JPH0761839A - Production of opaque quarts glass - Google Patents

Abstract

PURPOSE:To obtain an opaque quartz glass block high in heat resistance and excellent in the IR light-scattering property and the heat-shielding property. CONSTITUTION:The method for producing an opaque quartz glass containing fine cells by charging the powder of glass raw materials in a mold and subsequently thermally melting the charged glass raw materials, comprises charging the powder of glass raw materials having a smaller particle diameter than that of the powder of the glass raw materials in the external layer into a space occupying 10-70% of the glass raw material powder layer and 20-80% of its thickness in the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention efficiently produces an opaque quartz glass having high purity, high heat resistance and excellent heat shielding properties, particularly an opaque quartz glass plate useful as an infrared scattering and heat shielding material for a heat treatment furnace. And a method for manufacturing a solid opaque quartz glass block.

[0002]

2. Description of the Related Art Conventionally, quartz glass has a high purity,
Since it has excellent heat resistance, it has been used as a heat treatment furnace or heat treatment jig for the semiconductor industry. However, in the heat treatment furnace for the semiconductor industry, the temperature distribution in the furnace is very important, and in order to make the temperature in the furnace uniform, for example, Japanese Patent Laid-Open No.
A furnace core tube is made of opaque quartz glass as disclosed in Japanese Patent Publication No. 900, or is actually disclosed in Japanese Utility Model Publication No. Hei 1-162223.
A heat ray scattering plate made of opaque quartz glass has been provided at both ends of a boat on which a semiconductor wafer as disclosed in Japanese Patent Publication No. 4 is placed.

However, the opaque quartz glass furnace core tube described in the above-mentioned JP-A-5-900 certainly improves the soaking property of the quartz glass itself, but can prevent the scattering of heat rays to the end of the furnace core tube. There wasn't. In order to prevent the heat ray scattering at the end of the furnace core tube, it is desirable to install a heat ray scattering material of an opaque quartz glass plate as described in, for example, Japanese Utility Model Laid-Open No. 1-162234. For the production of such a heat ray scattering material, it is efficient to cut a solid quartz glass block into a plate shape.Therefore, glass raw material powder, in particular, crystal powder is filled in a heat resistant mold and then heated and melted in an electric furnace. A method of producing an opaque quartz glass block (hereinafter referred to as a filling-type melting method) has been adopted. However, in this conventional filling-type melting method, it was not possible to manufacture a high-purity opaque quartz glass block having a large void or the like in the center of the block and containing uniform bubbles and having excellent infrared scattering and heat shielding properties.

[0004]

The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, in filling the glass raw material powder, the raw material powder to be filled in the inner layer of the glass raw material powder layer. The present invention has been completed by discovering that an opaque quartz glass block containing uniform bubbles can be obtained by using a glass raw material powder having a particle size smaller than that of the raw material powder filling the outer layer.

That is, an object of the present invention is to provide a novel method for producing opaque quartz glass having high purity, high heat resistance, and excellent infrared scattering and heat shielding properties.

Another object of the present invention is to provide a method for producing opaque quartz glass useful as a heat shield for a silicon wafer heat treatment furnace.

[0007]

The present invention is a method for producing an opaque quartz glass containing fine bubbles formed by filling a glass raw material powder in a mold and heating and melting the glass raw material powder. The present invention relates to a method for producing opaque quartz glass, which comprises filling the center portion with glass raw material powder having a particle size smaller than that of the glass raw material powder of the outer layer.

The opaque quartz glass is an opaque quartz glass containing bubbles obtained by heating and melting glass raw material powder in a non-oxidizing atmosphere. As the glass raw material powder, crystalline quartz powder or amorphous powder is used,
As the crystalline powder, ultrapure crystal powder or crystal powder obtained by purifying high-purity crystal powder according to US Pat. No. 4,983,370 is preferable in terms of purity. Further, as the amorphous powder, powder of high-purity quartz glass or synthetic quartz glass crushed and washed to adjust the particle size to 350 μm to 50 μm is preferable.

By the way, it is said that the radiant heat conduction is dominant in the heat conduction to the quartz glass when the temperature is 1000 ° C. or higher. When bubbles are present in the quartz glass at the above temperature, reflection of heat rays occurs not only on the glass surface but also on the bubbles inside, so the surface area of the bubbles and their distribution in the opaque quartz glass have a great influence on the reflection and transmission of heat rays. Exert. Therefore, in order to use opaque quartz glass as a heat shield material for a heat treatment furnace, it is important to increase the total surface area of bubbles contained in a unit volume, increase the number of bubbles, and disperse the bubbles uniformly.

In the conventional filling type melting method, as shown in FIG.
As shown in FIG. 3A, the graphite mold 3 was filled with the crystal powder 1 and melted by an electric melting method in which hydroxyl groups were less mixed to produce an opaque quartz glass block as shown in FIG. 3B. However, even if the outer side is in a molten state, the unmelted layer 6 remains inside the opaque quartz glass block 5, and it becomes a large void, which is an obstacle to the production of a homogeneous opaque quartz glass block. According to the study by the present inventors, the unmelted layer of the block is 10 to 70 in the radial direction of the packing material powder layer.
%, 20% to 80% in the thickness direction. When heating is further continued in order to eliminate this unmelted layer, as shown in FIG. 4 (b), a very large layer of bubbles 4 is formed on the surface layer of the quartz glass block 5, and on the contrary, there are large bubbles at the bottom. A small number of semitransparent layers 7 are formed. However, when the central portion of the glass raw material powder layer was filled with the glass raw material powder having a smaller particle size than the outside to form the inner filling region 2 and electromelted, the unmelted layer was not formed and uniform bubbles were distributed. An opaque quartz glass block is obtained.

The fact that the particle size of the glass raw material powder filled in the central portion is small is understood not as a particle size distribution but as a maximum particle diameter difference, and the maximum particle diameter of the glass raw material powder filled in the central portion is the outer layer. It may be 70% or less, preferably 50% or less of the maximum particle diameter of the glass raw material powder to be filled. Since the particle size distribution of the glass raw material powder generally used in the electric melting method is 350 μm to 50 μm, the maximum particle size of the glass raw material powder used in the central portion is 250 μm or less, preferably 175 μm or less, and 250 μm. In the case of the above, uniform melting does not occur inside and outside, an unmelted portion is generated, and the distribution of bubbles becomes uneven.

In view of the distribution of the unmelted layer, the internal filling region of the glass raw material powder having the small particle diameter may be 10 to 70% in the radial direction of the filling raw material powder layer and 20 to 80% in the thickness direction. .

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

[0014]

Example 1 Quartz crystal of high purity grade (amount of impurities: Na;
0.1 ppm, K; 0.2 ppm, Li; 0.2 pp
m, Al; 10 ppm, Ca; 0.3 ppm, Fe;
0.1 ppm, Cu; ∠0.05 ppm, Mg; 0.1
(ppm) was pulverized to obtain a raw material crystal powder having a particle size distribution shown in Table 1. The crystal powder was sieved to obtain crystal powder A from which particles of 212 μm or more were removed, crystal powder B from which particles of 250 μm or more were removed, and crystal powder C from which particles of 150 μm or more were removed. The particle size distributions of the crystal powders A to C show the weight ratios of the openings of the mesh left on the sieve shown in the particle size column when the used crystal powders were sieved.

[0015]

[Table 1] Note) In the table, the values are% by weight.

The above raw quartz powder is placed in a graphite mold 3 having an inner diameter of 300 mm and a height of 400 mm from the bottom to 100 mm.
mm spread, outer diameter φ150 mm, thickness 2 at the center
mm quartz tube is erected, and quartz powder A is placed inside the quartz tube.
In addition, 100 mm of each raw material crystal powder was filled on the outside. Then, after slowly removing the quartz tube, a total of about 50 mm of raw material crystal powder was filled.

When the filling of the raw material powder is completed, the graphite mold 3 is placed in an electric furnace, the whole is evacuated, then nitrogen is flowed at a rate of 20 l / min, and the furnace temperature is from room temperature to 1600 ° C. At 20 ° C / min and again 160
The temperature was raised from 0 ° C to 1800 ° C at a rate of 5 ° C / minute and heated. Next, after holding at 1800 ° C. for 1 hour, the graphite mold was cooled, the opaque quartz glass block 5 was taken out, and 1 was taken from each part of the obtained opaque quartz glass block.
Cut out a thin piece of × 4 × 4 mm ³ , measure the number of bubbles with a microscope, convert the volume to 1 cm ³ , and measure the bubble density (number /
cm ³ ). The results obtained are shown in Table 2.

FIG. 2 shows a photograph of a cross section of the opaque quartz glass block in the vertical direction.

[0019]

Example 2 In Example 1, an outer layer was filled with crystal powder B and an inner layer was filled with crystal C, and an opaque quartz glass block was obtained in the same manner as in Example 1. The bubble density was measured and is shown in Table 2.

[0020]

Comparative Example 1 An opaque quartz glass block was manufactured in the same manner as in Example 1, except that a graphite mold was filled with only high-purity quartz powder. The unmelted layer 6 remained 50 mm from the surface of the obtained opaque quartz glass block and about 80 mm from the periphery, and was not vitrified.

[0021]

[Comparative Example 2] A graphite mold was filled with only raw material crystal powder, and heated under the same atmosphere and temperature raising conditions as in Example 1, and
Hold at 00 ° C for 3 hours. Although it was melted as a whole, extremely fine bubbles were concentrated in the upper part, the bubble densities in the middle and bottom were sparse, and the bubbles were large.

[0022]

[Table 2]

The numerical values shown in Table 2 above are bubble densities (cells / cm ³ ) at each position of the opaque quartz glass block. As is clear from the table, the opaque quartz glass block obtained by the production method of the present invention. It can be seen that fine air bubbles are uniformly dispersed in.

[0024]

As described above, according to the present invention, it is possible to manufacture an opaque quartz glass block in which the total surface area and the number of bubbles contained in a unit volume are large and the bubbles are uniformly dispersed. By cutting out, an opaque quartz glass plate having a high infrared scattering and heat shielding effect can be efficiently manufactured.

[Brief description of drawings]

1 shows a manufacturing method of the present invention.

FIG. 2 shows a cross-sectional photograph of an opaque quartz glass block obtained by the manufacturing method of the present invention.

FIG. 3 is a sectional view of an opaque quartz glass block manufactured by a conventional filling-type melting method.

FIG. 4 shows a cross-sectional view of an opaque quartz glass block when overheated by a conventional filling-type melting method.

[Explanation of symbols]

 1 Crystal powder 2 Internal filling area 3 Graphite type 4 Bubbles 5 Opaque quartz glass 6 Unmelted layer 7 Semi-transparent layer

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[Procedure amendment]

[Submission date] June 14, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

FIG. 2 shows a photograph of a cross section of the structure of an opaque quartz glass block obtained by the production method of the present invention.

Claims (3)

[Claims] 1. A method for producing an opaque quartz glass containing fine bubbles formed by filling glass raw material powder in a mold and heating and melting the glass raw material powder layer in the mold, wherein the central portion of the glass raw material powder layer is the outer glass raw material. A method for producing an opaque quartz glass, which comprises filling with a glass raw material powder having a particle size smaller than that of the powder. 2. The filling range of the glass raw material powder having a small particle diameter is 10 to 70% with respect to the radius of the glass raw material powder layer and 20 to 80% with respect to the thickness thereof. A method for producing the opaque quartz glass described above. 3. The maximum diameter of the glass raw material powder filled in the central portion is 70 times the maximum particle diameter of the glass raw material powder filled in the outer layer portion.
% Or less, The method for producing an opaque quartz glass according to claim 1, wherein