RF tuning method for an RF plasma reactor using frequency servoing and power, voltage, current or DI/DT control

• US 6,252,354 B1
• Filed: 11/04/1996
• Issued: 06/26/2001
• Est. Priority Date: 11/04/1996
• Status: Expired due to Fees

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Shel, Viktor, Collins, Kenneth, Buchberger, Douglas, Trow, John, Roderick, Craig
• Primary Examiner(s): Bettendorf, Justin P.
• Application Number:
  US08/743,059
• Time in Patent Office: 1,695 Days
• Field of Search: 333/17.3, 315/111.21, 315/111.51, 118/723.I, 118/723.IR, 156/345, 156/345.C
• 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 37/3299 Feedback systems
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance

Abstract

In an RF plasma reactor including a reactor chamber with a process gas inlet, a workpiece support, an RF signal applicator facing a portion of the interior of the chamber and an RF signal generator having a controllable RF frequency and an RF signal output coupled to an input of the RF signal applicator, the invention tunes the RF signal generator to the plasma-loaded RF signal applicator by sensing an RF parameter at the RF signal generator or at the RF signal applicator and then adjusting the frequency of the RF signal generator so as to optimize the parameter. The invention further controls the RF signal generator output magnitude (power, current or voltage) by optimizing the value of the same RF parameter or another RF parameter. The reactor preferably includes a fixed tuning circuit between the RF signal generator and the RF signal applicator.

Claims

1. In an RF plasma reactor comprising a reactor chamber with a process gas inlet, a workpiece support, an RF signal applicator facing a portion of the interior of said chamber, an RF signal generator having a controllable RF frequency and a controllable output power, and an RF signal output coupled to an input of said RF signal applicator, a tuning method comprising:

selecting a desired plasma ion density value;

measuring, near one of or between (a) the output of said generator and (b) at said signal applicator, a parameter governing a plasma ion density in said reactor, wherein said parameter consists of one of;

(a) a Fourier component of the magnitude of the RF current flow to said RF signal applicator

(b) the magnitude of the time rate of change in RF current flow in said RF signal applicator;

adjusting said frequency of said RF signal generator so as to at least nearly optimize said parameter near an optimum value corresponding to said desired plasma ion density value; and

adjusting said output power of said RF signal generator so as to maintain said parameter near said optimum value.

2. The method of claim 1 further comprising providing a tuning circuit between said RF signal generator and said RF signal applicator.

3. The method of claim 1 wherein said RF signal applicator comprises a capacitive electrode adjacent said reactor chamber and said RF signal generator furnishes RF plasma source signal.

4. The method of claim 1 wherein said reactor further comprises a bias RF signal generator having a controllable RF bias frequency and a bias signal output coupled to said workpiece support, said method further comprising:

measuring near said workpiece support a bias signal parameter related to a voltage of said workpiece;

adjusting said frequency of said bias RF signal generator within a second frequency range so as to at least nearly optimize said bias signal parameter to one of a maximum or minimum value.

5. The method of claim 4 further comprising providing a fixed tuning circuit between said bias RF signal generator and said wafer support.

6. The method of claim 4 wherein said bias signal parameter comprises a Fourier component of the voltage of said workpiece.

7. The method of claim 4 wherein said bias RF signal generator has a bias RF signal output level which is adjustable, said method further comprising:

varying said bias RF signal output level so as to set and maintain said bias signal parameter at least nearly at a desired set point.

8. The method of claim 4 further comprising providing a bias transformer between said bias RF signal generator and said wafer support.

9. The method of claim 8 wherein said bias transformer has a bias transformer ratio corresponding to an anticipated ratio between magnitudes of said bias load impedance at said wafer support and said output impedance of said bias RF signal generator.

10. The method of claim 4 further comprising:

providing bias transformer apparatus having plural selectable bias transformer ratios between said bias RF signal generator and said wafer support; and

selecting one of said bias ratios best corresponding to an anticipated ratio between magnitudes of said bias load impedance at said wafer support and said output impedance of said bias RF signal generator.

11. The method of claim 1 further comprising:

providing transformer apparatus having plural selectable transformer ratios between said RF signal generator and said RF signal applicator; and

selecting one of said ratios best corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

12. The method of claim 1 further comprising providing a transformer between said RF signal generator and said RF signal applicator.

13. The method of claim 12 wherein said transformer has a transformer ratio corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

14. The method of claim 1 wherein said RF signal applicator comprises an inductive coil antenna adjacent said reactor chamber and said RF signal generator furnishes RF plasma source signal.

15. An RF plasma reactor comprising:

a reactor chamber with a process gas inlet, said reactor chamber for containing a workpiece to be processed;

an RF signal applicator facing a portion of the interior of said chamber;

an RF signal generator having an RF frequency control input and an RF signal output at which an RF signal is produced;

a fixed tuning circuit connected between said RF signal output and said RF signal applicator;

a sensor coupled to at least one of or between (a) said RF signal applicator and (b) said RF signal output, and responsive to an RF parameter affecting plasma ion density measurable near one of or between (a) said RF signal applicator and (b) said RF signal output, wherein said parameter consists of one of;

(a) a Fourier component of the magnitude of the RF current flow to said RF signal applicator,

(b) the magnitude of the time rate of change in RF current flow to said RF signal anplicator;

an RF signal magnitude servo responsive to said sensor and programmed to adjust a magnitude of said RF signal produced at said RF signal output of said RF signal generator so as to set said parameter at least near to a value corresponding to a desired plasma ion density value.

16. The reactor of claim 15 wherein said desired value of said parameter is one of a maximum or a minimum value.

17. The reactor of claim 15 wherein said RF signal magnitude servo adjusts the magnitude of one of the following generator parameters:

delivered voltage, delivered current, delivered power, reflected power, time rate of change of current, product of current and voltage, a Fourier component of the voltage, a phase angle between the voltage and current, a phase angle between any two RF generator parameters.

18. In an RF plasma reactor comprising a reactor chamber with a process gas inlets said reactor chamber for containing a workpiece to be processed, an RF signal applicator facing a portion of the interior of said chamber;

an RF signal generator having an RF frequency control input and an RF signal output at which an RF signal is produced, a method of tuning said RF signal output to said RF signal applicator, comprising;

selecting a desired plasma ion density value;

providing a fixed tuning circuit connected between said RF signal output and said RF signal applicator;

sensing an RF parameter affecting plasma ion density measurable near one of or between (a) said RF signal applicator and (b) said RF signal output, wherein said parameter consists of one of;

(a) a Fourier component of the magnitude of the RF current flow to said RF signal applicator,

(b) the magnitude of the time rate of chance in RF current flow to said RF signal applicator; and

in response to said sensor, adjusting a magnitude of said RF signal produced at said RF signal output of said RF signal generator so as to optimize said parameter to a value corresponding to said desired plasma ion density value.

19. The method of claim 18 wherein said desired value of said parameter is one of a maximum or a minimum value.

20. The method of claim 18 wherein said adjusting adjusts the magnitude of one of the following generator parameters:

delivered voltage, delivered current, delivered power, reflected power, time rate of change of current, product of current and voltage, a Fourier component of the voltage, a phase angle between the voltage and current, a phase angle between any two RF generator parameters.

21. In an RF plasma reactor comprising a reactor chamber with a process gas inlet, said reactor chamber for containing a workpiece to be processed, an RF signal applicator facing a portion of the interior of said chamber, and an RF signal generator having a controllable RF frequency and an RF signal output coupled to an input of said RF signal applicator, a tuning method comprising:

sensing a parameter related to an RF voltage of said workpiece;

adjusting said frequency of said RF signal generator within a frequency range so as to optimize said parameter to one of a maximum or minimum value within said frequency range.

22. The method of claim 21 wherein said RF signal applicator is a capacitive electrode.

23. The method of claim 21 wherein said reactor further comprises a workpiece support inside said chamber and said RF signal generator is coupled to said workpiece support, whereby said RF signal applicator comprises said workpiece support.

24. The method of claim 21 further comprising providing a fixed tuning circuit between said RF signal generator and said RF signal applicator.

25. The method of claim 21 wherein said parameter comprises a Fourier component of the RF voltage of said RF signal applicator.

26. The method of claim 25 wherein said Fourier component comprises one of:

(a) a first harmonic, (b) a second harmonic, (c) a D.C. component.

27. The method of claim 21 wherein said bias RF signal generator has a bias RF signal output level which is adjustable, said method further comprising:

varying said RF signal output level so as to at least nearly set and maintain the magnitude of said parameter at a desired set point.

28. The method of claim 21 further comprising providing a transformer between said RF signal generator and said RF signal applicator.

29. The method of claim 28 wherein said transformer has a transformer ratio corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

30. The method of claim 21 further comprising:

providing transformer apparatus having plural selectable transformer ratios between said RF signal generator and said RF signal applicator; and

selecting one of said ratios best corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

31. An RF plasma reactor comprising:

a reactor chamber with a process gas inlet;

a workpiece support inside said chamber;

an RF signal applicator facing a portion of the interior of said chamber overlying said support;

an RF signal generator having a frequency control input, a controllable output power and an RF signal output coupled to an input of said RF signal applicator;

a sensor coupled to a current path to said RF signal applicator, said sensor being responsive to a parameter affecting plasma ion density related to RF current flow in said RF signal applicator, wherein said parameter consists of one of;

(a) a Fourier component of the magnitude of the RF current flow to said RF signal applicator,

(b) the magnitude of the time rate of chancre in RF current flow to said RF signal applicator;

a frequency servo connected to said frequency control input, said frequency servo being programmed to adjust said frequency of said RF signal generator within a frequency range so as to at least nearly optimize said parameter to a value corresponding to a desired plasma ion density value; and

a power servo connected to said RF signal generator capable of changing said output power.

32. The reactor of claim 31 further comprising a fixed tuning circuit between said RF signal generator and said RF signal applicator.

33. The reactor of claim 31 further comprising:

transformer apparatus having plural selectable transformer ratios between said RF signal generator and said RF signal applicator; and

at least one of said ratios best corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

34. The reactor of claim 33 wherein said transformer apparatus comprises:

plural transformer windings corresponding to respective ones of said plural transformer ratios;

plural RF switches connecting respective ones of said transformer windings to said RF signal applicator.

35. The reactor of claim 34 wherein said plural transformer windings are secondary windings, said transformer apparatus further comprising a primary winding coupled to said RF signal generator.

36. The reactor of claim 31 further comprising a transformer between said RF signal generator and said RF signal applicator.

37. The reactor of claim 36 wherein said transformer has a transformer ratio corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

38. The reactor of claim 31 wherein said RF signal applicator comprises a capacitive electrode adjacent said reactor chamber and said RF signal generator furnishes RF plasma source signal.

39. The reactor of claim 31 wherein said RF signal applicator comprises an inductive coil antenna adjacent said reactor chamber and said RF signal generator furnishes RF plasma source signal.

40. The reactor of claim 31 further comprising:

a bias RF signal generator having an RF bias frequency control input and a bias signal output coupled to said workpiece support;

a sensor responsive to a bias signal parameter related to a voltage of said workpiece relative to RF ground;

a bias frequency servo programmed to adjust said frequency within a bias frequency range of said bias RF signal generator so as to optimize said bias signal parameter to one of a maximum or minimum within said bias frequency range.

41. The reactor of claim 40 further comprising a fixed tuning circuit between said bias RF signal generator and said wafer support.

42. The reactor of claim 40 wherein said bias signal parameter comprises a Fourier component of the voltage of said workpiece.

43. The reactor of claim 40 further comprising:

bias transformer apparatus having plural selectable bias transformer ratios between said bias RF signal generator and said wafer support; and

at least one of said bias ratios best corresponding to an anticipated ratio between magnitudes of said bias load impedance at said wafer support and said output impedance of said bias RF signal generator.

44. The reactor of claim 40 wherein said bias RF signal generator comprises bias RF signal level control input, said reactor further comprising:

a bias signal servo connected to said sensor and programmed to vary said bias RF signal output level so as to set said bias parameter to at least near a desired set point.

45. The reactor of claim 40 further comprising a bias transformer between said bias RF signal generator and said wafer support.

46. The reactor of claim 45 wherein said bias transformer has a bias transformer ratio corresponding to an anticipated ratio between magnitudes of said bias load impedance at said wafer support and said output impedance of said bias RF signal generator.

47. In an RF plasma reactor comprising a reactor chamber with a process gas inlet, a workpiece support, an RF signal applicator facing a portion of the interior of said chamber, an RF signal generator having a controllable RF frequency and a controllable output power, and an RF signal output coupled to an input of said RF signal applicator, a method for tuning said RF signal generator to said RF signal applicator, comprising:

selecting a desired plasma ion density value;

measuring, near one of or between (a) the output of said signal generator and (b) at said signal applicator, a first RF generator parameter affecting plasma ion density, wherein said parameter consists of one of;

(a) a Fourier component of the magnitude of the RF current flow to said RF signal applicator,

(b) the magnitude of the time rate of change in RF current flow to said RF signal applicator;

adjusting said frequency of said RF signal generator so as to at least nearly optimize said RF generator parameter near an optimum value corresponding to said desired plasma ion density value; and

adjusting said output power so as to maintain said RP generator parameter near said optimum value.

48. The method of claim 47 further comprising:

measuring, near one of or between (a) the output of said signal generator and (b) at said signal applicator, second and third RF generator parameters affecting plasma ion density;

adjusting said second RF generator parameter so as to at least nearly optimize said third RF generator parameter to a value corresponding to said desired plasma ion density value.

49. The method of claim 48 wherein at least one of said first, second and third RF generator parameters is different from the other two.

50. The method of claim 48 wherein each of said first, second and third RF generator parameters is different from each of the others.

51. The method of claim 48 wherein said first, second and third RF generator parameters are the same RF generator parameter.

52. The method of claim 47 wherein said signal applicator comprises an RF source signal applicator.

53. The method of claim 52 wherein said reactor further comprises a bias signal applicator and a bias RF signal generator coupled to said bias signal applicator, said method further comprising:

measuring, near one of or between (a) the output of said bias signal generator and (b) at said bias signal applicator, a fourth RF generator parameter;

adjusting said frequency of said bias signal generator within a certain frequency range so as to at least nearly optimize said fourth RF generator parameter to one of a maximum or minimum value within said frequency range.

54. The method of claim 53 further comprising:

measuring, near one of or between (a) the output of said bias signal generator and (b) at said bias signal applicator, fifth and sixth RF generator parameters;

adjusting said fifth RF generator parameter of said bias signal generator so at to at least nearly optimize said sixth RF generator parameter with respect to a desired value thereof.

55. The method of claim 54 wherein said fourth, fifth and sixth RF generator parameters are the same RF generator parameter.

56. The method of claim 54 wherein at least one of said fourth, fifth and sixth RF generator parameters is different from the other two.

57. The method of claim 54 wherein said fourth, fifth and sixth RF generator parameters are each selected from among the following RF generator parameters:

delivered voltage, delivered current, delivered power, reflected power, time rate of change of current, a Fourier component of the voltage, a phase angle between the voltage and current, a phase angle between any two RF generator parameters.

58. The method of claim 47 wherein said signal applicator comprises an RF bias signal applicator.

59. An RF plasma reactor comprising:

a reactor chamber with a process gas inlet, said reactor chamber for containing a workpiece to be processed;

an RF signal applicator facing a portion of the interior of said chamber;

an RF signal generator having an RF frequency control input, a controllable output power and an RF signal output coupled to an input of said RF signal applicator;

a sensor coupled to said RF signal applicator and responsive to a parameter affecting plasma ion density related to an RF voltage of said RF signal applicator;

a frequency servo responsive to said sensor and programmed to adjust said frequency of said RF signal generator within a frequency range so as to optimize said parameter to a value corresponding to a desired plasma ion density value;

a power servo connected to said RF signal generator that can adjust said output power; and

a workpiece support inside said chamber wherein said RF signal generator is coupled to said workpiece support, whereby said RF signal applicator comprises said workpiece support.

60. The reactor of claim 59 further comprising a fixed tuning circuit between said RF signal generator and said RF signal applicator.

61. The reactor of claim 59 wherein said parameter comprises a Fourier component of the RF voltage of said RF signal applicator.

62. The reactor of claim 61 wherein said Fourier component comprises one of:

(a) a first harmonic, (b) a second harmonic, (c) a D.C. component.

63. The reactor of claim 59 wherein said RF signal generator has an RF signal level control input, said reactor further comprising:

a signal servo connected to said signal control input and programmed to vary said RF signal output level so as to set and maintain said parameter at least near a desired set point.

64. The reactor of claim 59 further comprising a transformer between said RF signal generator and said RF signal applicator.

65. The reactor of claim 64 wherein said transformer has a transformer ratio corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

66. The reactor of claim 59 further comprising:

a transformer apparatus having plural selectable transformer ratios between said RF signal generator and said RF signal applicator; and

at least one of said ratios best corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

67. The reactor of claim 59 wherein said RF signal applicator is a capacitive electrode.

68. An RF plasma reactor comprising:

a reactor chamber with a process gas inlet;

a workpiece support inside said chamber;

an RF signal applicator facing a portion of the interior of said chamber overlying said support;

an RF signal generator having a frequency control input and an RF signal output coupled to an input of said RF signal applicator;

a sensor coupled to a current path to said RF signal applicator, said sensor being responsive to a parameter related to RF current flow in said RF signal applicator;

a frequency servo connected to said frequency control input, said frequency servo being programmed to adjust said frequency of said RF signal generator within a frequency range so as to at least nearly optimize said parameter to one of a maximum or minimum value within said frequency range

transformer apparatus having plural selectable transformer ratios between said RF signal generator and said RF signal applicator, said transformer apparatus comprising;

plural transformer windings corresponding to respective ones of said plural transformer ratios said plural transformer windings comprising a multi-filar transmission line transformer

plural RF switches connecting respective ones of said transformer windings to said RF signal applicator;

at least one of said ratios best corresponding to an anticipated ratio between magnitudes of said load impedance at said input of said RF signal applicator and said output impedance of said RF signal generator.

69. An RF plasma reactor comprising:

a reactor chamber with a process gas inlet;

a workpiece support inside said chamber;

an RF signal applicator facing a portion of the interior of said chamber overlying said support;

an RF signal generator having a frequency control input and an RF signal output coupled to an input of said RF signal applicator;

a sensor coupled to a current path to said RF signal applicator, said sensor being responsive to a parameter related to RF current flow in said RF signal applicator;

a frequency servo connected to said frequency control input, said frequency servo being programmed to adjust said frequency of said RF signal generator within a frequency range so as to at least nearly optimize said parameter to one of a maximum or minimum value within said frequency range

a bias RF signal generator having an RF bias frequency control input and a bias signal output coupled to said workpiece support;

a sensor responsive to a bias signal parameter related to a voltage of said workpiece relative to RF ground;

a bias frequency servo programmed to adjust said frequency within a bias frequency range of said bias RF signal generator so as to optimize said bias signal parameter to one of a maximum or minimum within said bias frequency range; and

a bias transformer apparatus comprising;

plural bias transformer windings corresponding to respective ones of said plural bias transformer ratios;

plural bias RF switches connecting respective ones of said transformer windings to said workpiece support.

70. The reactor of claim 69 wherein said plural bias transformer windings are secondary bias windings, said bias transformer apparatus further comprising a primary bias winding coupled to said bias RF signal generator.

71. The reactor of claim 69 wherein said plural bias transformer windings comprise a multi-filar transmission line bias transformer.

72. In an RF plasma reactor comprising a reactor chamber with a process gas inlet, a workpiece support, an RF signal applicator facing a portion of the interior of said chamber, said signal applicator comprising an RF source signal applicator, an RF signal generator having a controllable RF frequency, an RF signal output coupled to an input of said RF signal applicator, a bias signal applicator and a bias RF signal generator coupled to said bias signal applicator, a method for tuning said RF signal generator to said RF signal applicator, comprising:

measuring, near one of or between (a) the output of said signal generator and (b) at said signal applicator, a first RF generator parameter;

adjusting said frequency of said RF signal generator within a certain frequency range so as to at least nearly optimize said RF generator parameter to one of a maximum or minimum value within said frequency range;

measuring, near one of or between (a) the output of said bias signal generator and (b) at said bias signal applicator, a fourth RF generator parameter;

adjusting said frequency of said bias signal generator within a certain frequency range so as to at least nearly optimize said fourth RF generator parameter to one of a maximum or minimum value within said frequency range;

measuring, near one of or between (a) the output of said bias signal generator and (b) at said bias signal applicator, fifth and sixth RF generator parameters;

adjusting said fifth RF generator parameter of said bias signal generator so at to at least nearly optimize said sixth RF generator parameter with respect to a desired value thereof;

wherein each of said fourth, fifth and sixth RF generator parameters is different from each of the others.