An electro-negative cleaning or etchant gas, such as fluorine, that was ionized from a stable supply gas such as NH3 in a secondary chamber and recombined in the primary chamber, is re-ionized within the primary chamber by electron attachment by ionizing an electron donor gas, such as helium, in the...http://www.google.com.au/patents/US6828241?utm_source=gb-gplus-sharePatent US6828241 - Efficient cleaning by secondary in-situ activation of etch precursor from remote plasma source
