Patent ID: 7359177

Claim:
A plasma reactor comprising: a vacuum chamber and an electrostatic chuck (ESC) within said vacuum chamber for supporting a wafer to be processed, and an ESC supply voltage source; a process gas inlet for furnishing process gases into said vacuum chamber; a plasma RF bias power supply and an RF power path having an input end coupled to said plasma RF bias power supply and an output end coupled to said ESC, and sensor circuits providing measurement signals representing measured voltage and measured current near the input end of said RF power path; a processor for 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 a feedback control loop controlling a D.C. supply voltage of said ESC to govern a clamping voltage comprising a difference between a D.C. component of said wafer voltage signal and the voltage of said D.C. supply voltage source of said ESC.