JPH01261293A - Quartz crucible for pulling silicon single crystal - Google Patents

Abstract

PURPOSE:To markedly improve the yield of conversion into silicon single crystal, by using such a crucible that the inner peripheral part of its wall is formed with synthetic quartz, while the outer peripheral part with natural quartz. CONSTITUTION:The inner peripheral part of the wall of a crucible is formed with high-purity synthetic quartz, but with high OH concentration (e.g., >=100ppm) to prevent erosion; while the outer peripheral part with natural quart with low OH concentration (e.g., <=100ppm) to prevent deformation or fracture due to elevated temperatures. Using this double-layered crucible, a single crystal is pulled up, resulting in accomplishment of high yield of conver sion (>=75%) into silicon single crystal.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a quartz crucible used when manufacturing single crystal silicon by melting polycrystalline silicon, which has a high single crystallization yield and The present invention relates to a quartz crucible that produces silicon single crystals with good characteristics.

[Conventional technology and problems]

Silicon single crystals for semiconductors are currently manufactured mainly by the Czochralski method (CZ method).

In the CZ method, polycrystalline silicon is filled inside a quartz crucible, heated and melted at about 1450° C., and a silicon single crystal is pulled from the molten silicon. At this time, the inner circumference of the crucible wall is eroded and impurities in the crucible are mixed into the molten silicon, resulting in a decrease in the single crystallization yield of polycrystalline silicon and the characteristics of the pulled single crystal (specific resistance, (crystal defects, etc.).

Therefore, it is desirable that the impurity concentration contained in the quartz crucible for pulling silicon single crystals be as low as possible.

Incidentally, in JP-A-53-113817, boron oxide 1
ppm or less, aluminum oxide, iron oxide, titanium oxide,
It states that the content of alkali metal oxides must be 1100 pp or less. However, there are limits to the purity of naturally occurring quartz (natural quartz), and it is not possible to obtain a satisfactory product.

On the other hand, synthetic quartz has much higher purity and fewer impurities than natural quartz. However, synthetic quartz has a problem of high OH concentration. When the OH concentration increases, the viscosity decreases when melted, so if a crucible is made of synthetic quartz, the shape of the crucible tends to become unstable, and the silicon single crystal may be deformed and destroyed by heating during pulling. There is a high possibility that this will occur.

[Knowledge related to problem solving]

As a result of research into the above-mentioned problems in quartz crucibles for pulling silicon single crystals, the present inventors used high-purity quartz on the inner circumferential side, which is eroded when melting polycrystalline silicon.
It has been found that the above-mentioned conventional problems can be solved by using a double-layered crucible using natural quartz for the outer circumferential portion that is not subject to erosion.

[Structure of the invention]

The present invention provides a quartz crucible for pulling a silicon single crystal, in which the inner peripheral side of the crucible wall is made of synthetic quartz and the outer peripheral side is made of natural quartz. In a preferred embodiment, the thickness of the synthetic quartz layer on the inner peripheral side of the crucible wall is 3 to 4.
To provide a quartz crucible in which the outer circumference side portion is made of natural quartz.

The impurity contents of synthetic quartz and natural quartz used in the present invention are illustrated in Table 1.

As shown in Table 1, synthetic quartz has significantly higher purity than natural quartz.Also, the concentration of 01 (concentration is less than 1100pp), which is usually contained in natural quartz, but synthetic quartz usually contains 10%
Contains 0pp+m or more of OH. As the OH concentration increases, the viscosity decreases when melted, so if a crucible is manufactured using only synthetic quartz, the viscosity decreases during arc melting during the manufacturing process, making the shape of the crucible likely to become unstable, making it difficult to pull silicon single crystals. In the present invention, the synthetic quartz is covered with natural quartz having a low concentration of OH groups, so that no deformation or destruction occurs.

In the present invention, the inner circumferential portion of the crucible wall refers to a region that is slightly thicker than the portion that is eroded by the molten silicon filling the crucible, in the range from the inner surface to the outer surface of the crucible wall. The melting point of Sin2) is approximately 1700
℃, which is about 25℃ higher than the melting temperature of silicon, which is about 1450℃.
Although the temperature is 0°C higher, the quartz crucible has softened to some extent and is eroded by friction with the stored molten silicon. The amount of erosion of synthetic quartz is the amount of erosion of natural quartz (0.5 to 9.7 mm)
It is considerably larger than that, usually 1.5 mm to 2.0 m.
It is m. Therefore, the thickness of the synthetic quartz layer needs to be slightly larger than that, 3 to 4 mm.

The thickness of the synthetic quartz is preferably about half or less of the thickness of the crucible wall in view of the strength of the crucible.

The quartz crucible of the present invention can be manufactured using normal crucible manufacturing equipment. First, natural quartz powder, which forms the outer part of the crucible, is filled inside a mold, and then synthetic quartz, which forms the inner part of the crucible, is filled on top of the mold, followed by melting and sintering.

〔Effect of the invention〕

The quartz crucible of the present invention has a much better single crystallization yield than conventional quartz crucibles.In practice, the single crystallization yield of a quartz crucible is required to be 70% or more, but the quartz crucible according to the present invention When using this method, a high single crystallization yield of 75% or more can be achieved.

[Examples and comparative examples]

Four types of crucibles as shown in Table 2 were manufactured using the three types of quartz shown in Table 1, and silicon single crystals were pulled using these quartz crucibles. Table 2 shows the single crystallization yield when using each quartz crucible.

Table 2 Tests 9i NQ 1 and 2 were examples of the present invention and had a single crystallization yield of 78%. Tests Nα3 and 4 relate to comparative examples, and in test Xα3, the quartz crucible was deformed during pulling of the silicon single crystal, and the pulling was stopped.

Furthermore, in Test No. 4, the single crystallization yield was extremely low at 50%.

Patent originator: Mitsubishi Metals Corporation 〃　　　Japan High Purity Quartz Co., Ltd. Agent: Patent attorney Masahiro Matsui (1 other person)

Claims (1)

[Scope of Claims] 1. A quartz crucible for pulling a silicon single crystal, in which the inner circumferential side of the crucible wall is made of synthetic quartz and the outer circumferential side is made of natural quartz. 2. The thickness of the synthetic quartz layer on the inner peripheral side of the crucible wall is 3.
The quartz crucible according to claim 1, having a diameter of 4 mm to 4 mm.