Effect of Excited Particles on Electron Production in Rare Gas RF Breakdown

Abstract

The characteristics of rare gas RF (13.56 MHz) breakdown are investigated, focusing our interest on the effect of excited particles on electron production specifically. First of all the pressure dependence of breakdown voltage, the breakdown voltage curve, is measured in parallel plate capacitively coupled RF discharge devices for four rare gases, He, Ne, Ar and Kr. For Ar and Kr typical well-known V-shaped type curves composed of the left and right branches are obtained, while for light rare gases, He and Ne, the L-shaped ones which show flat characteristics over a considerably broad range of pressure in the right branch are obtained. According to the similarity law for pd (p: pressure; d: electrode separation) which holds roughly in the right branch for any gases studied here, it is found that the breakdown voltage in the right branches of light gases increases with pressure through three regions, namely the gradual increase one, the flat one and the abrupt increase one. The numerical results by Kihara's breakdown criterion and the conventional Boltzmann analysis are as follows: as the working pressure increases, the dominant electron production process in the right branches of light gases shifts from the direct ionization which is the main electron production process in heavy rare gas breakdown, to the processes accompanied by excited particles and the flat region in the breakdown curve corresponds to the transition region of the dominant electron production process.