JPH0813716B2 - Silica glass crucible for pulling silicon single crystal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silica glass crucible for pulling a silicon single crystal, and more particularly to a silica glass crucible for pulling a silicon single crystal having an inner layer and an outer layer.

(B) Conventional Technology A silica glass crucible is used as a container for containing a molten silicon when pulling a silicon single crystal from the molten silicon by the Czochralski method. This silica glass crucible for pulling a silicon single crystal has been conventionally manufactured by an arc heating rotary molding method using a purified quartz powder obtained by crushing naturally occurring quartz or quartz and then refining it. There is.

Silicon single crystals require high purity,
In the silicon single crystal produced by the Czochralski method, the amount of impurities in the silicon single crystal is usually much higher than the amount of impurities in the raw material polycrystalline silicon because the amount of impurities in the silica glass crucible is much higher. Increasing the purity of the silica glass crucible is very important for the production of high-purity silicon single crystals, and the silica glass crucible has been highly purified.

(C) Problems to be Solved by the Invention As described above, the silica glass crucible is refined by refining naturally occurring quartz powder. A pure silica glass crucible cannot be obtained. Therefore, by applying an electric field to the molded silica glass crucible at a high temperature, Li ⁺ ions and Na ⁺ ions having high mobility are removed to purify the silica glass crucible. However, even when electric field refining is performed on a silica glass crucible, there are restrictions on the types of impurities that can be removed, and there is a problem in that, for example, aluminum (Al) ions and titanium (Ti) ions cannot be removed.

As described above, the achievement of higher purification of the silicon single crystal has reached a situation in which it is no longer possible to expect further improvement as long as a silica glass crucible made of natural quartz is used.

Therefore, there has been proposed a method for producing a silica crucible using a gel-like powder of high-purity synthetic silica obtained by the sol-gel method as a raw material.

(D) Means for Solving the Problems The inventors of the present invention produced a silica glass crucible to be provided for pulling a silicon single crystal by using various kinds of synthetic silica powder, and used the prototype. By pulling the silicon single crystal, the silica glass crucible for pulling the silicon single crystal has high purity, and (1) does not undergo thermal deformation at the operating temperature, that is, near 1450 ° C. (2) pulls the silicon single crystal. At the time of the above, crystallization progresses at the molten metal contact site on the inner surface of the silica glass crucible, which may peel off and hinder the growth of the silicon single crystal.Therefore, crystallization is not proceeded to prevent this. (3) It was discovered that it is necessary that the silica glass crucible does not abnormally foam when pulling the silicon single crystal.

Further, in order to obtain a silica glass crucible excellent in heat resistance, it is necessary to select a high viscosity silicon glass as a raw material at a high temperature to be used, but generally the viscosity of silica glass is an impurity derived from the raw material of the silica glass. Since it depends on the content and the OH group content, the raw material of silica glass is an important issue.

Therefore, the inventors of the present invention, in the case of silica glass produced by melting a synthetic silica raw material, its viscosity is not always constant even if the impurity content and the OH content are the same, but the synthesized cristobalite powder. It has been found that the silica glass produced by melting the body has a high viscosity. However, when a silicon single crystal is pulled using a silica glass crucible produced by melting synthetic cristobalite powder, the pulled silicon single crystal shows a disorder in the lattice at a high frequency and is also used. On the inner surface of the silica glass crucible, an unusually large number of cristobalite crystallites are deposited, whereas the silica glass crucible manufactured by melting the synthesized amorphous silica powder is used to produce silicon single crystals. If you pull the crystal,
It has been found that even if the silica glass crucible is deformed, the disorder of the lattice in the silicon single crystal is extremely low, and the precipitation of cristobalite crystals on the inner surface of the crucible is small.

The present invention provides a silica glass crucible for pulling a silicon single crystal having an inner layer portion and an outer layer portion having heat resistance and mechanically excellent properties when pulling a single crystal based on these discoveries. .

That is, the present invention is a silica glass crucible for pulling a silicon single crystal having an inner layer portion and an outer layer portion, wherein the outer layer portion is formed by melting a synthetic cristobalite powder, and the inner layer portion is a non-synthetic material. The gist is a silica glass crucible for pulling up a silicon single crystal, which is formed by melting crystalline silica powder.

In the present invention, the silica glass crucible for pulling up a silicon single crystal is manufactured by melting the synthetic cristobalite powder in the outer layer portion. Thus, when the outer layer portion is manufactured by melting the synthetic cristobalite powder, only the outer layer portion can be transformed into the crystal structure when pulling the silicon single crystal, so at the high temperature when pulling the silicon single crystal,
This is preferable because the viscosity of the crucible material can be increased and thermal deformation of the crucible can be avoided.

In the present invention, the silica glass crucible for pulling up a silicon single crystal is manufactured by melting the amorphous silica powder having the inner layer portion synthesized. It is preferable to melt and produce the amorphous silica powder in which the inner layer portion is synthesized as described above, since contamination of the pulled silicon single crystal can be reduced.

In the present invention, the silica glass crucible for pulling a silicon single crystal has an inner layer portion that prevents cristobalite from abnormally occurring during pulling of a silicon single crystal, and prevents silica glass from abnormally foaming so that a synthetic amorphous silica is used. The OH group content of the powder is preferably adjusted to 50 ppm (wt.) Or less, preferably 30 ppm or less.

Further, in the present invention, in order to make the outer layer portion of the crucible for pulling a silicon single crystal excellent in heat resistance, the purity of the synthetic cristobalite powder forming the outer layer portion is set to that of the alkali metal
It is necessary that the total content of Na, K, and Li is 1 ppm or less and the total content of other metal impurities is 5 ppm or less. This is because in the case of silica glass obtained by melting cristobalite powder synthesized in high purity, it is more preferable than other silica glasses obtained by melting because it is most likely to transfer to a crystal structure. is there. On the other hand, when the total content of alkali metals is 1 ppm or more and the total content of other metal impurities is 5 ppm or more,
This is not preferable because the risk of contaminating the semiconductor material increases.

The synthesized cristobalite powder used in the present invention is, for example, a metal alkoxide or an inorganic silicate as a raw material, and amorphous silicon dioxide produced by the sol-gel method is heated to β-cristobalite, and then this is obtained. It can be produced by cooling and transforming into α-cristobalite powder.

On the other hand, the synthesized amorphous silica powder used in the present invention can be produced by subjecting the amorphous silicon dioxide obtained by the sol-gel method to dehydration heating treatment in a dry atmosphere.

In the present invention, the synthesized cristobalite powder thus produced is molded into a predetermined shape in a rotating mold, and the synthesized amorphous silica powder is then molded into a predetermined shape. After that, it is melted by an arc heating rotary molding method.

(E) Action Since the silica glass crucible of the present invention is formed by melting the high-purity synthesized cristobalite powder in the outer layer portion, only the outer layer portion is promptly transformed into a crystal structure when the silicon single crystal is pulled up, and used. This is a crucible that can reduce deformation over time and thus has excellent heat resistance.

Furthermore, since the inner layer portion is formed by melting the synthesized amorphous silica powder containing a low OH group, not only can the cristobalite crystals generated when pulling the silicon single crystal be reduced, but also abnormal foaming, etc. I was able to solve the problem.

In the present invention, the synthesized cristobalite powder having a low total content of alkali metal and other metal impurities is melted to form the outer layer portion, and the inner layer portion is melted to the synthesized amorphous silica glass powder. Since it is formed as described above, it does not adversely affect the semiconductor to be processed.

(F) Examples Hereinafter, examples of the present invention will be described with reference to examples, but the present invention is not limited to the following description and examples.

Example 1 and Comparative Example 1 Tetraethyl orthosilicate _{(Si (OC 2 H 5)} 4) 1%
A 0.5% aqueous solution of NaOH was added to 100 kg of the gel obtained by mixing with an aqueous solution of acetic acid and hydrolysis and polycondensation, and the mixture was allowed to stand in a constant temperature layer at 60 ° C. for 100 hours to obtain silica glass powder. This was heated in an electric furnace at 1200 ° C. for 10 hours to form β-cristobalite, and then cooled to room temperature to obtain α-cristobalite powder. This powder in an electric furnace in a vacuum atmosphere at 1650 ℃ 5
It was heated for an hour to carry out dealkalization treatment.

The total content of alkali metals Na, K and Li in this powder was 0.6 ppm, and the total content of other metal impurities was 3 ppm.
(Sample for Example 1) The total content of alkali metal Na, K, and Li in the powder obtained by heating in an electric furnace in a vacuum atmosphere at 1650 ° C. for 1 hour was 1.
The total content of 5 ppm and other metal impurities was 20 ppm. (Sample for Comparative Example 1) The sample for Example 1 and the sample for Comparative Example 1 were melted by the oxyhydrogen flame melting method and then molded to obtain a tubular silica glass body. Then, heat treatment was performed at 1350 ° C. for 6 hours to form cristobalite nuclei on the surface layer of the silica glass body.

Comparative Example 2 The total content of alkali metals Na, K and Li is 1.5 ppm.
Natural quartz powder with a total content of other metal impurities of 20 ppm is melted by the oxyhydrogen flame melting method and then molded to form cristobalite nuclei in the surface layer of the tubular silica glass body at 1350 ° C for 6 hours. Heat treated.

Comparative Example 3 Silicon tetrachloride in which impurities were mixed at a constant ratio was used as a raw material and was hydrolyzed in an oxyhydrogen flame to obtain a silica glass body, which was then molded into a tubular shape. Next, to form cristobalite nuclei on the surface of the silica glass body
Heat treatment was performed at 1350 ° C. for 6 hours.

Comparative Example 4 A silica glass body was obtained by the same method as in Comparative Example 3 using high-purity silicon tetrachloride as a raw material, and the same heat treatment was performed.

Table 1 shows the analytical values of Na, K, Li and the other metallic impurities of the silica glass obtained in Example 1 and Comparative Examples 1, 2, 3 and 4.

In addition, the state of surface crystallization was observed in order to confirm the generation of cristobalite nuclei. Further, it was cut out from the surface at 100 μm and observed with a polarization microscope to confirm the presence or absence of cristobalite nucleation. The results are shown in Table 2.

Further, the viscosity at 1300 ° C. of Example 1 and Comparative Examples 1, 2, 3 and 4 was measured by the invagination method. Table 3 shows the results.

Next, Table 2 below shows Example 2 having the same Na, K, and Li contents as those of Example 1 of the present invention and comparative examples thereof.

Next, according to the present invention, the cristobalite powder having the same Na, K, and Li contents as in Example 1 and the Na, K, and Li contents are the same,
Crucibles were obtained by forming an inner layer and an outer layer using amorphous synthetic silica powders having different OH group contents. Table 4 shows the results of pulling a silicon single crystal using these crucibles.

As is clear from the above table, in the silica glass obtained by melting high-purity cristobalite powder as in Example 1,
It rapidly transferred to cristobalite nuclei and showed high viscosity when used. Moreover, since the content of impurities is low, the characteristics of the semiconductor material are not adversely affected in the semiconductor process.

(G) Effect of the Invention The present invention has a region of fine crystalline silica in the outer layer portion of the silica glass crucible. Therefore, when used for pulling Si single crystal, compared with a conventional silica glass crucible, It is possible to obtain excellent results in that the occurrence of foaming and fine crystals in the inner layer portion and the deformation of the silica glass crucible are reduced, and the occurrence rate of crystal disorder in the pulled Si single crystal is reduced. .

Claims (3)

[Claims] 1. A silica glass crucible for pulling a silicon single crystal having an inner layer portion and an outer layer portion, wherein the outer layer portion is formed by melting a synthetic cristobalite powder, and the inner layer portion is a synthesized amorphous. A silica glass crucible for pulling up a silicon single crystal, which is formed by melting a high quality silica powder. 2. The silica glass crucible for pulling up a silicon single crystal according to claim 1, wherein the synthesized amorphous silica powder has an OH group content of 50 ppm or less, preferably 30 ppm or less. 3. The purity of the synthesized cristobalite is such that the total content of alkali metals Na, K and Li is 1 ppm or less,
The silica glass crucible for pulling up a silicon single crystal according to claim 1, wherein the total content of other metallic impurities is 5 ppm or less.