An apparatus for plasma processing a substrate is provided. The apparatus comprises a processing chamber, a substrate support disposed in the processing chamber, and a lid assembly coupled to the processing chamber. The lid assembly comprises a conductive gas distributor coupled to a power source. A tuning electrode may be disposed between the conductive gas distributor and the chamber body for adjusting a ground pathway of the plasma. A second tuning electrode may be coupled to the substrate support, and a bias electrode may also be coupled to the substrate support.