Correlation between the gas composition and the stoichiometry of SnOx films prepared by DC magnetron reactive sputtering

The properties of tin oxide thin films deposited by d.c. magnetron sputtering of a Sn target are strongly dependent on the sputtering conditions. The aim of the present work is to investigate the discharge parameters such as discharge voltage, deposition rate and ion composition of the discharge as a function of the oxygen partial pressure and to compare them with the stoichiometry of the deposited films. Working in the constant current discharge mode, we observe, with increasing oxygen partial pressure, a decrease of the discharge voltage followed by a slight increase and a drop of the deposition rate. For each experimental condition, we measure the gas composition by glow discharge mass spectrometry (Sn+, SnO+, SnO2+, O+, O2+) and the stoichiometry of the deposited films by X-ray photoemission spectroscopy. The results are fitted by means of a model, taking into account the plasma–surface interactions. All the data are fitted by the same equation, with only four fitting parameters, namely the sticking-reaction coefficients of O and O2 on Sn and SnO surfaces.