JP2022015206A - Apparatus for producing silica particle, method for producing silica particle, method for producing silica sol, method for suppressing intermediate product in silica sol, and polishing method - Google Patents

Abstract

To provide an apparatus and a method for producing silica particles for obtaining silica sol having few intermediate products, and to provide a method for producing silica sol in order to obtain silica sol having few intermediate products.SOLUTION: An apparatus for producing silica particles according to this invention includes a reaction tank, a solvent/dispersion medium supply tank, and a circulation type filtration device. A method for producing silica particles of the invention uses the apparatus for producing silica particles. A method for producing a silica sol of the invention includes the method for producing silica particles. A method of suppressing intermediate products in silica sol according to this invention includes the removal of intermediate products in silica sol by means of the above-mentioned method for producing silica sol. And a polishing method of the present invention includes polishing using a polishing composition containing silica particles obtained by the method for producing the silica particles.SELECTED DRAWING: Figure 1

Description

The present invention comprises an apparatus for producing silica particles, a method for producing silica particles using the apparatus for producing silica particles, a method for producing a silica sol including a method for producing the silica particles, a method for suppressing intermediate products, and the obtained silica. The present invention relates to a polishing method using particles.

As a method for 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. In), the surface condition thereof greatly affects the semiconductor characteristics, so that the surfaces 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 (hummed silica, etc.), by deionization of alkali silicate such as water glass, hydrolysis reaction and condensation reaction of alkoxysilane (generally, "" It is called "sol-gel method". Hereinafter, it is described as "hydrolysis reaction / condensation reaction") and the like.

Many studies have been made on the method for producing a silica sol containing colloidal silica. For example, Patent Documents 1 and 2 disclose a method for producing a silica sol by a hydrolysis reaction / condensation reaction of alkoxysilane.

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

Intermediate products may be generated during or after the production of silica sol by hydrolysis / condensation reaction of alkoxysilane. This intermediate product is considered to be silica remaining as a solid with insufficient growth or silica precipitated from dissolved silicic acid after production. In addition, when synthesizing silica particles by hydrolysis / condensation reaction of alkoxysilane, it is generally necessary to remove alcohol and ammonia by distillation or the like, but the obtained silica may be redissolved and precipitated. It is considered that this precipitated silica is also contained in the intermediate product.

Since such an intermediate product is considered to be silica having a lower degree of condensation than the desired colloidal silica, the obtained polishing liquid deteriorates the mechanical properties of the colloidal silica in the obtained silica sol and lowers the polishing rate. It adversely affects the polishing properties of silica. Further, since silica having a low degree of condensation is contained in the obtained polishing liquid, the removability from the object to be polished after polishing with this polishing liquid is inferior. Further, problems such as aggregation, sedimentation, thickening, and gelation of silica in the silica sol and the polishing liquid are likely to occur, and the obtained silica sol and the obtained polishing liquid show unstable behavior and are inferior in storage stability.
Further, purification by filtration may be performed at the time of preparation of the polishing liquid, but since the silica sol containing an intermediate product has a high viscosity, there is a problem that filtration takes time or filtration cannot be performed.

The method for producing a silica sol by the hydrolysis reaction / condensation reaction of alkoxysilane disclosed in Patent Documents 1 and 2 has not been studied at all for dealing with such an intermediate product, and is intermediate depending on the production apparatus and production conditions. A silica sol containing a large amount of product will be obtained. A polishing liquid using a silica sol containing a large amount of intermediate products is inferior in polishing characteristics and inferior in the removability of the polishing liquid from the object to be polished after polishing; inferior in the storage stability of the obtained silica sol and the polishing liquid; The viscosity of the silica sol to be obtained is high, and the removal of intermediate products by filtration is also inferior;

As described above, in the conventional method, a silica sol containing a large amount of intermediate products can be obtained, but since the intermediate products in the silica sol have been used as a polishing liquid without being removed as they are, the polishing characteristics and storage stability of the obtained polishing liquid have been obtained. I couldn't say that the sex was enough. Moreover, since the silica sol containing the intermediate product has a high viscosity, it cannot be said that the handleability is sufficient.

The present invention has been made in view of such problems, and an object of the present invention is to provide an apparatus and a method for producing silica particles for obtaining a silica sol having a small amount of intermediate products and a low viscosity. be. Another object of the present invention is to provide a method for producing a silica sol for obtaining a silica sol having a small amount of intermediate products and a low viscosity.

As a result of diligent studies, the present inventors have obtained a silica sol having a small amount of intermediate products and a low viscosity by using a silica particle manufacturing apparatus including a reaction tank, a solvent / dispersion medium supply tank, and a circulation type filtration device. It was found that it could be obtained, and the present invention was completed.

That is, the gist of the present invention is as follows.
[1] A silica particle manufacturing apparatus including a reaction tank, a solvent / dispersion medium supply tank, and a circulation type filtration device.
[2] The silica particle manufacturing apparatus according to [1], wherein the circulation type filtration device includes an ultrafiltration membrane and a circulation pump.
[3] The apparatus for producing silica particles according to [2], wherein the ultrafiltration membrane has a molecular weight cut-off of 1,000 to 100,000.
[4] The apparatus for producing silica particles according to any one of [1] to [3], wherein the reaction tank is a reaction tank whose inner surface is coated with a resin.
[5] A method for producing silica particles, which comprises producing silica particles using the silica particle producing apparatus according to any one of [1] to [4].
[6] The method for producing silica particles according to [5], wherein the obtained silica particles have an average secondary particle diameter of 20 nm to 100 nm measured by the DLS method.
[7] The method for producing silica particles according to [5] or [6], which does not include a step of heating to 100 ° C. or higher.
[8] A method for producing silica sol, which comprises the method for producing silica particles according to any one of [5] to [7].
[9] The method for producing silica sol according to [8], wherein the content of silica particles in the obtained silica sol is 3% by mass to 50% by mass in 100% by mass of the total amount of silica sol.
[10] A method for suppressing 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 [8] or [9].
[11] 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 [5] to [7].

The silica particle manufacturing apparatus, the silica particle manufacturing method, and the silica sol manufacturing method of the present invention have excellent polishing properties of the polishing liquid obtained by using the silica sol, because the amount of intermediate products of the obtained silica sol is small and the viscosity is low. It is also excellent in removing the polishing liquid from the object to be polished after polishing. In addition, the obtained silica sol and the obtained polishing liquid are excellent in storage stability and handleability.

It is a schematic diagram which shows one Embodiment of the manufacturing apparatus of the silica particle of this invention. It is a figure which shows the secondary electron image observed by the FE-SEM of the silica sol obtained in the comparative example 1. FIG. It is a figure which shows the secondary electron image observed by the FE-SEM of the silica sol obtained in Example 1. FIG. It is a figure which shows the secondary electron image observed by the FE-SEM of the silica sol obtained in Example 2. FIG.

The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and can be variously modified and carried out within the scope of the gist thereof. In addition, when the expression "-" is used in this specification, it is used as an expression including numerical values or physical property values before and after the expression.

(Silica particle manufacturing equipment)
The apparatus for producing silica particles of the present invention is a reaction tank (a tank for reacting a reaction liquid containing a supplied solvent and / or a dispersion medium, a raw material, and a catalyst to obtain a silica sol which is a dispersion liquid of the silica particles) and a solvent. -Dispersion medium supply tank (tank for storing the solvent and / or dispersion medium supplied to the reaction tank), and circulation type filtration device (reaction liquid in the reaction tank is extracted, filtered to remove the filtrate, and in the reaction tank. Includes a device for returning the filtered residual liquid to.

FIG. 1 is a schematic view showing an embodiment of the silica particle manufacturing apparatus of the present invention. Hereinafter, the silica particle manufacturing apparatus of the present invention will be described with reference to FIG. 1, but the silica particle manufacturing apparatus of the present invention is not limited to that shown in FIG.

The silica particle manufacturing apparatus shown in FIG. 1 includes a reaction tank 10, a solvent / dispersion medium supply tank 21, a raw material supply tank 22, a catalyst supply tank 23, and a circulation type filtration device 30. The solvent / dispersion medium supply tank 21, the raw material supply tank 22, and the catalyst supply tank 23 are connected so that the solvent / dispersion medium, the raw material, and the catalyst can be supplied to the reaction tank 10, respectively. The reaction tank 10 and the circulation type filtration device 30 are capable of extracting the liquid in the reaction tank 10, filtering with the circulation type filtration device 30 to remove the filtrate, and returning the filtered residual liquid to the reaction tank 10 again. It is connected. The circulation type filtration device 30 includes an ultrafiltration membrane 31 and a circulation pump 32.

The reaction tank 10 is a tank for reacting a reaction liquid containing a supplied solvent and / or a dispersion medium, a raw material, and a catalyst to obtain a silica sol which is a dispersion liquid of silica particles.

Since the reaction tank 10 can suppress the mixing of metal impurities and increase the purity of the silica particles in the obtained silica sol, it is preferable that the inner surface (contact surface) of the tank is coated with a resin.
Examples of the resin of this coating layer include fluororesin, epoxy resin, phenol resin and the like. Among these resins, fluororesins are preferable, and tetrafluoroethylene resins are more preferable because they can suppress the mixing of metal impurities and further increase the purity of silica particles.

The solvent / dispersion medium supply tank 21 is a tank for storing the solvent and / or the dispersion medium to be supplied to the reaction tank 10. The solvent / dispersion medium will be described later.
It is preferable to have a regulating valve (not shown) between the solvent / dispersion medium supply tank 21 and the reaction tank 10 so that the amount of the solvent / dispersion medium supplied to the reaction tank 10 can be adjusted. In particular, when the liquid in the reaction tank 10 is taken out and filtered and circulated by the circulation type filtration device 30, the filtrate containing the solvent / dispersion medium is discharged to the outside of the system, so that the liquid of the solvent / dispersion medium in the reaction tank 10 is discharged. It is preferable to adjust with a regulating valve so that the fluctuation of the amount can be maintained within 20%.

As shown in FIG. 1, the silica particle manufacturing apparatus of the present invention preferably has a raw material supply tank 22.
The raw material supply tank 22 is a tank for storing the raw materials to be supplied to the reaction tank 10. Raw materials typified by tetraalkoxysilane will be described later.

As shown in FIG. 1, the silica particle manufacturing apparatus of the present invention preferably has a catalyst supply tank 23.
The catalyst supply tank 23 is a tank for storing the catalyst to be supplied to the reaction tank 10. The catalyst will be described later.
It is preferable to have a regulating valve (not shown) between the catalyst supply tank 23 and the reaction tank 10 so that the amount of the catalyst supplied to the reaction tank 10 can be adjusted. In particular, it is preferable to adjust the catalyst concentration of the reaction solution in the reaction vessel 10 so that the hydrolysis reaction / condensation reaction can be promoted by the catalyst supply amount adjusting valve.

The circulation type filtration device 30 is a device for extracting the reaction liquid in the reaction tank 10, filtering it to remove the filtrate, and returning the filtered residual liquid to the reaction tank 10.
The circulation type filtration device 30 preferably has an ultrafiltration membrane 31 because it can efficiently remove intermediate products while suppressing the removal of necessary silica particles. The ultrafiltration membrane 31 will be described later.
The circulation type filtration device 30 preferably has a circulation pump 32 because the filtration can be repeated a required number of times.

(Manufacturing method of silica particles)
In the method for producing silica particles of the present invention, silica particles are produced using the silica particle producing apparatus of the present invention. The method for producing silica particles of the present invention preferably includes the following steps (1) and (2).
Step (1): Hydrolysis reaction / condensation reaction of tetraalkoxysilane in a reaction tank to obtain silica sol Step (2): Step of filtering silica sol with a circulation type filtration device.

(Step (1))
Step (1) is a step of hydrolyzing and condensing tetraalkoxysilane in a reaction vessel to obtain a silica sol.
Since the method for producing silica particles of the present invention can produce silica particles without using a raw material containing a metal component by including step (1), it is possible to reduce the metal impurity content of the obtained silica sol. Can be done.
As the reaction tank, it is preferable to use the above-mentioned reaction tank.

Examples of the tetraalkoxysilane include tetraalkoxysilanes having an alkoxy group having 1 to 12 carbon atoms such as 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 unlikely to remain, the productivity is excellent, and a stable silica sol can be easily obtained. More preferred is methoxysilane.

As the raw material for producing 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, it is preferable to use tetraalkoxysilane, and the production of silica particles is preferable. It is preferable that the amount of tetraalkoxysilane is 50% by mass or more and the amount of raw materials other than tetraalkoxysilane is 50% by mass or less, and the amount of tetraalkoxysilane is 90% by mass or more and other than tetraalkoxysilane. It is more preferable that the raw material of silane is 10% by mass or less.

Examples of the solvent / dispersion medium used in the reaction for performing the hydrolysis reaction / condensation reaction include alcohols such as water, methanol, ethanol, propanol, isopropanol and ethylene glycol, ketones such as acetone and methyl ethyl ketone, and ethyl acetate. Examples include ester. As these solvents / dispersion media, one kind may be used alone, or two or more kinds may be used in combination. Among these solvents and dispersion media, those used in the hydrolysis reaction / condensation reaction and those used 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. ..

The hydrolysis reaction / condensation reaction may be carried out in the presence of a catalyst or in the absence of a catalyst, but it is preferably carried out in the presence of a catalyst because the hydrolysis reaction / 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. , Ammonia is more preferred.

(Relationship between process (1) and process (2))
The step (2) may be carried out during the step (1) or after the step (1), but the silica remains as a solid with insufficient growth, and the silica precipitated from the dissolved silicic acid after the production. Since it is possible to efficiently remove intermediate products such as silica which have been redissolved and precipitated, it is preferable to carry out after the step (1).

Further, by performing the step (2) after the step (1), it is possible to combine the removal of unnecessary components of the silica sol and the addition of the necessary components described later in the step (2), and the productivity of the silica sol is excellent. , Can contribute to energy saving.

(Step (2))
The step (2) is a step of filtering the silica sol by a circulation type filtration device.
By including the step (2), the method for producing silica particles of the present invention can efficiently remove intermediate products, reduce the viscosity of the silica sol, and enhance the storage stability of the silica sol.

In the present specification, the intermediate product is the tip of an arrow in FIG. 2 in an image of FE-SEM taken with a field emission scanning electron microscope (FE-SEM) at a magnification of 100,000 to 200,000 times. The part that looks like.
This intermediate product is obtained by redissolving silica that remains as a solid with insufficient growth during or after the production of silica sol by hydrolysis / condensation reaction of alkoxysilane, silica precipitated from dissolved silicic acid after production, and so on. It is considered to be precipitated silica or the like.

Filtration is preferably limited filtration because it can efficiently remove intermediate products while suppressing the removal of necessary silica particles.
The feature of ultrafiltration is that the components that pass through the pores by filtration with a filter paper or filter having a pore size on the order of microns, which is usually used, can be fractionated by molecular weight.

The fractional molecular weight of the ultrafiltration membrane used for ultrafiltration is preferably 1,000 to 100,000, more preferably 5,000 to 80,000, and even more preferably 7,000 to 60,000. When the molecular weight cut-off of the ultrafiltration membrane is 1,000 or more, the permeability is excellent. Further, when the molecular weight cut-off of the ultrafiltration membrane is 100,000 or less, the selectivity is excellent.

The ultrafiltration method may be a dead-end method or a cross-flow method, but the productivity of the silica sol is excellent, the filtration can be easily repeated as many times as necessary, and the ultrafiltration membrane can be used. The cross-flow method is preferable because it can be recycled.
The dead-end method is a method of filtering with a flow of liquid perpendicular to the surface of the filtration membrane.
The cross-flow method is a method of filtering with a flow of liquid parallel to the surface of the filtration membrane.

Since the cross-flow type ultrafiltration membrane is excellent in mechanical strength, a module having a hollow fiber membrane built in the housing is preferable.
The material of the hollow fiber membrane is preferably polyacrylonitrile because it has excellent mechanical strength.
Polysulfone is preferable as the material of the housing because it has excellent mechanical strength.

The average permeation amount of the cross-flow type ultrafiltration membrane is preferably 5 kg / m ² / hour or more, and more preferably 6 kg / m ² / hour to 30 kg / m ² / hour because of its excellent productivity and filterability. ..

The cross-flow type ultrafiltration membrane can be regenerated and reused by backwashing. When the average permeation amount of the cross-flow type ultrafiltration membrane is less than 5 kg / m ² / hour, it is preferable to backwash the ultrafiltration membrane.

(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 obtained 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 according to the present invention, the intermediate product is suppressed by adopting the step (2). Since the effect of suppressing intermediate products expected in the pressure heat treatment is reduced, it is preferable not to include a step of heating to 150 ° C. or higher, and more preferably not to include a step of heating to 100 ° C. or higher.

(Physical characteristics of silica particles)
The average primary particle diameter of the silica particles produced by the present invention (hereinafter, may be referred to as "silica particles of the present invention") is preferably 5 nm to 100 nm, more preferably 10 nm to 60 nm. When the average primary particle diameter of the silica particles is 5 nm or more, the storage stability of the silica sol is excellent. Further, when the average primary particle diameter 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 the silica particles is measured using an automatic specific surface area measuring device, and the average primary particle diameter is calculated using the following formula (1).
Average primary particle diameter (nm) = 6000 / (specific surface area (m ² / g) x density (g / cm ³ ))
... (1)

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

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

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

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

The cv value of the silica particles of the present invention 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 removal property 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 of the present invention 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 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 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 from the average primary particle diameter measured by the above-mentioned measuring method and the average secondary particle diameter measured by the above-mentioned measuring method by using the following formula (3).
Association ratio = average secondary particle diameter / average primary particle diameter ... (3)

The surface silanol group density of the silica particles of the present invention is preferably 0.1 pieces / nm ² to 10 pieces / nm ² , more preferably 0.5 pieces / nm ² to 7.5 pieces / nm ² , and 2.0. Pieces / nm ² to 7.0 pieces / nm ² are 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 pieces / 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 the 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 make the liquid volume 90 mL. In an environment of 25 ° C, add a 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 the sodium chloride, and finally the test. Add pure water 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. Titration A (mL) of the aqueous solution is measured.
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: Titration (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: Potency 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 × NA) / (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.
_NA : Avogadro's number (pieces / mol)
M: Amount of silica particles (1.5 g)
_SBET : Specific surface area of silica particles measured when calculating the average primary particle size (m ² / g)

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 / condensation reaction of the alkoxysilane.

The metal impurity content of the silica particles of the present invention 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 the silica particles is measured by high frequency inductively coupled plasma mass spectrometry (ICP-MS). Specifically, weigh accurately the silica sol containing 0.4 g of silica particles, add sulfuric acid and hydrofluoric acid, heat, dissolve, and evaporate, and add pure water to the remaining sulfuric acid droplets so that the total amount is exactly 10 g. Prepare a test solution and 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 the metal impurity content. do.

The metal impurity content of the silica particles can be 5 ppm or less by performing a hydrolysis reaction / condensation reaction using alkoxysilane as a main raw material to obtain silica particles.
In particular, in the present invention, by using a reaction tank provided with a resin coating layer on the inner surface of the tank as an apparatus for producing silica particles, the metal impurity content of the silica particles can be significantly reduced.
In the method by deionization of 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 the shapes of these 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.

Since the silica particles of the present invention are excellent in mechanical strength and storage stability, it is preferable that they do not have pores.
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 of the present invention are excellent in mechanical strength and storage stability, it is preferable to have an alkoxysilane condensate as a main component, and more preferably to have 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 a method for producing silica particles of the present invention.

As the silica sol produced by the method for producing the silica sol of the present invention (hereinafter, may be referred to as “the silica sol of the present invention”), the dispersion liquid of the silica particles obtained by the method for producing the silica particles of the present invention is used as it is. Alternatively, it may be produced by removing unnecessary components from the components in the obtained dispersion and adding necessary components.

The silica sol of the present invention preferably contains silica particles and a solvent / dispersion medium.
Examples of the solvent / dispersion medium in the silica sol include water, methanol, ethanol, propanol, isopropanol, and alcohols such as ethylene glycol. 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 silica particles in the silica sol of the present invention is preferably 3% by mass to 50% by mass, more preferably 4% by mass to 40% by mass, and further preferably 5% by mass to 30% by mass in 100% by mass of the total amount of silica sol. preferable. 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 of the present invention is preferably 50% by mass to 97% by mass, more preferably 60% by mass to 96% by mass, and 70% by mass to 95% by mass in the total amount of the silica sol of 100% by mass. Is more preferable. 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 90% 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 to 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, the silica sol of the present invention is an oxidizing agent, a preservative, an antifungal agent, a pH adjuster, a pH buffering agent, and a surfactant, as necessary, as long as the performance is not impaired. , Chelating agents, antibacterial / biocide and the like.
In particular, since the silica sol is excellent in storage stability, it is preferable to include an antibacterial / biocide in the silica sol.

Examples of antibacterial / biological agents 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.
Antibacterial and biocidal agents also include those generally referred to as fungicides.

The content of the antibacterial / biocide in the silica sol of the present invention 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 of the present invention 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 long-term storage stability of the silica sol is excellent. Further, when the pH of the silica sol is 8.0 or less, the aggregation of silica particles can be suppressed, and the dispersion stability of the silica sol is excellent.
The pH of the silica sol can be set in a desired range by adding a pH adjuster.

The viscosity of the silica sol of the present invention is preferably 30 mPa · s or less, more preferably 0 mPa · s to 20 mPa · s, and even more preferably 1 mPa · s to 10 mPa · s. When the viscosity of the silica sol is 30 mPa · s or less, the silica sol is excellent in handleability, filterability, and storage stability, and the polishing composition can be easily prepared.
The viscosity of the silica sol shall be a value measured using an E-type viscometer under the conditions of 25 ° C. and a shear rate of 150 / sec.

(Method of suppressing intermediate products in silica sol)
The method for suppressing an intermediate product in the silica sol of the present invention is a method for removing the intermediate product in the silica sol by the method for producing the silica sol of the present invention, and the specific method is as described above.

(Polishing 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 of the present invention and a 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 water affinity, and the functional group having a high water affinity 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, hydroxypropylmethyl 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, a cellulose derivative is preferable because it has a high affinity with the surface silanol group of the silica particles and acts synergistically to give good hydrophilicity to the surface of the object to be polished. 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 a 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 the silica sol and the water-soluble polymer of the present invention, the polishing composition may be a basic compound, a polishing accelerator, a surfactant, a hydrophilic compound, an antiseptic, or an antiseptic, as necessary, as long as the performance is not impaired. It may contain other components such as a mold, 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 is represented by a silicon wafer. 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 speed of the object to be polished represented by a 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, the 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, a polishing composition is dropped onto the polishing pad, and the surface of the silicon wafer is polished.

(Use)
The silica particles obtained by the apparatus for producing silica particles of the present invention, 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 a silica sol of the present invention are suitably used for polishing applications. It can be used, for example, for polishing semiconductor materials such as silicon wafers, polishing electronic materials such as hard disk substrates, polishing in the flattening process when manufacturing integrated circuits (chemical mechanical polishing), photomasks and liquid crystals. It can be used for polishing synthetic quartz glass substrates, polishing magnetic disk substrates, and the like. Above all, 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 Examples and Comparative Examples 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 following formula (1) was used, the density was set to 2.2 g / cm ³ , and the average primary particle size was calculated.
Average primary particle diameter (nm) = 6000 / (specific surface area (m ² / g) x density (g / cm ³ ))
... (1)

(Measurement of average secondary particle size and cv value)
The silica sol obtained in Examples and Comparative Examples 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). 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 diameter and average secondary particle diameter, the association ratio was calculated using the following formula (3).
Association ratio = average secondary particle diameter / average primary particle diameter ... (3)

(Measurement of surface silanol group density)
The amount of the silica sol obtained in Examples and Comparative Examples 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, add 30 g of sodium chloride and gradually add pure water to completely dissolve the sodium chloride, and finally the total volume of the test solution becomes 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 titration device "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 (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 was calculated using the following formula (5).
V = (A × f × 100 × 1.5) / (W × C) ・ ・ ・ (4)
A: Titration (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: Potency 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 × NA) / (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.
_NA : Avogadro's number (pieces / mol)
M: Amount of silica particles (1.5 g)
_SBET : Specific surface area of silica particles measured when calculating the average primary particle size (m ² / g)

(Viscosity of silica sol)
The viscosities of the silica sol obtained in Examples and Comparative Examples were measured using an E-type viscometer under the conditions of 25 ° C. and a shear rate of 150 / sec.

(Evaluation of intermediate products in silica sol)
For the silica sol obtained in Examples and Comparative 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 and a magnification of 150,000 times, from 100 to 200. 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 indicators. The intermediate product refers to a portion that looks like the tip of an arrow 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 reaction tank whose inner surface is coated with tetrafluoroethylene resin, a solvent / dispersion medium supply tank, a raw material supply tank and a catalyst supply tank are prepared, and the concentration of water is 13% by mass and the concentration of ammonia is 1.2% by mass. A solution in which methanol, pure water, and ammonia were mixed was charged into the reaction vessel so as to be. Further, a solution prepared by mixing tetramethoxysilane and methanol at a ratio of 2.3: 1 (volume ratio) was charged into the raw material supply tank. Further, a 3.8 mass% aqueous ammonia solution was charged into the catalyst supply tank. Pure water was charged in the solvent / dispersion medium supply tank.
While maintaining the temperature of the reaction solution at 40 ° C., the solution charged in the reaction tank, the solution charged in the raw material supply tank, and the solution charged in the catalyst supply tank were set to 0.77: 1: 0.31 (volume ratio). , The solution charged in the raw material supply tank and the solution charged in the catalyst supply tank were dropped into the reaction tank at a uniform rate for 287 minutes to obtain a dispersion liquid of silica particles.
The temperature of the obtained dispersion liquid of silica particles is raised while adjusting the amount of the liquid by adding pure water charged in the solvent / dispersion medium supply tank so that the content of the silica particles becomes about 20% by mass. Then, methanol and ammonia were removed to obtain a silica sol having a silica particle content of about 20% by mass.

The obtained silica particles had an average primary particle diameter of 33.8 nm, an average secondary particle diameter of 61.8 nm, a cv value of 27.4%, an association ratio of 1.83, and a surface silanol group density of 6.6 / nm ² . The obtained silica sol had a viscosity of 44.6 mPa · s.
The secondary electron image observed by the field emission scanning electron microscope (FE-SEM) of the obtained silica sol is shown in FIG.
The evaluation results of the obtained silica sol are shown in Table 1.

[Example 1]
A reaction tank whose inner surface is coated with tetrafluoroethylene resin, a solvent / dispersion medium supply tank, a raw material supply tank, a catalyst supply tank, a circulation pump and an ultrafiltration membrane are prepared, and the water concentration is 13% by mass and ammonia. A solution in which methanol, pure water, and ammonia were mixed was charged into the reaction vessel so that the concentration of the water was 1.2% by mass. Further, a solution prepared by mixing tetramethoxysilane and methanol at a ratio of 2.3: 1 (volume ratio) was charged into the raw material supply tank. Further, a 3.8 mass% aqueous ammonia solution was charged into the catalyst supply tank. Pure water was charged in the solvent / dispersion medium supply tank.
While maintaining the temperature of the reaction solution at 40 ° C., the solution charged in the reaction tank, the solution charged in the raw material supply tank, and the solution charged in the catalyst supply tank were set to 0.77: 1: 0.31 (volume ratio). , The solution charged in the raw material supply tank and the solution charged in the catalyst supply tank were dropped into the reaction tank at a uniform rate for 287 minutes to obtain a dispersion liquid of silica particles.
The obtained dispersion liquid of silica particles is circulated once with a circulation pump while adding pure water charged in a solvent / dispersion medium supply tank to keep the liquid volume constant, and an ultrafiltration membrane (trade name). Filtration with an average permeation amount of 5 g / m ² / hour by "Microza Pencil Module ACP-0053D", manufactured by Asahi Kasei Co., Ltd., fractional molecular weight 13,000, hollow fiber membrane material: polyacrylonitrile, housing material: polysulfone). did.
The temperature of the obtained dispersion liquid of silica particles is raised while adjusting the amount of the liquid by adding pure water charged in the solvent / dispersion medium supply tank so that the content of the silica particles becomes about 20% by mass. Then, methanol and ammonia were removed to obtain a silica sol having a silica particle content of about 20% by mass.

The obtained silica particles had an average primary particle diameter of 36.8 nm, an average secondary particle diameter of 66.9 nm, a cv value of 33.6%, an association ratio of 1.82, and a surface silanol group density of 7.3 particles / nm ² . The obtained silica sol had a viscosity of 8.4 mPa · s.
The secondary electron image observed by FE-SEM of the obtained silica sol is shown in FIG.
The evaluation results of the obtained silica sol are shown in Table 1.

[Example 2]
A reaction tank whose inner surface is coated with tetrafluoroethylene resin, a solvent / dispersion medium supply tank, a raw material supply tank, a catalyst supply tank, a circulation pump and an ultrafiltration membrane are prepared, and the water concentration is 13% by mass and ammonia. A solution in which methanol, pure water, and ammonia were mixed was charged into the reaction vessel so that the concentration of the water was 1.2% by mass. Further, a solution prepared by mixing tetramethoxysilane and methanol at a ratio of 2.3: 1 (volume ratio) was charged into the raw material supply tank. Further, a 3.8 mass% aqueous ammonia solution was charged into the catalyst supply tank. Pure water was charged in the solvent / dispersion medium supply tank.
While maintaining the temperature of the reaction solution at 40 ° C., the solution charged in the reaction tank, the solution charged in the raw material supply tank, and the solution charged in the catalyst supply tank were set to 0.77: 1: 0.31 (volume ratio). , The solution charged in the raw material supply tank and the solution charged in the catalyst supply tank were dropped into the reaction tank at a uniform rate for 287 minutes to obtain a dispersion liquid of silica particles.
The obtained dispersion liquid of silica particles is circulated three times with a circulation pump while adding pure water charged in a solvent / dispersion medium supply tank to keep the liquid volume constant, and an ultrafiltration membrane (trade name). Filtration with an average permeability of 7 g / m ² / hour by "Microza Pencil Module AHP-0013", manufactured by Asahi Kasei Co., Ltd., fractional molecular weight of 50,000, hollow fiber membrane material: polyacrylonitrile, housing material: polysulfone). did.
The temperature of the obtained dispersion liquid of silica particles is raised while adjusting the amount of the liquid by adding pure water charged in the solvent / dispersion medium supply tank so that the content of the silica particles becomes about 20% by mass. Then, methanol and ammonia were removed to obtain a silica sol having a silica particle content of about 20% by mass.

The obtained silica particles had an average primary particle diameter of 35.0 nm, an average secondary particle diameter of 61.6 nm, a cv value of 28.0%, an association ratio of 1.76, and a surface silanol group density of 6.9 particles / nm ² . The obtained silica sol had a viscosity of 5.5 mPa · s.
The secondary electron image observed by FE-SEM of the obtained silica sol is shown in FIG.
The evaluation results of the obtained silica sol are shown in Table 1.

As can be seen from Table 1, the silica sol of Comparative Example 1 produced without using the circulation type filtration device was produced by circulating filtration of the obtained dispersion of silica particles using the circulation type filtration device. The silica sol of Example 1 and Example 2 had a low viscosity.
Further, as can be seen from FIGS. 2 to 4, the silica sol of Comparative Example 1 produced without using the circulation type filtration device was obtained by using the circulation type filtration device while the intermediate product was confirmed. No intermediate product was confirmed in the silica sol of Example 1 and Example 2 produced by circulating filtration of the dispersion liquid of the silica particles.
Therefore, the silica sol obtained by the silica particle manufacturing apparatus of the present invention has a small amount of intermediate products and a low viscosity, so that the obtained polishing liquid has excellent polishing characteristics, and the polishing liquid from the object to be polished after polishing is excellent. It is expected to be excellent in removability, storage stability and handleability of the obtained silica sol and polishing liquid.

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

10 Reaction tank 21 Solvent / dispersion medium supply tank 22 Raw material supply tank 23 Catalyst supply tank 30 Circulation type filtration device 31 Ultrafiltration membrane 32 Circulation pump

Claims (11)

A device for producing silica particles, including a reaction tank, a solvent / dispersion medium supply tank, and a circulation type filtration device. The silica particle manufacturing apparatus according to claim 1, wherein the circulation type filtration device includes an ultrafiltration membrane and a circulation pump. The apparatus for producing silica particles according to claim 2, wherein the ultrafiltration membrane has a molecular weight cut-off of 1,000 to 100,000. The apparatus for producing silica particles according to any one of claims 1 to 3, wherein the reaction tank is a reaction tank whose inner surface is coated with a resin. A method for producing silica particles, which comprises producing silica particles using the silica particle producing apparatus according to any one of claims 1 to 4. The method for producing silica particles according to claim 5, wherein the obtained silica particles have an average secondary particle diameter of 20 nm to 100 nm measured by the DLS method. The method for producing silica particles according to claim 5 or 6, 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 5 to 7. The method for producing silica sol according to claim 8, wherein the content of silica particles in the obtained silica sol is 3% by mass to 50% by mass in 100% by mass of the total amount of silica sol. A method for suppressing 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 8 or 9. 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 5 to 7.

Images