A spray-free crucible for casting polysilicon

Abstract

The invention discloses a cast multi-crystalline silicon free-spraying crucible which comprises a crucible body. A first coating, a second coating and a third coating are sequentially sprayed onto theinner surface of the crucible body from inside to outside. The first coating comprises, in weight percent, 4.5-95% of silicon oxynitride, 4.5-95% of silicon dioxide and 0.5-5% of silica sol. The second coating comprises, in weight percent, 5-50% of silicon oxynitride, 0.5-50% of silicon dioxide, 0.5-50% of silicon nitride, 0.5-5% of silica sol and 0.5-5% of PVA (polyvinyl acetate). The third coating comprises, in weight percent, 0.5-95% of silicon oxynitride, 0.5-95% of silicon nitride, 0.5-5% of PVA and 0.5-5% of PAA (polyacrylic acid). Silicon nitride coatings in the second coating and thethird coating comprise silicon nitride with two particle sizes, and the silicon oxynitride is prepared by a specific method. According to the cast multi-crystalline silicon free-spraying crucible, therisk of falling of silicon nitride into silicon liquid can be decreased, and impurity stopping and smooth demolding effects are increased.

Description

technical field [0001] The invention relates to the field of preparation of crucible coatings for polysilicon casting, in particular to a high-efficiency spray-free crucible for polysilicon casting. Background technique [0002] Photovoltaic is an important green and sustainable energy, and cast polysilicon is one of the most important raw materials for making photovoltaic modules. In order to obtain higher photoelectric conversion efficiency, the less impurities and defects of cast polysilicon, the better. In the casting process of polysilicon, a high-purity quartz crucible is generally used as a container, but when the silicon material is melted at a high temperature, it will react with quartz, that is, silicon dioxide, causing the silicon liquid to penetrate into the crucible. In the case of inconsistent expansion coefficients, the infiltration of silicon liquid may cause the crucible to rupture, causing high-temperature silicon liquid to flow out, which may cause seriou...

AI Technical Summary

Problems solved by technology

However, although silicon nitride is sprayed on the crucible as a release agent, there are still many problems: first, the impurities in the quartz crucible can still diffuse through the silicon nitride coating at high temperature and enter the silicon liquid, causing polysilicon impurities and An increase in defects that reduces the efficiency of PV modules

Second, the bonding force between silicon nitride itself and the quartz crucible is not strong, so that silicon nitride is easy to fall into the silicon liquid during ingot casting, forming silicon nitride impurity spots. The hardness of silicon nitride impurity spots is very high, which not only increases The internal defects of the silicon ingot reduce the photoelectric conversion efficiency of the photovoltaic module, and it is easy to cause the diamond wire to break during subsequent diamond wire cutting, resulting in production accidents

Third, the wetting angle between silicon nitride itself and the silicon liquid is 45° to 50°. When the wetting angle is lower than 90°, the solid-liquid interface still has wetting, which not only makes silicon nitride The nitrogen element in the silicon is more likely to diffuse into the silicon liquid to cause pollution to the silicon ingot, and it increases the possibility of poor demoulding or even cracking of the ingot, which eventually causes the quality of the silicon ingot to be unstable.

However, nano silicon dioxide is not only costly and difficult to prepare, but also very easy to agglomerate, which does not match micron-sized silicon nitride particles, making it difficult to mix uniformly, and it is difficult to achieve the corresponding effect in the mass production process

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