STUDY OF THE NF3 PLASMA CLEANING OF REACTORS FOR AMORPHOUS-SILICON DEPOSITION

NF3 plasmas have been investigated for the cleaning of reactors for am orphous silicon (a-Si:H) deposition from silane. Optical emission spec troscopy, also time resolved, has been used to measure F, N2*, NF*, a nd SiF emitting species in the plasma phase. Measurements of mass spe ctrometry, etching rate and dc self-bias voltage at the rf powered ele ctrode have also been used for process diagnostics, The a-Si:H etching process by F atoms is shown to occur under loading conditions: the et ching rate does not correlate with F atom density. The recombination p rocesses NF(x)+F-->NF(x+1) (x=2,1) and NF+NF-->N2+2F together with the NF3 electron impact dissociation into NF(x)+F have been found to be s ignificant for the NF3 plasma chemistry as well as the fluorine conver sion into SiF4.