Synthesis of silicon oxynitride by ion beam sputtering and the effects of nitrogen ion-assisted bombardment

Thin silicon oxynitride (SiOxNy) films were synthesised without substrate heating by means of N-2(+) ion-beam sputtering of a silicon nitride target at an energy of 1000 eV in a N-2 and O-2 ambient with and without 200 eV N-s(+) ion assistance. Unassisted films were deposited in a controlled O-2 partial pressure ranging from ambient to 5.0 x 10(-3) Pa whereas assisted films were deposited at a fixed O-2 partial pressure of 1.0 x 10(-3) Pa. The O/(O + N) atomic fraction and the SiOxNy asymmetric stretch mode IR absorption peak wavenumber of unassisted films increased almost linearly with increasing O-2 partial pressure, from 0.2 to 1.0 and 860 cm(-1) to 1050 cm(-1), respectively, while their refractive indices decreased from 1.92 to 1.46. The behaviour of the SiOxNy film refractive index with the SiO2 fraction has been compared to that predicted by Drude, Lorentz-Lorenz and Bruggeman models under the assumption that the film is a mixture of SiO2 and Si3N4 phases. For a fixed O-2 partial pressure, the O content of the N-2(+) ion-assisted films increased with an increase in the N+ ion to Si atom arrival ratio from 0 to 3. This increase in O content correlate with changes in the film refractive index and SiOxNy asymmetric stretch mode absorption peak position, from 1.56 to 1.43 and 1014 cm(-1) to 1054 cm(-1), respectively, indicating that the O/N atomic ratio increases with increasing N+ ion to Si atom ratio until film properties consistent with stoichiometric SiO2 are obtained.