An equipment model has been developed for the low pressure chemical vapor deposition (LPCVD) of polycrystalline silicon in a horizontal tube furnace. The model predicts the wafer-to-wafer deposition rate down the length of the tube. Inputs to the 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 inner diameter. The model 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. The one dimensional finite difference model encompasses the convective and diffusive fluxes of silane and hydrogen in the annular space between the wafer load and tube walls. The reaction of silane is modeled with full account taken of the generation and transport of hydrogen. 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. Keywords: Semiconductors.

The low pressure chemical vapor deposition of polycrystalline silicon was studied to define the controlling process parameters and the requirements for commercial implementation. Silane and silane-nitrogen mixtures were utilized as source gases in a tubular reactor containing parallel disk substrates oriented with surface normals in the direction of flow. The results of the study showed that the deposition reaction is surface kinetic reaction controlled over the range of temperature studied, 600 to 700°C, that the reaction is first order with respect to silane, and with an activation energy of 1.33 x 105 J/g mole. A gradient in temperature along the reactor tube is sufficient to compensate for reactant depletion and to produce a uniform deposition rate.