Silicon oxynitride thin films were deposited by radio frequency sputtering from silicon target and using various Ar-O-2-N-2 atmospheres. The target self bias voltage and the deposition rate were found to decrease abruptly when the oxygen flow rate reaches 0.55 seem; this phenomenon is due to the oxidation of the target surface. When the oxygen content of the plasma is increased, the deposit composition varied from one close to Si3N4 to SiO2 one and the layer density decreased. These variations are accompanied by a shift of the infrared absorption peak towards higher wavenumbers. An estimation of the SiO and SiN bonding confirmed that the reactivity of oxygen with silicon is higher than the nitrogen one. The deposit structural defects were attributed to silicon neutral dangling bonds and the spin density was found to decrease with increasing the oxygen content. (c) 2006 Elsevier B.V All rights reserved.