Methods for etching layers within a MEMS device to achieve a tapered edge

• US 20080218840A1
• Filed: 08/18/2006
• Published: 09/11/2008
• Est. Priority Date: 08/19/2005
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Zee, Stephen, Wang, Chun-Ming, Sasagawa, Teruo, Tung, Ming-Hau, Qui, Chengin
• Granted Patent: US 7,660,058 B2
• Time in Patent Office: Days
• US Class Current: 359/276
• 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

Certain MEMS devices include layers patterned to have tapered edges. One method for forming layers having tapered edges includes the use of an etch leading layer. Another method for forming layers having tapered edges includes the deposition of a layer in which the upper portion is etchable at a faster rate than the lower portion. Another method for forming layers having tapered edges includes the use of multiple iterative etches. Another method for forming layers having tapered edges includes the use of a liftoff mask layer having an aperture including a negative angle, such that a layer can be deposited over the liftoff mask layer and the mask layer removed, leaving a structure having tapered edges.

Claims

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

forming an electrode layer;

forming a mask over the electrode layer;

patterning the electrode layer using the mask to form an isolated electrode member; and

tapering the electrode member to form an outwardly tapering edge portion, wherein at least a portion of the mask remains in place during the tapering.

2. The method of claim 1, wherein patterning the electrode layer and tapering the electrode member comprise a single etching process, and wherein the mask remains in place during the etching process.

3. The method of claim 1, additionally comprising forming an etch leading layer over the electrode layer, wherein the etch leading layer is formed between the mask and the electrode layer.

4. The method of claim 3, wherein tapering the electrode member comprises etching the electrode member using an etch which etches the etch leading layer at a greater rate than the electrode member.

5. The method of claim 3, wherein tapering the electrode member comprises:

etching a portion of the etch leading layer with a first etch which does not significantly etch the electrode member; and

subsequently etching the electrode member to form the outwardly tapering edge portion.

6. The method of claim 3, additionally comprising forming a sacrificial layer prior to deposition of the electrode layer, wherein the electrode layer is formed over the sacrificial layer.

7. The method of claim 6, wherein the etch leading layer is etchable by an etch which etches the sacrificial layer.

8. The method of claim 7, wherein tapering the electrode member further comprises:

etching a portion of the etch leading layer and the electrode member by a first etch which is non-selective between to the etch leading layer and the electrode member, wherein the first etch does not expose the first sacrificial layer; and

etching a portion of the electrode member by a second etch which is selective with respect to the etch leading layer, wherein the second etch exposes a portion of the first sacrificial layer.

9. The method of claim 8, further comprising:

removing the mask overlying the etch leading layer after performing the second etch; and

removing the etch leading layer via a third etch.

10. The method of claim 9, wherein the third etch is selective with respect to the electrode layer.

11. The method of claim 1, wherein forming the electrode layer comprises forming the electrode layer with varying properties over the thickness of the layer.

12. The method of claim 11, wherein forming the electrode layer having varying properties over the thickness of the layer comprises varying process conditions during deposition of the electrode layer.

13. The method of claim 11, wherein forming the electrode layer having varying properties over the thickness of the layer comprises:

depositing a first sublayer over the first sacrificial layer; and

depositing at least a second sublayer over the first sublayer, wherein the second sublayer is etchable by an etchant used in the tapering at a greater rate than the first sublayer.

14. The method of claim 1, wherein forming a mask over the electrode layer comprises depositing a mask having poor adhesion to the electrode layer.

15. The method of claim 1, wherein tapering the electrode member comprises:

etching an exposed portion of the electrode layer;

removing a portion of the mask, thereby exposing an additional portion of the electrode layer; and

etching the exposed portion of the electrode layer and the additional portion exposed by removal of a portion of the mask.

16. The method of claim 15, wherein removing the portion of the mask comprises partially ashing the mask.

17. The method of claim 15, additionally comprising forming an etch stop layer underneath the electrode layer.

18. The method of claim 1, additionally comprising:

forming a lower electrode layer over a substrate;

forming a first sacrificial layer over the lower electrode layer, wherein the isolated electrode member is formed over the first sacrificial layer.

19. The method of claim 18, additionally comprising:

forming a second sacrificial layer over the isolated electrode member;

pattering said second sacrificial layer to expose a portion of the isolated electrode member; and

forming a mechanical layer over the second sacrificial layer and the exposed portion of the isolated electrode member.

20. The method of claim 18, additionally comprising removing said first sacrificial layer, forming an air gap located between the lower electrode layer and the isolated electrode member.

21. The method of claim 1, wherein forming the electrode layer comprises forming a reflective layer having a substantially flat lower surface.

22. The method of claim 1, wherein the MEMS device is an interferometric modulator.

23. A MEMS device formed by the method of claim 1.

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

forming a sacrificial layer over a substrate;

patterning the sacrificial layer to form apertures;

forming a support layer over the patterned sacrificial layer;

forming a mask over the support layer;

patterning the support layer using the mask to form at least one support structure located at least partially within the aperture in the sacrificial layer; and

tapering the support structure to form a tapered edge, wherein at least a portion of the mask remains in place during the tapering.

25. The method of claim 24, wherein patterning the support layer and tapering the support structure comprise a single etching process, and wherein the mask remains in place during the etching process.

26. The method of claim 24, additionally comprising forming an etch leading layer over the support layer, wherein the etch leading layer is formed between the mask and the support layer.

27. The method of claim 26, wherein tapering the support structure comprises using an etch which etches the etch leading layer at a greater rate than the support structure.

28. The method of claim 26, wherein tapering the support structure comprises:

etching a portion of the etch leading layer using a first etch which does not significantly etch the support structure; and

subsequently etching the support layer to form the at least support structure.

29. The method of claim 24, wherein forming the support layer comprises forming a support layer having varying properties over the thickness of the layer.

30. The method of claim 29, wherein forming the support layer having varying properties over the thickness of the layer comprises varying process conditions during deposition of the support layer.

31. The method of claim 29, wherein forming the support layer having varying properties over the thickness of the support layer comprises:

depositing a first sublayer over the sacrificial layer; and

depositing at least a second sublayer over the first sublayer, wherein the second sublayer is etchable by an etchant used during the tapering at a greater rate than the first sublayer.

32. The method of claim 24, wherein forming a mask over the support layer comprises depositing a mask having poor adhesion to the support layer.

33. The method of claim 24, wherein tapering the support structure comprises:

etching an exposed portion of the support layer;

removing a portion of the mask, exposing an additional portion of the support structure; and

etching the exposed portion and the additional portion exposed by removal of a portion of the mask.

34. The method of claim 33, wherein removing a portion of the mask comprises partially ashing the mask.

35. The method of claim 33, additionally comprising forming an etch stop layer between the sacrificial layer and the support layer.

36. The method of claim 24, additionally comprising forming a movable layer adjacent the at least one support structure

37. The method of claim 36, wherein the movable layer is formed after deposition of the layer of support material and is formed over the at least one support structure.

38. The method of claim 36, wherein forming the movable layer comprises:

forming a reflective sublayer over the sacrificial layer; and

forming a mechanical sublayer over the reflective sublayer

39. The method of claim 24, additionally comprising performing a release etch to remove the sacrificial layer, forming an air gap located between the movable layer and the substrate.

40. The method of claim 24, additionally comprising forming a lower electrode layer over the substrate prior to deposition of the sacrificial layer, wherein the sacrificial layer is formed over the lower electrode layer

41. The method of claim 24, wherein the MEMS device is an interferometric modulator.

42. A MEMS device formed by the method of claim 24.