JP2021116208A - Method for producing silica particle, method for producing silica sol, method for removing intermediate product and polishing method - Google Patents

Abstract

To provide a method for producing a silica sol with a reduced amount of intermediate products, and provide a method for removing an intermediate product in a silica sol which can conveniently reduce the amount of the intermediate product in the silica sol.SOLUTION: A method for producing silica particles includes step (1) of subjecting tetraalkoxysilane to hydrolysis and condensation reactions, to obtain a silica sol and step (2) of subjecting the silica sol to ultrafiltration using an ultrafilter with a molecular weight cutoff of 5,000-80,000. There is also provided a method for producing a silica sol, including the method for producing silica particles. There is also provided a method for removing an intermediate product in a silica sol which removes the intermediate product in the silica sol, by using the method for producing the silica sol.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for producing silica particles, a method for producing silica sol, a method for removing intermediate products, and a polishing method.

As a method of polishing the surface of a material such as a metal or an inorganic compound, a polishing method using a polishing liquid is known. Among them, chemical mechanical polishing (CMP) such as final finish polishing of prime silicon wafers for semiconductors and these recycled silicon wafers, flattening of interlayer insulating films during semiconductor device manufacturing, metal plug formation, embedded wiring formation, etc. ), Since the surface condition greatly affects the semiconductor characteristics, the surface and end faces of these parts are required to be polished with extremely high precision.

In such precision polishing, a polishing composition containing silica particles is adopted, and colloidal silica is widely used as the abrasive grains which are the main components thereof. Colloidal silica is produced by thermal decomposition of silicon tetrachloride (fumed silica, etc.), by deionization of alkali silicate such as water glass, hydrolysis reaction and condensation reaction of alkoxysilane (generally, "" The method called "sol-gel method") is known.

Many studies have been made on the method for producing a silica sol containing colloidal silica. For example, Patent Documents 1 to 3 disclose a method for producing a silica sol by a hydrolysis reaction and a condensation reaction of alkoxysilane.

Japanese Unexamined Patent Publication No. 11-60232 International Publication No. 2008/123373 International Publication No. 2004/000922

By the way, an intermediate product may be generated during or after the production of the silica sol by the hydrolysis reaction and the condensation reaction of the alkoxysilane. This intermediate product is considered to be silica remaining as a solid with insufficient growth, silica precipitated from dissolved silicic acid after production, and the like. Further, since such silica is in a reaction active state, an intermediate product may be the starting point to generate fine particles of about 10 nm, or the particles may grow more than expected. Therefore, a silica sol having an intermediate product causes an increase in viscosity and gelation, and deteriorates its storage stability. Such an intermediate product or fine particles are considered to be silica having a lower degree of condensation than the desired colloidal silica. Therefore, the mechanical properties of the colloidal silica in the obtained silica sol are deteriorated, the polishing rate is lowered, and the polishing properties of the obtained polishing liquid are adversely affected. Further, when a polishing liquid containing fine particles is used for polishing, the fine particles cover the object to be polished, and colloidal silica in the polishing liquid, which should originally contribute to polishing, does not contribute to polishing. Further, when a polishing liquid containing silica having a low degree of condensation is used for polishing, the removability of the polishing liquid from the object to be polished after polishing is inferior.

The method for producing a silica sol by the hydrolysis reaction and the condensation reaction of alkoxysilane disclosed in Patent Documents 1 to 3 does not describe how to deal with such intermediate products and fine particles, and depends on the production conditions. A silica sol containing a large amount of intermediate products and fine particles is obtained. In particular, since the intermediate product is presumed to remain in the reaction active state, chemical changes proceed during storage of the silica sol, causing gelation and generation of fine particles. As a result, the storage stability of the silica sol is inferior, and not only the polishing characteristics of the obtained polishing liquid are adversely affected, but also the removability from the object to be polished is inferior.

The present invention has been made in view of such problems, and an object of the present invention is to provide a method for producing a silica sol having a small amount of intermediate products. Another object of the present invention is to provide a method for removing intermediate products in silica sol, which can easily reduce intermediate products in silica sol.

Conventionally, a silica sol containing intermediate products and fine particles has existed and has been used as a polishing liquid without removing the intermediate products and fine particles as it is. Therefore, it can be said that the polishing characteristics and storage stability of the obtained polishing liquid are sufficient. There wasn't. However, as a result of diligent studies, the present inventors have removed intermediate products that cause fine particles by ultrafiltration of silica sol with an ultrafiltration membrane having a specific molecular weight cut-off, and preserved the mixture. They have found that a silica sol having excellent stability can be obtained, and have completed the present invention.

That is, the gist of the present invention is as follows.
[1] A method for producing silica particles, which comprises the following steps (1) and (2).
Step (1): A step of hydrolyzing and condensing tetraalkoxysilane to obtain a silica sol.
Step (2): A step of ultrafiltration the silica sol using an ultrafiltration membrane having a molecular weight cut-off of 5,000 to 80,000.
[2] The method for producing silica particles according to [1], wherein the step (2) is performed after the step (1).
[3] The method for producing silica particles according to [1] or [2], wherein the content of the silica particles in the silica sol is 10% by mass to 50% by mass in 100% by mass of the total amount of the silica sol.
[4] The method for producing silica particles according to any one of [1] to [3], wherein the average secondary particle size of the silica particles measured by the DLS method is 20 nm to 100 nm.
[5] The method for producing silica particles according to any one of [1] to [4], which does not include a step of heating to 100 ° C. or higher.
[6] A method for producing silica sol, which comprises the method for producing silica particles according to any one of [1] to [5].
[7] A method for removing an intermediate product in a silica sol, which removes the intermediate product in the silica sol by the method for producing a silica sol according to [6].
[8] A polishing method for polishing using a polishing composition containing silica particles obtained by the method for producing silica particles according to any one of [1] to [5].

The method for producing a silica sol of the present invention can obtain a silica sol with a small amount of intermediate products, is excellent in storage stability of the obtained silica sol, is excellent in polishing characteristics of the obtained polishing liquid, and is covered with the obtained polishing liquid after polishing. Excellent removability from the polished body. Further, the method for removing intermediate products in the silica sol of the present invention can easily reduce the amount of intermediate products in the silica sol, has excellent storage stability of the obtained silica sol and the obtained polishing liquid, and has excellent polishing characteristics of the obtained polishing liquid. Excellent in removing the obtained polishing liquid from the object to be polished after polishing.

It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol containing an intermediate product. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol obtained in the comparative example 1. FIG. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol obtained in Example 1. FIG. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol obtained in Example 2. FIG. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol obtained in the comparative example 2. FIG. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol obtained in the comparative example 3. FIG. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol used in Reference Example 1. FIG. It is a figure which shows the secondary electron image observed by the field emission scanning electron microscope of the silica sol obtained in Reference Example 2. FIG.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof. When the expression "-" is used in the present specification, it is used as an expression including numerical values or physical property values before and after the expression.

(Manufacturing method of silica particles)
The method for producing silica particles of the present invention includes the following steps (1) and (2).
Step (1): A step of hydrolyzing and condensing tetraalkoxysilane to obtain a silica sol.
Step (2): A step of ultrafiltration the silica sol using an ultrafiltration membrane having a molecular weight cut-off of 5,000 to 80,000.

(Step (1))
Step (1) is a step of hydrolyzing and condensing tetraalkoxysilane to obtain a silica sol.
The method for producing silica particles of the present invention can reduce the metal impurity content of the obtained silica sol by including the step (1).

Examples of the tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. These tetraalkoxysilanes may be used alone or in combination of two or more. Among these tetraalkoxysilanes, tetramethoxysilane and tetraethoxysilane are preferable because the hydrolysis reaction is fast, unreacted substances are hard to remain, productivity is excellent, and a stable silica sol can be easily obtained. More preferred is methoxysilane.

As the raw material constituting the silica particles, a raw material other than tetraalkoxysilane such as a low condensate of tetraalkoxysilane may be used, but since it is excellent in reactivity, tetra is used in 100% by mass of all the raw materials constituting the silica particles. It is preferable that the amount of alkoxysilane is 50% by mass or more and the amount of raw material other than tetraalkoxysilane is 50% by mass or less, the amount of tetraalkoxysilane is 90% by mass or more, and the amount of raw material other than tetraalkoxysilane is 10% by mass or less. Is more preferable.

Examples of the solvent / dispersion medium used in the reaction for performing the hydrolysis reaction and the condensation reaction include water, methanol, ethanol, propanol, isopropanol, ethylene glycol and the like. As these solvents / dispersion media, one type may be used alone, or two or more types may be used in combination. Among these solvents and dispersion media, those used in the hydrolysis reaction and the condensation reaction and those produced as by-products are the same, and are excellent in manufacturing convenience. Therefore, water and alcohol are preferable, and water and methanol are more preferable. ..

When the hydrolysis reaction and the condensation reaction are carried out, they may be in the presence of a catalyst or in the absence of a catalyst, but the presence of a catalyst is preferable because the hydrolysis reaction and the condensation reaction can be promoted.
Examples of the catalyst include acid catalysts such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, formic acid and citric acid, and alkalis such as ethylenediamine, diethylenetriamine, triethylenetetraamine, ammonia, urea, ethanolamine and tetramethylammonium hydroxide. Examples include catalysts. Among these catalysts, an alkaline catalyst is preferable because it has excellent catalytic action and it is easy to control the particle shape, it is possible to suppress the mixing of metal impurities, it is highly volatile, and it is excellent in removability after a condensation reaction. , Alkaline catalyst is preferable, and ammonia is more preferable.

(Relationship between process (1) and process (2))
Step (2) may be carried out during step (1) or after step (1), but silica remaining as a solid with insufficient growth or silica precipitated from dissolved silicic acid after production. It is preferable to carry out after the step (1) because the intermediate products such as the above can be efficiently removed.

(Step (2))
Step (2) is a step of ultrafiltration the silica sol using an ultrafiltration membrane having a molecular weight cut-off of 5,000 to 80,000.
By including the step (2), the method for producing silica particles of the present invention can efficiently remove intermediate products such as silica remaining as a solid with insufficient growth and silica precipitated from dissolved silicic acid after production. , Suppresses deterioration such as gelation, and enhances storage stability of silica sol.

In the present specification, the intermediate product is surrounded by a black line in FIG. 1 in an image of FE-SEM taken at a magnification of 100,000 to 200,000 times using a field emission scanning electron microscope (FE-SEM). A part that looks like an exposed part.
The intermediate product is considered to be silica remaining as a solid with insufficient growth during or after production of the silica sol by hydrolysis reaction and condensation reaction of alkoxysilane, silica precipitated from dissolved silicic acid after production, and the like.

The fractional molecular weight of the ultrafiltration membrane is 5,000 to 80,000, preferably 6,000 to 60,000, more preferably 7,000 to 40,000. When the molecular weight cut-off of the ultrafiltration membrane is 5,000 or more, the permeability is excellent. Further, when the molecular weight cut-off of the ultrafiltration membrane is 80,000 or less, the selectivity is excellent.

The feature of ultrafiltration is that components that pass through the pores in the usual filtration with a filter paper having a pore size on the order of microns or a filter can be fractionated by molecular weight. Therefore, in order to increase the selectivity of fraction for each molecular weight by ultrafiltration, the method by centrifugation is preferable.

The centrifugal force of the ultrafiltration by centrifugation is preferably 500 g to 10,000 g, more preferably 800 g to 5,000 g. When the centrifugal force of the ultrafiltration is 500 g or more, the filtration rate is sufficient and the productivity of silica particles and silica sol is excellent. Further, when the centrifugal force of the ultrafiltration is 10,000 g or less, the selectivity of the ultrafiltration is excellent.

The rotation speed of the ultrafiltration by centrifugation is preferably 1,000 rpm to 20,000 rpm, more preferably 2,000 to 10,000 rpm. When the rotation speed of the extraneous filtration is 1,000 rpm or more, the filtration rate is sufficient and the productivity of silica particles and silica sol is excellent. When the rotation speed of the ultrafiltration is 20,000 rpm or less, the selectivity of the ultrafiltration is excellent.

The centrifugation time for ultrafiltration by centrifugation is preferably 10 minutes to 300 minutes, more preferably 20 minutes to 180 minutes. When the centrifugation time of the ultrafiltration is 10 minutes or more, intermediate products in the silica sol can be suppressed. Further, when the centrifugation time of the ultrafiltration is 300 minutes or less, the productivity of silica particles and silica sol is excellent.

(Steps other than step (1) and step (2))
The method for producing silica particles of the present invention may include steps other than steps (1) and (2) as long as the performance of the silica particles is not impaired.
Examples of the steps other than the step (1) and the step (2) include a pressure heat treatment step, but since the effect expected in the pressure heat treatment is reduced by suppressing intermediate products, the expected effect of the pressure heat treatment is reduced. It is preferable not to include a step of heating to 100 ° C. or higher, and more preferably not to include a step of heating to 150 ° C. or higher.

(Physical characteristics of silica particles)
The average primary particle size of the silica particles is preferably 5 nm to 100 nm, more preferably 10 nm to 60 nm. When the average primary particle size of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Further, when the average primary particle size of the silica particles is 100 nm or less, the surface roughness and scratches of the object to be polished represented by the silicon wafer can be reduced, and the sedimentation of the silica particles can be suppressed.

The average primary particle size of the silica particles is measured by the BET method. Specifically, the specific surface area of silica particles is measured using an automatic specific surface area measuring device, and the average primary particle size is calculated using the following formula (1).
Average primary particle size (nm) = 6000 / (specific surface area (m ² / g) x density (g / cm ³ )) ... (1)

The average primary particle size of the silica particles can be set in a desired range by known conditions and methods.

The average secondary particle size of the silica particles is preferably 10 nm to 200 nm, more preferably 20 nm to 100 nm. When the average secondary particle size of the silica particles is 10 nm or more, the removability of particles and the like in cleaning after polishing is excellent, and the storage stability of the silica sol is excellent. When the average secondary particle size of the silica particles is 200 nm or less, the surface roughness and scratches of the object to be polished represented by the silicon wafer during polishing can be reduced, and the removability of particles and the like during cleaning after polishing is excellent, and silica. It is possible to suppress the sedimentation of particles.

The average secondary particle size of the silica particles is measured by the DLS method. Specifically, the measurement is performed using a dynamic light scattering particle size measuring device.

The average secondary particle size of the silica particles can be set in a desired range by known conditions and methods.

The cv value of the silica particles is preferably 15 to 50, more preferably 20 to 40, and even more preferably 25 to 35. When the cv value of the silica particles is 15 or more, the polishing rate for the object to be polished represented by the silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Further, when the cv value of the silica particles is 50 or less, the surface roughness and scratches of the object to be polished represented by the silicon wafer during polishing can be reduced, and the removability of particles and the like in cleaning after polishing is excellent.

The cv value of the silica particles is calculated by measuring the average secondary particle size of the silica particles using a dynamic light scattering particle size measuring device and using the following formula (2).
cv value = (standard deviation (nm) / average secondary particle size (nm)) x 100 ... (2)

The association ratio of the silica particles is preferably 1.0 to 4.0, more preferably 1.1 to 3.0. When the association ratio of the silica particles is 1.0 or more, the polishing rate with respect to the object to be polished represented by the silicon wafer is excellent, and the productivity of the silicon wafer is excellent. Further, when the association ratio of the silica particles is 4.0 or less, the surface roughness and scratches of the object to be polished represented by the silicon wafer at the time of polishing can be reduced, and the aggregation of the silica particles can be suppressed.

The association ratio of the silica particles is calculated by using the following formula (3) from the average primary particle size measured by the above-mentioned measuring method and the average secondary particle size measured by the above-mentioned measuring method. ..
Association ratio = average secondary particle size / average primary particle size ... (3)

The surface silanol group density of the silica particles is preferably 0.1 pcs / nm ² to 10 pcs / nm ^2, more preferably 0.5 pcs / nm ^{2 to} 7.5 pcs / nm ² , and 2.0 pcs / nm. ^{2 to} 7.0 pieces / nm ² is more preferable. When the surface silanol group density of the silica particles is 0.1 element / nm ² or more, the silica particles have an appropriate surface repulsion and the dispersion stability of the silica sol is excellent. Further, when the surface silanol group density of the silica particles is 10 particles / nm ² or less, the silica particles have an appropriate surface repulsion, and the aggregation of the silica particles can be suppressed.

The surface silanol group density of silica particles is measured by the Sears method. Specifically, it is measured and calculated under the conditions shown below.
A silica sol corresponding to 1.5 g of silica particles is collected, and pure water is added to bring the liquid volume to 90 mL. In an environment of 25 ° C., add 0.1 mol / L hydrochloric acid aqueous solution until the pH reaches 3.6, add 30 g of sodium chloride, and gradually add pure water to completely dissolve sodium chloride, and finally test. Pure water is added until the total volume of the solution reaches 150 mL to obtain a test solution.
The obtained test solution is placed in an automatic titrator, and a 0.1 mol / L sodium hydroxide aqueous solution is added dropwise to obtain 0.1 mol / L sodium hydroxide required for the pH to change from 4.0 to 9.0. Measure the titration amount A (mL) of the aqueous solution.
Using the following formula (4), calculate the consumption V (mL) of 0.1 mol / L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to change from 4.0 to 9.0. Then, the surface silanol group density ρ (pieces / nm ² ) of the silica particles is calculated using the following formula (5).
V = (A × f × 100 × 1.5) / (W × C) ・ ・ ・ (4)
A: Drop quantification (mL) of 0.1 mol / L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to change from 4.0 to 9.0.
f: Titer of 0.1 mol / L sodium hydroxide aqueous solution used C: Concentration (mass%) of silica particles in silica sol
W: Amount of silica sol collected (g)
_{ρ = (B × N A)} / (10 18 × M × S BET) ··· (5)
B: Amount of sodium hydroxide (mol) required for the pH per 1.5 g of silica particles calculated from V to change from 4.0 to 9.0.
N _A: Avogadro's number (number / mol)
M: Amount of silica particles (1.5 g)
_SBET ^{: Specific surface area (m 2} / g) of silica particles measured when calculating the average primary particle size.

The method for measuring and calculating the surface silanol group density of the silica particles is described in "GW Sears, Jr., Analytical Chemistry, Vol. 28, No. 12, pp. 1981-1983 (1956).", " Shinichi Haba, Development of Polishing Agents for Semiconductor Integrated Circuit Processes, Doctoral Dissertation, Kochi University of Technology, pp.39-45, March 2004 ”,“ Patent No. 5967118 ”,“ Patent No. 6047395 ” ..

The surface silanol group density of the silica particles can be set in a desired range by adjusting the conditions of the hydrolysis reaction and the condensation reaction of the alkoxysilane.

The metal impurity content of the silica particles is preferably 5 ppm or less, more preferably 2 ppm or less.

In polishing a silicon wafer of a semiconductor device, metal impurities adhere to and contaminate the surface of the object to be polished, which adversely affects the wafer characteristics and diffuses inside the wafer to deteriorate the quality. The performance of manufactured semiconductor devices is significantly reduced.
In addition, when metal impurities are present in the silica particles, a coordinated interaction occurs between the surface silanol groups showing acidity and the metal impurities, which changes the chemical properties (acidity, etc.) of the surface silanol groups, or silica. It changes the three-dimensional environment of the particle surface (easiness of aggregation of silica particles, etc.) and affects the polishing rate.

The metal impurity content of silica particles is measured by high frequency inductively coupled plasma mass spectrometry (ICP-MS). Specifically, the silica sol containing 0.4 g of silica particles is accurately weighed, sulfuric acid and hydrofluoric acid are added, and the mixture is heated, dissolved, and evaporated, and pure water is added to the remaining sulfuric acid droplets so that the total amount is exactly 10 g. To prepare a test solution, measure using a high-frequency inductively coupled plasma mass spectrometer. The target metals are sodium, potassium, iron, aluminum, calcium, magnesium, zinc, cobalt, chromium, copper, manganese, lead, titanium, silver and nickel, and the total content of these metals is defined as the metal impurity content. do.

The metal impurity content of the silica particles can be 5 ppm or less by performing a hydrolysis reaction and a condensation reaction using alkoxysilane as a main raw material to obtain silica particles.
In the method of deionizing alkali silicate such as water glass, it is extremely difficult to reduce the metal impurity content of silica particles to 5 ppm or less because sodium or the like derived from the raw material remains.

Examples of the shape of the silica particles include a spherical shape, a chain shape, a cocoon shape (also referred to as a hump shape or a peanut shape), and an irregular shape (for example, a wart shape, a bent shape, a branched shape, etc.). Among these shapes of silica particles, if it is desired to reduce the surface roughness and scratches of the object to be polished represented by a silicon wafer during polishing, a spherical shape is preferable, and the polishing rate for the object to be polished represented by a silicon wafer is set. If you want to increase it, a different shape is preferable.

Silica particles are preferably free of pores because they are excellent in mechanical strength and storage stability.
The presence or absence of pores in the silica particles is confirmed by BET multipoint analysis using an adsorption isotherm using nitrogen as an adsorption gas.

Since the silica particles are excellent in mechanical strength and storage stability, it is preferable that the silica particles contain an alkoxysilane condensate as a main component, and more preferably a tetraalkoxysilane condensate as a main component. The main component means that it is 50% by mass or more in 100% by mass of all the components constituting the silica particles.
In order to obtain silica particles containing an alkoxysilane condensate as a main component, it is preferable to use alkoxysilane as a main raw material. In order to obtain silica particles containing a tetraalkoxysilane condensate as a main component, it is preferable to use tetraalkoxysilane as a main raw material. The main raw material means that it is 50% by mass or more in 100% by mass of all the raw materials constituting the silica particles.

(Manufacturing method of silica sol)
The method for producing a silica sol of the present invention includes the method for producing silica particles of the present invention.

As the silica sol, the dispersion liquid of the silica particles obtained by the method for producing silica particles of the present invention may be used as it is, and among the components in the obtained dispersion liquid, unnecessary components are removed and necessary components are used. It may be added and manufactured.

The silica sol preferably contains silica particles and a solvent / dispersion medium.
Examples of the solvent / dispersion medium of the silica sol include water, methanol, ethanol, propanol, isopropanol, ethylene glycol and the like. As the solvent / dispersion medium of these silica sol, one kind may be used alone, or two or more kinds may be used in combination. Among the solvents and dispersion media of these silica sol, water and alcohol are preferable, and water is more preferable, because they have excellent affinity with silica particles.

The content of the silica particles in the silica sol is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, still more preferably 5% by mass to 30% by mass, based on 100% by mass of the total amount of the silica sol. When the content of silica particles in the silica sol is 3% by mass or more, the polishing rate for the object to be polished represented by a silicon wafer is excellent. Further, when the content of the silica particles in the silica sol is 50% by mass or less, the aggregation of the silica particles in the silica sol or the polishing composition can be suppressed, and the storage stability of the silica sol or the polishing composition is excellent.

The content of the solvent / dispersion medium in the silica sol is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, still more preferably 70% by mass to 95% by mass, based on 100% by mass of the total amount of the silica sol. .. When the content of the solvent / dispersion medium in the silica sol is 50% by mass or more, aggregation of silica particles in the silica sol or the polishing composition can be suppressed, and the storage stability of the silica sol or the polishing composition is excellent. Further, when the content of the solvent / dispersion medium in the silica sol is 97% by mass or less, the polishing rate for the object to be polished represented by the silicon wafer is excellent.

The content of the silica particles and the solvent / dispersion medium in the silica sol shall be set within a desired range by removing unnecessary components from the components in the dispersion liquid of the silica particles and adding the necessary components. Can be done.

In addition to silica particles and solvents / dispersion media, silica sol can be used as an oxidizing agent, preservative, fungicide, pH adjuster, pH buffer, surfactant, chelating agent, if necessary, as long as its performance is not impaired. , Antibacterial / biocide and other other ingredients may be included.
In particular, it is preferable to include an antibacterial / biocide in the silica sol because the silica sol is excellent in storage stability.

Examples of antibacterial / biocide include hydrogen peroxide, ammonia, quaternary ammonium hydroxide, quaternary ammonium salt, ethylenediamine, glutaraldehyde, hydrogen peroxide, methyl p-hydroxybenzoate, and sodium chlorite. And so on. These antibacterial and biocide agents may be used alone or in combination of two or more. Among these antibacterial and biocide agents, hydrogen peroxide is preferable because it has an excellent affinity with silica sol.
Biocides also include what are commonly referred to as fungicides.

The content of the antibacterial / biocide in the silica sol is preferably 0.0001% by mass to 10% by mass, more preferably 0.001% by mass to 1% by mass, based on 100% by mass of the total amount of the silica sol. When the content of the antibacterial / biocide in the silica sol is 0.0001% by mass or more, the storage stability of the silica sol is excellent. When the content of the antibacterial / biocide in the silica sol is 10% by mass or less, the original performance of the silica sol is not impaired.

The pH of the silica sol is preferably 6.0 to 8.0, more preferably 6.5 to 7.8. When the pH of the silica sol is 6.0 or more, the dispersion stability is excellent and the aggregation of silica particles can be suppressed. Further, when the pH of the silica sol is 8.0 or less, the dissolution of silica particles is prevented and the storage stability for a long period of time is excellent.
The pH of the silica sol can be set in a desired range by adding a pH adjuster.

(Method of removing intermediate products in silica sol)
The method for removing the intermediate product in the silica sol of the present invention is the method according to the method for producing the silica sol of the present invention, and the specific production method is as described above.

(Abrasive composition)
The silica particles obtained by the method for producing silica particles of the present invention can be suitably used as a polishing composition.
The polishing composition preferably contains the above-mentioned silica sol and water-soluble polymer.

The water-soluble polymer enhances the wettability of the polishing composition with respect to the object to be polished represented by a silicon wafer. The water-soluble polymer is preferably a polymer having a functional group having a high hydrophilicity, and the functional group having a high hydrophilicity has a high affinity with the surface silanol group of the silica particles, and is contained in the polishing composition. The silica particles and the water-soluble polymer are stably dispersed in the vicinity. Therefore, the effects of the silica particles and the water-soluble polymer function synergistically when polishing the object to be polished represented by a silicon wafer.

Examples of the water-soluble polymer include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, copolymers having a polyvinylpyrrolidone skeleton, and polymers having a polyoxyalkylene structure.

Examples of the cellulose derivative include hydroxyethyl cellulose, hydrolyzed hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose and the like.
Examples of the copolymer having a polyvinylpyrrolidone skeleton include a graft copolymer of polyvinyl alcohol and polyvinylpyrrolidone.
Examples of the polymer having a polyoxyalkylene structure include polyoxyethylene, polyoxypropylene, and a copolymer of ethylene oxide and propylene oxide.

These water-soluble polymers may be used alone or in combination of two or more. Among these water-soluble polymers, cellulose derivatives are preferable because they have a high affinity for the surface silanol groups of silica particles and act synergistically to give good hydrophilicity to the surface of the object to be polished. Therefore, hydroxyethyl cellulose is preferable. Is more preferable.

The mass average molecular weight of the water-soluble polymer is preferably 1,000 to 3,000,000, more preferably 5,000 to 2,000,000, and even more preferably 10,000 to 1,000,000. When the mass average molecular weight of the water-soluble polymer is 1,000 or more, the hydrophilicity of the polishing composition is improved. Further, when the mass average molecular weight of the water-soluble polymer is 3,000,000 or less, the affinity with the silica sol is excellent, and the polishing rate for the object to be polished represented by the silicon wafer is excellent.

The mass average molecular weight of the water-soluble polymer is measured by size exclusion chromatography under the condition that a 0.1 mol / L NaCl solution is used as the mobile phase in terms of polyethylene oxide.

The content of the water-soluble polymer in the polishing composition is preferably 0.02% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the water-soluble polymer in the polishing composition is 0.02% by mass or more, the hydrophilicity of the polishing composition is improved. Further, when the content of the water-soluble polymer in the polishing composition is 10% by mass or less, the aggregation of silica particles at the time of preparing the polishing composition can be suppressed.

In addition to silica sol and water-soluble polymer, the polishing composition may contain basic compounds, polishing accelerators, surfactants, hydrophilic compounds, preservatives, fungicides, etc., as necessary, as long as the performance is not impaired. It may contain other components such as a pH adjuster, a pH buffer, a surfactant, a chelating agent, an antibacterial / killing agent, and the like.
In particular, it is possible to perform chemical polishing (chemical etching) by giving a chemical action to the surface of the object to be polished represented by a silicon wafer, and due to the synergistic effect with the surface silanol groups of silica particles, the surface of the object to be polished represented by a silicon wafer is represented. Since the polishing speed of the polished body can be improved, it is preferable to include a basic compound in the polishing composition.

Examples of the basic compound include organic basic compounds, alkali metal hydroxides, alkali metal hydrogen carbonates, alkali metal carbonates, ammonia and the like. These basic compounds may be used alone or in combination of two or more. Among these basic compounds, ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide, ammonium hydrogencarbonate, and ammonium carbonate are preferable because they are highly water-soluble and have excellent affinity with silica particles and water-soluble polymers. , Ammonia, tetramethylammonium hydroxide, tetraethylammonium hydroxide are more preferable, and ammonia is even more preferable.

The content of the basic compound in the polishing composition is preferably 0.001% by mass to 5% by mass, more preferably 0.01% by mass to 3% by mass, based on 100% by mass of the total amount of the polishing composition. When the content of the basic compound in the polishing composition is 0.001% by mass or more, the polishing rate of the object to be polished represented by the silicon wafer can be improved. Further, when the content of the basic compound in the polishing composition is 5% by mass or less, the stability of the polishing composition is excellent.

The pH of the polishing composition is preferably 8.0 to 12.0, more preferably 9.0 to 11.0. When the pH of the polishing composition is 8.0 or more, the aggregation of silica particles in the polishing composition can be suppressed, and the dispersion stability of the polishing composition is excellent. Further, when the pH of the polishing composition is 12.0 or less, dissolution of silica particles can be suppressed, and the stability of the polishing composition is excellent.
The pH of the polishing composition can be set in a desired range by adding a pH adjuster.

The polishing composition can be obtained by mixing the silica sol of the present invention, the water-soluble polymer, and other components as necessary, but in consideration of storage and transportation, once prepared at a high concentration, immediately before polishing. May be diluted with water or the like.

(Polishing method)
The polishing method of the present invention is a method of polishing using a polishing composition containing silica particles obtained by the method for producing silica particles of the present invention.
As the polishing composition, it is preferable to use the above-mentioned polishing composition.
Specific examples of the polishing method include a method in which the surface of a silicon wafer is pressed against a polishing pad, the polishing composition of the present invention is dropped onto the polishing pad, and the surface of the silicon wafer is polished.

(Use)
The silica particles obtained by the method for producing silica particles of the present invention and the silica sol obtained by the method for producing silica sol of the present invention can be suitably used for polishing applications, for example, polishing a semiconductor material such as a silicon wafer. Used for polishing electronic materials such as hard disk substrates, polishing in the flattening process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for photomasks and liquid crystals, polishing magnetic disk substrates, etc. It can be particularly preferably used for polishing silicon wafers and chemical mechanical polishing.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the description of the following Examples as long as it does not deviate from the gist thereof.

(Measurement of average primary particle size)
The silica sol obtained in Comparative Example 1 and Reference Example 1 was dried at 150 ° C., and the specific surface area of the silica particles was measured using an automatic specific surface area measuring device "BELSORP-MR1" (model name: Microtrac Bell Co., Ltd.). The measurement was carried out, and the density was set to 2.2 g / cm ³ using the following formula (1), and the average primary particle size was calculated.
Average primary particle size (nm) = 6000 / (specific surface area (m ² / g) x density (g / cm ³ )) ... (1)

(Measurement of average secondary particle size / cv value)
The silica sol obtained in Comparative Example 1 and Reference Example 1 was measured for the average secondary particle size of silica particles using a dynamic light scattering particle size measuring device "Zetersizer Nano ZS" (model name, manufactured by Malvern). Then, the cv value was calculated using the following formula (2).
cv value = (standard deviation (nm) / average secondary particle size (nm)) x 100 ... (2)

(Calculation of meeting ratio)
From the measured average primary particle size and average secondary particle size, the association ratio was calculated using the following formula (3).
Association ratio = average secondary particle size / average primary particle size ... (3)

(Measurement of surface silanol group density)
The amount of the silica sol obtained in Comparative Example 1 and Reference Example 1 corresponding to 1.5 g of silica particles was collected in a 200 mL tall beaker, and pure water was added to bring the liquid volume to 90 mL.
The pH electrode was inserted into a tall beaker in an environment of 25 ° C., and the test solution was stirred with a magnetic stirrer for 5 minutes. While stirring with a magnetic stirrer was continued, a 0.1 mol / L hydrochloric acid aqueous solution was added until the pH reached 3.6. With the pH electrode removed from the tall beaker and stirring with a magnetic stirrer continued, 30 g of sodium chloride was added, and pure water was gradually added to completely dissolve the sodium chloride, and finally the total volume of the test solution became 150 mL. Pure water was added until the test solution was added, and the test solution was stirred with a magnetic stirrer for 5 minutes to obtain a test solution.

Set the tall beaker containing the obtained test solution in the automatic titrator "COM-1600" (manufactured by Hiranuma Sangyo Co., Ltd.), insert the pH electrode and burette attached to the device into the tall beaker, and test with a magnetic stirrer. Titration of 0.1 mol / L sodium hydroxide aqueous solution required for pH to change from 4.0 to 9.0 by dropping 0.1 mol / L sodium hydroxide aqueous solution through a burette while stirring the liquid. A (mL) was measured.
Using the following formula (6), the consumption V (mL) of 0.1 mol / L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to change from 4.0 to 9.0 was calculated. Then, the surface silanol group density ρ (pieces / nm ² ) of the silica particles was calculated using the following formula (7).
V = (A × f × 100 × 1.5) / (W × C) ・ ・ ・ (6)
A: Drop quantification (mL) of 0.1 mol / L sodium hydroxide aqueous solution required for the pH per 1.5 g of silica particles to change from 4.0 to 9.0.
f: Titer of 0.1 mol / L sodium hydroxide aqueous solution used C: Concentration (mass%) of silica particles in silica sol
W: Amount of silica sol collected (g)
_{ρ = (B × N A)} / (10 18 × M × S BET) ··· (7)
B: Amount of sodium hydroxide (mol) required for the pH per 1.5 g of silica particles calculated from V to change from 4.0 to 9.0.
N _A: Avogadro's number (number / mol)
M: Amount of silica particles (1.5 g)
_SBET ^{: Specific surface area (m 2} / g) of silica particles measured when calculating the average primary particle size.

(Measurement of metal impurity content)
Accurately weigh the silica sol containing 0.4 g of the silica particles obtained in Comparative Example 1, add sulfuric acid and hydrofluoric acid, heat, dissolve, and evaporate, and pure water so that the total amount of the remaining sulfuric acid droplets is exactly 10 g. Was added to prepare a test solution, and the metal impurity content was measured using a high-frequency inductively coupled plasma mass spectrometer "ELEMENT2" (model name, manufactured by Thermo Fisher Scientific Co., Ltd.).

(Evaluation of intermediate products in silica sol)
For the silica sol obtained in Examples, Comparative Examples, and Reference Examples, the amount of intermediate products was evaluated by the following operation.
First, the silica sol was separated and diluted 5,000 times with ultrapure water. 5 μL of the diluted solution diluted 5,000 times was taken, dropped onto a mirror silicon wafer (manufactured by Electronics End Materials Corporation), and dried at 50 ° C. for 10 minutes. It is mounted on a field emission scanning electron microscope (FE-SEM, model name "S-5200", manufactured by Hitachi High-Technologies Co., Ltd.), and has an acceleration voltage of 5 kV, a magnification of 150,000 times, and 100 to 200 particles. Particles of colloidal silica were observed and images were taken.
From the captured images, the amount of intermediate products in the silica sol was evaluated by the following indexes. The intermediate product refers to a portion that looks like a portion surrounded by a black line in FIG.
A: Intermediate products cannot be confirmed or intermediate products can be slightly confirmed B: Intermediate products can be confirmed C: Intermediate products can be confirmed in large quantities

[Comparative Example 1]
A raw material solution in which tetramethoxysilane and methanol were mixed at a ratio of 2.3: 1 (volume ratio) and a 3% by mass aqueous ammonia solution as an auxiliary solvent were prepared. A reaction solvent in which methanol, pure water, and ammonia were mixed in advance was charged into a reaction vessel equipped with a thermometer, a stirrer, a supply pipe, and a distillation line. The concentration of water in the reaction solvent was 13% by mass, and the concentration of ammonia in the reaction solvent was 0.9% by mass.
While maintaining the temperature of the reaction solvent at 34 ° C., the reaction solvent, the raw material solution and the co-solvent were set to 0.77: 1: 0.31 (volume ratio), and the raw material solution and the co-solvent were mixed at a uniform rate for 150 minutes. It was added dropwise to the reaction vessel to obtain a silica sol. While adjusting the amount of the obtained silica sol by adding pure water so that the content of silica particles becomes about 20% by mass, the temperature is raised to remove methanol and ammonia, and the content of silica particles is increased. About 20% by mass silica sol was obtained.

The obtained silica particles had an average primary particle size of 30.7 nm, an average secondary particle size of 65.0 nm, a cv value of 30.6, an association ratio of 2.12, and a surface silanol group density of 6.2 particles / nm ² . there were.
The metal impurity content in the obtained silica particles was 1.1 ppm for sodium, 0.140 ppm for potassium, 0.015 ppm for iron, 0.135 ppm for aluminum, 0.075 ppm for calcium, and 0.07 ppm for zinc. , Magnesium, cobalt, chromium, copper, manganese, lead, titanium, silver and nickel were all less than 0.005 ppm.

The secondary electron image observed by the field emission scanning electron microscope of the obtained silica sol is shown in FIG. Table 1 shows the evaluation results of the amount of intermediate products in the obtained silica sol.

[Example 1]
4.51 g of the silica sol obtained in Comparative Example 1 was subjected to a centrifugal force of 1,075 g using an ultrafiltration membrane having a molecular weight cut off of 10,000 (trade name “Microsep Advance with 10K Omega MCP010C41”, manufactured by Pall Corporation). Ultrafiltration by centrifugation was performed under the conditions of a rotation speed of 3,100 rpm and a centrifugation time of 1 hour to obtain a silica sol. The amount of liquid that permeated the ultrafiltration membrane was 2.36 g, the transmittance was 52.3% by mass, and the silica concentration in the permeated liquid was 260 μg / g.
The secondary electron image observed by the field emission scanning electron microscope of the obtained silica sol is shown in FIG. The evaluation results of the obtained silica sol are shown in Table 1.

[Example 2]
The operation was carried out in the same manner as in Example 1 except that the fractional molecular weight of the ultrafiltration membrane (trade name "Microsep Advance with 30K Omega MCP010C41", manufactured by Pall Corporation) and the conditions for centrifugation were changed as shown in Table 1. A silica sol was obtained.
The secondary electron image observed by the field emission scanning electron microscope of the obtained silica sol is shown in FIG. The evaluation results of the obtained silica sol are shown in Table 1.

[Comparative Example 2]
The operation was carried out in the same manner as in Example 1 except that the fractional molecular weight of the ultrafiltration membrane (trade name "Microsep Advance with 3K Omega MCP010C41", manufactured by Pall Corporation) and the conditions for centrifugation were changed as shown in Table 1. A silica sol was obtained.
The secondary electron image observed by the field emission scanning electron microscope of the obtained silica sol is shown in FIG. The evaluation results of the obtained silica sol are shown in Table 1.

[Comparative Example 3]
The operation was carried out in the same manner as in Example 1 except that the fractional molecular weight of the ultrafiltration membrane (trade name "Microsep Advance with 100K Omega MCP010C41", manufactured by Pall Corporation) and the conditions for centrifugation were changed as shown in Table 1. A silica sol was obtained.
The secondary electron image observed by the field emission scanning electron microscope of the obtained silica sol is shown in FIG. The evaluation results of the obtained silica sol are shown in Table 1.

[Reference example 1]
A commercially available silica sol (trade name "PL-3", manufactured by Fuso Chemical Industry Co., Ltd.) was used as it was.
The silica particles used had an average primary particle size of 36.1 nm, an average secondary particle size of 71.2 nm, a cv value of 28.6, an association ratio of 1.97, and a surface silanol group density of 5.5 particles / nm ^2. rice field.
The secondary electron image observed by the field emission scanning electron microscope of the silica sol used is shown in FIG. The evaluation results of the silica sol used are shown in Table 1.

[Reference example 2]
A commercially available silica sol (trade name "PL-3", manufactured by Fuso Chemical Industry Co., Ltd.) was used, and the same operation as in Example 1 was performed except that the conditions for centrifugation were changed as shown in Table 1, to obtain a silica sol. ..
The secondary electron image observed by the field emission scanning electron microscope of the obtained silica sol is shown in FIG. The evaluation results of the obtained silica sol are shown in Table 1.

A large amount of intermediate products were confirmed in the silica sol obtained in Comparative Example 1 in which no extrafiltration was performed. On the other hand, almost no intermediate products were confirmed in the silica sol obtained in Examples 1 and 2 in which ultrafiltration was performed using an ultrafiltration membrane having a specific molecular weight cut-off. Further, the silica sol obtained in Comparative Examples 2 and 3 obtained by ultrafiltration using an ultrafiltration membrane having a molecular weight cut off from a specific range has a low transmittance and removal of intermediate products by ultrafiltration. The amount was small and intermediate products were confirmed.
It can be seen that the commercially available silica sol (trade name "PL-3", manufactured by Fuso Chemical Industry Co., Ltd.) does not have the problem of the present invention because there are few intermediate products in the first place.

The silica particles obtained by the method for producing silica particles of the present invention and the silica sol obtained by the method for producing silica sol of the present invention can be suitably used for polishing applications, for example, polishing a semiconductor material such as a silicon wafer. Used for polishing electronic materials such as hard disk substrates, polishing in the flattening process when manufacturing integrated circuits (chemical mechanical polishing), polishing synthetic quartz glass substrates used for photomasks and liquid crystals, polishing magnetic disk substrates, etc. It can be particularly preferably used for polishing silicon wafers and chemical mechanical polishing.

Claims (8)

A method for producing silica particles, which comprises the following steps (1) and (2).
Step (1): Hydrolysis reaction and condensation reaction of tetraalkoxysilane to obtain silica sol Step (2): Ultrafiltration of silica sol using an ultrafiltration membrane having a molecular weight cut-off of 5,000 to 80,000. Process to do The method for producing silica particles according to claim 1, wherein the step (2) is performed after the step (1). The method for producing silica particles according to claim 1 or 2, wherein the content of the silica particles in the silica sol is 3% by mass to 50% by mass in 100% by mass of the total amount of the silica sol. The method for producing silica particles according to any one of claims 1 to 3, wherein the average secondary particle size of the silica particles measured by the DLS method is 20 nm to 100 nm. The method for producing silica particles according to any one of claims 1 to 4, which does not include a step of heating to 100 ° C. or higher. A method for producing silica sol, which comprises the method for producing silica particles according to any one of claims 1 to 5. A method for removing an intermediate product in a silica sol, which removes the intermediate product in the silica sol by the method for producing a silica sol according to claim 6. A polishing method for polishing using a polishing composition containing silica particles obtained by the method for producing silica particles according to any one of claims 1 to 5.

Images