Industrially, magnetron sources are widely used for coating and surfaces treatments. The problem encountered by "classical" magnetron sputtering is the shadowing effect when complex substrates have to be treated. Neutral particles arrive on the substrate surface with a broad angular distribution of trajectories and as a consequence the deposited film is of poor quality. Ionizing the sputtered particles can solve this problem. Velocity control and normal trajectory of the ionized species can be achieved by applying a bias voltage to the substrate. For that purpose, a R.F. (13.56 MHz) power supplied copper coil (diameter of 4 cm) has been set up, between the DC tin magnetron target and the substrate holder. The applied R.F. power used to create the secondary plasma can be raised up to 200 W. The aim of this work is to estimate the RF coil influence on the chemical behaviour of both the discharge and the films during the deposition of SnOx thin films in a mixture Ar - O2. During the deposition, the discharge is characterized by the target voltage, the deposition rate and glow discharge mass spectrometry whereas the prepared films compositions are obtained from in-situ XPS measurements. During the work, we have observed the influence of both the gas mixture composition and the RF power on the discharge and on the films. By increasing the RF power on the coil, we have observed on both the plasma and the films compositions an increase of the oxidation level for the same ratio O2 / Ar. On the other hand, the metal – compound transition at the target, observed on the discharge voltage and on the deposition rate measurements are not influenced by the coil. So, using the RF coil the films oxidation can be reached at lower reactive gas flow and consequently at higher deposition rate.