Molecular beam sampling mass spectrometry combined with low-energy electron impact ionization has been used to detect and quantitate the stable molecules, ions, and silicon radicals created in the interaction of silane with a helium afterglow produced by a microwave discharge in pure helium. The observations are used to understand the afterglow chemistry and to elucidate some important features of the film growth mechanism in the remote plasma-enhanced chemical vapor deposition of silicon films.