Method for manufacturing a silica fine particle dispersion for polishing.

Abstract

When applied to grinding applications, it exhibits excellent grinding speed and can suppress scratch generation on the substrate to be ground. 【Solution means】A method for producing a silica fine particle dispersion liquid for grinding, including the following steps 1 to 4. (Step 1) A step of introducing an acidic silicic acid solution and an alkali into a reaction vessel maintained in a non-heated state to obtain a first formulation liquid. (Step 2) Following the above Step 1, a step of uniformly stirring, heating, and holding the first formulation liquid, and then adding an acidic silicic acid solution to obtain a second formulation liquid. (Step 3) Following the above Step 2, a step of simultaneously proceeding with the following treatments A and B. Treatment A: Add an acidic silicic acid solution and an alkali to the reaction vessel respectively to prepare a reaction solution. Treatment B: Extract a part of the reaction solution in the reaction vessel of Treatment A. (Step 4) A step of aging the reaction solution obtained in the above Step 3, and then adding and mixing the reaction solution extracted in Treatment B of the above Step 3 to obtain a silica fine particle dispersion liquid for grinding.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silica fine particle dispersion for polishing, which is suitable for polishing various electronic materials such as silicon wafers, silicon carbide wafers, sapphire wafers, compound semiconductor wafers, or magnetic disks. [Background technology]

[0002] Conventionally, silica sol, fumed silica, and fumed alumina have been used as polishing particles. In the manufacturing of semiconductor integrated circuit substrates, aluminum wiring is formed on a silicon wafer, and an oxide film such as silica is applied on top of this as an insulating film. In this case, irregularities occur due to the wiring, so the oxide film is polished to flatten it. In polishing such substrates, the polished surface must be flat without steps or irregularities, smooth without microscopic scratches, and have a high polishing speed.

[0003] A common method for achieving high polishing speeds is to use large abrasive grains. However, if the particle size of the abrasive grains becomes too large, the flatness of the substrate surface after polishing tends to deteriorate. Therefore, it is known that making the abrasive grains non-spherical, that is, making the abrasive grains irregularly shaped (irregularly shaped particles), is effective in obtaining high polishing speeds without deteriorating surface flatness. As a method for obtaining large, irregularly shaped particles, as described in Patent Document 1, a method is known in which porous silica gel is crushed using a bead mill or the like to prepare an irregularly shaped porous gel, and this irregularly shaped porous gel is grown using silicic acid or the like to obtain large, highly irregularly shaped particles.

[0004] Furthermore, it is known that using particles with a broad particle size distribution is also useful as another method for obtaining a high polishing rate. As a method for producing particles with a broad particle size distribution, as described in Patent Document 2, a method is known in which a silica sol with a broad particle size distribution is obtained by continuously adding a predetermined silica sol to a stirred and heated reaction vessel while adding silicic acid to the reaction vessel to grow the particles, and continuously withdrawing the reaction solution from the overflow line. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-177576 [Patent Document 2] Special Publication No. 2012-503586 [Overview of the project] [Problems that the invention aims to solve]

[0006] The irregularly shaped particles (non-spherical particles) described in Patent Document 1, when applied to polishing applications, exhibit a relatively higher polishing speed compared to perfectly spherical particles. However, the irregularly shaped particles described in Patent Document 1 have the problem of easily worsening the surface roughness and surface waviness of the substrate to be polished after polishing, and also being prone to scratching. Furthermore, when attempting to manufacture irregularly shaped particles using the manufacturing method described in Patent Document 1 multiple times, it was found that there were problems with poor reproducibility of particle size and variability in polishing performance.

[0007] The spherical silica fine particles with a broad particle size distribution described in Patent Document 2 are excellent in polishing rate as compared with spherical silica fine particles with a sharp particle size distribution. However, it has been known that even the silica fine particles with a broad particle size distribution do not reach the polishing rate by the silica fine particles with irregular shapes. Further, the method for producing spherical silica fine particles with a broad particle size distribution described in Patent Document 2 requires adding three components, i.e., seed particles (or a seed particle dispersion), an acidic silicic acid solution, and an alkaline component, into a reaction vessel while strictly controlling conditions (such as temperature and pH) simultaneously, which causes a problem of large equipment load and complicated management in production. In addition, when the authors actually conducted a tracing experiment, although the particle size distribution was broad, the particle size distribution was such that the large particle side was tapered. Therefore, even if the average particle size is a desirable size, extremely large-sized particles of several hundred nm to micron size are partially included in the silica fine particles, and the problem was that there were many scratches.

[0008] An object of the present invention is to provide a method for producing a polishing silica fine particle dispersion liquid that exhibits an excellent polishing rate and can suppress the generation of scratches on a polished substrate when applied to polishing applications.

Means for Solving the Problems

[0009] According to one aspect of the present invention, there is provided a method for producing a polishing silica fine particle dispersion liquid including the following steps 1 to 4. (Step 1) A step of introducing an acidic silicic acid solution and an alkali into a reaction vessel maintained in a non-heated state to obtain a first prepared liquid. (Step 2) Following the step 1, the first prepared liquid is uniformly stirred, then heated to 40°C or higher and 98°C or lower, held within the same temperature range, and then an acidic silicic acid solution is continuously or intermittently added while maintaining the same temperature range to obtain a second prepared liquid. (Step 3) Following the step 2, a step of simultaneously proceeding with the following treatments A and B. Treatment A: An acidic silicic acid solution and an alkali are each continuously or intermittently added to the reaction vessel filled with the second blending liquid to prepare a reaction liquid. Treatment B: A part of the reaction liquid in the reaction vessel of Treatment A is continuously or intermittently withdrawn (however, when the addition rate [g / min] (in terms of silica dry conversion) of the acidic silicic acid solution during addition is X and the withdrawal rate [g / min] (in terms of silica dry conversion) when withdrawing the reaction liquid is Z, the value of the ratio (X / Z) of the addition rate of the acidic silicic acid solution to the withdrawal rate of the reaction liquid satisfies at least the relationship 3.0 < (X / Z) ≤ 10.0). (Step 4) The reaction liquid remaining in the reaction vessel after going through Treatment A and Treatment B of Step 3 is aged within the range of 40°C or higher and 98°C or lower for 20 minutes or longer and 120 minutes or shorter, and then the reaction liquid withdrawn in Treatment B of Step 3 is added and mixed to obtain a silica fine particle dispersion liquid for polishing. [Advantages of the Invention]

[0010] According to the present invention, when applied to polishing applications, a method for producing a silica fine particle dispersion liquid for polishing that exhibits an excellent polishing rate and can suppress the generation of scratches on the polished substrate can be provided. [Embodiments for Carrying Out the Invention]

[0011] [Silica Fine Particle Dispersion Liquid for Polishing] First, the silica fine particle dispersion liquid for polishing obtained by the method for producing a silica fine particle dispersion liquid for polishing according to the present embodiment will be described. The silica fine particle dispersion liquid for polishing obtained in the present embodiment is one in which a particle group containing silica fine particles is dispersed in a solvent as abrasive grains for polishing. Further, it is preferable that the particle group satisfies the following Requirements 1 to 4. In this specification, the "silica fine particle dispersion liquid for polishing" may be simply referred to as the "dispersion liquid". Also, the "particle group containing silica fine particles" dispersed in the silica fine particle dispersion liquid for polishing may be simply referred to as the "particle group". The method for producing the silica fine particle dispersion for polishing according to this embodiment yields a silica fine particle dispersion for polishing that exhibits excellent polishing speed, improves the surface roughness of the substrate to be polished, and suppresses scratch generation when applied to polishing applications. The inventors of this invention speculate as follows. In other words, the particle group related to this embodiment has a broad particle size distribution. Therefore, the polishing speed can be improved compared to conventional abrasive grains. Furthermore, the particle size distribution has a peak on the larger particle size side, meaning that the larger particle size side does not tail off, and therefore does not contain extremely large particles. In addition, because the shape is perfectly spherical, the surface roughness is improved and the occurrence of scratches can be suppressed. Moreover, the particle group according to this embodiment mainly consists of perfectly spherical silica fine particles, while also containing a small amount of irregularly shaped silica fine particles. These irregularly shaped silica fine particles improve the polishing speed, and since these irregularly shaped silica fine particles are present in small amounts, they have little adverse effect on surface roughness or scratches. Furthermore, the method for producing the silica fine particle dispersion for polishing according to this embodiment involves adding an acidic silicic acid solution to a non-heated reaction vessel during preparation. Therefore, drying of the acidic silicic acid solution can be prevented, and since seed particles are not added during the preparation in step 3, the load on the manufacturing equipment can be reduced, the burden of process control can be reduced, and it becomes possible to efficiently produce the silica fine particle dispersion for polishing. The inventors surmise that the above-mentioned effects of the present invention are achieved in this manner.

[0012] (Particle diameter based on specific surface area) The specific surface area equivalent particle diameter of the particle group according to this embodiment is preferably in the range of 5 nm to 200 nm. If the specific surface area equivalent particle diameter is within the above range, using the silica fine particle dispersion for polishing according to this embodiment as polishing silica fine particles for polishing silicon wafers, magnetic disks, or semiconductor substrates can achieve a high polishing speed, suppress the occurrence of scratches on the object to be polished, and make the surface of the object to be polished smoother. If the particle diameter is less than 5 nm, it tends to become more difficult to achieve a practically sufficient polishing speed. If the particle diameter exceeds 200 nm, it tends to become more prone to scratches on the substrate to be polished. The specific surface area-based particle diameter of the particle group is preferably in the range of 10 nm to 150 nm, and more preferably in the range of 20 nm to 100 nm.

[0013] (Average sphericity) The average sphericity of the particle group according to this embodiment is preferably in the range of 0.85 to 1.00 (Requirement 1). The aforementioned particle group includes perfectly spherical particles. In this embodiment, perfectly spherical particles are particles whose average sphericity is in the range of 0.85 to 1.00. The average sphericity can be calculated by determining the short axis / long axis of individual silica nanoparticles from the observation results of electron microscope images described later and taking their simple average. When the average sphericity of the particle group is 0.85 or higher, applying the silica fine particle dispersion for polishing according to this embodiment, in which such a particle group is dispersed in a solvent, to a polishing application can smooth the surface roughness of the polished substrate and further suppress the occurrence of scratches. Even if the particle group contains irregularly shaped particles in the range of 1.0% to 10.0% or less, scratches can still be suppressed as long as the average sphericity of the particle group is within the aforementioned range. The effects of irregularly shaped particles (irregularly shaped silica particles) included in the particle group are described later. The average sphericity of the particle group is preferably in the range of 0.90 to 1.00, and more preferably in the range of 0.92 to 1.00. The specific method for measuring the average sphericity of the particle group according to this embodiment is described below.

[0014] (Weight-converted cumulative particle size distribution) In the weight-converted cumulative particle size distribution of the particle group according to the present embodiment, the cumulative 10% particle size (D 50 , , 90 , 10 , 90 , 10 , 50 , 50 , ), the cumulative 90% particle size (D 90 ) and the cumulative 50% particle size (D 50 ) preferably satisfy the following mathematical formula (F1) (Requirement 2). 0.5 ≦ (D 90 - D 10 ) / D 50 ≦ 3.0 ··· (F1) The value of (D 90 - D 10 ) / D 50 in the mathematical formula (F1) indicates the width of the particle size distribution, and the larger the value of (D 90 - D 10 ) / D 50 , the wider the particle size distribution. That is, when the value of (D 90 - D 10 ) / D 50 is large, it indicates that it has both small-sized particles and large-sized particles. Here, the large-sized particles show a high polishing rate, and the small-sized particles show a scratch repair effect. Therefore, it can be said that the silica fine particle dispersion liquid having such a particle size distribution can achieve both a high polishing rate and suppression of scratch generation. (D 90 - D 10 ) / D 50 If the value is in the range of 0.5 or more and 3.0 or less, it can be said that the particle size distribution is sufficiently broad and contains appropriate amounts of small particles and large particles. Generally, the larger the particle size, the higher the polishing rate. However, on the other hand, when the size increases, there is a problem that scratches are likely to occur on the substrate. However, if the particle size distribution satisfies the above range, the balance of the contents of large particles and small particles is good, and it is preferable because the small particles repair the scratches caused by the large particles. ((D 90 - D 10 ) / D 50The value of ) is preferably in the range of 0.6 or more and 2.0 or less, and more preferably in the range of 0.8 or more and 1.8 or less.

[0015] (Peak in particle size distribution) In the weight-based particle size distribution of the particle group according to this embodiment, it is preferable that the distribution peak is on the larger particle size side (Requirement 3). Here, having a distribution peak on the larger particle diameter side means that the weight-reduced particle diameter distribution is D 60 This means that the distribution peak is shown on the side of larger particle diameters than the cumulative 60% of particle diameters (calculated from the smallest particle diameters). When the particle size distribution has a peak on the larger particle size side, the distribution does not tail on the larger particle size side. On the other hand, a distribution that tails on the larger particle size side contains extremely large particles. Generally, the larger the particle size, the faster the polishing speed, but scratches tend to occur more easily and the surface roughness deteriorates. However, extremely large particles tend to cause irreparable scratches. Therefore, particles with a distribution that has a peak on the larger particle size side but does not tail on the larger particle size side tend to suppress fatal scratches. Furthermore, by combining requirement 2 and requirement 3, scratches generated by the peaks on the larger particle diameter side are repaired by the smaller particles, which have the function of smoothing the surface despite the slower polishing speed. This makes it possible to achieve both polishing speed and improvement of surface roughness.

[0016] (Ratio of irregularly shaped particles) In the particle group according to this embodiment, it is preferable that the particle group contains 1.0% to 10.0% of irregularly shaped particles that are not perfectly spherical (Requirement 4). Irregularly shaped particles that are not perfectly spherical are particles with a short-axis / long-axis ratio of less than 0.85, which can be calculated from the observation results of electron microscope images described later. Such irregularly shaped particles generally exhibit a high polishing speed, but tend to cause scratches on the substrate surface. However, if the irregularly shaped particle ratio (number of irregularly shaped particles / total number of particles × 100) is in the range of 1.0% to 10.0%, then when the particle group according to this embodiment is used as a polishing abrasive, the irregularly shaped particles included in the aforementioned % range contribute to a high polishing speed, while the remaining perfectly spherical particles suppress the occurrence of scratches on the substrate surface and can also repair any scratches that do occur. Thus, it is possible to achieve both a high polishing speed and smoothness of the polished substrate surface after polishing. If the irregularly shaped particle ratio of the particle group is less than 1.0%, no effect of improving the polishing speed due to irregularly shaped particles is observed. If the irregularly shaped particle ratio of the particle group exceeds 10.0%, the tendency for scratches due to irregularly shaped particles to increase becomes stronger. In this embodiment, the term "irregularly shaped particles" refers to irregularly shaped silica particles.

[0017] The fraction of irregularly shaped particles can be measured as follows: A dispersion of silica microparticles is observed using an electron microscope to obtain a photograph or image at a magnification of 200,000x. Specifically, a photograph is taken so that 200 or more particles are included in the same field of view, and the short-axis / long-axis ratio is measured for each of the 200 or more silica microparticles in the obtained photograph or image. The number of particles (n) with a short-axis / long-axis ratio of less than 0.85 (irregularly shaped particles) is determined, and the fraction of irregularly shaped particles is calculated using the following formula. Deformed particle ratio = (n / 200) × 100 [number of particles %] In addition, the percentage of irregularly shaped particles in the particle group according to this embodiment is preferably 1.3% or more and 9.0% or less, more preferably 1.5% or more and 8.0% or less, and particularly preferably 1.7% or more and 7.0% or less.

[0018] (Coefficient of variation of particle size distribution area) In this embodiment, it is preferable that the particle group further satisfies the following requirement 5. (Requirement 5) In the particle size distribution consisting of particle size / number of particles of the aforementioned particle group, the cumulative 1% particle size (D1) to the cumulative 99% particle size (D 99 The particle size range up to ) is divided into six equal parts, and when these particle size ranges are designated as S1, S2, S3, S4, S5, and S6, the coefficient of variation (CV value) of the particle size distribution area corresponding to each particle size range must be in the range of 10.0% or more and 70.0% or less. The particle size distribution of typical silica sol exhibits a normal distribution, resulting in a high CV value exceeding 70.0%. In contrast, when the CV value is in the range of 10.0% to 70.0%, it indicates that the areas of S1 to S6 are relatively uniform, and the shape of the particle size distribution is generally close to a trapezoid or rectangle, although it has a peak on the larger particle size side. Such a particle size distribution contains relatively uniform amounts of large particles for fast polishing speed, small particles to suppress scratches, and medium particles that offer a good balance between polishing speed and scratch suppression. Therefore, it is possible to achieve both high polishing speed and scratch suppression. When the CV value is less than 10.0%, it is practically difficult to obtain such a particle size distribution. On the other hand, when the CV value exceeds 70.0%, it approaches a normal distribution, and the polishing speed tends to be slower. The CV value is more preferably in the range of 11.0% to 65.0%, and particularly preferably in the range of 12.0% to 62.0%.

[0019] (Silica microparticles) The silica nanoparticles according to this embodiment can be confirmed, for example, by an ICP (Inductively Coupled Plasma Atomic Emission Spectrometer). 1 g of an aqueous dispersion containing the silica nanoparticles according to this embodiment was placed in a 30 mL lidded zirconia ball, dried (200°C, 20 minutes), and then dissolved with 22 g of Na2O and 1 g of NaOH for 15 minutes. Further dissolution was achieved by adding 10 mL of 98% by mass sulfuric acid and 10 mL of pure water, and then diluting with pure water to a total volume of 500 mL to obtain the sample. The silicon content of the obtained sample can be measured using an ICP instrument (Shimadzu Corporation, ICPS-8100, analysis software ICPS-8000).

[0020] The particle group according to this embodiment consists of silica, but may contain 10% by mass or less of components other than silica. Examples of components other than silica include Al, Ti, Fe, Ca, Mg, Cr, Ni, Cu, Zn, K, or Na, or oxides thereof. As described above, the fact that the particle group according to this embodiment consists of silica can be confirmed, for example, using an ICP apparatus. Furthermore, the content of components other than silica that may be included in the particle group according to this embodiment can be identified and quantified, for example, using an inductively coupled plasma emission spectrometer. Ni, Cu, K, and Na can be identified and quantified using an atomic absorption spectrophotometer.

[0021] (solvent) As described above, the dispersion according to this embodiment is obtained by dispersing the particle group according to this embodiment in a solvent. Examples of solvents include water, alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, ethers, esters, and water-soluble organic solvents such as ketones. A mixed solvent consisting of water and an organic solvent may also be used.

[0022] The content of the particle group contained in the dispersion according to this embodiment is preferably in the range of 1% by mass or more and 50% by mass or less, and more preferably in the range of 10% by mass or more and 50% by mass or less. Here, the content of the particle group was determined by subjecting the silica fine particle dispersion to a loss of volume at 1000°C, weighing the resulting solid content, and subtracting the alkali content, which was calculated separately and converted to oxides (such as Na2O), to obtain the concentration of the particle group according to this embodiment.

[0023] [Polishing composition] Next, we will describe a polishing composition using the polishing silica fine particle dispersion obtained by the method for producing the polishing silica fine particle dispersion according to this embodiment. The polishing composition contains a polishing silica fine particle dispersion or a group of particles obtained by the method for producing the polishing silica fine particle dispersion according to this embodiment, and a solvent, and further contains components that impart necessary properties, including polishing performance. The components that impart the necessary performance include polishing accelerators, surfactants, hydrophilic compounds, heterocyclic compounds, pH adjusters, and pH buffers. The polishing composition may contain only one of these components, or two or more, as components that impart the necessary performance. The polishing composition according to this embodiment is also referred to as a "polishing slurry."

[0024] A silica fine particle dispersion or polishing composition for polishing can be used, for example, as a CMP slurry to polish semiconductor wafers such as silicon wafers, or to polish hard disk drive substrates, liquid crystal glass, sapphire substrates, compound semiconductors, GaN substrates, or SiC substrates.

[0025] Examples of polishing accelerators include acids such as sulfuric acid, nitric acid, phosphoric acid, oxalic acid, and hydrofluoric acid, or sodium salts, potassium salts, ammonium salts of these acids, and mixtures thereof. When the composition of the present invention contains these polishing accelerators, a flat polished surface can be obtained by accelerating the polishing rate for specific components of the material to be polished when polishing a material made of complex components. If the polishing composition according to this embodiment contains a polishing accelerator, its content is preferably in the range of 0.1% by mass or more and 10% by mass or less, and more preferably in the range of 0.5% by mass or more and 5% by mass or less.

[0026] To improve the dispersibility and stability of the polishing composition, cationic, anionic, nonionic, amphoteric surfactants or hydrophilic compounds may be added as at least one of the surfactant and hydrophilic compound.

[0027] Both surfactants and hydrophilic compounds have the effect of reducing the contact angle with the surface to be polished, thereby promoting uniform polishing. As at least one of the surfactant and hydrophilic compound, for example, those selected from the following group can be used.

[0028] Examples of anionic surfactants include carboxylates, sulfonates, sulfate esters, and phosphate esters. Examples of carboxylates include soaps, N-acyl amino acid salts, polyoxyethylene or polyoxypropylene alkyl ether carboxylates, and acylated peptides. Examples of sulfonates include alkyl sulfonates, alkylbenzene and alkylnaphthalene sulfonates, naphthalene sulfonates, sulfosuccinates, α-olefin sulfonates, and N-acyl sulfonates. Examples of sulfate ester salts include sulfated oils, alkyl sulfates, alkyl ether sulfates, polyoxyethylene or polyoxypropylene alkylallyl ether sulfates, and alkylamide sulfates. Examples of phosphate ester salts include alkyl phosphates, polyoxyethylene or polyoxypropylene alkylallyl ether phosphates.

[0029] Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, benzalkonium chloride salts, benzethonium chloride, pyridinium salts, and imidazolinium salts. Examples of amphoteric surfactants include carboxybetaine type, sulfobetaine type, aminocarboxylate salts, imidazolinium betaine, lecithin, and alkylamine oxides.

[0030] Examples of nonionic surfactants include ether-type, ether-ester-type, ester-type, and nitrogen-containing types. Examples of ether-type surfactants include polyoxyethylene alkyl and alkylphenyl ethers, alkylallylformaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block polymers, and polyoxyethylene polyoxypropylene alkyl ethers. Examples of ether-ester-type surfactants include polyoxyethylene ethers of glycerin esters, polyoxyethylene ethers of sorbitan esters, and polyoxyethylene ethers of sorbitol esters. Examples of ester-type surfactants include polyethylene glycol fatty acid esters, glycerin esters, polyglycerin esters, sorbitan esters, propylene glycol esters, and sucrose esters. Examples of nitrogen-containing surfactants include fatty acid alkanolamides, polyoxyethylene fatty acid amides, and polyoxyethylene alkylamides. Other examples include fluorinated surfactants.

[0031] As the surfactant, anionic surfactants or nonionic surfactants are preferred. As the salt, examples include ammonium salts, potassium salts, and sodium salts, with ammonium salts and potassium salts being particularly preferred.

[0032] Furthermore, other surfactants and hydrophilic compounds include esters (glycerin esters, sorbitan esters, and alanine ethyl esters, etc.), ethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol alkenyl ether, alkyl polyethylene glycol, alkyl polyethylene glycol alkyl ether, alkyl polyethylene glycol alkenyl ether, alkenyl polyethylene glycol, alkenyl polyethylene glycol alkyl ether, alkenyl polyethylene glycol alkenyl ether, polypropylene glycol alkyl ether, polypropylene glycol alkenyl ether, alkyl polypropylene glycol, alkyl polypropylene glycol alkyl ether, alkyl polypropylene glycol alkenyl ether, and alkenyl polypropylene glycol, etc.), polysaccharides (alginic acid, pectinic acid, carboxymethylcellulose, curdlan, and pullulan, etc.), amino acid salts (glycine ammonium salts and glycine sodium salts, etc.), (and), polycarboxylic acids and their salts (polyaspartic acid, polyglutamic acid, polylysine, polymalic acid, polymethacrylic acid, polyammonium methacrylate, polymethacrylate sodium salt, polyamic acid, polymaleic acid, polyitaconic acid, polyfumaric acid, poly(p-styrene carboxylic acid), polyacrylic acid, polyacrylamide, aminopolyacrylamide, polyammonium acrylate, polyacrylate sodium salt, polyamic acid, polyamic acid ammonium salt, polyamic acid sodium salt, and polyglyoxylic acid), vinyl poly M (polyvinyl alcohol, polyvinylpyrrolidone and polyacrolein, etc.), sulfonic acids and their salts (ammonium methyltaurate, sodium methyltaurate, sodium methyl sulfate, ethylammonium sulfate, butylammonium sulfate, sodium vinylsulfonate, sodium 1-allylsulfonate, sodium 2-allylsulfonate, sodium methoxymethylsulfonate, ammonium ethoxymethylsulfonate, sodium 3-ethoxypropylsulfonate, etc.), and amides (propionamide,Examples include acrylamide, methylurea, nicotinamide, succinamide, and sulfanilamide.

[0033] Furthermore, while any surfactant can be suitably used when the substrate to be polished is a glass substrate, in the case of silicon substrates for semiconductor integrated circuits, where contamination by alkali metals, alkaline earth metals, or halides is undesirable, it is preferable to use an acid-based or ammonium salt-based surfactant.

[0034] If the polishing composition contains at least one surfactant and a hydrophilic compound, the total amount thereof is preferably in the range of 0.001 g to 10 g per liter of the polishing composition according to this embodiment, more preferably in the range of 0.01 g to 5 g, and particularly preferably in the range of 0.1 g to 3 g.

[0035] The surfactant or hydrophilic compound may be used alone, or two or more types may be used, and different types may be used in combination.

[0036] For polishing compositions, if the substrate to be polished contains metal, a heterocyclic compound may be included for the purpose of forming a passivation layer or dissolution-inhibiting layer on the metal to suppress erosion of the substrate. Here, "heterocyclic compound" refers to a compound having a heterocycle containing one or more heteroatoms. A heteroatom means an atom other than a carbon atom or a hydrogen atom. A heterocycle means a cyclic compound having at least one heteroatom. A heteroatom refers only to an atom that forms a component of the ring system of a heterocycle, and does not refer to an atom located outside the ring system, separated from the ring system by at least one non-conjugated single bond, or part of a further substituent of the ring system. Preferred heteroatoms include, but are not limited to, nitrogen, sulfur, oxygen, selenium, tellurium, phosphorus, silicon, and boron atoms. Examples of heterocyclic compounds that can be used include imidazole, benzotriazole, benzothiazole, and tetrazole. More specifically, examples include, but are not limited to, 1,2,3,4-tetrazole, 5-amino-1,2,3,4-tetrazole, 5-methyl-1,2,3,4-tetrazole, 1,2,3-triazole, 4-amino-1,2,3-triazole, 4,5-diamino-1,2,3-triazole, 1,2,4-triazole, 3-amino-1,2,4-triazole, and 3,5-diamino-1,2,4-triazole.

[0037] When a polishing composition contains a heterocyclic compound, its content is preferably in the range of 0.001% by mass or more and 1.0% by mass or less, more preferably in the range of 0.001% by mass or more and 0.7% by mass or less, and even more preferably in the range of 0.002% by mass or more and 0.4% by mass or less.

[0038] To enhance the effects of the above-mentioned additives, the pH of the polishing composition can be adjusted by adding an acid or base as needed.

[0039] When adjusting the pH of an abrasive composition to 7 or higher, an alkaline pH adjuster should be used. Preferably, amines such as sodium hydroxide, aqueous ammonia, ammonium carbonate, ethylamine, methylamine, triethylamine, and tetramethylamine should be used.

[0040] When adjusting the pH of an abrasive composition to less than 7, an acidic pH adjuster is used. For example, hydroxy acids such as lactic acid, citric acid, malic acid, tartaric acid, and glyceric acid are used.

[0041] To maintain a constant pH value in the polishing composition, a pH buffer may be used. Examples of pH buffers include phosphates and borates such as ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium tetraborate tetrahydrate, or organic acids.

[0042] The concentration of abrasive particles in the abrasive composition is preferably in the range of 0.5% by mass or more and 50% by mass or less, and more preferably in the range of 5% by mass or more and 30% by mass or less. If the concentration is less than 0.5% by mass, depending on the type of substrate and insulating film, the concentration may be too low, resulting in a slow polishing speed and productivity problems. If the concentration of abrasive particles exceeds 50% by mass, the stability of the abrasive material becomes insufficient, and the polishing speed and polishing efficiency will not improve further. Also, dried material may be generated and adhere during the process of supplying the dispersion liquid for the polishing treatment, which may cause scratches.

[0043] [Method for producing a dispersion of silica fine particles for polishing] Next, a method for producing a silica fine particle dispersion for polishing according to this embodiment will be described. The method for producing the dispersion according to this embodiment requires including the following steps 1 to 4.

[0044] (Process 1) In step 1, acidic silicic acid solution and alkali are introduced as raw materials into a reaction vessel kept unheated, and a solvent is added as needed to prepare the first preparation solution. In this specification, the first preparation solution is also referred to as step 1 solution. When these raw materials are introduced into the reaction vessel, splashing occurs on the bottom surface, inner wall, or liquid surface (the surface of the introduced acidic silica solution and alkali solution). If these materials are introduced into a heated reaction vessel, the splashed materials tend to dry out easily, leading to the formation of coarse aggregates, which can be problematic. If the raw materials are introduced gradually to avoid splashing, the mixing time increases, reducing economic efficiency. Furthermore, as in the process described in Patent Document 2, when the seed particle dispersion and alkali are added to a heated reaction vessel, the seed particle dispersion and alkali are heated from the moment of addition, which can lead to the problem of seed particle aggregation occurring at an early stage. The aforementioned "non-heating state" means that no operations are performed to raise the temperature of the reaction vessel. However, if the temperature of the reaction vessel exceeds 40°C in the non-heating state due to seasonal high temperatures or other reasons, it is recommended to cool the reaction vessel so that its temperature falls below 40°C. It is preferable that the temperatures of both the acidic silica solution and the alkali introduced into the reaction vessel be below 40°C.

[0045] (Acidic silica solution) As the acidic silicic acid solution, one obtained by dealkalizing an alkaline silicate aqueous solution with a cation exchange resin can be used. The concentration of the acidic silicic acid solution is preferably in the range of 0.1% to 10% by mass, more preferably in the range of 1% to 7% by mass, and particularly preferably in the range of 2% to 6% by mass, based on SiO2. The pH of the acidic silicic acid solution is preferably between 1 and 3. The amounts of acidic silica solution and alkali used are determined by adding them in the first preparation solution so that the molar ratio of silica to alkali (in oxide terms) is between 1 and 10, and further adjusting the silica concentration in the preparation solution by adding solvent as needed so that it is between 0.1% by mass and 15% by mass. Here, the molar ratio of silica to alkali (in oxide terms) is expressed as molar ratio = [number of moles of SiO2] / [number of moles of A2O] (where A represents alkali metals, ammonia, organic alkalis, or alkali metals in water glass). If the molar ratio of silica to alkali (in oxide terms) is less than 1, the amount of alkali is excessive, causing the ionic strength in the first preparation solution to become excessively high. This leads to the aggregation of silica nanoparticles produced in subsequent steps 2 and 3, making it impossible to obtain perfectly spherical particles, and making it easier for precipitates to form. Even if sedimentation does not occur, the number of silica nanoparticle aggregates increases, making it difficult to obtain a monodisperse silica sol. On the other hand, if the molar ratio of silica to alkali (in oxide terms) exceeds 10, the amount of silica is too large, resulting in only small particles being obtained, making it difficult to adjust to the desired size. Also, because the alkali is relatively low, when the acidic silicic acid solution is added in the subsequent step 2, the pH of the reaction solution becomes significantly lower. As a result, the added acidic silicic acid solution does not deposit on the surface of the generated silica fine particles, and self-nucleation by silicic acid occurs, ultimately making it difficult to obtain a silica sol with the desired particle size. The molar ratio of silica to alkali is preferably in the range of 2 to 8, and more preferably in the range of 2.5 to 6. If the silica concentration in the first formulation is less than 0.1% by mass, monodisperse silica fine particles are easily obtained, but production is not efficient and therefore uneconomical due to the low silica concentration in the first formulation. Also, if the silica concentration exceeds 15% by mass, the silica fine particles tend to aggregate during formulation, making it difficult to obtain monodisperse silica fine particles. It is more preferable that the silica concentration in the first formulation is between 0.2% by mass and 10% by mass, and particularly preferable that it is between 0.3% by mass and 8% by mass. Furthermore, if the molar ratio of silica to alkali (in oxide terms) and the silica concentration in the first compounding solution are set within the aforementioned range, most of the silica microparticles will avoid aggregation, but some will aggregate and become irregularly shaped particles. As a result, the silica microparticle dispersion in this embodiment will contain mostly spherical particles, but will also contain irregularly shaped particles of 1.0% to 10%.

[0046] (alkali) Examples of alkalis added in step 1 include alkali silicates such as sodium silicate (water glass) and potassium silicate, as well as alkali metals such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, ammonia, and organic alkalis such as organic amines. Here, the alkali is usually added as an aqueous alkali solution. There are no particular restrictions on the alkali concentration of the aqueous alkali solution, but it is usually used in the range of 1% by mass to 50% by mass.

[0047] (solvent) Examples of solvents that may be added as needed in step 1 include water, deionized water, pure water, ultrapure water, a mixed solvent containing water and a water-soluble organic solvent, and a water-soluble organic solvent.

[0048] (Process 2) In step 2, the preparation liquid prepared in step 1 is uniformly stirred, heated, and maintained at a constant temperature (40°C to 98°C) for a certain period of time. Subsequently, while maintaining the same temperature range, the acidic silicic acid solution is continuously or intermittently added to generate silica nanoparticles and obtain the second preparation liquid. In this specification, the second preparation liquid obtained in step 2 is also referred to as "step 2 liquid."

[0049] (Holding temperature and holding time) In step 2, the first formulation prepared in step 1 is heated to a temperature of 40°C to 98°C while being stirred, and maintained at this temperature range for a certain period of time. The holding time is preferably 10 minutes to 120 minutes, and more preferably 20 minutes to 90 minutes. This temperature maintenance allows the formulation to be sufficiently homogenized. If the holding time is less than 10 minutes, homogenization is insufficient, and the subsequent addition of the acidic silicic acid solution tends to result in uneven generation of silica fine particles and particle growth. If the holding time exceeds 120 minutes, the homogenization of the formulation does not progress further, and the longer holding time actually reduces production efficiency and worsens economic viability. Next, while maintaining the temperature of this mixture between 40°C and 98°C, silica nanoparticles are generated by adding an acidic silica solution. More specifically, in the initial stages of adding the acidic silica solution, core particles (polymers of silica) are formed first, and these core particles continuously grow in the added acidic silica solution, thereby generating silica nanoparticles. The addition time for the acidic silica solution is preferably between 3 and 48 hours. If the addition time is less than 3 hours, the rate of addition of the acidic silica solution is too fast, and self-nucleation by the acidic silica solution is likely to occur in addition to the desired silica nanoparticles. If the addition time exceeds 48 hours, self-nucleation of the acidic silica solution does not occur, but the preparation time becomes too long, which is economically unfeasible. The particle size distribution of the silica nanoparticles produced in this step 2 shows a normal distribution and is a relatively sharp particle size distribution. Regarding the amount (total amount) of acidic silica solution added in step 2, it is preferable that the value of M2S / M2A, where M2S is the molar ratio of SiO2 contained in the second preparation solution and M2A is the molar ratio of alkali A contained in the second preparation solution in terms of oxide (i.e., A2O), be in the range of 20 to 160. If the M2S / M2A value is less than 20, the growth of silica microparticles in the silica microparticle dispersion obtained by the manufacturing method according to this embodiment will be slow, and the size will be small, resulting in insufficient polishing speed when used as an abrasive. On the other hand, if the M2S / M2A value exceeds 160, the particle size of the silica microparticles in the silica microparticle dispersion obtained by the manufacturing method according to this embodiment will be excessively large, and when used as an abrasive, scratching may become significant, at least on the substrate to be polished, which is undesirable. In such cases, the mixing time will be very long, and economic efficiency will deteriorate. The M2S / M2A value is more preferably in the range of 40 to 140, even more preferably in the range of 50 to 130, and particularly preferably in the range of 60 to 120.

[0050] (Step 3) In step 3, following step 2, processes A and B are carried out simultaneously. Process A: Acidic silica solution and alkali are added continuously or intermittently to the reaction vessel filled with the second preparation solution to prepare the reaction solution. Process B: A portion of the reaction solution in the reaction vessel is withdrawn continuously or intermittently.

[0051] In step 3, process A is performed simultaneously to prepare a reaction solution by adding an acidic silicic acid solution to the second preparation liquid filling the reaction vessel, thereby growing silica nanoparticles to a desired size (here, alkali is added and an acidic silicic acid solution is added for particle growth at the same time in order to maintain the pH of the reaction solution), and process B is performed to remove a portion of the reaction solution from the reaction vessel. Furthermore, in step 3, the particle growth reaction proceeds immediately upon the addition of the acidic silicic acid solution to the second preparation solution (step 2 solution). Therefore, for convenience, from the start of the addition of the acidic silicic acid solution in step 3 onward, it will also be referred to as the "reaction solution" or "step 3 solution." As will be explained in more detail later, in the subsequent step 4, the reaction solution remaining in the reaction vessel after step 3 is aged at a high temperature, and then the reaction solution extracted in process B is added and mixed to obtain a silica fine particle dispersion for polishing according to this embodiment, which has a broader particle size distribution (wider particle size distribution range).

[0052] Regarding the amount of acidic silicic acid solution added to the liquid in step 3 in step 3, when M3S is the number of moles of silica contained in the liquid in step 3 and M3A is the number of moles of alkali in oxide equivalent contained in the liquid in step 3, the value of M3S / M3A is preferably in the range of 20 to 160. If the M3S / M3A value is less than 20, the growth of silica microparticles in the silica microparticle dispersion obtained by the manufacturing method according to this embodiment will be slow, the size will be small, and a broad distribution will not be achieved, resulting in insufficient polishing speed when used as an abrasive. On the other hand, if the M3S / M3A value exceeds 160, the particle size of the silica microparticles in the silica microparticle dispersion obtained by the manufacturing method according to this embodiment will be excessively large, and when used as an abrasive, scratching may become significant, at least on the substrate to be polished, which is undesirable. In such cases, the mixing time will be very long, and economic efficiency will deteriorate. Furthermore, the M3S / M3A value is more preferably in the range of 40 to 140, even more preferably in the range of 50 to 130, and particularly preferably in the range of 60 to 120.

[0053] (Reaction temperature) When adding the acidic silicic acid solution to the liquid in step 3, the temperature of the liquid in step 3 is preferably between 40°C and 98°C. If the temperature of the liquid in step 3 is below 40°C, the added acidic silicic acid solution will not dissolve easily and will not deposit easily on the surface of the silica nanoparticles. As a result, self-nucleation by silicic acid will occur, and the desired size will not be obtained. If the temperature of the liquid in step 3 is above 98°C, the added acidic silicic acid solution will dissolve sufficiently and the silica nanoparticles will grow, but the temperature of the silica nanoparticle dispersion or reaction solution will be excessively high, which is problematic in terms of energy efficiency and also poses a safety issue. When adding the acidic silicic acid solution to the liquid in step 3, the temperature of the liquid in step 3 is more preferably between 50°C and 98°C.

[0054] (Addition rate of acidic silica solution) In this embodiment, in process A of step 3, the rate at which the acidic silicic acid solution is added to the reaction vessel filled with the process 3 solution is expressed as the amount of silica dry [g] in the acidic silicic acid solution added per minute per unit mass [g] of silica particles contained in the solution in the reaction vessel. Here, the unit of the rate of addition of the acidic silicic acid solution to the liquid is [g / min·g]. The term "solution" is a convenient general term for the liquid filling the reaction vessel, and the silica fine particle dispersion filling the reaction vessel undergoes a particle growth reaction as the addition of the acidic silicic acid solution in process A begins, becoming the reaction solution. The term "solution" encompasses the silica fine particle dispersion or the reaction solution and refers to the liquid present in the reaction vessel. In this specification, the silica component contained in the liquid is also referred to as "silica dry". The preferred rate of adding the acidic silicic acid solution to the liquid is between 0.0001 g / min·g and 0.05 g / min·g. Within this range, the acidic silicic acid solution added for particle growth dissolves in the alkali in step 3 liquid and deposits on the surface of the silica microparticles, thereby promoting particle growth of the silica microparticles. If the rate of adding the acidic silicic acid solution to the liquid is less than 0.0001 g / min·g, the preparation time becomes too long for practical purposes, reducing both practicality and economic efficiency. If the rate of adding the acidic silicic acid solution to the liquid exceeds 0.05 g / min·g, self-nucleation may occur without the silicic acid depositing on the particle surface, which is undesirable. The rate at which the acidic silica solution is added to the liquid is more preferably in the range of 0.00015 g / min·g or more and 0.02 g / min·g or less, and particularly preferably in the range of 0.0002 g / min·g or more and 0.01 g / min·g or less. In process A of step 3 of this embodiment, the rate of addition of the acidic silica solution to the liquid can be calculated as the rate of addition (S) of the acidic silica solution (converted to dry silica) relative to the unit mass of dry silica contained in the solution in the reaction vessel, using the following formula. (S) = (Addition rate of acidic silica solution per dry silica) [g / min] ÷ (Mass of dry silica in the solution in the reaction vessel) [g] Here, for example, if the addition rate per unit of silica dry mass of the acidic silicic acid solution changes in two stages, the silica dry mass of particles in the reaction vessel is calculated using the silica dry mass in the reaction vessel at the end of the first and second stages of addition, respectively. If the addition rate does not change, it is calculated using the silica dry mass in the reaction vessel at the end of process A in step 3. Furthermore, in this specification, the rate of addition of the acidic silica solution is calculated as described above, based on the amount of acidic silica solution added per unit mass (unit area of ​​silica fine particles) per unit time (converted to silica dry), whether the addition of the acidic silica solution is continuous or intermittent.

[0055] Regarding the addition rate [g / min] of the acidic silica solution in step 3, it is preferable to maintain a constant addition rate or to reduce the addition rate. Specifically, it is recommended to perform the addition treatment of acidic silica solution using either A) or B) below. A) Add the acidic silica solution at a constant rate. B) The rate of adding the acidic silica solution is changed n or more times (n≧1), and the rate of the Xth addition is set to L X When [g / min] (where X is an integer from 1 to n), L is always x+1 ≤L x Add the necessary components to satisfy the given relationship. In the addition process described in A) above, the addition rate of the acidic silica solution in step 3 is kept constant throughout the process. In addition, in the addition process described in B) above, if the addition rate is changed one or more times, the addition rate for the Xth time is set to L x Let [g / min] be the rate of addition for the X+1th time, and set it to L x+1 If we use [g / min], then it is always L x+1 ≤L x It is preferable that the relationship is satisfied. In step 3, an acidic silicic acid solution is added to grow the silica nanoparticles to the desired size. However, in this embodiment, the reaction solution is continuously withdrawn, which reduces the number of silica nanoparticles. As a result, the acidic silicic acid solution may not deposit on the surface of the silica nanoparticles, and self-nucleation by silicic acid may occur. Self-nucleation easily leads to the generation of small particles, and the generation of small particles increases the overall surface area of ​​the generated silica nanoparticles, resulting in the problem that the silica nanoparticles do not grow to the desired particle size. Furthermore, if the rate of addition of the acidic silicic acid solution is increased, the tendency for small particles to be generated due to self-nucleation becomes stronger. Here, "small particles" refers to particles that are smaller than the average particle size of the silica nanoparticles obtained when the rate of addition of the acidic silicic acid solution in step 3 is kept constant or reduced. In this embodiment, by adding the acidic silica solution at a constant rate, or by reducing the rate of addition of the acidic silica solution from the second time onward, the occurrence of such self-nucleation can be suppressed, and silica nanoparticles can be grown to the desired size.

[0056] (Rate of alkali addition) In process A of step 3, it is desirable to add the acidic silica solution to the liquid of step 3 simultaneously with the continuous or intermittent addition of alkali to maintain the pH of the reaction solution. The rate of alkali addition cannot be uniformly restricted as it depends on the type and concentration of the alkali, but it is desirable to add it so that the pH of the reaction solution is in the range of 8.5 to 13.0. If the pH of the reaction solution is above 13.0, the ionic strength in the reaction solution becomes too high, which tends to cause silica particles to aggregate and settle, or the particles to become deformed, making it difficult to obtain the desired particle size. If the pH is below 8.5, the added acidic silica solution becomes difficult to dissolve, which tends to cause autonucleation by silica. It is more preferable that the pH of the reaction solution is between 9.0 and 12.5.

[0057] (Molar ratio of SiO2 / A2O in the solution in the reaction vessel) In step 3, acidic silica solution is added to the solution in the reaction vessel continuously or intermittently, while the reaction solution is continuously or intermittently withdrawn, which tends to lower the pH of the reaction solution. When the pH decreases, the added acidic silica solution becomes less soluble, which tends to lead to autonucleation by silica. Therefore, it is desirable to adjust the pH by adding alkali to maintain the pH of the solution in the reaction vessel. In this case, the pH can be adjusted to the desired level by adding alkali so that the SiO2 / A2O molar ratio of the solution in the reaction vessel is in the range of 20 to 160.

[0058] (pH of the solution in the reaction vessel) As mentioned above, there are no particular restrictions on the type of alkali added to adjust the SiO2 / A2O molar ratio of the solution in the reaction vessel to between 20 and 160, but examples include sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia, and organic amines. The pH of the reaction solution adjusted by alkali addition is preferably between 8.5 and 13.0, and more preferably between 9.0 and 12.5. If the pH is above 13.0, the ionic strength in the reaction solution becomes too high, which tends to cause silica particles to aggregate and settle, or the particles to become deformed, making it difficult to obtain the desired particles. If the pH is below 8.5, the added acidic silicic acid solution becomes difficult to dissolve, which tends to cause autonucleation by silicic acid.

[0059] (Process B) In process B of step 3, the reaction mixture is generated by continuously or intermittently adding acidic silica solution to the solution in the reaction vessel, while simultaneously continuously withdrawing a portion of the reaction mixture. Here, the withdrawn reaction mixture is also called the "withdrawal solution." In the initial stages of extraction, although the particle growth reaction has begun, the silica nanoparticles have not grown sufficiently, so small silica nanoparticles are extracted. However, in the later stages of extraction, the silica nanoparticles have grown sufficiently, so larger silica nanoparticles (in terms of particle size) are extracted. By continuously extracting the solution in this way, the solution can be made to contain silica nanoparticles with a wide particle size distribution. Furthermore, it is desirable to mix the reaction solution remaining in the reaction vessel after processes A and B in step 3 with the withdrawn solution. In step 3, withdrawal is performed continuously, but it is desirable to perform the withdrawal under conditions that the preparation solution remains in the reaction vessel. The remaining preparation solution contains the largest particles with the greatest particle growth. By mixing this preparation solution with the withdrawn solution, a wider distribution of particles can be obtained, and the components of the remaining reaction solution become the components of the large particle side peak of the silica fine particles according to this embodiment. The shape of the distribution can also be adjusted to have a distribution shape with a peak on the small particle side by adjusting the rate ratio, and the peak ratio between the small particle side and the large particle side can also be adjusted. Note that if the remaining preparation solution and the withdrawn solution are not mixed, the distribution shape will not have a peak on the large particle side. Furthermore, when the inventors conducted trace experiments, they found that in a process in which seed particle dispersion and acidic silica solution are continuously added in a reaction vessel equipped with an overflow line, as in the manufacturing method of Patent Document 1, even if the rate ratio is adjusted, a particle size distribution with a peak on the large particle side as in the present invention cannot be obtained.

[0060] (Ratio of the rate of addition of acidic silica solution to the rate of withdrawal of the reaction solution (X / Z)) The manufacturing method according to this embodiment is characterized by adding an acidic silica solution to the reaction solution to promote particle growth, while simultaneously withdrawing the reaction solution (withdrawal solution) for the purpose of broadening the particle size distribution. When X is the addition rate [g / min] (silica dry equivalent) of the acidic silica solution during process A of step 3, and Z is the withdrawal rate [g / min] (silica dry equivalent) when the reaction solution (withdrawal solution) is withdrawn from the reaction vessel during process B of step 3, the ratio of the addition rate of the acidic silica solution to the withdrawal rate of the reaction solution (X / Z), as defined by the following formula, must satisfy the relationship 3.0 < (X / Z) ≤ 10.0. Speed ​​ratio (X / Z) = (Silica dry in acidic silicic acid solution per hour [g]) / (Silica dry in extracted solution per hour [g]) In this specification, the "ratio of the rate of addition of acidic silica solution to the rate of withdrawal of the reaction solution (X / Z)" is also referred to as the "rate ratio (X / Z)" or "(X / Z)".

[0061] Regarding the value of this speed ratio (X / Z), when processes A and B of step 3 are carried out simultaneously, it is possible to keep the value of the speed ratio (X / Z) constant, or it is possible to change the value of the speed ratio (X / Z). In the former case, the relationship with the range is determined using the constant value of the speed ratio (X / Z). In the latter case, the relationship with the range is determined using the maximum value among the fluctuating values ​​of the speed ratio (X / Z). In other words, in this embodiment, "the value of the speed ratio (X / Z) satisfies the relationship 3.0 < (X / Z) ≤ 10.0" is equivalent to "the maximum value of the speed ratio (X / Z) satisfies the relationship 3.0 < (X / Z) ≤ 10.0". The maximum value of this speed ratio (X / Z) is preferably recommended to be 3.5 ≤ (X / Z) ≤ 9.0, and even more preferably 4.0 ≤ (X / Z) ≤ 8.5.

[0062] Generally, when the rate ratio (X / Z) is 1.0, the rate at which silica dry is added to the reaction vessel is the same as the rate at which silica dry is extracted. Therefore, the amount of silica dry in the reaction vessel remains constant, and although it depends on the concentration of the raw materials, the liquid level in the reaction vessel is usually roughly constant. When the rate ratio is greater than 1.0, the amount of silica dry extracted is small, so the amount of silica dry in the reaction vessel increases, and the liquid level in the reaction vessel usually gradually rises. On the other hand, when the rate ratio is less than 1.0, the amount of silica dry in the reaction vessel decreases, and the liquid level in the reaction vessel usually tends to gradually fall. If the rate ratio (X / Z) exceeds 10.0, it means that the amount of silica dry in the added silicic acid solution is significantly high, or that the amount of silica dry in the extraction solution is significantly low. If the amount of silica dry in the added silicic acid solution is significantly high, the added silicic acid solution does not contribute to particle growth and self-nucleates, making it difficult to obtain the desired size or particle size distribution. On the other hand, if the amount of silica dry in the extraction solution is significantly low, the particle size distribution of the final silica fine particle dispersion is less likely to be broad. In the manufacturing method according to this embodiment, if the value of the rate ratio (X / Z) is in the range of at least greater than 3.0 to 10.0 or less, self-nucleation of silicic acid is suppressed, and the particle size distribution is more likely to be broad.

[0063] In step 3, when adding the acidic silica solution, a base may be added as a pH adjuster as needed to adjust the pH of the dispersion to the aforementioned range. Basic nitrogen compounds such as alkali metal hydroxides like NaOH and KOH, metal carbonates like potassium oxide, sodium carbonate, and ammonium carbonate, amines like ammonia, monoethanolamine, and piperazine, and quaternary ammonium hydroxides like tetramethylammonium can be used as bases.

[0064] (Step 4) In step 4, the reaction liquid remaining in the reaction vessel after processes A and B in step 3 (the reaction liquid remaining in the reaction vessel at the end of step 3) is heated and aged, and then the reaction liquid extracted in process B of step 3 is mixed to obtain a dispersion of silica fine particles for polishing.

[0065] (heat aging) After processes A and B in step 3, it is necessary to heat-age the reaction solution remaining in the reaction vessel. The aging temperature must be in the range of 40°C to 98°C, and more preferably in the range of 60°C to 98°C. The aging time must be in the range of 20 minutes to 120 minutes, and more preferably in the range of 30 minutes to 90 minutes. This heat-aging process can complete the reaction. If heat-aging is not performed, the added acidic silicic acid solution may remain without depositing on the particle surface, which may impair the stability of the silica sol. While there are no particular restrictions on the temperature of the reaction solution remaining in the reaction vessel after processes A and B in step 3 and the extracted liquid when mixing them, it is generally preferable to mix them at room temperature by cooling or allowing them to cool.

[0066] (Mixing process) The reaction solution remaining in the reaction vessel after processes A and B in step 3 contains the largest particles with the greatest particle growth. By mixing this reaction solution with the extracted solution, a broader particle distribution can be obtained. Furthermore, when the reaction solution remaining in the reaction vessel after processes A and B in step 3 is mixed with the extracted solution, the particle size distribution will have a peak on the larger particle side. The shape of the distribution can also be adjusted to have a peak on the smaller particle side by adjusting the rate ratio, and the peak ratio between the small and large particle sides can also be adjusted. Note that if the extracted solution is not added and mixed with the reaction solution remaining in the reaction vessel, the distribution will have no peak on the larger particle side.

[0067] (concentration process) The silica fine particle dispersion obtained by the method for producing the abrasive silica fine particle dispersion according to this embodiment, including steps 1 to 4, may be concentrated to a desired concentration after adjusting the temperature to a range of room temperature to about 50°C. The concentration method is not particularly limited, but it can be concentrated using an ultrafiltration membrane or a rotary evaporator. If desired, coarse particles may be removed by filtration using centrifugation or a filter. [Examples]

[0068] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples. Also, regarding the measurement methods for various properties of the silica fine particles or the silica fine particle dispersion in the examples and comparative examples, unless otherwise specified, the methods described below were used.

[0069] (1) Particle size in terms of specific surface area The particle size in terms of specific surface area can be obtained by measuring the specific surface area Sa of the silica fine particles and using the following formula. (De) (nm) = 6000 / (ρ × Sa) (Here, ρ represents the density of the silica fine particles, 2.2 [g / cm 3 .) When the specific surface area of the silica fine particles is 100 m 2 / g or more, sintering progresses during firing in the BET method. In this case, the specific surface area (SA) was determined by the titration method, and the particle size in terms of specific surface area (De) was calculated from the formula (De) = 6000 / (SA × ρ). <BET method> 50 mL of a silica fine particle dispersion containing silica fine particles (silica concentration 40 mass%) was adjusted to pH 3.5 with HNO3, 40 mL of 1-propanol was added, and the sample dried at 110 °C for 16 hours was pulverized in a mortar and fired at 500 °C for 1 hour in a muffler furnace to obtain a measurement sample. Then, using a specific surface area measuring device (manufactured by Yuasa Ionics, model number MultiSorb 12), the specific surface area was calculated by the BET one-point method from the nitrogen adsorption amount using the nitrogen adsorption method (BET method). Specifically, 0.5 g of the sample was placed in the measurement cell, degassed at 300 °C for 20 minutes in a mixed gas stream of 30 v% nitrogen and 70 v% helium, and then the sample was maintained at liquid nitrogen temperature in the above mixed gas stream and nitrogen was adsorbed on the sample in equilibrium. Next, while flowing the above mixed gas, the sample temperature was gradually raised to room temperature, and the amount of nitrogen desorbed during that time was detected, and the specific surface area of the silica fine particles was calculated using a calibration curve prepared in advance. <Titration method> First, a sample equivalent to 1.5 g of SiO2 was placed in a beaker, then transferred to a constant-temperature reaction vessel (25°C), and pure water was added to bring the volume to 90 mL. The following operations were carried out in a constant-temperature reaction vessel maintained at 25°C. Next, a 0.1 mol / L hydrochloric acid solution was added to bring the pH to 3.6. Then, 30 g of sodium chloride was added, the mixture was diluted to 150 mL with pure water, and stirred for 10 minutes. Next, a pH electrode was set up, and a 0.1 mol / L sodium hydroxide solution was added dropwise while stirring to adjust the pH to 4.0. Furthermore, the sample adjusted to pH 4.0 was titrated with a 0.1 mol / L sodium hydroxide solution, and the titration volume and pH value were recorded at four or more points in the pH range of 8.7 to 9.3. A calibration curve was created by setting the titration volume of the 0.1 mol / L sodium hydroxide solution as X and the corresponding pH value as Y. Then, using the formula V=(A×f×100×1.5) / (W×C), the amount of 0.1 mol / L sodium hydroxide solution consumed per 1.5 g of SiO2 to achieve a pH of 4.0 to 9.0 was calculated (V(mL)). Using this, the specific surface area was calculated according to the formula SA=29.0V-28. In the above formula, A represents the titration volume (mL) of 0.1 mol / L sodium hydroxide solution required to bring the pH from 4.0 to 9.0 per 1.5 g of SiO2, f represents the titer of the 0.1 mol / L sodium hydroxide solution, C represents the SiO2 concentration (%) of the sample, and W represents the sample volume (g).

[0070] (2) Weight-based particle size distribution and weight-average particle size (D 50 ) and other measurements A silica particle dispersion was diluted with a 0.05% by mass sodium dodecyl sulfate aqueous solution to a solid content concentration of 2% by mass. 0.1 mL of this solution was then injected by syringe into a known disk centrifugal particle size analyzer (manufactured by CPS Instruments), and the particle size distribution was determined by weight conversion by measuring the dispersion in a density gradient solution of 8% to 24% sucrose at a measurement condition of 18,000 rpm. From the measurement results of the weight-converted particle size distribution, the cumulative 10% particle size (D) was calculated by accumulating from the smallest particle size. 10 ), cumulative 90% particle diameter (D 90 ) and cumulative 50% particle size (D50 ) was calculated.

[0071] (3) Average sphericity and rate of irregular particles of the particle group measured by the image analysis method Using a scanning electron microscope (magnification: 200,000 times), for 200 silica fine particles contained in the silica fine particle dispersion liquid, in an image or photograph containing 200 or more silica fine particles in the same field of view, for 200 randomly selected silica fine particles, the minor axis and major axis of each were measured, and the minor axis / major axis ratio of each was determined. This operation was performed for randomly selected fields of view to create the particle size distribution of the particle group. In this specification, as the scanning electron microscope, the ultra-high resolution field emission type scanning electron microscope S-5500 (manufactured by Hitachi High-Technologies Corporation) was used. For the specific measurement method of silica fine particles, the maximum diameter of the projected silica fine particle image was taken as the major axis, and its length was measured, and this value was taken as the major axis. Also, a point that bisects the major axis on the major axis was determined, two points where the straight line perpendicular to it intersects the outer edge of the silica fine particle image were obtained, the distance between the two points was measured and taken as the minor axis, and the degree of irregularity (minor axis / major axis ratio) was determined. From the particle size distribution of the particle group, the average sphericity of the particle group and the rate of irregular particles (number of irregular particles / number of all particles × 100) were calculated.

[0072] (4) Coefficient of variation of the particle size distribution area A silica fine particle dispersion liquid with a silica concentration of 1 mass% was prepared, and it was obtained from the weight-converted particle size distribution of the particle group using a disk centrifuge type particle size distribution measuring device (manufactured by CPS INSTRUMENTS). In the weight-converted particle size distribution of the particle group, from the cumulative 1% particle size (D1) from the smaller side of the particle size to the cumulative 99% particle size (D 99 ) up to the range of the particle size range was divided into 6 equal parts, and the particle size ranges were respectively designated as S1, S2, S3, S4, S5, and S6. The coefficient of variation (CV value) of the particle size distribution area corresponding to each particle size range at this time was calculated.

[0073] (5) Polishing test method <Polishing of SiO2 film> The abrasive dispersions obtained in each of the examples and comparative examples were prepared. The solid content concentration was 1.0% by mass, and nitric acid was added to adjust the pH to 6.0. Next, as the substrate to be polished, a substrate consisting of an SiO2 insulating film fabricated by deposition or a thermal oxide film made of SiO2 fabricated by thermal oxidation (both with a thickness of 2 μm) was prepared. Next, the substrate to be polished was placed in a polishing device (NF300, manufactured by Nanofactor Co., Ltd.), and polishing was performed using a polishing pad (IC-1000 / SUBA400 concentric type, manufactured by Nitta Haas Co., Ltd.) with a substrate load of 0.12 MPa, a table rotation speed of 87 rpm, and a polishing head rotation speed of 93 rpm, by supplying abrasive dispersion liquid at a rate of 20 mL / min for 30 minutes. Then, the change in weight of the substrate to be polished before and after polishing was determined, and the polishing speed was calculated.

[0074] <Polishing aluminum hard disks> The abrasive dispersions obtained in each of the examples and comparative examples were prepared. The solid content concentration was 9% by mass, and the pH was adjusted to 2.0 by adding nitric acid. An aluminum hard disk substrate was placed in a polishing machine (Nanofactor Co., Ltd., NF300), and polishing was performed using a polishing pad (Nitta Haas Co., Ltd., "Polytex φ12") with a substrate load of 0.05 MPa, a table rotation speed of 30 rpm, and a polishing head rotation speed of 60 rpm, supplying abrasive dispersion liquid at a rate of 20 mL / min for 10 minutes. The entire surface was then observed using an ultrafine defect visualization macro device (VISION PSYTEC, product name: Macro-Max) at Zoom 15, with a measurement of 65.97 cm². 2 The number of scratches (linear marks) present on the polished substrate surface corresponding to the specified condition was counted and totaled.

[0075] [Preparation of acidic silica solution] A sodium silicate aqueous solution (silica concentration 24.06% by mass, Na2O concentration 7.97% by mass) was mixed with pure water to obtain a sodium silicate aqueous solution (silica concentration 5% by mass). 18 kg of the obtained sodium silicate aqueous solution was mixed with 6 L of strongly acidic cation exchange resin (SK1BH, manufactured by Mitsubishi Chemical Corporation) at a space velocity of 3.0 h. -1The solution was passed through the liquid, yielding 18 kg (silica concentration 4.5% by mass, pH 2.7). In the following examples and comparative examples, this acidic silica solution or an equivalent acidic silica solution was used as a raw material after being appropriately concentrated or diluted.

[0076] [Example 1] ·Process 1 486 g of pure water was added to a 15 L unheated mixing tank, and then 2.4 g of potassium hydroxide aqueous solution (potassium hydroxide aqueous solution with a KOH concentration of 48.6% by mass (Super Kali R, manufactured by Toagosei Co., Ltd.)) was added. 68.0 g of acidic silica solution (SiO2 concentration of 4.50% by mass) was added, and the mixture was stirred until homogeneous to obtain the first formulation. ·Process 2 After stirring the first preparation solution, the temperature was raised to 70°C and held for 30 minutes. Then, 1.05 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 11 hours to obtain the second preparation solution. The addition rate of the acidic silicic acid solution was 1.59 g / min. Furthermore, 8427 g of pure water was added to the second preparation solution after the addition was complete. ·Process 3 After adding pure water, the temperature was maintained at 90°C, and 29.69 kg of acidic silica solution (SiO2 concentration 4.50% by mass), 0.67 kg of potassium hydroxide aqueous solution (KOH concentration 1.3% by mass), and 17.02 kg of potassium hydroxide aqueous solution (KOH concentration 0.1% by mass) were added over 79 hours. In step 3, the addition rates of the acidic silicic acid solution and potassium hydroxide aqueous solution were changed midway through the process, as shown in Tables 1 and 2. In Tables 1 and 2, these steps are conveniently labeled as steps 3-1, 3-2, and 3-3, respectively, according to their respective addition rates, and the amount of silicic acid solution used, its silica concentration, the amount of potassium hydroxide aqueous solution used, and its KOH concentration are recorded. In addition, in step 3, 47.34 kg of the reaction solution was withdrawn from the mixing tank at the same time as the addition of the acidic silica solution and the potassium hydroxide aqueous solution. The withdrawal rates of each reaction solution in steps 3-1, 3-2, and 3-3 are shown in Tables 1 and 2. Table 1 shows the rate at which the acidic silica solution was added to the silica dry at each time interval. After the addition and withdrawal were completed, 10.1 kg of reaction solution remained in the mixing tank. The ratio of dry silica in the acidic silica solution to dry silica in the extracted solution (dry silica in the acidic silica solution / dry silica in the extracted solution) for each time period during the preparation process is shown in Tables 1 and 2. ·Process 4 The reaction solution remaining in the mixing tank (10.1 kg) was held at 90°C for 1 hour and then cooled to room temperature. This mixture was then mixed with the extracted reaction solution (47.34 kg) until homogeneous. The resulting mixture had a pH of 10.0, a specific surface area equivalent particle size of 41.3 nm, and an SiO2 concentration of 2.41% by mass. This mixture was concentrated using an ultrafiltration membrane SIP-1013 manufactured by Asahi Kasei Corporation until the SiO2 concentration reached 12.0%, to obtain a silica fine particle dispersion for polishing. The resulting silica fine particle dispersion for polishing was then evaluated using the method described above, and the evaluation results are shown in Table 4.

[0077] [Example 2] ·Process 1 759 g of pure water was added to a 15 L unheated mixing tank, and then 3.6 g of potassium hydroxide aqueous solution (KOH concentration 48.6% by mass (Super Kali R, manufactured by Toagosei Co., Ltd.)) was added. 106.2 g of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added, and the mixture was stirred until homogeneous to obtain the first formulation. ·Process 2 After stirring the first preparation solution, the temperature was raised to 83°C and held for 30 minutes. Then, 1.57 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 11 hours to obtain the second preparation solution. The addition rate of the acidic silicic acid solution was 2.37 g / min. Furthermore, 985 g of pure water was added to the second preparation solution after the addition was complete. ·Process 3 After adding pure water, the temperature was maintained at 90°C. Next, 41.94 kg of acidic silica solution (SiO2 concentration 4.50% by mass) and 1.89 kg of potassium hydroxide aqueous solution (KOH concentration 2.3% by mass) were added over 92 hours. In step 3, the addition rates of the acidic silicic acid solution and potassium hydroxide aqueous solution were changed midway through the process, as shown in Tables 1 and 2. In Tables 1 and 2, for convenience, the steps are labeled as steps 3-1, 3-2, 3-3, 3-4, and 3-5, according to their respective addition rates, and the amount of silicic acid solution used, its silica concentration, the amount of potassium hydroxide aqueous solution used, and its KOH concentration are noted for each step. In step 3, simultaneously with the addition of the acidic silica solution and the potassium hydroxide aqueous solution, 37.84 kg of the reaction solution was withdrawn from the mixing tank. The withdrawal rates of the reaction solutions in steps 3-1, 3-2, 3-3, 3-4, and 3-5 are shown in Tables 1 and 2. The rate of addition of the acidic silica solution to the silica dry at each elapsed time is also shown in Table 1. After the addition and withdrawal were completed, 9.4 kg of the reaction solution remained in the mixing tank. The ratio of dry silica in the acidic silica solution to dry silica in the extracted solution (dry silica in the acidic silica solution / dry silica in the extracted solution) for each time period during the preparation process is shown in Tables 1 and 2. ·Process 4 The reaction solution remaining in the mixing tank (9.4 kg) was held at 90°C for 1 hour and then cooled to room temperature. This mixture was then mixed with the extracted reaction solution (37.84 kg) until homogeneous. The resulting mixture had a pH of 10.0, a specific surface area equivalent particle size of 45.5 nm, and an SiO2 concentration of 4.15% by mass. This mixture was concentrated using an ultrafiltration membrane SIP-1013 manufactured by Asahi Kasei Corporation until the SiO2 concentration reached 12.0%, to obtain a silica fine particle dispersion for polishing. The resulting silica fine particle dispersion for polishing was then evaluated using the method described above, and the evaluation results are shown in Table 4.

[0078] [Example 3] ·Process 1 385g of pure water was added to a 15L unheated mixing tank, and then 1.9g of potassium hydroxide aqueous solution (KOH concentration 48.6% by mass (Super Kali R, manufactured by Toagosei Co., Ltd.)) was added. 53.8g of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added, and the mixture was stirred until homogeneous to obtain the first formulation. ·Process 2 The first preparation was stirred and then heated to 50°C and held for 30 minutes. Subsequently, 0.83 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 11 hours to obtain the second preparation. The addition rate of the acidic silicic acid solution was 1.26 g / min. Finally, 386 g of pure water was added to the second preparation after the addition was complete. ·Process 3 After adding pure water, the temperature was maintained at 90°C. Next, 54.33 kg of acidic silica solution (SiO2 concentration 4.50% by mass) and 3.20 kg of potassium hydroxide aqueous solution (KOH concentration 1.8% by mass) were added over a period of 129 hours. In step 3, the addition rates of the acidic silicic acid solution and potassium hydroxide aqueous solution were changed midway through the process, as shown in Tables 1 and 2. In Tables 1 and 2, these steps are conveniently labeled as steps 3-1, 3-2, 3-3, and 3-4, respectively, according to their respective addition rates, and the amount of silicic acid solution used, its silica concentration, the amount of potassium hydroxide aqueous solution used, and its KOH concentration are indicated. In step 3, 48.56 kg of the reaction solution was withdrawn from the mixing tank simultaneously with the addition of the acidic silica solution and the potassium hydroxide aqueous solution. The withdrawal rates of the reaction solutions in steps 3-1, 3-2, 3-3, and 3-4 are shown in Tables 1 and 2. The rate of addition of the acidic silica solution to the silica dry at each time point is also shown in Table 1. After the addition and withdrawal were completed, 10.6 kg of the reaction solution remained in the mixing tank. The ratio of dry silica in the acidic silica solution to dry silica in the extracted solution (dry silica in the acidic silica solution / dry silica in the extracted solution) for each time period during the preparation process is shown in Tables 1 and 2. ·Process 4 The reaction solution remaining in the mixing tank (10.6 kg) was held at 90°C for 1 hour and then cooled to room temperature. This mixture was then mixed with the extracted reaction solution (48.56 kg) until homogeneous. The resulting mixture had a pH of 10.1, a specific surface area equivalent particle size of 39.2 nm, and an SiO2 concentration of 4.20% by mass. This mixture was concentrated using an ultrafiltration membrane SIP-1013 manufactured by Asahi Kasei Corporation until the SiO2 concentration reached 12.0%, to obtain a silica fine particle dispersion for polishing. The resulting silica fine particle dispersion for polishing was then evaluated using the method described above, and the evaluation results are shown in Table 4.

[0079] [Comparative Example 1] ·Process 1 1.59 kg of pure water was added to a 200 L unheated mixing tank, and then 44.4 g of potassium hydroxide aqueous solution (KOH concentration 48.6% by mass (Super Kali R, manufactured by Toagosei Co., Ltd.)) was added. 848.0 g of acidic silica solution (SiO2 concentration 4.50% by mass) was added, and the mixture was stirred until homogenized. ·Process 2 After stirring, the temperature was raised to 82°C and held for 30 minutes. Then, 3.06 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 3 hours. The addition rate of the acidic silicic acid solution was 16.99 g / min. Furthermore, 18.45 kg of acidic silica solution (SiO2 concentration 4.50% by mass) was added over 12 hours. The addition rate of the acidic silica solution was 25.63 g / min. After the addition was complete, 6.19 kg of pure water was added. In step 2, the rate at which the acidic silica solution was added was changed midway through the process, as shown in Table 3. In Table 3, each addition rate is conveniently labeled as step 2-1 and step 2-2, and the amount of silica solution used and its silica concentration are indicated. ·Process 3 After adding the pure water, the temperature was maintained at 90°C. Next, 43.38 kg of acidic silica solution (SiO2 concentration 4.50% by mass) and 115.5 kg of potassium hydroxide aqueous solution (KOH concentration 0.036% by mass) were added over 38.5 hours. Furthermore, simultaneously with the addition of the acidic silica solution and the potassium hydroxide aqueous solution, 3.90 kg of the reaction solution was withdrawn from the mixing tank. The addition rates of the acidic silica solution, the addition rates of the diluted potassium hydroxide aqueous solution, and the withdrawal rates are shown in Table 3. The addition rate of the acidic silica solution to the silica dry is also shown in Table 3. After the addition and withdrawal were completed, 185.2 kg of the reaction solution remained in the mixing tank. Table 3 shows the ratio of dry silica in the acidic silica solution to dry silica in the extracted solution (dry silica in the acidic silica solution / dry silica in the extracted solution) for each time period during the preparation process. ·Process 4 The reaction solution remaining in the mixing tank (185.2 kg) was held at 90°C for 1 hour and then cooled to room temperature. This mixture was then mixed with the extracted reaction solution (3.90 kg) until homogeneous. The resulting mixture had a pH of 9.9, a specific surface area equivalent particle size of 35.9 nm, and an SiO2 concentration of 1.56% by mass. This mixture was concentrated using an ultrafiltration membrane SIP-2013 manufactured by Asahi Kasei Corporation until the SiO2 concentration reached 12.0%, to obtain a silica fine particle dispersion for polishing. The resulting silica fine particle dispersion for polishing was then evaluated using the method described above, and the evaluation results are shown in Table 4.

[0080] [Comparative Example 2] ·Process 1 1.71 kg of pure water was added to a 200 L unheated mixing tank, and then 47.9 g of potassium hydroxide aqueous solution (KOH concentration 48.6% by mass (Super Kali R, manufactured by Toagosei Co., Ltd.)) was added. 915.1 g of acidic silica solution (SiO2 concentration 4.50% by mass) was added, and the mixture was stirred until homogenized. ·Process 2 After stirring, the temperature was raised to 82°C and held for 30 minutes. Then, 3.30 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 3 hours. The addition rate of the acidic silicic acid solution was 18.33 g / min. Furthermore, 29.56 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 18 hours. The addition rate of the acidic silicic acid solution was 27.37 g / min. After the addition was complete, 40.46 kg of pure water was added. In step 2, the rate at which the acidic silica solution was added was changed midway through the process, as shown in Table 3. In Table 3, each addition rate is conveniently labeled as step 2-1 and step 2-2, and the amount of silica solution used and its silica concentration are indicated. ·Process 3 After adding the pure water, the temperature was maintained at 90°C. Next, 51.07 kg of acidic silicic acid solution (SiO2 concentration 4.50 mass%) and 63.83 kg of potassium hydroxide aqueous solution (KOH concentration 0.055 mass%) were added over 56 hours. Simultaneously with the addition of the acidic silicic acid solution and the potassium hydroxide aqueous solution, 10.95 kg of the reaction solution was withdrawn from the mixing tank. The addition rates of the acidic silicic acid solution, the addition rates of the diluted potassium hydroxide aqueous solution, and the withdrawal rates are shown in Table 3. The addition rate of the acidic silicic acid solution to the silica dry is also shown in Table 3. After the addition and withdrawal were completed, 180.0 kg of the reaction solution remained in the mixing tank. Table 3 shows the ratio of dry silica in the acidic silica solution to dry silica in the extracted solution (dry silica in the acidic silica solution / dry silica in the extracted solution) for each time period during the preparation process. ·Process 4 The reaction solution remaining in the mixing tank (180.0 kg) was held at 90°C for 1 hour and then cooled to room temperature. This mixture was then mixed with the extracted reaction solution (10.95 kg) until homogeneous. The resulting mixture had a pH of 9.7, a specific surface area equivalent particle size of 38.1 nm, and an SiO2 concentration of 2.00% by mass. This mixture was concentrated using an ultrafiltration membrane SIP-2013 manufactured by Asahi Kasei Corporation until the SiO2 concentration reached 12.0%, to obtain a silica fine particle dispersion for polishing. The resulting silica fine particle dispersion for polishing was then evaluated using the method described above, and the evaluation results are shown in Table 4.

[0081] [Comparative Example 3] ·Process 1 385g of pure water was added to a 15L unheated mixing tank, and then 1.9g of potassium hydroxide aqueous solution (KOH concentration 48.6% by mass (Super Kali R, manufactured by Toagosei Co., Ltd.)) was added. 53.8g of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added, and the mixture was stirred until homogeneous to obtain the first formulation. ·Process 2 The first preparation was stirred and then heated to 50°C and held for 30 minutes. Subsequently, 0.83 kg of acidic silicic acid solution (SiO2 concentration 4.50% by mass) was added over 11 hours to obtain the second preparation. The addition rate of the acidic silicic acid solution was 1.26 g / min. Finally, 386 g of pure water was added to the second preparation after the addition was complete. ·Process 3 After adding pure water, the temperature was maintained at 90°C. Next, 54.41 kg of acidic silica solution (SiO2 concentration 4.50% by mass) and 3.20 kg of potassium hydroxide aqueous solution (KOH concentration 1.8% by mass) were added over 113 hours. In step 3, the addition rates of the acidic silicic acid solution and potassium hydroxide aqueous solution were changed midway through the process, as shown in Tables 1 and 2. In Tables 1 and 2, these steps are conveniently labeled as steps 3-1, 3-2, 3-3, and 3-4, respectively, according to their respective addition rates, and the amount of silicic acid solution used, its silica concentration, the amount of potassium hydroxide aqueous solution used, and its KOH concentration are indicated. In step 3, 48.56 kg of the reaction solution was withdrawn from the mixing tank simultaneously with the addition of the acidic silica solution and the potassium hydroxide aqueous solution. The withdrawal rates of the reaction solutions in steps 3-1, 3-2, 3-3, and 3-4 are shown in Tables 1 and 2. The rate of addition of the acidic silica solution to the silica dry at each time point is also shown in Tables 1 and 2. After the addition and withdrawal were completed, 10.7 kg of the reaction solution remained in the mixing tank. The ratio of dry silica in the acidic silica solution to dry silica in the extracted solution (dry silica in the acidic silica solution / dry silica in the extracted solution) for each time period during the preparation process is shown in Tables 1 and 2. ·Process 4 The reaction solution remaining in the mixing tank (10.7 kg) was held at 90°C for 1 hour and cooled to room temperature. This mixture was then mixed with the extracted reaction solution (48.56 kg) until homogeneous. The resulting mixture had a pH of 10.1, a specific surface area equivalent particle size of 17.4 nm, and an SiO2 concentration of 4.20% by mass. This mixture was concentrated using an ultrafiltration membrane SIP-1013 manufactured by Asahi Kasei Corporation until the SiO2 concentration reached 12.0%, to obtain a silica fine particle dispersion for polishing. The obtained silica fine particle dispersion was expected to have a specific surface area equivalent particle size (39.2 nm) equivalent to that of Example 3. However, by increasing the rate of addition of the silicic acid solution in step 3-2, smaller particles were generated, resulting in a particle size significantly smaller than the desired specific surface area equivalent particle size.

[0082] [Table 1]

[0083] [Table 2]

[0084] [Table 3]

[0085] [Table 4]

Claims

1. A method for producing a silica fine particle dispersion for polishing, comprising the following steps 1 to 4. (Step 1) This step involves introducing an acidic silica solution and an alkali into a reaction vessel while maintaining a non-heated state to obtain the first preparation solution. (Step 2) The process of obtaining a second mixture by uniformly stirring the first mixture, then heating it to 40°C or higher and 98°C or lower, maintaining the temperature within that range, and then continuously or intermittently adding the acidic silica solution while maintaining the temperature within that range. (Step 3) A step in which the following processes A and B are carried out simultaneously, following step 2. Process A: Acidic silica solution and alkali are added continuously or intermittently to the reaction vessel filled with the second preparation solution to prepare the reaction solution. Process B: A portion of the reaction solution in the reaction vessel from Process A is withdrawn continuously or intermittently (where X is the rate of addition of the acidic silica solution [g / min] (silica dry equivalent) when adding the acidic silica solution, and Z is the withdrawal rate [g / min] (silica dry equivalent) when withdrawing the reaction solution, and the ratio of the rate of addition of the acidic silica solution to the withdrawal rate of the reaction solution (X / Z) satisfies the relationship 3.0 < (X / Z) ≤ 10.0). (Step 4) The reaction solution remaining in the reaction vessel after processes A and B of step 3 is aged at a temperature of 40°C to 98°C for 20 minutes to 120 minutes, and then the reaction solution extracted in process B of step 3 is added and mixed to obtain a dispersion of silica fine particles for polishing.

2. A method for producing a silica fine particle dispersion for polishing according to claim 1, wherein the addition treatment of acidic silicic acid solution in step 3 is carried out by A) or B) below. A) Add the acidic silica solution at a constant rate. B) Change the rate of addition of the acidic silica solution n or more times (n≧1), and set the rate of addition for the Xth time to L Ｘ When [g / min] (where X is an integer from 1 to n), L is always ｘ＋１ ≤ L ｘ Add the necessary components to satisfy the given relationship.

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