INDICATION OF THE END-POINT REACTION BETWEEN XeF2 AND MOLYBDENUM

• US 20080318344A1
• Filed: 06/22/2007
• Published: 12/25/2008
• Est. Priority Date: 06/22/2007
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm, Inc.
• Inventors: Rafanan, Marjorio
• Granted Patent: US 7,569,488 B2
• Time in Patent Office: Days
• US Class Current: 438/5
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence
• CPC Class Codes: B81C 1/00801 Avoid alteration of functional structures by etching, e.g. using a passivation layer or an etch stop layer B81C1/00595, B81C1/00468 take precedence
• CPC Class Codes: B81C 2201/0138 Monitoring physical parameters in the etching chamber, e.g. pressure, temperature or gas composition
• CPC Class Codes: B81C 99/0065 Process control; Yield prediction

Abstract

Embodiments of the present invention relate to methods and systems for making a microelectromechanical system comprising supplying an etchant to etch one or more sacrificial structures of the system.

Claims

1. A method for making a microelectromechanical systems (MEMS) device, comprising:

(a) providing a chamber and an unreleased MEMS device situated therein, the unreleased MEMS device comprising a sacrificial structure;

(b) supplying an etchant to the chamber to thereby etch the sacrificial structure; and

(c) monitoring a process parameter related to the pressure within the chamber as a function of time to thereby provide an indication of the extent of etching of the sacrificial structure.

2. The method of claim 1, wherein the monitored process parameter is the change in pressure within the chamber as a function of time.

3. The method of claim 1, wherein the monitored process parameter comprises at least one of the temperature within the chamber and the change in temperature within the chamber as a function of time.

4. The method of claim 1, further comprising discontinuing the supplying of the etchant to the chamber.

5. The method of claim 1, further comprising:

(d) removing at least a portion of the gases from the chamber.

6. The method of claim 5, further comprising conducting one or more additional cycles by repeating at least steps (b), (c) and (d).

7. The method of claim 6, wherein the monitored process parameter is a change in a time derivative of a within-cycle pressure across cycles.

8. The method of claim 6, further comprising discontinuing an initiation of an additional cycle upon the providing of the indication.

9. The method of claim 6, wherein the indication is provided when the monitored process parameter corresponding to a specific time relative to the beginning of an additional cycle crosses a pre-selected threshold.

10. The method of claim 6, wherein the indication is provided when the monitored process parameter corresponding to a specific time relative to the beginning of an additional cycle crosses a pre-selected second threshold after having already crossed a pre-selected first threshold.

11. The method of claim 6, further comprising comparing a monitored process parameter measured at a specific time relative to the beginning of the first or additional cycle to a monitored process parameter measured at the same specific time relative to the beginning of a different additional cycle to thereby provide the indication.

12. The method of claim 1, wherein the indication is provided when the monitored process parameter crosses a pre-selected threshold.

13. The method of claim 12, wherein the pre-selected threshold is about zero.

14. The method of claim 12, wherein the pre-selected threshold is about 1%, about 5% or about 10% of a maximum process parameter relative to an initial process parameter.

15. The method of claim 12, wherein the pre-selected threshold is about 105% of a first pressure expected if the etchant does not react with another substance.

16. The method of claim 12, wherein the pre-selected threshold is a pressure change of about 0.2 mT per second or about −

0.2 mT per second.

17. The method of claim 1, wherein the unreleased MEMS device comprises:

a substrate;

one or more first layers positioned over the substrate;

a sacrificial layer comprising a sacrificial structure positioned over the one or more first layers; and

one or more second layers positioned over the sacrificial layer.

18. The method of claim 14, wherein the one or more first layers comprise a first electrode.

19. The method of claim 14, wherein the one or more second layers comprise a second electrode.

20. The method of claim 14, wherein a reaction between the etchant and the sacrificial structure produces primarily gaseous products.

21. The method of claim 14, wherein the sacrificial structure comprises molybdenum.

22. The method of claim 14, wherein the etchant comprises xenon difluoride.

23. The method of claim 14, further comprising:

positioning one or more additional unreleased MEMS devices in the chamber, the additional unreleased MEMS devices comprising additional one or more sacrificial structures.

24. The method of claim 1, wherein the unreleased MEMS device comprises an unreleased interferometric modulator.

25. An MEMS device manufactured by the method of claim 1.

26. An etching system, comprising:

an etching chamber configured to provide an etchant to the chamber and to house an unreleased MEMS device comprising a sacrificial structure;

a parameter monitor configured to monitor a parameter related to the pressure within the chamber; and

a component configured to indicate the extent of etching of the sacrificial structure based on changes in the parameter as a function of time.

27. The system of claim 26, wherein the parameter is the pressure within the chamber.

28. The system of claim 26, wherein the etching chamber is configured to provide the etchant to the chamber in a plurality of cycles.

29. The system of claim 28, wherein the parameter is the change in a time derivative of a within-cycle pressure across cycles.

30. The system of claim 28, wherein the component is further configured to compare the changes in the parameter across the cycles.

31. The system of claim 26, wherein the component is configured to determine when a change in the parameter as a function of time crosses a pre-selected threshold.

32. The system of claim 28, wherein the component is further configured to indicate when to discontinue the providing of the etchant.

33. The system of claim 32, wherein the component is further configured to

compare the change in the parameter as a function of time at a particular time relative to the cycle onset across cycles;

and

identify a cycle in which the change in the parameter as a function of time crosses a threshold.

34. The system of claim 33, wherein the component is further configured to identify a cycle in which the change in the parameter as a function of time crosses a threshold.

35. The system of claim 26, wherein the component comprises a computer.

36. A computer-readable medium having computer-executable instructions thereon for determining a stop etching time, the instructions comprising:

receiving a plurality of input parameters related to the pressure within an etching chamber housing an unreleased MEMS device comprising a sacrificial structure, wherein each of the input parameters corresponds to an etching cycle and a time relative to the onset of the etching cycle;

determining pressure-derivative parameters by calculating the change of the input parameter with respect to the time relative to the onset of the etching cycle; and

outputting an indicator of the extent of etching of the sacrificial structure by comparing at least one pressure-derivative parameter corresponding to a specified time relative to the onset of the corresponding etching cycle to a threshold.

37. The computer-readable medium of claim 36, wherein the indicator comprises a time in which an amount of etching has been or is expected to be achieved.

38. The computer-readable medium of claim 37, wherein the amount corresponds to etching of approximately all of the sacrificial structure.

39. The computer-readable medium of claim 36, wherein the outputting step further comprises determining a cycle in which one of the at least one pressure-derivative parameter is below the threshold and in which the corresponding pressure-derivative parameter from the preceding trial is above the threshold.

40. The computer-readable medium of claim 36, wherein the threshold is approximately zero.

41. An optical device formation system, comprising:

means for providing an etchant to interact with a sacrificial structure of an unreleased MEMS device;

means for monitoring a parameter related to pressure changes at least partially attributable to the interaction of the etchant with the sacrificial structure; and

means for indicating the extent of etching of the sacrificial structure based on the monitored parameter.

42. The system of claim 41, wherein the means for providing an etchant to interact with a sacrificial structure of an unreleased MEMS device comprises an etching chamber.

43. The system of claim 41, wherein the means for monitoring a parameter related to pressure changes at least partially attributable to the interaction of the etchant with the sacrificial structure comprises a pressure sensor.

44. The system of claim 41, wherein the means for indicating the extent of etching of the sacrificial structure based on the monitored parameter comprises a computer.

45. The system of claim 41, wherein the means for indicating the extent of etching of the sacrificial structure based on the monitored parameter comprises means for indicating a time in which a specific amount of etching of the sacrificial structure has been achieved.

46. The system of claim 45, wherein the means for indicating a time comprises a computer.

47. The system of claim 45, wherein the specific amount is approximately all of the sacrificial structure.

48. The system of claim 45, wherein the time comprises an etching cycle.

49. The system of claim 41, wherein means for indicating the extent of etching of the sacrificial structure based on the monitored parameter comprises means for determining an etching cycle for which a change in the monitored parameter with respect to time crosses a specified threshold.

50. The system of claim 49, wherein the means for determining an etching cycle comprises a computer.

51. The system of claim 49, wherein the threshold is approximately zero.