Accurate control of ion bombardment in remote plasmas using pulse-shaped biasing

This paper deals with a pulsed biasing technique employed to a downstream expanding thermal plasma. Two pulsed biasing approaches are presented: asymmetric rectangular pulses and modulated pulses with a linear voltage slope during the pulse, and their applicability is discussed on the basis of the intrinsic capacitance of the processed substrate-layer system. The substrate voltage and current waveforms are measured, and the relation to the obtained ion energy distributions is discussed. Accurate control of the ion bombardment is demonstrated for both aforementioned cases, and the cause of broadening of the peaks in the ion energy spectra is determined as well. Moreover, several methods to determine the modulated pulse duration, such that the sloping voltage exactly compensates for the drop of the substrate sheath potential due to charging, are presented and their accuracy is discussed. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3225690]