Patent ID: 7795153

Claim:
A method of processing a workpiece on workpiece support pedestal in a plasma reactor chamber in accordance with user-selected values of plural plasma parameters selected from a group comprising ion density, wafer voltage, etch rate, wafer current, by controlling chamber parameters selected from a group comprising source power, bias power, chamber pressure, magnet coil current, gas flow rates in respective zones and gas composition in respective zones, said method comprising: for each one of said plural plasma parameters, fetching from a memory a contour of a constant plasma parameter numerical value corresponding to the user-selected value of said one plasma parameter, said contour being defined in a space of a dimension equal to the number of said selected chamber parameters, and determining an intersection of the corresponding contours, said intersection corresponding to respective target values of the selected chamber parameters; setting the values of said selected chamber parameters to the respective target values; subsequently controlling plasma bias power in a feedback control loop by sensing a difference between the user-selected value of wafer voltage and a concurrently measured value of wafer voltage and changing the plasma bias power to reduce said difference; subsequently controlling plasma source power in a feedback control loop by sensing a difference between the user-selected value of plasma ion density or etch rate and a measured value of plasma ion density or etch rate and changing the plasma source power to reduce said difference; obtaining said measured values of wafer voltage and plasma ion density by the steps of; (a.) sampling values of RF electrical parameters at an input end of a transmission line coupling RF bias power to an electrode within said wafer support pedestal, said electrode being connected to an output end of the transmission line; (b.) computing said measured value of wafer voltage from the sampled values of the RF electrical parameters; and (c.) computing said measured value of plasma ion density or etch rate from the sampled values of the RF electrical parameters.