JP7618362B2 - Method for producing water-dispersed surface-treated colloidal silica - Google Patents

Description

The present invention relates to a method for producing water-dispersed surface-treated colloidal silica.

As semiconductor devices have become increasingly miniaturized in recent years, colloidal silica, which has small silica particles, is used in processes such as silicon wafer polishing and chemical mechanical polishing (hereinafter referred to as "CMP") of semiconductor devices.

For colloidal silica for CMP processes, high-purity colloidal silica with extremely low metal impurities is required to prevent contamination of silicon wafers and the like. Patent Document 1 discloses a method for producing colloidal silica modified with a silane coupling agent having a cationic group, which has a low content of metal impurities. However, the presence of cationic groups on the silica surface can cause hydrogen bonds to form between the cationic groups and silanol groups, or the cationic groups can act as a condensation catalyst between silanol groups, causing aggregation of silica particles.

In addition, producing colloidal silica having a high silica concentration is preferable not only because it improves production efficiency but also because it improves storage and transportation efficiency and allows the blending of the abrasive used in polishing to be freely adjusted, thereby increasing the degree of freedom in blending.
On the other hand, when colloidal silica is used in a CMP process, there is a problem that the viscosity of the colloidal silica increases when it is reused, and therefore the effectiveness of the colloidal silica as an abrasive cannot be fully demonstrated. Therefore, there is a demand for colloidal silica that is highly concentrated and has a small increase in viscosity over a long period of time.

Therefore, Patent Document 2 discloses a method of adding an inorganic or organic acid dispersant, such as sulfuric acid, nitric acid, or citric acid, to colloidal silica in order to improve the dispersibility of high-concentration colloidal silica. By using these dispersants, it is possible to improve the dispersibility of colloidal silica while preventing the inclusion of metal impurities, but there are cases in which silica aggregates or viscosity increases due to changes in the pH value during long-term storage.

JP 2005-162533 A Patent No. 5270344

Therefore, the present invention aims to provide a water-dispersed colloidal silica that is free of metal impurities and dispersants, has a high concentration, and exhibits little increase in viscosity during long-term storage.

As a result of intensive research conducted by the inventors in order to achieve the above object, it was discovered that by treating a portion of the surface of water-dispersed colloidal silica obtained by the sol-gel method in the presence of a hydrophilic organic solvent with a trifunctional silane compound or the like, and then replacing the dispersion medium with water, it is possible to obtain water-dispersed surface-treated colloidal silica that is free of metal impurities and dispersants, is highly concentrated, and exhibits little increase in viscosity over the long term, and thus the present invention has been completed.

That is, the present invention provides the following method for producing water-dispersed surface-treated colloidal silica.

[1]
A method for producing a water-dispersed surface-treated colloidal silica, comprising the following steps (A1), (A2), and (A3):
Step (A1): A step of obtaining colloidal silica by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), a partial hydrolysis condensate thereof, or a mixture thereof in a mixed liquid containing a hydrophilic organic solvent and water in the presence of a basic substance: Si(OR ¹ ) ₄ (I)
(In the formula, R ¹ independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Step (A2): A step of adding a trifunctional silane compound represented by the following formula (II), a partial hydrolysis condensate thereof or a mixture thereof to the colloidal silica obtained in step (A1) to introduce R ² SiO _3/2 units onto the surface of the colloidal silica, thereby obtaining a surface-treated colloidal silica: R ² Si(OR ³ ) ₃ (II)
(In the formula, ^R2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and ^R3 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Step (A3): A step of replacing the hydrophilic organic solvent in the dispersion medium of the surface-treated colloidal silica obtained in step (A2) with water [2]
The method for producing a water-dispersed surface-treated colloidal silica according to [ ₁ ], wherein the amount of the trifunctional silane compound represented by formula (II), its partial hydrolysis condensate, or a mixture thereof added in the step (A2) is 0.001 to 1 mol per 1 mol of SiO2 units in the colloidal silica obtained in the step (A1).
[3]
The method for producing a water-dispersed, surface-treated colloidal silica according to [1] or [2], wherein the produced water-dispersed, surface-treated colloidal silica has a metal impurity concentration of 0 to 1 ppm by mass.
[4]
The method for producing a water-dispersed, surface-treated colloidal silica according to any one of [1] to [3], wherein the concentration of the hydrophilic organic solvent in the produced water-dispersed, surface-treated colloidal silica is 0 to 1 mass %.
[5]
The method for producing a water-dispersed, surface-treated colloidal silica according to any one of [1] to [4], wherein the produced water-dispersed, surface-treated colloidal silica has a solid content concentration of 15 to 50 mass %.
[6]
The method for producing a water-dispersed, surface-treated colloidal silica according to any one of [1] to [5], wherein the produced water-dispersed, surface-treated colloidal silica has a kinetic viscosity at 25° ^C. of 1 to 100 mm 2 /s.

The water-dispersed surface-treated colloidal silica obtained by the manufacturing method of the present invention is free of metal impurities and dispersants, has a high concentration, and shows little increase in viscosity during long-term storage, making it suitable for use as abrasive grains in the polishing of silicon wafers and the CMP process of semiconductor devices.

The present invention will be described in detail below.
The method for producing a water-dispersed, surface-treated colloidal silica of the present invention is a method for producing a water-dispersed, surface-treated colloidal silica, which includes the following steps (A1), (A2), and (A3).
Step (A1): synthesis step for obtaining colloidal silica; Step (A2): surface treatment step with a trifunctional silane compound; Step (A3): substitution step of dispersion medium. Each step will be described below in order.

Step (A1): Synthesis Step of Obtaining Colloidal Silica This step is a step of obtaining colloidal silica by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), a partial hydrolysis condensate thereof, or a mixture thereof in a mixed liquid containing a hydrophilic organic solvent and water in the presence of a basic substance.
Si(OR ¹ ) ₄ (I)
(In the formula, R ¹ independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)

In the above formula (I), ^R1 is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, and particularly preferably 1 to 2 carbon atoms. Examples of the monovalent hydrocarbon group represented by ^R1 include a methyl group, an ethyl group, a propyl group, a butyl group, and a phenyl group, and are preferably a methyl group, an ethyl group, a propyl group, and a butyl group, and particularly preferably a methyl group and an ethyl group.

Examples of the tetrafunctional silane compound represented by the above formula (I) include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and tetraphenoxysilane, etc., and are preferably tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and are particularly preferably tetramethoxysilane and tetraethoxysilane. In addition, examples of the hydrolysis condensation products of the tetrafunctional silane compound represented by the above formula (I) include methyl silicate, ethyl silicate, etc.

Examples of basic substances include ammonia, dimethylamine, diethylamine, etc., and ammonia and diethylamine are preferred, with ammonia being particularly preferred. These basic substances can be used after dissolving the required amount in water.

There are no particular limitations on the hydrophilic organic solvent as long as it dissolves the compound represented by the above formula (I) and/or its partial hydrolysis condensate, as well as water. Examples of the hydrophilic organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and t-butanol; ethers such as tetrahydrofuran and dioxane; and glycols such as diethylene glycol and dipropylene glycol, with alcohols being preferred. As the number of carbon atoms in the alcohol increases, the particle size of the resulting silica particles increases, so the type of alcohol can be selected depending on the particle size of the desired silica particles.

The amount of water used in this step is preferably 0.5 to 5 moles, more preferably 0.6 to 2 moles, and particularly preferably 0.7 to 1 mole, per mole of the total of hydrocarbyloxy groups of the tetrafunctional silane compound represented by the above formula (I) and/or its partial hydrolysis condensate. When the above-mentioned basic substance is used by dissolving it in water, the water in which the basic substance is dissolved is also included in the "water" in this step.
The ratio of the hydrophilic organic solvent to water is preferably 0.2 to 10, and more preferably 0.3 to 5, in terms of the affinity between the silica particles and the mixed solvent and ease of production.
The amount of the basic substance is preferably 0.01 to 2 mol, and more preferably 0.03 to 0.5 mol, per 1 mol of the total of the hydrocarbyloxy groups of the tetrafunctional silane compound represented by formula (I) and/or its partial hydrolysis condensation product, from the viewpoint of the size of the obtained silica particles.

The reaction conditions for the hydrolysis and condensation in this step are preferably a reaction temperature of 20 to 120°C and a reaction time of 1 to 8 hours, more preferably a reaction temperature of 20 to 100°C and a reaction time of 1 to 6 hours.

The concentration of silica particles in the colloidal silica obtained in step (A1) is preferably 2 to 20% by mass, and more preferably 3 to 10% by mass.

Step (A2): Surface Treatment Step with Trifunctional Silane Compound This step is a step in which a trifunctional silane compound represented by the following formula (II), a partial hydrolysis condensate thereof, or a mixture of these is added to the colloidal silica obtained in step (A1) to introduce ^R2SiO3 _/2 units onto the colloidal silica surface, thereby obtaining a surface-treated colloidal silica.
^R2Si ( ^OR3 ) ₃ (II)
(In the formula, ^R2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and ^R3 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)

In the above formula (II), ^R2 is a monovalent hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and particularly preferably 1 to 3 carbon atoms. Examples of the monovalent hydrocarbon group represented by ^R2 include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, hexyl, octyl, and decyl, and particularly preferably methyl, ethyl, and propyl. In addition, some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as fluorine, chlorine, and bromine atoms, and preferably fluorine atoms.

In the above formula (II), ^R3 is a monovalent hydrocarbon group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, and particularly preferably 1 to 2 carbon atoms. Examples of the monovalent hydrocarbon group represented by ^R3 include a methyl group, an ethyl group, a propyl group, a butyl group, and a phenyl group, and are preferably a methyl group, an ethyl group, a propyl group, and a butyl group, and particularly preferably a methyl group and an ethyl group.

Specific examples of trifunctional silane compounds represented by the above formula (II) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, i-propyltrimethoxysilane, i-propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane, etc.

The amount of the trifunctional silane compound represented by the above formula (II) used is preferably 0.001 to 1 mol, more preferably 0.01 to 0.1 mol, and particularly preferably 0.01 to 0.05 mol, per mol of _SiO2 units (Si atoms derived from the above formula (I)) in the colloidal silica obtained in the step (A1).

In this step (A2), the trifunctional silane compound represented by the above formula (II) is added to the colloidal silica obtained in step (A1), and the surface treatment reaction of the silica with the trifunctional silane compound is carried out under the following reaction conditions. The reaction conditions in this step (A2) are preferably a reaction temperature of 40 to 60°C and a reaction time of 1 to 10 hours, more preferably a reaction temperature of 50 to 60°C and a reaction time of 1 to 8 hours.

The surface-treated colloidal silica obtained in this process preferably has a median diameter (D50) in the volume-based particle size distribution of 5 to 300 nm, more preferably 10 to 150 nm.

Step (A3): Dispersion Medium Replacement Step This step is a step of replacing the hydrophilic organic solvent in the dispersion medium of the surface-treated colloidal silica obtained in step (A2) with water. The hydrophilic organic solvent replaced in step (A3) includes the hydrophilic organic solvent used in step (A1) and volatile by-products such as alcohol generated by condensation.
As a method for the replacement, a heat concentration method in which the surface-treated colloidal silica obtained in the step (A2) is heated and concentrated while adding water in an amount equal to or greater than the amount of the distillate obtained by heating, or ultrafiltration using a filter can be used to easily and economically obtain a water-dispersed surface-treated colloidal silica.

From the viewpoint of the stability of the water-dispersed surface-treated colloidal silica, the amount of water added is preferably 0.5 to 4 times, more preferably 1.8 to 3.0 times by weight, the total amount of the hydrophilic organic solvent used and the amount of the alcohol produced.

The concentration of the hydrophilic organic solvent in the water-dispersed surface-treated colloidal silica obtained in this process is preferably 0 to 1 mass%, more preferably 0 to 100 ppm, and particularly preferably 0 to 10 ppm. The solids concentration in the water-dispersed surface-treated colloidal silica is preferably 15 to 50 mass%, more preferably 30 to 40 mass%.

The manufacturing method of the present invention provides water-dispersed, surface-treated colloidal silica that is low in metal impurities such as sodium, potassium, iron, calcium, magnesium, titanium, nickel, chromium, and copper, and is of high purity. The total concentration of these metal impurities is preferably 0 to 1 ppm by mass, and more preferably 0 to 0.5 ppm by mass, relative to the total mass of the water-dispersed, surface-treated colloidal silica.

Furthermore, the production method of the present invention makes it possible to obtain a water-dispersed surface-treated colloidal silica that exhibits little increase in viscosity during long-term storage and is excellent in stability, without using a dispersant such as sulfuric acid, nitric acid, ammonium sulfate, ammonium nitrate, citric acid, benzoic acid, ammonium benzoate, triammonium citrate, diammonium hydrogen citrate, or tetramethylammonium citrate.
The water-dispersed surface-treated colloidal silica produced by the production method of the present invention preferably has a kinetic viscosity at 25° C. of 1 to 100 mm ² /s, more preferably 5 to 20 mm ² /s. If the viscosity is within this range, it is suitable for use as an abrasive.

The present invention will be specifically described below using examples and comparative examples. Note that the following examples do not limit the present invention in any way. The water-dispersed colloidal silica obtained in each example and comparative example was evaluated as follows, and the results are shown in Table 1.

[Particle size distribution]
The water-dispersed colloidal silica was diluted with methanol so that the silica particles were 0.5% by mass, and the particle size distribution when the diluted colloidal silica was irradiated with ultrasonic waves for 10 minutes was measured using a dynamic light scattering nanotrac particle size distribution measuring device (NanotracWaveII-Ex150, manufactured by Microtrack Bell). Based on the obtained volume-based particle size distribution, the median diameter (D50) and cumulative 95% diameter (D95) were calculated.
The monodispersity of the particles was evaluated based on the CV value calculated by the following formula: The smaller the CV value, the higher the monodispersity of the particles.
CV [%] = (SD/MV) x 100
(In the formula, SD is the standard deviation in the measurement, and MV is the volume mean diameter.)

[Solid content]
1.5 g of the water-dispersed colloidal silica was precisely weighed and placed in an aluminum petri dish, and dried at 105° C. for 3 hours. The residue (X) g was precisely weighed and the silica solids concentration was calculated by the following formula.
Silica solid concentration (mass%)=(X/1.5)×100

[Measurement of remaining methanol amount]
The amount of remaining methanol in the water-dispersed colloidal silica was measured by analyzing the gas phase portion of the vial while heating at 60° C. for 30 minutes using a headspace gas chromatography measuring device set (HP6890 Series GC system, 5975 Mass Selective Detector, G1888 Network headspace Sampler, all manufactured by Agilent Technologies, Inc.).

[Measurement of metal impurity amount]
Metal elements were measured using an ICP optical emission spectrometer (Agilent 5110 ICP-OES, manufactured by Agilent Technologies, Inc.), and the amount of metal impurities in the water-dispersed colloidal silica was calculated.

[Kinematic Viscosity]
The kinetic viscosity of the water-dispersed colloidal silica at 25° C. was measured using a Cannon-Fenske viscometer.
Furthermore, 80 g of water-dispersed colloidal silica was placed in a 100 ml polyethylene bottle, which was then sealed and stored at 60° C., and the kinetic viscosity at 25° C. was measured after 14 days, 30 days, and 60 days.

[Example 1]
Step (A1)
In a 3-liter glass reactor equipped with a stirrer, a dropping funnel and a thermometer, 793.0 g of methanol, 32.1 g of ion-exchanged water and 40.6 g of 28% aqueous ammonia were mixed. The solution was adjusted to 53°C, and while stirring, 646.5 g of tetramethoxysilane and 160.9 g of 5.5% aqueous ammonia were simultaneously dropped, the former over 6 hours and the latter over 4 hours. After the dropwise addition of tetramethoxysilane was completed, stirring was continued for another 0.5 hours to carry out hydrolysis and condensation, thereby obtaining colloidal silica. The concentration of silica particles in this colloidal silica was 15.5% by mass.

Step (A2):
To the colloidal silica obtained in the above step (A1), 6.5 g of methyltrimethoxysilane (0.01 mole equivalent to 1 mole of _SiO2 units in the colloidal silica) was added at 25°C, and the mixture was stirred at 55°C for 1 hour to perform a surface treatment of the colloidal silica.

Step (A3):
1000 g of ion-exchanged water was added to the surface-treated colloidal silica obtained in the step (A2) at 25° C., and then methanol was distilled off. At this time, ion-exchanged water was added dropwise while distilling off methanol so as to keep the volume of the dispersion constant, and the dropwise addition of ion-exchanged water was terminated when the internal temperature reached 100° C. and the pH reached 7.5 or less, thereby obtaining 770 g of water-dispersed surface-treated colloidal silica (i).

[Example 2]
805 g of water-dispersed surface-treated colloidal silica ( _ii ) was obtained in the same manner as in Example 1, except that in the step (A2) of Example 1, the amount of methyltrimethoxysilane added was changed to 32.5 g (equivalent to 0.05 mol per 1 mol of SiO units of the colloidal silica).

[Example 3]
[0123] 783 g of water-dispersed surface-treated colloidal silica ( _{iii) was obtained in the same manner as in Example 1, except that in step (A2) of Example 1, 6.5 g of methyltrimethoxysilane was changed to 32.5 g of propyltrimethoxysilane (equivalent to 0.05 moles per mole of SiO units of the colloidal silica} ).

[Example 4]
795 g of water-dispersed surface-treated colloidal silica ( _iv ) was obtained in the same manner as in Example 1, except that in the step (A2) of Example 1, 6.5 g of methyltrimethoxysilane was changed to 10.5 g of 3,3,3-trifluoropropyltrimethoxysilane (equivalent to 0.01 mole per mole of SiO units of the colloidal silica).

[Example 5]
The same procedure as in Example 1 was conducted except that in the step (A1) of Example 1, the reaction temperature was changed to 36° C., to obtain 775 g of a water-dispersed surface-treated colloidal silica (v).

[Example 6]
The same procedure as in Example 1 was conducted except that in the step (A1) of Example 1, the reaction temperature was changed to 20° C., to obtain 778 g of water-dispersed surface-treated colloidal silica (vi).

[Comparative Example 1]
[0133] 771 g of water-dispersed colloidal silica (vii) was obtained in the same manner as in Example 1, except that the step (A2) was not performed.

[Comparative Example 2]
[0133] 775 g of water-dispersed colloidal silica (viii) was obtained in the same manner as in Example 5, except that the step (A2) was not performed.

[Comparative Example 3]
780 g of water-dispersed colloidal silica was obtained in the same manner as in Example 1, except that the step (A2) was not performed. 0.17 g of ammonium benzoate (660 ppm relative to the mass of the colloidal silica solids) was added to the obtained water-dispersed colloidal silica, and the mixture was stirred at room temperature for 1 hour to obtain water-dispersed colloidal silica (ix).

[Comparative Example 4]
Water-dispersed colloidal silica (x) was obtained in the same manner as in Comparative Example 3, except that the amount of ammonium benzoate added was changed to 0.084 g (330 ppm relative to the mass of the colloidal silica solids).

The above results show that the water-dispersed surface-treated colloidal silica obtained by the manufacturing method of the present invention does not contain metal impurities or dispersants, is highly concentrated, and exhibits little increase in viscosity during long-term storage.

The water-dispersed surface-treated colloidal silica obtained by the manufacturing method of the present invention does not contain metal impurities or dispersants, and even though it is highly concentrated, it shows little increase in viscosity during long-term storage, making it suitable for use as abrasive grains in the polishing of silicon wafers and the CMP process of semiconductor devices.

Claims (5)

A method for producing a water-dispersed surface-treated colloidal silica, comprising the following steps (A1), (A2), and (A3):
Step (A1): A step of obtaining colloidal silica by hydrolyzing and condensing a tetrafunctional silane compound represented by the following formula (I), a partial hydrolysis condensate thereof, or a mixture thereof in a mixed liquid containing a hydrophilic organic solvent and water in the presence of a basic substance: Si(OR ¹ ) ₄ (I)
(In the formula, R ¹ independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Step (A2): A step of adding a trifunctional silane compound represented by the following formula (II), its partial hydrolysis condensate or a mixture of these (not containing any other silane coupling agent) to the colloidal silica obtained in step (A1) in an amount of 0.001 to 1 mole per mole of SiO2 units _in the colloidal silica obtained in step (A1) to introduce ^R2SiO3 _/2 units onto the surface of the colloidal silica, thereby obtaining a surface-treated colloidal silica: ^R2Si ( ^OR3 ) ₃ (II)
(In the formula, ^R2 represents a halogen-substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and ^R3 independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms.)
Step (A3): A step of replacing the hydrophilic organic solvent in the dispersion medium of the surface-treated colloidal silica obtained in step (A2) with water. The method for producing water-dispersed surface-treated colloidal silica according to claim 1, wherein the concentration of metal impurities in the produced water-dispersed surface-treated colloidal silica is 0 to 1 mass ppm. 3. The method for producing a water-dispersed, surface-treated colloidal silica according to claim 1 , wherein the concentration of the hydrophilic organic solvent in the produced water-dispersed, surface-treated colloidal silica is 0 to 1 mass %. 4. The method for producing a water-dispersed, surface-treated colloidal silica according to any one of claims 1 to 3 , wherein the produced water-dispersed, surface-treated colloidal silica has a solid content concentration of 15 to 50 mass %. 5. The method for producing a water-dispersed, surface-treated colloidal silica according to claim 1, wherein the produced water-dispersed, surface-treated colloidal silica has a kinetic viscosity at 25° C. of 1 to 100 mm ² /s.