Apparatus and method for controlling etch uniformity

A system for processing a semiconductor wafer, the system comprising:

• a radio frequency (RF) power generator having a tunable frequency output, the tunable frequency output defined within a range;
• a processing chamber having a bottom electrode and a top electrode, a plasma region defined between the bottom and to electrodes, the processing chamber receiving RF power from the RF power generator;
• and
• a match network coupled between the RF power generator and the processing chamber, the match network including a feedback controller monitoring a bias voltage associated with the bottom electrode, the feedback controller configured to adjust an amount of power radially distributed over a surface of substrate being process within the processing chamber, wherein a tunable element representing a variable capacitance that affects the radial distribution of power in the plasma region is located within the match network the tunable element located between the RF power generator and the bottom electrode of the processing chamber, the tunable element adjusting a split between a grounding pathway defined within an inner region of the plasma region between the bottom electrode and the top electrode and a second grounding pathway defined within an outer region of the plasma region between the bottom electrode and a grounding shield disposed over a surface of a focus ring, the focus ring located around a periphery of the bottom electrode.

A method of processing a semiconductor substrate within a plasma chamber, comprising method operations of:

• delivering radio frequency (RF) power to a bottom electrode of the processing chamber at a first frequency value from a radio frequency (RF) generator;
• striking a plasma within a processing chamber;
• monitoring a bias voltage of the semiconductor substrate on the bottom electrode of the processing chamber;
• adjusting the first frequency value to a second frequency value from the radio frequency (RF) generator to obtain a desired bias voltage value through a tunable element located between the RF power generator and the bottom electrode of the processing chamber, and
• changing a ratio of power returned through an upper electrode ground path to power returned through a lower electrode ground path in response to adjusting the first frequency value, the lower electrode ground path defined through a grounding shield disposed over a surface of a focus ring, the focus ring located around a periphery of the bottom electrode.