Process for producing silicon single crystal

Details Process for producing silicon single crystal Process for producing silicon single crystal

1997-11-19

1999-11-02

Hiteshew, Felisa

Single-crystal, oriented-crystal, and epitaxy growth processes;

Processes of growth from liquid or supercritical state

Having pulling during growth

117 32, 117917, C30B 1520

Patent

active

059762462

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a method of manufacturing a silicon single crystal by the MCZ method.


BACKGROUND OF THE INVENTION

The diameter of silicon single crystals manufactured by using the Czochralski method (CZ method) has been increasing in recent years. In order to grow a large diameter crystal, a large amount, 100 kg or more, of the source material has to be melted using a large diameter quartz crucible. However, there may be a problem in the crystal quality. In order to obtain a quality crystal, the concentration of the interstitial oxygen contained in the crystal has to be low. However, the oxygen contained in the crystal is supplied by dissolution of the quartz crucible. Therefore, the oxygen supplied from the quartz crucible increases, resulting in an increase in the interstitial oxygen, as the quartz crucible becomes larger and the amount of the silicon melt increases.
In addition, when growing a crystal with a larger diameter, the increased amount of the melt increases the instability of the melt due to natural convection, making it harder to grow the crystal.
The MCZ method has been used as a method to solve the aforementioned problem. In the MCZ method, the melt convection and the introduction of oxygen dissolved in the melt into the crystal can be controlled by applying a magnetic field when pulling the crystal.
However, when a crystal with a large diameter is pulled with the MCZ method, a new problem arises in that the crystal becomes distorted. This distortion of the crystal happens more easily when the crystal rotation speed is increased. Once a twist occurs, the crystal is deformed and tends to lose the single crystal quality. When the crystal is distorted, the crystal growth rate has to be reduced and therefore there is a problem in that the manufacturing efficiency decreases, resulting in higher costs.
Therefore, in order to orvercome the problem of distortion, it is necessary to reduce the crystal rotation speed. However, the crystal rotation speed is an important growth parameter for obtaining a homogeneous distribution of the impurity in the obtained wafer, and problems will arise if the crystal rotation speed is reduced below a certain point.
Therefore, the object of the present invention is to provide a method of manufacturing a silicon single crystal with a large diameter using the MCZ method without causing distortion.


DISCLOSURE OF THE INVENTION

The invention provides a method of manufacturing a silicon single crystal with the MCZ method in which the crystal growth rate v.sub.1 (mm/min) and the crystal circumference velocity v.sub.2 (mm/min) satisfy the following conditions when the single crystal is pulled while being rotated:
The present invention is described in detail below.
The reason why the crystal tends to be distorted in the MCZ method is believed to be as follows: the application of the magnetic field increases the viscosity of the melt and as a result the load against the rotation of the crystal increases. The primary reasons why a crystal with a large diameter is particularly prone to distorting are believed to be as follows: a larger diameter of the crystal results in a larger heat capacity and therefore a reduced crystal cooling rate, and the velocity at the circumference of the crystal increases. That is, the diameter of the crystal, the crystal growth rate and the crystal rotation speed all influence the distortion of the crystal.
We discovered that, in order to solve the aforementioned problem of the distortion of the crystal, it is effective to choose the furnace structure which increases the cooling rate of the crystal or to choose appropriate ranges for the diameter of the crystal, the crystal growth rate and the crystal rotation speed.
However, a change in the cooling rate of the crystal would have a profound effect on the crystal defects and therefore is not practical. Therefore the effective method is to choose appropriate ranges for the diameter of the crystal, the crystal growth rate and the crystal rotation speed.
The upper

REFERENCES:
patent: 5196085 (1993-03-01), Szekely et al.
patent: 5306387 (1994-04-01), Fusegawa et al.
patent: 5327007 (1994-07-01), Imura et al.

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