RU2333900C1 - Method of production of quartz crucibles - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention is related to refractory industry, namely, to production of large-size quartz crucibles, which may be used in production of semi-conductor materials. Method of quartz crucibles production includes preparation of highly concentrated suspension of quartz glass, its stabilisation, casting into porous mold, drying and baking. At that after casting into porous mold additionally suspension of synthetic dioxide of silicon prepared by means of hydrolysis of silicon tetrachloride is applied onto prepared quartz crucible by method of slip casting.

EFFECT: provides possibility to manufacture quartz synthetic crucibles of wide assortment, including crucibles of large size and increase of purity of synthetic quartz crucibles.

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Description

The invention relates to the refractory industry, in particular to the production of large-sized quartz crucibles for melting silicon used in the semiconductor industry.

A known method for producing synthetic quartz products by spraying silicon dioxide obtained in the process of decomposition of a volatile silicon compound in a stream of oxygen-hydrogen plasma, on a heat-resistant former, followed by vitrification of the sprayed workpiece in vacuum (RF patent 2061111, IPC C30B 15/10 C30B 29/18, 1996.05.27.).

The disadvantage of this method is the inability to manufacture quartz crucibles of large diameter (over 330 mm) by spraying. This is due to the low density of the raw material component of 0.5-0.6 g / cm ³ , as a result of which the blanks of large-sized crucibles are destroyed under their own weight.

In addition, during operation, such products can “devitrify” and collapse, since amorphous silica recrystallizes at high temperature into cristobalite, causing local volume changes.

The closest set of essential features to the claimed is a method of manufacturing large-sized crucibles from quartz ceramics (RF patent 2264365, IPC С04В 35/14, 2005.11.20), which includes obtaining a highly concentrated suspension of silica glass (SiO ₂ > 99.5%), its stabilization , the introduction of granular aggregate (50-400 microns), molding by molding in porous forms, drying and firing, or hydrothermal treatment.

The disadvantage of this method is the lack of the necessary purity of the original fused silica.

In the inventive method, the goal is to obtain such a product that satisfies the following conditions:

- the possibility of manufacturing quartz synthetic crucibles of a wide range, including crucibles of large sizes, with a diameter of over 330 mm;

- increasing the purity of synthetic quartz crucibles.

This is achieved by the fact that in the method of manufacturing quartz crucibles, including obtaining a highly concentrated suspension of silica glass, stabilizing it, molding it into porous molds, drying, firing, after casting into a porous mold, a suspension of synthetic silicon dioxide is additionally applied to the obtained silica crucible by slip casting, obtained by hydrolysis of silicon tetrachloride.

In contrast to the prototype, in the proposed solution, after casting in a porous mold, a suspension of synthetic silicon dioxide obtained by hydrolysis of silicon tetrachloride is additionally applied to the obtained quartz crucible by slip casting.

The essence of the method of producing quartz crucibles is as follows:

a concentrated suspension of quartz glass was prepared, it was stabilized for 12 hours, then it was cast into a porous form, dried at a temperature of 120 ° C, fired at 550-750 ° C for 1 hour, so that the semi-finished product retained the ability to absorb moisture, as a result a quartz crucible was obtained, and then a suspension of synthetic silicon dioxide obtained by hydrolysis of silicon tetrachloride was deposited on its inner surface by slip casting, the resulting sample was dried and annealed at 1100-1200 ° С.

The application of an additional layer of synthetic silicon dioxide allows to obtain a material of high density (1.95-1.99 g / cm ³ ) and low porosity (7-5%).

When the temperature of firing a crucible made of quartz glass changes from 550 to 700 ° C, the ability to absorb moisture near the walls of the semi-finished product decreases, the duration of the mass gain of the internal crucible made of synthetic silicon dioxide increases, as a result of which the density of the finished products increases and the porosity decreases (Table 1).

Table 1
Effect of the temperature of annealing of a crucible made of quartz glass on the density and porosity of the finished product with an additional layer of synthetic silicon dioxide annealed at a temperature of 1150 ° C t ° C 550 600 650 700 750 800 The density of the preformed crucible, g / cm ³ 1,6 1.73 1.75 1.83 1.85 1.85 The density of the finished product, g / cm ³ 1.83 1.90 1.95 1.99 1.99 1.9 The porosity of the finished product,% 13.0 9.5 7.0 5,0 5,0 9.5

In addition, high purity of the inner wall of the synthetic silicon dioxide crucible, which is in contact with the melt when growing silicon single crystals, is ensured, since the total impurity content does not exceed 1.32 · 10 ^-3 wt.% (Table 2).

table 2
The chemical composition of the synthetic powder of silicon dioxide, 10 ^-4 wt.% Cu Ti Ni Sa Cr Fe Mg AT Na TO Cl SiO ₂ ≤0.07 ≤0.5 ≤0.3 ≤2.0 ≤0.04 ≤10.0 ≤0.08 ≤0.04 ≤0.08 ≤0.04 ≤0.05 rest

A specific example of the method.

To obtain a quartz crucible with a diameter of 406 mm, the waste of transparent quartz glass in the form of a tube break was subjected to mechanical activation. Then concentrated suspensions were prepared, the stabilization of which was carried out by stirring for 8 hours. The finished molding material was cast into a porous mold. Primary drying was carried out at room conditions (20-25 ° C) for 24 hours. Further drying was carried out at 120 ° C for 12 hours. Annealed at 700 ° C in an atmosphere of air for 1 hour, the result was a quartz crucible.

To obtain the next high-purity ceramic layer, silicon dioxide was prepared by sol-gel method using semiconductor purity silicon tetrachloride. The gel was dried at a temperature of 260 ° C. Xerogel was annealed at 1150 ° C for 2 hours. The resulting powder was subjected to mechanical activation.

Based on high purity silica, a suspension was prepared which was stabilized by stirring for 2 hours. The finished molding material by slip casting was applied to the inner walls of the previously obtained quartz crucible. Then the sample was dried for 24 hours at room conditions, for 12 hours at 120 ° C, annealed at 1150 ° C for one hour in an atmosphere of air.

The proposed method for producing synthetic quartz crucibles allows to obtain high-quality crucibles of a wide range of sizes, to simplify the purification scheme of the original natural quartz and, in addition, to solve the environmental problem of utilizing silicon tetrachloride formed during the processing of trichlorosilane, a toxic waste from semiconductor production.

Claims (1)

A method of manufacturing quartz crucibles, including obtaining a highly concentrated suspension of quartz glass, its stabilization, molding by molding in a porous form, drying and firing, characterized in that after casting into a porous form, a suspension of synthetic silicon dioxide obtained by hydrolysis of silicon tetrachloride.