2-DIMENSIONAL MODELING OF LOW-PRESSURE CHEMICAL VAPOR-DEPOSITION HOT WALL TUBULAR REACTORS .1. HYPOTHESES, METHODS, AND 1ST RESULTS

A new two-dimensional model taking into account hydrodynamics and mass transport with chemical reactions has been developed. The system of partial differential equations has been solved by finite differences procedures and a Gauss-Seidel algorithm. The case of pure polysilicon deposition is first described, taking into account the chemical species produced by silane pyrolysis, i.e., disilane and silylene. The concentration profiles of SiH4, Si2H6, SiH2, and H-2 in the gas phase have been calculated and the contributions of these different species to the silicon deposit have been evaluated: more than 90% of the silicon deposition results from the direct silane contribution and less than 10% from silylene. The small over-thicknesses thicknesses numerically observed at the wafer's periphery result from the silylene contribution.