JPS5832008A - Treatment of inner surface of mold for preparation of high purity silicon - Google Patents

Abstract

PURPOSE:To prevent the cracking of a high purity silicon rod formed in a mold, by applying SiC powder to the inner surface of the mold using chlorosilane, alkoxysilane, colloidal silica, etc. as a binder. CONSTITUTION:SiC powder is added to liquid chlorosilane, alkoxysilane or colloidal silica to obtain a slurry, which is applied to the inner surface of a mold for the preparation of high purity silicon and made of a heat-resistant material such as quartz, alumina, graphite, etc. The chlorosilane or the alkoxysilane is hydrolyzed, and the coating layer is dried to obtain the inner surface of the mold coated with SiN powder using the hydrolysis product or the colloidal silica as a binder. Preferably, the chlorosilane is trichlorosilane, etc., the alkoxysilane is tetramethoxysilane, etc., and the particle size of the SiN powder is finer than about 100 mesh.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating the inner surface of a mold for producing high-purity silicon.

High purity silicon for semiconductor industry @! To produce 1, a high-purity silicon rod (hereinafter simply referred to as a silicon rod) placed in a lv. A method is used in which polycrystalline silicon is precipitated on a silicon rod, taken out and melted in a crucible or the like, and a single crystal seed is added to grow it to obtain a single crystal.

The silicon rod used at this time is manufactured by pouring molten silicon into a quartz tubular mold, cooling it, and then taking out the molded body. At this time, if the silicon and mold are in close contact, there will be a difference in the coefficient of expansion between the two. This causes cracks in the silicon molded body.

Conventionally, after blasting the inner surface of a mold such as a quartz crucible, it is heated above the boiling point of a volatile liquid such as water, and then these liquids are
A method has been proposed in which silicon nitride is attached to the inner surface of the mold by spraying a slurry of dispersed high-purity silicon nitride powder onto the inner surface of a quartz crucible and evaporating the liquid (
U.S. Pat. No. 3,041°690). When molten silicon is poured into a mold coated with silicon nitride powder, it is difficult for the silicon nitride to get wet with the molten silicon, and since the silicon nitride is a powder, stress is generated due to the difference in shrinkage between the mold and the silicon. It has a buffering effect and prevents cracks from forming in the silicon molded body. However, this method is unsuitable because it is impossible to blast the elongated tubular mold used for manufacturing silicon rods or the complex-shaped inner surface of the mold.

The silicon nitride powder on the inner surface of the mold has the disadvantage that it easily falls off.

In order to solve the following 51 problems, the present inventor has made extensive studies and developed a hydrolyzed product of chlorosilane or alkoxysilane or colloidal silica (a trowel that fixes silicon nitride powder). It is less likely to peel off than the inner surface of the mold.
Furthermore, they discovered that a coated surface that does not cause damage to silicon molded bodies can be obtained, and the method of the present invention was completed.

That is, in the present invention, silicon nitride powder is added to liquid chlorosolane, alkoxysilane, or colloidal silica to form a slurry, and the slurry is coated on the inner surface of a mold for manufacturing high-purity silicon made of a heat-resistant material such as quartz, alumina, or graphite. A method for treating the inner surface of a mold for producing high-purity silicon, which comprises: hydrolyzing the chlorosilane or alkoxysilane and then drying the coated surface to coat the mold with silicon nitride powder using the mold as a binder.

If only colloidal silica is used, the hydrolysis step is omitted.

Examples of the liquid chlorosilane used in the present invention include trichlorosilane and tetrachlorosilane, and examples of the alkoxysilane include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane. A silicon nitride powder having a particle size of preferably 100 mesh or less is added to this to form a slurry and applied to the inner surface of the mold.

The slurry concentration is preferably about 30 to 70% by weight. Naturally, in order to obtain a high-purity silicon molded body, silicon nitride, chlorosilane, alkoxysilane, or colloidal silica must be of high purity.

In order to obtain a thick coating layer, the above operation may be repeated many times. Next, when chlorosilanes are used, the inner coating layer of the mold is brought into contact with humid air or the like to hydrolyze the chlorosilanes. In addition, when alkoxysilane is used, hydrolysis is performed with added hydrochloric acid. The hydrolysis products are estimated to be mainly amorphous silica, but these are
It becomes a polymer through the process, acts as a binder for the silicon nitride powder, and at the same time firmly adheres to the inner surface of the mold. Furthermore, the mold is heated and dried to remove moisture and hydrogen chloride, and in the case of using alkoxycin, alcohol is also removed during the lltl process. When colloidal silica is used, similar results can be obtained by simply heating or drying it.

As explained above, according to the method of the present invention, a binder mainly based on amorphous warping force is formed on the inner surface of the mold, so unlike the case where silicon nitride powder is simply physically deposited, blasting treatment of the inner surface of the mold is required. do not. Therefore, the silicon nitride powder can be easily applied to the inner surface of an elongated tubular mold or a mold of complex shape. In addition, it is possible to apply multiple layers of silicon nitride powder through the action of a binder, so when molding a silicon melt by pouring it into a heat-resistant mold, stress due to the difference in shrinkage between the mold and the silicon raw material is applied to the laminated silicon nitride particles. The rate of buffering due to mutual misalignment is high, and phenomena such as cracks in the molded product hardly occur.

In addition, conventionally, when manufacturing high-purity silicon, the mold material was limited to homogeneous quartz, etc., but according to the method of the present invention, silicon nitride powder is bound by a siliceous binder to form a coating layer on the inner surface of the mold. Since the mold material does not come into direct contact with high-purity silicon, it has various industrial advantages such as being able to use molds made of different materials such as graphite and alumina. As mentioned above, the method of the present invention is particularly useful as a method for treating the inner surface of one mold for molding a silicon rod, which is necessary when producing high-purity silicon, but it can also be applied to all other molds such as crucibles.

Example 1, Comparative Example In a quartz tube having a length of 1000 ra, an inner diameter of 3.5 mm, and a thickness of 0.5 m, 2 parts by weight of high-purity silicon nitride powder (average grain size 6-+50 mesh) and 3 parts tetrachlorosilane were placed. A slurry consisting of parts by weight was poured to coat the inner surface of the quartz tube. Next, when moist air is blown into one end of the quartz tube to hydrolyze the tetrachlorosilane, a rough coating film is formed in which the silicon nitride powder is fixed by the amorphous silica binder produced. This operation was repeated three times to obtain a coating film with a thickness of approximately 0.4111 mm. The quartz tube is then heated to about 100'C to remove moisture and hydrogen chloride. One end of the quartz tube with the inner surface treated in this way was immersed in a molten silicon bath at a temperature of approximately 1450°C, and the molten silicon was sucked out by a vacuum operation. A high-purity silicon rod with a diameter of 2.7 u and a length of 600 m was obtained, with no cracks observed at all.

For comparison, a quartz tube without a slurry of high-purity silicon nitride powder and tetrachlorosilane was used, and when molten silicon at about 1450°C was sucked in, the quartz tube cracked, and at the same time, the silicon rod developed many cracks and broke. Length approx. 10
Only silicon rods of about 111x were obtained.

Example 2 High purity silicon nitride powder (average particle size approximately 150 mesh) 2
A slurry consisting of 3 parts by weight of tricloxilaf triple wall part is applied to the inner surface of a quartz crucible having an internal volume of about 100 -. Next, humid air is sent to the coated surface to hydrolyze the trichlorosilane, forming a rough coating film in which the silicon nitride powder is fixed by the binder of the hydrolyzed product. This operation was repeated three times to obtain a coating film with a thickness of about 0.4 ff. Next, this quartz crucible is heated to about 100° C. to remove water and hydrogen chloride. The same molten silicon as in Example 1 was poured into the quartz crucible whose inner surface had been treated in this way, and allowed to cool and solidify.

The high-purity silicon ingot obtained in this manner was easily taken out without damaging the quartz crucible, and no cracks were observed.

Example 3 To 2.5 tnt of tetraethoxysilane, 5-ethyl alcohol is added, and while stirring, 2.5% hydrochloric acid is added. Further, 40 f of silicon nitride powder having an average particle size of about 150 mesh was added to form a slurry and applied to the inner wall of the quartz tube used in Example 1. Hydrolysis with hydrochloric acid is completed within 20 minutes. Next, this quartz tube was dried at 100° C., and the molten silicon was sucked and allowed to cool in the same manner as in Example 1. A high-purity silicon rod of the same type without any cracks was obtained.

Example 4 High purity silicon nitride powder with an average particle size of about 150 mesh per 10 g of colloidal silica with a solid content of 2ON 11% 15
Add f to make a slurry with a volume of 100tn! , applied to the inner wall of an alumina crucible and dried at room temperature. After performing this operation twice, the same molten silicon as in Example 1 was poured and cooled and solidified. The resulting high-purity silicon block was easily taken out and no cracks were observed.

Applicant: Osaka Soda Co., Ltd. Agent: Patent Attorney Toru Hamanaga 9-

Claims (1)

[Claims] Liquid chlorosilane, alkinosilane or colloidal silica powder is added to form a slurry, which is applied to the inner surface of a high-purity silicon production mold made of heat-resistant material such as quartz, alumina, or graphite, and then the above-mentioned After hydrolyzing chlorosilane or alkoxysilane, by drying the coated surface, silicon nitride powder with a hydrolysis product or colloidal silica as a binder is coated on the circular surface of the mold.''7 A method for treating the inner surface of silicon manufacturing molds.