Patent ID: 7375947

Claim:
In a plasma reactor having an electrostatic chuck (ESC) supporting a wafer to be processed, a method of processing the wafer while controlling an ESC clamping voltage, comprising: applying RF bias power to said ESC from a bias power source at an input to said ESC and applying a D.C. voltage at said input to said ESC from a D.C. voltage source; measuring voltage and current near said input to produce a measured voltage and a measured current; providing a wafer voltage signal as a sum of said measured voltage and said measured current multiplied by first and second coefficients respectively, said wafer voltage signal representing the voltage on a wafer supported on said ESC; and computing a wafer clamping voltage as a difference between a D.C. component of said wafer voltage signal and said D.C. voltage from said D.C. voltage source, and controlling said D.C. voltage to regulate said wafer clamping voltage.