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

A 13.56 MHz plasma atom source with an alumina discharge tube was character ized 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 x 10(19) at oms cm(-2)s(-1) and 1.66 X 10(20) atoms cm(-2)s(-1), respectively were calc ulated 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 posit ive ions with an average energy of 278 eV and electrons with an average ene rgy of 8 eV. The ion and electron spatial distributions were also measured. The electron and positive ion currents were measured as a function of sour ce pressure. Plasma emission spectra in the range 500-1000 nm were monitore d at two different source pressures corresponding to maximum and minimum di ssociation. No molecular lines could be observed making it impossible to co rrelate the optical measurements with the dissociation measurements. (C) 20 01 American Vacuum Society.