Nonlinear Electron Resonance Heating in Asymmetric Capacitive Discharges

Sebastian Wilczek, Ralf Peter Brinkmann, Thomas Mussenbrock

ICOPS 2016, Banff, Alberta, Canada, June 19-23 2016


In low-pressure capacitive discharges the concept of Nonlinear Electron Resonance Heating (NERH) becomes important to enhance Ohmic dissipation. Particularly in geometrically asymmetric capacitive discharges (generation of a DC self-bias), the nonlinearities of the boundary plasma sheaths lead to a strongly non-sinusoidal radio frequency current. The Fourier spectra of such a current can indicate harmonics which are in resonance with the Plasma Series Resonance (PSR). The scenario of PSR was investigated by different models (e.g. zero-dimensional, spatially resolved), which assume that the bulk current is carried by the electron current and the sheath current by the displacement current. Although these models are able to resolve the nonlinear behavior between bulk and sheath a detailed kinetic picture is missing. In this work, we discuss the particle dynamics in the regime of NERH on a nanosecond timescale by means of a self-consistent kinetic simulation. We use a 1d3v spherical Particle-In-Cell code in order to simulate an asymmetric discharge. It is shown that the excitation of harmonics is connected to the generation of multiple electron beams accelerated by the expanding plasma sheath. Furthermore, the interaction of these beams with bulk electrons leads to significant plasma oscillations and thus, to a moderate displacement current in the center of the discharge. These kinetic effects should be taken into account for future models in order to understand the comprehensive electron heating in capacitive discharges.