ANALYSIS OF TRANSITION REGIME FLOWS IN LOW-PRESSURE CHEMICAL VAPOR-DEPOSITION REACTORS USING THE DIRECT SIMULATION MONTE-CARLO METHOD

The direct simulation Monte Carlo method has been used to simulate transition regime flows in a horizontal multiple-wafer low pressure chemical vapor deposition (LPCVD) reactor. Both the region between two wafers and a long section of the entire LPCVD reactor tube were investigated. In the interwafer simulations, a binary mixture consisting of a representative reactant molecule and H-2 was used as a model system and the reactive sticking coefficient, configuration of wafers and gas composition were varied to determine their effects on growth rate uniformity. Additionally, a comparison was made with a continuum-based analytical model where the effective diffusion coefficient m the transition regime was determined and the importance of gas-surface interactions was established. In the multi-wafer simulations, the pressure drop and residence time distribution were determined for various wafer configurations and entering gas conditions with the bulk of the pressure drop occurring across the wafers as the molecules resided primarily in the upstream region. The distribution of species for gas mixtures was largely governed by diffusive effects with evidence of species separation occurring by means of pressure diffusion. For reactive gas flows, nonuniformity effects persisted in the simulations for reaction probabilities greater than 0.01.