RF Power Amplifier Stability Network

• US 20080180179A1
• Filed: 01/25/2007
• Published: 07/31/2008
• Est. Priority Date: 01/25/2007
• Status: Active Grant

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: MKS Instruments Incorporated
• Inventors: Polizzo, Salvatore
• Granted Patent: US 7,777,567 B2
• Time in Patent Office: Days
• US Class Current: 330/304
• 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: H03F 1/301 in MOSFET amplifiers H03F1/303, H03F1/305, H03F1/308 take precedence
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/265 with field-effect transistors only
• CPC Class Codes: H05H 1/46 using applied electromagnetic fields, e.g. high frequency or microwave energy H05H1/26 takes precedence

Abstract

A radio frequency (RF) generator for applying RF power to a plasma chamber includes a DC power supply (B+). A radio frequency switch generates the RF power at a center frequency f₀. A low-pass dissipative terminated network connects between the DC power supply (B+) and the switch and includes operates at a first cutoff frequency. The switch outputs a signal to an output network which improves the fidelity of the system. The output network generates an output signal fed to a high-pass subharmonic load isolation filter that passes RF power above a predetermined frequency. A low-pass harmonic load isolation filter may be inserted between the output network and the high-pass subharmonic load isolation filter, and a high-pass terminated network may connect to the output of the output network. The high-pass terminated network dissipates RF power above a predetermined frequency. An offline short or shunt network may connect between the output of the switch and the input of the output network for shorting the output of the switch at predetermined frequencies.

Claims

1. A radio frequency generator for applying RF power to a load, comprising:

a DC power supply;

at least one switch that generates the RF power at a center frequency; and

a low-pass terminated network connected between the DC power supply and the switch and having a first cutoff frequency that is less than the center frequency, the low-pass terminated network providing offline impedance control at a frequency less than the center frequency; and

a high-pass filter interposed between an output of the switch and the load, the high-pass filter having a second cutoff frequency less than the center frequency, the high-pass filter providing inline isolation of the switch from the load at a frequencies less than the center frequency.

2. The RF generator of claim 1 wherein the low-pass terminated network and high-pass filter are adapted to enable the RF generator to operate at the center frequency or a band of frequencies below the center frequency.

3. The RF generator of claim 1 further comprising an output network arranged in series with the high-pass filter.

4. The RF generator of claim 3 wherein the output network is interposed between the switch and the high-pass filter.

5. The RF generator of claim 3 wherein the output network and high pass filter include common components.

6. The RF generator of claim 1 wherein the low-pass terminated network includes a dissipative element.

7. The RF generator of claim 1 wherein the low-pass terminated network presents an inductive load to the transistor.

8. The RF generator of claim 1 wherein the first cutoff frequency is equal to about 0.6 times the center frequency.

9. The RF generator of claim 1 wherein the second cutoff frequency is equal to about 0.6 times the center frequency.

10. The RF generator of claim 1 further comprising a high-pass terminated network connected offline from the RF power and having a third cutoff frequency that is greater than the center frequency, the high-pass terminated network providing offline impedance control for the switch at a frequency greater than the center frequency.

11. The RF generator of claim 10 wherein the high-pass terminated network includes a dissipative element.

12. The RF generator of claim 10 wherein the high-pass terminated network presents a reactance in a predetermined frequency range.

13. The RF generator of claim 10 wherein the third cutoff frequency is equal to about 1.66 times the center frequency.

14. The RF generator of claim 1 further comprising a low-pass filter interposed between the load and the switch, the low-pass filter having a fourth cutoff frequency that is greater than the center frequency, the low-pass filter providing inline isolation of the switch from the load at a frequency greater than the center frequency.

15. The RF generator of claim 14 wherein the fourth cutoff frequency is equal to about 1.66 times the center frequency.

16. The RF generator of claim 1 further comprising a shunt network offline from the RF power and including a band-pass frequency.

17. The RF generator of claim 16 wherein the band-pass frequency is 0.5 times the center frequency.

18. A radio frequency generator for applying RF power to a plasma chamber, comprising:

a DC power supply;

a radio frequency transistor that generates the RF power at a center frequency; and

a stability network including;

a low-pass terminated network connected inline with the DC power supply and the transistor, the low-pass terminated network and having a first cutoff frequency less than the center frequency; and

a high-pass filter inline with the RF power, the high-pass filter having a second cutoff frequency less than the center frequency, low-pass terminated network and high-pass filter cooperating with the low-pass terminated network to control an impedance at the transistor over a predetermined frequency of operation below the center frequency.

19. The RF generator of claim 18 wherein the second cutoff frequency is equal to about 0.6 times the center frequency.

20. The RF generator of claim 18 wherein the high-pass dissipative terminated network includes a dissipative element.

21. The RF generator of claim 18 further comprising a fidelity network including:

a high-pass terminated network connected offline from the RF power and having a third cutoff frequency that is greater than the center frequency; and

a low-pass filter inline with the RF power, the low-pass filter having a fourth cutoff frequency that is greater than the center frequency, the high-pass terminated network and low-pass filter cooperating to control an impedance at the transistor over a predetermined frequency of operation above the center frequency.

22. The RF generator of claim 21 wherein the high-pass dissipative terminated network presents a reactance in a predetermined frequency range of operation.

23. The RF generator of claim 21 wherein the third cutoff frequency is equal to about 1.66 times the center frequency.

24. The RF generator of claim 21 wherein the fourth cutoff frequency is equal to about 1.66 times the center frequency.

25. The RF generator of claim 21 further comprising a band-pass filter connected to the RF power and including a band-pass center frequency that is less than the center frequency.

26. The RF generator of claim 25 wherein the band-pass center frequency is 0.5 times the center frequency.

27. A radio frequency generator for applying RF power to a plasma chamber, comprising:

radio frequency transistors that generate RF power at a center frequency;

low-pass dissipative terminated networks connected between respective ones of the transistors and associated DC power sources; and

a combiner that generates an RF power signal based on the RF power from the radio frequency transistors, wherein the RF power signal is applied to the load; and

wherein the low-pass dissipative terminated networks have a first cutoff frequency that is less than the center frequency.

28. The RF generator of claim 27 wherein the low-pass dissipative terminated networks include a respective dissipative element.

29. The RF generator of claim 27 wherein the low-pass dissipative terminated networks present a reactance in a predetermined frequency range.

30. The RF generator of claim 27 wherein the first cutoff frequency is equal to about 0.6 times the center frequency.

31. The RF generator of claim 27 further comprising high-pass filters in series with respective RF power from the transistors and having a second cutoff frequency that is less than the center frequency.

32. The RF generator of claim 31 wherein the second cutoff frequency is equal to about 0.6 times the center frequency.

33. The RF generator of claim 27 further comprising high-pass dissipative terminated networks connected to respective RF power from the transistors and including a third cutoff frequency that is greater than the center frequency.

34. The RF generator of claim 33 wherein the high-pass dissipative terminated networks include respective dissipative elements.

35. The RF generator of claim 33 wherein the high-pass dissipative terminated networks present a reactance at a predetermined frequency range.

36. The RF generator of claim 33 wherein the third cutoff frequency is equal to about 1.66 times the center frequency.

37. The RF generator of claim 27 further comprising a low-pass filter in series with respective RF power from the transistors and including a fourth cutoff frequency that is greater than the center frequency.

38. The RF generator of claim 37 wherein the fourth cutoff frequency is equal to about 1.66 times the center frequency.

39. The RF generator of claim 27 further comprising band-pass filters connected to respective RF power from the transistors and including a band-pass center frequency that is less than the center frequency.

40. The RF generator of claim 39 wherein the band-pass center frequency is 0.5 times the center frequency.

41. The RF generator of claim 27 further comprising a high-pass filter in series with the RF power signal and including a second cutoff frequency that is less than the center frequency.

42. The RF generator of claim 41 wherein the second cutoff frequency is equal to about 0.6 times the center frequency.

43. The RF generator of claim 27 further comprising a high-pass dissipative terminated network connected to the RF power signal and including a third cutoff frequency that is greater than the center frequency.

44. The RF generator of claim 43 wherein the high-pass dissipative terminated network includes a dissipative element.

45. The RF generator of claim 43 wherein the high-pass dissipative terminated network presents a reactance in a predetermined frequency range.

46. The RF generator of claim 43 wherein the third cutoff frequency is equal to about 1.66 times the center frequency.

47. The RF generator of claim 27 further comprising a low-pass filter in series with the RF power signal and including a fourth cutoff frequency that is greater than the center frequency.

48. The RF generator of claim 47 wherein the fourth cutoff frequency is equal to about 1.66 times the center frequency.

49. The RF generator of claim 27 further comprising a band-pass filter connected to the RF power signal and including a band-pass center frequency that is less than the center frequency.

50. The RF generator of claim 49 wherein the band-pass center frequency is 0.5 times the center frequency.

51. A radio frequency generator for applying RF power to a plasma chamber, comprising:

radio frequency transistors that generate RF power at a center frequency;

high-pass filters in series with respective RF power from the transistors and including a first cutoff frequency that is less than the center frequency; and

a combiner that generates an RF power signal based on the RF power from the radio frequency transistors, wherein the RF power signal is applied to the plasma generator.

52. The RF generator of claim 51 wherein the first cutoff frequency is equal to about 0.6 times the center frequency.

53. The RF generator of claim 51 further comprising high-pass dissipative terminated networks connected to the RF power from respective transistors and including a second cutoff frequency that is greater than the center frequency.

54. The RF generator of claim 53 wherein the high-pass dissipative terminated networks include a respective dissipative element.

55. The RF generator of claim 53 wherein the high-pass dissipative terminated networks present a reactance in a predetermined frequency range.

56. The RF generator of claim 53 wherein the second cutoff frequency is equal to about 1.66 times the center frequency.

57. The RF generator of claim 51 further comprising low-pass filters in series with the RF power from respective transistors and including a third cutoff frequency that is greater than the center frequency.

58. The RF generator of claim 57 wherein the third cutoff frequency is equal to about 1.66 times the center frequency.

59. The RF generator of claim 51 further comprising band-pass filters connected to the RF power from respective transistors and including a band-pass center frequency that is less than the center frequency.

60. The RF generator of claim 59 wherein the band-pass center frequency is 0.5 times the center frequency.

61. A radio frequency generator for applying RF power to a plasma chamber, comprising:

radio frequency transistors that generate RF power at a center frequency;

a combiner that generates an RF power signal based on the RF power from the radio frequency transistors; and

a stability network including a high-pass filter inline with the RF power and located in close proximity to an output of the radio frequency transistor, the high-pass filter having a first cutoff frequency less than the center frequency.

62. The radio frequency generator of claim 61 further comprising a low-pass terminated network connected inline with the DC power supply and the transistors, the low-pass terminated network having a second cutoff frequency less than the center frequency, the low-pass terminated network and high-pass filter cooperating with the low-pass terminated network to control an impedance at the transistor over a predetermined frequency of operation below the center frequency.

63. The RF generator of claim 61 wherein the first cutoff frequency is equal to about 0.6 times the center frequency.

64. The RF generator of claim 61 further comprising a high-pass dissipative terminated network connected offline from the RF power signal and including a third cutoff frequency that is greater than the center frequency.

65. The RF generator of claim 64 wherein the high-pass dissipative terminated network includes a dissipative element.

66. The RF generator of claim 64 wherein the high-pass dissipative terminated network presents a reactance in a predetermined frequency range.

67. The RF generator of claim 64 wherein the third cutoff frequency is equal to about 1.66 times the center frequency.

68. The RF generator of claim 62 further comprising a low-pass filter inline with the RF power signal and including a fourth cutoff frequency that is greater than the center frequency.

69. The RF generator of claim 68 wherein the fourth cutoff frequency is equal to about 1.66 times the center frequency.

70. The RF generator of claim 62 further comprising a band-pass filter connected to the RF power signal and including a band-pass center frequency that is less than the center frequency.

71. The RF generator of claim 70 wherein the band-pass center frequency is 0.5 times the center frequency.