Barrier layers for microelectromechanical systems

• US 6,849,471 B2
• Filed: 03/28/2003
• Issued: 02/01/2005
• Est. Priority Date: 03/28/2003
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Patel, Satyadev R., Doan, Jonathan C.
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): Vu, David
• Application Number:
  US10/402,789
• Publication Number:
  US 20040191937A1
• Time in Patent Office: 676 Days
• Field of Search: 438/21, 438421-422, 257536-537, 347/1, 347/20, 347/63
• US Class Current: 438/21
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81C 1/00793 Avoid contamination, e.g. absorption of impurities or oxidation
• CPC Class Codes: B81C 2201/053 Depositing a protective layers

Abstract

A method for processing microelectromechanical devices is disclosed herein. The method prevents the diffusion and interaction between sacrificial layers and structure layers of the microelectromechanical devices by providing selected barrier layers between consecutive sacrificial and structure layers.

Claims

1. A method comprising:

depositing a first sacrificial layer;

depositing a first barrier layer after the first sacrificial layer;

forming a structural layer of a microelectromechanical device after the first barrier layer;

releasing the microelectromechanical device by removing the first sacrificial layer and the first barrier layer; and

wherein the first barrier layer prevents diffusion and reaction between the first sacrificial layer and the structural layer.

2. The method of claim 1, further comprising:

before releasing the microelectromechanical device by removing the first sacrificial layer and the first barrier layer,

depositing a second barrier layer after the structural layer formed on the first barrier layer;

depositing a second sacrificial layer after the second barrier layer;

forming one or more structure layers of the microelectromechanical device after the second sacrificial layer; and

wherein the second barrier layer prevents diffusion and interaction between the second sacrificial layer and the structural layer formed underneath the second barrier layer; and

wherein the step of releasing the microelectromechanical device by removing the first sacrificial layer and the first barrier layer further comprises;

removing the second sacrificial layer and the second barrier layer.

3. The method of claim 2, wherein the second sacrificial material is amorphous silicon;

and wherein the structural layer formed on the first sacrificial layer is a metal element or a metal compound.

4. The method of claim 2, wherein the second barrier layer comprises one or more early transition metal elements.

5. The method of claim 4, wherein the non-etchant gaseous addictive is inert gas.

6. The method of claim 5, wherein the noble gas halide is xenon difluoride.

7. The method of claim 2, wherein the second barrier layer comprises one or more early transition metal alloys.

8. The method of claim 2, wherein the second barrier layer comprises one or more early transition metal compounds.

9. The method of claim 2, wherein the removal of the second sacrificial layer and the second barrier layer is achieved by etching the second sacrificial layer and the second barrier layer using isotropic gas-phase etching technique with non-plasma spontaneous chemical vapor-phase etchant.

10. The method of claim 2, wherein the microelectromechanical device is a micromirror device;

and the method further comprising;

before depositing the first sacrificial layer,

providing a substrate, on which the first sacrificial layer is deposited;

wherein the step of forming the structure layer of the microelectromechanical device on the first sacrificial layer further comprises;

depositing the structure layer, wherein the structure layer has a reflectivity to visible light higher than ninety percent (90%); and

patterning the deposited structural layer into a micromirror plate of the micromirror device for reflecting incident visible light; and

wherein the one or more structural layers on the second sacrificial layer are formed into a hinge, to which the micromirror plate of the micromirror device is attached such that the micromirror plate can rotate relative to the substrate after releasing the micromirror device.

11. The method of claim 2, wherein the second barrier layer neither diffuses into nor interacts with the first structural layer under 400°

C. (degree) within 30 minutes.

12. The method of claim 1, further comprising:

before releasing the microelectromechanical device by removing the first sacrificial layer and the first barrier layer,

depositing a second barrier layer after the structural layer formed on the first barrier layer;

depositing a second sacrificial layer after the second barrier layer,

forming one or more structural layers of the microelectromechanical device after the second sacrificial layer; and

wherein the second barrier layer prevents diffusion and interaction between the second sacrificial layer and the structure layer formed underneath the second barrier layer; and

wherein the step of releasing the microelectromechanical device by removing the first sacrificial layer and the first barrier layer further comprises;

removing the second sacrificial layer; and

wherein the second barrier layer is not removed after releasing the microelectromechanical device.

13. The method of claim 12, wherein the second sacrificial material is amorphous silicon;

and wherein the structure layer formed on the first sacrificial layer is a metal element or a metal compound.

14. The method of claim 12, wherein the second barrier layer comprises one or more inter-metallic metal compounds.

15. The method of claim 14, wherein the non-etchant gaseous additive is inert gas.

16. The method of claim 12, wherein the second barrier layer comprises one or more early transition metal nitrides.

17. The method of claim 12, wherein the second barrier layer comprise one or more early transition metal oxides.

18. The method of claim 12, wherein the second barrier layer comprise one or more early transition metal oxynitrides.

19. The method of claim 18, wherein the micromirror device is part of a micromirror array of a spatial light modulator.

20. The method of claim 18, wherein the substrate is transparent to visible light.

21. The method of claim 18, wherein the substrate is a silicon wafer.

22. The method of claim 12, wherein the second barrier layer comprise one or more early transition metal silicon nitrides.

23. The method of claim 22, wherein the spatial light modulator is part of a display system that further comprises:

a light source for providing visible light; and

one or more optical elements for directing the visible light onto the spatial light modulator.

24. The method of claim 12, wherein the removal of the second sacrificial layer is achieved by etching using isotropic gas-phase etching technique with non-plasma spontaneous chemical vapor-phase etchant.

25. The method of claim 24, wherein the display system further comprises:

one or more optical elements for directing reflected light from the spatial light modulator onto a display target.

26. The method of claim 12, further comprises:

after depositing the second barrier layer, patterning the deposited second barrier layer according to the structural layer.

27. The method of claim 12, further comprising:

patterning the second barrier layer.

28. The method of claim 12, wherein the microelectromechanical device is a micromirror device;

and the method further comprising;

before depositing the first sacrificial layer,

providing a substrate, on which the first sacrificial layer is deposited;

wherein the step of forming the structure layer of the microelectromechanical device on the first sacrificial layer further comprises;

depositing the structure layer, wherein the structure layer has a reflectivity to visible light higher than ninety percent (90%); and

patterning the deposited structural layer into a micromirror plate of the micromirror device for reflecting incident visible light; and

wherein the one or more structural layers on the second sacrificial layer are formed into a hinge, to which the micromirror plate of the micromirror device is attached such that the micromirror plate can rotate relative to the substrate after releasing the micromirror device.

29. The method of claim 12, wherein the second barrier layer neither diffuses into nor interacts with the first structural layer under 400°

C. (degree) within 30 minutes.

30. The method of claim 1, wherein the first sacrificial material is amorphous silicon;

and wherein the structural layer formed on the first sacrificial layer is a metal element or a metal compound.

31. The method of claim 1, wherein the first barrier layer comprises one or more early transition metal elements.

32. The method of claim 31, wherein the early transition metal element is molybdenum.

33. The method of claim 31, wherein the early transition metal element is tungsten.

34. The method of claim 31, wherein the early transition metal clement is tantalum.

35. The method of claim 34, wherein the early transition metal compound is early transition metal silicides.

36. The method of claim 31, wherein the early transition metal element is titanium.

37. The method of claim 1, wherein the first barrier layer comprises one or more early transition metal alloys.

38. The method of claim 1, wherein the first barrier layer comprises one or more early transition metal compounds.

39. The method of claim 38, wherein the early transition metal compound is early transition metal silicide.

40. The method of claim 39, wherein the early transition metal silicide is molybdenum silicide.

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

42. The method of claim 41, wherein the chemical vapor-phase etchant is vapor-phase interhalogen.

43. The method of claim 41, wherein the chemical vapor-phase etchant is vapor-phase noble gas halide.

44. The method of claim 41, wherein the chemical vapor-phase etchant is a mixture of noble gas halide and one or more non-etchant gaseous additives.

45. The method of claim 39, wherein the early transition metal silicide is tantalum silicide.

46. The method of claim 39, wherein the early transition metal silicide is titanium silicide.

47. The method of claim 46, wherein the noble gas halide is xenon difluoride.

48. The method of claim 47, wherein the chemical vapor-phase etchant is vapor-phase interhalogen.

49. The method of claim 47, wherein the chemical vapor-phase etchant is vapor-phase noble gas halide.

50. The method of claim 49, wherein the micromirror device is part of a micromirror array of a spatial light modulator.

51. The method of claim 49, wherein the spatial light modulator is part of a display system that further comprises:

a light source for providing visible light; and

one or more optical elements for directing the visible light onto the spatial light modulator.

52. The method of claim 49, wherein the display system further comprises:

one or more optical elements for directing reflected light from the spatial light modulator onto a display target.

53. The method of claim 49, wherein the substrate is transparent to visible light.

54. The method of claim 49, wherein the substrate is a silicon wafer.

55. The method of claim 47, wherein the chemical vapor-phase etchant is a mixture of noble gas halide and one or more non-etchant gaseous additives.

56. The method of claim 1, wherein the step of releasing the microelectromechanical device by removing the first sacrificial layer and the first barrier layer further comprises:

etching the first sacrificial layer and the first barrier layer using isotropic gas-phase etching technique with non-plasma spontaneous chemical vapor-phase etchant.

57. The method of claim 56, wherein the chemical vapor-phase etchant is vapor-phase interhalogen.

58. The method of claim 57, wherein the noble gas halide is xenon difluoride.

59. The method of claim 56, wherein the chemical vapor-phase etchant is vapor-phase noble gas halide.

60. The method of claim 56, wherein the chemical vapor-phase etchant is a mixture of noble gas halide and one or more non-etchant gaseous additives.

61. The method of claim 60, wherein the non-etchant gaseous addictive is inert gas.

62. The method of claim 1, wherein the first barrier layer is different from the first sacrificial layer.

63. The method of claim 1, wherein the first barrier layer neither diffuses into nor interacts with the first structural layer under 400°

C. (degree) within 30 minutes.