Abstract
Very high-frequency (VHF) plasma generated with a supersonic gas jet, which is attractive for high-speed and low-damage film deposition in plasma enhanced chemical vapour deposition (PECVD), were investigated experimentally and theoretically. When the gas flow rate was changed under a background pressure in the Torr regime, a unique beam-shaped plasma was clearly observed in the region where an underexpanded jet was generated. It was found through plasma measurement that the plasma parameters are strongly influenced by the spatial structure of the underexpanded gas jet. In particular, the ionization rate was greatly changed according to the local change of gas pressure due to the jet, and the temperature and density of electrons changed by double and one order of magnitude, respectively. These phenomena are considered to be useful to locally control the spatial distribution of plasma parameters.
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