Study of the emission characteristics of a rf plasma source for atomic oxygen: Measurements of atom, ion, and electron fluxes

Abstract

A 13.56 MHz rf plasma atom source with an alumina discharge tube was characterized for use with oxygen. For a rf input power of 500 W the maximum degree of dissociation was found to be 70% at an indicated source pressure of 0.20 Torr, and a dissociation of approximately 40% was obtained at an indicated source pressure of 0.60 Torr. Corresponding atom fluxes of 6.4×1019 atoms cm−2 s−1 and 1.66×1020 atoms cm−2 s−1, respectively were calculated at the source exit from the measured degree of dissociation and gas throughput. The energy distributions of the charged particle emissions from the source were also measured. It was found that the source produced positive ions with an average energy of 278 eV and electrons with an average energy of 8 eV. The ion and electron spatial distributions were also measured. The electron and positive ion currents were measured as a function of source pressure. Plasma emission spectra in the range 500–1000 nm were monitored at two different source pressures corresponding to maximum and minimum dissociation. No molecular lines could be observed making it impossible to correlate the optical measurements with the dissociation measurements.