Effect of slot antenna structures on production of large-area planar surface wave plasmas excited at 2.45 GHz

The effect of slot antenna structures on plasma production was investigated in the large-area planar surface wave plasmas (SWPs) excited with 2.45 GHz microwave energy. Plasma production characteristics were measured for various types of slot antennae (inclined, transverse, longitudinal and diverging slots) in Ar discharges. In all the slot antennae, we clearly observed the density jumps when the incident power and pressure were varied. These density jumps correspond to the mode jumps between transverse magnetic (TM) eigenmodes in the SWP. In spite of different slot antenna structures, the same optical emission patterns of the TM62 mode were observed at the almost same electron density, except for the diverging slots, in which the TM92 mode was selectively excited under the same operating conditions, where the incident power was 0.8-1.2 kW at a pressure of 100-280 mTorr. At lower pressures, say 10 mTorr, the plasmas entirely broadened over the chamber cross section for all the slot antennae. Among the four slot antennae, the transverse slot antenna was more efficient for plasma production under the same incident microwave power at a fixed pressure.