1. Field of the Invention
The present invention relates to a quartz crucible reproducing method for reusing a quartz crucible after being used for producing single crystal silicon by the Czochralski (CZ) method.
2. Description of the Prior Art
In producing a high purity single crystal silicon for a semiconductor by the CZ method, a quartz glass based crucible is essential to maintain silicon melt during a single crystal producing. The reason is as follows. In order to maintain silicon with a high activity at a high temperature in a molten state, it is required to maintain a container shape even at around 1450.degree. C. The quartz glass based crucible has a variety of advantageous characteristics, i.e., high heat resistance characteristics, high purity characteristics in which impurities are controlled at a level of ppm, and further, possession as a constituent element of oxygen that can be efficiently utilized even if it is dissolved in a silicon melt.
However, a high purity quartz crucible used for producing single crystal silicon by the CZ method is very expensive. Thus, the rate of the crucible cost in the manufacturing cost of single crystal silicon is large, which becomes a large obstacle in reducing the manufacturing cost.
A repeated use of the quartz crucibles is the most efficient to reduce the crucible cost. However, as it will be described later, crucible reusing technique has not been established yet. Therefore, there is proposed a continuous CZ method in which, while a crystal producing is carried out, a silicon raw material is additionally supplied, thereby increasing a crystal producing quantity per batch or a multiplying technique in which, after crystal producing has been completed, a silicon raw material is supplied to a residual silicon melt contained in the crucible, thereby repeating crystal producing.
However, in these techniques, there is a problem that, since crystal producing per batch takes more time, probability of causing dislocation is increased during this period, thus making it difficult to cause dislocation free producing. This problem has not been essentially solved.