Numerical Simulation of Plasma Chemical Vapor Deposition from Silane: Effects of the Plasma-Substrate Distance and Hydrogen Dilution

Rf plasma chemical vapor deposition from silane was numerically analyzed. When a substrate was moved away from the plasma, gas-phase polymerization increased the contribution of oligomer radicals to film deposition. In addition, the contribution of silylene radicals became lower compared with that of silyl radicals. As a result of the trade-off between these two effects, an optimal plasma-substrate distance, where a high-quality a-Si:H film was obtained, appeared. Dilution of feed silane with hydrogen effectively reduced gas-phase polymerization and enhanced the generation of hydrogen radicals that create silyl radicals selectively through a reaction with silane. Improvement of the film quality as a result of plasma-substrate separation and hydrogen dilution was thus explained by the change in the composition of film precursors.