Kinetic simulation of low pressure capacitively coupled plasmas: Analysis of an abrupt mode transition
Sebastian Wilczek, Jan Trieschmann, Julian Schulze, Ralf Peter Brinkmann, Thomas Mussenbrock
WELTPP-16, Kerkrade, The Netherlands, 21-22 November (oral contribution)
In low pressure capacitively coupled radio-frequency discharges electron heating is dominated by stochastic heating. By using 1D3V Particle-in-Cell simulations it is shown that the interaction of electrons with and reflection from the sheaths can produce highly energetic electron beams. Due to a low collisionality, these beams can traverse through the plasma bulk and interact with the opposite sheath without any collision. By varying the driving frequency or the gap size, the relative phase between the electron beam impact on the opposite sheath and the movement of the latter can be adjusted. Therefore the reflection of the beams can be strongly influenced. Only weak interaction is observed when the electron beam impinges the opposite sheath in its collapsing phase. However, once the electron beam impinges the opposite sheath in the expanding phase, an abrupt electron heating mode transition is observed for a distinct combination of gap size and driving frequency. This transition is complimented by the appearance of a hysteresis of the excited mode depending on the initial discharge conditions. To explain this complex behavior higher harmonics of the driving frequency play an important role.