Improving plasma uniformity using lens-shaped electrodes in a large area very high frequency reactor

Experiments using a lens-shaped circular electrode are described to measure the correction of plasma nonuniformity due to the standing wave effect in a large area very high frequency plasma reactor. This work is the experimental verification of the theoretical reactor design in cylindrical geometry recently presented by L. Sansonnens and J. Schmitt, Appl. Phys. Lett. 82, 182 (2003). It is found that the lens-shaped electrode effectively compensates the standing wave effects by creating a uniform rf vertical electric field in the plasma volume. The plasma is uniform, except for edge effects, for a wide range of parameters and consequently the design is suitable for plasma processing.