Patent ID: 8076247

Claim:
A method of processing a workpiece in a plasma reactor chamber, comprising: coupling, to a plasma in the chamber, power of an RF frequency via a ceiling electrode and coupling, to the plasma, power of at least approximately the same RF frequency via a workpiece support electrode; providing an edge ground return path; and adjusting the proportion between (a) current flow through a center RF current path between said electrodes and (b) current flow to the edge ground return path from said electrodes, wherein said adjusting comprises: (a) determining non-uniformity of radial distribution of plasma ion density in said chamber, (b) performing one of: (i) responding to a center-high nonuniformity by reducing a phase difference between RF voltages or currents at said ceiling electrode and said workpiece support electrode, (ii) responding to an edge high nonuniformity by increasing a phase difference between RF voltages or currents at said ceiling electrode and said workpiece support electrode.