Automatic impedance matching apparatus and method

• US 5,195,045 A
• Filed: 02/27/1991
• Issued: 03/16/1993
• Est. Priority Date: 02/27/1991
• Status: Expired due to Term

• Current Assignee: MKS Instruments Incorporated
• Original Assignee: Astec America Incorporated (Emerson Electric Company)
• Inventors: Hauer, Steven E., Keane, Anthony R. A.
• Primary Examiner(s): Trans, Vincent N.
• Application Number:
  US07/661,813
• Time in Patent Office: 748 Days
• Field of Search: 364/482, 364/483, 364/484, 333/17.3, 333/17.1, 333/17.2, 333/32, 315/111.51, 331/1 R, 331/36 R, 331/36 C, 331/36 L
• US Class Current: 702/107
• 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 37/32183 Matching circuits
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01J 37/32963 End-point detection
• CPC Class Codes: H03H 7/40 Automatic matching of load impedance to source impedance

Abstract

An automatic impedance matching apparatus for matching an RF-signal generator to a load, such as a plasma etching chamber, is disclosed. The matching apparatus comprises a matching network having two variable impedance devices, a tune detector for detecting the condition of the impedance match between the RF-signal and the load, and a controller for modifying the values of the variable impedance components in response to the measured tune condition. The present invention disclosed improve reset and convergence unit and eliminates the need for the "dead-band" provided around the matching point found in prior art impedance matching controllers. Also disclosed is an improved adjustment unit for adjusting the variable impedance components which is faster and more stable than found in prior art controllers. Also disclosed is a normalization unit for normalizing the input detection siganls such that variations in turning performance due to variations in input power level from the source are substantially reduced.

Claims

1. An automatic impedance matching apparatus having an input port coupled to a signal generator and an output port coupled to a load, said input and output ports each having a signal line and a ground line, said signal generator having a predetermined characteristic impedance, said apparatus comprising:

matching means coupled between said input port and output port for matching the impedance of said load to the impedance of said signal generator, said matching means including a first variable reactive component and a second variable reactive component;

a detection means for generating an amplitude tune signal related to the difference of the voltage waveform amplitude at said input port and the product of said predetermined characteristic impedance and the current waveform amplitude at said input port and for generating a phase tune signal related to the phase difference between the voltage and current waveforms at said input port, said amplitude tune signal increasing as said voltage amplitude increases and decreasing as said current amplitude increases, said phase tune signal being substantially equal to zero when said input voltage and input current waveforms are in phase, said phase tune signal increasing as said input voltage waveform leads said input current waveform and decreasing as said input voltage waveform lags said input current waveform; and

control means responsive to said amplitude and phase tune signals for adjusting the values of said first and second variable reactive components to provide a tuned condition at said input port, said control means including a first adjustment for modifying the value of said first variable reactive component as a function of said amplitude tune signal, a second adjustment means for modifying the value of said second variable reactive component as a function of said phase tune signal, reset means for setting the value of said first variable reactive component to a first predetermined reset value and for setting the value of said second variable reactive component to a second predetermined reset value when either said first variable reactive component reaches a first predetermined end value or said second variable reactive component reaches a second predetermined end value, and convergence means for directing the adjustments of said first and second variable components, said convergence means comprising means for generating a first tolerance standard signal when the magnitude of said amplitude tune signal is less than a predetermined first amplitude tolerance value and the magnitude of said phase tune signal is less than a predetermined first phase tolerance value and means responsive to said first tolerance standard signal for disabling said first and second adjustment means.

2. The automatic impedance matching apparatus of claim 1 wherein said first variable reactive component comprises a first variable capacitor coupled between said signal and ground lines of said input port, said second variable reactive component comprises a second variable capacitor coupled between said signal and ground lines of said output port, and wherein said matching means further comprises an inductor coupled between said input port signal line and said output port signal line.

3. The automatic impedance matching apparatus of claim 2 wherein said first adjustment means increases the capacitance of said first variable capacitance when said amplitude tune signal is greater than zero and decreases the capacitance of said first variable capacitor when said amplitude tune signal is less than zero and within said second adjustment means increases the capacitance of said second variable capacitance when said phase tune signal is greater than zero and decreases the capacitance of said second variable capacitor when said phase tune signal is less than zero.

4. The automatic impedance matching apparatus of claim 1 wherein said first variable reactive component comprises a variable capacitor coupled between said signal and ground lines of said input port and wherein said second variable reactive component comprises a variable inductor coupled between said input port signal line and said output port signal line.

5. The automatic impedance matching apparatus of claim 4 wherein said first adjustment means increases the capacitance of said variable capacitor when said amplitude tune signal is greater than zero and decreases the capacitance of said variable capacitor when said amplitude tune signal is less than zero and wherein said second adjustment means increases the inductance of said variable inductor when said phase tune signal is greater than zero and decreases the inductance of said variable inductor when said phase tune signal is less than zero.

6. The automatic impedance matching apparatus of claim 1 wherein said matching means further comprises an intermediate node and an inductor coupled between said input port signal line and said intermediate node, wherein said first variable reactive component comprises a first variable capacitor coupled between said signal and ground lines of said input port, and wherein said second variable reactive component comprises a second variable capacitor coupled between said intermediate node and said signal line of said output port.

7. The automatic impedance matching apparatus of claim 6 wherein said first adjustment means increases the capacitance of said first variable capacitance when said amplitude tune signal is greater than zero and decreases the capacitance of said first variable capacitor when said amplitude tune signal is less than zero and wherein said second adjustment means increases the capacitance of said second variable capacitance when said phase tune signal is greater than zero and decreases the capacitance of said second variable capacitor when said phase tune signal is less than zero.

8. The automatic matching apparatus of claim 1 wherein said first end value is less than said first reset value and said second end value is less than said second reset value.

9. The automatic matching apparatus of claim 8 wherein said first reset value is substantially equal to the maximum component value of said first variable component and said second reset value is substantially equal to the maximum component value of said second variable component.

10. The automatic matching apparatus of claim 8 wherein said first end value is substantially equal to the minimum component value of said first variable component and said second end value is substantially equal to the minimum component value of said second variable component.

11. The automatic matching apparatus of claim 1 wherein said matching network comprises indication means for generating a first position signal related to the component value of said first variable component and a second position signal related to the component value of said second variable component and wherein said reset means comprises means for receiving said first and second position signals.

12. The Automatic matching apparatus of claim 1 wherein said first adjustment means further comprises a step-width control means for adjusting said first variable component in variable increments, said step width control means comprising:

slope means for generating an amplitude slope signal related to the derivative of said amplitude tune signal with respect to the component value of said first variable component; and

first stepping means for adjusting the component value of said first variable component in increments equal in magnitude to a first predetermined step width when said amplitude slope signal is greater than zero and for adjusting the component value of said first variable component in increments equal in magnitude to a second predetermined step width when said amplitude slope signal is less than zero, said second step width being smaller than said first step width.

13. The automatic matching apparatus of claim 12 wherein said step-width control means further comprises:

a second stepping means for adjusting the component value of said first variable component in increments equal in magnitude to a third predetermined step width when said amplitude slope signal is less than zero and the magnitude of said amplitude tune signal is greater than a predetermined amplitude window level, said third step width being larger than said second step width and smaller than said first step width.

14. The Automatic matching apparatus of claim 1 wherein said second adjustment means further comprises a step-width control means for adjusting said second variable component in variable increments, said step width control means comprising:

slope means for generating a phase slope signal related to the derivative of said phase tune signal with respect to the component value of said second variable component; and

first stepping means for adjusting the component value of said second variable components in increments equal in magnitude to a first predetermined step width when said phase slope signal is greater than zero and for adjusting said second variable component in increments equal in magnitude to a second predetermined step width when said phase slope signal is less than zero.

15. The automatic matching apparatus of claim 14 wherein said step-width control means further comprises:

a second stepping means for adjusting the component value of said second variable component in increments equal in magnitude to a predetermined third step width when said phase slope signal is less than zero and the magnitude of said phase tune signal is greater than a predetermine phase window level, said third step width being larger than said second step width and smaller than said first step width.

16. The automatic matching apparatus of claim 1 wherein said detection means comprises means for generating a normalizing signal as a function of a selected one of said voltage waveform amplitude at said input port and said current waveform amplitude at said input port, and wherein said control means comprises amplitude normalization means for normalizing said amplitude tune signal with respect to said normalizing signal.

17. The automatic matching apparatus of claim 16 wherein said control means further comprises phase normalization means for normalizing said phase tune signal with respect to said normalizing signal.

18. The automatic matching apparatus of claim 1 wherein said first adjustment means adjusts the component value of said first variable component at a slower rate than said second adjustment means adjusts the component value of said second variable component.

19. The automatic matching apparatus of claim 1 wherein said first variable component comprises a mechanical adjustment shaft, wherein said first adjustment means comprises a first servomotor for adjusting said first variable component, said first servomotor having a mechanical shaft coupled to said mechanical adjustment shaft of said first variable component, wherein said second variable component comprises a mechanical adjustment shaft, and wherein said second adjustment means comprises a second servomotor for adjusting said second variable component, said second servomotor having a mechanical shaft coupled to said mechanical adjustment shaft of said second variable component.

20. An automatic impedance matching apparatus having an output port coupled to a load, said input and output ports each having a signal line and a ground line, said signal generator having a predetermined characteristic impedance, said apparatus comprising:

matching means coupled between said input port and output port for matching the impedance of said load to the impedance of said signal generator, said matching means including a first variable reactive component and a second variable reactive component;

a detection means for generating an amplitude tune signal related to the difference of the voltage waveform amplitude at said input port and the product of said predetermined characteristic impedance and the current waveform amplitude at said input port and for generating a phase tune signal related to the phase difference between the voltage and current waveforms at said input port, said amplitude tune signal increasing as said voltage amplitude increases and decreasing as said current amplitude increases, said phase tune signal being substantially equal to zero when said input voltage and input current waveforms are in phase, said phase tune signal increasing as said input voltage waveform leads said input current waveform and decreasing as said input voltage waveform lags said input current waveform; and

control means responsive to said amplitude and phase tune signals for adjusting the values of said first and second variable reactive components to provide a tuned condition at said input port, said control means including a first adjustment means for modifying the value of said first variable reactive component as a function of said amplitude tune signal, a second adjustment means for modifying the value of said second variable reactive component as a function of said phase tune signal, said control means further comprising a convergence means for directing the adjustments of said first and second variable components, said convergence means comprising;

means for generating a coarse tolerance standard signal when the magnitude of said amplitude tune signal is less than a predetermined first amplitude tolerance value and the magnitude of said phase tune signal is less than a predetermined first phase tolerance value;

means for generating a fine tolerance standard signal when the magnitude of said amplitude tune signal is less than a predetermined second amplitude tolerance value and the magnitude of said phase tune signal is less than a predetermined second phase tolerance value, said second amplitude tolerance value being less than said first amplitude tolerance value and said second phase tolerance value being less than said first phase tolerance value;

means for initially placing said convergence means in a tuning state and for initially enabling said first and second adjustment means;

means responsive to said fine tolerance standard signal for causing said convergence means to enter a hysteresis state when said convergence means is in said tuning state, said first and second adjustment means being disabled in said hysteresis state; and

means for placing said convergence means in said tuning state and for enabling said first and second adjustment means when said convergence means is in said hysteresis state and said coarse tolerance standard signal is not being generated.

21. The automatic matching apparatus of claim 20 wherein said tuning state comprises a track state and a tune state, said convergence means being in said track state when said coarse tolerance standard signal is being generated and said fine tolerance standard is not being generated, said convergence means being is said tune state when said fine tolerance standard signal is being generated.

22. The automatic matching apparatus of claim 20 wherein said first adjustment means further comprises a step-width control means for adjusting said first variable component in variable increments, said step width control means comprising:

slope means for generating an amplitude slope signal related to the derivative of said amplitude tune signal with respect to the component value of said first variable component; and

first stepping means for adjusting the component value of said first variable component in increments equal in magnitude to a first predetermined step width when said amplitude slope signal is greater than zero and for adjusting the component value of said first variable component in increments equal in magnitude to a second predetermined step width when said amplitude slope signal is less than zero, said second step width, being smaller than said first step width.

23. The automatic matching apparatus of claim 22 wherein said step-width control means further comprises:

a second stepping means for adjusting the component value of said first variable component in increments equal in magnitude to a third predetermined step width when said amplitude slope signal is less than zero and the magnitude of said amplitude tune signal is greater than a predetermined amplitude window level, said third step width being larger than said second step width and smaller than said first step width.

24. The automatic matching apparatus of claim 20 wherein said second adjustment means further comprises a step-width control means for adjusting said second variable component in variable increments, said step width control means comprising:

slope means for generating a phase slope signal related to the derivative of said phase tune signal with respect to the component value of said second variable component; and

first stepping means for adjusting the component value of said second variable component in increments equal in magnitude to a first predetermined step width when said phase slope signal is greater than zero and for adjusting said second variable component in increments equal in magnitude to a second predetermined step width when said phase slope signal is less than zero, said second step width being smaller than said first step width.

25. The automatic matching apparatus of claim 24 wherein said step-width control means further comprises:

a second stepping means for adjusting the component value of said second variable component in increments equal in magnitude to a third predetermined step width when said phase slope signal is less than zero and the magnitude of said phase tune signal is greater than a predetermine phase window level, said third step width being larger than said second step width and smaller than said first step width.

26. The automatic matching apparatus of claim 20 wherein said detection means comprises means for generating a normalizing signal as a function of a selected one of said voltage waveform amplitude at said input port and said current waveform amplitude at said input port, and wherein said control means comprises amplitude normalization means for normalizing said amplitude tune signal with respect to said normalizing signal.

27. The automatic matching apparatus of claim 26 wherein said control means further comprises phase normalization means for normalizing said phase tune signal with respect to said normalizing signal.

28. An automatic impedance matching apparatus having an input port coupled to a signal generator and an output port coupled to a load, said input and output ports each having a signal line and a ground line, said signal generator having a predetermined characteristic impedance, said apparatus comprising:

matching means coupled between said input port and output port for matching the impedance of said load to the impedance of said signal generator, said matching means including a first variable reactive component and a second variable reactive component;

a detection means for generating an amplitude tune signal related to the difference of the voltage waveform amplitude at said input port and the product of said predetermined characteristic impedance and the current waveform amplitude at said input port and for generating a phase tune signal related to the phase difference between the voltage and current waveforms at said input port, said amplitude tune signal increasing as said voltage amplitude increases and decreasing as said current amplitude increases, said phase tune signal being substantially equal to zero when said input voltage and input current waveforms are in phase, said phase tune signal increasing as said input voltage waveform leads said input current waveform and decreasing as said input voltage waveform lags said input current waveform; and

control means responsive to said amplitude and phase tune signals for adjusting the values of said first and second variable reactive components to provide a tuned condition at said input port, said control means including a first adjustment means for modifying the value of said first variable reactive component as a function of said amplitude tune signal, a second adjustment means for modifying the value of said second variable reactive component as a function of said phase tune signal, said first adjustment means further comprising a step-width control means for adjusting said first variable component in variable increments, said step width control means comprising;

slope means for generating an amplitude slope signal related to the derivative of said amplitude tune signal with respect to the component value of said first variable component; and

first stepping means for adjusting the component value of said first variable component in increments equal in magnitude to a first predetermined step width when said amplitude slope signal is greater than zero and for adjusting the component value of said first variable component in increments equal in magnitude to a second predetermined step width when said amplitude slope signal is less than zero, said second step width, being smaller than said first step width.

29. The automatic matching apparatus of claim 28 wherein said step-width control means further comprises:

a second stepping means for adjusting the increments equal in magnitude to a third predetermined step width when said amplitude slope signal is less than zero and the magnitude of said amplitude tune signal is greater than a predetermined amplitude window level, said third step width being larger than said second step width and smaller than said first step width.

30. The Automatic matching apparatus of claim 28 wherein said step-width control means comprises a first memory means for storing the sign of the previous adjustment increment of said first variable component, and wherein said slope means comprises:

a second memory means for storing a previous value of said amplitude tune signal; and

means for generating said amplitude slope signal as the value of the amplitude tune signal less the value stored in said second memory means when the sign value in said first memory means is negative and as the value stored in said second memory means less the value of the amplitude tune signal when the sign value stored in said first memory means is positive.

31. The automatic matching apparatus of claim 30 where said first memory means initially stores a first predetermined starting value and said second memory means initially stores a second predetermined starting value.

32. The automatic matching apparatus of claim 28 wherein said detection means comprises means for generating a normalizing signal as a function of a selected one of said voltage waveform amplitude at said input port and said current waveform amplitude at said input port, and wherein said control means comprises amplitude normalization means for normalizing said amplitude tune signal with respect to said normalizing signal.

33. The automatic matching apparatus of claim 32 wherein said control means further comprises phase normalization means for normalizing said phase tune signal with respect to said normalizing signal.

34. An automatic impedance matching apparatus having an input port coupled to a signal generator and an output port coupled to a load, said input and output ports each having a signal line and a ground line, said signal generator having a predetermined characteristic impedance, said apparatus comprising:

matching means coupled between said input port and output port for matching the impedance of said load to the impedance of said signal generator, said matching means including a first variable reactive component and a second variable reactive component;

a detection means for generating an amplitude tune signal related to the difference of the voltage waveform amplitude at said input port and the product of said predetermined characteristic impedance and the current waveform amplitude at said input port and for generating a phase tune signal related to the phase difference between the voltage and current waveforms at said input port, said amplitude tune signal increasing as said voltage amplitude increases and decreasing as said current amplitude increases, said phase tune signal being substantially equal to zero when said input voltage and input current waveforms are in phase, said phase tune signal increasing as said input voltage waveform leads said input current waveform and decreasing as said input voltage waveform lags said input current waveform; and

control means responsive to said amplitude and phase tune signals for adjusting the values of said first and second variable reactive components to provide a tuned condition at said input port, said control means including a first adjustment means for modifying the value of said first variable reactive component as a function of said amplitude tune signal, a second adjustment means for modifying the value of said second variable reactive component as a function of said phase tune signal, said second adjustment means further comprising a step-width control means for adjusting said second variable component in variable increments, said step width control means comprising;

slope means for generating a phase slope signal related to the derivative of said phase tune signal with respect to the component value of said second variable component; and

first stepping means for adjusting the component value of said second variable component in increments equal in magnitude to a first predetermined step width when said phase slope signal is greater than zero and for adjusting said second variable component in increments equal in magnitude to a second predetermined step width when said phase slope signal is less than zero, said second step width being smaller than said first step width.

35. The automatic matching apparatus of claim 34 wherein said step-width control means further comprises:

a second stepping means for adjusting the component value of said second variable component in increments equal in magnitude to a third predetermined step width when said phase slope signal is less than zero and the magnitude of said phase tune signal is greater than a predetermine phase window level, said third step width being larger than said second step width and smaller than said first step width.

36. The Automatic matching apparatus of claim 34 wherein said step-width control means comprises a first memory means for storing the sign of the previous adjustment increment of said second variable component, and wherein said slope means comprises:

a second memory means for storing a previous value of said phase tune signal; and

means for generating said phase slope signal as the value of the phase tune signal less the value stored in said second memory means when the sign value in said first memory means is negative and as the value stored in said second memory means less the value of the phase tune signal when the sign value stored in said first memory means is positive.

37. The automatic matching apparatus of claim 36 where said first memory means initially stores a first predetermined starting value and said second memory means initially stores a second predetermined starting value.

38. The automatic matching apparatus of claim 34 wherein said detection means comprises means for generating a normalizing signal as a function of a selected one of said voltage waveform amplitude at said input port and said current waveform amplitude at said input port, and wherein said control means comprises phase normalization means for normalizing said phase tune signal with respect to said normalizing signal.

39. The automatic matching apparatus of claim 38 wherein said control means further comprises amplitude normalization means for normalizing said amplitude tune signal with respect to said normalizing signal.

40. An automatic impedance matching apparatus having an input port coupled to a signal generator and an output port coupled to a load, said input and output ports each having a signal line and a ground line, said signal generator having a predetermined characteristic impedance, said apparatus comprising:

matching means coupled between said input port and output port for matching the impedance of said load to the impedance of said signal generator, said matching means including a first variable reactive component and a second variable reactive component;

a detection means for generating an amplitude tune signal related to the difference of the voltage waveform amplitude at said input port and the product of said predetermined characteristic impedance and the current waveform amplitude at said input port and for generating a phase tune signal related to the phase difference between the voltage and current waveforms at said input port, said amplitude tune signal increasing as said voltage amplitude increases and decreasing as said current amplitude increases, said phase tune signal being substantially equal to zero when said input voltage and input current waveforms are in phase, said phase tune signal increasing as said input voltage waveform leads said input current waveform and decreasing as said input voltage waveform lags said input current waveform, said detection means further comprising means for generating a normalizing signal as a function of a selected one of said voltage waveform amplitude at said input port and said current waveform amplitude at said input port; and

control means responsive to said amplitude and phase tune signals for adjusting the values of said first and second variable reactive components to provide a tuned condition at said input port, said control means including a first adjustment means for modifying the value of said first variable reactive component as a function of said amplitude tune signal, a second adjustment means for modifying the value of said second variable reactive component as a function of said phase tune signal, said control means further comprising amplitude normalization means for normalizing said amplitude tune signal with respect to said normalizing signal.

41. The automatic matching apparatus of claim 40 wherein said control means further comprises phase normalization means for normalizing said phase tune signal with respect to said normalizing signal.

42. An automatic impedance matching apparatus ..having an input port coupled to a signal generator and an output port coupled to a load, said input and output ports each having a signal line and a ground line, said signal generator having a predetermined characteristic impedance, said apparatus comprising:

matching means coupled between said input port and output port for matching the impedance of said load to the impedance of said signal generator, said matching means including a first variable reactive component and a second variable reactive component;

a detection means for generating an amplitude tune signal related to the difference of the voltage waveform amplitude at said input port and the product of said predetermined characteristic impedance and the current waveform amplitude at said input port and for generating a phase tune signal related to the phase difference between the voltage and current waveforms at said input port, said amplitude tune signal increasing as said voltage amplitude increases and decreasing as said current amplitude increases, said phase tune signal being substantially equal tn zero when said input voltage and input current waveforms are in phase, said phase tune signal increasing as said input voltage waveform leads said input current waveform and decreasing as said input voltage waveform lags said input current waveform, said detection means further comprising means for generating a normalizing signal as a function of a selected one of said voltage waveform amplitude at said input port and said current waveform amplitude at said input port; and

control means responsive to said amplitude and phase tune signals for adjusting the values of said first and second variable reactive components to provide a tuned condition at said input port, said control means including a first adjustment means for modifying the value of said first variable reactive component as a function of said amplitude tune signal, a second adjustment means for modifying the value of said second variable reactive component as a function of said phase tune signal, said control means further comprising phase normalization means for normalizing said phase tune signal with respect to said normalizing signal.

43. The automatic matching apparatus of claim 42 wherein said control means further comprises amplitude normalization means for normalizing said amplitude tune signal with respect to said normalizing signal.