Silicon dioxide has been deposited from electron cyclotron resonance silane/oxygen plasmas at temperatures below 150-degrees-C. Deposition rates over 4000 angstrom/min have been obtained. The refractive indexes in the measuring range of 1.5-4.5 eV were found to be almost insensitive to the different deposition rates and flux ratio regimes except in the near infrared region where small deviations from thermal oxide indexes were observed. Etch rates and refractive indexes were very close to the thermal oxide values for low silane/oxygen flow ratios 0.025, whereas the refractive index decreased and the etch rate increased for the largest flow ratios used (0.20). After a low temperature annealing, 500-degrees-C in nitrogen ambient, the refractive indexes reached the best obtained values and were independent of the conditions under which the layers were deposited.