Study of a fast high power pulsed magnetron discharge: role of plasma deconfinement on the charged particle transport

Abstract

In this paper, we report the influence of the various stages of the preionized high power pulsed magnetron discharge on the saturated ion substrate holder current. Our system allows superposition of a preionization low current dc discharge with high voltage pulses applied directly on the magnetron cathode. This system is characterized by a very fast and perfectly reproducible discharge current rise. For a 33 mm copper target, Ar pressure of ∼1 Pa, voltage applied in a pulse of ∼1 kV, the maximum cathode current of ∼40 A is reached in 6 µs. The dependence of the saturated ion substrate holder current was analyzed for varying time duration of the high power pulse from 2 up to 8 µs by 0.5 µs steps. It allows the discrimination of the contribution of elemental temporal intervals to the overall saturated ion substrate holder current. This analysis led to the conclusion that the transport of ballistic ions during the current pulse and in the afterglow is independent of time. We concluded that space charge effects are negligible for both discharge and post-discharge conditions and that electrons act as a neutralizing background. Finally, on the basis of a phenomenological kinetic model for the electron transport, physical explanations of these results are proposed which involve the transverse diffusion of low energy electrons out of the magnetized glow region through electron–ion Coulomb collisions.