Effect of gas flow rate on chemical reactions in Czochralski silicon crystal growth

Chemical deposits and graphite etching resulting from chemical reactions are related to crystal quality and cost reduction in CZ silicon growth. A chemical model implemented in CGSim software was applied to investigate the effect of gas flow rate on the distribution of deposited compounds and the carbon consumption for the heat shield and graphite heater. The results show that SiO2 layer is deposited only on the inside surface of heat shield, with a relatively low deposition rate of 10−19 to 10−13 μm/hr. The SiC deposition on heat shield appears an abrupt increase when gas flow rate is higher than 0.7 m/s. In terms of chemical reactions, the carbon consumption of heat shield decreases with increasing gas flow rate. Meanwhile, the heater surface is coated with Si and/or SiC layers, demonstrating neglectable effect on heating efficiency of the heater. As increasing the gas flow rate, the deposited Si layer gradually overspreads whole heater surfaces, along with decreasing the rate of graphite etching. Consequently, a medium gas flow range with inlet flow rate of 0.5-0.65 m/s is recommended as an optimum parameter for CZ silicon growth, based on a compromise between crystal quality and cost reduction.