Electrical and electron-spin-resonance measurements have been carried out on plasma-enhanced chemical-vapor-deposited SiO2 obtained using an N2O:SiH4 flow-rate ratio of 40 and a temperature of 300 °C. As-deposited films contain 2×1016 oxygen vacancy centers per cm3 while none were detectable in films annealed at 950 °C in Ar. 60Co γ radiation-induced defect creation is enhanced (>80 times for a dose of 20 Mrad) in as-deposited films with respect to thermal SiO2 consistent with the deposited film being in a state of densification (∼10%) with respect to undensified, fused silica. This result is in agreement with the results of density, refractive index, and infrared spectroscopy measurement. Annealed films, having a density close to thermal SiO2, are found to be very radiation sensitive in terms of positive fixed oxide charge creation but the relevant defects are not associated with paramagnetic centers. The origin of the enhanced radiation sensitivity in annealed samples may be related to the presence of incorporated nitrogen or excess silicon.
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R. A. B. Devine (1989) studied this question.
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