Resonant discharges: initiation and steady state; comparisons with theory, simulation and experiment

Summary form only given, as follows. Discharges driven at the series resonance frequency have many desirable properties. The input resistance is small, and the voltage and current are in phase. The voltage drive is small (/spl sim/Te) and the average plasma potential is low (/spl sim/10 Te). Such is observed experimentally and in our PIC-MCC simulations. Scaling laws at fixed pressure show peak electron density proportional to the cube of the drive frequency (capacitive discharge is as the square), permitting the density to be controlled. Simulation results show at low pressure, the ion energy distribution at the target has a sharp peak at the plasma potential with narrow angular spread about the normal. The V-I phase angle versus I curve is measured in simulation and compared with experimental results and the theoretical scaling laws are compared with simulation results and the transition of a capacitively coupled plasma to a resonantly sustained plasma is discussed. During this transition or "lock-on" (which occurs in a few RF cycles, a time scale much faster then ion related frequencies), the plasma changes dramatically: the electron kinetic energy and the plasma potential more than doubles; the circuit impedance of the discharge goes from capacitive to resistive; the motion of bulk plasma changes from nearly in phase to nearly out of phase with the voltage drive; and the characteristic heating pattern of these discharges takes shape. In these discharges, the formation of high velocity electron bunches in the sheath regions is seen. During an RF cycle, these bunches are alternately accelerated from each sheath into the bulk plasma. We speculate these bunches provide the ionization in resonantly sustained discharges. We also speculate that the lock-on process is similar to the mode-jumping seen in other resonantly and surface wave sustained discharges.