Time-resolved measurements of ion energy distributions in dual-mode pulsed-microwave/radio frequency plasma

Abstract

In the present work we systematically study the ion energy distribution functions (IEDFs) in argon discharges produced by a combination of pulsed (1–2 kHz) microwave (MW) and continuous wave (cw) radio frequency (rf) excitations. We show that the IEDFs for the pulsed MW discharges are structured, with individual features originating from different periods of the pulse. In the dual-mode MW/rf discharge, significant modulation of the self-bias voltage, Vb, during the MW pulse cycle is observed, which we attribute to changes in the overall plasma impedance: We demonstrate that in the pulsed-MW/cw-rf mode the impedance is highly resistive when the MW signal is on, while it is predominantly capacitive during the period between individual pulses. Using the measured time evolution of Vb in combination with time-resolved measurements of individual ion species, IEDFs at the rf-powered electrode at each instant of the MW pulse have been obtained. This approach is then used to reconstruct the total IEDF in pulsed-MW/cw-rf plasma in order to determine the total energy delivered by the impacting ions.