Power Gain and Loss Dynamics of γ- and δ- electrons in Low Pressure CCRF Discharges

Katharina Nösges, Aranka Derzsi, Benedekt Horvath, Julian Schulze, Ralf Peter Brinkmann, Sebastian Wilczek

9th bi-annual Radio Frequency Workshop, Dublin, Ireland, June 24-25 2019


Abstract

In low pressure capacitively coupled radio frequency (CCRF) discharges, secondary electrons (SEs), in particular, electron induced SEs (δ-electrons) are frequently neglected in theory and simulations. The generation of SEs in low CCRF discharges is one part of the plasma surface interaction, which strongly affects the electron dynamics. Especially at small gap sizes and high sheath voltages, the δ-electrons dominate the ionization process and can significantly increase the plasma density. Generally, the generation of δ-electrons depends on the dynamics of ion induced SEs (γ-electrons) due to their very high energies. Therefore, it is important to consider the dynamics of the different electrons (δ-electrons and γ-electrons) separately. With this separation, the electron power gain and loss as well as the generation of each species can be understood on a nanosecond timescale. In order to study this issue, 1d3v particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations of a symmetric CCRF discharge are performed in the low pressure regime (p ≈ 1 Pa). In this work, the gap size is varied and the effects of the nonlocal and nonlinear dynamics of γ-electrons and δ-electrons on the discharge are investigated by using a realistic model for the electron-surface interactions in the simulations. It is shown, that particularly for small gap sizes (Lgap < 30 mm) the δ-electrons dominate the discharge population of electrons in the range of 50% and lead to the generation of multiple SE beams during one RF period.

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