Method for fabricating micromachined members coupled for relative rotation

• US 6,426,013 B1
• Filed: 10/28/1999
• Issued: 07/30/2002
• Est. Priority Date: 10/18/1993
• Status: Expired due to Fees

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Xros, Inc. (Nortel Networks Corporation)
• Inventors: Slater, Timothy G., Neukermans, Armand P.
• Primary Examiner(s): DANG, THI D
• Application Number:
  US09/428,946
• Time in Patent Office: 1,006 Days
• Field of Search: 216/24, 438/52, 438/48
• US Class Current: 216/24
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 26/085 the reflecting means being moved or deformed by electromagnetic means
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129

Abstract

A method for fabricating an integrated, micromachined structure, such as a torsional scanner, that includes a reference member, such as a frame, a pair of torsion hinges, and a dynamic member that is coupled to the reference member by the torsion hinges. The method includes providing a wafer that has been formed from silicon material, and that has both a frontside and a backside. A membrane is formed in the wafer by etching a cavity in the silicon material from the backside of the wafer. The method also includes establishing a pattern that defines the mirror surface and the torsion hinges on the frontside of the wafer at the membrane formed therein. The frontside of the wafer is processed to form therein the dynamic member and the torsion hinges that support the dynamic member for rotation about the axis.

Claims

1. A micromachining method for fabricating a torsional scanner that includes:

a micromachined mirror having a mirror surface; and

a pair of hinges each having ends that are joined to the micromachined mirror, the hinges supporting said micromachined mirror for rotation about an axis;

the micromachining method for forming the torsional scanner comprising the steps of;

providing a wafer that has been formed from silicon material, and that has both a frontside and a backside;

forming a membrane in the wafer by etching a cavity in the silicon material of the backside of the wafer;

establishing a pattern that defines the mirror surface and the hinges on the frontside of the wafer at the membrane formed therein; and

forming in the frontside of the wafer the mirror surface and the hinges whereby the hinges support said micromachined mirror for rotation about the axis.

2. The micromachining method for making the torsional scanner of claim 1 wherein the wafer provided includes a single crystal epitaxial layer forming the frontside of wafer in which the mirror surface and the hinges are formed.

3. The micromachining method for making the torsional scanner of claim 2 wherein the epitaxial layer has a thickness of one micron to tens of microns.

4. The micromachining method for making the torsional scanner of claim 2 wherein the epitaxial layer is provided in a Simox wafer.

5. The micromachining method for making the torsional scanner of claim 1 wherein the wafer includes a silicon dioxide layer that is located between the frontside of the wafer and the backside thereof.

6. The micromachining method for making the torsional scanner of claim 5 wherein the silicon dioxide layer has a thickness of about two-thousand (2,000) angstroms (“

Å

”

).

7. The micromachining method for making the torsional scanner of claim 5 wherein the silicon dioxide layer is provided in a Simox wafer.

8. The micromachining method for making the torsional scanner of claim 1 further comprising the step of providing drive means for communicating a reciprocating torsional force to the micromachined mirror to thereby permit establishing oscillatory rotary motion of the micromachined mirror about the axis.

9. A micromachining method for fabricating an integrated, micromachined structure that includes:

a reference member;

a pair of hinges projecting from said reference member;

a dynamic member that is coupled by said hinges to said reference member to be thereby supported from said reference member for rotation about an axis;

the micromachining method for forming the micromachined structure comprising the steps of;

providing a wafer that has been formed from silicon material, and that has both a frontside and a backside;

forming a membrane in the wafer by etching a cavity in the silicon material of the backside of the wafer;

establishing a pattern that defines the mirror surface and the hinges on the frontside of the wafer at the membrane formed therein; and

forming in the frontside of the wafer the dynamic member and the hinges whereby the hinges support said dynamic member for rotation about the axis.

10. The micromachining method for making the micromachined structure of claim 9 wherein the wafer provided includes a single crystal epitaxial layer forming the frontside of wafer in which the dynamic member and the hinges are formed.

11. The micromachining method for making the micromachined structure of claim 10 wherein the epitaxial layer has a thickness of one micron to tens of microns.

12. The micromachining method for making the micromachined structure of claim 10 wherein the epitaxial layer is provided in a Simox wafer.

13. The micromachining method for making the micromachined structure of claim 9 wherein the wafer includes a silicon dioxide layer that is located between the frontside of the wafer and the backside thereof.

14. The micromachining method for making the micromachined structure of claim 13 wherein the silicon dioxide layer has a thickness of about two-thousand (2,000) Å

.

15. The micromachining method for making the micromachined structure of claim 13 wherein the silicon dioxide layer is provided in a Simox wafer.

16. The micromachining method for making the micromachined structure of claim 9 further comprising the step of providing drive means for communicating a reciprocating torsional force to the dynamic member to thereby permit establishing oscillatory rotary motion of the dynamic member about the axis.

17. A method for fabricating an integrated, micromachined structure that includes:

a reference member;

a pair of torsion hinges projecting from the reference member; and

a dynamic member that is coupled by the torsion hinges to the reference member to be thereby supported from the reference member for rotation about an axis with respect to the reference member;

the method for forming the micromachined structure comprising the steps of;

providing as starting material a first wafer having both a top layer and a base layer that are separated by an etch stop layer;

etching from a backside of the first wafer a cavity into the base layer which extends to the etch stop layer;

patterning the top layer to define the dynamic member, the torsion hinges and the reference member thereby exposing a region of the etch stop layer; and

removing at least enough of the exposed region of the etch stop layer so the dynamic member is supported from the reference member by the torsion hinges and is free to rotate about an axis with respect to the reference member.

18. The method of claim 17 further comprising the step of coating the dynamic member with metal for enhanced reflectivity thereby adapting the micromachined structure for use as a torsional scanner.

19. The method of claim 18 wherein both sides of the dynamic member are coated with metal.

20. The method of claim 18 wherein the dynamic member is coated with metal after the dynamic member is supported from the reference member by the torsion hinges and is free to rotate about an axis with respect to the reference member.

21. The method of claim 17 further comprising the step of placing at least three contact pads along at least one of the torsion hinges to establish a torsion sensor thereon.

22. The method of claim 21 further comprising the step of doping the top layer of the first wafer to restrict electrical current in the torsion sensor to the top few microns of the torsion hinge.

23. The method of claim 17 wherein the dynamic member has a thickness equal to the torsion hinges.

24. The method of claim 17 wherein the dynamic member has a thickness determined by the top layer.

25. The method of claim 17 wherein the dynamic member has a thickness equal to that of the first wafer.

26. The method of claim 17 wherein the dynamic member has a thickness a fraction of that of the first wafer.

27. The method of claim 17 wherein the torsion hinges have a thickness equal to that of the top layer.

28. The method of claim 17 wherein the torsion hinges have a thickness unequal to that of the top layer.

29. The method of claim 17 wherein the first wafer about a center of the dynamic member is mostly etched away.

30. The method of claim 29 wherein etching about the center of the dynamic member produces a box frame structure.

31. The method of claim 17 wherein the torsion hinges have rounded corners.

32. The method of claim 31 wherein the rounded corners have a radius at least equal to a thickness of the torsion hinges.

33. The method of claim 31 wherein the round ed corners have a radius near a width of the torsion hinges.

34. The method of claim 17 further comprising the step of hardening a surface of the torsion hinges.

35. The method of claim 34 wherein the surface of the torsion hinges is hardened by exposure to ammonia at an elevated temperature.

36. The method of claim 34 wherein the surface of the torsion hinges is hardened by exposure to hydrocarbons at an elevated temperature.

37. The method of claim 34 wherein the surface of the torsion hinges is hardened by conversion into silicon carbide.

38. The method of claim 34 wherein the surface of the torsion hinges is hardened by conversion into silicon nitride.

39. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein material forming the etch stop layer is silicon dioxide.

40. The method of claim 39 wherein the first wafer is a Simox wafer.

41. The method of claim 39 wherein the first wafer is a silicon on insulator (“

SOI”

) wafer.

42. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein a junction between two layers of differently doped silicon forms the etch stop layer, and wherein the cavity is electrolytically etched from the backside of the first wafer.

43. The method of claim 42 wherein the top layer of the first wafer provided as starting material has n-type doping, and the base layer thereof has p-type doping.

44. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein material forming the top layer is single crystal silicon.

45. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein the top layer is an epitaxial layer.

46. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein etching to form the cavity includes exposing the backside to an anisotropic etchant.

47. The method of claim 46 wherein the anisotropic etchant is ethylene diamine/pyrocatechol/water (“

EDP”

or “

EPW”

).

48. The method of claim 46 wherein the anisotropic etchant is potassium hydroxide/water (“

KOH”

).

49. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form straight walled torsion hinges includes reactive ion etching.

50. The method of claim 49 wherein reactive ion etching is performed using chlorine.

51. The method of claim 49 wherein reactive ion etching is performed using fluorine.

52. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form trapezoidal cross-section torsion hinges includes exposing the top layer to an anisotropic etchant.

53. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the torsion hinges includes exposing the top layer to an isotropic etchant.

54. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the dynamic member includes reactive ion etching.

55. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the dynamic member includes exposing the top layer to an anisotropic etchant.

56. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the dynamic member includes exposing the top layer to an isotropic etchant.

57. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the reference member includes reactive ion etching.

58. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the reference member includes exposing the top layer to an anisotropic etchant.

59. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein patterning the top layer to form the reference member includes exposing the top layer to an isotropic etchant.

60. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38, wherein to provide a dust cover for shielding the dynamic member from environmental contamination, further comprises the steps of:

providing as starting material a second wafer;

forming a layer of etch resistant material on a frontside of the second wafer;

etching from a backside of the second wafer a cavity which extends through the second wafer to the etch stop layer to thereby establish with the second wafer the dust cover;

joining the dust cover to the micromachined structure.

61. The method of claim 60 wherein silicon nitride forms the layer of etch resistant material.

62. The method of claim 60 wherein silicon carbide forms the layer of etch resistant material.

63. The method of claim 60 wherein boron nitride forms the layer of etch resistant material.

64. The method of claim 60 wherein the dust cover is joined to the micromachined structure using anodic bonding.

65. The method of claim 60 wherein the dust cover is joined to the micromachined structure in a vacuum environment that the joined dust cover and micromachined structure thereafter maintain about the dynamic member.

66. The method of claim 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 2728, 29, 30, 31, 32, 33, 34, 35, 36, 37 or 38 wherein stress free material forms the top layer of the first wafer whereby the dynamic member, after patterning the top layer and being freed from the reference member by removing the etch stop layer to permit rotation about an axis with respect to the reference member, is flat.

67. The method of claim 21 or 22 wherein during pattering of the top layer the torsion hinges are oriented with respect to material forming the top layer for optimal shear stress and for near insensitivity to uniaxial strains.

68. The method of claim 67 wherein the top layer is n-type silicon and the torsion hinges are aligned in the <

110>

direction.

69. The method of claim 67 wherein the top layer is p-type silicon and the torsion hinges are aligned in the <

100>

direction.