JP3048800B2 - 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 efficiently manufactures opaque quartz glass having high purity, high heat resistance, and excellent heat shielding properties, particularly an opaque quartz glass sheet useful as a material for infrared scattering and heat shielding in a heat treatment furnace. To manufacture a solid opaque quartz glass block.

[0002]

2. Description of the Related Art Conventionally, quartz glass has a high purity,
Because of their excellent heat resistance, they have been used as heat treatment furnaces and heat treatment jigs for the semiconductor industry. However, in the heat treatment furnace for the semiconductor industry, the temperature distribution in the furnace is very important.
The furnace core tube is made of opaque quartz glass as disclosed in Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 4 (1999) -1995 discloses a scattered plate made of opaque quartz glass at both ends of a boat on which a semiconductor wafer is mounted.

However, the opaque quartz glass furnace tube described in Japanese Patent Laid-Open No. 5-900 does improve the uniformity of the quartz glass itself, but can prevent the scattering of heat rays to the end of the furnace tube. Did not. In order to prevent 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. In order to manufacture such a heat ray scattering material, it is efficient to cut a solid quartz glass block into a plate shape. Therefore, after filling glass raw material powder, particularly quartz powder, in a heat-resistant mold, it is heated and melted in an electric furnace. (Hereinafter referred to as a filling-type melting method) for producing an opaque quartz glass block. However, this conventional filling-type melting method cannot produce a high-purity opaque quartz glass block having large voids or the like in the center of the block, containing uniform bubbles, and having excellent infrared scattering and heat shielding properties.

[0004]

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

SUMMARY OF THE INVENTION The present invention relates to 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, characterized in that a center portion is filled with a glass raw material powder having a smaller particle size than 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, ultrahigh-purity crystal powder or crystal powder obtained by subjecting high-purity crystal powder to a purification treatment described in US Pat. No. 4,983,370 is preferable from the viewpoint of purity. As the amorphous powder, a powder obtained by crushing and washing high-purity quartz glass or synthetic quartz glass and adjusting the particle size to 350 μm to 50 μm is preferable.

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

In the conventional filling type melting method, FIG.
As shown in FIG. 3A, a quartz powder 3 is filled in a graphite mold 3 and melted by an electro-melting method in which hydroxyl groups are less mixed to produce an opaque quartz glass block as shown in FIG. 3B. However, even when the outside is in a molten state, the unfused layer 6 remains inside the opaque quartz glass block 5, which becomes a large void, which hinders the production of a homogeneous opaque quartz glass block. According to the study of the present inventors, the unmelted layer of the block is 10 to 70 in the radial direction of the filling material powder layer.
%, 20% to 80% in the thickness direction. When the heating is further continued to eliminate the unmelted layer, a layer having a large number of bubbles 4 is formed on the surface layer of the quartz glass block 5 as shown in FIG. A small number of translucent layers 7 are formed. However, when the glass material powder having a smaller particle diameter than the outside was filled in the center portion of the glass material powder layer to form an inner filling region 2 and then electromelted, uniform bubbles were distributed without forming the unmelted layer. An opaque quartz glass block is obtained.

The fact that the particle size of the glass raw material powder filled in the center portion is small is regarded not as a particle size distribution but as a maximum particle size difference. The glass raw material powder to be filled has a maximum particle size of 70% or less, preferably 50% or less. In general, the particle size distribution of the glass raw material powder used in the electric melting method is 350 μm to 50 μm, so that 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 occurs, and the distribution of bubbles becomes uneven.

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

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

[0014]

Embodiment 1 High-purity grade quartz (impurity amount: 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) to obtain a raw material quartz powder having a particle size distribution shown in Table 1. The crystal powder was sieved to obtain a crystal powder A from which particles of 212 μm or more were removed, a crystal powder B from which particles of 250 μm or more were removed, and a crystal powder C from which particles of 150 μm or more were removed. The particle size distribution of these quartz powders A to C shows the weight ratio of the openings of the mesh remaining on the sieve indicated in the particle size column when the used quartz powder is sieved.

[0015]

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

The above-mentioned raw material 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 a depth of 100 mm.
mm, outer diameter φ150mm at center, thickness 2
mm quartz tube, and put quartz powder A inside the quartz tube,
The outside was filled with 100 mm of raw material quartz powder. Next, the quartz tube was slowly pulled out, and then a raw material quartz powder of about 50 mm in total was filled.

When the charging of the raw material powder is completed, the graphite mold 3 is placed in an electric furnace, the whole is evacuated, nitrogen is flowed at a rate of 20 l / min, and the furnace temperature is raised from room temperature to 1600 ° C. At 20 ° C./min.
The temperature was raised from 0 ° C. to 1800 ° C. at a rate of 5 ° C./min and heated. Next, after maintaining the temperature at 1800 ° C. for 1 hour, the graphite mold was cooled and the opaque quartz glass block 5 was taken out.
A slice of × 4 × 4 mm ³ was cut out, the number of bubbles was measured with a microscope, the volume was converted to 1 cm ³ , and the bubble density (pieces /
cm ³ ). Table 2 shows the obtained results.

FIG. 2 shows a vertical cross-sectional photograph of the opaque quartz glass block.

[0019]

Example 2 An opaque quartz glass block was obtained in the same manner as in Example 1 except that the outer layer was filled with crystal powder B and the inner layer was filled with crystal C. 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 the 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 quartz powder, and heated under the same atmosphere and temperature raising conditions as in Example 1.
It was kept at 00 ° C. for 3 hours. Although melted as a whole, extremely fine bubbles were concentrated at the top, the bubble density at the middle and bottom portions was low, and the bubbles were large.

[0022]

[Table 2]

The numerical values shown in Table 2 above are the cell 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 is used. It can be seen that the fine bubbles are uniformly dispersed.

[0024]

According to the present invention, as described above, it is possible to manufacture an opaque quartz glass block in which the total surface area and the number of bubbles contained per 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 the drawings]

FIG. 1 shows a manufacturing method of the present invention.

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

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

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

[Explanation of symbols]

 1 Quartz Powder 2 Internal Filling Area 3 Graphite Type 4 Bubbles 5 Opaque Quartz Glass 6 Unmelted Layer 7 Translucent Layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-61838 (JP, A) JP-A-7-61827 (JP, A) JP-A-5-254882 (JP, A) JP-A-7-618 69661 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 1/00-14/00 C03B 20/00

Claims (3)

(57) [Claims] 1. 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. A method for producing opaque quartz glass, characterized by filling with glass raw material powder having a smaller particle size than powder. 2. The glass material powder having a small particle size has a filling range of 10 to 70% with respect to the radius of the glass material powder layer and 20 to 80% with respect to the thickness of the glass material powder layer. A method for producing the opaque quartz glass described above. 3. The maximum diameter of the glass raw material powder to be filled in the center part is 70 times the maximum particle diameter of the glass raw material powder to be filled in the outer layer part.
%. The method for producing opaque quartz glass according to claim 1, wherein