Effect Of Single Crystal Silicon Substrate On Si-Al Alloy Growth Bulk Silicon Smelting In Temperature Gradient Zone Melting

Metallurgical method is an exclusive purification process for the manufacture of solargrade polysilicon,which has the advantages of low cost,low energy consumption and low pollution compared to Siemens method.Among them,alloy solidification and refining has the characteristics of low temperature refining and efficient de-cluttering.However,refined primary silicon is evenly distributed in the whole melting region with large slats,which is not conducive to the separation of the purified primary crystal silicon.In order to realize the effective separation of primary crystal silicon in alloy refining,the temperature gradient regional smelting method is used to grow block silicon in The Si-Al alloy melt,and combined with the liquid phase extension growth technology,the specific orientation of monocrystalline silicon substrate is introduced on the basis of alloy directional solidification,in order to achieve the purpose of low-cost purification of growth block silicon.The solidification interface,crystal structure and growth rate of the solidified silicon on different substrate types were compared.The effects of different refining processes on the growth of block silicon under the single-crystal silicon lining are also discussed,and the distribution of different impurities is discussed,and the following conclusions are concluded:(1)The model of Al-Si alloy refined growth block silicon on the monocrystalline silicon substrate is: metallurgical silicon source,Al-Si alloy,monocrystalline silicon substrate.Under a positive temperature gradient,the continuous dissolution of the silicon source plays the role of supplementing the continuous growth of silicon atoms in the melt,the Al-Si alloy strengthens the impurity coagulation effect and has a decontamination effect,and the single-grain silicon substrate at the bottom provides a nucleus site and a specific grain orientation,which strengthens the growth of block silicon.(2)The effective separation of block silicon can be realized on different substrates by using temperature gradient area smelting technology.In the Al-Si alloy melt on the single-crystal silicon substrate,the growth of large-particle monocrystalline silicon with the same orientation as the substrate orientation,compared with the column polysilicon growing on graphite,the number of quasi-single crystalline silicon boundary is significantly reduced,impurities in the crystal boundary of the enrichment is also greatly reduced,for the purification of primary silicon has a better effect.(3)The addition of a single-crystal line silicon substrate promotes the block silicon at the bottom of the melt to grow upward with a straight interface,which is conducive to the separation of block silicon and alloy and reduces inclusion.At a temperature gradient of 2.4K/mm,the growth rate of block silicon is reduced from 0.108 um/s on graphite crucible to 0.075 um/s on the Si(100)substrate.Under the same temperature gradient and growth time,the average growth rate of block silicon on the Si(100)surface is significantly faster than that of the Si(111)surface.(4)In the growth process of block silicon,the silicon substrate must be re-melted in order to play the lead effect.With the increase of insulation time,the average growth rate of block silicon in the silicon substrate is gradually reduced,and the growth rate of block silicon changes linearly with the increase of temperature gradient.(5)Under the condition of non-equilibrium solidification growth,the bulk silicon forms al enriched layer at the front of solidification interface.When the temperature gradient is 1.4 K/mm,the thickness of Al enriched layer is 15 um,and when the temperature gradient is increased to 2.4 K/mm,the thickness of enriched layer is reduced to 10 um In addition,the larger the temperature gradient,the greater the cooling rate and the more uneven the solidification interface of bulk silicon.During the process of alloy refining,the metal impurities Al,Fe and Ti exist in the alloy melt in the form of needle and bone,while the non-metal impurities B mainly exist in the eutectic al phase.