The reactions of silane in the afterglow of a helium–nitrogen plasma

Optical emission and infrared spectroscopy have been used to study the reactions of nitrogen atoms with silane introduced into the afterglow of an atmospheric-pressure helium–nitrogen plasma. Our experimental observations show that the direct reaction between silane and ground-state nitrogen atoms is slow, with an estimated rate constant no greater than 4 × 10 −16 cm 3 s −1 , which is 2 × 10 2 –3 × 10 5 times lower than the values previously reported. Using numerical modelling based on the spectroscopic measurements, we propose that silane dissociation occurs via a two-step process in which energy is first transferred to the molecule from vibrationally excited N 2 and then the activated species collides with N atoms to form SiH 3 and NH. A kinetic model has been developed that allows one to predict the distribution of gas-phase intermediates generated in a remote plasma-enhanced chemical vapour deposition process for silicon nitride.