A novel method for gas flow and impurity control in directional solidification of multi-crystalline silicon

In this paper the potential of a specially designed argon gas injector for controlling the gas flow and transport of impurities in directional solidification of multi-crystalline silicon is evaluated. The gas injector which consists of a valve allows one to control the flow direction independently in the vertical and horizontal directions. Based on a gas flow model derived from a semi-industrial crystallization furnace the impact of different gas injection combinations on the gas flow pattern and impurity transport is studied. Special focus is given to the SiO evacuation from the melt-free surface, the CO formation at graphite surfaces and the CO evacuation from the furnace interior. It is found that for gas flow pattern formed through horizontal rather than vertical gas injection, SiO and CO are evacuated most effectively from the furnace interior and the formation of CO is inhibited. Such a type of gas injector presents a versatile tool for controlling the flow and impurity transport in the gas phase and possibly improving the material properties of crystalline silicon.