Study On Polysilicon Quality Influencing Factors In Improved Siemens Process

Polysilicon is the most important functional materials in the electronic information industry and solar photovoltaic power generation industry.Improved Siemens method is the mainstream techniqe for polysilicon production,at present there are more than 80% of the global polysilicon production is produced by improved Siemens method.The quality of polysilicon products is directly affected the function of electronic devices and the conversion efficiency of solar photovoltaic cells,so it’s really important to improve the quality of polysilicon products.In this paper,from the national solar-grade polysilicon standard GB/T 25074 and national electronic-grade polysilicon standard GB/T 12963 product quality indicators requirement,in combination with a polysilicon production practice,the main influencing factors of polysilicon products quality were analyzed in improved Siemens method,and corresponding quality control measures are put forward according to the characteristics of the different processes.The main process of polysilicon products quality by improved Siemens method include,(1)the quality of purchased raw materials such as trichlorosilane and silicon powder,(2)the efficiency of trichlorosilane distillation process,mainly includes the hydrogenated trichlorosilane crude distillation,high purity trichlorosilane distillation and dry recovery distillation,etc.(3)the quality of hydrogen including the original hydrogen and dry recycle hydrogen in exhaust gas,(4)hydrogen reduction process,the reaction temperature,ratio of mixture and replacement of reduction furnace,(5)the product post-processing procedure,including silicon rod out,storage,transportation,crushing,sorting,packing,or packing after cleaning process and so on,(6)environmental cleanliness process,including equipment cleanliness and area cleanliness.The process of trichlorosilane distillation is a key process in improved Siemens method for the production of polysilicon,the product quality of polysilicon is directly affected by the purity of distillation trichlorosilane.According to the principle of distillation technology,improvements of the separation efficiency of tower equipment is the key to improve distillation product quality.By optimizing the distillation system as well as operation conditions,the quality of trichlorosilane products can be improved.The operation stability of modified distillation system was verified by long-term running of the system,and the qualified rate of polysilicon product increased by 5.2%.Detailed classification for the appearance quality of solar-grade polysilicon products is investigated,and the appearance quality classification of solar-grade polysilicon products is formulated in our work as well.