Single crystal, tunneling and capacitive, three-axes sensor using eutectic bonding and a method of making same

• US 20040048403A1
• Filed: 08/11/2003
• Published: 03/11/2004
• Est. Priority Date: 08/01/2000
• Status: Active Grant

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Kubena, Randall L., Chang, David T.
• Granted Patent: US 6,835,587 B2
• Time in Patent Office: Days
• US Class Current: 438/22
• CPC Class Codes: B81B 2201/0242 Gyroscopes
• CPC Class Codes: B81B 2201/025 Inertial sensors not provided for in B81B2201/0235 - B81B2201/0242
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers
• CPC Class Codes: B81C 2203/036 Fusion bonding
• CPC Class Codes: B81C 2203/058 Aligning components using methods not provided for in B81C2203/051 - B81C2203/052
• CPC Class Codes: B81C 3/002 Aligning microparts
• CPC Class Codes: G01C 19/5656 the devices involving a micromechanical structure
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/0894 by non-contact electron transfer, i.e. electron tunneling
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape
• CPC Class Codes: H01H 1/0036 Switches making use of microelectromechanical systems [MEMS] for electromagnetic relays H01H50/005; for electrostatic relays H01H59/0009
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

A three axis MEM tunneling/capacitive sensor and method of making same. Cantilevered beam structures for at least two orthogonally arranged sensors and associated mating structures are defined on a first substrate or wafer, the at least two orthogonally arranged sensors having orthogonal directions of sensor sensitivity. A resonator structure of at least a third sensor is also defined, the third sensor being sensitive in a third direction orthogonal to the orthogonal directions of sensor sensitivity of the two orthogonally arranged sensors and the resonator structure having a mating structure thereon. Contact structures for at least two orthogonally arranged sensors are formed together with mating structures on a second substrate or wafer, the mating structures on the second substrate or wafer being of a complementary shape to the mating structures on the first substrate or wafer. The mating structures of the first substrate are disposed in a confronting relationship with the mating structures of the second substrate or wafer. A eutectic bonding layer associated with one of the mating structures facilitates bonding between the respective mating structures. At least a portion of the first substrate or wafer is removed to release the cantilevered beam structures and the resonator structure.

Claims

1. A method of making a three axis MEM tunneling/capacitive sensor comprising the steps of:

(a) defining cantilevered beam structures for at least two orthogonally arranged sensors and associated mating structures on a first substrate or wafer, the at least two orthogonally arranged sensors having orthogonal directions of sensor sensitivity;

(b) forming a resonator structure of at least a third sensor on the first substrate or wafer, the third sensor being sensitive in a third direction orthogonal to both directions of sensor sensitivity of the two orthogonally arranged sensors, the resonator structure having a mating structure thereon;

(c) forming contact structures for at least two orthogonally arranged sensors and forming mating structures on a second substrate or wafer, the mating structures on the second substrate or wafer being of a complementary shape to the mating structures on the first substrate or wafer;

(d) positioning the mating structures of the first substrate into a confronting relationship with the mating structures of the second substrate or wafer;

(e) eutecticly bonding a layer associated with said mating structures on the first substrate or wafer with a layer associated with the mating structures on the second substrate or wafer;

(f) removing at least a portion of the first substrate or wafer to release the cantilevered beam structures and the plate structure.

2. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 1 wherein the second substrate or wafer is formed of silicon.

3. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 2 wherein the silicon forming the second substrate or wafer is of a single crystalline structure.

4. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 3 wherein the crystalline structure of the silicon is <

100>

.

5. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 4 wherein the silicon is n-type.

6. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 1 wherein the first substrate or wafer is formed of silicon.

7. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 6 wherein the silicon forming the first substrate or wafer is of a single crystalline structure.

8. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 7 wherein the crystalline structure of the silicon in the first substrate or wafer is <

100>

.

9. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 8 wherein the silicon of the first substrate or wafer is n-type.

10. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 1 wherein heat is applied together with pressure between the two substrates so as to cause the eutectic bond to occur between the two mating structures.

11. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 1 wherein the two orthogonally arranged sensors are tunneling rotation rate gyros.

12. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 1 wherein the resonator structure forms the coriocis tranduction element for a capacitive rotation rate gyro.

13. A method of making a three axis MEM tunneling/capacitive sensor as claimed in claim 1 wherein the cantilevered beams and resonator structures are formed by:

(a) forming an epitaxial layer of silicon on said first substrate or wafer, said epitaxial layer being doped;

(b) masking and etching the epitaxial layer of silicon to define a beam structure disposed on said first substrate or wafer; and

(c) removing the first substrate or wafer by etching.

14. A method of making a three axis MEM tunneling sensor as claimed in claim 13 wherein a contact is formed on an end of said beam structure by depositing a metal through a small opening in a temporary mask layer, the small opening being sufficiently small that the metal being deposited tends to overhang the small opening increasingly as the deposition of the metal proceeds whereby the contact being deposited through the small opening assumes an elongate shape of decreasing cross section as the deposition proceeds.

15. A method of making a three axis MEM tunneling sensor as claimed in claim 13 wherein the epitaxial layer is doped with boron at a sufficient concentration to reduce the resistivity of the epitaxial layer to less than 0.05 Ω

-cm.

16. A method of making a three axis MEM tunneling sensor as claimed in claim 15 wherein etching accomplished by ethylenediamine pyrocatechol as an etchant.

17. A method of making a three axis MEM tunneling sensor as claimed in claim 16 wherein a layer of metal, preferably Ti/Pt/Au, is selectively deposited on said epitaxial layer and sintered at an elevated temperature to form first and second ohmic contacts on said epitaxial layer, said second ohmic contact being disposed near a distal end of the beam structure and the first ohmic contact forming the mating structure on the first substrate.

18. A method of making a three axis MEM tunneling sensor as claimed in claim 17 wherein a relatively thick layer of metal, preferably Ti/Pt/Au, is deposited on the sintered and relatively thin metal layer, preferably Ti/Pt/Au, a first portion of the relatively thick layer of metal forming the mating structure on the first substrate and overlying said first ohmic contact and a second portion of the relatively thick layer of metal forming a pointed contact at said second ohmic contact.

19. A method of making a three axis MEM tunneling sensor as claimed in claim 18 further including forming Ti/Pt/Au contacts on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining the mating structure on the second substrate or wafer.

20. A method of making a three axis MEM tunneling sensor as claimed in claim 19 wherein the layer for producing an eutectic bond is provided by a layer of Au—

Si eutectic deposited on the Ti/Pt/Au contact on said second substrate and/or by a layer of Au—

Si eutectic deposited on first portion of the relatively thick layer of Ti/Pt/Au on the first substrate or wafer.

21. A method of making a three axis MEM tunneling sensor as claimed in claim 16 wherein a layer of Ti/Pt/Au is selectively deposited on said epitaxial layer and sintered at an elevated temperature to form first and second ohmic contacts on said epitaxial layer, said second ohmic contact being disposed near a distal end of the beam structure and said first ohmic contact forming the mating structure on the first substrate.

22. A method of making a three axis MEM tunneling sensor as claimed in claim 18 further including forming a protruding portion which protrudes from a major surface of said second substrate or wafer.

23. A method of making a three axis MEM tunneling sensor as claimed in claim 22 further including forming Ti/Pt/Au contacts on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining, in combination with the protruding portion, the mating structure on the second substrate or wafer.

24. A method of making a three axis MEM tunneling sensor as claimed in claim 23 wherein the eutectic layer is provided by a layer of Au—

Si eutectic deposited on the Ti/Pt/Au contact on said second substrate and/or by a layer of Au—

Si eutectic deposited on first ohmic contact on the first substrate or wafer.

25. A method of making a three axis MEM tunneling sensor as claimed in claim 22 wherein silicon for the eutectic bond is provided by the silicon substrate of the second substrate or w at the mating structure.

26. A method of making a three axis MEM tunneling sensor as claimed in claim 15 where layer of Ti/Pt/Au is selectively deposited on said epitaxial layer to form first and second interconnected contacts on said epitaxial layer, the contacts being interconnected by an elongate ribbon layer of Ti/Pt/Au, said second interconnected contact being disposed near a distal end of the beam structure, the elongate ribbon being disposed longitudinally on the beam structure preferably substantially narrower than the cantilever beam structure, said first interconnected contact forming the mating structure on the first substrate.

27. A method of making a three axis MEM tunneling sensor as claimed in claim 25 further including forming a protruding portion which protrudes from a major surface of said second substrate or wafer.

28. A method of making a three axis MEM tunneling sensor as claimed in claim 27 further including forming Ti/Pt/Au contacts on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining, in combination with the protruding portion, the mating structure on the second substrate or wafer.

29. A method of making a three axis MEM tunneling sensor as claimed in claim 28 wherein the eutectic layer is provided by a layer of Au—

Si eutectic deposited on the Ti/Pt/Au contact on said second substrate and/or by a layer of Au—

Si eutectic deposited on first interconnected contact on the first substrate or wafer.

30. A method of making a three axis MEMS tunneling sensor as claimed in claim 27 wherein silicon for the eutectic bond is provided by the silicon substrate of the second substrate or wafer at the mating structure.

31. A method of making a three axis MEMS tunneling/capacitive sensor as claimed in claim 13 wherein a center post in resonator structure is bonded to the mating structure on the second substrate or wafer.

32. A method of a making a three axis MEM tunneling/capacitive sensor as claimed in claim 13 wherein an outer frame of the resonator structure is bonded to the mating structure on the second substrate or wafer.

33. A method of making a MEM tunneling sensor as claimed in claim 1 wherein the cantilevered beams and resonator structures are formed by:

(a) forming a etch stop layer on said first substrate or wafer,

(a) forming an epitaxial layer of silicon on said etch stop layer, said epitaxial layer being undoped or lightly doped;

(b) masking and etching the epitaxial layer of silicon to define a beam structure disposed adjacent said first substrate or wafer;

(c) removing the first substrate or wafer by use of an etchant to which said etch stop layer is resistant; and

(d) removing said etch stop layer using an etchant to which said cantilevered beam structure is resistant.

34. A method of making a three axis MEM tunneling sensor as claimed in claim 33 wherein a layer of Ti/Pt/Au is selectively deposited on said epitaxial layer to form first and second metal contacts on said epitaxial layer, said second contact being disposed near a distal end of said beam structure and said first contact forming the mating structure on the first substrate.

78. A three axis MEM tunneling/capacitive sensor as claimed in claim 1 in which a third wafer is bonded to the top of the sensor in a vacuum to vacuum seal the sensor.

35. A three axis MEM tunneling sensor assembly for making a three axis MEM tunneling sensor therefrom, the assembly comprising:

(a) orthogonally arranged beam structures, a resonator structure and associated mating structures defined on a first substrate or wafer;

(b) contact structures and mating structures defined on a second substrate or wafer, the mating structures on the second substrate or wafer being of a complementary shape to the mating structures on the first substrate or wafer; and

(c) a pressure/heat sensitive bonding layer disposed on said mating structures on at least one of said first and second substrates or wafers for bonding the mating structures defined on the first substrate or wafer to mating structures on the second substrate in response to the application of pressure/heat therebetween.

36. A three axis MEM tunneling sensor assembly as claimed in claim 35 wherein the second substrate or wafer is formed of silicon.

37. A three axis MEM tunneling sensor assembly as claimed in claim 36 wherein the silicon forming the second substrate or wafer of a single crystalline structure.

38. A three axis MEM tunneling sensor assembly as claimed in claim 37 wherein the crystalline structure of the silicon is <

100>

.

39. A three axis MEM tunneling sensor assembly as claimed in claim 38 wherein the silicon is n-type.

40. A three axis MEM tunneling sensor assembly as claimed in claim 35 wherein the first substrate or wafer is formed of silicon.

41. A three axis MEM tunneling sensor assembly as claimed in claim 40 wherein the silicon forming the first substrate or wafer of a single crystalline structure.

42. A three axis MEM tunneling sensor assembly as claimed in claim 41 wherein the crystalline structure of the silicon in the first substrate or wafer is <

100>

.

43. A three axis MEM tunneling sensor assembly as claimed in claim 42 wherein the silicon of the first substrate or wafer is n-type silicon.

44. A three axis MEM tunneling sensor assembly as claimed in claim 35 wherein the cantilevered beam and resonator structures are formed from an epitaxial layer of silicon on said first substrate or wafer, said epitaxial layer being doped with a dopant.

45. A three axis MEM tunneling sensor assembly as claimed in claim 44 wherein a pointed contact is disposed on an end of said beam structure.

46. A three axis MEM tunneling sensor assembly as claimed in claim 44 wherein the epitaxial layer is doped with Boron at a sufficient concentration to reduce the resistivity of the epitaxial layer to less than less than 0.05 Ω

-cm.

47. A three axis MEM tunneling sensor assembly as claimed in claim 46 further including first and second ohmic Ti/Pt/Au contacts on said epitaxial layer, said second ohmic contact being disposed near a distal end of the beam structure and said first ohmic contact forming the mating structure on the first substrate or wafer.

48. A three axis MEM tunneling sensor assembly as claimed in claim 47 wherein a relatively thick layer of Ti/Pt/Au is disposed on the first and second ohmic Ti/Pt/Au contacts, a first portion of the relatively thick layer of Ti/Pt/Au being disposed on said first ohmic Ti/Pt/Au contact and providing the mating structure on the first substrate and a second portion of the relatively thick layer of Ti/Pt/Au forming a pointed contact on said second ohmic Ti/Pt/Au contact.

49. A three axis MEM tunneling sensor assembly as claimed in claim 48 further including Ti/Pt/Au contacts disposed on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining the mating structure on the second substrate or wafer.

50. A three axis MEM tunneling sensor assembly as claimed in claim 49 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the Ti/Pt/Au contact on said second substrate and/or by a layer of Au—

Si eutectic disposed on the first portion of the relatively thick layer of Ti/Pt/Au on the first substrate or wafer.

51. A three axis MEM tunneling sensor assembly as claimed in claim 49 wherein the silicon for the eutectic bond is provided by the silicon substrate of the first or second wafers at the mating structure.

52. A three axis MEM tunneling sensor assembly as claimed in claim 46 further including first and second ohmic contacts on said epitaxial layer, said second ohmic contact being disposed near a distal end of the beam structure and said first ohmic contact forming the mating structure on the first substrate.

53. A three axis MEM tunneling sensor assembly as claimed in claim 52 further including a protruding portion which protrudes from a major surface of said second substrate or wafer and Ti/Pt/Au contacts on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining, in combination with the protruding portion, the mating structure on the second substrate or wafer.

54. A three axis MEM tunneling sensor assembly as claimed in claim 53 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the Ti/Pt/Au contact on said second substrate and/or by a layer of Au—

Si eutectic disposed on first ohmic contact.

55. A three axis MEM tunneling sensor assembly as claimed in claim 44 wherein first and second interconnected Ti/Pt/Au contacts are disposed on said epitaxial layer, the contacts being interconnected by an elongate ribbon layer of Ti/Pt/Au, said second interconnected contact being disposed near a distal end of the beam structure, the elongate ribbon being disposed longitudinally on the beam structure and said first interconnected contact forming the mating structure on the first substrate.

56. A three axis MEM tunneling sensor assembly as claimed in claim 55 wherein a protruding portion protrudes from a major surface of said second substrate or wafer, Ti/Pt/Au contacts are disposed on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining, in combination with the protruding portion, the mating structure on the second substrate or wafer.

57. A three axis MEM tunneling sensor assembly as claimed in claim 56 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the Ti/Pt/Au contact on said second substrate and/or by a layer of Au—

Si eutectic disposed on first interconnected contact.

58. A three axis MEM tunneling sensor assembly as claimed in claim 35 wherein a center post in resonator structure is bonded to the mating structure on the second substrate or wafer.

59. A three axis MEM tunneling sensor assembly as claimed in claim 35 wherein an outer frame of the resonator structure is bonded to the mating structure on the second substrate or wafer.

60. A three axis MEM tunneling sensor assembly comprising:

(a) orthogonally arranged beam structures, an associated resonator structure and associated mating structures arranged on a first substrate or wafer;

(b) one contact structures and associated mating structures defined on a second substrate or wafer, the mating structures on the second substrate or wafer being of a complementary shape to the mating structures on the first substrate or wafer; and

(c) an eutectic bonding layer of disposed said mating structures on at least one of substrates or wafers for bonding the mating structures defined on the first substrate or wafer to mating structures on the second substrate in response to the application of pressure and heat therebetween, the mating structures being joined one to another at said eutectic bonding layer.

61. A three axis MEM tunneling sensor assembly as claimed in claim 60 wherein the first and second substrates or wafers are each formed of single crystal silicon.

62. A three axis MEM tunneling sensor assembly as claimed in claim 60 wherein the crystalline structure of the silicon is <

100>

.

63. A three axis MEM tunneling sensor assembly as claimed in claim 60 wherein the cantilevered beam structure is formed from an epitaxial layer of silicon on said first substrate or wafer, said epitaxial layer being doped with a dopant.

64. A three axis MEM tunneling sensor assembly as claimed in claim 63 wherein the epitaxial layer is doped with Boron at a sufficient concentration to reduce the resistivity of the epitaxial layer to less than less than 0.05 Ω

-cm.

65. A three axis MEM tunneling sensor assembly as claimed in claim 63 further including first and second ohmic contacts on said epitaxial layer, said second ohmic contact being disposed near a distal end of the beam structure and said first ohmic contact forming the mating structure on the first substrate or wafer.

66. A three axis MEM tunneling sensor assembly as claimed in claim 65 wherein a relatively thick layer of metal is disposed on the first and second ohmic contacts, a first portion of the relatively thick layer of metal being disposed on said first ohmic contact and providing the mating structure on the first substrate and a second portion of the relatively thick layer of metal forming a pointed contact on said second ohmic contact.

67. A three axis MEM tunneling sensor assembly as claimed in claim 66 further including metal contacts disposed on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining the mating structure on the second substrate or wafer.

68. A three axis MEM tunneling sensor assembly as claimed in claim 67 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the metal contact on said second substrate and/or by a layer of Au—

Si eutectic disposed on the first portion of the relatively thick layer of metal on the first substrate or wafer.

69. A three axis MEM tunneling sensor assembly as claimed in claim 67 wherein the silicon for the eutectic bond is provided by the silicon substrate of the first or second wafers at the mating structure.

70. A three axis MEM tunneling sensor assembly as claimed in claim 64 further including first and second ohmic contacts on said epitaxial layer, said second ohmic contact being disposed near a distal end of the beam structure and said first ohmic contact forming the mating structure on the first substrate.

71. A three axis MEM tunneling sensor assembly as claimed in claim 60 further including a protruding portion which protrudes from a major surface of said second substrate or wafer and metal contacts on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining, in combination with the protruding portion, the mating structure on the second substrate or wafer.

72. A three axis MEM tunneling sensor assembly as claimed in claim 71 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the metal contact on said second substrate and/or by a layer of Au—

Si eutectic disposed on first ohmic contact.

73. A three axis MEM tunneling sensor assembly as claimed in claim 60 wherein first and second interconnected metal contacts are disposed on said epitaxial layer, the contacts being interconnected by an elongate ribbon of metal, said second interconnected contact being disposed near a distal end of the beam structure, the elongate ribbon being disposed longitudinally on the beam structure and said first interconnected contact forming the mating structure on the first substrate.

74. A three axis MEM tunneling sensor assembly as claimed in claim 73 wherein a protruding portion protrudes from a major surface of said second substrate or wafer, metal contacts are disposed on said second substrate or wafer, at least one of said contacts on the second substrate or wafer defining, in combination with the protruding portion, the mating structure on the second substrate or wafer.

75. A three axis MEM tunneling sensor assembly as claimed in claim 74 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the metal contact on said second substrate and/or by a layer of Au—

Si eutectic disposed on first interconnected contact.

76. A three axis MEM tunneling sensor assembly as claimed in claim 60 wherein a center post in resonator structure is bonded to the mating structure on the second substrate or wafer.

77. A three axis MEM tunneling sensor assembly as claimed in claim 60 wherein an outer frame of the resonator structure is bonded to the mating structure on the second substrate or wafer