Patent ID: 8313664

Claim:
A method of processing a wafer while controlling an electrostatic chuck clamping voltage, comprising: applying a first RF current to the electrostatic chuck through an RF match network at a first frequency from a first RF power source; applying a second RF current to the electrostatic chuck through the RF match network at a second frequency from a second RF power source; applying DC voltage to the electrostatic chuck; measuring a third RF current at the match network attributable to the first frequency; measuring a fourth RF current at the match network attributable to the second frequency; calculating a wafer voltage at the first and second frequencies based upon the measured third and fourth currents; calculating a DC component of the wafer voltage attributed to each frequency; calculating a total DC voltage at the wafer based upon the DC component attributable to each frequency and a DC component attributable to an intermodulation of the first and second frequency; and adjusting the applied DC voltage to maintain a predetermined difference between the applied DC voltage and the total DC voltage at the wafer.