We present a combined experimental and numerical investigation of the plasma properties in an asymmetric capacitively coupled radio frequency plasma source using argon discharge. Besides driving the system in the conventional way, which results in a high negative self-bias voltage due to the asymmetric configuration, we also connect a 'quarter-wavelength filter' to the powered electrode, which lifts its DC potential to zero. At the powered side of the plasma, we employ electrodes with conducting and insulating surfaces, as well as electrodes combining both in different proportions ('hybrid electrodes'). Measurements are carried out for the plasma potential, the electron density and temperature in the bulk plasma, as well as for the flux-energy distribution of the ions at the grounded surface of the system. The nature of the surface of the powered electrode as well as the presence of the quarter-wavelength filter are found to highly influence the plasma potential, . For the electrode with a conducting surface 20 V and ∼150 V are found in the absence and the presence of the filter, respectively. For the electrode with an insulating surface, the self-bias voltage builds up directly at the plasma interface, thus the filter has no effect and a plasma potential of ∼20 V is found. For the electrodes with different conducting/insulating proportions of their surface, ranges between the above values. Particle-in-Cell/Monte Carlo Collisions calculations for identical conditions with hybrid electrodes predict double-peaked ion energy distribution at the powered electrode with peaks corresponding to and along with a lowering of the plasma potential (whencompared to wholly conducting electrode), a trend that is observed experimentally. These studies are of great importance for the application of similar plasma sources with in-situ cleaning of mirrors in fusion devices and the results can be extended to a variety of plasma processing applications.
Extraction of positive and negative ion beams from large area plasma sources