Modelling of transport phenomena in a low-pressure CVD reactor

The present work reports the analysis of transport phenomena in a low-pressure chemical vapour deposition (CVD) reactor. A two-dimensional unsteady model has been used to compute flow, chemical reactions and mass transfer rates within the reactor. The formation of zinc sulphide from the reaction of zinc vapour and gaseous hydrogen sulphide has been analysed. Two geometric designs of the reactor have been studied for assessing the overall deposition characteristics. The mathematical model comprises of the conservation equations of mass, momentum and the mass fractions of the reactant and product species. The governing partial differential equations have been solved by the finite volume method. The deposition surface has been taken to be chemically passive. There is an uncertainty in the boundary condition for the depositing species on the passive surface. The difficulty has been resolved by utilizing a homogenous Dirichlet condition at the surface. The present approach yields an upper bound on the deposition rate. The numerical results obtained show that the species concentration field, correlates closely to the flow field in the reactor. Over the range of Reynolds numbers studied namely 10-200, a recirculation pattern adjacent to the side walls is revealed and a stagnation zone forms ahead of the block. Reactant species mix predominantly in the zone close to the inflow plane and the product species are transported by advection. The reactor with a convex substrate streamlines the flow better as compared to the concave. As a result, higher concentrations of the product species reach the substrate. At a Reynolds number of 100, the deposition rate for the convex substrate was seen to increase by a factor of two with respect to the concave. (C) 2004 Elsevier B.V. All rights reserved.