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

NF3 plasmas have been investigated for the cleaning of reactors for amorphous silicon (a-Si:H) deposition from silane. Optical emission spectroscopy, also time resolved, has been used to measure F*, N2*, NF*, and SiF* emitting species in the plasma phase. Measurements of mass spectrometry, etching rate and dc self-bias voltage at the rf powered electrode have also been used for process diagnostics, The a-Si:H etching process by F atoms is shown to occur under loading conditions: the etching rate does not correlate with F atom density. The recombination processes 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 significant for the NF3 plasma chemistry as well as the fluorine conversion into SiF4.