Reactive gas effects in pulsed magnetron sputtering: Time-resolved investigation

A pulsed magnetron deposition discharge in argon with different admixtures of oxygen as reactive component has been studied. The target material used was magnesium and the pulsed discharge was operated in metallic and reactive mode. The discharge evolution during each pulse has been characterised by the time-resolved Langmuir double probe and time-resolved optical emission spectroscopy. Charge carrier density and optical emission exhibit two more or less strong peaks at the beginning of the “on” phase, the second of which being the most dominant. The temporal development of the discharge is clearly different for the two discharge modes: in the reactive mode, the structures in the “on” phase — except of the first maximum — significantly shift to shorter times compared to the metallic mode. This is suggested to be due to the much higher secondary electron emission coefficient (γ) of MgO in comparison to Mg leading to increased ionisation starting with the second maximum. The first maximum, however, is attributed to residual electrons from the precedent pulse and is thus independent of the γ coefficient. A significant feedback from the discharge to the power supply is observed by changes in the voltage waveform: the more efficient discharge development is accompanied by a sharper and lower peak in the voltage.