Sputter-cleaning of an aluminum alloy using a thermionically assisted triode plasma system

Polished aluminum alloy (6061) samples were cleaned using Ar plasma in a diode or triode plasma system. By monitoring cathode current, the changes of surface state and removal (cleaning) rate were determined and compared based on various setup. A modified mathematical model, based on Berg's reactive sputtering model, is derived and proposed to simulate the cleaning process. The results show that it is possible to sputter-clean the substrate under a triode setup with low bias and high ion bombardment rate (i.e. -500 V, triode, 1.3 Pa). This triode cleaning process was comparable with high bias and high working pressure diode process (i.e. -2500 V, diode, 3.3 Pa). Cleaning with high energy particle bombardment can create rough surface in nano-scale, although with the similar efficiency. Also, according to the regressive fitting on the cathode current-time curve, it is found that the average secondary electron yield for the oxide compound is around 0.33 if the average secondary electron yield for aluminum metal is 0.1.