2D PIC simulations of geometrically asymmetric capacitive RF plasmas driven by tailored voltage waveforms*

Two different types of electrical asymmetry effects, i.e. the amplitude and slope asymmetry, have been investigated in geometrically asymmetric capacitive RF discharges (having a smaller powered electrode area with respect to the grounded one) operated in argon at low pressure by 2D Particle-In-Cell/Monte Carlo collision simulations. Significantly different effects of these electrical asymmetries are observed in geometrically asymmetric discharges compared to those observed in geometrically symmetric discharges as a result of a waveform dependent constructive or destructive superposition of the geometrical and electrical asymmetries. This coupling effect strongly changes the plasma density and charged particle distribution functions at boundary surfaces, e.g. a reduced plasma density is observed in the valleys- and sawtooth-down waveform cases as compared to the peaks- and sawtooth-up waveforms. By including realistic energy and material dependent secondary electron emission coefficients in the simulations, the electron induced secondary electrons are found to greatly contribute to the ionization at low pressures, especially in the peaks- and sawtooth-up cases.