Patent ID: 7553679

Claim:
In a plasma reactor chamber having a wafer support pedestal for supporting a wafer inside the reactor, said pedestal having an insulated electrode beneath the wafer and a transmission line coupling said electrode to a bias impedance match element for an RF bias generator, a method of determining plasma ion density, wafer voltage, etch rate and wafer current in said chamber, said method comprising: sensing RF parameters corresponding to an input impedance, an input current and an input voltage at the input of said impedance match element to said transmission line; computing a junction admittance of a junction between said transmission line and the electrode within the wafer pedestal from said input impedance, input current and input voltage and from parameters of the transmission line; providing shunt electrical quantities of a shunt capacitance between the electrode and a ground plane; providing load electrical quantities of a load capacitance between the electrode and a wafer on the pedestal; computing at least one of said etch rate, plasma ion density and wafer voltage and wafer current from said junction admittance, said shunt electrical quantities, said load electrical quantities and a frequency of RF bias power applied to said electrode.