JP2005047727A - Silica particle and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particle comprising a fine particle of silica hardly causing the problems of pollution when used for polishing a silicon wafer or a substrate for a hard disk and exhibiting more rapid polishing rate than that of the conventional amorphous silica when used for polishing. <P>SOLUTION: The silica particle comprises cristobalite having 50-300 nm primary particle diameter. In the method of manufacturing the silica particle, silica is hydrothermally treated at 250-350°C in an aqueous solution containing fluorine ion and/or 0.01-0.5 M concentration hydroxyl ion. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to silica particles suitable as an abrasive for polishing silicon wafers and polishing hard disk substrates, and a method for producing the same.
[0002]
[Prior art]
Fine amorphous silica (SiO ₂ ) particles having a primary particle size of 50 nm to 300 nm are known as fumed silica (consisting of amorphous SiO ₂ particles) and the like. Dispersed materials are known as colloidal silica (see, for example, Patent Document 1), which is an abrasive that requires extremely small surface roughness, such as for polishing silicon wafers and polishing hard disk substrates. It is also used as a resin filler. Then, colloidal silica, for example, be prepared by the SiO ₂ to hydrothermal treatment at a temperature range of 120 ° C. or higher 180 ° C. or less (e.g., see Patent Document 1.). Fumed silica is produced by burning silicon tetrachloride.
[0003]
These amorphous silica particles are known to cause less contamination problems when used for polishing electronic materials such as silicon wafers and hard disk substrates, and are excellent in that respect. However, there is a problem that the polishing rate is slow, and improvement of this point has been demanded.
[0004]
[Patent Document 1]
JP-A-2002-338951
[Problems to be solved by the invention]
An object of the present invention is to provide particles made of silica fine particles and exhibiting a high polishing rate when used as an abrasive.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve such problems, the present inventor used fine particles comprising cristobalite, which is one of silica crystal phases, having a primary particle size in the range of 50 nm to 300 nm as an abrasive. It has been found that a faster polishing rate can be obtained than when conventional fine particles made of amorphous silica are used, and the fine silica particles made of cristobalite have a silica content of fluorine ions and / or a concentration of 0.01 M or more and 0.000. It has been found that it can be obtained by hydrothermal treatment under a certain condition in an aqueous solution containing 1 M or less of hydroxide ions, and the present invention has been completed.
[0007]
That is, the present invention provides silica particles characterized in that the primary particle size is in the range of 50 nm to 300 nm and is made of cristobalite. Further, the present invention is characterized in that hydrothermal treatment is performed on silica in an aqueous solution containing fluorine ions and / or hydroxide ions having a concentration of 0.01M to 0.5M in a temperature range of 250 ° C to 350 ° C. A method for producing silica particles is provided.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The silica particles of the present invention are made of cristobalite. Cristobalite is one of the crystalline phases of silica, and is a crystalline phase produced when heated to a high temperature of 1470 ° C. or higher and melting point (1730 ° C.) or lower. When the silica particles are made of this cristobalite, a high polishing rate can be obtained by using the silica particles as an abrasive. When the silica particles are composed of α-quartz and tridymite generated at a lower temperature than cristobalite, the polishing rate may not be high even when the silica particles are used as an abrasive.
[0009]
And the silica particle of this invention is the range whose primary particle size is 50 to 300 nm. When the primary particle size is less than 50 nm, when the silica particles of the present invention are used as an abrasive, the polishing rate may not be faster than when conventional amorphous silica particles are used as an abrasive. On the other hand, when the thickness exceeds 300 nm, the surface roughness of the object to be polished increases, which is not suitable for precise polishing.
[0010]
Next, the manufacturing method of the silica particle of this invention is demonstrated. The silica particles of the present invention are made of cristobalite produced at a high temperature, but can be produced by hydrothermal treatment as follows without using a high temperature of 1470 ° C. or higher.
[0011]
First, the starting material used in the production method of the present invention may be silica (SiO ₂ ), for example, amorphous silica such as colloidal silica, fumed silica, quartz glass; crystalline silica such as α-quartz. Amorphous silica is preferably used. In consideration of the rate of dissolution during hydrothermal treatment in an aqueous solution used in hydrothermal treatment, these silicas are preferably powders rather than lumps, more preferably those having primary particles of 10 nm to 10 μm, and more preferably 10 nm to 1 μm. .
[0012]
Next, in the production method of the present invention, silica is hydrothermally treated in an aqueous solution containing fluorine ions and / or hydroxide ions having a concentration of 0.01M to 0.5M in a temperature range of 250 ° C to 350 ° C. Do. If the temperature of the hydrothermal treatment is less than 250 ° C., cristobalite is not generated, and if it exceeds 350 ° C., cristobalite particles having a primary particle size exceeding 300 nm are generated, so the hydrothermal treatment temperature range is 250 ° C. or more and 350 ° C. It is below and the range of 270 degreeC or more and 330 degrees C or less is preferable. The hydrothermal treatment time is usually about 1 to 50 hours.
[0013]
Here, in the production method of the present invention, the aqueous solution used in the hydrothermal treatment contains fluorine ions and / or hydroxide ions having a concentration of 0.01M to 0.5M. The aqueous solution used in the hydrothermal treatment is preferably an aqueous solution containing fluorine ions because the crystallinity of the cristobalite produced is high. When fluorine ions are contained in the aqueous solution, cristobalite is not generated when chlorine ions or bromine ions are contained in the aqueous solution instead of fluorine ions, even if it is a halogen element ion, and fluorine is contained in the aqueous solution. A cristobalite is generated when If the concentration of the fluorine ion contained is too low, amorphous silica tends to be produced, and if it is too high, corrosion of the container used for production may be a problem. 0.1M to 2M is preferable. An aqueous solution containing fluorine ions can be produced by, for example, dissolving a water-soluble fluorine-containing compound such as an alkali metal fluoride such as sodium fluoride or potassium fluoride in water.
[0014]
When the aqueous solution contains a hydroxide ion having a concentration of 0.01 M or more and 0.5 M or less, the concentration of the hydroxide ion is preferably in the range of 0.05 M or more and 0.12 M. If the hydroxide ion concentration is too low, amorphous silica tends to be formed, and if it is too high, corrosion of the container used for production may be a problem. The aqueous solution containing hydroxide ions is preferably an aqueous solution of an alkali metal hydroxide.
The amount of the starting silica is preferably in the range of about 1 g / L to about 100 g / L with respect to the aqueous solution. The starting silica is preferably dispersed in advance in an aqueous solution, and a method such as stirring or ultrasonic irradiation can be used for dispersion.
[0015]
Hydrothermal treatment is usually performed using an autoclave. A metal autoclave can be used, but a corrosion-resistant material or a surface-treated one is preferable in order to reduce particle adhesion and contamination. For example, an autoclave coated with hastelloy or fluororesin can be used. The autoclave can be used in both a batch type and a continuous type.
[0016]
The influence of the rate of temperature increase and the rate of temperature decrease is not particularly recognized, and there is no problem as long as it can be controlled by a normal apparatus. For example, the heating can be carried out by a method in which an autoclave containing an aqueous solution containing fluorine and silica as a starting material is installed in a dryer set at a hydrothermal treatment temperature, and an average of 1 ° C./min to 10 generated at that time. A heating rate of about ° C./min can be used.
[0017]
Next, after the container such as an autoclave is sufficiently cooled, the lid is opened and the silica particles immersed in the aqueous solution are taken out to obtain silica particles made of cristobalite of the present invention. However, when fluorine is used in an aqueous solution containing fluorine, or when an alkali metal fluoride is used to contain fluorine in the aqueous solution, the alkali metal is attached to the obtained silica particles. If metal becomes a problem, it can be removed by washing with water after hydrothermal treatment. Washing with water is performed by a method such as filtering the aqueous solution in which the silica particles are immersed, pouring water into the obtained cake and further filtering, or dispersing the cake in water and filtering again. it can.
[0018]
Thus, the silica particles obtained by hydrothermal treatment may be agglomerated, but for example, they can be dispersed by a generally industrially used method such as ultrasonic irradiation, ball mill, vibration mill, dyno mill or the like.
[0019]
As described above, silica particles composed of cristobalite and having a primary particle size of 50 nm to 300 nm can be obtained by the production method of the present invention. Since the silica particles have high crystallinity, crystal habit of a cristobalite crystal phase is seen on the particle surface, and there are corners where different crystal planes intersect with each other.
[0020]
A polishing composition can be prepared using the silica particles of the present invention as an abrasive. The polishing composition is a slurry in which the silica particles of the present invention are dispersed in a dispersion. As the dispersion, water or an organic solvent can be used depending on the application. A surfactant can be added to the dispersion to improve wettability with silica particles and a polishing pad. Moreover, a corrosion inhibitor, a disinfectant, etc. can also be added in order to improve the stability of the slurry. The polishing composition using the silica particles of the present invention made of cristobalite has a high polishing rate and can be polished with high accuracy (small surface roughness). Therefore, a silicon semiconductor, a compound semiconductor wafer such as gallium arsenide, It is suitable for polishing hard disk substrates and quartz substrates.
[0021]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these.
1. Observation of Particle Shape The shape of primary particles was observed with powdered SEM (scanning electron microscope, T-300 manufactured by JEOL Ltd.) and TEM (transmission electron microscope, TEMH9000NAR manufactured by Hitachi, Ltd.).
2. Measurement of Crystal Phase of Powder X-ray diffraction (XRD) pattern of powder was measured with an X-ray diffractometer (RINT 2500 TTR type, manufactured by Rigaku) to identify the crystal phase.
[0022]
Example 1
1.0 g of amorphous silica (Nipsil VN3 (trade name)) manufactured by Nippon Silica Industry was dispersed in 15 ml of a 0.33 M NaF aqueous solution, and the mixture was irradiated with ultrasonic waves for 15 minutes and stirred. The obtained slurry was placed in a Hastelloy autoclave and maintained at 300 ° C. for 24 hours for hydrothermal treatment. The generated particles were stirred for 15 minutes while irradiating with ultrasonic waves, then washed with distilled water, finally washed with acetone and vacuum dried to obtain silica particles. The crystal structure identified by XRD was cristobalite, and the primary particle size was in the range of 50 to 300 nm.
[0023]
Example 2
Amorphous silica (Nipsil VN3 (trade name)) manufactured by Nippon Silica Industry Co., Ltd. was dispersed in a solution of 15 ml of 0.33M KF, placed in an autoclave whose inner surface was coated with a fluororesin, and kept at 300 ° C. for 12 hours. Hydrothermal treatment was performed. The generated particles were washed and dried to obtain silica particles. The crystal structure identified by XRD was cristobalite, and the primary particle size was in the range of 50 to 300 nm.
[0024]
Example 3
Amorphous silica manufactured by Nippon Silica Industry (Nipsil VN3 (trade name)) 1.5 g is dispersed in 15 ml of a 0.33 M aqueous KF solution and kept at 300 ° C. for 24 hours using an autoclave whose inner surface is coated with a fluororesin. Then, hydrothermal treatment was performed. The generated particles were washed and dried to obtain silica particles. The crystal structure by XRD was cristobalite, and the primary particle size was in the range of 50 to 300 nm.
[0025]
Example 4
Amorphous silica (Nippil VN3 (trade name)) manufactured by Nippon Silica Kogyo Co., Ltd. is dispersed in 15 ml of KF aqueous solution with a concentration of 0.33M and kept at 300 ° C for 48 hours using an autoclave whose inner surface is coated with fluororesin. Then, hydrothermal treatment was performed. The generated particles were washed with water and dried to obtain silica particles. The crystal structure by XRD was cristobalite.
[0026]
Example 5
1.0 g of amorphous silica (Nippil VN3 (trade name)) manufactured by Nippon Silica Kogyo Co., Ltd. is dispersed in 15 ml of a 0.075M NaOH aqueous solution, placed in an autoclave whose inner surface is coated with fluorine, and kept at 300 ° C. for 8 hours. Hydrothermal treatment was performed. The generated particles were washed with water and dried to obtain silica particles. The crystal structure identified by XRD was cristobalite, and the primary particle size was in the range of 100 to 300 nm.
[0027]
Example 6
1.0 g of amorphous silica (Nipsil VN3 (trade name)) manufactured by Nippon Silica Kogyo Co., Ltd. is dispersed in 15 ml of NaOH aqueous solution having a concentration of 0.10 M, and placed in an autoclave whose inner surface is coated with fluorine, and kept at 300 ° C. for 3 hours. Hydrothermal treatment was performed. The generated particles were washed with water and dried to obtain silica particles. The crystal structure identified by XRD was cristobalite, and the primary particle size was in the range of 100 to 300 nm.
[0028]
Example 7
A slurry having a concentration of 30% by weight was prepared using the particles obtained in Example 1, and the pH was set to 10 and then pulverized for 24 hours by a wet ball mill to prepare a polishing liquid. Using this polishing liquid, a silicon substrate polishing test was performed under the following conditions. The polishing rate was calculated from the weight reduction of the silicon substrate.
Polishing machine manufacturer: Engis Corporation
Surface plate rotation speed: 200 rpm
Polishing pressure: 500 g / cm ²
Polishing time: 5 minutes Polishing liquid supply amount: 10 ml / minute The polishing rate was 0.62 μm / minute.
[0029]
Comparative Example 1
A silicon substrate polishing test was conducted in the same manner as in Example 5 using commercially available colloidal silica (silica doll 40L (trade name), manufactured by Nippon Chemical Industry Co., Ltd.). The polishing rate calculated from the weight reduction of the silicon substrate was 0.47 μm / min.
[0030]
Comparative Example 2
Hydrothermal treatment was performed by dispersing 1.0 g of fumed silica (manufactured by Degussa Co., Ltd.) in 15 ml of a 0.33M NaOH aqueous solution and holding it at 200 ° C. for 24 hours using a fluorine-coated autoclave. The generated particles were washed and dried to obtain silica particles. The crystal structure by XRD was amorphous.
[0031]
Comparative Example 3
The same procedure as in Example 1 was performed except that the treatment temperature was 400 ° C. The produced particles became amorphous.
[0032]
【The invention's effect】
Since the silica particles of the present invention are fine particles of silica and exhibit a faster polishing rate than conventional silica particles made of amorphous silica when used as an abrasive, silicon wafers, compound semiconductor wafers such as gallium arsenide, It is suitable as an abrasive for polishing hard disk substrates and quartz substrates, and according to the production method of the present invention, the primary particle diameter is 50 nm to 300 nm, and the silica particles of the present invention comprising cristobalite can be produced. Therefore, it is extremely useful industrially.

Claims (5)

A silica particle having a primary particle size in the range of 50 nm to 300 nm and comprising cristobalite. Silica particles are hydrothermally treated in a temperature range of 250 ° C. to 350 ° C. in an aqueous solution containing fluorine ions and / or hydroxide ions having a concentration of 0.01 M or more and 0.5 M or less. . The method according to claim 2, wherein the aqueous solution is an aqueous solution of an alkali metal fluoride. The production method according to claim 2 or 3, wherein the concentration of fluorine ions in the aqueous solution is 0.1 M or more and 2 M or less. The method according to claim 2, wherein the aqueous solution is an aqueous solution of an alkali metal hydroxide.