An investigation into the variation in bombardment intensity from ion plating discharges by sputter weight loss experiments

Work is reported on the use of sputter weight loss measurements tocharacterize the spatial distribution of energetic species in typical d.c. diode and thermionic triode discharges. The findings highlight the influence of workpiece geometry on uniformity of bombardment in diode configurations. Furthermore, the use of an ionization-enhancing thermionic emitter is quantified, indicating that (i) it can impart an exponentially decreasing bombardment effect with distance from the emitter and (ii) bombardment has a preferred direction. We show that (i) is primarily related to the mean free path for impact ionization by thermionically emitted electrons and suggest that (ii) may be caused by anisotropic charge carrier motion in the plasma. These effects are discussed in relation to the relative location of ionization-intensifying electrodes and vapour sources in practical deposition systems.