Study On The Transfer-kinetics Of Synergistic Deposition Of Polysilicon And Impurity Boron

Electronic grade polysilicon is the basic material of integrated circuits and the cutting-edge technology industry,and the demand has been growing steadily year by year.However,most of China's electronic grade polysilicon is still dependent on imports from abroad.China's electronic grade polysilicon production enterprises are still in their infancy,and the content of impurities produced is much higher than that of foreign enterprises.At present,for the production method,the currently used method on the market is the Modified Siemens Method,which has the advantages of mature technology,high silicon deposition efficiency and low pollution.Boron is the main impurity affecting the purity of polysilicon.The rectified trichlorosilane and a small amount of boron trichloride enter the Siemens reduction furnace,and a chemical vapor deposition reaction occurs on the surface of the heated silicon rod,resulting in the doping of B during the growth,but the research at home and abroad has not yet been involved.This paper studies these practical problems and carries out the following research works:Firstly,the chemical vapor deposition reaction of BCl₃ gas and hydrogen was carried out based on the laboratory tube reduction furnace,the experiment found that there are two chemical equations in the chemical vapor deposition experiment of BCl₃..The non-linear regression of the experimental data was used to fit the dimensionless deposition rate equation of B chemical vapor deposition.Second,the transfer-kinetic model of the laboratory tube reduction furnace was established.The validity of the established model was verified by comparing with the experimental data and analyzing the temperature and velocity field maps.The effects of inlet composition,inlet velocity and surface temperature of silicon wafer on chemical vapor deposition of BCl₃ gas were studied by using this model.These results show that increasing the BCl₃ gas in the inlet composition,increasing the inlet velocity and increasing the surface temperature of the silicon wafer,the deposition rate of B increases.Third,the transfer-kinetic model of silicon in the laboratory-scale polysilicon reduction furnace was established,and the validity of the established model was proved by comparison with the real literature data and analyzing the temperature and velocity field maps.The model was used to analyze the effects of inlet composition,inlet velocity,silicon surface temperature,initial temperature of feed gas and pressure in the reduction furnace on the deposition rate of silicon on the surface of the silicon rod.The results show that increasing the composition of the inlet gas H₂,would make the deposition rate of silicon on the surface of the silicon rod first increase and then decrease;when the inlet speed is increased,the deposition rate of silicon on the surface of the silicon rod first increases and then tends to be gentle;The temperature of the inlet or the surface of the silicon rod and the reaction pressure are increased,and the deposition rate of the silicon rods is increased.Finally,a transfer-kinetic model of coupled boron in the reduction furnace of Siemens was established based on the chemical vapor deposition transfer-kinetic model of boron and silicon.The model was used to study the effects of feed gas composition,inlet velocity and surface temperature of silicon rod on the deposition of impurity B during polysilicon deposition,which indicates that for the actual production process,the purity of polysilicon can be improved by increasing the molar ratio of hydrogen and the temperature of the surface silicon rod,and decreasing the inlet velocity in a reasonable production range.