JPH08133719A - High purity synthetic cristobalite powder, its production and silica glass - Google Patents

Abstract

PURPOSE: To obtain high purity synthetic cristobalite powder having low alkali metal and alkaline earth metal contents, having high viscosity at high temp. and excellent in heat resistance by treating high purity synthetic silica glass powder together with high purity water in an autoclave. CONSTITUTION: High purity synthetic silica glass powder and water of >=99.999wt.% purity are charged into an autoclave and treated in the temp. range of 300-1,000 deg.C and the pressure range of 100-2,000kgf/cm<2> to obtain the objective cristobalite powder. This cristobalite powder is synthetic one obtd. by treating high purity synthetic silica glass powder at high temp. and pressure in an atmosphere of steam and contg. Li, Na and K as alkali metals and Ca and Mg as alkaline earth metals at <=100wt.ppb concn. each and Ti, Cr, Fe, Ni and Cu as transition metals at <=50wt.ppb concn. each. This cristobalite powder is used as the material of a jig for heat treatment of a semiconductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-purity synthetic cristobalite powder, particularly high-viscosity silica glass and high-purity synthetic cristobalite, which is a raw material for growing synthetic quartz, a method for producing the same, and silica glass.

[0002]

2. Description of the Related Art Conventionally, silica glass has a high purity, a low coefficient of thermal expansion, and a high temperature viscosity, so that a jig material for heat treatment such as a silicon wafer boat, a glass chamber in an electric furnace, and a diffusion chamber is used. Has been used as. As this silica glass, so-called "fused quartz glass" has been used in which crystalline silica powder obtained by crushing natural high-purity crystal or quartz is fused and vitrified by an electric heating melting method or a flame Bernoulli method. However, high-purity quartz and quartz, which are raw materials for the fused silica glass, are gradually depleted, and it is difficult to obtain them. Further, when quartz or quartz having low purity is used as a raw material, various kinds of metal impurities are contained in the fused silica glass, which is diffused and transferred to the silicon wafer during heat treatment and contaminates the silicon wafer. there were. In order to solve these problems, high-purity synthetic silica glass using silicon compounds such as silicon tetrachloride as a raw material has been studied as a material for heat treatment jigs. When it was used as a heat treatment jig for a silicon wafer having a large size and a large weight, it was not suitable as a jig material because it caused large thermal deformation during heat treatment. To solve the drawbacks of this synthetic silica glass, a method for producing silica glass using high-temperature-viscosity synthetic cristobalite powder,
For example, it has been proposed in JP-A-62-113729, JP-A-63-166730 and JP-A-1-176243. In all of the production methods described in the above publications, an alkali component is added to synthesize cristobalite, so that the cristobalite powder contains a high concentration of an alkali element impurity, and its removal treatment is expensive and the production cost is high.

[0003]

In view of the current situation,
As a result of intensive studies, the present inventors have found that when high-purity synthetic silica glass powder is treated at high temperature and high pressure in the presence of water, the content of alkali metal elements, alkaline earth metal elements, and transition metal elements is low. High-purity cristobalite is obtained,
The inventors have found that the silica glass using this as a raw material is a silica glass with high purity and high temperature viscosity, and completed the present invention. Ie

An object of the present invention is to provide a high-purity synthetic cristobalite powder having a low alkali element content.

An object of the present invention is to provide silica glass having high heat resistance and high-purity synthetic cristobalite powder useful as a raw material for synthetic quartz.

[0006] It is an object of the present invention to provide a silica glass having a high purity and a high temperature viscosity, which is produced from the above synthetic cristobalite powder as a raw material.

Another object of the present invention is to provide a novel method for producing the above-mentioned high-purity synthetic cristobalite powder.

[0008]

Means for Solving the Problems The present invention, which achieves the above objects, provides an alkali metal element concentration of lithium, sodium and potassium and calcium and magnesium obtained by subjecting high-purity synthetic silica glass powder to high-temperature and high-pressure treatment in a steam atmosphere. The present invention relates to a synthetic cristobalite powder having an alkaline earth metal element concentration of 100 wtppb or less, and a transition metal element concentration of titanium, chromium, iron, nickel, and copper of 50 wtppb or less, a method for producing the same, and silica glass.

The high-purity synthetic silica glass powder used in the present invention is a synthetic silica obtained by synthesizing a volatile silicon compound such as silicon tetrachloride by an oxyhydrogen flame hydrolysis method, a propane flame hydrolysis method, a plasma method or the like. A glass powder, or a synthetic silica glass powder produced by a sol-gel method using a metal alkoxide or an inorganic silicate as a raw material, and having a particle size of 1 to 1,000 μm.
The powder in the range of. Among the synthetic silica glass powders, the synthetic silica glass powder manufactured by the sol-gel method is preferable because it is low in cost and can be manufactured at low cost. Further, contained in the synthetic silica glass powder, lithium, sodium,
The concentration of alkali metal element of potassium and the concentration of alkaline earth metal element of calcium and magnesium are each 100 wtp.
The transition metal element concentration of pb or less, titanium, chromium, iron, nickel, copper is 50 wtppb or less, preferably the alkali metal element concentration or the alkaline earth metal element concentration is 1 each.
It is important that the concentration of the transition metal element be 0 wtppb or less and the concentration of the transition metal element be 5 wtppb or less. If the concentration of each element exceeds the above range, the silicon wafer is contaminated during the heat treatment, and a high-quality silicon wafer cannot be obtained. Further, if the particle size of the synthetic silica glass powder deviates from the above range, bubbles are likely to be generated during vitrification and are taken into the glass, which deteriorates the quality of the silica glass.

The above high-purity synthetic silica glass powder was placed in a high-pressure, high-pressure container together with high-purity water, particularly water having a purity of 99.999 wt% or more, and the temperature range was 300 to 1,000 ° C.
Preferably, the temperature is 500 to 800 ° C., and the pressure range is 100 to 2,
000 Kgf / cm ² , preferably 500 to 1,000
The high purity cristobalite of the present invention is synthesized by treating with Kgf / cm ² for 1 to 14 days. In the above-mentioned manufacturing method, since alkali is not used during manufacturing as described above, the synthesized cristobalite maintains high purity without increasing the impurity concentration of the raw material. In the above-mentioned manufacturing method, when the treatment temperature is lower than 300 ° C., the transition to cristobalite does not occur, and when it exceeds 1,000 ° C., contamination by impurities from the surroundings increases. In addition, the pressure is 100
If it is less than Kgf / cm ^2, it does not transfer to cristobalite,
A high pressure exceeding 2,000 Kgf / cm ² will increase the size of the apparatus and increase the cost industrially. The practically preferable range is
Temperature 500-800 ° C, Pressure 500-1,000Kgf
/ Cm ² .

The silica glass of the present invention is manufactured by vitrifying the synthetic cristobalite powder obtained above as a raw material by an electric melting method or the like. The obtained silica glass has a high temperature equal to or higher than the viscosity of fused silica glass obtained by the electric melting method of natural quartz, for example, 10 ^12.8 poise or more at 1,200 ° C. and 10 ^14.8 poise or more at 1,100 ° C. Indicates viscosity. The reason is that silica glass obtained by melting synthetic cristobalite powder has a fine crystal structure remaining,
It is presumed that this makes the viscosity high at high temperature. However, since the crystal structure is not detected by the X-ray diffraction method, it is considered to be within several nm.

The synthetic cristobalite powder of the present invention is useful not only as a raw material for producing silica glass but also for synthesizing a single crystal of artificial quartz, and has strength, transparency, morphological anisotropy, and thermal conductivity. In terms of properties, it is comparable to artificial quartz obtained by hydrothermal synthesis using other natural quartz as a raw material, and is also useful as a reinforcing material filler or spacer.

[0013]

【Example】

Examples 1-6 (Production of raw material silica glass powder) (a) tetraethoxysilane _{(Si (OC 2 H 5)} 4) 1
0.01 mol of ammonia water is added to 3 mol of raw material.
Mol and methanol were mixed and stirred at a ratio of 4 mol to prepare a sol solution, which was poured into a plastic beaker and left at 60 ° C. for 10 hours in a constant temperature bath. The obtained gel is heated to 200 ° C in an electric furnace, dried, and further heated to 1,000 ° C.
After being heated in, the powder was pulverized with a ball mill made of synthetic silica glass and classified with a sieve to obtain a powder of 20 to 200 μm.

(B) Argon gas was blown as a carrier gas into an evaporator containing distilled and purified silicon tetrachloride to prepare a raw material gas containing 100 g / h of silicon tetrachloride in 20 Nl / h of argon gas. Was hydrolyzed in an oxyhydrogen flame to deposit silica granules. Then, classification with a sieve was performed to obtain a synthetic silica glass fine powder having a particle size of 5 to 50 μm.

(Synthesis of Cristobalite) 100 g of each of the above synthetic silica glass powders was placed in a high temperature and high pressure container whose inner surface was lined with gold foil, and then 5 cc of water having a purity of 99.999 wt% or more was introduced. The lid of the container was closed, and the treatment was performed at each temperature, pressure, and treatment time shown in Table 1. Identification of minerals in the obtained powder by powder X-ray diffraction method (data for identification is JCPDS, J
oint Committee On PowerDi
ffraction Standards)
And the impurity concentrations of the powders obtained in Examples 1 and 4 were measured, and the results are shown in Tables 1 and 2.

(Production of Quartz Glass) The above-prepared powder was fused and vitrified at 1750 ° C. for 1 hour in an electric furnace in a vacuum atmosphere to produce silica glass. About the obtained silica glass, 1,200 ° C. by the beam-guding method
Viscosity (Keiji Kobayashi, Ryosuke Yokota, Journal of Ceramic Industry Association,
Vol. 76, No. 7, 1968, pp. 218-2
23) and impurity element analysis (by atomic absorption spectrophotometry), and the results are shown in Tables 1 and 2.

Comparative Example 1 Using the raw material (a) of Example 1, in a dry atmosphere filled with nitrogen gas in the absence of water, 500 ° C., 500 Kgf
/ Cm ² for 7 days. The same evaluation as in Example 1 was performed on the obtained powder and silica glass. Table 1 shows the results.

Comparative Example 2 In Comparative Example 1, water was allowed to exist in the high temperature and high pressure container.
The obtained powder and silica glass were evaluated by treating them at 500 ° C. and 500 Kgf / cm ² for 7 days, and the results are shown in Table 1.
Shown in

Comparative Example 3 The raw material (a) of Example 1 was treated with a NaOH solution so that Na was uniformly present in the raw material, and then at 1,500 ° C.
The treatment was carried out at 1 Kgf / cm ² for 3 days. The obtained powder and silica glass were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

[0020]

[Table 1]

[0021]

[Table 2] (Unit: wtppb)

As shown in Tables 1 and 2 above, the synthetic cristobalite powder obtained by the production method of the present invention has a high purity, and particularly has a low alkali element impurity concentration. The silica glass using this synthetic cristobalite powder as a raw material has a high temperature viscosity equal to or higher than that of fused silica glass obtained by melting and vitrifying natural quartz. On the other hand, the silica glasses of Comparative Examples 1 and 2 which do not satisfy the production conditions of the present invention show only the high temperature viscosity of the synthetic silica glass.

Further, as shown in Table 2, the synthetic cristobalite of the present invention has a much higher purity than the silica glass of Comparative Example 3 obtained by the conventional method. there were.

[0024]

The cristobalite powder of the present invention contains few alkali metal elements and alkaline earth metal elements that adversely affect the characteristics of silicon wafers in the semiconductor industry, and silica glass made from it has a high purity and a high impurity element concentration, In particular, it is useful as a jig material for semiconductor heat treatment because of its low alkali element concentration and high heat resistance.

Claims (6)

[Claims] 1. High-purity synthetic silica glass powder subjected to high-temperature and high-pressure treatment in a steam atmosphere, the concentration of alkali metal elements of lithium, sodium and potassium and the concentration of alkaline earth metal elements of calcium and magnesium are each 100 wtppb or less, and titanium and chromium. , A synthetic cristobalite powder having a transition metal element concentration of 50 wtppb or less for each of iron, nickel, and copper. 2. The synthetic cristobalite powder according to claim 1, wherein each concentration of the alkali metal element and each concentration of the alkaline earth metal element are 10 wtppb or less and each concentration of the transition metal element is 5 wtppb or less. 3. High-purity synthetic silica glass powder and a purity of 99.
Water of 999 wt% or more is put in a high temperature and high pressure container, and the temperature range is 300 to 1,000 ° C. and the pressure range is 100 to 2,000.
A method for producing a synthetic cristobalite powder, which comprises treating with Kgf / cm ² . 4. The method for producing a synthetic cristobalite powder according to claim 3, wherein the temperature range is 500 to 800 ° C. and the pressure range is 500 to 1,000 Kgf / cm ² . 5. A high-purity synthetic silica glass powder produced by a flame hydrolysis method or a sol-gel method, having a particle size of 1 to 1,000 μm.
The method for producing a synthetic cristobalite powder according to claim 3 or 4, wherein the powder is m. 6. A silica glass characterized by melting and vitrifying the synthetic cristobalite powder according to claim 1.