AN EQUIPMENT MODEL FOR POLYSILICON LPCVD

An equipment model has been developed for the low pressure chemical vapor deposition (LPCVD) of polycrystalline silicon in a horizontal tube furnace using a methodology which combines physical modeling with statistical experimental design. The model predicts the wafer to wafer deposition rate down the length of the tube and is intended to aid the process engineer in the operation of equipment, including the selection of optimum process parameters and process control based on measured deposition thickness. The model is also flexible enough to aid in the design of new equipment. Inputs to the one dimensional finite difference model include: silane flow rates from three injectors, injector locations, locations of and temperatures at three thermocouples, operating pressure, the number of wafers, wafer diameter, the location of the wafer load, and other physical dimensions of the furnace such as tube length, and liner diameter. Kinetic and injection parameters in the model were calibrated using a series of nine statistically designed experiments which varied four parameters over three levels. The model accurately predicts the axial deposition profile over the full range of experimentation, and demonstrates good extrapolation beyond the range of experimental calibration. The model was used to predict a set of process parameters that would result in the least variation of deposition rate down the tube. The predicted parameters agree well with experimentally determined optimum conditions.