A kind of crucible and preparation method thereof

Abstract

The invention provides a crucible and a preparation method thereof. The crucible comprises: a crucible body, a first coating, a second coating and a third coating, wherein the crucible body comprisesa bottom wall and a side wall; the first coating layer is arranged on the bottom wall and the side wall for preventing metal impurities from diffusing to crystalline grains in the crucible body, the second coating is arranged on the outside of the first coating layer on the side wall, the second coating layer is used to assist in nucleating the crystalline grains within the crucible body; the third coating is arranged on the outside of the first coating layer on the bottom wall, the third coating layer is used to assist in separating the crystalline grains within the crucible body from the crucible body. The crucible of the invention can effectively reduce diffusion of the metal impurities in the crucible body into polycrystalline crystals located in the crucible body, so that purity of the prepared polycrystalline silicon is high.

Description

Technical field [0001] The present invention relates to a crucible, the crucible and its preparation particularly relates to a method for preparing polycrystalline silicon. Background technique [0002] In recent years, with the increasing depletion of non-renewable energy, the solar cell has been rapid development. Due to the preparation process of casting polycrystalline silicon is relatively simple, cost far less than monocrystalline silicon, polycrystalline silicon gradually replace the Czochralski silicon solar cell materials leading position in the market, become the most important industry of photovoltaic material. However, with respect to the Czochralski silicon, the polycrystalline silicon in a variety of casting defects such as grain boundaries, dislocations, micro defects and impurities carbon and oxygen in the material, the polycrystalline silicon solar cell conversion efficiency is lower than the Czochralski single crystalline silicon solar cells, polycrystalline sil...

AI Technical Summary

Problems solved by technology

[0004] However, the crucibles currently on the market and various crystal foundry manufacturers focus on solving the problem of small polycrystalline nucleation at the bottom, ignoring the side of the crucible, which is relatively dense due to the relatively smooth sprayed silicon nitride powder, during the ingot casting process. The bottom will also nucleate. Since no good nucleation conditions similar to the bottom are created, the initial nucleation is random and free, not the optimized grain and crystal orientation, and the grain size is different, and the local defect density is high. , and the large dendrites formed on the side will squeeze the excellent columnar crystals at the bottom, either change the growth direction of the original columnar crystals, make them grow obliquely, and increase dislocation propagation, or "swallow" the bottom columnar crystals, resulting in good bottom crystal grains Failure in competitive growth, weakening the effect of the bottom high-efficiency layer

Moreover, if the silicon nitride coating on the side is relatively loose and uneven during spraying, although it creates conditions for the nucleation of small crystal grains on the side, the metal impurities in the crucible body far exceed those in silicon nitride and silicon materials. Through the loose silicon nitride coating, it will continuously diffuse into the crystal, resulting in a wider red zone on the side of the silicon wafer

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