Magnetic enhancement was determined to be effective in reduction of the plasma potential. In extremely high-excitation-frequency plasma, the self-bias voltage of the electrode was substantially reduced, while the plasma potential remained constant. The plasma potential was effectively controlled by utilizing a DC-biased shield electrode, and found to be very effective in minimizing the chamber material contamination. The dual rf excitation plasma processing equipment was proposed and found to be capable of controlling the self-bias of the substrate without altering the target self-bias voltage.