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 analyz ed. When a substrate was moved away from the plasma, gas-phase polymer ization increased the contribution of oligomer radicals to film deposi tion. In addition, the contribution of silylene radicals became lower compared with that of silyl radicals. As a result of the trade-off bet ween these two effects, an optimal plasma-substrate distance; where a high-quality a-Si:H film was obtained, appeared. Dilution of feed sila ne with hydrogen effectively reduced gas-phase polymerization and enha nced the generation of hydrogen radicals that create silyl radicals se lectively through a reaction with silane. Improvement of the film qual ity as a result of plasma-substrate separation and hydrogen dilution w as thus explained by the change in the composition of film precursors.