JPH066495B2 - Method for producing high-purity quartz glass - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-purity quartz glass from a natural siliceous raw material, and particularly to a quartz glass material for semiconductor industry, I
An object of the present invention is to provide high-purity quartz glass suitable as a filler for C, LSI plastic packages and the like.

(Prior art and problems) At present, as circuits are highly integrated in the semiconductor industry, quartz glass jigs used in the semiconductor manufacturing industry, as well as silica fillers for IC, LSI plastic packages, etc. There is a strong demand for high quality and high purification, and in particular, trace amounts of radioactive elements such as uranium and alkali elements are a problem.

Natural siliceous materials such as silica stone, silica sand, and quartz have been conventionally used as raw materials for quartz glass, but these contain a small amount of radioactive elements such as uranium. When it is used as a filler for IC and LSI plastic packages, there is a drawback that a so-called soft error is caused by α rays from radioactive elements.

Regarding the above-mentioned silica stone, silica sand, etc., there has been proposed a method of removing impurities such as sodium, potassium, iron and aluminum by crushing and classifying them, calcining them and then dipping them in hydrofluoric acid. However, it is difficult to remove a trace amount of uranium element, alkali element, etc. contained in them, and establishment of an efficient and economical purification method thereof is desired.

(Structure of the Invention) The present invention provides a method for efficiently producing high-purity quartz glass from a natural siliceous raw material at a low cost with an economical liquid. It is characterized in that it is heat-treated at a high temperature in an atmosphere containing it, then immersed in a mixed solution of hydrofluoric acid and nitric acid, washed with water and then vitrified.

The present invention will be described in detail below.

Examples of the natural siliceous raw material include quartz, quartz, silica stone, silica sand and the like. In refining them by the method of the present invention, they are first pulverized and classified. The particle size after pulverization is preferably in the range of 1 to 1000 μm, particularly 50 to 500 μm. If the particles are too coarse, the desired purification becomes difficult and the purpose of removing uranium element, alkali element, etc. cannot be achieved. On the other hand, if it is too fine, the dissolution loss will be large, which is disadvantageous.

The pulverized and classified raw material is then heat-treated at high temperature in an atmosphere containing halogen or its compound. Examples of the halogen or its compound used here include halogen such as fluorine, chlorine and bromine, and halogen compounds such as hydrogen fluoride, hydrogen chloride, hydrogen bromide and silicon tetrachloride.
Generally, chlorine and hydrogen chloride are preferable. Incidentally, these are used as they are as an atmospheric gas or mixed with a carrier gas such as air or an inert gas. It is desirable that the temperature is 500 ° C. or higher, preferably in the range of 700 ° C. to 1400 ° C., and it is difficult to remove impurities at a temperature of 500 ° C. or lower, while there is no further effect of impurity removal even at a temperature of 1400 ° C. or higher. On the contrary, there arises a problem that sintering of the siliceous flow body occurs. It is necessary that the heating time is approximately 30 minutes to 10 hours within the above-mentioned desirable temperature range.

The siliceous raw material that has been subjected to the heat treatment is then immersed in a mixed solution of hydrofluoric acid and nitric acid. The concentration of the mixed solution is preferably in the range of 2.5 to 30% by weight of hydrofluoric acid and 1 to 20% by weight of nitric acid. The dipping treatment time varies depending on the concentration and temperature conditions of the mixed solution used and cannot be stated in a uniform manner, but it is necessary to dip the mixed solution for the purpose of removing impurities as much as possible. The dissolution loss (weight reduction) of the raw materials brought to
In particular, it is desirable that the treatment time be 10% by weight or more. In addition, it is economically disadvantageous to set the treatment time at which the dissolution loss exceeds 30% by weight, because no further remarkable effect can be expected for the removal of impurities. On the other hand, when the treatment time is less than 5% by weight, the effect is small. Dissolution loss of 5
It is desirable to set the value to be 20% by weight. In addition, it is desirable that the dipping treatment is performed under appropriate stirring.

The siliceous raw material that has been subjected to the above-mentioned immersion treatment is washed with water and dried to obtain a fine powder of alkali metal 5 ppm or less and radioactive element 5 ppb or less of uranium or the like, which is melted to produce high-purity quartz glass.

As described above, the present invention is characterized by firstly a high temperature heat treatment in an atmosphere of halogen or its compound, and secondly an immersion treatment with a mixed solution of hydrofluoric acid and nitric acid. By the high-temperature heat treatment in the above-mentioned halogen or its compound atmosphere, the impurity component migrates to the surface portion of the powder particles, and this surface portion is dissolved and removed by the dipping treatment. Therefore, radioactive elements such as uranium and alkali metals, etc. The impurity component of can be removed very efficiently and economically.

(Examples) Examples of the present invention will be described below.

Example 1 Na250ppm, K250ppm, Li250pp, which was crushed and classified by a usual method to perform magnetic separation and flotation.
Natural quartz powder having a particle size of 50 μm to 500 μm at m and U 400 ppb was prepared as a raw material. 1 kg of the above powder was placed in a quartz crucible, set in a high temperature heating furnace, and 1200 in nitrogen gas containing 5% by volume of hydrogen chloride vapor and 5% by volume of chlorine.
Heat treatment was performed at ℃ for 5 hours. This powder was added to hydrofluoric acid 15
After soaking in a mixed solution of 10% by weight of nitric acid and 10% by weight of nitric acid for 2 hours,
Wash 5 times with 0.05 wt% nitric acid and thoroughly with distilled water,
It was dried in a vacuum dryer. This powder was melted at 2100 ° C. by Bernoulli method to obtain quartz glass.

Comparative Example 1 Quartz glass was obtained by performing heat treatment in a hydrogen chloride vapor and nitrogen gas containing no chlorine, and performing other treatments in the same manner as in Example 1.

Comparative Example 2 Quartz glass was obtained by performing immersion treatment with a 15% by weight hydrofluoric acid solution and performing other treatments in the same manner as in Example 1.

Comparative Example 3 Quartz glass was obtained by performing heat treatment in nitrogen glass containing no hydrogen chloride vapor and chlorine, and dipping treatment with a 15% by weight solution of hydrofluoric acid, and performing other treatments in the same manner as in Example 1.

In this way, when the impurity contents of the silica glass obtained in Example 1 and Comparative Examples 1 to 3 were examined, the results shown in Table 1 below were obtained.

Analytical method (1) Na, K, Li atomic absorption spectrophotometry (2) U fluorescence spectrophotometry (NaFNaKCO
₃ Melt) As described in detail above, according to the present invention, a siliceous raw material having a high impurity content is heat-treated at a high temperature in an atmosphere containing a halogen element or a compound thereof, and then hydrofluoric acid and nitric acid are added. Impurities can be removed efficiently, economically, and easily by dipping in a mixed solution with a mixture of water, alkali metal 5ppm or less, and radioactive elements such as uranium 5p.
A silica glass raw material having an extremely low impurity content of pb or less can be obtained.

The present invention has an industrially important meaning in that it has established a method for producing optical purity quartz glass that is extremely suitable for the current semiconductor industry.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Kenmochi 88 Kawakubo, Kanaya, Tamura-cho, Koriyama-shi, Fukushima Shin-Etsu Quartz Co., Ltd. Quartz Research Laboratory (56) Reference JP-A-58-204830 (JP, A)

Claims (3)

[Claims] 1. A natural siliceous powder raw material is heat-treated at a high temperature in an atmosphere containing halogen or a compound thereof, then immersed in a mixed solution of hydrofluoric acid and nitric acid, and washed with water,
A method for producing high-purity quartz glass, which comprises melting and vitrifying. 2. The natural siliceous powder raw material has a particle diameter of 10 to 10.
The method for producing high-purity quartz glass according to claim 1, which is pulverized and classified to 1000 μm. 3. The method for producing high-purity quartz glass according to claim 1, wherein the alkali metal is 5 ppm or less and the radioactive element such as uranium is 5 ppb or less.