JP3343923B2 - Manufacturing method of high purity silica glass powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity silica glass powder used in a semiconductor-related field such as a crucible for pulling a silicon single crystal or a sealing material for an LSI.

[0002]

2. Description of the Related Art In a general method for producing glass, a method is used in which raw materials are melted in a vessel and then cooled. However, in this production method, high-purity glass is obtained by mixing impurities from the vessel used for melting. Did not. 2. Description of the Related Art In recent years, high-performance glass called new glass has been actively developed, and its manufacturing process includes a sol-gel method, a gas phase reaction method, glass melting in a zero-gravity state, and a rapid quenching method.

[0003] Of these, there are a wide variety of types of glass produced by a sol-gel method using an organometallic compound such as a metal alkoxide as a starting material, and this is a glass production method having a very wide range of application. In this method, a sol in which fine particles of a metal hydroxide or an oxide obtained by hydrolyzing the above-mentioned organometallic compound are dispersed in a solution is generated, and after gelation, drying, firing, pulverization, melting, etc. Make glass through the process.

As a metal alkoxide, tetramethoxysilane or tetraethoxysilane is often used as a starting material, but other silicon alkoxides can be used as a starting material. In the sol-gel method, there is no need to worry about contamination of impurities from the container, and the raw material can be easily purified by means such as distillation, so that high-purity glass can be obtained, and bulk materials, fibers and other shapes can be obtained. Although it has advantages such as being able to be produced and being capable of producing glass at a relatively low temperature, it also has disadvantages such as generally expensive raw materials and long process times.

In the production of a high-purity glass powder by a liquid phase method such as a sol-gel method, a gel is formed, dried and dried.
Pulverization and firing steps are required, and these steps are bottlenecks in production. In particular, in the baking step, it is necessary to remove moisture and organic substances remaining inside the gel after drying, so that baking is performed slowly over several hours to several tens of hours. The firing temperature at this time may be lower if the particle size of the gel to be fired is smaller, and the firing time tends to be shorter. However, since the temperature is generally as high as 800 to 1300 ° C., if the temperature control is incorrect, Since there is a risk of sintering the particles, care must be taken to make the temperature distribution in the firing furnace uniform.

[0006] Further, since the product is of high purity, care must be taken in handling the gel or calcined product between or within these steps, and contamination of impurities must be avoided as much as possible. As a method for calcining the gel, generally, a method of calcining silica gel in a calcining furnace in a stationary state (Japanese Patent Laid-Open No. 168538/1986) is general. Further, although not practically used, a document suggesting that silica gel is calcined in a fluidized bed (Japanese Patent Laid-Open No.
81315) are also known.

[0007]

However, in the method of firing in a stationary state in a firing furnace, the gel is usually placed in a high-purity container and charged into the firing furnace in order to avoid contamination with impurities. Baking is performed, but the method of performing baking once in a container is not suitable for large-scale baking because productivity is not improved due to troubles such as charging and discharging into the container, and limitation of the size of the container. In addition, impurities may be mixed during handling in the process.

[0008] Therefore, in order to continuously bake a large amount of silica gel powder, it is desirable that a treatment method such as a fluidized bed type or a moving bed type can be adopted. Friction is severe, and there is a drawback that an inner wall component generally made of brick or the like is mixed as an impurity. In addition, in the case of the moving bed type, if the particle size of the target powder is generally not more than several mm, it cannot be smoothly moved in the apparatus and is considered to be unsuitable.
It was thought that stable treatment would not be possible with fine particles of about m.

[Means for Solving the Problems]

In view of the above circumstances, the present inventors have conducted intensive studies on a method for producing a high-purity silica glass powder by continuously firing a dried high-purity silica gel powder, and as a result, have adopted a specific means. It has been found that, when firing is carried out in a moving bed system, smooth processing can be performed even with fine silica powder, and extremely excellent results can be obtained, thereby completing the present invention. That is, an object of the present invention is to sinter a high-purity silica gel powder in an industrially advantageous manner. The gist of the present invention is to produce a high-purity silica glass powder by sintering a high-purity silica gel powder. In this case, using a vertical moving bed apparatus equipped with heating means, a moving bed system in which the raw material silica powder is continuously supplied from the upper part of the apparatus and discharged from the lower part, and a small amount is moved from the lower part of the moving bed to the upper part. Gas and 1000 to 1300
A method for producing a high-purity silica glass powder, characterized by firing at a temperature of ° C.

Hereinafter, the present invention will be described in more detail.
In the present invention, the high-purity silica gel powder to be calcined is usually a sol having alkoxysilane as a starting material.
High-purity silica gel powder obtained by a gel method is exemplified. In this sol-gel method, a sol in which fine particles of silicon hydroxide or oxide are dispersed by hydrolyzing alkoxysilane is formed, and after gelling, dried, pulverized and calcined, silica glass powder is obtained. And then subjecting it to a process such as grinding and melting to produce a high-purity silica glass product.

In the present invention, in addition to the above-mentioned sol-gel method, finely divided silica may coexist at the time of hydrolysis, or for example, a sol-gel method using alkali silicate as a starting material, or a silicon halide may be used. High-purity silica gel powder obtained by hydrolysis, gas phase method or the like as a starting material can also be used. Although the particle size of the high-purity silica gel powder used in the present invention varies depending on its density, it is usually 1 particle size.
It is 00 to 800 μm, preferably 100 to 500 μm. The bulk density of the powder is usually 0.6 to 0.7 g /
cm ³ . And this bulk density changes to 1.0-1.5 g / cm < ³ > by baking processing. The siliceous powder targeted in the present invention is of high purity.
The content of alkali metals such as a and K and all metal components such as Fe, Cu, and Ni is 1 ppm or less, and preferably 0.1 ppm or less.
pm or less. Further, the water content of the silica gel powder to be subjected to the baking treatment is usually 10% by weight or less.

In the present invention, in firing the high-purity silica gel powder as described above, a vertical moving bed apparatus equipped with a heating means is used, and the powder is continuously supplied from the upper part of the apparatus and discharged from the lower part. In this method, a small amount of gas is allowed to flow from the lower part of the moving layer to the upper part, and the temperature is set at 1000 to 1300 ° C. The firing time at the temperature is usually 1 to 30 hours, preferably 3 to 2 hours.
0 hours. The residence time of the high-purity siliceous powder in the moving bed apparatus is about 1 to 50 hours.

The moving bed apparatus used in the present invention is generally cylindrical and preferably in a circular cross section in terms of processing the main body or in terms of making the temperature distribution in the bed uniform, but it is short, polygonal or elliptical. Any shape may be used. Furthermore, various shapes are conceivable, such as a device in which the diameter of the device does not change in the vertical direction depending on the location, a device having a slope in the lower portion, and a device in which the lower portion is narrowed, and the type is a vertical type.
Although the size of the moving bed apparatus is not particularly limited, a typical industrial apparatus has, for example, an inner diameter of 20 to 150 cm and a height of about 3 to 20 m.

The heat source for heating includes electricity, liquid fuel,
Any of gaseous fuels and the like can be used, and the heating method can be internal heating, external heating, or a combination thereof. An external heating method is desirable from the viewpoint of impurity contamination in the product, but if the heating part is lined with siliceous glass or silicon carbide, silicon nitride, etc.,
There is no problem with internal heating. In order to make the temperature distribution in the radial direction more uniform, internal heating may be performed.

In the present invention, the vertical moving bed apparatus used to form the moving bed has a heat resistant and abrasion resistant inner surface in contact with the siliceous powder to be fired, such as siliceous glass, silicon carbide or silicon nitride. An apparatus formed of a material is desirable because impurities are less likely to be mixed into the fired product. In the present invention, it is an essential requirement that a small amount of gas flow from the lower part of the moving bed toward the upper part during firing. Examples of the gas include a gas such as air, nitrogen, argon, and helium. It is desirable that the water content of the gas is small, and a dry gas is usually used. Preheating these gases saves energy for heating. For preheating of these gases, indirect heat exchange with the exhaust gas is good, and the heat exchange reduces the total energy consumption. Furthermore, the overall energy efficiency is improved by indirectly heating the raw material supplied to the apparatus with the exhaust gas. The gas supply port may be divided into a plurality of parts in order to improve gas dispersibility.

In the present invention, the moving layer refers to a particle layer in which particles filled in a container move downward by mechanical operation such as gravity or vibration. The amount of gas to be blown also has a role to carry out at least a gas such as moisture or carbon dioxide generated during firing out of the system.
000 cm / min, preferably 10 to 200 cm / min, more preferably 30 to 100 cm / min. Firing temperature,
The firing time greatly varies depending on the particle size distribution of the high-purity siliceous powder, but the firing temperature is suitably in the range of 1000 to 1300C, preferably in the range of 1000 to 1200C. If the firing temperature is too high, the particles will sinter together, making it impossible to operate the firing furnace. The sintering temperature of the particles changes depending on the particle diameter, and the sintering temperature decreases as the particle diameter decreases. The firing time is usually 1 to 30 hours, preferably 3 to 20 hours. In the present invention, in the moving bed apparatus, the siliceous powder is sequentially heated,
After firing and cooling, the target silica glass powder can be finally obtained. The silanol group concentration in the silica glass powder obtained here is 1000 ppm or less, preferably 100 ppm or less.

Regarding the firing pressure, normal pressure operation is simple due to the structure of the apparatus, but pressurization and decompression operations may be performed. In the pressurizing and depressurizing operations, it is necessary to consider the problem of sealing in the raw material supply section and the discharge section of the product, the strength of the apparatus, and the like. The moving layer has the advantages that the residence time of the particles is easy to control, there is little powdering and dust generation, and it is easier to obtain a high-purity product than other firing methods. The particle size of the siliceous powder targeted in the present invention is usually 100 to
It is 800 μm, preferably 100 to 500 μm. When the particle diameter is small, not only the ventilation in the moving layer is deteriorated, but also sintering may occur. Therefore, it is necessary to adjust the moving speed of the powder, the supplied gas amount, the firing temperature, and the like.

In the present invention, the high-purity silica gel powder is continuously supplied from the upper part of the vertical moving bed apparatus and discharged from the lower part.
This includes not only supplying the powder from the upper part of the apparatus without interruption but discharging it from the lower part, but also performing the supplying and discharging operations intermittently. The moving speed of the moving bed is usually 10 to 50 cm / hr. The supply and discharge of the powder include the supply from the upper part, that is, the top or upper side, of the vertical moving bed apparatus, and the discharge from the lower part, that is, the bottom or lower side.

Next, the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic explanatory view showing an example of a vertical moving bed apparatus used in the present invention. The raw material high-purity silica gel powder is supplied from the raw material supply port 3 through the raw material supply valve 2 to the apparatus body 6.
Supplied inside. The supplied material to be fired gradually moves downward withdrawal from the lower part of the apparatus.
Heating is performed by the heater 1 and firing is performed. After a sufficient residence time, it is cooled in the lower part of the apparatus and finally discharged out of the system by the fired material feeder 10. As the type of the fired material feeder, any type such as a rotary type typified by a table feeder or the like, a reciprocating type typified by a vibration feeder or the like, or a container receiving type such as a screw feeder can be used.

On the other hand, gas enters through the gas supply port 11 and
After the particles are uniformly dispersed in the apparatus by the gas dispersing apparatus, the particles rise up between the particles, and are finally discharged from the gas discharging port 4. As described above, the energy efficiency can be improved by indirectly exchanging the exhaust gas with the gas fed to the gas supply port 11. Also fired material feeder 1
Cooling water is supplied from the refrigerant inlet 8 to protect the fired product and to facilitate handling after removal, thereby cooling the fired product. The refrigerant heated by heat exchange with the fired product is purged from the refrigerant outlet 7 to the outside of the system. The refrigerant is not limited to water, and other refrigerants may be used. If the inner surface of the apparatus main body 6 is lined with a heat-resistant and abrasion-resistant ceramic such as siliceous glass, silicon carbide, or silicon nitride, contamination of impurities due to abrasion due to contact between particles and a wall can be suppressed.

[0021]

According to the method of the present invention, since sintering can be performed continuously in a moving bed, a large amount of siliceous powder can be efficiently treated, and the internal temperature distribution of the sinter is relatively uniform. Therefore, a product having less variation in quality depending on the place, less pulverization as compared with the fluidized bed system, and a sharp particle size distribution can be obtained. It is very unexpected that fine particles such as silica particles can be treated in a moving bed, but the cause is not clear, but in the case of the present invention,
Since a small amount of gas is circulated below the moving bed, this is presumed to have some desirable effect.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of a vertical moving device used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 Material supply valve 3 Material supply port 4 Gas discharge port 5 Object to be fired 6 Main body of apparatus 7 Refrigerant outlet 8 Refrigerant inlet 9 Gas dispersion device 10 Sintered material feeder 11 Gas supply port

Continuation of the front page (56) References JP-A-63-236721 (JP, A) JP-A-4-182311 (JP, A) JP-A-59-54632 (JP, A) JP-A-52-81315 (JP, A) JP-A-61-168539 (JP, A) JP-A-52-43810 (JP, A) JP-B-38-20816 (JP, B2) JP-B-41-10327 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 33/00-39/54 C03B 20/00

Claims (2)

(57) [Claims] In producing a high-purity silica glass powder by sintering a high-purity silica gel powder, a raw silica powder is continuously supplied from an upper part of the apparatus using a vertical moving bed apparatus equipped with a heating means. High-purity silica glass powder characterized in that it is a moving bed method of discharging from a part, a small amount of gas is passed from a lower part to an upper part of the moving bed, and firing is performed at a temperature of 1000 to 1300 ° C. Manufacturing method. 2. The method for producing a high-purity silica glass powder according to claim 1, wherein an inner surface of the vertical moving bed apparatus used in contact with the high-purity silica material powder is composed of silica glass, silicon carbide, and silicon nitride. A method characterized by being formed of a material selected from the group consisting of: