Particle model analyses of N2O dilution with He on electrical characteristics of radio-frequency discharges

Abstract

The electrical characteristics (voltage, electric field, charged particle densities, dissipated power, particle energy, etc.) are analyzed in the case of low pressure (0.5 and 1 Torr) radio-frequency (rf) discharges in nitrous oxide (N2O)/Helium (He) mixtures. An optimized and validated particle model has been used for these analyses in the case of gradual dilutions of N2O with He buffer gas. A specific care is carried on the power density evolution and variation which show a complex behavior as a function of He proportion (up to 85%). These analyses are based on a microscopic approach enabling one to show the contribution of the different inelastic processes mainly between electrons and respectively N2O and He gases. This approach enables also one to show the discharge region (the positive column or the plasma region) where the power is preferentially dissipated. The power density variation is found to be mainly proportional to the electron density variation. The latter is dependent on the different processes occurring between the charged particles [i.e., electrons, negative ions (O− and NO−), and positive ions (N2O+ and He+)] and the neutral gas mixture (N2O and He). Furthermore, the particle model shows the role of the electron-He collisions on the variation in the electron energy and distribution. This allows more particularly explaining the effects of N2O dilution with He on the dissipated power variation in terms of creation and loss of electrons through collision processes.