Planar magnetron glow discharge on copper - the Thornton relation revisited

Among the empirical and semi-empirical relations linking discharge current I and the absolute value of cathode voltage V in magnetron-assisted abnormal glow discharges, the 'Thornton law' has been widely used. In the literature the most parameters were referred as depending on several characteristics as target material, discharge gas, discharge pressure, geometry and magnetic configuration. However that dependence is not normally shown. In this work, experimental results are presented that were obtained for Ar sputtering of copper target on a planar magnetron cathode of our own design and construction. The Thornton relation fits quite well to data. A change in curve behavior which is independent of the pressure, is reported at about 400 V. The variation of the model parameters with the pressure, is studied systematically. The results are discussed and physical interpretations are suggested. (orig.)