Structural and optical investigations of SiOxNy thin films deposited by R.F. sputtering

Silicon oxynitride thin films were deposited by radio-frequency magnetron sputtering using Si3N4 target under argon/oxygen gas mixture. The films were characterised by Rutherford Backscaterring Spectroscopy, Fourier Transform-Infrared Spectroscopy, Electron Spin Resonance and optical absorption. The influence of the oxygen/argon flow ratio, the total pressure and the power density on the composition, structure and optical properties of the deposits was studied. The film composition is mainly sensitive to the process parameters. Deposits with a composition close to SiO2 can be obtained with 5% of oxygen in the sputtering gas at 3 Pa pressure. The main IR absorption peak in the 600–1300 cm− 1 range which is related to the Si–O and Si–N stretching modes shifts to higher frequencies as the oxygen content increases. It is linked to the difference of electron negativity between oxygen and nitrogen. The g-factor and linewidth (ΔHpp) values obtained by EPR investigation, seem to indicate that the film defects result from a mixture of neutral dangling bonds on silicon atoms bonded to three other atoms which could be either Si, O or N. y, the variation of the film composition induces modifications of its refractive index and optical gap.