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

Thin silicon oxynitride (SiO _xN _y) 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 ₂⁺ ion assistance. Unassisted films were deposited in a controlled O ₂ partial pressure ranging from ambient to 5.0 × 10 ^-3 Pa whereas assisted films were deposited at a fixed O ₂ partial pressure of 1.0 × 10 ^-3 Pa. The O/(O+N) atomic fraction and the SiO _xN _y 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 SiO _xN _y film refractive index with the SiO ₂ fraction has been compared to that predicted by Drude, Lorentz-Lorenz and Bruggeman models under the assumption that the film is a mixture of SiO ₂ and Si ₃N ₄ 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 SiO _xN _y 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 SiO ₂ are obtained.