Colloidal Silica

Abstract

The present invention provides colloidal silica that, when used as an abrasive for polishing electronic materials such as semiconductor wafers, exhibits a high degree of suppression of metal contamination on the polished surface, and can form a polished surface with excellent flatness while demonstrating a superior polishing speed. [Solution] 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, the zinc content is less than 1 ppb by mass, and the amount of silanol groups per unit weight is 3.5 × 10⁻⁶ 21 This colloidal silica is characterized by containing silica particles with a particle count of 0.2 μm or less per gram, and having a coarse particle content of 0.2 μm or larger at a concentration of 1% by mass of silica particles, with a particle count of 10,000,000 particles / mL or less.

Description

[Technical Field]

[0001] This invention relates to colloidal silica. [Background technology]

[0002] In the semiconductor manufacturing process, semiconductor wafers are held in place by a component called a carrier, and a slurry containing chemicals and abrasive particles is passed through them while the wafers are brought into contact with and rotated against a polishing pad. This process polishes the semiconductor wafers to a flat surface.

[0003] In the polishing methods described above, chemical mechanical polishing (CMP), which utilizes both chemical polishing action by chemicals and mechanical polishing action by abrasive grains, is also being used.

[0004] In the chemical mechanical polishing (CMP) of the above-mentioned semiconductor devices, nanoparticles such as silica are used as abrasive particles. 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-mentioned colloidal silica, a method is known in which high-purity colloidal silica with a low metal content is produced by hydrolysis and condensation using alkoxysilane as a raw material (see, for example, Patent Documents 1 to 3).

[0006] Specifically, it is believed that ultra-high-purity colloidal silica with reduced metal concentration can be obtained by using highly purified alkoxysilane, from which metal components have been removed by distillation purification or ion exchange treatment, as a raw material, and synthesizing silica particles in a reaction vessel whose inner walls are coated with fluororesin or the like, in the presence of alcohol and a basic catalyst. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] WO2024 / 122583 Specification [Patent Document 2] Japanese Patent Publication No. 2013-220976 [Patent Document 3] Japanese Patent Publication No. 2018-080331 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0008] Incidentally, in the chemical mechanical polishing (CMP) of semiconductor devices, the following properties are now required of the colloidal silica mentioned above. (1) The metal content should be low in order to reduce the risk of metal contamination of the polished surface. (2) It must be capable of exhibiting a high polishing speed on the surface to be polished. (3) The content of coarse particles that cause deterioration of the flatness of the polished surface should be low. In particular, with the miniaturization and increasing density of semiconductors in recent years, the inclusion of metals in semiconductor devices is now controlled more strictly than before, and abrasive grains used for chemical mechanical polishing (CMP) of semiconductor devices are required to have an 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 highly pure tetraalkoxysilane, whose metal concentration has been reduced by distillation purification, as a raw material, and by carrying out hydrolysis and dehydration condensation reactions of the tetraalkoxysilane in a reaction vessel whose inner wall is coated with fluororesin.

[0010] However, the present inventors investigated and found that the colloidal silica obtained by the manufacturing method described in Patent Document 1 was synthesized under low temperature conditions of 22°C (see Example 1 of Patent Document 1), and therefore the siloxane bonds of the silica particles were not densely formed. Consequently, it was found that when used as an abrasive in chemical mechanical polishing (CMP) of semiconductor devices, it could not exhibit a sufficient polishing speed.

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

[0012] However, upon investigation by the present inventors, it was found that the colloidal silica obtained by the manufacturing method described in Patent Document 2 was produced under high temperature conditions of 70°C during the silica particle synthesis reaction, and as a result, a large amount of metal components leached out from the substrate of the reaction vessel during the manufacturing process, resulting in a high metal concentration. In other words, even if the reaction vessel has a coating layer made of glass or fluororesin on its inner wall, it was found that these coating layers contain minute through-holes called pinholes, and when the silica particle synthesis reaction is carried out under high-temperature conditions, a large amount of metal components are leached from the substrate of the reaction vessel through the chemical solution that seeps into these pinholes. Therefore, colloidal silica obtained by the manufacturing method described in Patent Document 2 is also difficult to apply to chemical mechanical polishing (CMP) applications of semiconductor devices in recent years, where miniaturization has progressed and metal contamination is more strictly controlled than before, from the standpoint of suppressing metal contamination of the polished surface.

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

[0014] In the manufacturing method described in Patent Document 3, similar to Patent Document 2, Because the hydrolysis and dehydration condensation reactions of tetraalkoxysilane are carried out under relatively high temperature conditions of 40°C (see Examples 3 and 10 of Patent Document 3), a large amount of metal components are leached from the substrate of the reaction vessel through the chemical solution that seeps 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, ion exchange treatment is further performed with both ion exchange resins, so it was thought that most of the leached metal components are removed.

[0015] However, the present inventors investigated and found that colloidal silica purified using both ion exchange resins described in Patent Document 3 suffers from reduced dispersion stability of silica particles and aggregation of silica particles due to pH fluctuations during the ion exchange treatment, resulting in an increase in the content of coarse particles. Therefore, when the above colloidal silica is applied to the chemical mechanical polishing (CMP) of semiconductor devices, it was thought that the flatness of the polished surface would decrease due to the influence of the large amount of coarse particles it contains.

[0016] Under these circumstances, the present invention aims to provide colloidal silica that, when used as an abrasive for polishing electronic materials such as semiconductor wafers, can highly suppress metal contamination of the polished surface, exhibit excellent polishing speed, and form a polished surface with excellent flatness. [Means for solving the problem]

[0017] In order to solve the above technical problems, the inventors conducted diligent research and 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, the zinc content is less than 1 ppb by mass, and the amount of silanol groups per unit weight is 3.5 × 10⁻⁶. 21We discovered that the amount of silica particles containing less than 10,000,000 particles / mL, and the amount of coarse particles with a particle size of 0.2 μm or larger, can be eliminated by colloidal silica containing less than 10,000,000 particles / mL when the silica particle concentration is 1% by mass. Based on this finding, we completed the present invention.

[0018] In other words, the present invention is 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, with a silanol group content of 3.5 × 10⁻¹⁶ per unit weight. 21 It contains silica particles with a concentration of less than 1 / g, The content of coarse particles with a particle size of 0.2 μm or larger is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Colloidal silica characterized by This provides... [Effects of the Invention]

[0019] According to the present invention, when used as an abrasive grain for polishing electronic materials such as semiconductor wafers, colloidal silica is provided that highly suppresses metal contamination of the polished surface, exhibits excellent polishing speed, and can form a polished surface with excellent flatness. [Modes for carrying out the invention]

[0020] First, let me explain the colloidal silica according to the present invention. The colloidal silica according to the present invention has a total content of less than 100 ppb by mass of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt, and a zinc content of less than 1 ppb by mass. The amount of silanol groups per unit weight is 3.5 × 10 21 It contains silica particles with a concentration of less than 1 / g, The content of coarse particles with a particle size of 0.2 μm or larger 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 less than 100 ppb by mass 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).

[0022] The colloidal silica according to the present invention preferably has a total content of 95 ppb by mass or less (0 ppb by mass or more and 95 ppb by mass or less) of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt, and more preferably has a total content of 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 the colloidal silica according to the present invention can be suitably used as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices while suppressing metal contamination of the surface to be polished.

[0024] The colloidal silica according to the present invention preferably has a sodium content of less than 40 ppb by mass (0 ppb or more and less than 40 ppb by mass), more preferably less than 39 ppb by mass (0 ppb or more and less than 39 ppb by mass), and even more preferably less than 38 ppb by mass (0 ppb or more and less than 38 ppb by mass).

[0025] The colloidal silica according to the present invention is particularly suitable for use as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices because its sodium content is within the above range. In other words, because sodium has high electrical mobility when ionized, the presence of sodium in colloidal silica makes it easy to diffuse into the insulating layer that makes up semiconductor devices, which can easily lead to a deterioration of semiconductor device characteristics. In contrast, with the colloidal silica according to the present invention, since the sodium content is within the above range, the inclusion of sodium is limited even when 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.

[0026] The colloidal silica according to the present invention preferably has a potassium content of less than 30 ppb by mass (0 ppb or more and less than 30 ppb by mass), more preferably less than 28 ppb by mass (0 ppb or more and less than 28 ppb by mass), and even more preferably less than 26 ppb by mass (0 ppb or more and less than 26 ppb by mass).

[0027] The colloidal silica according to the present invention is particularly suitable for use as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices because its potassium content is within the above range. In other words, because potassium has high electrical mobility when ionized, the presence of potassium in colloidal silica makes it easy to diffuse into the insulating layer that makes up semiconductor devices, which can easily lead to a deterioration of semiconductor device characteristics. In contrast, with the colloidal silica according to the present invention, the potassium content is within the above range, so even when used as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices, the inclusion of potassium is limited, making it 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 has a zinc content of less than 1 ppb by mass (0 ppb by mass or more 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 mass ppb (0 mass ppb or more and less than 5 mass ppb), more preferably less than 4 mass ppb (0 mass ppb or more and less than 4 mass ppb), and even more preferably less than 3 mass ppb (0 mass ppb or more and less than 3 mass ppb).

[0030] The colloidal silica according to the present invention is particularly suitable for use as an abrasive grain for chemical mechanical polishing (CMP) of semiconductor devices because its iron content is within the above range. In other words, iron easily diffuses into silicon crystals used as the substrate for semiconductor devices, and it can form recombination centers in silicon, shortening the lifetime of carriers such as electrons and holes, and thus degrading the performance of semiconductor devices. In contrast, with respect to the colloidal silica according to the present invention, since the iron content is within the above range, the inclusion of iron is limited even when 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 sodium, potassium, zinc, or iron content within the above ranges, and therefore, 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 this application, the individual content (metal concentration) or total content (total metal concentration) of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt refers to the values ​​measured by the following methods.

[0033] <Method for measuring metal concentration> After dissolving the silica particles by adding hydrofluoric acid to colloidal silica, the hydrofluoric acid is removed by heating, and then ultrapure water is added to the resulting residue to prepare the measurement solution. Using the above-mentioned measurement solution, the content (concentration of each metal) of sodium, potassium, iron, aluminum, calcium, magnesium, titanium, nickel, chromium, copper, zinc, lead, silver, manganese, and cobalt is measured using a high-frequency plasma mass spectrometer (ICPM-8500, Shimadzu Corporation). The sum of these individual content (concentration of each metal) is then defined as the total content (total metal concentration) of each of the above-mentioned metal components. As described above, by dissolving silica particles with hydrofluoric acid, metal components contained within the silica particles can be detected with high precision, and the concentration of each metal can be appropriately evaluated. In other words, if the metal concentration is measured without dissolving the silica particles, it becomes impossible to detect the metal components contained inside the silica particles or adsorbed on the surface of the silica particles, resulting in an underestimation of the metal concentration. For this reason, in this application, hydrofluoric acid is added to 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 preferably, 29 The product contains silica particles in which, in the Si-solid-state NMR spectrum, the peak area ratio of the peak originating from the Q4 structure to the sum of the peaks originating from the Q1 structure, Q2 structure, Q3 structure, and Q4 structure is 73.0% or more (73.0% to 100.0%).

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

[0036] the above 29 In a Si-solid-state NMR spectrum, the higher the peak area ratio of the peak derived from the Q4 structure (the ratio of the Q4 structure) to the sum of the peaks derived from the Q1, Q2, Q3, and Q4 structures, the higher the proportion of siloxane bonds (Si-O-Si bonds) in the silica particles. Therefore, a high proportion of the above-mentioned Q4 structure means that the silica particles constituting colloidal silica contain a high proportion of silica particles in which siloxane bonds are densely formed.

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

[0038] The colloidal silica according to the present invention contains, as silica particles, 29 In the Si-solid NMR spectrum, it is desirable to contain those in which the peak area ratio of the peak derived from the Q4 structure to the total of the peak derived from the Q1 structure, the peak derived from the Q2 structure, the peak derived from the Q3 structure, and the peak derived from the Q4 structure is within the above range, and a siloxane bond (Si-O-Si bond) is densely formed. In this case, 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 the present application documents, the 29 In the Si-solid NMR spectrum, the peak derived from the Q1 structure, the peak derived from the Q2 structure, the peak derived from the Q3 structure, and the peak derived from the Q4 structure of the silica particles are solid 29 Those determined by the Si-DD / MAS-NMR spectrum, and the ratio of the Q4 structure of the silica particles is calculated based on the peak area of each obtained peak.

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

[0041] <Method for measuring peaks originating from the Q1 structure and peaks originating from the Q4 structure of silica particles, and method for calculating the ratio of Q4 structures> [Step 1] Colloidal silica is centrifuged at 77400G, 5°C, 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 silica dry powder. [Step 2] The silica dry powder obtained in step 1 is solid 29 The analysis was performed using Si-DD / MAS-NMR. 29 Obtain a Si-solid-state NMR spectrum. The DD-MAS method is used for this NMR analysis. The NMR spectrometer used is the ECZ500R manufactured by JEOL Ltd., and the probe used for detecting the NMR signal is the 8mm HXMAS probe manufactured by JEOL Ltd. [Step 3] Obtained in step 2 29 By analyzing the Si-solid-state NMR spectral data, and considering the signal of the silicon atoms in tetramethylsilane as 0 ppm, the peak with a chemical shift of approximately -84 ppm is identified as the peak originating from the Q1 structure, the peak with approximately -92 ppm as the peak originating from the Q2 structure, the peak with approximately -101 ppm as the peak originating from the Q3 structure, and the peak with approximately -111 ppm as the peak originating from the Q4 structure. The signal areas of the peaks originating from the Q1 to Q4 structures are then determined as peak areas a1 to a4, respectively. In the analysis of spectral data, for each peak in the spectrum after the Fourier transform, the center position, height, and full width at half maximum of the peak shape, created by mixing Lorentz and Gaussian waveforms, are used as variable parameters, and optimization calculations are performed using the nonlinear least squares method. [Step 4] From the peak areas a1 to a4 of the peaks derived from the Q1 structure to the peaks derived from the Q4 structure, obtained in Step 3, the ratio of the peak area of ​​the peak derived from the Q4 structure to the total peaks derived from the Q1 structure to the peaks derived from the Q4 structure (the ratio of the 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 × 10⁻¹⁶ per unit weight of silica particles. 21 pieces / g or less (0.0×10 21 pieces / g~3.5×10 21 (pieces / g), 3.2 × 10 21 pieces / g or less (0.0×10 21 pieces / g~3.2×10 21 Preferably, the quantity is 2.9 × 10 (pieces / g), and the quantity is 2.9 × 10 21 pieces / g or less (0.0×10 21 pieces / g~2.9×10 21 It is more preferable if the quantity is (pieces / 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 suppressed to within the above range, resulting in a relatively high proportion of siloxane bonds (Si-O-Si bonds) in the silica particles, and thus the siloxane bonds (Si-O-Si bonds) are densely formed. Therefore, in the colloidal silica according to the present invention, even if the amount of silanol groups per unit weight of silica particles is within the above range, a high polishing speed can be easily achieved when the colloidal silica according to the present invention is used as an abrasive for polishing electronic materials such as semiconductor wafers.

[0044] In this application, the amount of silanol groups per unit weight of silica particles is determined by the method described above. 29 This refers to the values ​​calculated using the following formula, based on the peak areas a1, a2, a3, and a4 of the peaks originating from the Q1, Q2, Q3, and Q4 structures of the silica particles in the Si-solid-state NMR spectrum, and the formula weights of the above Q1, Q2, Q3, and Q4 structures. 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)} Note that in the above equation, N A Avogadro's number is 6.02 × 10⁻¹⁰. 23 It represents.

[0045] The colloidal silica according to the present invention preferably has an alkoxy group content of 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 typically produced using alkoxysilanes such as tetraalkoxysilanes as raw materials. Therefore, in the colloidal silica according to the present invention, the alkoxy group content of the silica particles is suppressed to within the above range, which allows the reaction of the raw materials to proceed, resulting in a relatively high proportion of siloxane bonds (Si-O-Si bonds) in the resulting silica particles, and thus the siloxane bonds (Si-O-Si bonds) are densely formed. Therefore, even if the alkoxy group content of the silica particles in the colloidal silica according to the present invention is within the above range, a high polishing speed can be easily achieved when the colloidal silica according to the present invention is used as an abrasive grain in chemical mechanical polishing (CMP) of semiconductor devices.

[0047] In this application, the alkoxy group content of silica particles refers to the value calculated by the following method.

[0048] <Method for measuring the alkoxy group content of silica particles> Colloidal silica is centrifuged at 215,000 G for 90 minutes, the supernatant is discarded, and the solids are vacuum-dried at 60°C for 90 minutes. 0.5 g of the obtained silica dry material is weighed and placed in 50 mL of 1 M sodium hydroxide aqueous solution. The silica is dissolved by heating at 50°C for 24 hours while stirring, and the resulting silica solution is analyzed by gas chromatography to determine the alcohol content, which is then used as the alkoxy group content of the silica particles. A flame ionization detector (FID) is used as the detector for the gas chromatograph described above, and the gas chromatographic analysis is performed in accordance with JIS K0114.

[0049] The colloidal silica according to the present invention has a peak intensity I (490 cm²) derived from the four-membered ring structure of silica when silica particles are evaluated by Raman spectroscopy. ―1 The peak intensity I (800cm) originates from the asymmetric stretching vibration of the siloxane bond (Si-O-Si bond) between ) and silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 Preferably, the ratio is 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 cm²). ―1 ) / I(800cm ―1 The fact that the above-mentioned parameters are suppressed to within the specified range also makes it possible to easily achieve a high polishing speed when used as polishing abrasive grains for chemical mechanical polishing (CMP) of semiconductor devices.

[0051] When silica particles constituting colloidal silica are analyzed by Raman spectroscopy, a Raman shift of approximately 490 cm⁻¹ is detected. ―1 The peaks that appear originate from the four-membered ring structure of silica. Furthermore, when the silica particles constituting colloidal silica are analyzed by Raman spectroscopy, a Raman shift of approximately 800 cm² is detected. ―1 The peaks that appear originate from the asymmetric stretching vibrations of the siloxane bonds (Si-O-Si bonds) in silica. Therefore, the above Raman shift is approximately 490 cm. ―1 The peak intensity that appears is "I (490cm) ―1 )" and the above Raman shift is approximately 800cm ―1 The intensity of the peak that appears is "I (800cm) ―1 )" and the peak intensity ratio "I (490cm)―1 ) / I(800cm ―1 The peak intensity ratio "I(490cm)" is an indicator of the proportion of four-membered ring structures contained in silica, and the above peak intensity ratio "I(490cm)" is an indicator of the proportion of four-membered ring structures contained in silica. ―1 ) / I(800cm ―1 A low value of ) indicates a low proportion of four-membered ring structures. Here, the "four-membered ring structure of silica" refers to a structure in which four SiO4 tetrahedra are linked in a ring shape 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 smaller, causing localized strain. This makes 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 defect site where silica fracture begins when an external force is applied. Therefore, in the colloidal silica according to the present invention, the above peak intensity ratio I (490 cm) ―1 ) / I(800cm ―1 By keeping this within a predetermined range, the proportion of four-membered ring structures, which tend to function as defect sites where silica fracture begins when external force is applied, is reduced, making it easy to increase the mechanical strength of silica particles. Therefore, as colloidal silica according to the present invention, the above peak intensity ratio I (490 cm) ―1 ) / I(800cm ―1 By employing abrasive grains in which the ) are suppressed within a predetermined range, a high polishing speed can be easily achieved when used as polishing abrasive grains for chemical mechanical polishing (CMP) of semiconductor devices.

[0052] In this application, when silica particles are evaluated by Raman spectroscopy, the intensity of the peak originating from the four-membered ring structure of silica is "I(490cm²)". ―1 The peak intensity "I(800cm)" originates from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 )" and the peak intensity ratio "I (490cm) ―1 ) / I(800cm ―1 )" refers to the value calculated using the following method.

[0053] <Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 ) Measurement method > Two mL of colloidal silica, adjusted to a silica concentration of 20% by mass, is taken and placed in the sample holder of a Raman spectrometer (Xplora Raman microscope, 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: 600 gr / mm Slit: 100 μm Detector: CCD detector From the Raman spectrum measured under the above conditions, the Raman shift originating from the four-membered ring structure of silica is approximately 490 cm⁻¹. ―1 Peak intensity at "I(490cm)" ―1 )" and the Raman shift originating from the asymmetric stretching vibration of the Si-O-Si bond in silica is approximately 800 cm. ―1 Peak intensity at "I(800cm)" ―1 )" requested, "I (490cm ―1 )" to "I (800cm ―1 By dividing by "", the peak intensity ratio "I(490cm)" is obtained. ―1 ) / I(800cm ―1 Calculate ")".

[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) to an organic solvent containing water at a constant rate, thereby hydrolyzing and dehydrating to form a dimer, and this dimer polymerizes (oligomerizes) to form spherical silica primary particles in the solvent. Colloidal silica is formed when these spherical silica primary particles are dispersed in the solvent. Furthermore, the colloidal silica described above includes not only primary silica particles but also secondary silica particles formed by the association of these primary silica particles, and these secondary silica particles are dispersed in the solvent together with the primary silica particles.

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

[0056] The average primary particle diameter 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] Because the average primary particle diameter of the silica particles contained in the colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0058] The average primary particle diameter 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] Because the average primary 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 speed can be easily achieved when polishing using the colloidal silica according to the present invention.

[0060] In this application, the average primary particle size of the silica particles contained in colloidal silica refers to the value measured by the BET method described below. Specifically, first, colloidal silica is pre-dried on a hot plate at 150°C, then heat-treated at 800°C for 1 hour to prepare a sample for measurement. The specific surface area (BET specific surface area) S is then measured using the obtained sample by the BET method. For nearly perfectly spherical particles, the average primary particle diameter (nm) of silica particles is given by the following formula: Average primary particle diameter of silica particles (nm) = 6000 / (BET specific surface area S (m²) 2 / g) x true density (g / cm 3 )) This can be determined by the following formula, where the true density of silica particles is 2.2 g / cm³. 3 Based on this, the average primary particle diameter (nm) of silica particles is given by the following formula Average primary particle diameter of silica particles (nm) = 2727 / BET specific surface area S (m²) 2 / g) This can be determined by [method].

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

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

[0063] The average secondary particle diameter 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] Because the average secondary particle diameter of the silica particles contained in the colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0065] The average secondary particle diameter 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] Because 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 speed can be easily achieved when polishing using the colloidal silica according to the present invention.

[0067] In this application, the average secondary particle diameter of the silica particles contained in colloidal silica refers to the value measured by the dynamic light scattering method described below. Specifically, first, a 0.3% by mass citric acid aqueous solution is added to the colloidal silica sample to be measured, and the mixture is uniformly diluted to a silica particle concentration of 0.8% by mass. The resulting diluted solution is then used as the measurement sample. Using the above-mentioned sample for measurement, measurements were performed using the dynamic light scattering method with the zeta potential, particle size, and molecular weight measurement system "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd. The hydrodynamic diameter was determined by analyzing the autocorrelation function derived from the temporal change in scattered light intensity using the cumulant method, and the obtained hydrodynamic diameter was taken as the average secondary particle diameter of the silica particles.

[0068] In the colloidal silica according to the present invention, the following formula Association ratio = Average secondary particle diameter of silica particles (nm) ÷ Average primary particle diameter of silica particles (nm) The association ratio of silica particles calculated by this method is preferably between 1.0 and 3.0.

[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, by having an association ratio of the above value (upper limit) or less, when the colloidal silica according to the present invention is used as an abrasive grain for polishing, it becomes easier to improve the flatness of the polished surface.

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

[0071] The colloidal silica according to the present invention preferably has a cumulative 50% particle diameter 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] Because the cumulative 50% particle diameter D50 of the silica particles contained in the colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the colloidal silica according to the present invention, a polished surface with superior flatness can be easily formed.

[0073] The colloidal silica according to the present invention preferably has a cumulative 50% particle diameter D50 from the small particle size 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] Because the cumulative 50% particle size 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 speed can be easily achieved when polishing using the colloidal silica according to the present invention.

[0075] In this application, the cumulative 50% particle size D50 of the silica particles contained in colloidal silica refers to the value measured by the method described below. Specifically, first, a 0.3% by mass citric acid aqueous solution is added to the colloidal silica sample to be measured, and the mixture is uniformly diluted to a silica particle concentration of 0.8% by mass. The resulting diluted solution is then used as the measurement sample. Using the above-mentioned sample for measurement, measurements are performed using the zeta potential, particle size, and molecular weight measurement system "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd. From the cumulative count frequency obtained from the measurement, the particle size at which the cumulative number of particles from the small particle size side reaches 50% is determined and defined as the cumulative 50% particle size D50.

[0076] The colloidal silica according to the present invention preferably has a cumulative 95% particle diameter D95 from the small particle size 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] Because the cumulative 95% particle size D95 of the silica particles contained in the colloidal silica according to the present invention is less than or equal to the above value (upper limit), when polishing is performed using the colloidal silica according to the present invention, a polished surface with superior flatness can be formed.

[0078] The colloidal silica according to the present invention preferably has a cumulative 95% particle diameter 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] Because the cumulative 95% particle size 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 speed can be easily achieved when polishing using the colloidal silica according to the present invention.

[0080] In this application, the cumulative 95% particle size D95 of the silica particles contained in colloidal silica refers to the value measured by the method described below. Specifically, first, a 0.3% by mass citric acid aqueous solution is added to the colloidal silica sample to be measured, and the mixture is uniformly diluted to a silica particle concentration of 0.8% by mass. The resulting diluted solution is then used as the measurement sample. The above-mentioned sample is used for measurement, and the measurement is performed using the zeta potential, particle size, and molecular weight measurement system "ELSZ-2000S" manufactured by Otsuka Electronics Co., Ltd. From the cumulative count frequency obtained from the measurement, the particle size at which the cumulative number of particles from the small particle size side reaches 95% is determined and defined as the cumulative 95% particle size D95.

[0081] In the colloidal silica according to the present invention, the value (D95-D50) / D50, which is the difference between the cumulative 95% particle diameter D95 and the cumulative 50% particle diameter D50 of the 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 ratio 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, by having (D95-D50) / D50 be less than or equal to the above value (upper limit), it becomes easier to improve the flatness of the polished surface when the colloidal silica according to the present invention is used as an abrasive grain for polishing.

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

[0084] The colloidal silica according to the present invention has a coarse particle content of 0.2 μm or larger, which is 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 with a particle size of 0.2 μm or more is preferably 10,000,000 particles / mL or less, 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 with 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, the content of coarse particles with a particle size of 0.2 μm or more is less than or equal to the above value (upper limit) when the silica particle concentration is 1% by mass. Therefore, when performing chemical mechanical polishing (CMP) using the colloidal silica according to the present invention, surface roughness caused by the presence of coarse particles is suppressed, and a highly flat polished surface can be easily formed.

[0087] In the colloidal silica according to the present invention, there is no particular lower limit to the content of coarse particles with a particle size of 0.2 μm or larger. However, in the colloidal silica according to the present invention, the content of coarse particles with a particle size of 0.2 μm or larger contained in the silica particles 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 this application, the content of coarse particles with a particle size of 0.2 μm or larger refers to the value measured by the particle size distribution method using the counting method described below. <Method for measuring the content of coarse particles with a particle size of 0.2 μm or larger> The colloidal silica to be measured is diluted with ultrapure water until the silica particle concentration reaches 1% by mass. The resulting diluted solution was used as the measurement sample, and the number of coarse particles with a particle size of 0.2 μm or larger was measured using an Accusizer FX-nano manufactured by Particle Sizing System Inc. under the following measurement conditions. <System Setup> ·Stirred Vessel Volume: 13.22mL • 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 obtained by liquid-phase displacement of the silica particles constituting the colloidal silica. 3 Preferably, it is 1.9 g / cm³ or more. 3 It is more preferable that the amount is greater than or equal to 2.0 g / cm³. 3 It is even more preferable if the above conditions are met.

[0090] In the colloidal silica according to the present invention, the particle density of the silica particles constituting the colloidal silica, obtained by liquid-phase displacement, is equal to or greater than the above value (lower limit). Therefore, when the colloidal silica according to the present invention is used as an abrasive grain for polishing, it is possible to easily form a polished surface with reduced surface roughness while exhibiting excellent polishing performance.

[0091] The colloidal silica according to the present invention has a particle density of 2.2 g / cm³ obtained by liquid-phase displacement of the silica particles constituting the colloidal silica. 3 The following are preferred:

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

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

[0094] The silica particle content (silica particle concentration) in the colloidal silica according to the present invention 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 colloidal silica content is 100% by mass.

[0095] By ensuring that the silica particle content in the colloidal silica according to the present invention is equal to or greater than the above value (lower limit), the polishing performance when the colloidal silica according to the present invention is used as an abrasive grain can be further improved.

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

[0097] In this application, the silica particle content (silica particle concentration) in the colloidal silica according to the present invention refers to the value measured by the following measurement method. In other words, it refers to the value calculated using the following formula, where 10.0 g of colloidal silica is dried on a hot plate at 150°C, then heated at 800°C for 1 hour to remove moisture, and the resulting amount of solids is denoted as Wg. Silica particle content (mass%) in colloidal silica = (W / 10.0) × 100

[0098] The pH of the colloidal silica according to the present invention can be set appropriately according to its application and is not particularly limited, but it is preferably 2.0 to 11.0.

[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. By having a pH of colloidal silica according to the present invention that is equal to or greater than the above value (lower limit), the long-term dispersion stability of the silica particles of the colloidal silica according to the present invention is more easily improved.

[0100] Furthermore, 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. By ensuring that the pH of the colloidal silica according to the present invention is below the above value (upper limit), it becomes easier to improve the long-term dispersion stability of the colloidal silica.

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

[0102] One method for producing colloidal silica according to the present invention is the method for producing colloidal silica described later.

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

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

[0105] In the preferred method for producing colloidal silica according to the present invention, it is preferable to carry out at least the above reaction step in a reaction vessel whose inner wall is coated with fluororesin or glass.

[0106] In the preferred method for producing colloidal silica according to the present invention, the basic catalyst constituting the mother liquor is preferably one or more selected from organic amines and ammonia, from the viewpoint of preventing contamination with impurities, and more preferably one or more selected from ethylenediamine, diethylenetriamine, triethylenetetraamine, 3-ethoxypropylamine (3-EOPOA), ammonia, urea, ethanolamine, and tetramethylammonium hydroxide, with ammonia being even more preferred. In the preferred method for producing colloidal silica according to the present invention, when the basic catalyst constituting the mother liquor is the one described above, it exhibits excellent catalytic activity, high volatility, and can be easily removed in subsequent processes.

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

[0108] In the preferred 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 preferred 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% by mass, more preferably 5.0 to 28.0% by mass, and even more preferably 7.0 to 26.0% by mass. In the preferred method for producing colloidal silica according to the present invention, by adjusting the concentration of water in the mother liquor to the above range and controlling the mixing ratio of the mother liquor and the raw material solution, the hydrolysis and dehydration condensation reactions of the tetraalkoxysilane described later are more readily promoted.

[0110] In the preferred method for producing colloidal silica according to the present invention, the alcohol constituting the mother liquor is preferably one or more selected from methanol, ethanol, isopropanol, etc.

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

[0112] In the preferred method for producing colloidal silica according to the present invention, the concentration of the alcohol constituting the mother liquor is preferably 70 to 90% by mass, more preferably 72 to 88% by mass, and even more preferably 74 to 86% by mass. In the preferred method for producing colloidal silica according to the present invention, the concentration of alcohol in the mother liquor being within the above range results in excellent dispersibility of the tetraalkoxysilane described later, and facilitates the hydrolysis reaction.

[0113] In the preferred method for producing colloidal silica according to the present invention, the alcohol constituting the raw material solution is preferably one or more selected from methanol, ethanol, isopropanol, etc.

[0114] In the preferred 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 the hydrolysis of the tetraalkoxysilane described later. For example, if the tetraalkoxysilane described later is tetramethoxysilane (TMOS), methanol is preferred as the alcohol constituting the raw material solution. In a preferred method for producing colloidal silica according to the present invention, by using the same alcohol as the alcohol produced by the hydrolysis of tetraalkoxysilane described later as the alcohol constituting the raw material solution, the recovery and reuse of the alcohol can be easily achieved.

[0115] In a preferred method for producing colloidal silica according to the present invention, the tetraalkoxysilane constituting the raw material solution is the following general formula (1) Si(OR)4(1) (In the above general formula (1), the R group is an alkyl group having 1 to 8 carbon atoms.) Examples of tetraalkoxysilanes or their derivatives can be given.

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

[0117] In a tetraalkoxysilane or derivative represented by general formula (1), the R group can be one or more selected from, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, and an octyl group, with one or more selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group being preferred.

[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 derivatives of the tetraalkoxysilane represented by general formula (1) include low-condensation products obtained by partially hydrolyzing the tetraalkoxysilane represented by general formula (1). Among the tetraalkoxysilanes or derivatives represented by general formula (1), tetramethoxysilane (TMOS) is preferred because it is easy to control the hydrolysis rate, it is easy to obtain silica particles with densely formed siloxane bonds, it is easy to obtain fine silica particles, and there is little residue of unreacted substances.

[0119] In the preferred 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 preferred method for producing colloidal silica according to the present invention, the concentration of tetraalkoxysilane in the raw material solution being within the above range facilitates the hydrolysis and dehydration condensation reaction of tetraalkoxysilane.

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

[0122] In a preferred method for producing colloidal silica according to the present invention, when adding a raw material solution containing alcohol and tetraalkoxysilane to a mother liquor containing the basic catalyst, water, and alcohol, the amount of the raw material solution added per 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 a preferred method for producing colloidal silica according to the present invention, by controlling the amount of the raw material solution added to 100 parts by mass of the mother liquor within the above range, the hydrolysis and dehydration condensation reaction of the tetraalkoxysilane in the raw material solution can be effectively facilitated.

[0124] In the preferred 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 alcohol and tetraalkoxysilane are reacted such that the ratio of the content of water in the reaction solution constituting the mother liquor to the content of tetraalkoxysilane constituting the raw material solution in the reaction solution (content of water in the reaction solution constituting the mother liquor / content of tetraalkoxysilane constituting the raw material solution in the reaction solution) is 3.5 to 20.0 in molar ratio, more preferably 4.0 to 15.0, and even more preferably 4.5 to 13.0.

[0125] In the preferred method for producing colloidal silica according to the present invention, by carrying out the reaction step such that the content of water constituting the mother liquor in the reaction solution / the content of tetraalkoxysilane constituting the raw material solution in the reaction solution is within the above range, the hydrolysis and dehydration condensation reaction of tetraalkoxysilane in the raw material solution can be easily carried out, while the particle size of silica particles in the resulting colloidal silica can be easily controlled to a desired range.

[0126] In the preferred method for producing colloidal silica according to the present invention, the contact between the mother liquor and the raw material solution can be carried out under any pressure conditions, such as reduced pressure, atmospheric pressure, or pressurized pressure, but it is preferable to carry it out under atmospheric pressure.

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

[0128] In a preferred method for producing colloidal silica according to the present invention, the raw material solution is added to the mother liquor at a constant rate. If the total amount of raw material solution added to the mother liquor is w (g), and the total time of addition of the raw material solution to the mother liquor is t (minutes), then when a constant amount of raw material solution is added continuously to the mother liquor 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 at which the raw material solution is added to the mother liquor can vary to a certain extent over time depending on the method of addition. Therefore, in the preferred 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) or more and 1.1 s (g / min) over the entire addition time (where s (g / min) is the theoretical addition rate mentioned above).

[0129] In a preferred method for producing colloidal silica according to the present invention, the average rate of addition of the raw material solution per 1 part by mass of the mother liquor when adding the raw material solution to the mother liquor is 1.00 × 10⁻⁶ ―4 ~1.25×10 ―3 Preferably, the ratio is parts by mass / minute / 1 part by mass of mother liquor, and 1.30 × 10 ―4 ~1.20×10 ―3 It is more preferably parts by mass / minute / 1 part by mass of mother liquor, and 1.50 × 10 ―4 ~1.15×10 ―3 It is even more preferable that the amount is parts by mass / minute / 1 part by mass of mother liquor.

[0130] Note that the average rate of addition of the raw material solution per 1 part by mass of mother liquor is equal to the total amount of raw material solution added w 原料 w 母液 parts by mass, total time of addition of raw material solution to mother liquor t 原料A minute is defined by the following formula: Average rate of addition 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 a preferred method for producing colloidal silica according to the present invention, by controlling the average addition rate of the raw material solution per 1 part by mass of the mother liquor within the above range, silica particles in which siloxane bonds are densely formed can be easily synthesized.

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

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

[0134] In the preferred 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 with densely formed siloxane bonds can be easily produced even under low temperature conditions of 25 to 35°C.

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

[0136] In the preferred method for producing colloidal silica according to the present invention, the colloidal silica obtained in the reaction step contains organic solvents 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 solution may be concentrated as needed.

[0137] The method for replacing the organic solvent with water is not particularly limited. For example, one method involves continuously adding water while concentrating the reaction solution obtained by the reaction step using an ultrafiltration membrane, thereby replacing the organic solvent with water.

[0138] In the preferred 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 include heating concentration, membrane concentration, and reduced pressure method.

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

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

[0141] As described in detail above, it is possible to provide a simple method for producing colloidal silica that, when used as an abrasive for polishing electronic materials such as semiconductor wafers, can highly suppress metal contamination of the polished surface, exhibit excellent polishing speed, and form a polished surface with excellent flatness. [Examples]

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

[0143] (Example 1) (1) Reaction process Ultra-high purity colloidal silica was prepared using tetramethoxysilane, methanol, 28% ammonia water, and ultrapure water with an electrical resistivity of 18.0 MΩ·cm or higher as raw materials, with the metal concentration reduced to 1 ppb or less by distillation purification. First, 2359 parts by mass of ultrapure water, 440 parts by mass of 28% ammonia water, and 8102 parts by mass of methanol were charged into a metal reaction vessel whose inner walls were coated with tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (PFA) to form the mother liquor. Furthermore, 2214 parts by mass of tetramethoxysilane (TMOS) and 601 parts by mass of methanol were mixed to prepare the raw material solution. While maintaining the liquid temperature in the reaction system at 35°C, the raw material solution was injected at a constant rate into the mother liquor in the reaction vessel over a period of 692 minutes, bringing the two into contact and mixing to synthesize silica sol. (2) Concentration and solvent replacement step 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 below. After the concentration process described above, the silica sol was further subjected to cross-flow filtration using an ultrafiltration membrane while controlling its temperature to 35°C or below. Simultaneously, ultrapure water was added to the silica sol to completely replace the solvent with water, thereby obtaining colloidal silica in which silica nanoparticles were dispersed in water.

[0144] The above manufacturing conditions are shown in Table 1. Furthermore, the concentrations of metals in the obtained colloidal silica, namely 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), as well as the total concentration, were measured. The results are shown in Table 2. Furthermore, the ratio of Q4 structures in the obtained colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm) of the peak originating from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also determined. ―1 ) and the peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 The result was calculated. The results are shown in Table 3. In addition, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), and (D95-D50) / D50 were determined for the obtained colloidal silica. The results are shown in Table 4. Then, using the obtained colloidal silica, the filtration rate, polishing rate, and polished surface roughness (surface roughness of the polished surface) were evaluated under the following conditions. The results are shown in Table 5.

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

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

[0147] (Method for measuring polishing speed) The film thickness of the TEOS film before and after polishing under the above polishing conditions was measured using a reflectance spectrometer (Ava Spec-2048, manufactured by AVANTES). The polishing rate was calculated from the difference in thickness and the polishing time based on the following formula. Polishing speed (nm / min) = (TEOS film thickness before polishing (nm) - TEOS film thickness after polishing (nm)) ÷ Polishing time (min) When calculating the polishing speed using the method described above, a polishing speed of 100 nm / min or higher was judged to be good, and a polishing speed of less than 100 nm / min was judged to be poor.

[0148] (Method for measuring surface roughness of polished surfaces) After polishing the silicon wafer under the above polishing conditions, the surface roughness (surface roughness of the polished surface) was measured using an atomic force microscope under the following conditions. Atomic force microscope: SPM-9700HT manufactured by Shimadzu Corporation Cantilever: OLYMPUS, MICRO CANTILEVER OMCL-AC240TS-R3 Observation mode: Dynamic Scanning range: 3.0 μm square Scanning speed: 1.00 Hz Number of observation fields: Five arbitrary fields per wafer after polishing were observed (observation range per field: 3 μm × 3 μm). At five observation fields (five fields) on the wafer polishing surface, the root mean square roughness x i (nm) was measured, and the root mean square roughness x i (nm) in the five fields calculated by the following formula was taken as the polishing surface roughness Rms (nm). When the polishing surface roughness Rms was measured by the above method, if the polishing surface roughness Rms was 5.000 nm or less, the polishing property was judged to be good, and if the polishing surface roughness Rms exceeded 5.000 nm, the polishing property was judged to be poor.

[0149] (Example 2) In the reaction step of (1) of Example 1, while maintaining the temperature in the reaction system at 25°C, the raw material solution was injected into the mother liquor in the reaction vessel at a constant rate over 506 minutes with respect to the above mother liquor, and the two were brought into contact and mixed to synthesize a silica sol. Colloidal silica was obtained under the same conditions as in Example 1 except for this. The above manufacturing conditions are shown in Table 1. In addition, in the obtained colloidal silica, metal concentration, ratio of the Q4 structure of silica particles, amount of silanol groups per unit weight of silica particles, content of alkoxy groups in silica particles, content of coarse particles with a particle size of 0.2 μm or more, particle density of silica particles by the liquid phase substitution method, intensity I of the peak derived from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy (490 cm ―1 ) and the intensity I of the peak derived from the asymmetric stretching vibration of the Si-O-Si bond of silica (800 cm ―1 ) and the peak intensity ratio I(490 cm ―1) / I(800cm ―1 The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), and (D95-D50) / D50 were determined for the obtained 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 using the same method as in Example 1. The results are shown in Table 5.

[0150] (Example 3) Colloidal silica was obtained under the same conditions as in Example 1, except that in step (1) of the reaction of Example 1, 3033 parts by mass of tetramethoxysilane (TMOS) and 823 parts by mass of methanol were mixed to form a starting material solution, and while maintaining the temperature in the reaction system at 25°C, the starting material solution was injected at a constant rate into the mother liquor in the reaction vessel over 505 minutes to bring the two into contact and mix to synthesize silica sol. The above manufacturing conditions are shown in Table 1. Furthermore, the metal concentration, the ratio of Q4 structures in the obtained colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm²) of the peak originating from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the aggregation ratio of the silica particles, the cumulative 50% particle diameter D50 in the cumulative number frequency distribution of the silica particles, the cumulative 95% particle diameter D95 in the cumulative number frequency distribution of the silica particles, and (D95 - D50) / D50 in the obtained colloidal silica were determined. The results are shown in Table 4. In addition, in the obtained colloidal silica, the filtration flow rate, polishing rate, and polished surface roughness were evaluated in the same manner as in Example 1. The results are shown in Table 5.

[0151] (Example 4) In the (1) reaction step of Example 1, 3852 parts by mass of tetramethoxysilane (TMOS) and 1046 parts by mass of methanol were mixed to form a raw material solution. While maintaining the temperature in the reaction system at 25°C, the raw material solution was injected into the mother liquor in the reaction vessel at a constant rate over 519 minutes with respect to the above mother liquor, and the two were brought into contact and mixed to synthesize a silica sol. Colloidal silica was obtained under the same conditions as in Example 1, except for this. The above production conditions are shown in Table 1. Also, in the obtained colloidal silica, 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 by the liquid phase replacement method, and the intensity I(490 cm ―1 ) of the peak derived from the four-membered ring structure of silica and the intensity I(800 cm ―1 ) of the peak derived from the asymmetric stretching vibration of the Si - O - Si bond of silica and the peak intensity ratio I(490 cm ―1 ) / I(800 cm ―1 ) were determined. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter of the silica particles, the average secondary particle diameter of the silica particles, the aggregation ratio of the silica particles, the cumulative 50% particle diameter D50 in the cumulative number frequency distribution of the silica particles, the cumulative 95% particle diameter D95 in the cumulative number frequency distribution of the silica particles, and (D95 - D50) / D50 in the obtained colloidal silica were determined. 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 using the same method as in Example 1. The results are shown in Table 5.

[0152] (Example 5) Colloidal silica was obtained under the same conditions as in Example 1, except that in step (1) of the reaction of Example 1, 4705 parts by mass of tetramethoxysilane (TMOS) and 1277 parts by mass of methanol were mixed to form a starting material solution, and while maintaining the temperature in the reaction system at 25°C, the starting material solution was injected at a constant rate into the mother liquor in the reaction vessel over 515 minutes to bring the two into contact and mix to synthesize silica sol. The above manufacturing conditions are shown in Table 1. Furthermore, the metal concentration, the ratio of Q4 structures in the obtained colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm²) of the peak originating from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), and (D95-D50) / D50 were determined for the obtained 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 using the same method 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 step (1) of the reaction step in Example 1, the temperature in the reaction system was maintained at 22°C, and the raw material solution was injected at a constant rate into the mother liquor in the reaction vessel over 200 minutes, bringing the two into contact and mixing to synthesize silica sol. The above manufacturing conditions are shown in Table 1. Furthermore, the metal concentration, the ratio of Q4 structures in the obtained colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm²) of the peak originating from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), and (D95-D50) / D50 were determined for the obtained 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 using the same method 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 step (1) of the reaction step in Example 1, the temperature in the reaction system was maintained at 40°C, and the raw material solution was injected at a constant rate into the mother liquor in the reaction vessel over a period of 1380 minutes, bringing the two into contact and mixing to synthesize silica sol. The above manufacturing conditions are shown in Table 1. Furthermore, the metal concentration, the ratio of Q4 structures in the obtained colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm²) of the peak originating from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), and (D95-D50) / D50 were determined for the obtained 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 using the same method 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 manufacturing conditions are shown in Table 1. Furthermore, the metal concentration, the ratio of Q4 structures in the purified colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm²) 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 peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), 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 using the same method 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 step (1) of the reaction step in Example 1, the temperature in the reaction system was maintained at 70°C, and the raw material solution was injected at a constant rate into the mother liquor in the reaction vessel over 180 minutes, bringing the two into contact and mixing to synthesize silica sol. The above manufacturing conditions are shown in Table 1. Furthermore, the metal concentration, the ratio of Q4 structures in the obtained colloidal silica, the amount of silanol groups per unit weight of silica particles, the alkoxy group content of silica particles, the content of coarse particles with a particle size of 0.2 μm or larger, the particle density of silica particles obtained by liquid-phase displacement, and the intensity I (490 cm²) of the peak originating from the four-membered ring structure of silica when the silica particles were evaluated by Raman spectroscopy were also measured. ―1 ) and the peak intensity I (800cm) originating from the asymmetric stretching vibration of the Si-O-Si bond in silica. ―1 ) Peak intensity ratio I (490cm) ―1 ) / I(800cm ―1 The following was calculated. The results are shown in Tables 2 and 3. Furthermore, the average primary particle diameter, average secondary particle diameter, association ratio, cumulative 50% particle diameter (D50), cumulative 95% particle diameter (D95), and (D95-D50) / D50 were determined for the obtained 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 using the same method 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] Table 2 shows that the colloidal silica obtained by the specific manufacturing methods in Examples 1 to 5 has an extremely low amount of metal impurities, with a total content of specific metals of less than 100 ppb by mass and a zinc content of less than 1 ppb by mass. Furthermore, as shown in Tables 3 and 5, the colloidal silica obtained by the specific manufacturing method in Examples 1 to 5 has a silanol group content of 3.5 × 10⁶ per unit weight. 21 Because it contains silica particles at a concentration of less than 1 / g, it exhibits excellent polishing speed when used as an abrasive for polishing silicon wafers. Furthermore, as can be seen from Tables 3 and 5, the colloidal silica obtained by the specific manufacturing method in Examples 1 to 5 has a content of coarse particles with a particle size of 0.2 μm or larger of 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Therefore, when used as an abrasive for polishing silicon wafers, it has a low polished surface roughness Rms and can suppress surface roughness.

[0163] On the other hand, as can be seen from Tables 1, 3, and 5, the colloidal silica obtained in Comparative Example 1 was synthesized under low temperature conditions of 22°C, and therefore the amount of silanol groups per unit weight of silica particles is 3.6 × 10⁻⁶. 21 The particle count is high at 38 nm / min, which explains why, when used as an abrasive for polishing silicon wafers, the polishing speed is inferior at 38 nm / min.

[0164] Furthermore, as can be seen from Tables 1 and 2, the colloidal silica obtained in Comparative Example 2 was obtained by hydrolysis and dehydration condensation of tetraalkoxysilane under high temperature conditions of 40°C. As a result, due to metal impurities leached from the reaction vessel, the zinc content was high at 12 mass ppb, and the total content of specific metals was high at 443 mass ppb or more and less than 449 mass ppb, making it unsuitable for use as an abrasive for polishing silicon wafers.

[0165] Furthermore, as can be seen from Tables 1 and 2, the colloidal silica obtained in Comparative Example 3 was obtained by hydrolysis and dehydration condensation of tetraalkoxysilane under high temperature conditions of 40°C. However, because the resulting silica sol was further subjected to ion exchange treatment, the total content of specific metals is reduced compared to the colloidal silica obtained in Comparative Example 2. On the other hand, as shown in Table 2, the colloidal silica obtained in Comparative Example 3 has a high zinc content of 8 ppb by mass, making it unsuitable for use as an abrasive for polishing silicon wafers. Furthermore, as shown in Tables 3 and 5, the colloidal silica obtained in Comparative Example 3 exhibits poor filterability, with a filtration rate of 0.6 g / second, due to the aggregation of silica particles caused by pH fluctuations during the ion exchange treatment, resulting in the generation of a large amount of coarse particles larger than 0.2 μm. Additionally, when used as an abrasive for polishing silicon wafers, it exhibits low flatness, with a polished surface roughness Rms of 8.935 nm.

[0166] Furthermore, as can be seen from Tables 1 and 2, the colloidal silica obtained in Comparative Example 4 was obtained by hydrolysis and dehydration condensation of tetraalkoxysilane under high temperature conditions of 70°C. As a result, due to metal impurities leached from the reaction vessel, the zinc content was high at 9 mass ppb, and the total content of specific metals was high at 358 mass ppb or more and less than 363 mass ppb, making it unsuitable for use as an abrasive for polishing silicon wafers. [Industrial applicability]

[0167] According to the present invention, when used as an abrasive grain for polishing electronic materials such as semiconductor wafers, colloidal silica is provided that highly suppresses metal contamination of the polished surface, exhibits excellent polishing speed, and can form a polished surface with excellent flatness.

Claims

[Claim 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. The amount of silanol groups per unit weight is 1.1 × 10²¹ ions / g or more, or 3.5 × 10²¹ ions / g or more. ２１ It contains silica particles with a particle count of 1 / g or less, The content of coarse particles with a particle size of 0.2 μm or larger is 10,000,000 particles / mL or less when the silica particle concentration is 1% by mass. Colloidal silica characterized by the following features.

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