JP3449654B2 - Method for producing opaque quartz glass - 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 efficiently producing opaque quartz glass having high purity and excellent heat resistance and heat shielding properties, particularly opaque quartz glass useful as an infrared scattering and heat shielding material for a heat treatment furnace.

[0002]

2. Description of the Related Art Conventionally, quartz glass has been used as a heat treatment furnace or a heat treatment jig for the semiconductor industry because it has high purity and excellent heat resistance. In this heat treatment furnace for the semiconductor industry, it is important to make the temperature distribution in the furnace uniform, and for that purpose, as shown in JP-A-5-900, 100,000 bubbles / cm ³ or less of bubbles Or 6000 pieces / c at both ends of the boat on which a furnace core tube is made of opaque quartz glass containing silicon or a silicon wafer is mounted as described in Japanese Utility Model Laid-Open No. 162362/1989.
A heat ray scattering plate of opaque quartz glass containing bubbles of less than m ³ was provided.

In order to manufacture the above-mentioned opaque quartz glass plate, it is efficient to cut a solid opaque quartz glass block into a plate shape. Therefore, after filling the raw material silicon dioxide powder into a heat-resistant mold, it is heated in an electric furnace. A method of producing an opaque quartz glass block by heating and melting (hereinafter referred to as a filling-type melting method) has been adopted.

However, in the above-mentioned filling-type melting method, quartz powder is filled in a heat-resistant mold such as graphite, and it is melted by an electric melting method in which a hydroxyl group is less mixed. However, there is a defect that abnormal air bubbles are generated by mixing with the powder, or the raw material collapses at the time of sintering the raw material and cracks occur in the opaque quartz glass.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made extensive studies to solve these problems, and as a result, inserted a quartz glass tube into a heat-resistant mold and put a specific silicon dioxide powder inside the tube. The present invention has been completed by finding that the above problems can be solved by filling in, and sintering and melting it. Ie

An object of the present invention is to provide a method for efficiently producing opaque quartz glass having high purity and excellent heat resistance and heat shielding properties.

Another object of the present invention is to provide a method for producing a homogeneous and solid opaque quartz glass which does not contain abnormal bubbles and is free of cracks.

[0008]

According to the present invention for achieving the above object, a quartz glass tube is inserted into a heat-resistant mold, and a particle diameter of 50 to 200 μm and a bulk density of 1.2 to 1.6 g / c
Cell diameter of 10 to 300, characterized by being filled with m ³ of silicon dioxide powder and then sintered and melted in an inert atmosphere
The present invention relates to a method for producing opaque quartz glass containing bubbles having a diameter of 100 μm and a cell density of 100,000 to 1,000,000 cells / cm ² .

The silicon dioxide powder used in the production method of the present invention is a natural crystalline quartz powder and an amorphous powder. For example, the purification method described in US Pat. No. 4,983,370 is used for Na purification. The concentration of alkali metal elements of K and K is 0.5 pp, respectively.
m or less, Fe element concentration 0.2 ppm or less, Mg element concentration 0.1 ppm or less, Cu element concentration 0.05 ppm
Purified below, particle size 50-200 μm, bulk density 1.2
It is a silicon dioxide powder adjusted to ˜1.5 g / cm ³ .
If the purity of the silicon dioxide powder exceeds the above range, it is unsuitable as an opaque quartz glass forming a highly purified heat treatment furnace for semiconductors, and if the particle size is less than 50 μm, it is too fine to achieve good opacity and the particle size is 200 μm. If it exceeds, large bubbles are generated and the heat shield property is poor. Furthermore, the bulk density is 1.2
If it is less than g / cm ³ , the powder layer serves as a heat insulating material and the sintering does not proceed to the center, only the outer peripheral portion is sintered, the central portion is not melted and solid opaque quartz glass is not formed, and the bulk density is 1. 5 g
It is difficult to prepare a silicon dioxide powder exceeding / cm ³ within the above particle size range. When the above-mentioned silicon dioxide powder adjusted in purity, particle size and bulk density is sintered and melted in a heating and melting furnace at a temperature not higher than the melting temperature of the silicon dioxide powder, the bubble diameter is 10 to 300 μm and the bubble density is 100. , 00
0 to 1,000,000 closed cells / cm ³ are uniformly dispersed, and an opaque quartz glass having a bulk density of 1.7 to 2.15 g / cm ³ is obtained. The opaque quartz glass has high heat resistance, high purity, and excellent heat shielding properties because the closed cells are uniformly dispersed. When the bubble diameter and the bubble density deviate from the above ranges, the heat shielding property becomes poor, and when the bulk density is less than 1.7 g / cm ³ , the number of bubbles is large and the mechanical strength of the quartz glass is lowered, resulting in a bulk density. Is 2.15 g /
If it exceeds ³ cm ³ , the transparency is increased and the light scattering effect is reduced, resulting in a poor function as a heat shield.

A graphite mold is preferable as the heat-resistant mold into which the quartz glass tube is inserted in the above-mentioned manufacturing method, and a heating and melting furnace for sintering and melting is an electric melting furnace in which OH groups are less mixed, for example, High-purity carbon, silicon carbide,
A resistance heating type reduced pressure electric furnace having a heat resistant type or a heat resistant case made of silicon nitride or the like is preferable, and an electric furnace made of high-purity graphite is particularly preferable.

The temperature for sintering and melting the above-mentioned silicon dioxide powder for vitrification is 1,600 to 2,000 ° C, preferably 1,700 to 1,800 ° C. Temperature is 1,60
If the temperature is lower than 0 ° C, the quartz powder is not sufficiently melted and cracks occur in the glass body. On the contrary, if the melting temperature is 2,000
If the temperature exceeds ℃, the melting proceeds excessively and softens, and the bubbles in the glass body are communicated with each other, and the independence of the bubbles becomes low.

When heated in the above temperature range, the bulk density is 1.2 to
10 to 20% of silicon dioxide powder having 1.5 g / cm ³
Contract. Due to this shrinkage, a gap is created between the mold and the silicon dioxide powder layer, and the so-called powder drop in which the silicon dioxide powder falls from the upper part of the silicon dioxide powder layer occurs, causing cracks in the opaque quartz glass. In the present invention, since silicon dioxide powder is filled in the quartz glass tube, when heated to the above temperature, the viscosity η of the quartz glass tube is 10 ⁸ at 1650 ° C., for example.
It drops to a poise level and is deformed by its own weight to fill the gap. Therefore, the opaque quartz glass obtained by the present invention does not crack. Further, since the silica glass protects the silicon dioxide powder, graphite contaminants do not affect the opaque silica glass.

Nitrogen gas is preferable as the inert gas used at the time of sintering and melting. By sintering in this inert gas atmosphere, the active gas is replaced with the inert gas, and the active gas in the bubbles is reduced.

[0014]

The present invention will be described in detail below with reference to specific examples, but the present invention is not limited thereto.

The bubble density as used in the present invention is DIN5.
According to 8927, a thin piece of opaque quartz glass with a fixed volume is photographed with transmitted light, and the number of bubbles contained is counted,
The number is the value converted to 1 cm ³ of opaque quartz glass.

Example 1 In a graphite mold 2 having an inner diameter of 270 mm and a height of 300 mm shown in FIG. 1, an outer diameter of 270 mm, a wall thickness of 4 mm, and a height of 3
A 00 mm quartz glass tube 3 was inserted. Inside the quartz glass tube 3, the particle diameter is 50 to 200 μm, and the average particle diameter is about 1
Natural quartz crystal powder with a diameter of 00 μm and a bulk density of 1.4 g / cm ³ 1
And placed in an electric furnace 4 with a heater 5 for 10 to 2
The air remaining between the particles was removed by evacuation below torr. Then, the inside of the furnace was vacuum-disrupted with nitrogen, and 5 l /
Flowing nitrogen gas at a flow rate of min for 1,200 ° C in 120 minutes, 1,200 ° C to 1,630 ° C in 9 minutes
In 0 minutes, the temperature was raised from 1,630 ° C to 1,750 ° C in 240 minutes, heated for 60 minutes while maintaining it at 1750 ° C, then stopped heating and cooled to room temperature, and the opaque quartz glass block was taken out. It was A disk of about 4 mm was cut out from the obtained opaque quartz glass block, and the surface was burnt with an oxyhydrogen flame to prepare a sample. When the infrared transmittance of 2 μm of the sample was measured, the transmittance was 5
%, And no abnormal foaming or foreign matter was found.

The impurity contents of the outer peripheral portion and the central portion of the above disk were measured and the results are shown in Table 1.

Example 2 In Example 1, the particle size was 100 μm or less and the bulk density was 1.
Opaque quartz glass was produced in the same manner except that 2 g / cm ³ of natural quartz crystal powder was used. A disk was cut out from the obtained opaque quartz glass block to prepare a sample, and the infrared transmittance was measured in the same manner as in Example 1. The transmittance was 5% or less, but white lumps of fine bubbles were observed. 15 points
Have been confirmed.

The impurity contents of the outer peripheral portion and the central portion of the above disk were measured and the results are shown in Table 1.

Comparative Example 1 Opaque quartz glass was manufactured under the conditions of Example 1 without using a quartz glass tube. A disk was cut out from the obtained opaque quartz glass block to prepare a sample, and the infrared transmittance was measured in the same manner as in Example 1. It was found that 80% of the opaque quartz glass disk had a transmittance of 5% or less. , The rest 2
0% had a transmittance of 5 to 20%. Further, 20 bubbles having a diameter of 3 mm or more were confirmed in the peripheral portion. The impurity contents of the outer peripheral portion and the central portion of this quartz glass disk were measured. The results are shown in Table 1.

[0021]

[Table 1]

[0022]

EFFECTS OF THE INVENTION According to the production method of the present invention, fine bubbles are uniformly dispersed, and an opaque quartz glass that is homogeneous and has high heat resistance can be produced. The opaque quartz glass obtained by the above-mentioned manufacturing method is excellent in infrared ray scattering and heat shielding properties, and has high purity, and thus is useful as a material for forming a heat treatment furnace or jig for the semiconductor industry.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an electric furnace filled with natural quartz crystal powder according to the present invention.

[Explanation of symbols]

1 Natural quartz crystal powder 2 Graphite formwork 3 Quartz glass tube 4 electric furnace 5 heater

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hitoshi Sekine Kawamura Kubo, Tamura-cho, Koriyama City, Fukushima 88 88 Shin-Etsu Quartz Co., Ltd. Quartz Research Laboratory (72) Toru Yokota 88 Kawakubo, Kaneya, Tamura-cho, Koriyama-shi, Fukushima Prefecture Shin-Etsu Quartz Co., Ltd., Quartz Technology Laboratory (72) Inventor Eiko Kamiyama 88, Kawakubo, Kanaya, Tamura-cho, Koriyama City, Fukushima Prefecture Shin-Etsu Quartz Co., Ltd., Quartz Technology Laboratory (56) Reference JP-A-63-282134 (JP, A) ) JP-A-3-54125 (JP, A) JP-A-6-135741 (JP, A) JP-A-6-128100 (JP, A) JP-A-3-202111 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C03B 20/00 C03B 19/01 C03B 19/09 C03C 11/00

Claims (3)

(57) [Claims] 1. A quartz glass tube is inserted into a heat-resistant mold, and the particle size is 50 to 200 μm and the bulk density is 1.2 to 1.6 inside.
A method for producing an opaque quartz glass, which comprises filling g / cm ³ of silicon dioxide powder, followed by sintering and melting in an inert atmosphere. 2. The bubble diameter of opaque quartz glass is 10 to 30.
0 μm, bubble density 100,000 to 1,000,000
The method for producing opaque quartz glass according to claim 1, wherein the number is 0 / cm ³ . 3. A silicon dioxide powder having a sodium and potassium element concentration of 0.5 ppm or less and an Fe element concentration of 0.2 p.
The opaque quartz glass manufacturing method according to claim 1 or 2, wherein the pm or less, the Mg element concentration is 0.1 ppm or less, and the Cu element concentration is 0.05 ppm or less.