Ion species and electron behavior in capacitively coupled Ar and O2 plasma

Abstract

We investigated the change in electron density using the plasma frequency by the wave cutoff method, and the behavior of ion species with a quadrupole mass spectrometer (QMS) in pure Ar and O2 and mixed O2∕Ar plasmas. The change in electron and ion density in pure Ar and O2 plasmas was evaluated while varying such process conditions as rf power and pressure. We found that electron density in a pure Ar and O2 discharge is closely correlated to loss and generation of ions. The electron densities in both pure Ar and O2 plasmas increase with rf plasma power but show different dependence on pressure due to different loss mechanism for each type of gas. The addition of Ar to an O2 plasma significantly enhances the electron density due to the rapid increase of Ar+ ions regardless of the pressure. Also, Ar addition results in more dissociation of O2, which gives more atomic O. These results indicate that the electron density calculated from the plasma frequency, measured by the wave cutoff method, is well explained by the ion behavior, as characterized by QMS.