Chemical and physical sputtering of aluminium and gold samples using Ar–H2 DC-glow discharges

We present a series of sputtering experiments on aluminium samples performed with an Ar–H2 DC-glow discharge at varying Ar–H2 gas-composition, driven at a discharge voltage of –300 V and a pressure of 0.2 mbar, in conjunction with measurements of the corresponding ion-energy distributions of the ions bombarding the discharge cathode (Ar+, Ar2+, ArH+, H2+ and H3+). Similar measurements on gold samples, which have been published, have shown that the Au-sputtering efficiency of an Ar–H2 glow discharge as a function of gas-composition could be adequately described by the corresponding change in the measured ion-energy distributions, under the assumption of a purely physical sputtering process. The experiments presented here show that this is not the case for aluminium (effectively Al2O3). In this case, a measured optimal gas-composition of 80% H2 was found for Al-sputtering, while the energy-distributions suggest an optimum at 20% (as for gold). This clearly suggests that hydrogen-enhanced chemical sputtering is taking place.