A kind of monocrystalline silicon crystal growth method and thermal field structure

Abstract

A silicon-like crystal growth method and a thermal field structure, the invention relates to the technical field of solar crystal silicon materials. A single plate-shaped seed crystal is used to grow a quasi-square crystal whose height is slightly equal to the width from silicon melt from top to bottom along the thickness direction of the seed crystal under the induction of the seed crystal. In order to realize the crystal growth method, the thermal field structure of the present invention includes main and auxiliary furnace chambers, seed crystal loading chambers, ingot unloading chambers, crystal pulling mechanisms, crucibles, heaters, heat preservation baskets, heat insulation plates and other components, auxiliary The crystal pulling mechanism in the furnace chamber mounts the seed crystal to induce crystal growth. During the crystal growth process, the preparation of the seed crystal module and the removal of the crystal rod are carried out in the seed crystal loading chamber and crystal rod unloading chamber. After the crystal rod growth is completed, The crystal pulling mechanism can quickly unload and remount the seed crystal block to grow the next crystal. The quasi-monocrystalline silicon crystal grown in the invention has the characteristics of uniform crystal orientation, low proportion of edge leather, high product pass rate, low defect density and high 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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