Quartz crucible is a container commonly used in the process of polycrystalline silicon ingot casting. During the production process of polycrystalline silicon ingots, it is common to encounter the situation of silicon liquid overflow. The occurrence of silicon overflow is closely related to the crucible. The following are the problems that may occur and their solutions:
1. Hidden cracks in the crucible. The crucible used to hold silicon ingots is usually made of quartz ceramic material, and its production methods are divided into injection molding and injection solidification molding. However, regardless of which method is used to produce the crucible, there will be defects such as hidden cracks and pores. These quartz crucibles will undergo two or more developer transparency checks before leaving the factory, but there may still be cracked crucibles that are missed. In addition, during transportation or handling, they may also encounter vibrations or bumps, which may cause hidden cracks in the crucible. If these crucibles are not detected before loading, silicon overflow may occur during the melting process. So after unpacking the crucible, strict testing is required before spraying. A more convenient operation is to use a strong light source to conduct transparency testing on the five sides of the crucible.
2. The material is compressed. When loading, if there are large pieces of silicon material approaching the corners of the crucible, special attention should be paid to leaving a certain gap between the silicon materials to prevent overloading and overflow. This is because after the loading is too crowded, the liquid silicon may flow to the bottom of the quartz crucible and solidify due to the temperature being too cold. If there is not enough space for it to expand, it will cause compression of the crucible wall, leading to the rupture of the crucible and overflow. Therefore, the closer the position is to the corner, the more likely it is to overflow due to unreasonable loading.
3. Unreasonable process parameters. During the casting process, when heated to the initial melting stage, the longitudinal temperature gradient inside the thermal field will be relatively large, and the temperature in the middle and lower parts of the quartz crucible will be relatively low for a long time. Excessive power or heating rate can cause significant differences in the vertical crystal phase transformation rate of the crucible, resulting in prolonged stretching and easy cracking, which can lead to overflow phenomenon. Therefore, many ingot casting processes will maintain a temperature of around 1200 ℃ for a period of time, and then continue to heat up after the temperature above and below the crucible is relatively uniform.
Therefore, if similar problems are encountered during the production process using quartz crucibles, the methods mentioned above can be tried to improve the problem of silicon liquid overflow, thereby greatly improving the production quality of the product.