Mask etch plasma reactor with cathode providing a uniform distribution of etch rate

A plasma reactor for etching a workpiece such as a rectangular or square mask, includes a vacuum chamber having a ceiling and a sidewall and a workpiece support pedestal within the chamber including a cathode having a surface for supporting a workpiece, the surface comprising plural respective zones, the respective zones of the surface being formed of respective materials of different electrical characteristics. The zones can be arranged concentrically relative to an axis of symmetry of the wafer support pedestal.