JP2010269985A - Sulfonic acid-modified aqueous anionic silica sol and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide sulfonic acid-modified aqueous anionic silica sol having high stability under an acidic condition, low content of metallic impurities and excellent filterability, and a method for producing the same. <P>SOLUTION: The method for producing the sulfonic acid-modified anionic silica sol includes: adding a silane coupling agent having a functional group chemically convertible to a sulfonic acid group into colloidal silica; and then, converting the functional group to the sulfonic acid group. The sulfonic acid-modified aqueous anionic silica sol is obtained by using the method and has ≤-15 mV zeta potential in an acidic environment of ≥pH 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sulfonic acid-modified aqueous anionic silica sol and a method for producing the same.

  Specifically, the present invention relates to a sulfonic acid-modified aqueous anionic silica sol provided with anionicity by sulfonic acid modification of the surface of colloidal silica (silica sol) using an aqueous medium and a method for producing the same.

  Colloidal silica (silica sol) using an aqueous medium is used as a physical property improving agent in the fields of paper, fiber, steel, and the like, and is used as an abrasive for semiconductor wafers. Silica sol has a problem that silica particles are aggregated under an acidic condition and inferior in stability, and a silica sol having excellent stability in a wide pH range is required.

  Patent Document 1 describes a modified colloidal silica that is highly stable under acidic conditions. Specifically, modified colloidal silica obtained by modifying colloidal silica obtained by hydrolyzing and condensing a hydrolyzable silicon compound with a modifying agent is described, and in particular, a cationic group is used as the modifying agent. A silane coupling agent is used (claim 1, paragraph [0018], etc. of Patent Document 1).

  Patent Document 2 describes a highly stable modified colloidal silica in which anionicity is imparted to the silica surface, contrary to the above. Specifically, an anionic silica sol in which anionicity is imparted to the silica surface by reacting colloidal silica with an aluminate such as sodium aluminate has been described (claim 1, claim 2, invention of Patent Document 2). Effect).

  There is room for further improvement when these conventional modified colloidal silicas are used for applications such as abrasives for semiconductor wafers, particularly under acidic conditions.

  That is, the cationic silica sol of Patent Document 1 has a positive zeta potential in the acidic region and is highly stable. However, in the case of a cationic sol, it passes through the isoelectric point where the zeta potential becomes zero while the liquidity changes from neutral to alkaline, and it does not have high stability in a wide range from acidic to alkaline. Absent. Further, in Patent Document 2, since an aluminate is reacted, the anionic silica sol contains an aluminum element in addition to silicon, and in some applications, particularly chemical mechanical polishing (CMP) applications that dislike impurity metal elements. Not suitable for. In addition, when used as an abrasive, etc., it is necessary to filter the coarse liquid before supplying the polishing liquid to the polishing apparatus, and the polishing liquid is filterable due to the design of circulating and repeatedly using the polishing liquid. Is required to be high. That is, it is necessary to prevent the modified colloidal silica from aggregating or gelling during filtration. Further, when metal impurities are contained in the modified colloidal silica, scratches or the like may occur in the semiconductor wafer, so that the metal impurity content is required to be as low as possible. In this respect, the conventional modified colloidal silica does not sufficiently satisfy the above requirements, and there is room for further improvement.

JP 2005-162533 A WO2008 / 111383 pamphlet

  An object of the present invention is to provide a sulfonic acid-modified aqueous anionic silica sol having high stability under acidic conditions, low metal impurity content, and good filterability, and a method for producing the same.

  As a result of intensive studies to achieve the above object, the present inventor treated the silica surface in colloidal silica (silica sol) with a silane coupling agent having a specific functional group, and then converted the functional group into a sulfonic acid group. The present inventors have found that the object can be achieved by the production method to be converted, and have completed the present invention.

That is, the present invention relates to the following sulfonic acid-modified aqueous anionic silica sol.
1. A sulfonic acid-modified aqueous anionic silica sol having a zeta potential of -15 mV or less at an acidity of pH 2 or higher.
2.1) Alkali metal selected from sodium and potassium, 2) Alkaline earth metal selected from calcium and magnesium, and 3) From aluminum, iron, titanium, nickel, chromium, copper, zinc, lead, silver, manganese and cobalt Item 2. The sulfonic acid-modified aqueous anionic silica sol according to Item 1, wherein the selected heavy metal and light metal contents are each 1 ppm by weight or less.
3. Item 3. The sulfonic acid-modified aqueous anionic silica sol according to Item 1 or 2, wherein aggregation or gelation is prevented for 2 weeks or more after preparation under acidic conditions.
4). A method for producing a sulfonic acid-modified aqueous anionic silica sol, wherein a silane coupling agent having a functional group that can be chemically converted into a sulfonic acid group is added to colloidal silica, and then the functional group is converted into a sulfonic acid group.
5). Item 5. The production method according to Item 4, wherein the functional group that can be chemically converted to a sulfonic acid group is a mercapto group.
6). The said colloidal silica is a manufacturing method of the said claim | item 4 or 5 obtained by hydrolyzing and condensing the hydrolysable silicon compound.

Hereinafter, the sulfonic acid-modified aqueous anionic silica sol of the present invention and the production method thereof will be described in detail.

  The sulfonic acid-modified aqueous anionic silica sol of the present invention is a method for producing a colloidal silica by adding a silane coupling agent having a functional group that can be chemically converted to a sulfonic acid group, and then converting the functional group to a sulfonic acid group ( Hereinafter, the “production method of the present invention”) is obtained.

  The colloidal silica of the raw material is not limited as long as it has a silanol group on the surface, but considering that the semiconductor does not contain diffusible metal impurities or corrosive ions such as chlorine, a hydrolyzable silicon compound ( For example, colloidal silica obtained by hydrolysis / condensation using alkoxysilane or a derivative thereof as a raw material is preferable. These silicon compounds can be used alone or in combination of two or more.

  In the present invention, an alkoxysilane represented by the following general formula 1 or a derivative thereof is preferable.

Si (OR) ₄ (1)
[In formula, R is an alkyl group, Preferably it is a C1-C8 lower alkyl group, More preferably, it is a C1-C4 lower alkyl group. ]
Examples of R include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group, a hexyl group, and the like. Tetramethoxysilane in which R is a methyl group and tetra in which R is an ethyl group Ethoxysilane and tetraisopropoxysilane in which R is an isopropyl group are preferred. Moreover, as a derivative | guide_body of alkoxysilane, the low condensate obtained by partially hydrolyzing alkoxysilane can also be illustrated. In the present invention, it is preferable to use tetramethoxysilane because it is easy to control the hydrolysis rate, easy to obtain single-nm fine silica particles, and few unreacted substances remain.

  The silicon compound is hydrolyzed and condensed in a reaction solvent to form colloidal silica. As the reaction solvent, water or an organic solvent containing water is used.

  Examples of organic solvents include hydrophilicity such as methanol, ethanol, isopropanol, n-butanol, t-butanol, pentanol, alcohols such as ethylene glycol, propylene glycol, and 1,4-butanediol, and ketones such as acetone and methyl ethyl ketone. An organic solvent is mentioned. Among these organic solvents, it is particularly preferable to use alcohols such as methanol, ethanol, and isopropanol, and from the viewpoint of post-treatment of the reaction solvent, etc., it has the same alkyl group as the alkyl group (R) of the raw silicon compound. More preferably, alcohols are used. These organic solvents can be used alone or in combination of two or more.

  Although the usage-amount of an organic solvent is not specifically limited, About 5-50 mol is preferable per 1 mol of silicon compounds. When the amount is less than 5 mol, the compatibility with the silicon compound may be lost. If it exceeds 50 moles, the production efficiency may decrease.

  The amount of water added to the organic solvent is not particularly limited as long as the amount required for hydrolysis of the silicon compound is present, and is preferably about 2 to 15 mol per mol of the silicon compound. Note that the amount of water mixed in the organic solvent greatly affects the particle size of the colloidal silica formed. If the amount of water added is relatively increased, the particle size of the colloidal silica can be relatively increased. If the amount of water added is relatively reduced, the particle size of the colloidal silica can be made relatively small. Therefore, the particle diameter of the colloidal silica produced can be arbitrarily adjusted by changing the mixing ratio of water and the organic solvent.

  It is preferable to adjust the reaction solvent to be alkaline by adding a basic catalyst to the reaction solvent. Thereby, the reaction solvent is preferably adjusted to pH 8 to 11, more preferably pH 8.5 to 10.5, and colloidal silica can be formed quickly. As the basic catalyst, organic amines and ammonia are preferable in consideration of impurities, and ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine, tetramethylammonium hydroxide and the like are particularly preferable.

  In order to hydrolyze and condense the silicon compound in the reaction solvent, the raw material compound may be added to the organic solvent and stirred at a temperature of 0 to 100 ° C., preferably 0 to 50 ° C. Colloidal silica having a spherical shape and a uniform particle size can be obtained by hydrolyzing and condensing a silicon compound in an organic solvent containing water while stirring.

  In the present invention, a colloidal silica is modified with sulfonic acid by adding a silane coupling agent having a functional group that can be chemically converted to a sulfonic acid group, and then converting the functional group into a sulfonic acid group. . This is based on the fact that a silane coupling agent having a sulfonic acid group is difficult to obtain because the sulfonic acid group has high acidity and causes hydrolysis.

  Examples of the silane coupling agent having a functional group that can be chemically converted to a sulfonic acid group include 1) a silane coupling agent having a sulfonic acid ester group that can be converted to a sulfonic acid group by hydrolysis, and 2) a sulfonic acid by oxidation. Examples include a coupling agent having a mercapto group and / or a sulfide group that can be converted into a group. In addition, since the sulfonic acid modification on the surface of colloidal silica is performed in a solution, it is preferable to use the latter coupling agent having a mercapto group and / or a sulfide group in order to increase the modification efficiency.

  Examples of the silane coupling agent having a mercapto group include 3-mercaptopropyltrimethoxysilane, 2-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the like.

  Examples of the coupling agent having a sulfide group include bis (3-triethoxysilylpropyl) disulfide.

  When adding a coupling agent to colloidal silica, considering the solubility of the coupling agent, it is preferable that the colloidal silica contains a hydrophilic organic solvent. In this regard, when colloidal silica is obtained by a Stover method in which alkoxysilane is hydrolyzed and condensed in an alcohol-water solvent with a basic catalyst, alcohol is contained in the reaction solution, so it is necessary to add a hydrophilic organic solvent. There is no. At this time, since the hydrophilic organic solvent is more preferably 50% by mass or more with respect to the water in the colloidal silica, it is adjusted by concentrating the reaction solution as necessary.

  On the other hand, when adding a silane coupling agent to water-dispersed colloidal silica, a hydrophilic solvent is added to such an extent that the silane coupling agent is dissolved. Examples of the hydrophilic organic solvent include alcohols such as isopropyl alcohol, ethanol and methanol. Among these, it is preferable to use the same alcohol as the alcohol generated by hydrolysis of the silicon compound. This is because the recovery and reuse of the solvent can be facilitated by using an alcohol of the same type as that generated by hydrolysis of the silicon compound.

  The addition amount of the coupling agent is about 0.1 to 10% by mass with respect to silica. If the amount added is small, the zeta potential in acidity may not be sufficiently stable. If the amount added is large, the modified silica sol may gelate over time.

  Although the temperature at the time of adding a coupling agent is not limited, The boiling point is preferable from normal temperature (about 20 degreeC). Although the reaction time is not limited, it is preferably 10 minutes to 10 hours, more preferably 30 minutes to 2 hours. Although the pH at the time of addition is not limited, it is preferably 7 or more and 11 or less. A strong alkali of 11 or more is not preferable because the silane coupling agent does not react with the silica surface and the silane coupling agents may self-condense.

  As a method for oxidizing the modified mercapto group and sulfide group, an oxidizing agent can be used. Examples thereof include nitric acid, hydrogen peroxide, oxygen, ozone, organic peracid (percarboxylic acid), bromine, hypochlorite, potassium permanganate, and chromic acid. Among these oxidizing agents, hydrogen peroxide and organic peracids (peracetic acid and perbenzoic acids) are preferable because they are relatively easy to handle and the oxidation yield is good. In view of a substance by-produced in the reaction, it is most preferable to use hydrogen peroxide.

  The addition amount of the oxidizing agent is preferably 3 to 100 times mol of the silane coupling agent. There is no particular upper limit for the amount added, but about 50 times mole is more preferred. Note that colloidal silica and silane coupling agents have no by-products because they have a stable structure in the oxidation reaction except for functional groups that are oxidized (converted) to sulfonic acid groups.

  Since the sulfonic acid-modified aqueous anionic silica sol obtained according to the above method contains a solvent other than water, in order to improve the long-term storage stability of the silica sol, a dispersion medium mainly containing a reaction solvent is used as necessary. Can be replaced with water. In addition, you may perform this water substitution before adding an oxidizing agent after adding a coupling agent.

  A method for replacing the dispersion medium mainly containing the reaction solvent with water is not particularly limited, and examples thereof include a method in which water is added dropwise in a certain amount while heating the silica sol. In addition, there may be mentioned a method in which the silica sol is separated from a dispersion medium mainly composed of a reaction solvent by precipitation / separation, centrifugation, or the like and then redispersed in water.

  In the sulfonic acid-modified aqueous anionic silica sol obtained by the production method of the present invention, since the silica surface in the sol is modified with a sulfonic acid group, aggregation and gelation of the silica sol are suppressed even in an acidic dispersion medium. It can be stably dispersed for a long time. For example, aggregation or gelation is prevented under acidic conditions for 2 weeks or more after preparation. Moreover, since it is modified by a sulfonic acid group, the reason is unknown, but the transparency of silica sol is higher than that of colloidal silica whose surface is not modified (only silanol group).

  Moreover, the silica sol obtained by the production method of the present invention includes 1) an alkali metal selected from sodium and potassium, 2) an alkaline earth metal selected from calcium and magnesium, and 3) aluminum, iron, titanium, nickel, chromium, The contents of heavy metals and light metals selected from copper, zinc, lead, silver, manganese and cobalt are as low as 1 ppm by weight or less, respectively, and they have high purity without containing halogen elements such as corrosive chlorine and bromine.

  The particle size of the modified silica contained in the silica sol is 1000 nm or less, preferably 5 to 500 nm, more preferably 10 to 300 nm.

The silica sol of the present invention is excellent in long-term dispersion stability in a wide pH range. The stability of the silica sol can be evaluated by measuring the zeta potential of the silica sol. The zeta potential is the potential difference that occurs at the interface between the solid and the liquid that are in contact with each other when they move relative to each other. If the absolute value of the zeta potential increases, the repulsion between particles is strong. Stability increases and the closer the absolute value of the zeta potential is to zero, the easier the particles will aggregate.
In particular, the silica sol of the present invention has high stability in the acidic region. Since a coupling agent having an anionic group is used as the modifier, the zeta potential when the dispersion medium is acidic at pH 2 or higher is a negative potential (−15 mV or less), and high dispersion stability even when the dispersion medium is acidic. Have Thus, since the absolute value of the zeta potential is large, it has high dispersion stability, and accordingly, the kinematic viscosity of the silica sol is small.

  The silica sol of the present invention can be increased in concentration. As disclosed in JP-A-2005-060219 “Silica sol and method for producing the same”, WO2008 / 015943 “Silica sol and method for producing the same”, an alkali is added to maintain the colloidal silica at a highly stable pH, or Although attempts have been made to increase the concentration by adding a small amount of a salt of an organic acid, the silica concentration of about 40 wt% was the limit in these conventional products. On the other hand, the anionic silica sol of the present invention modified with a sulfonic acid group can achieve a high concentration of 50% by mass or more in a wide range from acidic to alkaline.

  The silica sol of the present invention can be used for various applications such as abrasives and paper coating agents, and can be stably dispersed for a long time in a wide pH range, and the amount of metal impurities such as sodium, iron, nickel, and aluminum. Has a high purity of 1 ppm by weight or less. The majority of defects in semiconductor products are caused by contamination, and contamination by heavy metals such as iron, nickel, chromium, copper, and zinc, and alkali metals such as sodium and calcium are attached and contaminated mainly by contact with liquids. The If there is metal contamination, it may lead to dielectric breakdown of the oxide film, so it is important not to make metal impurities contact. Therefore, the sulfonic acid-modified aqueous anionic silica sol of the present invention in which the amount of metal impurities is kept low can be suitably used as a polishing agent for CMP polishing of semiconductor wafers.

  The silica sol of the present invention has good filterability. Although the kinematic viscosity of the silica sol can be reduced by anionization or cationization of a dispersant or silanol group, it does not directly affect filterability. On the other hand, by performing sulfonic acid modification, a silica sol with excellent filterability is surely obtained. In particular, when the silica sol of the present invention is used as a CMP abrasive (polishing liquid), it is necessary to perform filtration before supplying the polishing liquid to the polishing apparatus. High is advantageous.

  When using silica sol as a polishing agent in CMP, the recycled slurry contains large or small foreign matter such as polishing debris generated during the initial polishing and dressing debris to stabilize the state of the polishing pad. If it is used as it is, the scratches are generated on the wafer, and the wafer itself becomes unusable.

  Further, even in a system that does not recycle the slurry, there is a problem of microscratching due to relatively large particles, and in order to avoid this, filtering immediately before the CMP apparatus is considered to be an important process.

  In the silica sol production process, not only the target silica particles but also agglomerates in which the particles are agglomerated are produced, so that filtration is necessary in the final process of commercialization.

  The filtration process is an industrially important process not only for CMP but also for silica sol applications where coarse particles are a problem. To improve the filterability of silica sol itself, the life of the filter itself used for filtration can be extended. It can be said that this is a beneficial improvement in physical properties.

  The sulfonic acid-modified aqueous anionic silica sol of the present invention has a zeta potential of -15 mV or less when the pH is 2 or higher. And even if a dispersion medium is acidic, it has high dispersion stability. Thus, since the absolute value of the zeta potential is large, it has high dispersion stability, and accordingly, the kinematic viscosity of the silica sol is small. Further, the concentration can be increased and the filterability is good. In particular, when the raw material colloidal silica is obtained by hydrolyzing and condensing a hydrolyzable silicon compound, the content of metal impurities can be significantly reduced. Therefore, the silica sol of the present invention is also suitable as a CMP polishing agent for semiconductor wafers. Can be used.

  The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples.

Example 1
A mixture of 787.9 g of pure water, 786.0 g of 26% aqueous ammonia (basic catalyst) and 12924 g of methanol, and a mixture of 1522.2 g of tetramethoxysilane and 413.0 g of methanol, while maintaining the liquid temperature at 35 ° C. It was added dropwise over 55 minutes to obtain a silica sol using water and methanol as a dispersion medium.

  This silica sol was heated and concentrated to 5000 ml under normal pressure. To this concentrated liquid, 6.0 g of 3-mercaptopropyltrimethoxysilane was added as a silane coupling agent, and the mixture was refluxed at the boiling point and thermally aged. Thereafter, methanol and ammonia were replaced with water while adding pure water to keep the volume constant, and when the pH reached 8 or less, the temperature of the silica sol was once lowered to room temperature. Next, 53.5 g of 35% hydrogen peroxide was added and heated again, and the reaction was continued for 8 hours. After cooling to room temperature, a sulfonic acid-modified aqueous anionic silica sol was obtained.

Example 2
While maintaining a liquid temperature of 20 ° C., a mixture of pure water 2212.7 g, 26% ammonia water (basic catalyst) 567.3 g, and methanol 12391 g is mixed with tetramethoxysilane 1522.2 g and methanol 413.0 g. The solution was added dropwise over 25 minutes to obtain a silica sol using water and methanol as a dispersion medium.

  This silica sol was heated and concentrated to 2500 ml under normal pressure. To this concentrated liquid, 6.0 g of 3-mercaptopropyltrimethoxysilane was added as a silane coupling agent, and the mixture was refluxed at the boiling point and thermally aged. Thereafter, methanol and ammonia were replaced with water while adding pure water to keep the volume constant, and when the pH reached 8 or less, the temperature of the silica sol was once lowered to room temperature. Next, 28 g of 35% hydrogen peroxide was added and heated again, and the reaction was continued for 8 hours. After cooling to room temperature, a sulfonic acid-modified aqueous anionic silica sol was obtained.

Comparative Example 1
While maintaining a liquid temperature of 20 ° C., a mixture of pure water 2212.7 g, 26% ammonia water (basic catalyst) 567.3 g, and methanol 12391 g is mixed with tetramethoxysilane 1522.2 g and methanol 413.0 g. The solution was added dropwise over 25 minutes to obtain a silica sol using water and methanol as a dispersion medium.

  This silica sol was heated and concentrated to 2500 ml under normal pressure. In order to keep the volume of the concentrated solution constant, methanol and ammonia were replaced with water while adding pure water, and colloidal silica was obtained by adjusting the pH to 8 or less.

Comparative Example 2
To 1800 g of the colloidal silica obtained in Comparative Example 1, 2.65 g of a commercially available sodium aluminate aqueous solution having an Al ₂ O ₃ content of 18.8% was diluted with 10 g of pure water while maintaining the liquid temperature at 25 ° C. with stirring. An aqueous solution was added. Next, it was refluxed at the boiling point for 2 hours to obtain alkaline aluminum modified colloidal silica.

  At room temperature, 30 g of a cation exchange resin (Amberlite IR-124H) was added to the obtained alkaline aluminum-modified colloidal silica and stirred until the pH was 3.5 or less. Thereafter, the cation exchange resin was removed to obtain acidic aluminum modified colloidal silica.

  The physical properties of the sulfonic acid-modified aqueous anionic silica sol obtained in each Example and the colloidal silica obtained in each Comparative Example are shown in Table 1 below.

  The amount of metal impurities was measured using an atomic absorption measuring device. The zeta potential was measured by a dynamic light scattering Doppler method using a measuring device ELS-Z (manufactured by Otsuka Electronics Co., Ltd.).

Test Example 1 (Observation over time)
The pH of the sulfonic acid-modified aqueous anionic silica sol obtained in Examples 1 and 2 and the colloidal silica obtained in Comparative Example 1 were adjusted to 3 and 4.5, and stored in a constant temperature bath at 43 ° C and 60 ° C. The time course after 2 weeks and after 2 weeks was examined.

  The kinematic viscosity was measured with a Canon Fenske viscometer.

  The primary particle diameter was calculated by converting from the specific surface area. The secondary particle size (ELS value) was measured by a sodium dodecyl sulfate aqueous solution or citric acid aqueous solution dilution method.

  The measurement results for Example 1 are shown in Table 2 below. The measurement results for Example 2 are shown in Table 3 below. The measurement results for Comparative Example 1 are shown in Table 4 below. In the table, “association ratio” is a numerical value obtained by dividing the secondary particle diameter by the primary particle diameter.

Test Example 2 (permeation (filterability) evaluation)
The permeation amount (filterability) of the sulfonic acid-modified aqueous anionic silica sol obtained in Example 2 and the colloidal silica obtained in Comparative Example 1 was examined. Specifically, the above silica sol or colloidal that performs suction filtration using a membrane filter (model number: A300A047A) with an aperture of 3 μm made by Advantech Toyo Co., Ltd. under a reduced pressure of −0.07 MPa and permeates the filter paper for 10 minutes. Filterability was evaluated by measuring the amount of silica permeation.

  Taking into account the variation in the measurement data, each measurement was performed six times, and the average value of the four measurement data was evaluated excluding the maximum and minimum values of the measured transmission amount. Table 1 also shows the results of the amount of colloidal silica permeating through the filter paper for 10 minutes. From the results in Table 1, it can be seen that the sulfonic acid-modified aqueous anionic silica sol obtained in Example 2 has a permeation amount (filterability) about 2.7 times greater than that of the colloidal silica of Comparative Example 1.

Claims (6)

  A sulfonic acid-modified aqueous anionic silica sol having a zeta potential of -15 mV or less at an acidity of pH 2 or higher. 1) Alkali metal selected from sodium and potassium, 2) Alkaline earth metal selected from calcium and magnesium, and 3) Aluminum, iron, titanium, nickel, chromium, copper, zinc, lead, silver, manganese and cobalt The sulfonic acid-modified aqueous anionic silica sol according to claim 1, wherein the contents of heavy metal and light metal are each 1 ppm by weight or less.
  The sulfonic acid-modified aqueous anionic silica sol according to claim 1 or 2, wherein aggregation or gelation is prevented for 2 weeks or more after preparation under acidic conditions.   A method for producing a sulfonic acid-modified aqueous anionic silica sol, wherein a silane coupling agent having a functional group that can be chemically converted into a sulfonic acid group is added to colloidal silica, and then the functional group is converted into a sulfonic acid group.   The production method according to claim 4, wherein the functional group that can be chemically converted to a sulfonic acid group is a mercapto group.   The said colloidal silica is a manufacturing method of Claim 4 or 5 obtained by hydrolyzing and condensing the hydrolysable silicon compound.