The effect of rapid thermal annealing in oxygen and nitrogen ambients on the properties of silicon oxide films of different stoichiometry was studied. The films were deposited on silicon wafers by plasma enhanced chemical vapour deposition (PECVD) from silane (SiH4) and nitrous oxide (N2O) at different N2O/SiH4 flow ratios. It was found that rapid thermal annealing significantly affects the thickness of deposited oxides and the total mechanical stress in the film. The density and the refractive index of the film hardly changed. The hydrogen content of the films has been discussed on the basis of Fourier transform infrared transmission spectroscopy, and is related to the changes in the him properties.