Investigation of 4% carbon in hydrogen electron cyclotron resonance microwave plasmas using ethane as the source gas

Supersonic pulse, plasma sampling mass spectrometry has been used to probe electron cyclotron resonance microwave plasmas consisting of 2% ethane in h ydrogen and 2% ethane in deuterium. The overall hydrocarbon chemistry and i nterconversion of species within these plasmas were determined by comparing the composition of these two chemically equivalent plasmas. The ethane in hydrogen plasma is shown to consist of 58% unreacted ethane (C2H6), 16% eth ylene (C2H4), 12% acetylene (C2H2), 9% methane (CH4), with the remaining 4% of the counts attributed to the ethylene radical species (C2H3) and the et hane radical species (C2H5). The mass spectrum of the analogous deuterium p lasma reveals the ethane to remain entirely undeuterated, while the ethylen e and acetylene exhibit significant deuteration. The observation of signifi cantly deuterated ethylenes indicates a new reaction channel is available i n these ethane-based plasmas, that is not available to hydrocarbon plasmas based on acetylene or ethylene. Specifically, the reaction of the ethane ra dical (C2H5) With a hydrogen atom results in the cleavage of the carbon-car bon bond forming two methyl radicals (CH3). Once formed, the methyl radical s may undergo repeated cycles of hydrogen (deuterium) atom additions and ab stractions (analogous to those previously observed for acetylene) before re combining to yield the deuterated ethane radicals (C2DxH5-x) which then by abstraction of a hydrogen (or deuterium) forms the observed deuterated ethy lenes. Overall, the chemistry of these hydrocarbon plasmas is shown to be c ompletely consistent with the neutral molecule reactions previously observe d in combustion chemistry literature. (C) 1999 American Vacuum Society. [S0 734-2101(99)10805-4].