Colloidal silica and method for producing colloidal silica

Abstract

Provided is a colloidal silica which, when used as abrasive grains for polishing electronic materials such as semiconductor wafers, highly suppresses metal contamination of the surface to be polished, exhibits an excellent polishing rate, and can form a polished surface with excellent flatness. The total content of Na, K, Fe, Al, Ca, Mg, Ti, Ni, Cr, Cu, Zn, Pb, Ag, Mn, and Co is less than 100 ppb by mass, 29 The colloidal silica contains silica particles in which the peak area ratio of the peak derived from the Q4 structure to the total peak area of ​​the peaks derived from the Q1 structure to the Q4 structure in a Si-solid-state NMR spectrum is 73.0% or more, and the content of coarse particles with a particle size of 0.2 μm or more is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass.

Description

[Technical Field]

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

[0002] In the semiconductor manufacturing process, semiconductor wafers are held by a component called a carrier, and the wafer is brought into contact with and rotated on a polishing pad while a slurry containing chemicals and abrasive grains is poured over it, polishing the semiconductor wafer until it is flat.

[0003] In the above-mentioned polishing methods, chemical mechanical polishing (CMP) is also used, which utilizes the chemical polishing action of chemicals and the mechanical polishing action of abrasive grains.

[0004] In the chemical mechanical polishing (CMP) of the semiconductor device, nanoparticles of silica or the like are used as the abrasive grains, and specifically, colloidal silica in which the silica particles are dispersed in a medium such as water is used.

[0005] As a method for producing the above colloidal silica, a method is known in which high-purity colloidal silica with a low metal content is produced by hydrolyzing and condensing alkoxysilane as a raw material (see, for example, Patent Documents 1 to 3).

[0006] Specifically, high-purity alkoxysilane, from which metal components have been removed by distillation purification or ion exchange treatment, is used as the raw material, and silica particles are synthesized in a reaction vessel whose inner walls are coated with fluororesin or the like in the presence of alcohol and a basic catalyst, thereby producing ultra-high-purity colloidal silica with a reduced metal concentration. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] WO2024 / 122583 specification [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-220976 [Patent Document 3] Japanese Patent Application Publication No. 2018-080331 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0008] In the chemical mechanical polishing (CMP) of semiconductor devices, the colloidal silica is now required to have the following properties: (1) The metal content must be low to reduce the risk of metal contamination on the polished surface. (2) It must be capable of exerting a high polishing rate on the surface to be polished. (3) The content of coarse particles that can cause deterioration of the flatness of the polished surface must be low. In particular, with the recent trend toward miniaturization and increased density of semiconductors, the inclusion of metals in semiconductor devices has become more strictly controlled than ever before, and abrasive grains used in chemical mechanical polishing (CMP) of semiconductor devices are now required to have even lower metal content than before.

[0009] In this regard, Patent Document 1 describes that ultra-high purity colloidal silica can be obtained by using, as a raw material, high-purity tetraalkoxysilane whose metal concentration has been reduced by distillation purification, and carrying out hydrolysis and dehydration condensation reactions of the tetraalkoxysilane in a reaction vessel whose inner walls are coated with a fluororesin.

[0010] However, the inventors of the present invention have found that the colloidal silica obtained by the manufacturing method described in Patent Document 1 is synthesized at a low temperature of 22°C (see Example 1 of Patent Document 1), and therefore the siloxane bonds of the silica particles are not densely formed. Therefore, when used as an abrasive in chemical mechanical polishing (CMP) of semiconductor devices, it is not possible to achieve a sufficient polishing rate.

[0011] Furthermore, Patent Document 2 describes a method for producing colloidal silica by using a highly pure raw material whose metal concentration has been reduced by distillation purification, and carrying out hydrolysis and dehydration condensation reactions of tetraalkoxysilane in a reaction vessel whose inner wall is made of glass. The colloidal silica obtained by the manufacturing method described in Patent Document 2 is synthesized under high-temperature conditions of 70°C, and therefore it is believed that the siloxane bonds of the silica particles are densely formed, and therefore it is believed that when used as an abrasive in chemical mechanical polishing (CMP) of semiconductor devices, it will exhibit a high polishing rate (see Examples 1 and 2 of Patent Document 2).

[0012] However, the inventors of the present invention have found that the colloidal silica obtained by the manufacturing method described in Patent Document 2 has a high metal concentration because the silica particle synthesis reaction is carried out at a high temperature of 70°C, and as a result, a large amount of metal components are eluted from the base material in the reaction vessel during the manufacturing process. In other words, even if the reaction vessel has a coating layer made of glass, fluororesin, etc. on the inner wall, these coating layers have tiny through holes called pinholes, and it was found that when a silica particle synthesis reaction is carried out under high temperature conditions, a large amount of metal components are leached from the base material of the reaction vessel through the chemical solution that has seeped into the pinholes. For this reason, from the perspective of suppressing metal contamination of the polished surface, the colloidal silica obtained by the manufacturing method described in Patent Document 2 is also difficult to apply to chemical mechanical polishing (CMP) of recent semiconductor devices, where miniaturization has progressed and metal contamination has come to be controlled more strictly than before.

[0013] Furthermore, Patent Document 3 describes a method for producing high-purity colloidal silica by using a high-purity raw material whose metal concentration has been reduced by distillation purification, carrying out hydrolysis and dehydration condensation reactions of tetraalkoxysilane in a reaction vessel whose inner wall is coated with a fluororesin, and further removing impurities with an ion exchange resin.

[0014] In the manufacturing method described in Patent Document 3, as in Patent Document 2, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane is carried out under relatively high temperature conditions of 40°C (see Examples 3 and 10 of Patent Document 3), and therefore a large amount of metal components are eluted from the base material of the reaction vessel through the chemical solution that has soaked into the inner wall of the reaction vessel (pinholes present in the fluororesin layer) during the manufacturing process. However, in the method described in Patent Document 3, an ion exchange treatment is further carried out using both ion exchange resins, and therefore it is believed that most of the eluted metal components are removed.

[0015] However, the inventors of the present invention have found that, in the case of colloidal silica obtained by purification treatment using the amphoteric ion exchange resin described in Patent Document 3, the dispersion stability of the silica particles decreases due to pH fluctuations that occur during the amphoteric ion exchange treatment, causing aggregation of the silica particles and resulting in an increase in the content of coarse particles. For this reason, when the colloidal silica is applied to chemical mechanical polishing (CMP) of semiconductor devices, it is thought that the large amount of coarse particles contained therein will cause a decrease in the flatness of the polished surface.

[0016] Under these circumstances, an object of the present invention is to provide colloidal silica that, when used as abrasive grains for polishing electronic materials such as semiconductor wafers, highly suppresses metal contamination of the surface to be polished, exhibits an excellent removal rate, and is capable of forming a polished surface with excellent flatness, as well as to provide a method for producing the colloidal silica. [Means for solving the problem]

[0017] In order to solve the above technical problems, the present inventors have conducted extensive research and have found that the total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is less than 100 ppb by mass, and 29 The present inventors have found that colloidal silica containing silica particles in which the peak area ratio of the peak derived from the Q4 structure to the total of the peaks derived from the Q1 structure, the peaks derived from the Q2 structure, the peaks derived from the Q3 structure, and the Q4 structure in a Si-solid-state NMR spectrum is 73.0% or more, and in which the content of coarse particles having a particle size of 0.2 μm or more is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass, can be eliminated. Based on this finding, the present invention has been completed.

[0018] That is, the present invention is (1) The total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is less than 100 ppb by mass, and 29 The silica particles contain silica particles in which the peak area ratio of the peak due to the Q4 structure to the total of the peaks due to the Q1 structure, the peaks due to the Q2 structure, the peaks due to the Q3 structure, and the peaks due to the Q4 structure in a Si-solid-state NMR spectrum is 73.0% or more, The content of coarse particles with a diameter of 0.2 μm or more is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Colloidal silica characterized by: (2) The colloidal silica according to (1) above, having a sodium content of less than 40 ppb by mass. (3) The colloidal silica according to (1) above, having a potassium content of less than 30 ppb by mass. (4) The colloidal silica according to (1) above, having a zinc content of less than 1 ppb by mass. (5) The amount of silanol groups per unit weight of the silica particles is 3.5 × 10 21 The colloidal silica according to (1) above, having a particle size of 1 / g or less. (6) The colloidal silica according to (1), wherein the alkoxy group content of the silica particles is 20,000 ppm by mass or less. (7) When the silica particles are evaluated by Raman spectroscopy, the intensity of the peak due to the four-membered ring structure of silica (490 cm ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 ) is 3.50 or less. (8) A method for producing colloidal silica according to (1) above, comprising the steps of: A raw material solution containing alcohol and tetraalkoxysilane is added to a mother liquor containing a basic catalyst, water, and alcohol at a constant rate over a period of 500 to 700 minutes at a temperature of 25 to 35°C, thereby carrying out a reaction step of hydrolyzing and dehydrating condensing the tetraalkoxysilane. A method for producing colloidal silica, This provides: [Effects of the Invention]

[0019] According to the present invention, it is possible to provide colloidal silica that, when used as abrasive grains for polishing electronic materials such as semiconductor wafers, highly suppresses metal contamination of the surface to be polished, exhibits an excellent removal rate, and is capable of forming a polished surface with excellent flatness, and it is also possible to provide a simple method for producing the colloidal silica. DETAILED DESCRIPTION OF THE INVENTION

[0020] First, the colloidal silica according to the present invention will be described. The colloidal silica according to the present invention has a total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt of less than 100 ppb by mass, 29The silica particles contain silica particles in which the peak area ratio of the peak due to the Q4 structure to the total of the peaks due to the Q1 structure, the peaks due to the Q2 structure, the peaks due to the Q3 structure, and the peaks due to the Q4 structure in a Si-solid-state NMR spectrum is 73.0% or more, The content of coarse particles with a diameter of 0.2 μm or more is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. It is characterized by the following.

[0021] The colloidal silica according to the present invention has a total content of sodium (Na), potassium (K), iron (Fe), aluminum (Al), calcium (Ca), magnesium (Mg), titanium (Ti), nickel (Ni), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), silver (Ag), manganese (Mn), and cobalt (Co) of less than 100 ppb by mass (not less than 0 ppb by mass and less than 100 ppb by mass).

[0022] The colloidal silica according to the present invention preferably has a total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt of 95 ppb by mass or less (0 ppb by mass or more and 95 ppb by mass or less), and more preferably 90 ppb by mass or less (0 ppb by mass or more and 90 ppb by mass or less).

[0023] In the colloidal silica according to the present invention, the total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is within the above range, so that the colloidal silica according to the present invention can be suitably used as polishing abrasive grains in chemical mechanical polishing (CMP) of semiconductor devices while suppressing metal contamination of the polished surface.

[0024] The colloidal silica according to the present invention preferably has a sodium content of less than 40 ppb by mass (not less than 0 ppb by mass and less than 40 ppb by mass), more preferably less than 39 ppb by mass (not less than 0 ppb by mass and less than 39 ppb by mass), and even more preferably less than 38 ppb by mass (not less than 0 ppb by mass and less than 38 ppb by mass).

[0025] The colloidal silica according to the present invention, having a sodium content within the above range, can be particularly suitably used as an abrasive for chemical mechanical polishing (CMP) of semiconductor devices. That is, because sodium has high electrical mobility when ionized, when sodium is present in colloidal silica, it is likely to diffuse into the insulating layers that constitute semiconductor devices, which is likely to cause deterioration in the characteristics of the semiconductor devices. In contrast, in the colloidal silica according to the present invention, the sodium content is within the above range, so that even when the colloidal silica is used as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices, the inclusion of sodium is limited, making it particularly suitable for use as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices.

[0026] The colloidal silica according to the present invention preferably has a potassium content of less than 30 ppb by mass (not less than 0 ppb by mass and less than 30 ppb by mass), more preferably less than 28 ppb by mass (not less than 0 ppb by mass and less than 28 ppb by mass), and even more preferably less than 26 ppb by mass (not less than 0 ppb by mass and less than 26 ppb by mass).

[0027] The colloidal silica according to the present invention, having a potassium content within the above range, can be particularly suitably used as an abrasive for chemical mechanical polishing (CMP) of semiconductor devices. That is, potassium has high electrical mobility when ionized, and therefore, if potassium is present in colloidal silica, it will easily diffuse into the insulating layer that constitutes the semiconductor device, which will likely cause a deterioration in the characteristics of the semiconductor device. In contrast, in the colloidal silica according to the present invention, the potassium content is within the above range, so that even when the colloidal silica is used as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices, the inclusion of potassium is limited, making the colloidal silica particularly suitable for use as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices.

[0028] The colloidal silica according to the present invention preferably has a zinc content of less than 1 ppb by mass (not less than 0 ppb by mass and less than 1 ppb by mass).

[0029] The colloidal silica according to the present invention preferably has an iron content of less than 5 ppb by mass (not less than 0 ppb by mass and less than 5 ppb by mass), more preferably less than 4 ppb by mass (not less than 0 ppb by mass and less than 4 ppb by mass), and even more preferably less than 3 ppb by mass (not less than 0 ppb by mass and less than 3 ppb by mass).

[0030] The colloidal silica according to the present invention, having an iron content within the above range, can be particularly suitably used as an abrasive for chemical mechanical polishing (CMP) of semiconductor devices. Iron easily diffuses into the silicon crystals used as the base of semiconductor devices, and also forms recombination centers in the silicon, shortening the lifetime of carriers such as electrons and holes, which can easily cause deterioration in the performance of semiconductor devices. In contrast, in the colloidal silica according to the present invention, the iron content is within the above range, so that the inclusion of iron is limited even when the colloidal silica is used as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices, making it particularly suitable for use as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices.

[0031] The colloidal silica according to the present invention has a sodium content, potassium content, zinc content, or iron content within the above range, so that even when the colloidal silica according to the present invention is used as an abrasive for polishing electronic materials such as semiconductor wafers, metal contamination of the polished surface can be suitably suppressed.

[0032] In the present application, the individual contents (metal concentrations) or total contents (total metal concentration) of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt refer to values ​​measured by the following method.

[0033] <Metal concentration measurement method> Hydrofluoric acid is added to colloidal silica to dissolve the silica particles, and then the solution is heated to remove the hydrofluoric acid. Ultrapure water is then added to the resulting residue to prepare a measurement solution. Using the above measurement solution, the contents (concentrations of each metal) of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt are measured using a high-frequency plasma mass spectrometer (Shimadzu ICPM-8500).The sum of these contents (concentrations of each metal) is then taken as the total content (total metal concentration) of each of the above metal components. By performing the dissolution treatment of silica particles with hydrofluoric acid as described above, it is possible to detect metal components contained inside the silica particles with high accuracy, and to appropriately evaluate the concentration of each metal. That is, if the metal concentration is measured without dissolving the silica particles, the metal components contained inside the silica particles or adsorbed on the surface of the silica particles cannot be detected, and the metal concentration will be underestimated. For this reason, in the present application, hydrofluoric acid is added to the colloidal silica in advance to dissolve the silica particles, and then the concentration of each metal component is measured.

[0034] The colloidal silica according to the present invention is 29 The silica particles contain silica particles in which the peak area ratio of the peak originating from the Q4 structure to the total of the peaks originating from the Q1 structure, the peaks originating from the Q2 structure, the peaks originating from the Q3 structure, and the peaks originating from the Q4 structure in the Si-solid state NMR spectrum is 73.0% or more (73.0% or more and 100.0% or less).

[0035] Here, the Q1 structure of silica particles means a structure in which one siloxane bond (Si-O-Si bond) is formed via one of the four bonds between a Si atom and an O atom. Furthermore, the Q2 structure of silica particles means a structure in which two siloxane bonds (Si-O-Si bonds) are formed via two of the four bonds between the Si atom and the O atom. Furthermore, the Q3 structure of silica particles means a structure in which three siloxane bonds (Si-O-Si bonds) are formed via three of the four bonds between the Si atom and the O atom. The Q4 structure of silica particles means a structure in which four siloxane bonds (Si-O-Si bonds) are formed via four of the four bonds between Si atoms and O atoms. In the Q1 to Q3 structures of silica particles, of the four bonds between Si atoms and O atoms, the bonds that do not form siloxane bonds (Si-O-Si bonds) usually form silanol groups (Si-OH). The Q1 structure of the silica particles is SiO 1 / 2 It can also be expressed as (OH)3, and its formula weight is 87.11 g / mol. The Q2 structure of the silica particles can also be expressed as SiO(OH)2, and its formula weight is 78.10 g / mol. The Q3 structure of the silica particles can also be expressed as SiO 3 / 2 (OH) and has a formula weight of 69.09 g / mol. In addition, the Q4 structure of the silica particles can be expressed as SiO2 and has a formula weight of 60.08 g / mol.

[0036] the above 29 In the Si-solid-state NMR spectrum, the higher the peak area ratio (Q4 structure ratio) of the peak originating from the Q4 structure to the total of the peaks originating from the Q1 structure, the peaks originating from the Q2 structure, the peaks originating from the Q3 structure, and the peaks originating from the Q4 structure, the higher the proportion of siloxane bonds (Si-O-Si bonds) present in the silica particles. Therefore, a high ratio of the Q4 structure means that the content of silica particles in which siloxane bonds are densely formed is high among the silica particles that make up the colloidal silica.

[0037] The colloidal silica according to the present invention is 29 The silica particles contain silica particles in which the peak area ratio of the peak derived from the Q4 structure to the total of the peaks derived from the Q1 structure, the peaks derived from the Q2 structure, the peaks derived from the Q3 structure, and the peaks derived from the Q4 structure in the Si-solid-state NMR spectrum is 73.0% or more (73.0% or more and 100.0% or less), preferably 74.0% or more (74.0% or more and 100.0% or less), and more preferably 74.5% or more (74.5% or more and 100.0% or less).

[0038] The colloidal silica according to the present invention comprises, as silica particles: 29 The compound contains a substance in which siloxane bonds (Si-O-Si bonds) are densely formed, and in which the peak area ratio of the peak derived from the Q4 structure to the total of the peaks derived from the Q1 structure, the peaks derived from the Q2 structure, the peaks derived from the Q3 structure, and the peaks derived from the Q4 structure in the Si-solid state NMR spectrum is within the above range. Therefore, when the colloidal silica according to the present invention is used as abrasive grains for polishing in chemical mechanical polishing (CMP) of semiconductor devices, a high polishing rate can be easily achieved.

[0039] In this application, silica particles 29 In the Si-solid-state NMR spectrum, the peaks due to the Q1 structure, the peaks due to the Q2 structure, the peaks due to the Q3 structure, and the peaks due to the Q4 structure are 29 This means the value determined by Si-DD / MAS-NMR spectrum, and the ratio of the Q4 structure in the silica particles is calculated based on the peak area of ​​each peak obtained.

[0040] Specifically, in the present application documents, the peaks derived from the Q1 structure, the peaks derived from the Q2 structure, the peaks derived from the Q3 structure, and the peaks derived from the Q4 structure of the silica particles, as well as the ratio of the Q4 structure of the silica particles, are calculated by the following method.

[0041] <Method for measuring peaks derived from Q1 structure to Q4 structure of silica particles and method for calculating the ratio of Q4 structure> [Step 1] The colloidal silica is centrifuged at 77,400 G, 5°C, and for 90 minutes, and the resulting precipitate is dried under reduced pressure at 60°C and a gauge pressure of -0.1 MPa or less for 90 minutes to obtain a dry silica powder. [Step 2] The dried silica powder obtained in step 1 was solidified. 29 Analyzed by Si-DD / MAS-NMR, 29 Obtain a Si-solid state NMR spectrum. The NMR analysis uses the DD-MAS method. The NMR device used is an ECZ500R manufactured by JEOL Ltd., and the probe used for detecting NMR signals is an 8 mm HXMAS probe manufactured by JEOL Ltd. [Step 3] Obtained in step 2 29 The Si-solid-state NMR spectrum data is analyzed, and when the signal of the silicon atom of tetramethylsilane is set to 0 ppm, the peak at a chemical shift of approximately -84 ppm is determined to be the peak derived from the Q1 structure, the peak at approximately -92 ppm is determined to be the peak derived from the Q2 structure, the peak at approximately -101 ppm is determined to be the peak derived from the Q3 structure, and the peak at approximately -111 ppm is determined to be the peak derived from the Q4 structure. The signal areas of the peaks derived from the Q1 structure to the Q4 structure are calculated as peak areas a1 to a4, respectively. In analyzing the spectral data, optimization calculations are performed for each peak in the spectrum after Fourier transformation using the nonlinear least squares method, with the center position, height, and half-width of the peak shape created by mixing Lorentzian and Gaussian waveforms as variable parameters. [Step 4] From the peak areas a1 to a4 of the peaks derived from the Q1 structure to the Q4 structure obtained in step 3, the peak area ratio of the peak derived from the Q4 structure to the total area of ​​the peaks derived from the Q1 structure to the Q4 structure (ratio of Q4 structure) is calculated using the following formula. Q4 structure ratio = a4 × 100 ÷ (a1 + a2 + a3 + a4)

[0042] The colloidal silica according to the present invention has a silanol group content of 3.5×10 per unit weight of silica particles. 21 pieces / g or less (0.0×10 21 pieces / g~3.5×10 21 3.2 × 10 21 pieces / g or less (0.0×10 21 pieces / g~3.2×10 21 2.9 × 10 21 pieces / g or less (0.0×10 21 pieces / g~2.9×10 21 It is more preferable that the average particle size is 1 / g.

[0043] In the colloidal silica according to the present invention, the amount of silanol groups (Si-OH) per unit weight of silica particles is controlled to fall within the above range, and therefore the proportion of siloxane bonds (Si-O-Si bonds) in the silica particles is relatively high, and the siloxane bonds (Si-O-Si bonds) are formed densely. Therefore, in the colloidal silica according to the present invention, if the amount of silanol groups per unit weight of silica particles is within the above range, a high removal rate can be easily achieved when the colloidal silica according to the present invention is used as abrasive grains for polishing electronic materials such as semiconductor wafers.

[0044] In the present application, the amount of silanol groups per unit weight of silica particles is determined by the above-mentioned method. 29It means a value calculated by the following formula from the peak areas a1, a2, a3, and a4 of the peaks derived from the Q1 structure, Q2 structure, Q3 structure, and Q4 structure of the silica particles in the Si-solid state NMR spectrum, and the formula weights of the Q1 structure, Q2 structure, Q3 structure, and Q4 structure. Amount of silanol groups per unit weight of silica particles =[{(a1×3)+(a2×2)+(a3×1)}×N A ] ÷{(a1×87.11)+(a2×78.10)+(a3×69.09)+(a4×60.08)} In the above formula, N A Avogadro's number is 6.02 x 10 23 Represents.

[0045] The colloidal silica according to the present invention is silica particles having an alkoxy group content of preferably 20,000 ppm by mass or less (0 to 20,000 ppm by mass), more preferably 17,000 ppm by mass or less (0 to 17,000 ppm by mass), and even more preferably 14,000 ppm by mass or less (0 to 14,000 ppm by mass).

[0046] The colloidal silica according to the present invention is usually produced using an alkoxysilane such as tetraalkoxysilane as a raw material. Therefore, in the colloidal silica according to the present invention, the alkoxy group content of the silica particles is controlled within the above range, so that the reaction of the raw materials proceeds, and the proportion of siloxane bonds (Si-O-Si bonds) in the produced silica particles becomes relatively high, and the siloxane bonds (Si-O-Si bonds) are formed densely. Therefore, in the colloidal silica according to the present invention, when the alkoxy group content of the silica particles is within the above range, a high removal rate can be easily achieved when the colloidal silica according to the present invention is used as abrasive grains for polishing in chemical mechanical polishing (CMP) of semiconductor devices.

[0047] In the present application, the alkoxy group content of silica particles means a value calculated by the following method.

[0048] <Method for measuring the alkoxy group content of silica particles> The colloidal silica is centrifuged at 215,000 G for 90 minutes, the supernatant is discarded, and the solid content is vacuum dried at 60° C. for 90 minutes. 0.5 g of the obtained dried silica was weighed out, placed in 50 mL of 1 M aqueous sodium hydroxide solution, and heated at 50°C for 24 hours with stirring to dissolve the silica. The obtained silica solution was analyzed by gas chromatography to determine the alcohol content, which was taken as the alkoxy group content of the silica particles. A flame ionization detector (FID) is used as the detector for the gas chromatograph, and the gas chromatographic analysis is carried out in accordance with JIS K0114.

[0049] The colloidal silica according to the present invention has a peak intensity I (490 cm) derived from the four-membered ring structure of silica when the silica particles are evaluated by Raman spectroscopy. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the siloxane bond (Si-O-Si bond) of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 ) is preferably 3.50 or less (0.00 to 3.50), more preferably 3.45 or less (0.00 to 3.45), and even more preferably 3.40 or less (0.00 to 3.40).

[0050] The colloidal silica according to the present invention has the above peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 ) is controlled to fall within the above range, a high removal rate can be easily achieved when used as abrasive grains for polishing in chemical mechanical polishing (CMP) of semiconductor devices.

[0051] The Raman shift of approximately 490 cm detected when silica particles constituting colloidal silica are analyzed by Raman spectroscopy. ―1 The peak that appears in the graph is due to the four-membered ring structure of silica. In addition, when silica particles that make up colloidal silica are analyzed by Raman spectroscopy, the Raman shift is detected as approximately 800 cm ―1 The peak that appears in the graph is due to the asymmetric stretching vibration of the siloxane bond (Si-O-Si bond) of silica. Therefore, the Raman shift is about 490 cm ―1 The intensity of the peak appearing at 490 cm ―1 ) and the Raman shift is about 800 cm ―1 The intensity of the peak appearing at 800 cm ―1 ) and the peak intensity ratio "I (490 cm ―1 ) / I(800cm ―1 ) is an index of the proportion of four-membered ring structures contained in silica, and the above peak intensity ratio "I(490cm ―1 ) / I(800cm ―1 )" indicates that the proportion of four-membered ring structures is low. Here, the above-mentioned "four-membered ring structure of silica" means a structure in which four SiO4 tetrahedra are bonded in a ring via a shared oxygen atom. In the above-mentioned "four-membered ring structure of silica," the bond angle of the siloxane bond (Si-O-Si bond) becomes small, causing local distortion and making the Si-O bond more likely to break when an external force is applied. Therefore, the region where the above-mentioned "four-membered ring structure of silica" exists is more likely to function as a defective site where the silica begins to break when an external force is applied. Therefore, in the colloidal silica according to the present invention, the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 ) is controlled to be within a predetermined range, the proportion of four-membered ring structures that tend to function as defect sites that initiate destruction of silica when an external force is applied can be reduced, and the mechanical strength of the silica particles can be easily increased. Therefore, as the colloidal silica according to the present invention, the above peak intensity ratio I (490 cm ―1 ) / I(800cm ―1) is controlled to fall within a predetermined range, a high polishing rate can be easily achieved when used as a polishing abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices.

[0052] In the present application, when silica particles are evaluated by Raman spectroscopy, the intensity of the peak derived from the four-membered ring structure of silica, "I (490 cm ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica, "I (800 cm ―1 ) and the peak intensity ratio "I (490 cm ―1 ) / I(800cm ―1 )" means the value calculated in the following manner.

[0053] <Peak intensity ratio I (490cm ―1 ) / I(800cm ―1 ) Measurement method> 2 mL of colloidal silica adjusted to a silica concentration of 20 mass % is taken and placed in the sample holder of a Raman spectrometer (Xplora Raman microscope manufactured by Horiba, Ltd.), and measured under the conditions shown below. (Raman spectroscopy measurement conditions) Measurement mode: Macro-Raman Measurement arrangement: 180° scattering Light source: Laser / 532nm Laser power: 20~25mW Diffraction grating: 600gr / mm Slit: 100μm Detector: CCD detector From the Raman spectrum measured under the above conditions, the Raman shift due to the four-membered ring structure of silica is approximately 490 cm ―1 Peak intensity at I (490 cm ―1 ) and the Raman shift due to the asymmetric stretching vibration of the Si-O-Si bond of silica is approximately 800 cm ―1 Peak intensity at I(800cm ―1 ) and find "I(490cm ―1 )" to "I(800cm ―1 ) to obtain the peak intensity ratio "I(490cm―1 ) / I(800cm ―1 )" is calculated.

[0054] As will be described later, one method for preparing colloidal silica according to the present invention is to add, for example, tetramethoxysilane (Si(OCH3)4) at a constant rate to an organic solvent containing water, thereby forming a dimer through hydrolysis and dehydration condensation, and this dimer then polymerizes (oligomerizes) to form spherical primary silica particles in the solvent. These spherical primary silica particles dispersed in the solvent correspond to colloidal silica. The colloidal silica contains not only primary silica particles but also secondary silica particles formed by association of the primary silica particles, and these secondary silica particles are dispersed in the solvent together with the primary silica particles.

[0055] The average primary particle size of the silica particles contained in the colloidal silica according to the present invention (average diameter of the primary silica particles) is not particularly limited, but is preferably 5 nm or more and 120 nm or less.

[0056] The average primary particle size of the silica particles contained in the colloidal silica according to the present invention is preferably 120 nm or less, more preferably 110 nm or less, and even more preferably 100 nm or less.

[0057] When the average primary particle size of the silica particles contained in the colloidal silica according to the present invention is the above-mentioned value (upper limit value) or less, a polished surface with superior flatness can be formed when polishing is performed using the colloidal silica according to the present invention.

[0058] The average primary particle size of the silica particles contained in the colloidal silica according to the present invention is preferably 5 nm or more, more preferably 6 nm or more, and even more preferably 7 nm or more.

[0059] When the average primary particle size of the silica particles contained in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), a high polishing rate can be easily achieved when polishing is performed using the colloidal silica according to the present invention.

[0060] In the present application, the average primary particle size of silica particles contained in colloidal silica refers to a value measured by the BET method described below. That is, first, colloidal silica is pre-dried on a hot plate at 150°C, and then heat-treated at 800°C for 1 hour to prepare a measurement sample. The specific surface area S of the obtained measurement sample is measured by the BET method (BET specific surface area). For nearly spherical particles, the average primary particle diameter (nm) of silica particles is calculated using the following formula: Average primary particle diameter of silica particles (nm) = 6000 / (BET specific surface area S (m 2 / g) x true density (g / cm 3 )) where the true density of the silica particles is 2.2 g / cm 3 Based on this, the average primary particle size (nm) of silica particles is calculated by the following formula: Average primary particle diameter of silica particles (nm) = 2727 / BET specific surface area S (m 2 / g) It can be calculated by:

[0061] The colloidal silica according to the present invention contains secondary silica particles formed by association of primary silica particles. The secondary silica particles contained in the colloidal silica according to the present invention, together with the primary silica particles contained in the colloidal silica according to the present invention, constitute the main particles of the silica particles, and are distinguished from coarse particles (described below) formed by aggregation of the secondary silica particles.

[0062] The average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention (average diameter of the secondary silica particles) is preferably 10 to 150 nm.

[0063] The average secondary particle size of the silica particles contained in the colloidal silica according to the present invention is preferably 150 nm or less, more preferably 145 nm or less, even more preferably 140 nm or less, even more preferably 135 nm or less, and even more preferably 130 nm or less.

[0064] When the average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is the above-mentioned value (upper limit value) or less, a polished surface with superior flatness can be formed when polishing is performed using the colloidal silica according to the present invention.

[0065] The average secondary particle size of the silica particles contained in the colloidal silica according to the present invention is preferably 10 nm or more, more preferably 12 nm or more, even more preferably 15 nm or more, and particularly preferably 20 nm or more.

[0066] When the average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), a high polishing rate can be easily achieved when polishing is performed using the colloidal silica according to the present invention.

[0067] In the present application, the average secondary particle size of silica particles contained in colloidal silica refers to a value measured by the dynamic light scattering method described below. That is, first, a 0.3% by mass aqueous solution of citric acid is added to colloidal silica to be used as a measurement sample, and the colloidal silica is uniformly diluted to a silica particle concentration of 0.8% by mass, and the resulting diluted solution is used as a measurement sample. Using the above measurement sample, measurements are performed by dynamic light scattering using the Zeta Potential, Particle Size, and Molecular Weight Measurement System "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd., and the hydrodynamic diameter is determined by analyzing the autocorrelation function derived from the temporal change in scattered light intensity using the cumulant method, and the obtained hydrodynamic diameter is taken as the average secondary particle diameter of the silica particles.

[0068] In the colloidal silica according to the present invention, Association ratio = average secondary particle size of silica particles (nm) ÷ average primary particle size of silica particles (nm) The association ratio of the silica particles calculated by the above formula is preferably 1.0 or more and 3.0 or less.

[0069] In the colloidal silica according to the present invention, the association ratio of silica particles is preferably 3.0 or less, more preferably 2.8 or less, and even more preferably 2.4 or less. In the colloidal silica according to the present invention, when the association ratio is the above-mentioned value (upper limit value) or less, when the colloidal silica according to the present invention is used as abrasive grains for polishing, the flatness of the polished surface can be easily improved.

[0070] In the colloidal silica according to the present invention, the association ratio of silica particles is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.4 or more. In the colloidal silica according to the present invention, when the association ratio of silica particles is equal to or greater than the above value (lower limit), a high removal rate can be easily achieved when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0071] The colloidal silica according to the present invention preferably has a cumulative 50% particle size D50 from the small particle size side in the cumulative number frequency distribution of silica particles of 150 nm or less, more preferably 140 nm or less, and even more preferably 130 nm or less.

[0072] When the cumulative 50% particle diameter D50 of the silica particles contained in the colloidal silica according to the present invention is the above-mentioned value (upper limit value) or less, a polished surface with superior flatness can be easily formed when polishing is performed using the colloidal silica according to the present invention.

[0073] The colloidal silica according to the present invention preferably has a cumulative 50% particle diameter D50 from the small particle diameter side in the cumulative number frequency distribution of silica particles of 7 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more.

[0074] When the cumulative 50% particle diameter D50 of the silica particles contained in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), a high polishing rate can be easily achieved when polishing is performed using the colloidal silica according to the present invention.

[0075] In the present application, the cumulative 50% particle diameter D50 of silica particles contained in colloidal silica refers to a value measured by the method described below. That is, first, a 0.3% by mass aqueous solution of citric acid is added to colloidal silica to be used as a measurement sample, and the colloidal silica is uniformly diluted to a silica particle concentration of 0.8% by mass, and the resulting diluted solution is used as a measurement sample. Using the above measurement sample, measurements are taken using the "ELSZ-2000S" Zeta Potential, Particle Size, and Molecular Weight Measurement System manufactured by Otsuka Electronics Co., Ltd. From the cumulative number frequency obtained in the measurement, the particle diameter when the cumulative number from the small particle size side reaches 50% is determined, and this is taken as the cumulative 50% particle diameter D50.

[0076] The colloidal silica according to the present invention preferably has a cumulative 95% particle diameter D95 from the small particle diameter side in the cumulative number frequency distribution of silica particles of 200 nm or less, more preferably 190 nm or less, and even more preferably 180 nm or less.

[0077] When the cumulative 95% particle diameter D95 of the silica particles contained in the colloidal silica according to the present invention is the above-mentioned value (upper limit value) or less, a polished surface with superior flatness can be formed when polishing is performed using the colloidal silica according to the present invention.

[0078] The colloidal silica according to the present invention preferably has a cumulative 95% particle size D95 from the small particle size side in the cumulative number frequency distribution of silica particles of 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more.

[0079] When the cumulative 95% particle diameter D95 of the silica particles contained in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), a high polishing rate can be easily achieved when polishing is performed using the colloidal silica according to the present invention.

[0080] In the present application, the cumulative 95% particle diameter D95 of silica particles contained in colloidal silica refers to a value measured by the method described below. That is, first, a 0.3% by mass aqueous solution of citric acid is added to colloidal silica to be used as a measurement sample, and the colloidal silica is uniformly diluted to a silica particle concentration of 0.8% by mass, and the resulting diluted solution is used as a measurement sample. Using the above measurement sample, measurements are taken using the "ELSZ-2000S" Zeta Potential, Particle Size, and Molecular Weight Measurement System manufactured by Otsuka Electronics Co., Ltd. From the cumulative number frequency obtained in the measurement, the particle diameter at which the cumulative number from the small particle size side reaches 95% is determined, and this is taken as the cumulative 95% particle diameter D95.

[0081] In the colloidal silica according to the present invention, (D95-D50) / D50, which is the difference between the cumulative 95% particle diameter D95 and the cumulative 50% particle diameter D50 of silica particles divided by the cumulative 50% particle diameter D50, is preferably 0.30 or more and 0.65 or less.

[0082] In the colloidal silica according to the present invention, the (D95-D50) / D50 of the silica particles is preferably 0.65 or less, more preferably 0.62 or less, and even more preferably 0.60 or less. In the colloidal silica according to the present invention, when (D95-D50) / D50 is the above-mentioned value (upper limit value) or less, when the colloidal silica according to the present invention is used as abrasive grains for polishing, it becomes easier to improve the flatness of the polished surface.

[0083] In the colloidal silica according to the present invention, the (D95-D50) / D50 of the silica particles is preferably 0.30 or more, more preferably 0.33 or more, and even more preferably 0.35 or more. In the colloidal silica according to the present invention, when the (D95-D50) / D50 of the silica particles is equal to or greater than the above value (lower limit), a high removal rate can be easily achieved when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0084] The colloidal silica according to the present invention has a content of coarse particles having a particle size of 0.2 μm or more of 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass.

[0085] In the colloidal silica according to the present invention, the content of coarse particles having a particle size of 0.2 μm or more is 10,000,000 particles / mL or less, preferably 9,800,000 particles / mL or less, and more preferably 9,600,000 particles / mL or less, when the silica particle concentration is 1% by mass.

[0086] In the colloidal silica according to the present invention, coarse particles having a particle size of 0.2 μm or more are included as part of the silica particles. In the colloidal silica according to the present invention, when the content of coarse particles having a particle size of 0.2 μm or more is set to the above-mentioned value (upper limit) or less when the silica particle concentration is set to 1 mass %, roughness of the polished surface due to the presence of coarse particles can be suppressed when chemical mechanical polishing (CMP) is performed using the colloidal silica according to the present invention, and a polished surface with high flatness can be easily formed.

[0087] In the colloidal silica according to the present invention, there is no particular lower limit for the content of coarse particles having a particle size of 0.2 μm or more. However, in the colloidal silica according to the present invention, the content of coarse particles having a particle size of 0.2 μm or more contained in the silica particles is preferably 0 particles / mL or more, and can be 1,000 particles / mL or more, when the silica particle concentration is 1% by mass.

[0088] In the present application, the content of coarse particles having a particle size of 0.2 μm or more means the value measured by the particle size distribution measurement method using a number counting method described below. <Method for measuring the content of coarse particles with a particle size of 0.2 μm or more> Ultrapure water is added to colloidal silica to be measured and diluted to a silica particle concentration of 1% by mass. The obtained diluted solution is used as a measurement sample, and the number of coarse particles with a particle size of 0.2 μm or more is measured using an Accusizer FX-nano manufactured by Particle Sizing Systems Inc. under the following measurement conditions. <System Setup> ·Stirred Vessel Volume: 13.22mL Sample Loop Volume: 0.52mL ·Autodilution delay time: 3sec. ·Normal Speed ​​Flow Rate: 15mL / min <Sensor Setup Menu> ·FX-Nano HG Minimum Size: 0.15μm ·FX-Nano HG Maximum Size: 0.27μm ·FX-Nano HG Collection Time: 60sec. ·HG Starting Concentration : 8000♯ / mL

[0089] The colloidal silica according to the present invention has a particle density of 1.8 g / cm3 as determined by a liquid phase substitution method. 3 Preferably, it is 1.9 g / cm or more. 3 More preferably, it is 2.0 g / cm or more. 3 More preferably, the above is true.

[0090] In the colloidal silica according to the present invention, the particle density of the silica particles constituting the colloidal silica, as determined by a liquid phase substitution method, is at least the above value (lower limit value), so that when the colloidal silica according to the present invention is used as abrasive grains for polishing, it is possible to easily form a polished surface with reduced surface roughness while exhibiting excellent polishing properties.

[0091] The colloidal silica according to the present invention has a particle density of 2.2 g / cm3 as determined by a liquid phase substitution method.3 The following is preferred:

[0092] In the present application, the particle density measured by the liquid phase displacement method refers to a value measured by drying a colloidal silica sample on a hot plate at 150°C, heating and holding the sample in a furnace at 300°C for 1 hour, and then measuring the particle density by the liquid phase displacement method using ethanol.

[0093] The content of silica particles in the colloidal silica according to the present invention is not particularly limited, but is preferably 2% by mass or more and 50% by mass or less, when the content of colloidal silica is taken as 100% by mass.

[0094] The content of silica particles in the colloidal silica according to the present invention (silica particle concentration) is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, when the content of colloidal silica is taken as 100% by mass.

[0095] When the content of silica particles in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), the polishing performance can be further improved when the colloidal silica according to the present invention is used as abrasive grains for polishing.

[0096] The content of silica particles in the colloidal silica according to the present invention (concentration of silica particles) is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, based on 100% by mass of the colloidal silica content. When the content of silica particles in the colloidal silica according to the present invention is the above value (upper limit) or less, the long-term dispersion stability of the silica particles can be further improved.

[0097] In the present application, the content of silica particles (concentration of silica particles) in the colloidal silica according to the present invention means a value measured by the following measurement method. That is, 10.0 g of colloidal silica is dried on a hot plate at 150°C, and then heat-treated at 800°C for 1 hour to remove moisture. The amount of the resulting solid content is defined as Wg, and the value is calculated using the following formula. Silica particle content in colloidal silica (mass%) = (W / 10.0) x 100

[0098] The pH of the colloidal silica according to the present invention may be appropriately set depending on the application, and is not particularly limited, but is preferably 2.0 or more and 11.0 or less.

[0099] The pH of the 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. When the pH of the colloidal silica according to the present invention is equal to or higher than the above value (lower limit), the long-term dispersion stability of the silica particles in the colloidal silica according to the present invention can be easily improved.

[0100] The pH of the colloidal silica according to the present invention is preferably 11.0 or less, more preferably 10.7 or less, and even more preferably 10.5 or less. When the pH of the colloidal silica according to the present invention is equal to or less than the above value (upper limit), the long-term dispersion stability of the colloidal silica can be easily improved.

[0101] In the present application, pH refers to a value measured using a benchtop pH / water quality analyzer (F-2000PI manufactured by Horiba, Ltd.).

[0102] As a method for producing the colloidal silica according to the present invention, the method for producing the colloidal silica according to the present invention described below can be mentioned.

[0103] According to the present invention, it is possible to provide colloidal silica that, when used as an abrasive for polishing electronic materials such as semiconductor wafers, highly suppresses metal contamination of the surface to be polished, exhibits an excellent removal rate, and can form a polished surface with excellent flatness.

[0104] Next, a method for producing colloidal silica according to the present invention will be described. The method for producing colloidal silica according to the present invention is a method for producing the above-described colloidal silica according to the present invention, A raw material solution containing alcohol and tetraalkoxysilane is added to a mother liquor containing a basic catalyst, water, and alcohol at a constant rate over a period of 500 to 700 minutes at a temperature of 25 to 35°C, thereby carrying out a reaction step of hydrolyzing and dehydrating condensing the tetraalkoxysilane. It is characterized by the following.

[0105] In the method for producing colloidal silica according to the present invention, at least the reaction step is preferably carried out in a reaction vessel the inner wall of which is coated with a fluororesin or glass.

[0106] In the method for producing colloidal silica according to the present invention, the basic catalyst constituting the mother liquid is preferably one or more selected from organic amines and ammonia, from the viewpoint of preventing the inclusion of impurities. In particular, one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, 3-ethoxypropylamine (3-EOPOA), ammonia, urea, ethanolamine, tetramethylammonium hydroxide, etc. is more preferred, and ammonia is even more preferred. In the method for producing colloidal silica according to the present invention, when the basic catalyst constituting the mother liquid is one of those described above, the mother liquid has excellent catalytic activity and is highly volatile, allowing it to be easily removed in a subsequent step.

[0107] In the method for producing colloidal silica according to the present invention, the concentration of the basic catalyst in the mother liquor is preferably 0.2 to 3.0 mass %, more preferably 0.3 to 2.5 mass %, and even more preferably 0.5 to 1.8 mass %. In the method for producing colloidal silica according to the present invention, by ensuring that the concentration of the basic catalyst in the mother liquor is within the above range, the particle size of the silica particles in the resulting colloidal silica can be easily controlled within a desired range.

[0108] In the method for producing colloidal silica according to the present invention, the water constituting the mother liquor is preferably pure water or ultrapure water in order to minimize the inclusion of metal impurities.

[0109] In the method for producing colloidal silica according to the present invention, the concentration of water constituting the mother liquor is preferably 3.0 to 30.0 mass %, more preferably 5.0 to 28.0 mass %, and even more preferably 7.0 to 26.0 mass %. In the method for producing colloidal silica according to the present invention, by controlling the blending ratio of the mother liquid to the raw material solution while adjusting the water concentration in the mother liquid to be within the above range, it becomes easier to favorably promote the hydrolysis and dehydration condensation reaction of tetraalkoxysilane, which will be described later.

[0110] In the method for producing colloidal silica according to the present invention, the alcohol constituting the mother liquid is preferably at least one selected from methanol, ethanol, isopropanol, and the like.

[0111] In the method for producing colloidal silica according to the present invention, the alcohol constituting the mother liquid is more preferably the same alcohol as the alcohol produced by hydrolysis of a tetraalkoxysilane, which will be described later. For example, when the tetraalkoxysilane, which will be described later, is tetramethoxysilane (TMOS), the alcohol constituting the mother liquid is preferably methanol. In the method for producing colloidal silica according to the present invention, by using, as the alcohol constituting the mother liquid, the same alcohol as that produced by hydrolysis of tetraalkoxysilane, which will be described later, the alcohol can be easily recovered and reused.

[0112] In the method for producing colloidal silica according to the present invention, the concentration of the alcohol constituting the mother liquid is preferably 70 to 90 mass %, more preferably 72 to 88 mass %, and even more preferably 74 to 86 mass %. In the method for producing colloidal silica according to the present invention, when the concentration of alcohol in the mother liquor is within the above range, the dispersibility of the tetraalkoxysilane described below is excellent and the hydrolysis reaction is easily and suitably promoted.

[0113] In the method for producing colloidal silica according to the present invention, the alcohol constituting the raw material solution is preferably at least one selected from methanol, ethanol, isopropanol, and the like.

[0114] In the method for producing colloidal silica according to the present invention, the alcohol constituting the raw material solution is more preferably the same alcohol as the alcohol produced by hydrolysis of a tetraalkoxysilane, which will be described later. For example, when the tetraalkoxysilane, which will be described later, is tetramethoxysilane (TMOS), the alcohol constituting the raw material solution is preferably methanol. In the method for producing colloidal silica according to the present invention, by using, as the alcohol constituting the raw material solution, the same alcohol as that produced by hydrolysis of tetraalkoxysilane, which will be described later, the alcohol can be easily recovered and reused.

[0115] In the method for producing colloidal silica according to the present invention, the tetraalkoxysilane constituting the raw material solution is a tetraalkoxysilane represented by 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 the tetraalkoxysilane include tetraalkoxysilanes represented by the following formula:

[0116] In the tetraalkoxysilane or derivative thereof represented by the general formula (1), the R group is an alkyl group having 1 to 8 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms.

[0117] In the tetraalkoxysilane represented by general formula (1) or a derivative thereof, examples of the R group include one or more groups selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group, and preferably one or more groups selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group.

[0118] The tetraalkoxysilane represented by general formula (1) is preferably 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 the derivatives of tetraalkoxysilane represented by general formula (1) include low condensates obtained by partially hydrolyzing tetraalkoxysilane represented by general formula (1). As the tetraalkoxysilane represented by general formula (1) or its derivative, tetramethoxysilane (TMOS) is preferred because the hydrolysis rate can be easily controlled, silica particles in which siloxane bonds are densely formed can be easily obtained, fine silica particles can be easily obtained, and little unreacted material remains.

[0119] In the method for producing colloidal silica according to the present invention, the concentration of tetraalkoxysilane in the raw material solution is preferably 4.0 to 6.5 mol / L, more preferably 4.0 to 6.0 mol / L, and even more preferably 4.3 to 6.0 mol / L.

[0120] In the method for producing colloidal silica according to the present invention, when the concentration of the tetraalkoxysilane in the raw material solution is within the above range, the hydrolysis and dehydration condensation reaction of the tetraalkoxysilane is easily promoted.

[0121] In the method for producing colloidal silica according to the present invention, a raw material solution containing an alcohol and a tetraalkoxysilane is added at a constant rate to the mother liquor containing the basic catalyst, water, and an alcohol.

[0122] In the method for producing colloidal silica according to the present invention, when a raw material solution containing an alcohol and a tetraalkoxysilane is added to a mother liquor containing the basic catalyst, water, and an alcohol, the amount of the raw material solution added relative to 100 parts by mass of the mother liquor is preferably 5 to 70 parts by mass, more preferably 8 to 65 parts by mass, and even more preferably 10 to 60 parts by mass.

[0123] In the method for producing colloidal silica according to the present invention, by controlling the amount of the raw material solution added relative to 100 parts by mass of the mother liquid within the above range, it becomes easier to effectively proceed with the hydrolysis and dehydration condensation reaction of the tetraalkoxysilane in the raw material solution.

[0124] In the method for producing colloidal silica according to the present invention, in the reaction step, the mother liquor containing the basic catalyst, water, and alcohol and the raw material solution containing the alcohol and tetraalkoxysilane are reacted so that the ratio of the content of water constituting the mother liquor in the reaction solution to the content of tetraalkoxysilane constituting the raw material solution in the reaction solution (content of water constituting the mother liquor in the reaction solution / content of tetraalkoxysilane constituting the raw material solution in the reaction solution) is, in molar ratio, preferably 3.5 to 20.0, more preferably 4.0 to 15.0, and even more preferably 4.5 to 13.0.

[0125] In the method for producing colloidal silica according to the present invention, the reaction is carried out in the reaction step so that the ratio of the content of water constituting the mother liquor in the reaction solution to the content of tetraalkoxysilane constituting the raw material solution in the reaction solution falls within the above-mentioned range, thereby making it possible to easily control the particle size of silica particles in the resulting colloidal silica to fall within a desired range while easily progressing the hydrolysis-dehydration condensation reaction of tetraalkoxysilane in the raw material solution.

[0126] In the method for producing colloidal silica according to the present invention, the mother liquor and the raw material solution can be brought into contact with each other under any pressure condition, such as reduced pressure, normal pressure, or increased pressure, but is preferably brought into contact with each other under normal pressure.

[0127] In the method for producing colloidal silica according to the present invention, the temperature (reaction temperature) when the mother liquor and the raw material solution are brought into contact with each other to obtain a reaction liquid is 25 to 35°C. In the method for producing colloidal silica according to the present invention, by setting the reaction temperature in the reaction step within the above range, silica particles in which siloxane bonds are densely formed can be easily synthesized while suitably suppressing elution of metal components from the reaction vessel.

[0128] In the method for producing colloidal silica according to the present invention, the raw material solution is added to the mother liquor at a constant rate. When the total amount of raw material solution added to the mother liquor is w (g) and the total time for adding the raw material solution to the mother liquor is t (minutes), and the raw material solution is continuously added to the mother liquor in a constant amount over the entire addition time, the theoretical addition rate of the raw material solution, s (g / minute), is s = w / t. On the other hand, in reality, the rate of addition of the raw material solution to the mother liquor may vary over time to a certain extent depending on the addition method. Therefore, in the method for producing colloidal silica according to the present invention, adding the raw material solution to the mother liquor at a constant rate means continuously supplying the raw material solution to the mother liquor at an addition rate of 0.9 s (g / min) to 1.1 s (g / min) over the entire addition time (where s (g / min) is the above-mentioned theoretical addition rate).

[0129] In the method for producing colloidal silica according to the present invention, when the raw material solution is added to the mother liquor, the average addition rate of the raw material solution per part by mass of the mother liquor is 1.00 × 10 ―4 ~1.25×10 ―3 It is preferable that the ratio is 1.30×10 ―4 ~1.20×10 ―3 Parts by mass / minute / 1 part by mass of mother liquor is more preferably 1.50 × 10 ―4~1.15×10 ―3 It is more preferable that the rate is part by mass / minute / 1 part by mass of mother liquor.

[0130] The average addition rate of the raw material solution per 1 mass part of the mother liquor is calculated by dividing the total amount of the raw material solution by w 原料 The total amount of mother liquor is w 母液 The total addition time of the raw material solution to the mother liquor is t 原料 minutes, is defined by the following formula: Average addition rate of raw material solution per 1 part by mass of mother liquor (parts by mass / minute / 1 part by mass of mother liquor) = (w 原料 / t 原料 ) / w 母液

[0131] In the method for producing colloidal silica according to the present invention, by controlling the average addition rate of the raw material solution per part by mass of the mother liquid within the above range, silica particles in which siloxane bonds are densely formed can be easily synthesized.

[0132] In the method for producing colloidal silica according to the present invention, the addition time (reaction time) when the raw material solution is added to the mother liquor is 500 to 700 minutes, preferably 505 to 697 minutes, and more preferably 510 to 695 minutes.

[0133] In the method for producing colloidal silica according to the present invention, the raw material solution is added to the mother liquor at a constant rate, whereby the hydrolysis and dehydration condensation reaction of the tetraalkoxysilane proceeds, and silica particles are formed.

[0134] In the method for producing colloidal silica according to the present invention, by adding the raw material solution to the mother liquor at a constant rate over a long period of time as described above, colloidal silica containing silica particles in which siloxane bonds are densely formed can be easily produced even at a low temperature condition of 25 to 35°C.

[0135] As described above, in the past, when colloidal silica was obtained by subjecting tetraalkoxysilane to hydrolysis and dehydration condensation, in order to obtain silica particles in the colloidal silica in which siloxane bonds were densely formed, it was necessary to carry out the hydrolysis and dehydration condensation of tetraalkoxysilane under high-temperature conditions, for example, at 40°C or higher. In response to this problem, the present inventors conducted research and found that, even at low temperatures of 25 to 35°C in the reaction step, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane proceeds favorably by adding the raw material solution to the mother liquor at a constant rate over a long period of time, and silica particles in which siloxane bonds are densely formed can be easily formed. Based on this finding, the present invention was completed.

[0136] In the method for producing colloidal silica according to the present invention, the colloidal silica obtained in the reaction step contains an organic solvent such as alcohol 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 or the reaction solution may be subjected to a concentration treatment, if necessary.

[0137] The method for replacing the organic solvent with water is not particularly limited, and an example thereof is a method in which the organic solvent is replaced with water by continuously adding water while concentrating the reaction solution obtained by subjecting the reaction step to membrane concentration using an ultrafiltration membrane.

[0138] In the method for producing colloidal silica according to the present invention, the method for concentrating the reaction solution obtained by the reaction step is not particularly limited, and examples thereof include a heat concentration method, a membrane concentration method, and a reduced pressure method.

[0139] In the method for producing colloidal silica according to the present invention, in order to suppress aggregation of silica particles due to pH fluctuations that occur during the ion exchange process, it is desirable not to subject the colloidal silica obtained in the reaction step to an ion exchange treatment using an ion exchange resin such as an amphoteric ion exchange resin after the reaction step.

[0140] Details of the colloidal silica obtained by the production method according to the present invention are as described above in detail in the description of the colloidal silica according to the present invention.

[0141] According to the present invention, it is possible to provide a method for simply producing colloidal silica that, when used as an abrasive for polishing electronic materials such as semiconductor wafers, highly suppresses metal contamination of the surface to be polished, exhibits an excellent removal rate, and is capable of forming a polished surface with excellent flatness. [Example]

[0142] Next, the present invention will be explained in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples in any way.

[0143] Example 1 (1) Reaction process Ultra-high purity colloidal silica was prepared from raw materials including tetramethoxysilane, methanol, 28 mass% ammonia water, and ultra-pure water with an electrical resistivity of 18.0 MΩ·cm or higher, in which the metal concentration had been reduced to 1 mass ppb or less by distillation purification. First, 2359 parts by mass of ultrapure water, 440 parts by mass of 28% by mass ammonia water, and 8102 parts by mass of methanol were charged into a metal reaction vessel whose inner wall was coated with tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (PFA) to prepare a mother liquor. Also, 2214 parts by mass of tetramethoxysilane (TMOS) and 601 parts by mass of methanol were mixed to prepare a raw material solution. While maintaining the liquid temperature in the reaction system at 35°C, the raw material solution was poured into the mother liquid in the reaction vessel at a constant rate over 692 minutes, and the two were brought into contact and mixed to synthesize silica sol. (2) Concentration and solvent replacement process The obtained silica sol was concentrated to a silica concentration of 20% by mass by cross-flow filtration using an ultrafiltration membrane while controlling the temperature of the silica sol to 35°C or less. After the concentration was completed, cross-flow filtration was carried out using an ultrafiltration membrane while maintaining the temperature of the silica sol at 35°C or less. At the same time, ultrapure water was added to the silica sol to completely replace the solvent in the silica sol with water, yielding colloidal silica in which silica nanoparticles were dispersed in water.

[0144] The above production conditions are shown in Table 1. The metal concentrations in the resulting colloidal silica, i.e., the individual concentrations and total concentration of sodium (Na), potassium (K), iron (Fe), aluminum (Al), calcium (Ca), magnesium (Mg), titanium (Ti), nickel (Ni), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), silver (Ag), manganese (Mn), and cobalt (Co), were also measured. The results are shown in Table 2. Furthermore, in the obtained colloidal silica, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by a liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Table 3. In addition, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. The resulting colloidal silica was then used to evaluate the filtration rate, polishing rate, and polished surface roughness (surface roughness of the polished surface) under the following conditions. The results are shown in Table 5.

[0145] <Filtration rate> The colloidal silica was filtered using a membrane filter with a pore size of 0.20 μm and a diameter of 47 mm, under a pressure of 0.05 MPa. The time required to filter 300 g of colloidal silica was measured, and the filtration rate was calculated as follows: Filtration rate (g / sec) = 300 (g) ÷ time required for filtration (sec) When the filtration rate was 3.0 g / sec or more, the filterability was judged to be good, and when the filtration rate was less than 3.0 g / sec, the filterability was judged to be poor.

[0146] <Polishing speed and polished surface roughness> Ultrapure water was added to the obtained colloidal silica to adjust the silica particle concentration to 5.0 mass %, and then 85% phosphoric acid was added to adjust the pH to 3.0 to prepare a polishing composition. Using the obtained polishing composition, a 3 cm square silicon wafer having a 1 μm thick tetraethoxysilane film (TEOS film) formed on its surface was polished under the following conditions. (polishing conditions) Polishing machine: Nanofactor Co., Ltd., NF-300CMP Polishing pad: Nitta DuPont, IC1000TMPad Slurry supply rate: 50 mL / min Head rotation speed: 32 rpm Platen rotation speed: 32 rpm Grinding pressure: 4psi Polishing time: 1 min

[0147] (Method for measuring polishing rate) The thickness of the TEOS film before and after polishing under the above polishing conditions was measured using a reflectance spectroscopic film thickness meter (Ava Spec-2048 manufactured by AVANTES), and the polishing rate was calculated from the difference and the polishing time according to the following formula. Polishing rate (nm / min) = (thickness of TEOS film before polishing (nm) - thickness of TEOS film after polishing (nm)) ÷ polishing time (min) When the polishing rate was calculated using the above method, polishing properties were judged to be good when the polishing rate was 100 nm / min or more, and polishing properties were judged to be poor when the polishing rate was less than 100 nm / min.

[0148] (Method for measuring polished surface roughness) After polishing under the above polishing conditions, the polished surface roughness (surface roughness of the polished surface) of the silicon 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 range: 3.0 μm square Scanning speed: 1.00Hz Number of observation fields: Five arbitrary fields were observed per polished wafer (observation area per field: 3 μm×3 μm). The root mean square roughness x of each of the five observation fields (five fields) on the polished surface of the wafer was measured. i (nm) and calculate the root mean square roughness x in five fields of view using the following formula: i The arithmetic mean value of (nm) was taken as the polished surface roughness Rms (nm). JPEG0007804843000001.jpg41170When the polished surface roughness Rms was measured using the above method, the polishing properties were judged to be good if the polished surface roughness Rms was 5,000 nm or less, and poor if the polished surface roughness Rms was more than 5,000 nm.

[0149] Example 2 Colloidal silica was obtained under the same conditions as in Example 1, except that in the reaction step (1) of Example 1, the temperature in the reaction system was maintained at 25°C, and the raw material solution was poured into the mother liquor in the reaction vessel at a constant rate over 506 minutes to bring the two into contact with each other and mix them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0150] Example 3 In the reaction step (1) of Example 1, colloidal silica was obtained under the same conditions as in Example 1, except that a raw material solution was prepared by mixing 3,033 parts by mass of tetramethoxysilane (TMOS) and 823 parts by mass of methanol, and the raw material solution was injected into the mother liquid in the reaction vessel at a constant rate over 505 minutes while maintaining the temperature in the reaction system at 25°C, thereby bringing the two into contact and mixing them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0151] Example 4 In the reaction step (1) of Example 1, colloidal silica was obtained under the same conditions as in Example 1, except that a raw material solution was prepared by mixing 3,852 parts by mass of tetramethoxysilane (TMOS) and 1,046 parts by mass of methanol, and the raw material solution was poured into the mother liquid in the reaction vessel at a constant rate over 519 minutes while maintaining the temperature in the reaction system at 25°C, thereby bringing the two into contact and mixing them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0152] Example 5 In the reaction step (1) of Example 1, colloidal silica was obtained under the same conditions as in Example 1, except that a raw material solution was prepared by mixing 4705 parts by mass of tetramethoxysilane (TMOS) and 1277 parts by mass of methanol, and the raw material solution was poured into the mother liquid in the reaction vessel at a constant rate over 515 minutes while maintaining the temperature in the reaction system at 25°C, thereby bringing the two into contact and mixing them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0153] (Comparative Example 1) Colloidal silica was obtained under the same conditions as in Example 1, except that in the reaction step (1) of Example 1, the temperature in the reaction system was maintained at 22°C, and the raw material solution was poured into the mother liquor in the reaction vessel at a constant rate over 200 minutes to bring the two into contact with each other and mix them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0154] (Comparative Example 2) Colloidal silica was obtained under the same conditions as in Example 1, except that in the reaction step (1) of Example 1, the temperature in the reaction system was maintained at 40°C, and the raw material solution was poured into the mother liquor in the reaction vessel at a constant rate over 1,380 minutes to bring the two into contact with each other and mix them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0155] (Comparative Example 3) The colloidal silica obtained under the same conditions as in Comparative Example 2 was further subjected to ion exchange treatment using both ion exchange resins to obtain purified colloidal silica. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by a liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm ―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the purified colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the purified colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0156] Comparative Example 4 Colloidal silica was obtained under the same conditions as in Example 1, except that in the reaction step (1) of Example 1, the temperature in the reaction system was maintained at 70°C, and the raw material solution was poured into the mother liquor in the reaction vessel at a constant rate over 180 minutes to bring the two into contact with each other and mix them to synthesize silica sol. The above production conditions are shown in Table 1. In addition, the metal concentration, the ratio of the Q4 structure of the silica particles, the amount of silanol groups per unit weight of the silica particles, the alkoxy group content of the silica particles, the content of coarse particles with a particle size of 0.2 μm or more, the particle density of the silica particles measured by the liquid phase displacement method, and the intensity I (490 cm) of the peak derived from the four-membered ring structure of the silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the intensity of the peak due to the asymmetric stretching vibration of the Si-O-Si bond of silica I (800 cm―1 ) and the peak intensity ratio I (490 cm ―1 ) / I(800cm ―1 The results are shown in Tables 2 and 3. Furthermore, the average primary particle size, average secondary particle size, association ratio, 50% cumulative particle size D50 in the cumulative number frequency distribution of silica particles, 95% cumulative particle size D95 in the cumulative number frequency distribution of silica particles, and (D95-D50) / D50 were determined for the resulting colloidal silica. The results are shown in Table 4. In addition, the filtration rate, polishing rate, and polished surface roughness of the obtained colloidal silica were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0157] [Table 1]

[0158] [Table 2]

[0159] [Table 3]

[0160] [Table 4]

[0161] [Table 5]

[0162] From Table 2, it can be seen that the colloidal silica obtained by the specific manufacturing method in Examples 1 to 5 has an extremely low amount of metal impurities, with the total content of specific metals being less than 100 ppb by mass. Furthermore, from Tables 3 and 5, it can be seen that the colloidal silica obtained by the specific production methods in Examples 1 to 5 has the following properties:29 The silica particles contain silica particles with a densely formed siloxane bond, and the ratio of Q4 structures in the Si-solid state NMR spectrum is 73.0% or more. Therefore, when used as an abrasive for polishing silicon wafers, it is found to have an excellent polishing rate. Furthermore, Tables 3 and 5 show that the colloidal silica obtained by the specific manufacturing methods in Examples 1 to 5 has a content of coarse particles having a particle size of 0.2 μm or more of 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Therefore, when used as abrasive grains for polishing silicon wafers, the polished surface roughness Rms is low and surface roughness can be suppressed.

[0163] On the other hand, Tables 1, 3, and 5 show that the colloidal silica obtained in Comparative Example 1 was synthesized under the low temperature condition of 22°C, and therefore had a low ratio of Q4 structure of 69.0%, and therefore when used as an abrasive for polishing silicon wafers, the polishing rate was poor at 38 nm / min.

[0164] Furthermore, Tables 1 and 2 show that the colloidal silica obtained in Comparative Example 2 was obtained by hydrolysis and dehydration condensation of tetraalkoxysilane under high-temperature conditions of 40°C, and therefore had a high metal content of 443 ppb by mass or more but less than 449 ppb by mass due to metal impurities eluted from the reaction vessel, making it difficult to use as an abrasive grain for polishing silicon wafers.

[0165] Furthermore, Tables 1 and 2 show that the colloidal silica obtained in Comparative Example 3 was obtained by hydrolysis and dehydration condensation of tetraalkoxysilane under high-temperature conditions of 40°C, but the resulting silica sol was further subjected to ion exchange treatment, and therefore the metal content was reduced compared to the colloidal silica obtained in Comparative Example 2. On the other hand, as shown in Tables 3 and 5, the colloidal silica obtained in Comparative Example 3 had poor filterability, with a filtration rate of 0.6 g / sec, because silica particles aggregated due to pH fluctuations during the ion exchange treatment, resulting in the generation of a large amount of coarse particles of 0.2 μm or more.Furthermore, when used as an abrasive for polishing silicon wafers, the polished surface roughness Rms was 8.935 nm, resulting in poor flatness.

[0166] In addition, Tables 1 and 2 show that the colloidal silica obtained in Comparative Example 4 was obtained by hydrolysis and dehydration condensation of tetraalkoxysilane under high-temperature conditions of 70°C, and therefore had a high metal content of 358 ppb by mass or more but less than 363 ppb by mass due to metal impurities eluted from the reaction vessel, making it difficult to use as an abrasive for polishing silicon wafers. [Industrial Applicability]

[0167] According to the present invention, it is possible to provide colloidal silica that, when used as abrasive grains for polishing electronic materials such as semiconductor wafers, highly suppresses metal contamination of the surface to be polished, exhibits an excellent removal rate, and is capable of forming a polished surface with excellent flatness, and it is also possible to provide a simple method for producing the colloidal silica.

Claims

1. The total content of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is less than 100 ppb by mass, and The zinc content is less than 1 ppb by mass, ２９ The silica particles contain silica particles in which the peak area ratio of the peak due to the Q4 structure to the total of the peaks due to the Q1 structure, the peaks due to the Q2 structure, the peaks due to the Q3 structure, and the peaks due to the Q4 structure in a Si-solid state NMR spectrum is 73.0% or more, The content of coarse particles with a particle diameter of 0.2 μm or more is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Colloidal silica characterized by:

2. 2. The colloidal silica according to claim 1, having a sodium content of less than 40 ppb by mass.

3. 2. The colloidal silica according to claim 1, having a potassium content of less than 30 ppb by mass.

4. The amount of silanol groups per unit weight of the silica particles is 3.5×10 ２１ 2. The colloidal silica according to claim 1, wherein the number of particles per gram is not more than 1.

5. 2. The colloidal silica according to claim 1, wherein the alkoxy group content of the silica particles is 20,000 ppm by mass or less.

6. The colloidal silica according to claim 1, wherein, when the silica particles are evaluated by Raman spectroscopy, the peak intensity ratio I(490 cm-1) / I(800 cm-1) of the peak intensity I(490 cm-1) derived from the four-membered ring structure of silica to the peak intensity I(800 cm-1) derived from the asymmetric stretching vibration of the Si-O-Si bond of silica is 3.50 or less.

7. 2. A method for producing the colloidal silica of claim 1, comprising: a reaction step of hydrolyzing and dehydrating condensing the tetraalkoxysilane by adding a raw material solution containing an alcohol and a tetraalkoxysilane to a mother liquor containing a basic catalyst, water, and an alcohol at a constant rate over a period of 500 to 700 minutes at a temperature of 25°C to 35°C so that the amount of the raw material solution added is 5 to 70 parts by mass per 100 parts by mass of the mother liquor; Here, adding the raw material solution to the mother liquor at a constant rate means continuously supplying the raw material solution to the mother liquor over the entire addition time at an addition rate of 0.9 s (g / min) or more and 1.1 s (g / min) or less, relative to a theoretical addition rate s (g / min) calculated by the formula s = w / t, where w (g) is the total amount of the raw material solution added to the mother liquor and t (min) is the total addition time of the raw material solution to the mother liquor. A method for producing colloidal silica, comprising:

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