Patent ID: 7879731

Claim:
A method of processing a workpiece in a plasma reactor chamber having electrodes including at least a ceiling electrode and a workpiece support electrode, said method comprising: coupling respective RF power sources of respective VHF frequencies f 1 and f 2 to one of: (a) respective ones of the electrodes, and (b) a common one of the electrodes, where f 1 is sufficiently high to produce a center-high non-uniform plasma ion distribution and f 2 is sufficiently low to produce a center-low non-uniform plasma ion distribution; adjusting a ratio of an RF parameter at the f 1 frequency to the RF parameter at the f 2 frequency so as to control plasma ion density distribution, said RF parameter being one of: (a) RF power, (b) RF voltage, and (c) RF current, wherein said adjusting comprises one of: (a) providing a desired first reduction in a center-high plasma ion density distribution by decreasing the ratio of the RF parameter at the f 1 frequency relative to the RF parameter at the f 2 frequency in proportion to said desired first reduction; (b) providing a desired second reduction in an edge-high plasma ion density distribution nonuniformity by decreasing the ratio of the RF parameter at the f 2 frequency relative to the RF parameter at the f 1 frequency in proportion to said desired second reduction.