Sacrificial spacer process and resultant structure for MEMS support structure

• US 20080094686A1
• Filed: 10/19/2006
• Published: 04/24/2008
• Est. Priority Date: 10/19/2006
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: U'Ren, Gregory David
• Granted Patent: US 7,545,552 B2
• Time in Patent Office: Days
• US Class Current: 359/291
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81B 2203/0109 Bridges
• CPC Class Codes: B81B 2203/053 Translation according to an axis perpendicular to the substrate
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: B81C 2201/017 Methods for controlling internal stress of deposited layers not provided for in B81C2201/0164 - B81C2201/0169
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26

Abstract

Disclosed is a microelectromechanical systems (MEMS) device and method of manufacturing the same. MEMS such as an interferometric modulator include a sidewall spacer formed adjacent to a movable mirror. The sidewall spacer may be a sacrificial spacer that is removed during fabrication, or it may remain in the final product. Increased clearance is provided between the movable mirror and a support structure during actuation of the movable mirror, thereby avoiding contact during operation of the interferometric modulator. The deformable layer may be deposited in a more continuous fashion over the contour of a lower layer as determined by the contour of the sidewall spacer, resulting in a stronger and more resilient deformable layer.

Claims

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

forming a conductive layer over a first sacrificial layer;

patterning a movable conductor from the conductive layer;

forming a sidewall spacer on a sidewall of the movable conductor; and

forming a deformable layer over the movable conductor, wherein the deformable layer attaches to the movable conductor at one or more points.

2. The method of claim 1, wherein forming the sidewall spacer comprises depositing a blanket layer over the movable conductor and selectively removing portions of the blanket layer from horizontal surfaces.

3. The method of claim 2, wherein forming the blanket layer comprises chemical vapor deposition.

4. The method of claim 2, wherein selectively removing portions of the blanket layer comprises anisotropic dry etching.

5. The method of claim 2, wherein selectively removing portions of the blanket layer comprises selectively etching a material of the blanket layer relative to a material of the first sacrificial layer.

6. The method of claim 1, wherein the spacer forms a substantially convex up transition from a top of the movable conductor to the first sacrificial layer.

7. The method of claim 6, further comprising forming a second sacrificial layer over the spacer and the movable conductor prior to forming the deformable layer, wherein the second sacrificial layer comprises a convex up transition that substantially conforms to the convex up transition of the spacer.

8. The method of claim 7, further comprising:

forming a first opening in the first sacrificial layer and the second sacrificial layer; and

forming an oxide layer over the first opening, and the second sacrificial layer, wherein the oxide layer comprises a convex up transition that substantially conforms to the convex up transition of the second sacrificial layer.

9. The method of claim 8, further comprising patterning the oxide layer so as to form a support structure over the first opening, and wherein the convex up transition of the oxide layer remains after the patterning.

10. The method of claim 9, further comprising forming a second opening in the second sacrificial layer, wherein the second opening in the second sacrificial layer is over the movable conductor.

11. The method of claim 10, wherein forming the deformable layer comprises forming the deformable layer over the oxide layer, the second sacrificial layer and the second opening to attach to the movable conductor, wherein the deformable layer substantially conforms to the convex up transition of the oxide layer.

12. The method of claim 7, further comprising removing the second sacrificial layer after forming the deformable layer.

13. The method of claim 12, further comprising removing the spacer while removing the second sacrificial layer.

14. The method of claim 12, wherein the spacer remains after removing the second sacrificial layer.

15. The method of claim 1, wherein patterning the movable conductor results in a reentrant profile between the patterned edge of the movable conductor and the first sacrificial layer.

16. A method of making an interferometric modulator, comprising:

forming an electrode over a substrate, wherein the electrode is at least partially transparent;

forming a first sacrificial layer over the transparent electrode;

forming a reflective layer over the first sacrificial layer;

patterning a movable mirror from the reflective layer; and

forming a sacrificial spacer on a sidewall of the movable mirror.

17. The method of claim 16, wherein forming the spacer comprises depositing a blanket layer over the movable mirror and selectively removing portions of the blanket layer from horizontal surfaces.

18. The method of claim 16, wherein the spacer forms a substantially convex up transition from a top of the movable mirror to the first sacrificial layer.

19. The method of claim 18, further comprising:

forming a second sacrificial layer over the spacer and the movable mirror, wherein the second sacrificial layer substantially conforms to the convex up transition of the spacer; and

forming a deformable layer over the second sacrificial layer, wherein the deformable layer substantially conforms to the convex up transition of the spacer.

20. The method of claim 19, further comprising:

removing the second sacrificial layer after forming the deformable layer; and

removing the spacer while removing the second sacrificial layer.

21. The method of claim 19, further comprising removing the second sacrificial layer after forming the deformable layer, wherein the spacer remains after removing the second sacrificial layer.

22. The method of claim 16, wherein patterning the movable mirror results in a reentrant profile between the patterned edge of the movable mirror and the first sacrificial layer, and wherein the spacer substantially fills in the reentrant profile.

23. The method of claim 16, wherein the reflective layer comprises aluminum.

24. An interferometric modulator, comprising:

a substrate;

an optical stack over the substrate;

a deformable layer;

a plurality of support structures arranged over the substrate and configured to support the deformable layer;

a cavity defined by the optical stack, the support structures, and the deformable layer; and

a movable mirror disposed within the cavity, wherein the movable mirror is secured to the deformable layer, wherein a cavity ceiling spaced above an edge of the mirror comprises a step transitioning toward the substrate and defining a lower corner at the bottom of the step;

wherein a distance from a sidewall of the movable mirror to the lower corner of the ceiling step is more than 25 percent greater than a distance from an upper surface of the movable mirror to the cavity ceiling above the edge of the mirror when the interferometric modulator is in a relaxed condition.

25. The interferometric modulator of claim 24, wherein the sidewall of the movable mirror comprises a downward edge angle in a range from about 85 degrees to about 95 degrees.

26. The interferometric modulator device of claim 24, wherein the plurality of support structures and the deformable layer are formed from the same material.

27. The interferometric modulator device of claim 24, wherein the plurality of support structures comprise posts supporting the deformable layer on a lower surface of the deformable layer facing the substrate.

28. The interferometric modulator device of claim 24, wherein the plurality of support structures comprise rivets overlying the deformable layer in depressions defined by the deformable layer.

29. The interferometric modulator device of claim 24, wherein the movable conductor comprises aluminum.

30. The interferometric modulator device of claim 24, further comprising a sidewall spacer attached to the sidewall of the movable mirror, wherein the sidewall spacer comprises a substantially convex top surface away from the substrate.

31. The interferometric modulator device of claim 30, wherein the deformable layer conforms to the upwardly convex surface of the sidewall spacer.

32. The interferometric modulator device of claim 24, wherein the distance from the sidewall of the movable mirror to the lower corner of the ceiling step is about 50 percent to about 200 percent greater than the distance from the upper surface of the movable mirror to the cavity ceiling above the edge of the mirror when the interferometric modulator is in the relaxed condition.

33. The interferometric modulator device of claim 24, wherein the distance from the sidewall of the movable mirror to the lower corner of the ceiling step is about 0.3 μ

m to about 0.8 μ

m.

34. An array of interferometric modulators, comprising the interferometric modulator of claim 24.

35. A display device comprising:

an array of interferometric modulators as claimed in claim 34;

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.

36. The display device of claim 35, further comprising a driver circuit configured to send at least one signal to the array.

37. The apparatus as recited in claim 36, further comprising a controller configured to send at least a portion of the image data to the driver circuit.

38. The apparatus as recited in claim 35, further comprising an image source module configured to send the image data to the processor.

39. The apparatus as recited in claim 38, wherein the image source module comprises at least one of a receiver, transceiver, and transmitter.

40. The apparatus as recited in claim 35, further comprising an input device configured to receive input data and to communicate the input data to the processor.

41. A microelectromechanical systems (MEMS) device, comprising:

a substrate;

a deformable layer;

a plurality of support structures arranged over the substrate and configured to support the deformable layer;

a cavity defined by the substrate, the support structures, and the deformable layer; and

a movable conductor disposed within the cavity, wherein the movable conductor is secured to the deformable layer, and wherein the movable conductor comprises a side wall with an inward reentrant region;

wherein the deformable layer comprises an upwardly convex surface proximal to the inward reentrant region of the sidewall of the movable conductor.

42. The MEMS device of claim 41, wherein the plurality of support structures and the deformable layer are formed from the same material.

43. The MEMS device of claim 41, wherein the movable conductor comprises aluminum.

44. The MEMS device of claim 41, further comprising a sidewall spacer attached to the sidewall of the movable conductor, wherein the sidewall spacer comprises a substantially convex top surface away from the substrate.

45. The MEMS device of claim 44, wherein the upwardly convex surface of the deformable layer is of substantially the same shape as the convex top surface of the sidewall spacer.

46. An interferometric modulator, comprising the MEMS device of claim 41.

47. The interferometric modulator of claim 46, wherein a cavity ceiling spaced above an edge of the movable conductor comprises a step transitioning toward the substrate and defining a lower corner at the bottom of the step, and wherein a distance from the sidewall of the movable conductor to the lower corner of the ceiling step is about 50% to about 200% greater than a distance from an upper surface of the movable conductor to the cavity ceiling above the edge of the conductor when the interferometric modulator is in a relaxed condition.

48. The interferometric modulator of claim 46, wherein a cavity ceiling spaced above an edge of the movable conductor comprises a step transitioning toward the substrate and defining a lower corner at the bottom of the step, and wherein a distance from the sidewall of the movable conductor to the lower corner of the ceiling step is about 0.3 μ

m to about 0.8 μ

m.

49. An interferometric modulator comprising:

means for transmitting light;

means for reflecting light;

means for movably supporting the reflecting means and for providing a restoring force in response to a movement of the reflecting means towards or away from the transmitting means;

a cavity defined by the reflecting means and the supporting means, wherein the reflecting means is disposed within the cavity; and

means for horizontally spacing an edge of the supporting means more than a vertical distance between an upper surface of the reflecting means and a lower surface of the supporting means.

50. The interferometric modulator of claim 49, wherein the spacing means comprises a gap created by a removed sacrificial sidewall spacer on edges of the reflecting means.

51. The interferometric modulator of claim 49, wherein the spacing means comprises a sidewall spacer on edges of the reflecting means.

52. The interferometric modulator of claim 49, wherein the transmitting means comprises an optical stack.

53. The interferometric modulator of claim 49, wherein the reflecting means comprises a movable mirror.

54. The interferometric modulator of claim 49, wherein the supporting means comprises a deformable layer.