Pulsed dc operation of a Penning-type opposed target magnetron

Abstract

This article describes the medium frequency pulsed dc power operation of a Penning-type (opposed target) magnetron to sputter copper in an argon atmosphere. The current–voltage characteristics of the magnetron are detailed in dc and pulsed dc conditions. The variations in optical emission from the excited species in the plasma are measured as a function of time during the applied pulses. The intensity of the argon emissions closely follows the variations of the target voltage but the different behavior of the copper emissions shows some evidence of self-sputtering of the target by copper ions. The energy and flux of the ions arriving at the substrate are measured as a function of time and it is shown that during pulsed operation, as the pulse off-period is extended, there are large increases in ion energy and ion flux. The initial overshoots in the target voltage cause a rapid expansion of the plasma sheath at the analyzer probe and wide variations in plasma potential leading to an initial pulse of high energy ions during the first 500ns. The plasma potential then settles to ∼40eV and there is a second peak in ion flux at this energy with a peak at ∼4000ns due to the increased ion drift resulting from electron extraction from the target.