A very high silane dissociation rate (⩾95&percent;) has been measured using mass spectrometric analysis of neutral species in a low pressure (a few mTorr) high density (⩾1011cm−3for a radio frequency source power of 800 W) oxygen/silane (O2/SiH4) helicon deposition reactor. Energy selective mass spectrometric measurements of positive ions have been performed for O2/SiH4flow rate ratios varying from 1 to 10 and for a constant power of 800 W. A simple model of the ion-induced deposition rate has been developed and the results have been compared to the measured deposition rate. It appears that 20&percent;–50&percent; of the silicon atoms in the near-stoichiometric deposited oxides could result from the flux of silicon-containing ions (essentially Si+and SiOH+) to the substrate during deposition. An oxidation process via O2+ions and an etching process via H3+ions could possibly be involved in the ion-induced deposition mechanism. ©1997 American Institute of Physics.