Low-energy linear oxygen plasma source.

A new version of a constricted plasma source is described, characterized by all metal-ceramic construction, a linear slit exit of 180mm length, and cw operation (typically 50kHz) at an average power of 1.5kW. The plasma source is here operated with oxygen gas, producing streaming plasma that contains mainly positive molecular and atomic ions, and to a much lesser degree, negative ions. The maximum total ion current obtained was about 0.5A. The fraction of atomic ions reached more than 10% of all ions when the flow rate was less then 10SCCM O2, corresponding to a chamber pressure of about 0.5Pa for the selected pumping speed. The energy distribution functions of the different ion species were measured with a combined mass spectrometer and energy analyzer. The time-averaged distribution functions were broad and ranged from about 30to90eV at 200kHz and higher frequencies, while they were only several eV broad at 50kHz and lower frequencies, with the maximum located at about 40eV for the grounded anode case. ...