SiO ₂ -like films are deposited in a low-pressure rf helicon reactor using oxygen-rich O ₂ /TEOS (tetraethoxysilane) mixtures. A model based on the deposition rate variation with the distance to the TEOS injection is used to estimate the TEOS electron-impact dissociation coefficient k_e and the effective sticking coefficient of reactive fragments s. In the helicon diffusion chamber where the electron temperature and density are about 4 eV and 10¹⁰  cm ^-3, respectively, k_e and s are found to be 1.82×10^-7  cm ³  s ^-1 and 0.035, respectively. Under these low-pressure plasma conditions, the TEOS dissociation by electron impact is dominant over dissociation by oxygen atoms. © 2000 American Vacuum Society.