Method and apparatus for preventing instabilities in radio-frequency plasma processing

• US 7,304,438 B2
• Filed: 09/22/2004
• Issued: 12/04/2007
• Est. Priority Date: 09/22/2003
• Status: Active Grant

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: MKS Instruments Incorporated
• Inventors: Kishinevsky, Michael
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US10/947,397
• Publication Number:
  US 20050093459A1
• Time in Patent Office: 1,168 Days
• Field of Search: 315/247, 315/246, 315/291, 315/307, 315/224, 315/225, 315/209.R
• US Class Current: 315/247
• CPC Class Codes: H01J 37/32082 Radio frequency generated discharge H01J37/32357, H01J37/32366, H01J37/32394 and H01J37/32403 take precedence
• 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
• CPC Class Codes: H01J 37/3299 Feedback systems
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence

Abstract

A method and apparatus for controlling a power supply to prevent instabilities due to dynamic loads in RF plasma processing systems, operating at frequencies of from 1 MHz and up, uses a feedforward type of control loop to tightly regulate the power supplied to the dynamic electrical load, such as loads caused by variable and inconsistent plasma impedance. A feedback control loop can also be used in combination with the feedforward loop, but at a slower rate, to help regulate the amount of power provided to the load.

Claims

1. An RF power supply for providing power to a dynamic load, comprising:

a power circuit for converting an input power to output RF power, the circuit having low stored energy;

a control circuit providing a control signal to the power circuit to regulate an input power consumption by the RF power supply;

a first circuit for providing a measurement of an input power to the RF power supply that is used to adjust the control signal to the power circuit at a first rate, such that the input power is substantially constant; and

a second circuit for measuring an output power at an output of the RF power supply that is used to compensate the power control signal to the RF power supply at a second rate, wherein the first rate is greater than the second rate.

2. The RF power supply of claim 1 wherein the first rate corresponds to a switching frequency of a switching power supply that feeds DC current to the RF power supply.

3. The RF power supply of claim 1 wherein a weighting factor is used to cause the first rate to be greater than the second rate.

4. The RF power supply of claim 1 wherein an output of the RF power supply energizes a plasma load.

5. The RF power supply of claim 1 further comprising at least one of a resonant inverter, a buck-type switching regulator, a boost regulator, a DC switching power supply, and a gate drive circuit of an inverter or switching power supply.

6. The RF power supply of claim 2 wherein the input power is measured for each cycle of the switching power supply.

7. The RF power supply of claim 6 wherein the output power signal is not measured for each cycle of the switching power supply.

8. The RF power supply of claim 5 wherein said control signal is updated for each cycle of the switching power supply.

9. The RF power supply of claim 5 wherein said control signal is not updated for each cycle of the switching power supply.

10. The RF power supply of claim 2, wherein the input power measurement is determined by measuring a total charge that flows through an input terminal of the switching power supply during each cycle.

11. The RF power supply of claim 1, wherein the first rate adjusts the power control signal once per cycle, and the second rate is slower than a response time of the electrical load.

12. The RF power supply of claim 11 wherein the second rate is slower than a response time of a gas supply system that supplies the electrical load.

13. An RF power supply for providing power to a variable-impedance load, comprising:

a control circuit providing a control signal to the RF power supply to regulate a power output level from the RF power supply;

a first circuit for providing a measurement of an input power to the RF power supply that is used to adjust the control signal at a first rate to maintain substantially constant input power; and

a second circuit for measuring an output power at an output of the RF power supply that is used to compensate the power control signal to the RF power supply at a second rate, wherein the first rate is greater than the second rate.

14. The RF power supply of claim 13 wherein the input power is constant.

15. The RF power supply of claim 13 wherein a weighting factor is used to cause the first rate to be greater than the second rate.

16. The RF power supply of claim 13 wherein an output of the RF power supply energizes a plasma load.

17. The RF power supply of claim 13 further comprising a matching circuit between the RF generator and the load.

18. The RF power supply of claim 13 further comprising at least one of a resonant inverter, a buck-type switching regulator, a boost regulator, a DC switching power supply, and a gate drive circuit of an inverter or switching power supply.

19. The RF power supply of claim 13 wherein the input power is measured for each cycle of the power supply.

20. The RF power supply of claim 19 wherein the output power is not measured for each cycle of the power supply.

21. The RF power supply of claim 18 wherein the control signal is updated for each cycle of the power supply.

22. The RF power supply of claim 18 wherein the control signal is not updated for each cycle of the power supply.

23. The RF power supply of claim 13 wherein the electrical load comprises a plasma generation system.

24. The RF power supply of claim 13 wherein the control signal controls a pulse width modulation of the power supply.

25. The RF power supply of claim 24, wherein the amount of pulse width modulation is determined on a cycle by cycle basis.

26. The RF power supply of claim 13, wherein the first rate adjusts the control signal once per cycle, and the second rate is slower than a response time of the electrical load.

27. The RF power supply of claim 26 wherein the second rate is slower than a response time of a gas supply system that supplies the electrical load.

28. An RF plasma generator comprising:

an power source; and

an AC switching power supply receiving power from the source comprising;

a control circuit providing a control signal to the power supply to regulate a power output level from the power supply;

a first circuit for providing a measurement of an input power to the power supply that is used to adjust the control signal to the power supply at a first rate to maintain substantially constant input power; and

a second circuit for measuring an output power at an output of the power supply that is used to compensate the control signal to the power supply at a second rate, wherein the first rate is greater than the second rate,

wherein an ouput of the switching power supply provides power to an RF generation section.

29. The RF plasma generator of claim 28 wherein the first rate corresponds to a switching frequency of the switching power supply.

30. The RF plasma generator of claim 28 wherein a weighting factor is used to cause the first rate to be greater than the second rate.

31. The RF plasma generator of claim 28 wherein an output of the RF generation section energizes a plasma load.

32. The RF plasma generator of claim 28 further comprising a matching circuit between the RF generation section and the load.

33. The RF plasma generator of claim 28 wherein the switching power supply comprises at least one of a resonant inverter, a buck-type switching regulator, a boost regulator, a DC switching power supply, and a gate drive circuit of an inverter or switching power supply.

34. The RF plasma generator of claim 28 wherein the control signal is updated for each cycle of the switching power supply.

35. The RF plasma generator of claim 34 wherein the control signal is not updated for each cycle of the switching power supply.

36. The RF plasma generator of claim 28 wherein the input power is determined by measuring a total charge that flows through an input terminal of the switching power supply during each cycle.

37. The RF plasma generator of claim 28 wherein the electrical load comprises a plasma generation system.

38. The RF plasma generator of claim 28 wherein the control signal controls a pulse width modulation of the switching power supply.

39. The RF plasma generator of claim 38 wherein the amount of pulse width modulation is determined on a cycle by cycle basis.

40. The RF plasma generator of claim 28 wherein the first rate adjusts the control signal once per cycle, and the second rate is slower than a response time of the electrical load.

41. The RF plasma generator of claim 40 wherein the second rate is slower than a response time of a gas supply system that supplies the electrical load.

42. A method of regulating power to a variable-impedance load, comprising the steps of:

providing a control circuit that provides a control signal to an switching power supply to regulate a power output level from an RF generator;

adjusting the control signal to the switching power supply at a first rate based on a first power measured at an input side of the switching power supply;

compensating the control signal to the switching power supply at a second rate based on a second power measured at an output side of the RF generator, wherein the first rate is greater than the second rate.

43. The method of claim 42 wherein the first rate corresponds to a frequency of the switching power supply.

44. The method of claim 42 wherein a weighting factor is used to cause the first rate to be greater than the second rate.

45. The method of claim 42 wherein an output of the RF generator energizes a plasma load.

46. The method of claim 42 comprising a matching circuit between the RF generator and the load.

47. The method of claim 42 wherein the power supply comprises at least one of a resonant inverter, a buck-type switching regulator, a boost regulator, a DC switching power supply, and a gate drive.

48. The method of claim 42 wherein the input power is measured for each cycle of the switching power supply.

49. The method of claim 48 wherein the output power is not measured for each cycle of the power supply.

50. The method of claim 42 wherein the first power is determined by measuring a total charge that flows through an input terminal of the switching power supply during each cycle.

51. The method of claim 42 wherein the control signal is updated for each cycle of the switching power supply.

52. The method of claim 51 wherein the control signal is not updated for each cycle of the switching power supply.

53. The method of claim 42 wherein the electrical load comprises a plasma generation system.

54. The method of claim 42 wherein the control signal controls a pulse width modulation of the power supply.

55. The method of claim 54 wherein the amount of pulse width modulation is determined on a cycle by cycle basis.

56. The method of claim 42 wherein the first rate adjusts the control signal once per cycle, and the second rate is slower than a response time of the electrical load.

57. The method of claim 56 wherein the second rate is slower than a response time of a gas supply system that supplies the electrical load.