MEMS device having support structures configured to minimize stress-related deformation and methods for fabricating same

• US 7,747,109 B2
• Filed: 08/18/2006
• Issued: 06/29/2010
• Est. Priority Date: 08/19/2005
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Kogut, Lior, Zhong, Fan
• Primary Examiner(s): Le; Uyen-Chau N
• Assistant Examiner(s): TRAN, HOANG Q
• Application Number:
  US11/506,594
• Publication Number:
  US 20070041076A1
• Time in Patent Office: 1,411 Days
• Field of Search: 438/700, 385/1
• US Class Current: 385/1
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81B 2203/0163 Spring holders
• CPC Class Codes: B81B 2203/019 characterized by their profile
• CPC Class Codes: B81B 2203/0307 Anchors
• 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 1/00142 Bridges deformable micromirrors G02B26/0841
• CPC Class Codes: B81C 1/00666 Treatments for controlling internal stress or strain in MEMS structures
• CPC Class Codes: B81C 2201/0167 by adding further layers of materials having complementary strains, i.e. compressive or tensile strain
• 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
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: Y10S 359/90 Methods

Abstract

Embodiments of MEMS devices include a movable layer supported by overlying support structures, and may also include underlying support structures. In one embodiment, the residual stresses within the overlying support structures and the movable layer are substantially equal. In another embodiment, the residual stresses within the overlying support structures and the underlying support structures are substantially equal. In certain embodiments, substantially equal residual stresses are be obtained through the use of layers made from the same materials having the same thicknesses. In further embodiments, substantially equal residual stresses are obtained through the use of support structures and/or movable layers which are mirror images of one another.

Claims

1. A method of fabricating a MEMS device, comprising:

providing a substrate;

depositing an electrode layer over the substrate;

depositing a sacrificial layer over the electrode layer;

patterning the sacrificial layer to form apertures;

forming support structures at least partially within apertures in the sacrificial layer, wherein forming the support structure comprises depositing a layer of conformal support post material over the sacrificial layer and apertures, the support post having an internal residual stress; and

depositing a movable layer over the support structures after forming the support structures, wherein the movable layer comprises a material having an internal residual stress, and wherein the materials of the movable layer and the support structures are selected such that the residual stress in the movable layer is balanced by residual stress in the support structures such that deflection of the movable layer caused by the residual stresses is minimized.

2. The method of claim 1, additionally comprising etching the sacrificial layer to remove the sacrificial layer, thereby forming a cavity between the movable layer and the electrode layer.

3. The method of claim 1, wherein the support structures are formed over the movable layer.

4. The method of claim 1, wherein the coefficient of thermal expansion of the movable layer is substantially equal to the coefficient of thermal expansion of the support structures.

5. The method of claim 1, wherein the support structures and the movable layer comprise substantially the same material.

6. The method of claim 5, additionally forming an etch barrier layer over the movable layer between the support structures and the movable layer.

7. The method of claim 5, wherein forming the movable layer comprises:

forming a reflective sublayer; and

forming a mechanical sublayer over the reflective layer, wherein the reflective sublayer comprises a different material than the mechanical sublayer.

8. The method of claim 7, wherein forming the support structure comprises:

forming a first sublayer, wherein the first sublayer comprises the same material as the mechanical sublayer; and

forming a second sublayer, wherein the second sublayer comprises the same material as the reflective sublayer.

9. The method of claim 8, wherein the first sublayer is substantially the same thickness as the mechanical sublayer, and wherein the second sublayer is substantially the same thickness as the reflective sublayer.

10. The method of claim 8, wherein the thickness of the first sublayer is within 5% of the thickness of the mechanical sublayer, and wherein the thickness of the second sublayer is within 5% of the reflective sublayer.

11. The method of claim 9, wherein the first sublayer is formed over the second sublayer.

12. The method of claim 9, wherein the second sublayer is formed over the first sublayer.

13. The method of claim 6, additionally comprising forming a layer of partially reflective material over the substrate prior to forming the sacrificial layer.

14. The method of claim 6, wherein the MEMS device comprises an interferometric modulator.

15. A MEMS device fabricated by the method of claim 1.

40. The method of claim 1, wherein forming a support structure comprises forming a support structure having a horizontally extending wing portion on the outer edge of the support structure, wherein the horizontally extending wing portion is vertically spaced apart from the electrode layer by an air gap.

16. A MEMS device, comprising:

a substrate;

an electrode layer located over the substrate;

a movable layer located over the electrode layer, wherein the movable layer is generally spaced apart from the electrode layer by an air gap, wherein the movable layer comprises a reflective sublayer and a mechanical sublayer, the reflective sublayer on the side of the movable layer facing the electrode layer, and wherein the reflective sublayer comprises a different material than the mechanical sublayer; and

rigid support structures formed vertically adjacent the movable layer such that the support structures and the movable layer overlap one another within a support post region, wherein the support structures comprise a first sublayer comprising the same material as the mechanical sublayer and a second sublayer comprising the same material as the reflective sublayer, the first and second sublayers formed of different materials.

17. The MEMS device of claim 16, wherein the residual stress in the movable layer is substantially equal to the residual stress in the support structures.

18. The MEMS device of claim 16, wherein the coefficient of thermal expansion of the movable layer is substantially equal to the coefficient of thermal expansion of the support structures.

19. The MEMS device of claim 16, wherein the rigid support structures overlie the movable layer.

20. The MEMS device of claim 16, wherein the rigid support structures underlie the movable layer.

21. The MEMS device of claim 16, wherein the first sublayer is substantially the same thickness as the mechanical sublayer, and wherein the second sublayer is substantially the same thickness as the reflective sublayer.

22. The method of claim 16, wherein the thickness of the first sublayer is within 5% of the thickness of the mechanical sublayer, and wherein the thickness of the second sublayer is within 5% of the reflective sublayer.

23. The MEMS device of claim 16, wherein the first sublayer is located over the second sublayer.

24. The MEMS device of claim 16, wherein the second sublayer is located over the first sublayer.

25. The MEMS device of claim 16, additionally comprising a partially reflective layer located on the same side of the air gap as the electrode layer.

26. The MEMS device of claim 16, wherein the MEMS device comprises an interferometric modulator.

27. The MEMS device of claim 16, additionally comprising:

a processor that is configured to communicate with at least one of said electrode layer and said movable layer, said processor being configured to process image data; and

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

28. The MEMS device of claim 27, further comprising a driver circuit configured to send at least one signal to at least one of said electrode layer and said movable layer.

29. The MEMS device of claim 28, further comprising a controller configured to send at least a portion of the image data to the driver circuit.

30. The MEMS device of claim 27, further comprising an image source module configured to send said image data to said processor.

31. The MEMS device of claim 30, wherein the image source module comprises at least one of a receiver, transceiver, and transmitter.

32. The MEMS device of claim 27, further comprising an input device configured to receive input data and to communicate said input data to said processor.

33. The device of claim 16, wherein the second sublayer and the reflective sublayer comprise aluminum.

34. The device of claim 16, wherein the first sublayer and the mechanical sublayer comprise nickel.

35. An electromechanical device, comprising:

a substrate;

an electrode layer located over the substrate;

a plurality of rigid support structures each comprising a first sublayer of a first material and a second sublayer of a second material, the first and second materials being different from one another; and

a movable layer extending over at least a portion of the rigid support structures, wherein the movable layer is generally spaced apart from the electrode layer by an air gap, wherein the movable layer comprises a reflective sublayer and a mechanical sublayer, the reflective sublayer on the side of the movable layer facing the electrode layer, wherein the reflective sublayer comprises the first material and the mechanical sublayer comprises the second material.

36. The electromechanical device of claim 35, wherein the first sublayer of the rigid support structure directly overlies the second sublayer of the rigid support structure.

37. The electromechanical device of claim 35, wherein the second sublayer of the rigid support structure directly overlies the first sublayer of the rigid support structure.

38. The electromechanical device of claim 35, wherein the first material comprises aluminum.

39. The electromechanical device of claim 35, wherein the second material comprises nickel.