A method and process for controlling the growth of polysilicon ingot

Abstract

The invention discloses a polycrystalline silicon cast ingot growth control method and a process. A temperature difference between the top and the bottom of a crucible is adopted as a newly introducedparameter delta t for controlling growth with a polycrystalline silicon cast ingot growth process; in the preparation process of cast ingots, a curve delta t is firstly increased and then reduced, and is further increased and finally reduced to 0; when the value delta t reaches the maximum peak, a silicon material inside the crucible starts to be molten, the value delta t has a peak of minimal values when the silicon material is completely molten, the temperature of the peak of the value delta t cannot be lower than 160 DEG C, once the temperature is lower than 160 DEG C, a melt-through phenomenon can be caused for a seed crystal layer at the bottom of the crucible, a red zone can be increased, and at the same time the red zone at a corner of the crucible can extend upwards along the wallof the crucible. A delta t peak judging method can be used as a criterion of the silicon ingot casting process, the polycrystalline silicon cast ingot growth process is provided, and the polycrystalline silicon cast ingot growth control method has the advantages that the thickness of a red zone in polycrystalline silicon is reduced, the quality of the polycrystalline silicon is improved, the utilization efficiency of the polycrystalline silicon is improved, and the cost is lowered.

Description

technical field [0001] The patent of the invention relates to the field of polysilicon production, in particular to a polysilicon ingot growth control method and process. Background technique [0002] As of 2017, the country's energy consumption is still dominated by non-renewable energy, and renewable resources account for less than 10% of the total energy. Therefore, all countries are supporting the development of clean energy, the most prominent of which is solar energy. There are three main types of solar cells: crystalline silicon, thin film and concentrating solar cells. The crystalline silicon cell is the most used by people, which has the advantages of high conversion efficiency and high cost performance. Polysilicon in crystalline silicon cells is widely used in the photovoltaic industry due to its low price. Polysilicon materials at home and abroad have been improved in technology and cost, which has accelerated and expanded the development of the photovoltaic mark...

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Problems solved by technology

[0003] The quality of solar-grade crystalline silicon materials is determined by the defect density in crystalline silicon. Dislocations, grain boundaries and metal impurities are the main factors causing crystal defects. At present, the main solar cells are monocrystalline silicon and polycrystalline silicon cells, which account for the world's total respectively. 49% and 47% of the shipments, monocrystalline silicon is prepared by the Tschakelski method, and polysilicon is prepared by the directional casting method. The directional casting method used in polysilicon is a new type of silicon material growth method developed in recent years. The directional casting method is to place the silicon raw material in a crucible, and obtain a square silicon ingot with a columnar crystal structure neatly arranged along the growth direction by melting and recrystallizing the silicon raw material. quality, the seed layer on the polysilicon prepared by the existing polysilicon ingot growth process is easy to melt through, which seriously affects the yield of the polysilicon ingot. The main factor is the red zone in the polysilicon ingot. The so-called red zone mainly refers to In the silicon ingot area where the minority carrier lifetime is less than 2μs, the red zone in the polycrystalline silicon ingot is mainly distributed at the bottom and top, and the seed crystal layer melt-through in the polycrystalline silicon ingot growth process will increase the thickness of the red zone, but in the directional solidification The red area in the polysilicon ingot grown by casting method cannot be used in the production of solar cells and needs to be cut off, resulting in a low utilization rate of the polysilicon ingot produced and causing waste

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