Envelope follower end point detection in time division multiplexed processes

• US 20040238489A1
• Filed: 05/06/2004
• Published: 12/02/2004
• Est. Priority Date: 05/09/2003
• Status: Active Grant

• Current Assignee: Plasma-Therm Corporation
• Original Assignee: Unaxis USA Incorporated (Unaxis)
• Inventors: Johnson, David, Westerman, Russell
• Granted Patent: US 7,101,805 B2
• Time in Patent Office: Days
• US Class Current: 216/60
• CPC Class Codes: B81C 1/00587 Processes for avoiding or controlling over-etching not provided for in B81C1/00571 - B81C1/00579
• CPC Class Codes: B81C 2201/0132 Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling
• 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: H01L 21/30655 comprising alternated and repeated etching and passivation steps, e.g. Bosch process

Abstract

The present invention provides a method and an apparatus for establishing endpoint during an alternating cyclical etch process or time division multiplexed process. A substrate is placed within a plasma chamber and subjected to an alternating cyclical process having an etching step and a deposition step. A variation in plasma emission intensity is monitored using known optical emission spectrometry techniques. An amplitude information is extracted from a complex waveform of the plasma emission intensity using an envelope follower algorithm. The alternating cyclical process is discontinued when endpoint is reached at a time that is based on the monitoring step.

Claims

1. A method for etching a feature in a substrate comprising the steps of:

subjecting the substrate to an alternating process within a plasma chamber;

monitoring a variation in plasma emission intensity;

extracting an amplitude information from said plasma emission intensity using an envelope follower algorithm; and

discontinuing said alternating process at a time based on said monitoring step.

2. The method of claim 1 wherein the substrate to be etched contains silicon.

3. The method of claim 1 wherein the substrate to be etched contains a group-III element.

4. The method of claim 1 wherein the substrate to be etched contains a group-V element.

5. The method of claim 1 wherein said alternating process further comprising at least one etching step and at least one deposition step.

6. The method of claim 1 wherein said alternating process further comprising a plurality of etching steps and a plurality of deposition steps.

7. The method of claim 1 wherein at least one process parameter varies over time within said alternating process.

8. The method of claim 1 wherein said plasma emission intensity is periodic.

9. The method of claim 1 wherein said monitoring step further comprising monitoring a plurality of regions of plasma emission intensity.

10. The method of claim 9 wherein said plurality of regions of plasma emission intensity are chosen using a statistical method.

11. The method of claim 10 wherein said statistical method further comprising factor analysis.

12. The method of claim 9 wherein said plurality of regions of plasma emission intensity are chosen using an off-line analysis.

13. The method of claim 12 wherein said off-line analysis further comprising spectra differencing.

14. The method of claim 9 wherein said plurality of regions of plasma emission intensity are background corrected.

15. The method of claim 9 wherein said monitoring step further comprising performing mathematical operations on said multiple regions of plasma emission intensity.

16. The method of claim 1 wherein said extracting step further comprising using a plurality of peak detect algorithms.

17. The method of claim 16 wherein said plurality of peak detect algorithms are reset sequentially in a round robin fashion.

18. The method of claim 17 wherein said reset further comprising a clock period that is longer than a half period of a lowest frequency of interest.

19. A method of establishing endpoint during a time division multiplex process comprising the steps of:

subjecting a substrate to the time division multiplex process;

monitoring an attribute of a signal generated from the time division multiplex process;

processing said attribute of the periodic signal generated from the time division multiplex process using an envelope follower; and

discontinuing the time division multiplex process at a time based on the processing step.

20. The method of claim 19 wherein said attribute is plasma emission intensity.

21. The method of claim 20 wherein said monitoring step further comprising monitoring a plurality of regions of plasma emission intensity.

22. The method of claim 21 wherein said plurality of regions of plasma emission intensity are chosen using a statistical method.

23. The method of claim 22 wherein said statistical method further comprising factor analysis.

24. The method of claim 21 wherein said plurality of regions of plasma emission intensity are chosen using an off-line analysis.

25. The method of claim 24 wherein said off-line analysis further comprising spectra differencing.

26. The method of claim 21 wherein said plurality of regions of plasma emission intensity are background corrected.

27. The method of claim 21 wherein said monitoring step further comprising performing mathematical operations on said multiple regions of plasma emission intensity.

28. The method of claim 19 wherein said attribute is plasma impedance.

29. The method of claim 19 wherein said processing step further comprising using a plurality of peak detect algorithms.

30. The method of claim 29 wherein said plurality of peak detect algorithms are processed in parallel.

31. The method of claim 29 wherein said plurality of peak detect algorithms are reset sequentially in a round robin fashion.

32. The method of claim 31 wherein said reset further comprising a clock period that is at least half the process period of the time division multiplex process.

33. The method of claim 19 wherein said processing step further comprising post processing of an extracted amplitude detection signal.

34. The method of claim 33 wherein said post processing is digital signal processing.

35. The method of claim 34 wherein said digital signal processing comprises a filter.

36. The method of claim 35 wherein said filter is an infinite impulse response filter.

37. The method of claim 35 wherein said filter is a finite impulse response filter.

38. A method for establishing endpoint during a time division multiplexed process, the method comprising the steps of:

a. etching a surface of a substrate in an etching step by contact with a reactive etching gas to removed material from the surface of the substrate and provide exposed surfaces;

b. passivating the surface of the substrate in a passivating step during which the surfaces that were exposed in the preceding etching step are covered by a passivation layer thereby forming a temporary etching stop;

c. alternatingly repeating the etching step and the passivating step;

d. analyzing an intensity of at least one wavelength region of a plasma emission through the use of an envelope follower algorithm; and

e. discontinuing the time division multiplexed process at a time which is dependent on said analysis step.

39. A method of establishing endpoint during a time division multiplex process comprising the steps of:

subjecting a substrate to the time division multiplex process;

monitoring an attribute of a signal generated from the time division multiplex process;

processing said attribute of the periodic signal generated from the time division multiplex process using a peak-hold and decay algorithm; and

discontinuing the time division multiplex process at a time based on the processing step.

40. The method of claim 39 wherein said attribute is plasma emission intensity.

41. The method of claim 39 wherein said processing step further comprising using a linear decay algorithm.

42. The method of claim 39 wherein said processing step further comprising using a non-linear decay algorithm.

43. The method of claim 39 wherein said processing step further comprising post processing of an extracted amplitude detection signal.

44. The method of claim 43 wherein said post processing is digital signal processing.

45. The method of claim 44 wherein said digital signal processing comprises a filter.

46. The method of claim 45 wherein said filter is an infinite impulse response filter.

47. The method of claim 45 wherein said filter is a finite impulse response filter.