Method and system for monitoring RF impedance to determine conditions of a wafer on an electrostatic chuck
A method and system for monitoring and/or controlling the conditions of a wafer on an electrostatic chuck during plasma processing. The method and system include utilizing backflow gas pressure and DC clamping voltage as control variables to adjust the wafer temperature based upon impedance measurements determined by RF sensors located in the electrostatic chuck RF feed line. The method and system further include utilizing the clamping status of the wafer on the electrostatic chuck to monitor impedance during the plasma process.
1. A method for monitoring wafer temperature during wafer processing, comprising:
measuring an impedance of a load within the wafer process;
determining a temperature of the wafer based upon the measured impedance:
setting a backflow gas pressure and a DC clamping voltage to a series of combinations of values;
measuring wafer temperature for the various processing parameters during the experimental runs at each of the combinations of backflow gas pressure and DC clamping voltage;
measuring impedance for each measured wafer temperature;
correlating the measured impedance to the measured wafer temperature to provide correlated data;
comparing the measured impedance and the correlated data to determine a temperature of the wafer; and
controlling at least one of said backflow gas pressure and DC voltage to adjust said temperature of said wafer,
wherein the impedance is measured at multiple frequencies of the DC clamping voltage during the experimental runs.
2. The method of claim 1 , wherein said measuring of impedance includes measuring voltage and current in a transmission line of the wafer process.
3. The method of claim 2 , further comprising modulating at least one of said dc voltage and said backflow gas pressure for at least one selected frequency.
4. The method of claim 3 , wherein when the dc voltage is modulated the backflow gas pressure is set to a constant value, and
wherein when the backflow gas pressure is modulated, the dc voltage is set to a constant value.
5. The method of claim 1 , further comprising repeating said setting, said temperature measuring, said impedance measuring and said correlating for a series of sets of different processing parameters and wherein said comparing includes determining which of said sets of processing parameters is most similar to processing parameters for an actual process run.
6. The method of claim 1 , further comprising controlling at least one of backflow gas pressure and dc voltage in response to said measuring to adjust said temperature of the wafer.
7. The method of claim 1 , wherein the backflow gas pressure is set in a range of 1 Torr to 100 Torr.
8. The method of claim 1 , wherein the dc clamping voltage is set in a range of 500 to 2000 volts.