Load Pump Heads for Precision Tubing, Avantor (MFLX07514-10) and a Masterflex L / S Analog Modular Drive Replacement Controllers, Avantor (MFLX07559-04) for the pump, and a Masterflex silicone hydrolysis-resistant tube (96400-25) for the tube to obtain colloidal silica.

[0219] During ultrafiltration, ultrapure water was added to the colloidal silica to keep the liquid volume of the colloidal silica constant.

[0220] The liquid volume that permeated through the ultrafiltration membrane was 220.5 g, and the time required for ultrafiltration was 152 minutes.

[0221]

Table 2

[0222]

Table 3

[0223] [2] Evaluation results Examples 1 to 6 are colloidal silicas produced by a method for producing colloidal silica including a step of heat-treating a silica sol composed of water and silica particles at the boiling point of water under normal pressure.

[0224] The colloidal silicas of Examples 1 to 6 had (i) an average secondary particle diameter of 20 nm to 250 nm and (ii) a fine particle content parameter 1 of 15.0 or less.

[0225] The colloidal silica of the example was able to keep the content of fine particles low.

[0226] Comparative Examples 1 to 5 are colloidal silicas produced by a method for producing colloidal silica that does not include a heat treatment step.

[0227] Comparative Examples 1 to 5 are examples that simulate the prior art.

[0228] Comparative Example 1 is an example that simulates Patent Documents 1 and 3, and was unable to effectively reduce fine particles of 15 nm or less.

[0229] Comparative Example 2 is an example that simulates Patent Documents 2 and 3, and was unable to effectively reduce fine particles of 15 nm or less.

[0230] Comparative Example 3 is an example that simulates Patent Documents 2 to 4, and was unable to effectively reduce fine particles of 15 nm or less.

[0231] Comparative Example 4 is an example that simulates Patent Documents 2 to 5, and was unable to effectively reduce fine particles of 15 nm or less.

[0232] Comparative Example 5 is an example that simulates Patent Documents 2 to 5 and attempted to reduce the amount of fine particles by performing ultrafiltration for a long time. An increase in the average secondary particle diameter due to particle aggregation was confirmed.

[0233] [3] Industrial applicability The method for producing colloidal silica of the present invention includes a step of heat-treating a silica sol composed of water and silica particles at the boiling point of water under normal pressure.

[0234] The colloidal silica of the present invention has an average secondary particle diameter of (i) 20 nm to 250 nm, and a fine particle content parameter 1 defined as follows of 15.0 or less.

[0235] Definition of fine particle content parameter 1 (i) Add ultrapure water with an electrical resistivity of 18.2 MΩ or more (hereinafter referred to as "ultrapure water") to colloidal silica and dilute it to a silica concentration of 2% by mass (wt%) (diluted solution).

[0236] (ii) Take 9.1 g of the diluted solution and separately place it in a centrifuge tube (model number: S303922A) manufactured by Eppendorf Highmark Technologies Co., Ltd. Centrifuge it under the conditions of a centrifugal rotation speed of 50,000 rpm, a centrifugal temperature of 5 °C, and a centrifugal time of 60 minutes using a centrifuge rotor S58A and a centrifuge CS100FNX (all manufactured by Eppendorf Highmark Technologies Co., Ltd.).

[0237] (iii) After centrifugation, collect 2 mL of the supernatant from the centrifuge tube, and mix 2 mL of this post - centrifugation supernatant with a silica sol obtained by diluting ultrapure colloidal silica PL - 3 manufactured by Fuso Chemical Industry Co., Ltd. 10 - fold with ultrapure water in the following mass ratio (mixed solution).

[0238] Post - centrifugation supernatant: 10 - fold diluted solution of PL - 3 = 9:1 (mass ratio) (iv) Measure the particle size distribution of the obtained mixed solution using a particle size distribution measuring device based on the scanning electro - mobility diameter measurement method.

[0239] (v) From the measured values of the obtained particle size distribution, define the value calculated using the following formula (1) as the fine particle content parameter 1 of colloidal silica.

[0240] Formula (1) Fine particle content parameter 1 = (Total number of detected particles with a size of 15 nm or less) ÷ (Total number of detected particles with a size of 25 nm or more) The colloidal silica of the present invention has a low content of fine particles.

[0241] When CMP is carried out using the colloidal silica of the present invention as an abrasive grain, compared with the case of using conventional colloidal silica as an abrasive grain, the amount of residual fine particles on the polished surface is significantly reduced, and it is possible to reduce the surface roughness of the polished surface.

Claims

[Claim 1] Colloidal silica, The fine particle content parameter 1, defined as follows, is 15.0 or less, Colloidal silica with an average secondary particle size of 20nm to 69.3nm. Definition of fine particle content parameter 1 (i) The colloidal silica is diluted with ultrapure water having an electrical resistivity of 18.2 MΩ or more (hereinafter referred to as "ultrapure water") to a silica concentration of 2 mass % (wt%) (diluted solution). (ii) 9.1 g of the diluted solution is transferred to a centrifuge tube (model number: S303922A) manufactured by Eppendorf-Himac Technologies Co., Ltd., and centrifuged using a centrifuge rotor S58A and a centrifuge CS100FNX under conditions of a centrifuge speed of 50,000 rpm, a centrifuge temperature of 5°C, and a centrifugation time of 60 minutes (all manufactured by Eppendorf-Himac Technologies Co., Ltd.). (iii) After centrifugation, 2 mL of the supernatant is collected from the centrifuge tube, and this 2 mL of the supernatant after centrifugation is mixed with silica sol obtained by diluting ultra-high purity colloidal silica PL-3 manufactured by Fuso Chemical Co., Ltd. 10 times with ultra-pure water in the following mass ratio (mixture). Supernatant after centrifugation: 10-fold dilution of PL-3 = 9:1 (mass ratio) (iv) The particle size distribution of the resulting mixture is measured using a particle size distribution measuring device based on a scanning electrical mobility diameter measurement method. (v) The value calculated from the obtained particle size distribution measurement value using the following formula (1) is defined as the fine particle content parameter 1 of the colloidal silica. Equation (1) Fine particle content parameter 1 = (Total number of particles detected that are 15 nm or less) ÷ (Total number of particles detected that are 25 nm or more)

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