ELIMINATE RELEASE ETCH ATTACK BY INTERFACE MODIFICATION IN SACRIFICIAL LAYERS

• US 20080311690A1
• Filed: 04/02/2008
• Published: 12/18/2008
• Est. Priority Date: 04/04/2007
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Gousev, Evgeni, Heald, David, Tu, Thanh Nghia, Chiang, Chih-Wei, Luo, Qi, Yang, Chia Wei
• Granted Patent: US 8,222,066 B2
• Time in Patent Office: Days
• US Class Current: 438/29
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence

Abstract

Methods of making a microelectromechanical system (MEMS) device are described. In some embodiments, the method includes forming a sacrificial layer over a substrate, treating at least a portion of the sacrificial layer to form a treated sacrificial portion, forming an overlying layer over at least a part of the treated sacrificial portion, and at least partially removing the treated sacrificial portion to form a cavity situated between the substrate and the overlying layer, the overlying layer being exposed to the cavity.

Claims

1. A method of making a microelectromechanical system (MEMS) device, comprising:

forming a sacrificial layer over a substrate;

treating at least a portion of the sacrificial layer to form a treated sacrificial portion;

forming an overlying layer over at least a part of the treated sacrificial portion; and

at least partially removing the treated sacrificial portion to form a cavity situated between the substrate and the overlying layer, the overlying layer being exposed to the cavity.

2. The method of claim 1, wherein the treating comprises oxidizing.

3. The method of claim 1, wherein the treating comprises exposing the sacrificial layer to one or more of nitrogen, fluorine, and chlorine.

4. The method of claim 1, wherein the cavity is an interferometric modulation cavity.

5. The method of claim 1, wherein the treated sacrificial portion comprises an upper treated sacrificial layer, and a remaining portion of the sacrificial layer comprises a lower substantially untreated sacrificial layer.

6. The method of claim 5, wherein the upper treated sacrificial layer is substantially uniform in depth as measured in a direction perpendicular to the substrate.

7. The method of claim 5, comprising removing at least a portion of the upper treated sacrificial layer and at least a portion of the lower substantially untreated sacrificial layer, wherein an etch rate of the upper treated sacrificial layer is greater than an etch rate of the lower substantially untreated sacrificial layer.

8. The method of claim 5, wherein the lower substantially untreated sacrificial layer comprises molybdenum.

9. The method of claim 8, wherein the upper treated sacrificial layer comprises a molybdenum oxide.

10. The method of claim 1, wherein the overlying layer comprises a metal.

11. The method of claim 10, wherein the metal comprises aluminum.

12. The method of claim 11, comprising selecting treatment conditions, for the treating of the sacrificial layer to form the treated sacrificial portion, to reduce hillock formation in the overlying aluminum layer subsequent to the at least partial removal of the treated sacrificial portion, the method further comprising exposing the MEMS device to an otherwise hillock-inducing condition subsequent to the at least partial removal of the treated sacrificial portion.

13. The method of claim 12, comprising selecting the treatment conditions to reduce the number of the hillocks.

14. The method of claim 12, comprising selecting the treatment conditions to reduce the size of the hillocks.

15. The method of claim 12, wherein the hillocks comprise heat-induced hillocks.

16. The method of claim 12, wherein the otherwise hillock-inducing condition comprises exposing the MEMS device to a temperature greater than about 100°

C.

17. The method of claim 12, wherein the otherwise hillock-inducing condition comprises exposing the MEMS device to a temperature greater than about 200°

C.

18. The method of claim 12, wherein the otherwise hillock-inducing condition comprises exposing the MEMS device to a temperature greater than about 500°

C.

19. The method of claim 5, comprising selecting treatment conditions, for the treating of the sacrificial layer to form the treated sacrificial portion, to increase a combined thickness of the upper treated sacrificial layer and the lower substantially untreated sacrificial layer, as compared to the sacrificial layer prior to the treating.

20. The method of claim 1, comprising selecting treatment conditions, for the treating of the sacrificial layer to form the treated sacrificial portion, to decrease the degree of adhesion between the overlying layer and the treated sacrificial portion during the at least partial removal of the treated sacrificial portion.

21. The method of claim 1, wherein the overlying layer comprises a passivation layer and an electrically conductive layer formed over the passivation layer, the passivation layer being configured to aid in allowing the treated sacrificial portion to separate from the electrically conductive layer during the at least partial removal of the treated sacrificial portion.

22. The method of claim 1, comprising selecting treatment conditions, for the treating of the sacrificial layer to form the treated sacrificial portion, to provide a surface of the treated sacrificial portion that is smoother than the surface of the sacrificial layer prior to the treatment.

23. The method of claim 22, wherein the treatment conditions comprise an N₂O or O₂ treatment, or both.

24. The method of claim 1, wherein the treating of the at least a portion of the sacrificial layer comprises exposing a surface of the sacrificial layer to oxygen-containing molecules or radicals.

25. The method of claim 24, wherein the oxygen comprises ionized oxygen.

26. The method of claim 1, wherein the treating of the at least a portion of the sacrificial layer comprises heating the sacrificial layer.

27. The method of claim 1, wherein the treating of the at least a portion of the sacrificial layer comprises exposing the sacrificial layer to a plasma.

28. The method of claim 1, comprising removing substantially all of the treated sacrificial portion.

29. The method of claim 1, further comprising:

treating a surface of the sacrificial layer by exposing the surface of the sacrificial layer to sulfur hexafluoride; and

forming the overlying layer over the sulfur hexafluoride-treated surface.

30. The method of claim 1, further comprising:

forming an electrode over the substrate; and

forming the sacrificial layer over the electrode,

wherein the cavity is situated between the electrode and the overlying layer.

31. The method of claim 30, further comprising forming an insulating layer over the electrode.

32. The method of claim 30, further comprising forming at least one support structure that separates the electrode and the overlying layer.

33. An interferometric display device, comprising:

a first electrode formed over a substrate;

a movable second electrode situated over the first electrode and being substantially parallel to the first electrode, wherein the second electrode comprises a treated surface contour facing a cavity formed between the first electrode and the second electrode; and

a plurality of supports between the first electrode and the movable second electrode situated to support the movable second electrode.

34. The interferometric display device of claim 33, wherein the movable second electrode comprises aluminum.

35. The interferometric display device of claim 34, wherein the treated surface contour of the cavity-side of the movable second electrode is substantially insensitive to high temperatures.

36. The device of claim 35, further comprising an insulating layer situated on the first electrode.

37. The device of any of claims 35 to 36, wherein the high temperatures are greater than about 100°

C.

38. The device of any of claims 35 to 36, wherein the high temperatures are greater than about 200°

C.

39. The device of any of claims 35 to 36, wherein the high temperatures are greater than about 500°

C.

40. The interferometric display device of any of claims 35 to 36, wherein the treated surface contour of the cavity-side of the second electrode is configured to have a reduced tendency to form hillocks upon exposure to high temperatures.

41. A display device comprising an array of the interferometric display devices of claim 33.

42. The display device of claim 41, further comprising:

a processor that is configured to communicate with the array, the processor being configured to process image data; and

a memory device that is configured to communicate with the processor.

43. The display device of claim 42, further comprising a driver circuit configured to send at least one signal to the array.

44. The device of claim 43, further comprising a controller configured to send at least a portion of the image data to the driver circuit.

45. The device of claim 42, further comprising an image source module configured to send the image data to the processor.

46. The device of claim 45, wherein the image source module comprises at least one of a receiver, transceiver, and transmitter.

47. The device of claim 42, further comprising an input device configured to receive input data and to communicate the input data to the processor.

48. An unreleased interferometric display device, comprising:

a first electrode formed over a substrate;

a first sacrificial layer formed over at least a portion of the first electrode, the first sacrificial layer comprising a first sacrificial material;

a second sacrificial layer formed over at least a portion of the first sacrificial layer, wherein the second sacrificial layer comprises a treated variant of the first sacrificial material;

a second electrode formed over at least a portion of the second sacrificial layer; and

a plurality of supports between the first electrode and the second electrode situated to support the second electrode upon removal of the first sacrificial layer and the second sacrificial layer.

49. The unreleased interferometric display device of claim 48, wherein the treated variant comprises an oxidized variant.

50. The unreleased interferometric display device of claim 48, wherein the second sacrificial layer is substantially uniform in depth as measured substantially perpendicular to the substrate.

51. The unreleased interferometric display device of claim 48, wherein the first sacrificial layer comprises molybdenum.

52. The unreleased interferometric display device of claim 51, wherein the second sacrificial layer comprises molybdenum-oxide.

53. The unreleased interferometric display device of claim 48, wherein the overlying layer comprises a metal.

54. The unreleased interferometric display device of claim 53, wherein the metal comprises aluminum.

55. An interferometric display device, comprising:

first means for supporting at least a portion of the display device;

first means for reflecting light, the first reflecting means being at least partially reflective to light and at least partially transmissive to light and formed over the supporting means;

second means for reflecting light, the second reflecting means being at least partially reflective to light, the second reflecting means being movable and situated over the first reflecting means and being parallel to the first reflecting means, wherein the second reflecting means comprises a treated surface contour facing an interferometric cavity between the first reflecting means and the second reflecting means; and

second means for supporting the second reflecting means over the first reflecting means.

56. The display device of claim 55, wherein the first supporting means comprises a substrate.

57. The display device of claim 55, wherein the first reflecting means comprises an optical stack.

58. The display device of claim 55, wherein the second reflecting means comprises a movable reflective layer.

59. The display device of claim 55, wherein the second supporting means comprises support posts.

60. A method of depositing a silver-containing film, comprising:

treating a surface of an underlying layer to form a treated surface; and

depositing the silver-containing film on the treated surface;

wherein said treating reduces hillock formation in the silver-containing film.

61. The method of claim 60, wherein the hillock formation comprises heat-induced hillock formation.

62. The method of claim 60, wherein treating the surface of the underlying layer comprises exposing the surface to one or more of sulfur hexafluoride, oxygen and a plasma.

63. The method of claim 60, wherein treating the surface of the underlying layer comprises heating the surface.

64. The method of claim 60, further comprising heating the silver-containing film to an otherwise hillock-inducing temperature.

65. The method of claim 60, further comprising removing at least a portion of the underlying layer to thereby expose at least a portion of the silver-containing film previously in contact with the treated surface.

66. The method of claim 65, comprising removing the underlying layer before heating the silver-containing film to the otherwise hillock-inducing temperature.

67. The method of claim 60, wherein treating the surface of the underlying layer comprises smoothing the surface.