The effect of discharge chamber geometry on the characteristics of low-pressure RF capacitive discharges

We report the measured extinction curves and current-voltage characteristics (CVCs) in several gases of RF capacitive discharges excited at 13.56 MHz in chambers of three different geometries: 1) parallel plates surrounded by a dielectric cylinder ("symmetric parallel plate"); 2) parallel plates surrounded by a metallic cylinder ("asymmetric confined"); and 3) parallel plates inside a much larger metallic chamber ("asymmetric unconfined"), similar to the gaseous electronics conference reference cell. The extinction curves and the CVCs show differences between the symmetric, asymmetric confined, and asymmetric unconfined chamber configurations. In particular, the discharges exist over a much broader range of RF voltages and gas pressures for the asymmetric unconfined chamber. For symmetric and asymmetric confined discharges, the extinction curves are close to each other in the regions near the minima and at lower pressure, but at higher pressure, the extinction curve of the asymmetric confined discharge runs at a lower voltage than the one for the discharge in a symmetric chamber. In the particular cases of an " asymmetric unconfined chamber"discharge or "asymmetric confined" one, the RF discharge experiences the transition from a "weak-current" mode to a "strong-current" one at lower RF voltages than is the case for a "symmetric parallel-plate" discharge.