Dual plasma source process using a variable frequency capacitively coupled source to control plasma ion density

Abstract

A method of processing a workpiece in the chamber of a plasma reactor includes introducing a process gas into the chamber, simultaneously (a) capacitively coupling VHF plasma source power into a process region of the chamber that overlies the wafer, and (b) inductively coupling RF plasma source power into the process region, and controlling plasma ion density by controlling the effective frequency of the VHF source power. In a preferred embodiment, the step of coupling VHF source power is performed by coupling VHF source power from different generators having different VHF frequencies, and the step of controlling the effective frequency is performed by controlling the ratio of power coupled by the different generators.