Plasma process uniformity across a wafer by controlling RF phase between opposing electrodes

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;
• determining nonuniformity of radial distribution of plasma ion density in said chamber;
• and
• performing one of:
• (a) responding to a center high nonuniformity by increasing an impedance of a center RF current path between said electrodes relative to impedance of said edge ground return path by adjusting the reactance of a reactive element coupled to one of said electrodes,
• (b) responding to an edge high nonuniformity by increasing an impedance of said edge ground return path relative to impedance of said center RF current path by adjusting the reactance of a reactive element coupled to one of said electrodes.

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;
• determining whether radial distribution of plasma ion density in said chamber has a nonuniformity that is one of (i) center high, (ii) edge high;
• and
• performing one of:
• (a) responding to a center high nonuniformity by adjusting the phase angle between the RF currents at the two electrodes to increase impedance of a center RF current path between said electrodes relative to impedance of said edge ground return path,
• (b) responding to an edge high nonuniformity by adjusting said phase angle to increase impedance of said edge ground return path relative to impedance of said center RF current path if said nonuniformity is edge high.