Hysteresis Effects and Confinement of Beam Electrons in Capacitive Discharges

Sebastian Wilczek, Jan Trieschmann, Ralf Peter Brinkmann, Julian Schulze, Schüngel, Edmund, Derzsi, Aranka, Korolov, Ihor, Hartmann, Peter, Donkó, Zoltán, Thomas Mussenbrock

ICOPS 2016, Banff, Alberta, Canada, June 19-23 2016 (invited)


In low-pressure capacitive discharges the radio-frequency modulated plasma sheaths generate a number of highly energetic beam electrons traversing the discharge gap. These electrons are important for sustaining the plasma via ionization. In this work, we investigate the dynamics of these electron beams as well as their effect on the plasma by means of Particle-In-Cell simulations for different process parameters (driving frequency, gap size, pressure). Especially at low pressures (large electron mean free path ?m) and small gap sizes Lgap (?m/Lgap>1), the interaction of electron beams with the opposing sheath becomes important1. Under a certain combination of parameters, electron beams generated at one electrode can approach the other electrode, when the local sheath length is minimum. These energetic electrons can overcome the sheath potential at this time and can be lost at this electrode. In that case, the plasma density decreases abruptly. Varying the process parameters (e.g., increasing or decreasing the driving frequency) indicates a hysteresis at this abrupt transition. In order to explain this hysteresis, the electron dynamics is investigated on a nanosecond timescale. From these results it is shown that the interaction of beam and bulk electrons is the governing mechanism.

    1. Wilczek et al.“ The effect of the driving frequency on the confinement of beam electrons and plasma density in low-pressure capacitive discharges”, 2015 Plasma Sourc. Sci. Technol. 24 024002