Colloidal silica and method for producing colloidal silica

Abstract

The present invention provides: a colloidal silica which is in a single-digit nanometer size or has a small particle diameter close to the single-digit nanometer size, and which is substantially free from aggregation; and a method for producing the colloidal silica.　This colloidal silica is characterized in that: the surface is modified; the BET diameter is 12 nm or less; and the colloidal silica is not substantially aggregated. This method for producing the colloidal silica is characterized by including: a starting material preparation step for preparing a starting material colloidal silica having a BET diameter of 12 nm or less by supplying an easily decomposable organosilicate to a reaction liquid that contains a hydrolysis catalyst composed of an organic amine and reacting the easily decomposable organosilicate with the reaction liquid; a concentration adjustment step for setting the solid content concentration of the starting material colloidal silica to 13 mass% or less and setting the concentration of an alcohol generated from the starting material preparation step to 1-25 mass%; a modification step for modifying the concentration-adjusted starting material colloidal silica; and a concentration step for concentrating the modified colloidal silica so that the residual organic solvent in the modified colloidal silica becomes 1 mass% or less.

Description

Colloidal silica and method for producing colloidal silica The present invention relates to colloidal silica and a method for producing colloidal silica. As methods for industrially producing high purity colloidal silica, a method of ion exchanging an aqueous sodium silicate solution, a method of thermal decomposition of silicon tetrachloride, a method of hydrolyzing an organosilicate in a water-alcohol mixed solvent in the presence of an acid catalyst or an alkali catalyst, and the like have been proposed and put into practice. However, the method of hydrolyzing an organosilicate allows the use of high purity organosilicate, catalyst, solvent, etc., for the reaction, and therefore the amount of impurities derived from these raw materials, etc. is extremely small, and is therefore suitable as a method for producing high purity colloidal silica with a particularly small content of metal impurities, and several methods for the hydrolysis of organosilicate have been proposed so far. Regarding colloidal silica used for various applications, particularly colloidal silica used in the field of, for example, an abrasive for semiconductor wafers, with the increasing integration density of today's LSIs, various types of metal wiring, oxide films, and the like are present on a single wafer, and each semiconductor wafer is required to have its own appropriate polishing performance, and therefore colloidal silica with various subtle differences in composition and properties is required. Furthermore, for colloidal silica used in applications where even slight alkali metal impurities should not be contained, such as binders for hard coating agents and ceramics, chromate-based metal surface treatment agents, and ground improvement grouting agents, acidic colloidal silica is required, and several proposals for methods for producing such acidic colloidal silica have been proposed. For example, the applicant of the present application has investigated a method for easily producing colloidal silica having predetermined properties, such as spherical colloidal silica, which does not require special post-treatment such as acid treatment, ion exchange treatment, or further modification treatment, has an extremely low content of metal impurities including alkali metals, and has an average particle size in the range of 5 to 500 nm, a standard deviation of 20 or less, and a polydispersity index of 0.15 or less, as determined by particle size distribution analysis using an electron microscope, and has proposed that neutral colloidal silica with a pH of 5 to 8 can be easily produced without special post-treatment such as acid treatment, ion exchange treatment, or the like, by using an easily hydrolyzable organosilicate having a high hydrolysis rate and a specific hydrolysis catalyst as a hydrolysis catalyst, and adding and reacting this hydrolysis catalyst so that at least the ratio of hydrolysis catalyst (A) to silica (B) in the reaction mixture at the end of the reaction {catalyst remaining molar ratio (A / B)} is a predetermined value or less (Patent Document 1). Incidentally, in the field of polishing agents for semiconductor wafers, for example, it has become necessary to meet various demands in recent years, and with conventionally manufactured colloidal silica of several tens of nanometers (nm), fine adjustment during polishing is difficult, and problems arise such as the surface being over-etched or a clean surface not being formed. In addition, there is also the situation of semiconductors becoming increasingly finer. Therefore, there is a demand for colloidal silica with a particle size smaller than that of conventional colloidal silica, that is, a particle size of a few nm, or a particle size close to that.However, when the particle size is such, the tendency of particles to aggregate due to the solid content of colloidal silica increases, and even if the particle size is close to single nano size, there is a concern that the characteristics (e.g., polishability, improvement of the number of defects on the polished object, etc.) cannot be fully utilized.In this regard, according to the study by the inventors of the present application, it has been found that aggregation becomes more prominent, especially as the solid content concentration of colloidal silica increases. That is, colloidal silica that has a particle size of single nano size or close to single nano size and has a stable dispersed state without causing aggregation even when the solid content concentration is relatively high has not been found so far. JP 2007-153732 A International Publication No. WO 2016 / 117560 A International Publication No. WO 2023 / 007938 A Japanese Patent Application Publication No. 2004-315300 A Japanese Patent Application Publication No. 2023-072344 A Japanese Patent Application Publication No. 2018-002569 A International Publication No. 2012 / 161157 Kojiro Aoki, Journal of the Japan Rubber Association, Vol.59, No.11, 1986, 610-619. M.-CB Salon, et al., Colloids and Surfaces A: Physicochem. Eng. Aspects, 2008, 312, 83-91. Therefore, the inventors of the present application conducted extensive research to develop colloidal silica having a small particle size of single nano size or a similar range, which does not substantially aggregate even when the solid concentration is relatively high. As a result, they discovered that this can be achieved by devising a raw material preparation process, a concentration adjustment process, etc., and by subjecting colloidal silica to a modification treatment at a predetermined timing, thereby completing the present invention. Therefore, an object of the present invention is to provide colloidal silica having a small particle size of single nano size or close to that size and substantially no aggregation, and a method for producing the same. Several techniques for modifying colloidal silica have been reported. Here, Patent Document 2 is related to modified colloidal silica that can improve the stability of polishing rate over time when used as abrasive grains with few microparticles, but does not specifically teach colloidal silica with a single nano size or a small particle size close to that, and does not disclose particle size in its examples.In addition, in the manufacturing method described in Patent Document 2, it is essential to provide a process of concentrating the colloidal silica so that the residual organic solvent concentration is 1 mass% or less (organic solvent distillation process) before the modification process of modifying the colloidal silica.Therefore, in such a manufacturing process, when trying to obtain colloidal silica with a small particle size close to that of single nano size, there is a risk of aggregation before the modification process is performed. Patent Document 3 relates to a chemical mechanical polishing composition capable of selectively polishing a silicon nitride film by sufficiently increasing the polishing rate of a silicon nitride film relative to the polishing rate of a silicon oxide film. In the examples of Patent Document 3, it is shown that a colloidal silica particle dispersion having a predetermined solid content concentration, primary particle size, and secondary particle size obtained by the method described in Example 8 or Example 1 of Patent Document 4 is mixed with 3-mercaptopropyltrimethoxysilane and heated under reflux to obtain a thiolated silica sol, and then hydrogen peroxide is added to the silica sol and heated under reflux to obtain a dispersion containing abrasive grains D or E having the predetermined solid content concentration, primary particle size, and secondary particle size. In the dispersions containing Abrasive Grain D or Abrasive Grain E, the primary particle diameter is 10 nm or less at the concentration (4% by mass) when the dispersions are obtained, the secondary particle diameter is not significantly different from the primary particle diameter, and the association ratio is about 1.2, and it is understood that there is little aggregation at that concentration. However, when the inventors of the present application verified this, as shown in Reference Experimental Examples 1 and 2 described below, it was found that these dispersions would aggregate and gel if the solids concentration was significantly greater than 10% by mass, and that there was a high probability that they would not be stable over time. Furthermore, Patent Document 5 provides a chemical mechanical polishing composition capable of polishing molybdenum films and silicon oxide films at a stable polishing rate and capable of suppressing the corrosion of the molybdenum film and the occurrence of defects in the silicon oxide film. In the examples of Patent Document 5, it is shown that a (3-triethoxysilyl)mercapto group-containing silane coupling agent is dropped into a colloidal silica dispersion and stirred, and then hydrogen peroxide is added and refluxed under normal pressure to obtain an aqueous dispersion J containing silica particles surface-modified with sulfo groups and having an average secondary particle size of 7.4 nm (paragraph

[0106] ). The primary particle diameter of the silica particles was 7.0 nm. Patent Document 6 provides a method for converting the silica particles into nanoparticles having a diameter of 10 nm or less by mixing ordinary silica particles such as powder or granules, water, and a metal alkoxide compound having a chain group having an amino group to prepare a reaction mixture, and heating the reaction mixture at 75° C. or higher for a certain period of time. In the examples of Patent Document 6, a method is shown in which powdered silica gel, 3-aminopropyltrimethoxysilane, and distilled water are charged into a reaction vessel equipped with a reflux device, and the mixture is heated and stirred. The aqueous solution obtained after the reaction is a sol solution containing colloidal silica, and the particles observed with a tunneling electron microscope (TEM) are all nanoparticles having a diameter of 10 nm or less, and are observed in a dispersed state without aggregation (see paragraphs

[0057] ,

[0061] , etc.). However, the aqueous dispersion obtained in Patent Document 5 and the sol solution containing silica obtained in Patent Document 6 are likely to aggregate when the solid content concentration is increased due to their production methods, and are also highly likely to lack stability over time. Incidentally, Patent Document 7 discloses an organic solvent-dispersed silica sol in which colloidal silica is dispersed in a dispersion medium containing an organic solvent, in which a silane compound having at least one ether structure is bonded to the surface of colloidal silica particles, and as confirmed in the examples, the particle size measured by dynamic light scattering remains unchanged even after storage for one month in a thermostatic chamber at 50° C., demonstrating that the particle size is relatively stable. However, the BET diameter is not necessarily small. Furthermore, the organic solvent-dispersed silica sol described in Patent Document 7 uses a large amount of benzyl alcohol in the dispersion solvent, exceeding 80 mass %, and has a different purpose from the colloidal silica of the present application. That is, the gist of the present invention is as follows. (1) A colloidal silica having a modified surface, a BET diameter of 12 nm or less, and being substantially free of aggregation. (2) BET specific surface area is 227 m ２ / g or more. (3) The colloidal silica according to (1), wherein the modification is anion-modified or cation-modified. (4) The colloidal silica according to (3), wherein the anion-modification is performed with a sulfo group. (5) The colloidal silica according to (3), wherein the cation modification is performed by a primary amino group. (6) The colloidal silica according to (1), having a solid content of 12% by mass or more. (7) The colloidal silica according to (1), which has a solid content concentration of 12% by mass or more, and which exhibits, with respect to a cumulant average diameter measured by a dynamic light scattering method, a rate of change in the cumulant average diameter after being kept at a temperature of 60° C. for one week, compared to that before the keeping, of within 20%. (8) A method for producing the colloidal silica according to any one of (1) to (7), comprising the steps of: a raw material preparation step of supplying and reacting a readily decomposable organosilicate to a reaction solution containing a hydrolysis catalyst made of an organic amine to prepare raw material colloidal silica having a BET diameter of 12 nm or less; a concentration adjusting step of adjusting the solid content concentration of the raw material colloidal silica to 13% by mass or less and adjusting the concentration of alcohols generated in the raw material preparation step to 1 to 25% by mass; a modification treatment step of modifying the raw colloidal silica having the adjusted concentration; a concentrating step of concentrating the modified colloidal silica so that a residual organic solvent in the modified colloidal silica is 1 mass % or less; A method for producing colloidal silica, comprising: (9) The method for producing colloidal silica according to (8), wherein in the raw material preparing step, the reaction is carried out under conditions in which the feed rate of the easily hydrolyzable organosilicate is less than 1.5 mass% / min of the total amount of the easily hydrolyzable organosilicate fed, the reaction time is 6 hours or less, and the reaction temperature is 70° C. or lower. (10) The method for producing colloidal silica according to (8), wherein in the concentrating step, the colloidal silica after the modification treatment step is concentrated so that the solid content concentration in the colloidal silica is 12 mass% or more. (11) The method for producing colloidal silica according to (8), characterized in that the modification treatment step comprises a step of reacting a modifier having a functional group that can be converted into an anionic group with the colloidal silica after the concentration adjustment step, and a step of converting the functional group in the modifier after the reaction into an anionic group. (12) The method for producing colloidal silica according to (11), wherein the modifying agent has a mercapto group and / or a sulfide group, and the mercapto group and / or the sulfide group are converted to a sulfo group by treating with an oxidizing agent to obtain colloidal silica having sulfo groups on the surface. (13) The method for producing colloidal silica according to (8), wherein the modification treatment step comprises a step of reacting a modifying agent having a cationic group with the colloidal silica after the concentration adjustment step. According to the present invention, it is possible to obtain colloidal silica that has a small particle size of single nano size or close to that size and does not substantially undergo aggregation even when the solid content concentration is relatively high. FIG. 1 shows an SEM image (500,000 times) of the colloidal silica obtained in Example 1. FIG. 2 shows an SEM image (500,000 times) of the colloidal silica obtained in Example 2. FIG. 3 is a photograph showing the aggregated gel state in Comparative Example 2. (FIG. 3A) is a photograph showing the state in which the colloidal silica particles are placed in a spherical glass container, (FIG. 3B) is a photograph showing the state in which a part of the gel is taken out and placed on a petri dish, and (FIG. 3C) is a photograph showing the state in which the gel is crushed. FIG. 4 is a photograph showing the state in which the colloidal silica particle dispersion obtained in Reference Experimental Example 1 is concentrated, a part of it is taken, cooled at room temperature, and the container is turned upside down. (*) in the figure indicates an aggregated gel. FIG. 5 is a photograph showing the state in which the colloidal silica particle dispersion obtained in Reference Experimental Example 2 is concentrated, a part of it is taken, cooled at room temperature, and the container is turned upside down. (*) in the figure indicates an aggregated gel. <Colloidal Silica> The colloidal silica of the present invention is surface-modified, has a BET diameter of 12 nm or less, and is substantially free of aggregation. The colloidal silica used as the raw material is not limited as long as it has a silanol group on the surface, but considering that it does not contain metal impurities or corrosive ions such as chlorine, colloidal silica obtained by hydrolysis and condensation using a hydrolyzable silicon compound as the raw material (for example, an easily hydrolyzable organosilicate or its derivative described below) is preferred. The colloidal silica used as the raw material can be used alone or in combination of two or more types. First, the BET diameter will be described. As described above, the colloidal silica of the present invention has a small particle size of single nano size or close to single nano size, and has a BET diameter of 12 nm or less. As exemplified in the industrial applicability described below, small particle colloidal silica having a BET diameter of 12 nm or less is useful in that it can be easily prepared as an abrasive for semiconductor wafers and is less likely to be scratched during polishing. The BET diameter is preferably 12 nm or less, more preferably 10 nm or less, in terms of polishing efficiency, etc. The lower limit of the BET diameter is not limited, but can be appropriately set in consideration of the application, characteristics, etc. For example, in order to ensure dispersion stability, it is preferably 1 nm or more, more preferably 5 nm or more. Here, in the present invention, the significance of using the BET diameter to express a small particle diameter is that, for example, as will be explained later, not only monodispersed spherical products but also colloidal silica produced by two- or three-dimensional coalescence of a plurality of particles may be used, and the production method of the present invention produces colloidal silica with an uneven surface and a relatively high specific surface area. In light of these realities, it is preferable to adopt the BET diameter assuming a spherical shape while also taking into account the specific surface area in judging the performance relative to the particle shape. That is, in the present invention, the BET diameter is the BET specific surface area S (unit: m ２ / g) and true density ρ (unit: g / cm ３Specifically, it can be calculated from the following formula (1). BET diameter (nm) = 6000 / (S x ρ) ... (1) where ρ is SiO ２ and a typical true density of 2.2 g / cm ３ It is. The colloidal silica of the present invention has a BET specific surface area of ​​227 m ２ / g or more. This BET specific surface area is preferable in terms of polishing efficiency. The preferred BET specific surface area is 230 m ２ / g or more, more preferably 300m ２ Although there is no upper limit for the BET specific surface area, it is not recommended to use an upper limit of 500 m ２ / g or less, and more preferably 400m ２ / g or less. Next, the modification will be described. The colloidal silica of the present invention is obtained by subjecting raw colloidal silica to a modification treatment. Here, the modification treatment in the present invention is not limited as long as it contributes to the improvement or modification of the properties such as the improvement of dispersion stability, the suppression of aggregation, and the affinity with the object to be polished, which are the objects of the present invention, and can be appropriately selected from the modification treatments of colloidal silica known in the art. For example, nonionic modification, anionic modification, cationic modification, etc. can be mentioned. Specifically, it is preferable to subject colloidal silica to anionic or cationic modification, and more preferably anionic modification. As such a modification treatment, anionic or cationic modification is preferable, and although the reason why anionic modification is more preferable is not necessarily clear, it is presumed that the surface potential of colloidal silica is changed by modification, and the action of attracting with the object to be polished is expected, and the selectivity of the object to be polished is improved. In particular, compared with colloidal silica that has not been modified, the dispersion stability tends to be improved not only in alkaline conditions but also in acidic conditions where it is metastable and relatively prone to aggregation, so it is more preferable to perform anionic modification. As described above, the modification treatment can be appropriately selected from known methods, but as a preferred embodiment of the modification treatment, an anion modification treatment and a cation modification treatment will be described below. For an anion modification treatment, for example, JP-A-2010-269985 and JP-A-2013-041992 can be referred to. For a cationic modification treatment, for example, JP-A-2005-162533 and JP-A-2020-73445 can be referred to. The specific method of anion modification is not limited, but for example, a method of chemically bonding a modifier having an anion group to the surface of colloidal silica can be mentioned.In addition, as another method, a method of chemically bonding a modifier having a functional group that can be converted to an anion group by a chemical method or the like to the surface of colloidal silica, and then performing a process of converting the functional group to an anion group to form an anion group on the surface of colloidal silica can be mentioned.Because of the efficiency of modification, the fact that an anion group can be stably introduced into colloidal silica, and the fact that it is difficult to directly obtain a modifier having an anion group, a method of using a modifier having a functional group that can be converted to an anion group is preferred. The compound (modifier) ​​having a functional group that can be converted into an anion group is not limited, but for example, a silane coupling agent having a functional group that can be converted into an anion group can be suitably mentioned. Here, the anion group is not limited, but for example, a sulfo group, a carboxy group, a phosphate group, etc. can be mentioned. It may be ionic bonded with a cation to form a salt. Even with such an anion group, the cation is released in an aqueous solution and functions as an anion group. Examples of the cation that ionic bonds with the anion group include alkali metal ions such as sodium ions and potassium ions, and alkaline earth metal ions such as calcium ions. From the viewpoint of improving the selectivity of the polishing object, among the anion groups, a sulfo group and a carboxy group are preferable, and a sulfo group is more preferable. As a preferred embodiment of the anion group, a sulfo group will be described as an example. Modifiers having a functional group that can be converted to a sulfo group include silane coupling agents having a sulfonic acid ester group that can be converted to a sulfo group by hydrolysis, and silane coupling agents having a mercapto group and / or a sulfide group that can be converted to a sulfo group by oxidation. Among these, the method using a silane coupling agent having a mercapto group and / or a sulfide group is more preferred because it is easy to modify colloidal silica. In the present invention, the modifier may be one type only, or two or more types may be used in combination. Examples of silane coupling agents having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, etc. Examples of silane coupling agents having a sulfide group include bis(3-triethoxysilylpropyl)disulfide. A more specific method of the anion modification treatment will be described in detail in the explanation of the manufacturing method described later, but the amount of the above-mentioned modifier used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 0.8 to 6 parts by mass, relative to 100 parts by mass of the solid content of the raw colloidal silica. That is, the modifier is preferably 0.1 to 10% by mass, more preferably 0.5 to 7% by mass, and even more preferably 0.8 to 6% by mass in the solid content of the colloidal silica after modification. If the amount used is within this range, the particle surface of the colloidal silica can be sufficiently anionized. Furthermore, if the amount used is such, it is possible to produce a colloidal silica that has been stably anion-modified without aggregation. In addition, a solvent (water, a hydrophilic organic solvent, etc.) for dissolving the modifier may be used during the modification treatment. In addition, as for the cationic modification, for example, a method of chemically bonding a modifying agent having a cationic group to the surface of colloidal silica, a method of chemically bonding a modifying agent having a functional group that can be converted to a cationic group by a chemical method or the like to the surface of colloidal silica, and then performing a treatment to convert the functional group to a cationic group to form a cationic group on the surface of colloidal silica, etc. are exemplified. Preferably, a method of chemically bonding a silane coupling agent having a cationic group to the surface of colloidal silica is exemplified. The cationic group is not limited, but may be, for example, a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, or an iminium group. A primary amino group, a secondary amino group, a tertiary amino group, or a quaternary ammonium group is preferable. A primary amino group is more preferable. The cationic group may be ionically bonded with an anion to form a salt. Even in the case of such a cationic group, the anion is released in the mixed liquid and the cationic group functions as a cationic group. Examples of an anion ionically bonded with the cationic group include fluoride ions, chloride ions, bromide ions, iodide ions, hydrochloride ions, acetate ions, sulfate ions, hydrofluoric acid ions, and carbonate ions. Examples of silane coupling agents having a cationic group include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, and N-phenyl-3-aminopropyltrimethoxysilane. A more specific method of the cation modification treatment will be described in detail in the explanation of the manufacturing method described later, but as described above, it is preferable to use a method using a modifying agent having a cationic group. The amount of the modifying agent having a cationic group is preferably 0.1 to 1.5 parts by mass, more preferably 0.5 to 1.2 parts by mass, and even more preferably 0.6 to 1 part by mass, relative to 100 parts by mass of the solid content of the raw colloidal silica. That is, the amount of the modifying agent having a cationic group in the solid content of the colloidal silica after cation modification is preferably 0.1 to 1.5% by mass, more preferably 0.5 to 1.2% by mass, and even more preferably 0.6 to 1% by mass. If the amount is within this range, the particle surface of the colloidal silica can be sufficiently cationized. Furthermore, if the amount is such, it is possible to produce a cation-modified colloidal silica stably without aggregation. In addition, a solvent (water, a hydrophilic organic solvent, etc.) for dissolving the modifying agent may be used during the modification treatment. The modified colloidal silica of the present invention obtained by the above-mentioned modification treatment (hereinafter, sometimes referred to as "modified colloidal silica") has excellent dispersion stability and does not substantially aggregate even when the solid content concentration is relatively low, and is suitable for various applications. The solid content concentration is usually about 6% by mass due to the manufacturing process, etc., but it is preferably 12% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, and particularly preferably 19% by mass or more, because it can improve the polishing performance and reduce the transportation cost. The solid content concentration can be appropriately set depending on the application, etc. On the other hand, the upper limit of the solid content concentration is not limited, but it is preferably 50% by mass or less because there is a tendency for the handleability to decrease due to the increase in viscosity, etc., and the dispersion stability to decrease. It is known that, in general, as the solid content increases, the distance between particles decreases, and therefore, colloidal silica becomes more susceptible to aggregation. However, the modified colloidal silica of the present invention has a relatively small particle size as described above, and does not substantially aggregate even at a relatively high solids concentration as described above, and a practical colloidal silica of this kind has not yet been clearly identified. As described above, the colloidal silica of the present invention is substantially not aggregated. Here, the wording "substantially" is used for the following reason. That is, in general, in order to confirm that colloidal silica is aggregated, there are methods such as a method of confirming with an electron microscope, measuring the increase in viscosity, and a method of measuring the cumulant mean diameter by dynamic light scattering (DLS), but it is difficult to completely grasp whether each and every particle of the colloidal silica of the present invention, which is a very small particle having a BET diameter of 12 nm or less, is monodispersed. Since it is considered that the above-mentioned methods can only grasp or understand the dispersion state of the particles with a certain degree of certainty, if there is substantially no aggregation to the extent that does not cause any practical problem, the colloidal silica will not exhibit its functions or cause any problems in use. In order to grasp the above-mentioned "substantially not aggregated" more specifically, it can be measured by the above-mentioned method, but since it is a small particle, there is a possibility that some parts are difficult to grasp with an electron microscope. Therefore, it is preferable to use dynamic light scattering (DLS) and judge by the change in the cumulant mean diameter measured by it. More specifically, it is good to confirm the change (or the absence of change) in the cumulant mean diameter by DLS measurement over time. For example, in the manufacturing method of the present invention, in the concentration step described below, the presence or absence of aggregation can be confirmed by confirming the DLS measurement results before and after concentration. That is, by grasping the presence or absence of aggregation with an increase in solid content concentration, it becomes possible to confirm whether the colloidal silica has a property that aggregation is likely to occur. This is because, as mentioned above, there is a reality that aggregation occurs less when the solid content concentration is relatively low, and aggregation becomes more likely as the solid content concentration increases. Such a tendency usually tends to be prominent when the solid content concentration is 10% by mass or more, more specifically, 12% by mass or more. Among the methods using DLS measurement, a more practical method for grasping aggregation is to measure the change in particle diameter by DLS measurement after holding for a certain time (period) under heated conditions. In this method, it is possible to confirm whether the colloidal silica has the property of easily causing aggregation without causing an active change in solid content concentration. Specifically, as is also performed in the examples described below, the change in the cumulant mean diameter after holding for 7 days at at least 60°C as a temperature at which particles are easily aggregated is confirmed, and it can be determined that there is no aggregation if the change rate is within 20%. Here, the reason why the method of holding at 60°C or higher for 7 days is preferably applied is because it is known that the condition of 60°C for 7 days is approximately equivalent to the aging test in a state held at room temperature for 1 year, and thus the occurrence or absence of aggregation can be confirmed in the aging test at least at room temperature for 1 year. And, preferably, the change rate of the cumulant mean diameter by DLS measurement is within 10%, more preferably within 5%. Here, in such DLS measurement, for the above-mentioned reasons, the solid content concentration is preferably maintained or measured at 12% by mass or more, more specifically 18% by mass or more, even more specifically 19% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The solid content concentration at this time is not limited, and it is preferable that the DLS measurement is performed at a solid content concentration suited to the application or practical use. In addition, the colloidal silica of the present invention may have any shape or other properties depending on the application or purpose, so long as it has the above-mentioned properties of BET diameter, modification, and substantial absence of aggregation. In particular, the colloidal silica obtained by the present invention preferably has the above-mentioned BET specific surface area, a relatively high particle surface area, and preferably has a large number of irregular small protrusions and a shape like a confetti candy as a whole particle. Such a shape has a large BET specific surface area compared to a large SEM average particle diameter measured by measuring the arithmetic mean of particle images observed by SEM, and also has a high particle density (true specific gravity) measured by liquid phase displacement method, in other words, a high hardness, and has an excellent polishing rate, making it suitable for a CMP abrasive. The shape of the colloidal silica particles of the present invention can be controlled by the charged composition, etc., to be monodisperse spherical (spherical product), or to be an association shape of particles that are bonded together (association product).For example, by adding a large amount of catalyst and relatively slowly adding organosilicate as a silica raw material to the reaction field, the organosilicate is hydrolyzed quickly and uniformly and grows mildly, so that the seed particles grow gradually while maintaining their spherical shape, and can be made into a spherical product.In addition, by adding a small amount of catalyst and relatively quickly adding organosilicate as a silica raw material to the reaction field, the organosilicate is hydrolyzed non-uniformly, so that it acts like an adhesive between particles, and as a result, it is possible to make an association product in which the particles are associated. The colloidal silica of the present invention preferably has a viscosity of 1 to 100 mPa·s, more preferably 1 to 50 mPa·s, and even more preferably 1 to 20 mPa·s. As described above, the colloidal silica of the present invention may be a monodisperse spherical product, or may be an associated product (cocoon-shaped, chain-like, branched, etc.) having a shape that appears to be formed by a plurality of particles two-dimensionally or three-dimensionally coalescing when observed under an electron microscope. The colloidal silica of the present invention may be adjusted to a pH that does not impair the dispersion stability, depending on the above-mentioned modification treatment, etc. For example, in the case of the anion-modified colloidal silica, the pH is preferably 1 to 5, and more preferably 2 to 3. For example, in the case of the cation-modified colloidal silica, the pH is preferably 8 to 11, and more preferably 8.5 to 10. Adjusting the pH to such a range is preferable in terms of the dispersion stability of the colloidal silica. Furthermore, the colloidal silica of the present invention preferably has a metal impurity content of 1 ppm or less, more preferably 0.01 ppm or less, and even more preferably 0.0001 ppm or less. Although there are no limitations on the purity of such colloidal silica, for example, in the production method described below, the silica source, hydrolysis catalyst, and water used as raw materials in the hydrolysis reaction for obtaining the raw material colloidal silica can be achieved by using those that satisfy the above-mentioned metal impurity contents. <Method of producing colloidal silica> The method for producing colloidal silica of the present invention essentially includes the following steps. (a) a raw material preparation step of supplying and reacting a readily decomposable organosilicate to a reaction liquid containing a hydrolysis catalyst made of an organic amine, thereby preparing raw material colloidal silica having a BET diameter of 12 nm or less. (b) a concentration adjusting step of adjusting the solid content concentration of the raw material colloidal silica to 13% by mass or less and adjusting the concentration of alcohols generated in the raw material preparation step to 1 to 25% by mass. (c) a modification treatment step of modifying the raw material colloidal silica having its concentration adjusted in the step (b). (d) a concentration step of concentrating the colloidal silica modified in the step (c) so that the residual organic solvent in the colloidal silica is 1 mass % or less. These steps are described below. [Step (a)] First, in step (a), a colloidal silica having a BET diameter of 12 nm or less is prepared by supplying and reacting an easily decomposable organosilicate to a reaction solution containing a hydrolysis catalyst made of an organic amine. In the present invention, the colloidal silica prepared in step (a) is called raw colloidal silica. Although a commercially available product can be used as the raw colloidal silica, a hydrolysis method is used because it reduces metal impurities, can obtain colloidal silica with a relatively large surface area, and can produce particles with high uniformity. As the hydrolysis method, a method is used in which a silica source is supplied to a reaction solution containing a hydrolysis catalyst and hydrolyzed, and a method is used in which a easily decomposable organosilicate is supplied as a silica source to a reaction solution containing a hydrolysis catalyst made of an organic amine and hydrolyzed because it is easy to control the particle diameter. Here, the silica source preferably used in step (a) is an easily hydrolyzable organosilicate with a fast hydrolysis rate. The easily hydrolyzable organosilicate is preferably one which is hydrolyzed within 1 hour by stirring 10 g of organosilicate and 100 g of pure water with impurities of 0.1 ppb or less at 25°C. Specific examples of such easily hydrolyzable organosilicate include trimethyl silicate (hydrolysis reaction time until hydrolysis reaction is completed: about 3 minutes), tetramethyl silicate (hydrolysis reaction time: about 5 minutes), triethyl silicate (hydrolysis reaction time: about 5 minutes), and methyl trimethyl silicate (hydrolysis reaction time: about 7 minutes). Tetraethyl silicate and organosilicates with a larger carbon number than tetraethyl silicate have a slow hydrolysis rate and tend to gel easily (hydrolysis reaction time: 24 hours or more for both), so the above-mentioned easily decomposable organosilicate is preferably used. In addition, the organic amines used as hydrolysis catalysts in step (a) are not limited, but may be one or a mixture of two or more selected from quaternary ammoniums, tertiary amines, secondary amines, and primary amines, as well as their carbonates, bicarbonates, and silicates. For example, the quaternary ammoniums include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), trimethylethylammonium hydroxide, trimethylethanolammonium hydroxide (choline), triethylethanolammonium hydroxide, tetrapropylammonium hydroxide, butylammonium hydroxide, and other quaternary ammoniums, as well as their carbonates, bicarbonates, and silicates. Since a relatively high pH is desirable for the hydrolysis reaction, tetramethylammonium hydroxide (TMAH), choline, or tetraethylammonium hydroxide (TEAH) is preferred. In addition, the primary amines, secondary amines, and tertiary amines of the organic amines used as the hydrolysis catalyst are not limited, and examples thereof include aminoalcohols, morpholines, piperazines, aliphatic amines, aliphatic ether amines, etc. Here, as for the aminoalcohols, various aminoalcohols including ethanolamine derivatives can be used, and preferably ethanolamine derivatives, such as monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-di-n-butylethanolamine, N-(β-aminoethyl)ethanolamine, N-methylethanolamine, N-methyldiethanolamine, N-ethylethanolamine, Nn-butylethanolamine, Nn-butyldiethanolamine, N-tert-butylethanolamine, and N-tert-butyldiethanolamine, etc. can be mentioned. Furthermore, for the morpholines of the organic amines used as the hydrolysis catalyst, various morpholine derivatives can be used, but preferred examples include morpholine, N-methylmorpholine, and N-ethylmorpholine. Furthermore, for the piperazines of the organic amines used as the hydrolysis catalyst, various piperazine derivatives can be used, but preferred examples include piperazine and hydroxyethylpiperazine. Regarding the aliphatic amines and aliphatic etheramines of the organic amines used as the hydrolysis catalyst, preferred examples of the aliphatic amines include alkylamines having 1 to 8 carbon atoms, such as triethylamine, dipropylamine, pentylamine, hexylamine, heptylamine, and octylamine. Preferred examples of the aliphatic etheramines include aliphatic etheramines having 1 to 8 carbon atoms, such as 2-methoxyethylamine, 3-methoxypropylamine, 3-ethoxypropylamine, 3-propoxypropylamine, 3-isopropoxypropylamine, and 3-butoxypropylamine. The above organic amines used as the hydrolysis catalyst may be used alone or, if necessary, in the form of a mixture of two or more kinds. The reaction liquid essentially contains an easily decomposable organosilicate as a silica source and a hydrolysis catalyst as described above, but other than that, water, alcohols, aldehydes, ketones, surfactants, etc. can be used. It is preferable that the total amount of the silica source, the hydrolysis catalyst, and water is 90% by mass or more. More preferably, the total amount of these is 95% by mass or more. In the mixture obtained after the reaction of the silica source with the hydrolysis catalyst (hereinafter, this may be referred to as the "reaction mixture"), or in the reaction mixture after the reaction, for example, by adjusting the solid content concentration or the alcohol concentration or by treating the dispersion stabilization with an acid as described below (hereinafter, this may be particularly referred to as the "reaction concentrate"), it is preferable to add the hydrolysis catalyst to the reaction system so that the ratio of the hydrolysis catalyst (A) to the silica (B) {catalyst remaining molar ratio (A / B)} is 0.012 or less, more preferably in the range of 0.00035 to 0.012, and even more preferably in the range of 0.0035 to 0.011, to carry out the hydrolysis reaction. This is preferable because the pH of the reaction mixture or reaction concentrate can be optimized and thickening or gelation can be suppressed. The method for achieving such a catalyst remaining molar ratio is not particularly limited, and examples thereof include a method of continuously or intermittently introducing a silica source calculated so that the final catalyst remaining molar ratio (A / B) falls within the above-mentioned range into a reaction vessel charged with water and the hydrolysis catalyst (A); a method of continuously or intermittently introducing a hydrolysis catalyst and a silica source calculated so that the final catalyst remaining molar ratio falls within the above-mentioned range into a reaction vessel charged with only water; and a method of continuously or intermittently introducing a hydrolysis catalyst and a silica source calculated so that the final catalyst remaining molar ratio falls within the above-mentioned range into a reaction vessel charged with water and a small amount of the hydrolysis catalyst (A). Alternatively, prior to the hydrolysis reaction of the silica source, colloidal silica seeds having particle growth properties may be charged into the reaction system for the hydrolysis reaction, and the silica source and the hydrolysis catalyst may be gradually added to this reaction system so that the catalyst remaining molar ratio (A / B) falls within the above-mentioned range. This is preferable because it enables the production of colloidal silica having uniform particles. The silica source, hydrolysis catalyst and water used as raw materials for the hydrolysis reaction preferably have a metal impurity content of 1 ppm or less, more preferably a high purity of 0.01 ppm or less, so that the raw colloidal silica obtained and the modified colloidal silica obtained after modification also satisfy the above-mentioned range of metal impurity content. In the step (a), the method for adjusting the BET diameter of the raw material colloidal silica to 12 nm or less is not limited, but it is preferable to adjust the rate at which the silica source is dropped into the reaction liquid (supply rate), the reaction temperature and the reaction time. When a readily decomposable organosilicate is used as the silica source, the supply rate is preferably less than 1.5 mass% / min of the total amount of readily decomposable organosilicate added, more preferably 1.3 mass% or less / min, and even more preferably 1.2 mass% or less / min. If the supply rate is 1.5 mass% or more / min, the particles tend not to be uniformly dispersed or to be close to a perfect sphere. Here, the reason why the total amount is used as the standard is that the amount added varies depending on the production scale, etc., and it is preferable to consider completing the supply within the reaction time described below. That is, it is preferable to make the supply rate as slow as possible, which makes it easier to form the desired small particle size. There is no lower limit to the supply rate, but if the supply rate is too slow, there is a risk that the target particle size will not be achieved, so it is preferably 1.0 mass% / min or more of the total amount added. The reaction temperature is preferably 70° C. or less, more preferably 65° C. or less, and even more preferably 60° C. or less. If the reaction temperature exceeds 70° C., the reaction solution will volatilize more and the liquid composition will be more likely to change, which may make it difficult to control the particle size. On the other hand, the lower limit of the reaction temperature can be set appropriately, but if the temperature is too low, the hydrolysis reaction tends to be slow and particle growth may be promoted, so it is preferably 20° C. or more. The reaction time is preferably within 6 hours, more preferably within 3 hours, and even more preferably within 2 hours. If the reaction time exceeds 6 hours, the target particle size may not be obtained. On the other hand, the lower limit of the reaction time can be appropriately set, but if the reaction time is too short, the hydrolysis reaction may not be completed, and particle formation or particle growth may not be sufficiently performed, so that the reaction time is preferably 20 minutes or more. In step (a), the solid content concentration during the reaction is preferably 3 to 13% by mass. If the solid content concentration is less than 3% by mass, particle formation and particle growth may not be sufficient. On the other hand, if the solid content concentration is too high, particle aggregation is likely to occur. In step (a), the solid content concentration of the colloidal silica after the reaction is preferably within the range of 3 to 10% by mass. [Step (b)] In step (b), the solid content concentration of the raw colloidal silica obtained in step (a) is adjusted to 13% by mass or less. By adjusting the solid content concentration to 13% by mass or less, even if the BET diameter is 12 nm or less, the occurrence of aggregation can be reduced, and the next step (c) (modification treatment step) can be performed without causing aggregation gelation. Preferably, the solid content concentration is 10% by mass or less, more preferably 8% by mass or less. Here, although it is difficult to clearly define or classify, the term "aggregation gelation" generally refers to a state in which the aggregation of colloidal silica has progressed further and has become a jelly-like mass when viewed with the naked eye (for example, see FIG. 3 in Comparative Example 2 described later). Here, if the solid content concentration of the raw material colloidal silica obtained in step (a) is already 13 mass% or less, it is not necessary to actively adjust the solid content concentration in step (b), and in that case, it may be treated as a step of confirming the solid content concentration, or a step of maintaining the solid content concentration as it is, etc. Ensuring that the solid content concentration is certainly 13 mass% or less in this step (b) before the modification treatment in the next step (c) is a characteristic step in obtaining the finally modified colloidal silica of the present invention that is substantially non-aggregated and has a relatively high solid content concentration. The method of adjusting the solid content concentration in step (b) is not limited, but it is preferable to add the same solvent as that contained in the raw colloidal silica.The solvent to be added is preferably water and / or alcohols, more preferably water, methanol and / or ethanol, and even more preferably water and / or methanol.In addition, the solvent to be added may include water, alcohols, aldehydes, ketones, surfactants, etc., as described above. In step (b), the concentration of the alcohols produced in step (a) is adjusted to 1 to 25% by mass. In step (a), the hydrolysis reaction produces alcohols depending on the easily decomposable organosilicate used as the silica source. For example, when the easily decomposable organosilicate used has a methoxy group, such as trimethyl silicate or tetramethyl silicate, methanol is produced as the alcohol. When the easily decomposable organosilicate used has an ethoxy group, such as triethyl silicate, ethanol is produced as the alcohol. The same applies to other organosilicates. Here, although the detailed mechanism of the need to adjust the concentration of the alcohols generated from the hydrolysis reaction in step (a) to 1 to 25% by mass is not clear, it is presumed that by maintaining the concentration of the organic solvent in this range, the occurrence of aggregation can be reduced even if the BET diameter is 12 nm or less due to the polarity of the solvent, and the next step (c) (modification treatment step) can be performed without causing aggregation gelation. The concentration of the generated alcohols can be appropriately adjusted by the amount of the easily decomposable organosilicate used in step (a) or by replacing the alcohols with pure water by distillation, but the preferred lower limit is 5% by mass or more, and the more preferred lower limit is 12% by mass or more. On the other hand, the preferred upper limit is 20% by mass or less. In addition, as in the case of the adjustment of the solid content concentration (13% by mass or less) in this step (b), if the concentration of the alcohols in the raw colloidal silica obtained in step (a) is already 1 to 25% by mass, it is not necessary to actively adjust the concentration of the alcohols. In that case, it may be handled as a step of confirming the concentration of the alcohols, or as a step of maintaining the concentration of the alcohols produced in step (a) as it is. In this step (b), before the modification treatment in the next step (c), ensuring that the concentration of the alcohols is 1 to 25% by mass is a characteristic step in obtaining a substantially non-aggregated colloidal silica of the present invention having a relatively high solid content concentration, as in the case of the adjustment of the solid content concentration (13% by mass or less) described above. In addition, the alcohols can be a part of the solvent in the modification treatment in the next step (c). The method of adjusting the concentration of the alcohols in this step (b) is not limited, but when adjusting to increase the concentration of the alcohols, it is preferable to add an organic solvent containing the same organic solvent as the produced alcohols as the main component (e.g., 95% by mass or more). The organic solvent added here may contain water, alcohols, aldehydes, ketones, surfactants, etc., as described above. On the other hand, as a method of adjusting to decrease the concentration of the alcohols, for example, a method of distilling the alcohols from a distillation tube equipped with a condenser while volatilizing them by heating, as performed in Comparative Example 1 described later, can be mentioned. In this case, pure water may be added. [Step (c)] In step (c), the raw colloidal silica, the solid content concentration of which and the concentration of the generated alcohols have been adjusted through step (b), is modified. As described above, the modification is not limited and can be selected from known modification treatments, but anion modification or cation modification is preferred, and anion modification is more preferred. Here, the anion modification or the cation modification is as exemplified above, and the anion modification is preferred, and a suitable method for the anion modification is a method in which a modifying agent having a functional group that can be converted to an anion group by a chemical method or the like is chemically bonded to the surface of the colloidal silica. Among the anion modifications, the sulfo group exemplified as a preferred embodiment will be taken as an example. Also, among the cation modifications, the primary amino group exemplified as a preferred embodiment will be taken as an example. (Embodiment of anion modification treatment using sulfo group as an example) To form sulfo group on the surface of colloidal silica, it can be carried out by a known method as described above.Preferably, a method can be mentioned in which a modifying agent having a functional group that can be converted to a sulfo group by chemical method or the like is chemically bonded to the surface of colloidal silica, and then the functional group is converted to a sulfo group, and a modifying agent having a functional group that can be converted to a sulfo group by oxidation is preferable.Among these, a preferred modifying agent is a silane coupling agent having a mercapto group and / or a sulfide group as described above, and a representative one will be described below. In this method, it is preferable to include a step (step c1) of reacting the raw colloidal silica, the solid content concentration of which has been adjusted through the steps (a) and (b) as described above, in the presence of the silane coupling agent, and a step (step c2) of oxidizing the reaction product of the step c1 to convert the mercapto group and / or sulfide group to a sulfo group. The steps c1 and c2 can also be performed with reference to the above-mentioned JP-A-2010-269985 and JP-A-2013-041992. It should be noted that other steps may be appropriately included as long as they do not impair the object of the present invention. Examples of other steps include adjusting the viscosity of the reaction solution and adjusting the pH. (Step c1) In step c1, the raw colloidal silica, the solid content of which has been adjusted through steps (a) and (b), is reacted in the presence of a silane coupling agent having a mercapto group and / or a sulfide group, so that the silane coupling agent is chemically bonded to the surface of the raw colloidal silica. The reaction in step c1 can be carried out within a temperature range suitable for use of the denaturant, and is not limited thereto, but can be carried out, for example, at a temperature range of 40° C. or higher and below the boiling point of the reaction liquid (solvent). In order to improve reactivity, the reaction is preferably carried out at a temperature of 50° C. or higher, more preferably 60° C. or higher, and preferably below the boiling point of the reaction liquid (solvent), 100° C. or lower. The reaction time is also not limited, but is preferably carried out for, for example, 10 minutes to 10 hours, more preferably 1 to 8 hours. In the reaction of step c1, a solvent can be added to improve the solubility of the modifier or silane coupling agent within the scope that does not impair the object of the present invention. Such a solvent can include hydrophilic solvents, for example, alcohols such as methanol, ethanol, isopropanol, etc., but are not limited thereto. It is more preferable to use the same alcohols as those produced by the hydrolysis reaction to obtain raw colloidal silica. As described above, the amount of the modifying agent (silane coupling agent) used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 0.8 to 5 parts by mass, relative to 100 parts by mass of the solid content in the raw material colloidal silica. The reaction in step c1 can also be understood, for example, by analyzing the functional groups introduced into the colloidal silica. For example, the functional groups can be qualitatively and / or quantitatively analyzed using pulsed NMR (TD-NMR). (Step c2) In step c2, the functional groups introduced onto the surface of the raw colloidal silica in step c1 are converted into anionic groups by a chemical method. Here, a method for converting the functional groups introduced by a silane coupling agent having a mercapto group and / or a sulfide group into sulfo groups by oxidation treatment will be described. The method of converting the mercapto group and / or sulfide group to a sulfo group by oxidation treatment is not limited, but may be the use of an oxidizing agent. Examples of the oxidizing agent include nitric acid, hydrogen peroxide, oxygen, ozone, organic peracid (percarboxylic acid), bromine, hypochlorite, potassium permanganate, chromic acid, etc. Among these, hydrogen peroxide and organic peracid (peracetic acid, perbenzoic acid) are preferred in terms of handling and reactivity (oxidation yield). It is most preferred to use hydrogen peroxide because it produces few by-products in the reaction. The amount of the oxidizing agent added may be in excess of the amount of the modifier (silane coupling agent), but it is preferable to minimize the amount of the residual oxidizing agent, and it is more preferred to use 3 to 5 moles of the oxidizing agent per mole of the silane coupling agent in order to ensure sufficient oxidation reaction. The oxidation reaction is not limited, but may be carried out under suitable reaction conditions for the oxidizing agent used within a range that does not impair the object of the present invention. For example, it is preferable to carry out the reaction at a temperature not lower than room temperature and not higher than the boiling point of the solvent used in the reaction solution (for example, not higher than 100° C.) for a period of 3 to 5 hours. By this step c2, colloidal silica having an anion group (sulfo group) on the surface can be obtained. In addition, in step c2, other steps may be included after the oxidation treatment. For example, a step for removing the oxidizing agent, a step for adjusting the pH of the solution after the reaction, etc. may be included, and these steps may be appropriately selected and performed within a range that does not impair the object of the present invention. (Embodiment of cationic modification treatment using amino group as an example) To form amino groups on the surface of colloidal silica, known methods can be used as described above. A preferred method is to carry out a treatment in which a modifying agent having an amino group is chemically bonded to the surface of colloidal silica. As described above, a preferred modifying agent among these is a silane coupling agent having an amino group, which will be described below as a representative example. In this method, it is preferable to include a step of reacting raw colloidal silica in which the solid content concentration has been adjusted through step (a) and step (b) in the presence of the silane coupling agent. Such a step can also be carried out with reference to the above-mentioned JP-A-2005-162533 and JP-A-2020-73445. As long as it does not impair the object of the present invention, other steps may be appropriately included. Other steps include, for example, adjusting the viscosity of the reaction solution and adjusting the pH, but for dispersion stability, it is preferable to adjust the pH before performing the cation modification treatment. The pH adjusted at this time is preferably 8 to 11, more preferably 8.5 to 10. The pH can be adjusted by a method using a known compound (pH adjuster), but a preferred method is to use the same compound as the hydrolysis catalyst used in step (a) as the pH adjuster. That is, the raw colloidal silica, the solid content of which has been adjusted through steps (a) and (b), is reacted in the presence of a silane coupling agent having an amino group, whereby the silane coupling agent is chemically bonded to the surface of the raw colloidal silica. This reaction can be carried out within a temperature range suitable for use of the modifying agent, and is not limited thereto, but can be carried out, for example, at a temperature range of 40° C. or higher and below the boiling point of the reaction liquid (solvent). In order to improve reactivity, the reaction is preferably carried out at a temperature of 50° C. or higher, more preferably 60° C. or higher, and preferably below the boiling point of the reaction liquid (solvent), 100° C. or lower. The reaction time is also not limited, but is preferably carried out for 10 minutes to 10 hours, and more preferably 1 to 8 hours. In this reaction, a solvent can be added to improve the solubility of the modifier or silane coupling agent within the scope that does not impair the purpose of the present invention. Such a solvent can include hydrophilic solvents, for example, alcohols such as methanol, ethanol, isopropanol, etc., but are not limited thereto. It is more preferable to use the same alcohols as those produced by the hydrolysis reaction to obtain the raw colloidal silica. As described above, the amount of the modifying agent (silane coupling agent) used is preferably 0.1 to 1.5 parts by mass, more preferably 0.5 to 1.2 parts by mass, and even more preferably 0.6 to 1 part by mass, relative to 100 parts by mass of the solid content in the raw material colloidal silica. This reaction can also be understood, for example, by analyzing the functional groups introduced into the colloidal silica. For example, pulsed NMR (TD-NMR) can be used to perform qualitative and / or quantitative analysis of the functional groups. Further, for the sake of dispersion stability, it is preferable to adjust the pH even after the cationic modification treatment is performed. The pH adjusted in this case is preferably 8 to 11, more preferably 8.5 to 10. As described above, the pH can be adjusted by a method using a known compound (pH adjuster), but a preferred method is, for example, to use the same compound as the hydrolysis catalyst used in step (a) as the pH adjuster. [Step (d)] After carrying out the step (c), in step (d), the residual organic solvent in the colloidal silica obtained after step (c) is concentrated to 1 mass % or less. Preferably, the residual organic solvent is 0.1 mass % or less, more preferably 0.05 mass % or less. That is, the colloidal silica obtained through the step (d) is dispersed in a dispersion medium having a residual organic solvent of 0.1 mass % or less. Such a dispersion medium is, for example, an aqueous solution having a residual organic solvent of 0.1 mass % or less, and is preferably substantially water, as in the embodiment described in the examples below. It is not excluded that the dispersion medium contains trace amounts of alcohols, aldehydes, ketones, surfactants, etc., and these are also preferably 0.1 mass % or less. By reducing the residual organic solvent to this range, the solid content concentration can be adjusted or increased to a predetermined range, and in the case of a highly volatile residual organic solvent, it is preferable because the concentration of colloidal silica can be prevented from fluctuating due to the evaporation of the organic solvent. In addition, when the colloidal silica of the present invention is used, there is an advantage that it is not necessary to consider the resistance of the material used in the application to residual organic solvents. The method for removing and concentrating the residual organic solvent is not particularly limited, and any known method can be used, for example, a method in which the residual organic solvent is distilled by heating using an apparatus equipped with a distillation tube with a condenser can be used. In this step (d), the solid content concentration can be adjusted to a level suitable for use, taking into consideration the intended use and purpose, by concentrating the process of removing the residual organic solvent and water. In the present invention, the modified colloidal silica is obtained through the above-mentioned steps (a) to (c), and even if the solid content concentration is relatively high in this step (d), a colloidal silica that does not substantially aggregate can be obtained. In consideration of such features of the present invention and the intended use and purpose of the colloidal silica, as described above, the solid content concentration in the colloidal silica after the modification step (c) is preferably 12% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, and particularly preferably 19% by mass or more. The upper limit of the solid content concentration is the same as described above, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. The colloidal silica of the present invention can be produced by carrying out the above steps (a) to (d), but other steps may be appropriately included after step (d) as long as they do not impair the object of the present invention. For example, it is preferable to subject the colloidal silica after step (d) to dispersion stabilization. The dispersion stabilization treatment may be a known treatment. Colloidal silica that has been subjected to the dispersion stabilization treatment by the method of the present invention exhibits excellent dispersion stability for a period of at least one week, and even for a period of several years, and is free from the phenomenon of two-layer separation. In the present invention, colloidal silica having a small particle size, such as a BET diameter of 12 nm or less, can be obtained as described above. However, as in conventional methods, a method in which the obtained colloidal silica is used as seed particles, and a silica source is supplied to a reaction liquid containing the seed particles and the hydrolysis catalyst and reacted with the seed particles to grow the particle size is also possible. Hereinafter, preferred embodiments of the present invention will be described in detail based on examples and comparative examples. [Example 1] In a 5 liter (L) glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3200 g of pure water having a metal impurity content of 0.1 ppb or less and 3.42 g of triethanolamine (boiling point (bp): 361°C) having a metal impurity content of 10 ppb or less were charged, and while the liquid temperature in the reaction vessel was kept at 60°C using a mantle heater, 706 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) having a metal impurity content of 10 ppb or less was continuously fed under stirring over a period of 90 minutes. The obtained raw colloidal silica was subjected to various analyses, and the results are shown in <1> of Table 1. Next, 3900 g of the resulting reaction product (colloidal silica, solid content concentration 6.45 mass%, methanol concentration 15 mass%) was added to a 5 L glass vessel, and no operation was performed to change the solid content concentration or methanol concentration. Next, while maintaining the temperature at 80° C., a solution of 13.1 g of 3-mercaptopropyltrimethoxysilane dissolved in 117.9 g of methanol was continuously fed over 6 hours. After the feeding, 22.7 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 80° C., and the raw colloidal silica was modified. After the hydrogen peroxide solution was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, the pressure in the system was reduced with a vacuum pump, and then heating was resumed, the reaction mixture in the reaction vessel was further heated to 52 to 68°C, and the generated methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C, and 250 g of pure water was further added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid concentration of about 20% by mass. The residual organic solvent in the obtained colloidal silica was 0.1% by mass. The obtained colloidal silica was subjected to various analyses, and the results are shown in <2> of Table 1. Furthermore, the obtained colloidal silica was stored at 60° C. for 7 days, and various analyses of the obtained colloidal silica were performed. It was confirmed, particularly from the results of DLS measurement, that substantially no aggregation had occurred. The results are shown in <3> of Table 1. [Example 2] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3374 g of pure water containing 0.1 ppb or less of metal impurities and 3.608 g of triethanolamine (bp: 361° C.) containing 10 ppb or less of metal impurities were charged, and while the liquid temperature in the reaction vessel was kept at 70° C. using a mantle heater, 1122 g of tetramethylsilicate containing 10 ppb or less of metal impurities (manufactured by Tama Chemicals Co., Ltd.) was continuously fed with stirring over a period of 270 minutes. Various analyses of the obtained raw colloidal silica were carried out, and the results are shown in <4> of Table 1. Next, 2000 g of the resulting reaction product (colloidal silica, solid content concentration 10.38 mass%, methanol concentration 20 mass%) was added to a 2 L glass container, and no operation was performed to change the solid content concentration or methanol concentration. Next, while maintaining the temperature at 80° C., 6.71 g of 3-mercaptopropyltrimethoxysilane dissolved in 60.35 g of methanol was continuously fed over 6 hours. After the feeding, 11.63 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 80° C., and the raw colloidal silica was modified. After the hydrogen peroxide solution was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, the pressure in the system was reduced by a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68°C, and the generated methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C. Further, water and methanol were distilled off while adding 320 g of pure water, to obtain colloidal silica having a solid content concentration of about 20 mass%. Various analyses of the obtained colloidal silica were carried out, and the results are shown in <5> of Table 1. Furthermore, the obtained colloidal silica was stored at 60°C for 7 days, and various analyses of the obtained colloidal silica were carried out, and it was confirmed that substantially no aggregation had occurred, particularly from the results of DLS measurement. The results are shown in <6> of Table 1. [Example 3] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3463 g of pure water containing 0.1 ppb or less of metal impurities and 0.336 g of triethanolamine (bp: 361°C) containing 10 ppb or less of metal impurities were charged, and while the liquid temperature in the reaction vessel was kept at 70°C using a mantle heater, 911.6 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was continuously fed under stirring over a period of 90 minutes. Various analyses of the obtained raw colloidal silica were carried out, and the results are shown in <7> of Table 1. Next, 4200 g of the resulting reaction product (colloidal silica, solid content concentration 8.82 mass%, methanol concentration 17 mass%) was added to a 5 L glass vessel, and no operation was performed to change the solid content concentration or methanol concentration. Next, while maintaining the temperature at 80° C., 11.98 g of 3-mercaptopropyltrimethoxysilane dissolved in 107.8 g of methanol was continuously fed over 6 hours. After the feeding, 20.77 g of 30 mass% hydrogen peroxide solution was further continuously fed over 4 hours while maintaining the temperature at 80° C., and the raw colloidal silica was modified. After the hydrogen peroxide solution was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, the pressure in the system was reduced by a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68°C, and the generated methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C. 700 g of pure water was further added while distilling off water and methanol to obtain colloidal silica having a solid content concentration of about 20% by mass. Various analyses of the obtained colloidal silica were carried out, and the results are shown in <8> of Table 1. Furthermore, the obtained colloidal silica was stored at 60°C for 7 days, and various analyses of the obtained colloidal silica were carried out, and it was confirmed that no aggregation had occurred, particularly from the results of DLS measurement. The results are shown in <9> of Table 1. [Comparative Example 1] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3200 g of pure water containing 0.1 ppb or less of metal impurities and 3.42 g of triethanolamine (bp: 361° C.) containing 10 ppb or less of metal impurities were charged, and while maintaining the liquid temperature in the reaction vessel at 60° C. using a mantle heater, 706 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was continuously fed with stirring over a period of 90 minutes. Various analyses of the obtained raw colloidal silica were carried out, and the results are shown in <10> of Table 2. Subsequently, 3,900 g of the obtained reaction product (colloidal silica) was added to a 5 L glass vessel, and, unlike in Examples 1 to 3, the vessel was heated to 52° C. to 72° C. at this point, and the produced methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67° C., and further, 1,800 g of pure water was added while distilling off water and methanol. 3900 g of the reaction product (colloidal silica, solid content concentration 6.45 mass%, methanol concentration 0.1 mass%) from which water and methanol had been distilled off was added to a 5 L glass vessel, and no operation was performed to change the solid content concentration. Next, while maintaining the temperature at 100°C, a solution of 13.7 g of 3-mercaptopropyltrimethoxysilane dissolved in 123.6 g of methanol was continuously fed over a period of 6 hours. After the feeding, 23.8 g of 30 mass% hydrogen peroxide solution was further continuously fed over a period of 4 hours while maintaining the temperature at 100°C, and the raw colloidal silica was modified. After the hydrogen peroxide solution was supplied, the temperature in the reaction vessel was temporarily lowered to 40°C, the pressure in the system was reduced by a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68°C, and a colloidal silica having a solid content concentration of about 20% by mass was obtained. Various analyses of the obtained colloidal silica were carried out, and the results are shown in <11> of Table 2. From the analysis results, particularly the results of the DLS measurement, it was confirmed that the change in the cumulant mean diameter by the DLS measurement exceeded 20%, and the colloidal silica was aggregated. The obtained colloidal silica was further stored at 60°C for 7 days, and various analyses of the obtained colloidal silica were carried out. The results are shown in <12> of Table 2. Since the colloidal silica was aggregated at the time of the result <11>, the DLS result in this result <12> was also comparable to the result <11> and higher than the result <10>. [Comparative Example 2] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3200 g of pure water containing 0.1 ppb or less of metal impurities and 3.42 g of triethanolamine (bp: 361° C.) containing 10 ppb or less of metal impurities were charged, and while keeping the liquid temperature in the reaction vessel at 60° C. using a mantle heater, 706 g of tetramethylsilicate containing 10 ppb or less of metal impurities (manufactured by Tama Chemicals Co., Ltd.) was continuously fed with stirring over a period of 90 minutes. Various analyses of the obtained colloidal silica were carried out, and the results are shown in <13> of Table 2. Next, 4500 g of the resulting reaction product (colloidal silica, solid content concentration 6.01% by mass, methanol concentration 15% by mass) was added to a 3 L glass container, and no operation was performed to change the solid content concentration or methanol concentration. Then, without performing a modification treatment step, the mixture was heated at 52°C to 72°C, and the generated methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67°C. Pure water was further added while distilling off water and methanol, and when the solid content concentration reached 16% by mass, the mixture aggregated and gelled. The state of the aggregation and gelling is shown in FIG. 3. [Comparative Example 3] In a 5L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3463 g of pure water containing 0.1 ppb or less of metal impurities and 0.336 g of triethanolamine (bp: 361°C) containing 10 ppb or less of metal impurities were charged, and while the liquid temperature in the reaction vessel was kept at 80°C using a mantle heater, 1136 g of tetramethylsilicate (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was continuously fed under stirring for 480 minutes. Various analyses of the obtained colloidal silica were carried out, and the results are shown in <14> of Table 2. In this Comparative Example 3, the BET diameter exceeded 12 nm due to the temperature at the time of adding the silica source. [Example 4] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3889 g of pure water containing 0.1 ppb or less of metal impurities and 3.42 g of triethanolamine (bp: 361°C) containing 10 ppb or less of metal impurities were charged, and while the temperature of the liquid in the reaction vessel was kept at 60°C using a mantle heater, 707 g of tetramethylsilicate containing 10 ppb or less of metal impurities (manufactured by Tama Chemicals Co., Ltd.) was continuously fed with stirring over a period of 90 minutes. The obtained raw colloidal silica was subjected to various analyses, and the results are shown in <15> of Table 3. Next, 3800 g of the resulting reaction product (colloidal silica, solid content concentration 6.39 mass%, methanol concentration 13 mass%) and 20 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were added to a 5 L glass container, and no operation was performed to change the solid content concentration or the methanol concentration. The pH of the colloidal silica at this time was 8.9. Next, while maintaining the temperature at 80°C, a modifying agent obtained by dissolving 1.71 g of 3-aminopropyltrimethoxysilane in 50 g of methanol was continuously supplied over 6 hours to modify the raw colloidal silica. After the modifier was supplied, the temperature in the reaction vessel was temporarily lowered to 40° C., 20 g of triethanolamine (bp: 361° C.) having a metal impurity content of 10 ppb or less was added, the pressure in the system was reduced using a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68° C., and the produced methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32 to 67° C., and 670 g of pure water was further added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid content concentration of about 20 mass%. The obtained colloidal silica was subjected to various analyses, and the results are shown in <16> of Table 3. Furthermore, the obtained colloidal silica was stored at 60°C for 7 days, and various analyses of the obtained colloidal silica were performed. It was confirmed, particularly from the results of DLS measurement, that substantially no aggregation had occurred. The results are shown in <17> of Table 3. [Example 5] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3890 g of pure water containing 0.1 ppb or less of metal impurities and 3.42 g of triethanolamine (bp: 361°C) containing 10 ppb or less of metal impurities were charged, and while the temperature of the liquid in the reaction vessel was kept at 60°C using a mantle heater, 707 g of tetramethylsilicate containing 10 ppb or less of metal impurities (manufactured by Tama Chemicals Co., Ltd.) was continuously fed with stirring over a period of 90 minutes. The obtained raw colloidal silica was subjected to various analyses, and the results are shown in <18> of Table 3. Next, 4001 g of the resulting reaction product (colloidal silica, solid content concentration 6.41 mass%, methanol concentration 13 mass%) and 20 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were added to a 5 L glass container, and no operation was performed to change the solid content concentration or the methanol concentration. The pH of the colloidal silica at this time was 9.0. Next, while maintaining the temperature at 80°C, a modifying agent obtained by dissolving 1.83 g of 3-aminopropyltrimethoxysilane in 54 g of methanol was continuously supplied over 6 hours to modify the raw colloidal silica. After the modifier was supplied, the temperature in the reaction vessel was lowered to 40° C., 10 g of triethanolamine (bp: 361° C.) having a metal impurity content of 10 ppb or less was added to 1,975 g of the reaction mixture, the pressure in the system was reduced with a vacuum pump, heating was then resumed, and the reaction mixture in the reaction vessel was further heated to 52 to 68° C., and the produced methanol was distilled from a distillation tube equipped with a condenser at a distillation temperature of 32 to 67° C., and 340 g of pure water was added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid content concentration of about 20 mass%. The obtained colloidal silica was subjected to various analyses, and the results are shown in <19> of Table 3. Furthermore, the obtained colloidal silica was stored at 60°C for 7 days, and various analyses of the obtained colloidal silica were performed. It was confirmed, particularly from the results of DLS measurement, that substantially no aggregation had occurred. The results are shown in <20> of Table 3. [Example 6] In a 5 L glass vessel equipped with a stirrer, a thermometer, a distillation tube with a condenser, and an organosilicate inlet tube, 3890 g of pure water containing 0.1 ppb or less of metal impurities and 3.43 g of triethanolamine (bp: 361°C) containing 10 ppb or less of metal impurities were charged, and while the liquid temperature in the reaction vessel was kept at 60°C using a mantle heater, 707 g of tetramethylsilicate containing 10 ppb or less of metal impurities (manufactured by Tama Chemicals Co., Ltd.) was continuously fed with stirring over a period of 90 minutes. The obtained raw colloidal silica was subjected to various analyses, and the results are shown in <21> of Table 3. Next, 2350 g of the resulting reaction product (colloidal silica, solid content concentration 6.47 mass%, methanol concentration 13 mass%) and 12 g of triethanolamine (bp: 361°C) with a metal impurity content of 10 ppb or less were added to a 5 L glass container, and no operation was performed to change the solid content concentration or the methanol concentration. The pH of the colloidal silica at this time was 8.9. Next, while maintaining the temperature at 80°C, a modifying agent obtained by dissolving 1.08 g of 3-aminopropyltrimethoxysilane in 30 g of methanol was continuously supplied over 6 hours to modify the raw colloidal silica. After the modifying agent was supplied, the temperature in the reaction vessel was temporarily lowered to 40° C., 12 g of triethanolamine (bp: 361° C.) having a metal impurity content of 10 ppb or less was added, the pressure in the system was reduced using a vacuum pump, and then heating was resumed. The reaction mixture in the reaction vessel was further heated to 52 to 68° C., and the produced methanol was distilled from the distillation tube equipped with a condenser at a distillation temperature of 32 to 67° C., and 351 g of pure water was added while distilling off the water and methanol, thereby obtaining colloidal silica with a solid content concentration of about 20 mass%. The obtained colloidal silica was subjected to various analyses, and the results are shown in <22> of Table 3. Furthermore, the obtained colloidal silica was stored at 60°C for 7 days, and various analyses of the obtained colloidal silica were performed. It was confirmed, particularly from the results of DLS measurement, that substantially no aggregation had occurred. The results are shown in <23> of Table 3. Next, as described above, using a colloidal silica particle dispersion having a predetermined solid content concentration, primary particle size, and secondary particle size obtained by the method described in Example 8 or Example 1 described in Patent Document 4, a dispersion containing Abrasive D or Abrasive E described in Patent Document 3 was prepared in the following manner, and the dispersion was evaluated. That is, the following [Reference Experimental Example 1] and [Reference Experimental Example 2] show the evaluation results of colloidal silica particle dispersions corresponding to Abrasives D and E prepared by procedures almost identical to those described in paragraph 0075 of Patent Document 3 and Example 8 (paragraph 0053) of Patent Document 4 described therein, and in paragraph 0076 of Patent Document 3 and Example 1 (paragraph 0045) of Patent Document 4 described therein, respectively. [Reference Experimental Example 1] (procedure) A solution of 250 parts of methanol, 10 parts of pure water containing 10 ppb or less of metal impurities, and 2 parts of 29% aqueous ammonia was prepared in a reaction vessel and kept at a temperature of 63° C. After that, 27 parts of tetramethoxysilane (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities was added under stirring conditions at 1 cm ３The mixture was added dropwise at a rate of 1000 ml / min·L to carry out hydrolysis and polycondensation reactions. Here, the unit of the dropping rate was defined as described in paragraph 0029 of Patent Document 4. After the reaction was completed, the mixture was aged for 1 hour, and then 80 parts were distilled off by simple distillation, and 200 parts of ultrapure water were added. As described in Patent Document 4, the colloidal solution turned slightly white, so 5 parts of 29% aqueous ammonia were added to return it to a transparent state. 5 kg of the thus obtained colloidal silica particle dispersion having a silica concentration of 3.8% by mass, a primary particle diameter of 9.0 nm, and a secondary particle diameter of 10.1 nm was mixed with 2 g of 3-mercaptopropyltrimethoxysilane and heated under reflux for 2 hours to obtain a thiolated silica sol. Hydrogen peroxide was added to the silica sol and heated under reflux for 8 hours to obtain a dispersion containing 3.7% by mass of abrasive grains having a primary particle diameter of 9.0 nm and a secondary particle diameter of 10.1 nm, with sulfo groups fixed to the surfaces of the silica particles. This colloidal silica particle dispersion was distilled at a distillation temperature of 32 to 67° C. from a distillation tube equipped with a condenser by simple distillation in the same manner as in the method described in Example 1 above, and concentrated to 12% by mass, resulting in aggregation and gelation, as shown in Figure 4. Figure 4 is a photograph of a container in which a portion of the colloidal silica particle dispersion concentrated to approximately 12% by mass was taken and allowed to cool at room temperature, and then turned upside down, and it can be seen that the colloidal silica particle dispersion at the bottom side of the container (i.e., the upper side of the photograph) has aggregated and gelled and does not fall down. [Reference Experimental Example 2] (procedure) A solution of 310 parts of methanol, 16 parts of pure water containing 10 ppb or less of metal impurities, and 3 parts of 29% aqueous ammonia was prepared in a reaction vessel, and the temperature was kept at 60° C. After that, a mixed diluted solution of 38 parts of tetramethoxysilane (manufactured by Tama Chemicals Co., Ltd.) containing 10 ppb or less of metal impurities and 18 parts of methanol was poured into the reaction vessel at 1 cm ３ The solution was dropped at a dropping rate of 100 / min·L to carry out hydrolysis and polycondensation reactions, thereby obtaining a colloidal silica particle dispersion having a solid content concentration of about 3.8% by mass. Here, the unit of the dropping rate was defined according to paragraph 0029 of Patent Document 4. 5 kg of the thus obtained colloidal silica particle dispersion having a silica concentration of 3.8% by mass, a primary particle diameter of 5.9 nm, and a secondary particle diameter of 7.3 nm was mixed with 2 g of 3-mercaptopropyltrimethoxysilane and heated under reflux for 2 hours to obtain a thiolated silica sol. Hydrogen peroxide was added to the silica sol and heated under reflux for 8 hours to obtain a dispersion containing 3.8% by mass of abrasive grains having a primary particle size of 5.7 nm and a secondary particle size of 7.0 nm, with sulfo groups fixed to the surfaces of the silica particles. This colloidal silica particle dispersion was distilled at a distillation temperature of 32 to 67° C. from a distillation tube equipped with a condenser by simple distillation in the same manner as in the method described in Example 1 above, and concentrated to 11% by mass, resulting in aggregation and gelation, as shown in Figure 5. Figure 5 is a photograph of a part of the colloidal silica particle dispersion concentrated to approximately 11% by mass, which was taken and allowed to cool at room temperature, and then the container was turned upside down, and it can be seen that, similar to Figure 4, the colloidal silica particle dispersion at the bottom side of the container (i.e., the upper side of the photograph) has aggregated and gelled and does not fall down. [Results and Discussion] As described above, when each of the colloidal silica particle dispersions containing abrasive grains corresponding to Abrasive grain D or Abrasive grain E described in Patent Document 3 is concentrated to a concentration of at least 12 mass %, the colloidal silica particle dispersions all aggregate and gel, and therefore the colloidal silica having a BET diameter of 12 nm or less and a solids concentration of 12 mass % or more shown in the above-mentioned embodiment of the present application is not obtained, and therefore it can be said that the same stability over time as that shown in the embodiment of the present application is not provided. (Consideration) Here, the reason why the colloidal silica particle dispersion prepared by the method shown in Patent Document 3 cannot exceed 12% by mass is considered to be influenced by the following two points (i) and (ii), that is, (i) the alcohol (methanol) content concentration of the silica particle dispersion during the thiolation reaction (modification treatment process) and (ii) the presence or absence of methanol dilution of the silane coupling agent (3-mercaptopropyltrimethoxysilane). Regarding this (i), when the alcohol contained in the silica colloid particle dispersion is replaced with pure water before the modification treatment process as in the above-mentioned Comparative Example 1, as explained in the above-mentioned Comparative Example 1 and shown in Table 2, the change in the cumulant average diameter by DLS measurement exceeded 20% before and after the modification treatment process, and a tendency to aggregate was observed. Since a simple distillation operation is performed after the preparation of the silica particles in Example 8 of Patent Document 4, it is considered that the abrasive D of Patent Document 3 using the silica particle dispersion could not be concentrated to 12% by mass even after the modification treatment. In addition, it was confirmed that the abrasive grain E of Patent Document 3 (using Example 1 of Patent Document 4), which is subjected to a modification treatment process without performing a simple distillation operation after the preparation of silica particles, also gels in the same way, but this is thought to be due to the above reason (ii). In the above-mentioned Example 1, the silane coupling agent is diluted with alcohol and then continuously supplied (i.e., added dropwise) for 6 hours during the modification treatment process, while in Patent Document 3, it is mixed without dilution before heating and refluxing. Regarding this, for example, in the above-mentioned Non-Patent Document 1 (Aoki Shinjiro, Journal of the Japan Rubber Association, Vol. 59, No. 11, 1986, 610-619.), which teaches the trend of modification using coupling agents, it is written in "3.1 Silane" on page 611 that "Structurally, RSi(OCH3)3, R is an organic functional group, and a polar polymer is selected and combined. It dissolves in methanol and water, hydrolyzes, and condenses to form silane triol, which is chemically adsorbed to silica-based powders and fibers. (Diagram omitted) When the solvent is evaporated and weakly heated, it becomes a thin film with organic functional groups that chemically bond with the polymer. It undergoes hydrolysis and chemical reaction, and chemical adsorption and crosslinking / polymerization at the interface. ' It is known that in the reaction of general silane coupling agents, including 3-mercaptopropyltrimethoxysilane, after the alkoxy group of the silane coupling agent is hydrolyzed, the self-condensation reaction between the silane coupling agents (resulting in the formation of aggregates) and the modification reaction to the silica particles compete with each other, but in the modification treatment process, as in the above-mentioned Example 1, it is confirmed that an efficient modification reaction to the silica particles proceeds by diluting the silane coupling agent with methanol and continuously supplying it. The effect of concentration and temperature on such modification reactions is shown, for example, in the above-mentioned non-patent document 2 (M.-CB Salon, et al., Colloids and Surfaces A: Physicochem. Eng. Aspects, 2008, 312, 83-91.). This document is a paper titled "Kinetics of hydrolysis and self condensation reactions of silanes by NMR spectroscopy," and in "3.4.1. Silane concentration" on page 89, the effect of the concentration of the silane coupling agent on the reaction is investigated. A comparison is made between 10% and 4% silane coupling agent in an alcohol solvent. As a result of 4% versus 10%, "The hydrolysis rate decreased (complete hydrolysis within 10 h). The silanol formation T 0 H was also slowed down (only 80% of such species within 6 h reaction). 0 H The production of silanol was also slowed down (only 80% was produced after 6 hours of reaction). Furthermore, in an experiment in which a different silane coupling agent was used and the concentration was increased to 20%, the following result was reported: "However, the maximum of formed silanol units (T 0 H ) was reduced to 50% probably because of the increase of self condensation reactions; the T 1 and T 2However, the silanol units (T 0 H ) was reduced to 50%, presumably due to an increase in self-condensation reactions.) and the conclusion regarding the concentration study stated, "These data show that a concentration of 10% gave optimal experimental conditions to enhance the maximum silanol formation and to lower self condensation reactions." Furthermore, on page 90, in "3.4.2. Effect of the temperature," the effect of temperature on the reaction is investigated. That is, as described in "The hydrolysis reaction was started at room temperature (25℃) for 2h. Then the temperature was kept to 70℃ (corresponding to the boiling temperature of the solvent mixture), as displayed in Fig. 9c," Fig. 9c shows the time course of hydrolysis and self-condensation of the silane coupling agent when heated to 70℃. The hydrolysis rate (T 0 H The decrease in T 1 A sudden increase in followed by T 2The gradual increase in the temperature indicates that the self-condensation reaction is greatly promoted. Therefore, according to the authors, when modifying an inorganic material with a silane coupling agent, for example, the temperature must be kept as low as possible if self-condensation is to be suppressed. Then, on page 91, in "4. Conclusion," it is stated that "The optimal concentration of silanes hydrolysis was found to be around 10% (w / w) with respect to the solvents and the temperature raise enhanced drastically the self condensation reactions." Therefore, it is believed that the abrasive grain E of Patent Document 3 could not be concentrated to 12 mass % due to the method of adding the silane coupling agent during the modification treatment. The physical properties of the resulting colloidal silica were evaluated by the following methods. (1) BET specific surface area, BET diameter: Measured using a NOVA4200e (manufactured by Anton Paar). The BET specific surface area S (m ２ / g) and SiO ２ True density 2.2 g / cm ３ ) and the above formula (1), the particle diameter is calculated by the formula 2727 / S, which is the BET diameter. (2) Cumulant mean diameter by dynamic scattering method: Measured using an SZ-100 (manufactured by Horiba, Ltd.) When measuring, the silica content in the measurement sample was adjusted to 1.13 g with pure water and ammonium nitrate, and the adjusted liquid was measured. (3) Silica solids concentration: Using an SMS-70 (manufactured by A&D Co., Ltd.) as an apparatus, the residue obtained after evaporating the water content was taken as the silica concentration. (4) pH: Measured at 25° C. using an instrument D-51 (manufactured by Horiba, Ltd.). (5) Viscosity: Measured at 25° C. using a VM-10A (manufactured by Sekonic Corporation). (6) Methanol concentration: Measured using a GC-2025 (Shimadzu Corporation). The colloidal silica of the present invention is suitable for applications such as abrasives (silicon wafers, hard disks, etc.), coating agents (eyeglasses, displays, building materials, paper, etc.), and binders (ceramics, catalysts, etc.).

Claims

1. A colloidal silica having a modified surface, a BET diameter of 12 nm or less, and being substantially free of aggregation.

2. BET specific surface area is 227m ２ 2. The colloidal silica according to claim 1, wherein the molecular weight of the colloidal silica is 1 / g or more.

3. The colloidal silica according to claim 1, characterized in that the modification is anion-modified or cation-modified.

4. The colloidal silica according to claim 3, characterized in that the anion-modified silica is a sulfo group.

5. The colloidal silica according to claim 3, characterized in that the cation modification is by a primary amino group.

6. The colloidal silica according to claim 1, characterized in that the solid content is 12% by mass or more.

7. Colloidal silica according to claim 1, characterized in that the solids concentration is 12 mass% or more, and the rate of change in the cumulant average diameter measured by dynamic light scattering after being kept at 60°C for 7 days is within 20% compared to the value before said keeping.

8. A method for producing colloidal silica according to any one of claims 1 to 7, comprising: a raw material preparation step of supplying and reacting an easily decomposable organosilicate with a reaction liquid containing a hydrolysis catalyst consisting of an organic amine to prepare raw material colloidal silica having a BET diameter of 12 nm or less; a concentration adjustment step of adjusting the solid content concentration of the raw material colloidal silica to 13 mass % or less and adjusting the concentration of alcohols generated from the raw material preparation step to 1 to 25 mass %; a modification treatment step of modifying the raw material colloidal silica whose concentration has been adjusted; and a concentration step of concentrating the modified colloidal silica so that the residual organic solvent in the modified colloidal silica is 1 mass % or less.

9. The method for producing colloidal silica according to claim 8, characterized in that in the raw material preparation step, the reaction is carried out under conditions in which the feed rate of the easily hydrolyzable organosilicate is less than 1.5 mass% / min of the total amount of the easily hydrolyzable organosilicate fed, the reaction time is 6 hours or less, and the reaction temperature is 70°C or lower.

10. The method for producing colloidal silica according to claim 8, characterized in that in the concentrating step, the colloidal silica after the modification treatment step is concentrated so that the solid content concentration in the colloidal silica is 12 mass % or more.

11. The method for producing colloidal silica according to claim 8, characterized in that the modification treatment step comprises the steps of reacting a modifier having a functional group that can be converted into an anionic group with the colloidal silica after the concentration adjustment step, and converting the functional group in the modifier after the reaction into an anionic group.

12. The method for producing colloidal silica according to claim 11, characterized in that the modifying agent has mercapto groups and / or sulfide groups, and the mercapto groups and / or sulfide groups are converted to sulfo groups by treating with an oxidizing agent to obtain colloidal silica having sulfo groups on the surface.

13. The method for producing colloidal silica according to claim 8, characterized in that the modification treatment step comprises a step of reacting a modifying agent having a cationic group with the colloidal silica after the concentration adjustment step.

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