Control of ion species in inductively coupled oxidation plasma by inert gas mixing

Abstract

We have controlled and investigated the ion density ratio ([O+]∕[O2+]) in oxidation plasma by He and Xe mixing. The ion density ratio increases from 0.26 to 0.97 by He mixing, and decreases to 0.015 by Xe mixing. The ratio is a strong function of the electron density and electron temperature. When the other conditions are fixed, the ion density ratio is proportional to the electron density in all the cases: the He∕O2 and Xe∕O2 mixtures as well as pure O2 plasma. This may be due to the increase in the dissociation rate and the process of ionization from O to O+. The rate of increase in the ion density ratio with the electron density is different in the two cases: In the He∕O2 mixture, the rate of increase is slightly higher than that in the pure O2 plasma. However, the rate is very low in the Xe∕O2 mixture. In the Xe∕O2 mixture, the ion density ratio is actually a strong function of the electron temperature rather than the electron density.