Quasi-monocrystalline silicon crystal growth method and thermal field structure

Abstract

The invention discloses a quasi-monocrystalline silicon crystal growth method and a thermal field structure, and relates to the technical field of solar crystalline silicon materials. Single platy seed crystals are used, and under seed crystal induction, a quasi-square crystal with the height slightly equal to the width grows from silicon melt in the seed crystal thickness direction from top to bottom. In order to implement the crystal growth method, the thermal field structure comprises a main furnace room, an auxiliary furnace room, a seed crystal loading cavity, a crystal bar unloading cavity, a crystal listing mechanism, a crucible, a heater, a heat preservation basket, a heat insulation board and the like; the crystal lifting mechanism in the auxiliary furnace room mounts the seed crystals to induce crystal growth; in the crystal growth process, seed crystal module preparation and crystal bar taking are conducted in the crystal loading cavity and the crystal bar unloading cavity,after crystal bar growth is completed, the crystal lifting mechanism can rapidly unload and re-mount a seed crystal block to grow the next crystal. The grown quasi-monocrystalline crystal has the advantages of being uniform in crystal orientation, low in edge leather ratio, high in product qualification ratio, low in defect density and high in production efficiency.

Description

technical field [0001] The invention relates to the technical field of solar silicon materials, in particular to a method for growing silicon-like crystals and a thermal field structure. Background technique [0002] Solar photovoltaic power generation is the main way of solar photovoltaic application because of its environmental friendliness, high conversion efficiency, and convenient installation. In the past ten years, the cost of photovoltaic power generation has dropped rapidly to the on-grid electricity price close to that of traditional thermal power, which provides strong support for the further large-scale application of photovoltaic power generation. [0003] Monocrystalline silicon wafers and polycrystalline silicon wafers are two basic materials for making photovoltaic cells. Monocrystalline silicon wafers are grown and cut by pulling (Cz) crystals. They are characterized by less defects, high minority carrier life, and stable quality, so they are favored by hig...

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Problems solved by technology

[0006] However, there are also important deficiencies in the cast single crystal process: first, the seed crystal needs to be laid on the bottom of the crucible first, and undergoes the entire high-temperature melting process. Special control of the thermal field and process is required to avoid complete melting of the seed crystal, resulting in Seedless-induced crystal growth renders the cast monocrystalline silicon process completely ineffective

In order to suppress the internal growth of polycrystalline grains on the side wall of the crucible and destroy the integrity of the cast single crystal silicon crystal, the size of the crucible is usually enlarged to cut off this part of the crystal, which causes an additional loss in the yield of the final product

Fourth, due to the lack of grain boundaries of cast single crystal silicon crystals, and due to the large size of the crystal ingot, thermal stress is generated due to uneven temperature in the body, resulting in the generation of defects in the upper part of the crystal ingot and the rapid increase in value, which reduces the quality of cast single crystals and performance Even lower than ordinary polysilicon

Fifth, since the seed crystal has to go through a long process of melting and crystal growth, the thermal stress causes damage to the crystal structure of the seed crystal, and is affected by the diffusion of impurities from the silicon material and the crucible, and the content of metal impurities increases, resulting in a decline in the quality of the recovered seed crystal , is not conducive to the recycling of seed crystals, and increases the cost of using seed crystals

Sixth, the growth characteristic of the casting method is that the crystal is directional solidified from the bottom of the crucible from bottom to top. Due to segregation, the final solidified part of the top of the crystal ingot has a high content of metal impurities. During the subsequent cooling process of the crystal, the metal impurities diffuse back, Causes the low number of red areas on the head; the low number of red areas on the head, bottom, and sides are inherent defects in the directional growth of crystals in the crucible, resulting in a product pass rate of only 50% to 60%, which is lower than that of Cz single crystal

However, this invention, like the ordinary casting process, cannot improve the low-minority red zone at the head, side and tail of the crystal ingot caused by the diffusion of metal impurities, resulting in a loss of about 25% of the yield of the crystal ingot

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