Methods and apparatus for controlling a plasma processing system
A method and apparatus for compensating a bias voltage at the wafer by measuring RF voltage signals in RF driven plasma including at least an electrostatic, chuck (ESC), a capacitive divider, a signal processing and signal conditioning network is disclosed. The bias compensation device includes a capacitive divider to detect the RF voltage at the ESC, a signal conditioning network for the purpose of filtering specific RF signals of interests, and a signal processing unit for computing the DC wafer potential from the filtered RF signals.
1. A method comprising:
obtaining a radio frequency (RF) voltage signal from an RF sensing mechanism via a high impedance path, the RF voltage signal having multiple RF frequencies associated with multiple RF generators, the multiple frequencies including a first frequency and a second frequency, said RF sensing mechanism is an RF rod, wherein said RF rod is proximate to a component of an electrostatic chuck (ESC) subsystem, wherein the component is outside a region having plasma when formed in a plasma chamber, wherein the RF rod is used for sensing said RF voltage signal, said RF rod providing said RF voltage signal to a capacitor divider network;
processing said RF voltage signal to generate a plurality of signals, one of the signals in said plurality of signals having the first frequency and another one of the signals in said plurality of signals having the second frequency;
applying a transfer function to the signal having the first frequency and the other signal having the second frequency to derive a wafer potential; and
providing the wafer potential as a control signal to control at least a subsystem of said plasma processing system.
2. The method of claim 1 , wherein said component is a base plate.
3. The method of claim 1 , wherein said plurality of signals includes at least a signal corresponding to an unfiltered broadband version of said RF voltage signal.
4. The method of claim 1 , wherein said processing includes calibrating said plurality of signals wherein said calibrating is responsive to said capacitor divider network.
5. The method of claim 1 , wherein said transfer function is a linear transfer function.
6. The method of claim 5 , wherein said linear transfer function is obtained using multi-variate analysis.
7. The method of claim 1 , wherein said transfer function is a non-linear transfer function.
8. The method of claim 7 , wherein said non-linear function is obtained using a power equation.
9. The method of claim 1 , wherein said processing includes analog filtering.
10. The method of claim 1 , wherein said processing includes digital signal processing.
11. The method of claim 1 , wherein said processing comprises filtering the signals in said plurality of signals to split the signals into the signal having the first frequency and the other signal having the second frequency.
12. The method of claim 1 , wherein said processing comprises generating a peak magnitude of the signal having the first frequency and a peak magnitude of the other signal having the second frequency.
13. A plasma processing system configured for processing at least one wafer disposed on an electrostatic chuck (ESC), the plasma processing system comprising:
a radio frequency (RF) sensing mechanism, said RF sensing mechanism is proximate to a component of said ESC to obtain an RF voltage signal, wherein the component is outside a region having plasma when formed in a plasma chamber, the RF voltage signal having multiple frequencies associated with multiple RF generators, the multiple frequencies including a first frequency and a second frequency, said RF sensing mechanism is an RF rod and said component is a base plate;
a high impedance voltage probe arrangement coupled to said RF rod, wherein said high impedance voltage probe arrangement is implemented at least by a capacitor divider network to facilitate acquisition of said RF voltage signal from said RF rod while reducing perturbation of RF power driving the plasma in said plasma processing system;
a signal processing arrangement configured to receive said RF voltage signal, the signal processing arrangement for generating a plurality of signals from said RF voltage signal, one of the signals in the plurality of signals having the first frequency and another one of the signals in the plurality of signals having the second frequency, the signal processing arrangement for applying one of a digital and analog version of the signal having the first frequency and the other signal having the second frequency to a transfer function to obtain a wafer bias; and
an ESC power supply subsystem configured to receive said wafer bias as a feedback signal to control said plasma processing system during processing of said at least one wafer.
14. The plasma processing system of claim 13 , wherein said RF voltage signal is processed by said signal processing arrangement into the plurality of signals that includes at least a signal corresponding to an unfiltered broadband version of said RF voltage signal.
15. The plasma processing system of claim 14 , wherein said signal processing arrangement is configured to calibrate said plurality of signals wherein said calibrating is responsive to said capacitor divider network.
16. The plasma processing system of claim 13 , wherein said transfer function represents a linear transfer function.
17. The plasma processing system of claim 13 , wherein said transfer function represents a non-linear transfer function.
18. The plasma processing system of claim 13 , wherein the signal processing arrangement is configured to filter the signals in said plurality of signals to split the signals into the signal having the first frequency and the other signal having the second frequency.
19. The plasma processing system of claim 13 , wherein the signal processing arrangement is configured to generate a peak magnitude of the signal having the first frequency and a peak magnitude of the other signal having the second frequency.