Electrical characterization of an rf planar magnetron in inert gases

Electrical aspects of an rf planar magnetron discharge in noble gases at pressures below 50 mTorr are discussed. The electrical parameters of the experimental device are measured by a diagnostic system consisting of two probes, a capacitive voltage divider and a current loop. The measurements of the rf current and voltage and the fast Fourier transform treatment of recorded signals are used to verify the validity of the `subtraction' method in order to estimate the power deposited into the plasma. This technique shows a better power coupling with a metallic target, up to 90% of the rf delivered power, than for an insulating target for which the power efficiency hardly reaches 50%. In addition, the elementary mechanisms sustaining the rf planar magnetron discharge are analysed. A transition from a combination of α (`wave-riding') and γ (secondary electron emission) regimes above a critical pressure to an α dominant regime at very low pressure is pointed out. This phenomenon is explained by the results of a particle-in-cell Monte Carlo collision simulation.