Simulation of Silicon Dioxide Deposition in a Vertical 300 mm LPCVD Furnace

Combining the chemical reaction mechanism for silicon-dioxide LPCVD from TEOS, as proposed by Coltrin and coworkers, and the commercially available CFD program CFD-ACE+, 2-D and 3-D models have been constructed for the gas flow, multi-component transport phenomena, gas phase chemistry and deposition chemistry in a vertical LPCVD reactor for batches of 120 wafers with 300 mm diameter. Deposition rates and uniformities on different wafers in the batch have been studied for various temperatures, pressures and flowrates, and simulation results have been validated against experimental data. Silicon-dioxide deposition from TEOS is found to be strongly influenced by gas-phase reactions, producing a reactive intermediate that is responsible for the majority of deposition. The amount of intermediate formed depends on reactor geometry and on process conditions. Large amounts of intermediate are found in regions with large local volume-to-surface ratios. Our 2-D simulations were capable of accurately predicting wafer averaged growth rates, as well as trends in deposition uniformities, for various process conditions. Intra-wafer uniformity was found to improve for reduced pressure, reduced temperature and increased TEOS flowrate. Increasing the volume-to-surface ratio by increasing the reactor diameter at fixed wafer packing density and fixed wafer diameter was found to lead to strongly increased growth rates and non-uniformities, due to increased intermediate formation. The quantitative disagreement between predicted and and experimental radial growth profiles is probably due to simplifications in the 2-D representation of the reactor geometry. Better agreement was found in preliminary 3-D simulations.