Measuring and controlling parameters of a plasma generator

• US 8,624,501 B2
• Filed: 12/08/2010
• Issued: 01/07/2014
• Est. Priority Date: 12/08/2010
• Status: Active Grant

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: MKS Instruments Incorporated
• Inventors: Nagarkatti, Siddharth P., Shajii, Ali, Benzerrouk, Souheil
• Primary Examiner(s): TRAN, THUY V
• Application Number:
  US12/963,209
• Publication Number:
  US 20120146508A1
• Time in Patent Office: 1,126 Days
• Field of Search: 315/111.51, 315/344, 315/352, 315/354, 156/345.48, 156/345.49
• US Class Current: 315/111.51
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

Methods, systems, and computer program products are described for measuring and controlling parameters of a plasma generator. A current in a primary winding of a transformer or inductive element that generates a plasma is measured. A voltage across a secondary winding of the transformer or inductive element is measured. Based on the current of the primary winding and the voltage across the secondary winding, a parameter of the plasma is determined. The parameter includes a resistance value associated with the plasma, a power value associated with the plasma, or both.

Claims

1. A method comprising:

measuring a current of a primary winding of a transformer that generates a plasma;

measuring a voltage across a secondary winding of the transformer; and

determining a parameter of the plasma comprising a resistance value associated with the plasma, or a power value associated with the plasma, or both, wherein determining the parameter of the plasma comprises;

estimating a current in the secondary winding based on the current of the primary winding; and

estimating the parameter based on the current in the secondary winding and the voltage across the secondary winding.

2. The method of claim 1, further comprising updating the parameter of the plasma based on measured values of the current of the primary winding and the voltage across the secondary winding.

3. The method of claim 1, further comprising determining a root-mean-square (RMS) equivalent of the current of the primary winding and determining an RMS equivalent of the voltage across the secondary winding.

4. The method of claim 3, wherein determining the RMS equivalent of the current of the primary winding comprises:

rectifying the current in the primary winding;

computing an average of the rectified primary current;

sampling the average of the rectified primary current; and

converting the sampled average of the rectified primary current to the RMS equivalent current of the primary winding.

5. The method of claim 3, wherein determining the RMS equivalent of the voltage across the secondary winding comprises:

rectifying the voltage in the secondary winding;

computing an average of the rectified secondary voltage;

sampling the average of the rectified secondary voltage; and

converting the sampled average of the rectified secondary voltage to the RMS equivalent voltage of the secondary winding.

6. The method of claim 1, wherein determining the parameter of the plasma comprises the steps of:

(a) estimating an RMS current of the secondary winding and an RMS voltage of the secondary winding;

(b) estimating a phase between the estimated RMS current of the secondary winding and the RMS voltage of the secondary winding;

(c) estimating the power value based on the estimated RMS current of the secondary winding, the RMS voltage of the secondary winding and the phase;

(d) estimating the resistance value based on the RMS voltage of the secondary winding and the estimated power value; and

(e) repeating steps (a) through (d) until an error associated with estimating the resistance value satisfies a predetermined criterion.

7. The method of claim 6, wherein the RMS current of the secondary winding is estimated based on an RMS current of the primary winding and a correction factor computed based on the resistance value, a core inductance value, and an angular frequency.

8. The method of claim 6, wherein the phase is estimated based on the resistance value, a plasma inductance value, and a frequency.

9. The method of claim 1, further comprising regulating power delivered to the plasma based on the determined power value.

10. The method of claim 9, wherein regulating the power delivered to the plasma comprises the steps of:

computing a difference between a predetermined power setpoint and the determined power value; and

determining a new power value based on the difference.

11. The method of claim 9, wherein the power is regulated in a feedback loop.

12. The method of claim 1, further comprising measuring an input voltage supplied to the plasma and compensating for input-line voltage ripple based on the input voltage.

13. The method of claim 12, wherein compensating for input-line voltage ripple comprises adjusting a switching frequency to regulate the power supplied to the plasma.

14. The method of claim 1, further comprising monitoring at least one of the power value and the resistance value to detect an unsafe operating condition associated with a toroidal plasma chamber.

15. The method of claim 1, further comprising detecting a deviation of at least one of the power value and the resistance value from a predetermined value.

16. A method for controlling a toroidal plasma, the method comprising:

measuring a current of a primary winding of a transformer that generates the toroidal plasma;

measuring a voltage across a secondary winding of the transformer;

measuring an input voltage supplied to the transformer;

estimating a power value of the plasma comprising;

i) determining a current in the secondary winding using the current of the primary winding and ii) estimating the power value based on the current in the secondary winding and the voltage across the secondary winding; and

regulating a power delivered to the plasma based on the estimated power value.

17. The method of claim 16, wherein regulating the power delivered to the plasma comprises the steps of:

computing a difference between a predetermined power setpoint and the estimated power value; and

determining a new power value based on the difference.

18. The method of claim 17, wherein the power is regulated in a feedback loop.

19. The method of claim 16, further comprising compensating for input-line voltage ripple based on the measured input voltage.

20. The method of claim 19, wherein compensating for input-line voltage ripple comprises adjusting a switching frequency based on the measured input voltage.

21. A toroidal plasma generator, comprising:

a plasma chamber;

a transformer having a magnetic core surrounding a portion of the plasma chamber and a primary winding;

a power supply in electrical communication with the primary winding, the power supply supplying a current to the primary winding, and the supplied current inducing a toroidal plasma in the plasma chamber; and

a module for estimating a parameter of the toroidal plasma by i) measuring the current of the primary winding and a voltage across a secondary winding of the transformer, ii) determining a current in the secondary winding based on the current of the primary winding; and

iii) estimating the parameter based on the current in the secondary winding and the voltage across the secondary winding, the parameter comprising a resistance value associated with the toroidal plasma, or a power value associated with the toroidal plasma, or both.

22. A system comprising:

a first module configured to measure a current of a primary winding of a transformer that generates a toroidal plasma and a voltage across a secondary winding of the transformer; and

a second module in communication with the first module, the second module configured to determine a parameter of the toroidal plasma comprising a resistance value associated with the plasma, or a power value associated with the plasma, or both, wherein the parameter is determined by i) determining a current in the secondary winding based on the current of the primary winding; and

ii) estimating the parameter based on the current in the secondary winding and the voltage across the secondary winding.

23. The system of claim 22, further comprising a third module configured to determine an RMS equivalent of the current of the primary winding and an RMS equivalent of the voltage across the secondary winding.

24. The system of claim 23, wherein the third module comprises:

a rectifier configured to rectify the current in the primary winding;

a differential amplifier in cooperation with a filter configured to compute an average of the rectified primary current;

a converter configured to sample the average of the rectified primary current; and

a processor module configured to convert the sampled average of the rectified primary current to the RMS equivalent current of the primary winding.

25. The system of claim 23, wherein the third module comprises:

a rectifier configured to rectify the voltage across the secondary winding;

a differential amplifier in cooperation with a filter configured to compute an average of the rectified secondary voltage;

a converter configured to sample the average of the rectified secondary voltage; and

a processor module configured to convert the sampled average of the rectified secondary voltage to the RMS equivalent voltage of the secondary winding.

26. The system of claim 22, wherein the second module includes an iterative filter configured to estimate the parameter of the plasma based on a model of the plasma that relates the current of the primary winding to the voltage across the secondary winding.

27. A computer program product, tangibly embodied in a non-transitory information carrier, the computer program product including instructions being operable to cause a data processing apparatus to:

receive a measured value of a current of a primary winding of a transformer used to generate a plasma in a plasma chamber;

receive a measured value of a voltage across a secondary winding of the transformer; and

determine a parameter of the plasma comprising a resistance value associated with the plasma, or a power value associated with the plasma, or both, wherein the parameter is determined by i) determining a current in the secondary winding based on the current of the primary winding and ii) estimating the parameter based on the current in the secondary winding and the voltage across the secondary winding.

28. A method comprising:

measuring a current of a primary winding of a transformer that generates a plasma;

measuring a voltage across a secondary winding of the transformer; and

determining a parameter of the plasma based on i) an RMS equivalent of the current of the primary winding and ii) an RMS equivalent of the voltage across the secondary winding, the parameter comprising a resistance value associated with the plasma, or a power value associated with the plasma, or both.

29. A method for controlling a toroidal plasma, the method comprising:

measuring a current of a primary winding of a transformer that generates the toroidal plasma;

measuring a voltage across a secondary winding of the transformer;

measuring an input voltage supplied to the transformer;

estimating a power value of the plasma based on an RMS equivalent of the current of the primary winding and an RMS equivalent of the voltage across the secondary winding; and

regulating a power delivered to the plasma based on the estimated power value.

30. A system comprising:

a first module configured to measure a current of a primary winding of a transformer that generates a toroidal plasma and a voltage across a secondary winding of the transformer; and

a second module in communication with the first module, the second module configured to determine a parameter of the toroidal plasma based on i) an RMS equivalent of the current of the primary winding and ii) an RMS equivalent of the voltage across the secondary winding, the parameter comprising a resistance value associated with the plasma, or a power value associated with the plasma, or both.

31. A computer program product, tangibly embodied in a non-transitory information carrier, the computer program product including instructions being operable to cause a data processing apparatus to:

receive a measured value of a current of a primary winding of a transformer used to generate a plasma in a plasma chamber;

receive a measured value of a voltage across a secondary winding of the transformer; and

determine a parameter of the plasma according to a model relating the parameter of the plasma to i) an RMS equivalent of the current of the primary winding and ii) an RMS equivalent of the voltage across the secondary winding, the parameter comprising a resistance value associated with the plasma, or a power value associated with the plasma, or both.