Methods for forming and releasing microelectromechanical structures

• US 6,960,305 B2
• Filed: 03/28/2003
• Issued: 11/01/2005
• Est. Priority Date: 10/26/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Reid, Jason S., Patel, Satyadev R., Doan, Jonathan C., Huibers, Andrew G.
• Primary Examiner(s): OLSEN, ALLAN W
• Application Number:
  US10/402,777
• Publication Number:
  US 20040035821A1
• Time in Patent Office: 949 Days
• Field of Search: 216/2, 216/79, 438/48
• US Class Current: 216/2
• CPC Class Codes: B81B 2201/045 Optical switches
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence
• CPC Class Codes: C03C 17/36 at least one coating being a metal
• CPC Class Codes: C03C 17/3663 specially adapted for use as mirrors
• CPC Class Codes: C23F 4/00 Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H01L 21/32135 by vapour etching only

Abstract

A method for making a spatial light modulator is disclosed, that comprises forming an array of micromirrors each having a hinge and a micromirror plate held via the hinge on a substrate, the micromirror plate being disposed in a plane separate from the hinge and having a hinge made of a transition metal nitride, followed by releasing the micromirrors in a spontaneous gas phase chemical etchant. Also disclosed is a projection system that comprises such a spatial light modulator, as well as a light source, condensing optics, wherein light from the light source is focused onto the array of micromirrors, projection optics for projecting light selectively reflected from the array of micromirrors onto a target, and a controller for selectively actuating the micromirrors in the array.

Claims

1. A method for making a microelectromechanical device, the method comprising:

depositing a sacrificial material on a substrate;

forming an array of MEMS elements comprised of plates and hinges, wherein the hinges of the MEMS elements comprise an early transition metal (groups 3b-7b of the periodic table) nitride; and

releasing the MEMS elements by removing the sacrificial material in a spontaneous gas phase chemical etchant selected from interhalogens and noble gas halides, wherein the early transition metal nitride is exposed to the etchant during removal of the sacrificial material but remains after the MEMS elements are released.

2. The method of claim 1, wherein the hinges are titanium nitride or titanium silicon nitride and the etchant is xenon difluoride.

3. The method of claim 1, wherein the hinges are a laminate comprising a layer of silicon nitride and a layer of an early transition metal nitride.

4. The method of claim 1, wherein the hinges comprise both an early transition metal nitride and a late transition metal.

5. The method of claim 1, wherein the hinges comprise a material selected from NbN, VN, HfN, ZrN and YN.

6. The method of claim 1, wherein the hinges have a length to width ratio of 2:

1 to 40;

1.

7. The method of claim 1, wherein the hinges have a length to thickness ratio of from 50:

1 to 200;

1.

8. The method of claim 1, wherein the length of each hinge is less than 20 micrometers.

9. The method of claim 1, wherein the width of each hinge is greater than 0.1 micrometers and less than 2 micrometers.

10. The method of claim 1, further comprising packaging the MEMS element array and placing the packaged array in a projection display apparatus.

11. The method of claim 1, wherein the hinges are electrically conductive.

12. The method of claim 1, wherein the hinges are multi-layer hinges.

13. The method of claim 12, wherein the hinges comprise a layer of titanium silicon nitride and a layer of titanium nitride.

14. The method of claim 12, wherein a layer of the multi-layer hinges comprises titanium.

15. The method of claim 12, wherein a layer of the multilayer hinges comprise tungsten.

16. The method of claim 1, wherein the etchant is an interhalogen.

17. The method of claim 16, wherein the etchant is BrF3 or BrCl3.

18. The method of claim 1, wherein the etchant is a noble gas halide.

19. The method of claim 18, wherein the etchant is xenon difluoride.

20. The method of claim 18, wherein the sacrificial material comprises amorphous silicon.

21. The method of claim 18, wherein the sacrificial material comprises an early transition metal.

22. The method of claim 1, wherein the vertical depth of each hinge is from 30 to 1000 Angstroms.

23. The method of claim 22, wherein the vertical depth of each hinge is from 300 to 600 Angstroms.

24. The method of claim 1, wherein the hinges are formed by reactively sputtering a target in a nitrogen gas.

25. The method of claim 24, wherein the hinges are formed by reactively sputtering an early transition metal target in a nitrogen or nitrogen/oxygen gas.

26. The method of claim 24, wherein the hinges are formed by reactively sputtering an early transition metal silicide target in a nitrogen or nitrogen/oxygen gas.

27. The method of claim 1, wherein the step of forming the array of MEMS elements comprises:

depositing the sacrificial material in a first layer;

depositing further sacrificial material in a second layer;

wherein plates are deposited and patterned on one of the sacrificial layers and hinges are deposited and patterned on the other of the sacrificial layers.

28. The method of claim 27, wherein the first and second sacrificial layers comprise the same material.

29. The method of claim 27, wherein the forming of the array of MEMS elements comprises:

forming the plates on the deposited sacrificial material in the first layer and;

forming the hinges on said further sacrificial material in the second layer.

30. The method of claim 29, wherein the substrate is a substrate transmissive to visible light.

31. The method of claim 27, wherein the forming the array of MEMS elements comprises:

forming the hinges on the deposited sacrificial material in first layer and;

forming the plates on said further sacrificial material in the second layer.

32. The method of claim 31, wherein the substrate is a semiconductor substrate.

33. The method of claim 1, wherein the MEMS elements are operable in binary mode and are rotatable from a non-deflected state to an ON state, the ON state being at least 10 degrees from the non-deflected state.

34. The method of claim 33, wherein the ON state is at least 12 degrees from the non-deflected state.

35. The method of claim 34, wherein the ON state is at least 14 degrees from the non-deflected state.

36. The method of claim 1, herein the early transition metal of the early transition metal nitride is selected from titanium, tantalum, chromium, molybdenum and tungsten.

37. The method of claim 36, wherein the plates comprise a reflective aluminum layer.

38. The method of claim 36, wherein the plates comprise a reflective silver layer.

39. The method of claim 36, wherein the early transition metal is tungsten.

40. The method of claim 39, wherein the hinges comprise tungsten silicon nitride.

41. The method of claim 39, wherein the hinges comprise tungsten titanium nitride.

42. The method of claim 39, wherein the hinges comprise tungsten oxynitride or tungsten carbonitride.

43. The method of claim 36, wherein the early transition metal is molybdenum.

44. The method of claim 43, wherein the hinges comprise molybdenum silicon nitride.

45. The method of claim 36, wherein the early transition metal is tantalum.

46. The method of claim 45, wherein the hinges comprise tantalum oxynitride.

47. The method of claim 45, wherein the hinges comprise tantalum nitride.

48. The method of claim 45, wherein the hinges comprises tantalum silicon nitride or tantalum silicon oxynitride.

49. The method of claim 45, wherein the hinges comprise tantalum titanium nitride.

50. The method of claim 45, wherein the hinges comprises tantalum titanium silicon oxynitride.

51. The method of claim 36, wherein the hinges further comprise silicon nitride.

52. The method of claim 51, wherein the hinges further comprise a late transition metal.

53. The method of claim 36, wherein the early transition metal is titanium.

54. The method of claim 53, wherein the hinges comprise titanium silicon nitride.

55. The method of claim 53, wherein the hinges comprise titanium nitride.

56. The method of claim 53, wherein the hinges comprise titanium oxynitride.

57. The method of claim 56, wherein the hinges comprise titanium silicon oxynitride.

58. The method of claim 36, wherein the early transition metal is chromium.

59. The method of claim 58, wherein the hinges comprise chromium nitride.

60. The method of claim 59, wherein the hinges comprise chromium oxynitride.

61. A method for making a micromirror array for a projection display, comprising:

depositing a sacrificial material on a substrate;

forming an array of micromirrors comprised of mirror plates and hinges, wherein the hinges of the micromirrors comprise an early transition metal (groups 3-7 of the periodic table) nitride; and

releasing the micromirrors by removing the sacrificial material in a spontaneous gas phase chemical etchant selected from interhalogens and noble gas halides, wherein the early transition metal nitride is exposed to the etchant during removal of the sacrificial material but remains after the micromirrors are released.

62. A method of making a micromirror array device, the method comprising:

deposition a sacrificial material on a substrate;

forming an array of micromirrors comprised of mirror plates and hinges, wherein the hinges comprise TiN_x; and

releasing the micromirrors by removing the sacrificial material in a spontaneous gas phase etchant comprising gas phase xenon difluoride, wherein the TiN_x is exposed to the etchant during removal of the sacrificial material but remains after the micromirrors being released.

63. The method of claim 62, wherein the hinge further comprises silicon nitride.

64. The method of claim 62, wherein the substrate is a light transmissive substrate.

65. The method of claim 62, wherein the step of forming an array of micromirrors further comprises:

depositing the sacrificial material in a first layer;

depositing the sacrificial material in a second layer;

wherein the plates are deposited and patterned on one of the first and second layers; and

wherein the hinges are deposited and patterned on the other one of the first and second layers.

66. The method of claim 65, wherein the sacrificial material on the first and second layer comprise the same material.

67. The method of claim 65, wherein the hinges are deposited and patterned before the plates.

68. The method of claim 65, wherein the plates are deposited and patterned before the hinges.