Single crystal, dual wafer, tunneling sensor and a method of making same

• US 20030207487A1
• Filed: 05/06/2003
• Published: 11/06/2003
• Est. Priority Date: 08/01/2000
• Status: Active Grant

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.), HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: Hughes Electronics Corporation (AT&T, Inc.), HRL Laboratories LLC (The Boeing Co.)
• Inventors: Little, Michael J., Hackett, LeRoy H., Kubena, Randall L.
• Granted Patent: US 6,730,978 B2
• Time in Patent Office: Days
• US Class Current: 438/52
• CPC Class Codes: B81B 2201/0292 Sensors not provided for in B81B2201/0207 - B81B2201/0285
• CPC Class Codes: B81C 1/0015 Cantilevers switches using MEMS H01H1/0036; electrostatic relays using micromechanics H01H59/0009; microelectro-mechanical resonators H03H9/02244
• CPC Class Codes: B81C 2203/036 Fusion bonding
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

A method of making a micro electromechanical switch or tunneling sensor. A cantilevered beam structure and a mating structure are defined on a first substrate or wafer; and at least one contact structure and a mating structure are defined on a second substrate or wafer, the mating structure on the second substrate or wafer being of a complementary shape to the mating structure on the first substrate or wafer. A bonding layer, preferably a eutectic bonding layer, is provided on at least one of the mating structures. The mating structure of the first substrate is moved into a confronting relationship with the mating structure of the second substrate or wafer. Pressure is applied between the two substrates so as to cause a bond to occur between the two mating structures at the bonding or eutectic layer. Then the first substrate or wafer is removed to free the cantilevered beam structure for movement relative to the second substrate or wafer.

Claims

1. A method of making a MEM tunneling sensor comprising the steps of:

(a) defining a cantilevered beam structure and a mating structure on a first substrate or wafer;

(b) forming at least one contact structure and a mating structure on a second substrate or wafer, the mating structure on the second substrate or wafer being of a complementary shape to the mating structure on the first substrate or wafer;

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

(d) bonding a layer associated with said mating structure on the first substrate or wafer with a layer associated with the mating structure on the second substrate or wafer; and

(e) removing at least a portion of the first substrate or wafer to release the cantilevered beam structure.

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

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

100>

.

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

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

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

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

11. A method of making a MEM tunneling sensor as claimed in claim 1 wherein the cantilevered beam structure is 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.

12. A method of making a MEM tunneling sensor as claimed in claim 11 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.

13. A method of making a MEM tunneling sensor as claimed in claim 11 wherein etching accomplished by ethylenediamine pyrocatechol as an etchant.

14. A method of making a MEM tunneling sensor as claimed in claim 11 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.

15. A method of making a MEM tunneling sensor as claimed in claim 14 wherein a layer of metal 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 or wafer.

16. A method of making a MEM tunneling sensor as claimed in claim 15 wherein the layer of metal is formed of individual layers of Ti, Pt and Au.

17. A method of making a MEM tunneling sensor as claimed in claim 16 wherein a relatively thick layer of Ti/Pt/Au is deposited and then sintered on a relatively thin metal layer of Ti/Pt/Au, a first portion of the relatively thick layer of Ti/Pt/Au forming the mating structure on the first substrate or wafer 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.

18. A method of making a MEM tunneling sensor as claimed in claim 17 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.

19. A method of making a MEM tunneling sensor as claimed in claim 18 wherein the bonding occurs eutectically and 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 or wafer 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.

20. A MEM tunneling sensor assembly for making a MEM tunneling sensor therefrom, the assembly comprising:

(a) a beam structure and a mating structure defined on a first substrate or wafer;

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

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

21. A MEM tunneling sensor assembly as claimed in claim 20 wherein the second substrate or wafer is formed of silicon.

22. A MEM tunneling sensor assembly as claimed in claim 21 wherein the silicon forming the second substrate or wafer is of a single crystalline structure.

23. A MEM tunneling sensor assembly as claimed in claim 22 wherein the crystalline structure of the silicon is <

100>

.

24. A MEM tunneling sensor assembly as claimed in claim 23 wherein the silicon is n-type.

25. A MEM tunneling sensor assembly as claimed in claim 20 wherein the first substrate or wafer is formed of silicon.

26. A MEM tunneling sensor assembly as claimed in claim 25 wherein the silicon forming the first substrate or wafer is of a single crystalline structure.

27. A MEM tunneling sensor assembly as claimed in claim 26 wherein the crystalline structure of the silicon in the first substrate or wafer is <

100>

.

28. A MEM tunneling sensor assembly as claimed in claim 27 wherein the silicon of the first substrate or wafer is n-type silicon.

29. A MEM tunneling sensor assembly as claimed in claim 20 wherein a pointed contact is disposed on an end of said beam structure.

30. A MEM tunneling sensor assembly as claimed in claim 29 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.

31. A MEM tunneling sensor assembly as claimed in claim 30 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.

32. A MEM tunneling sensor assembly as claimed in claim 31 wherein the first and second ohmic contacts are formed of layers of Ti, Pt and Au.

33. A MEM tunneling sensor assembly as claimed in claim 32 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.

34. A MEM tunneling sensor assembly as claimed in claim 32 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.

35. A MEM tunneling sensor assembly as claimed in claim 34 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.

36. A MEM tunneling sensor assembly as claimed in claim 31 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.

37. A MEM tunneling sensor assembly comprising:

(a) a beam structure and a mating structure defined on a first substrate or wafer;

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

(c) a bonding layer is disposed on at least one of said mating structures for bonding the mating structure, defined on the first substrate or wafer to the mating structure on the second substrate or wafer, the mating structures being joined one to another at said bonding layer.

38. A MEM tunneling sensor assembly as claimed in claim 37 wherein the first and second substrates or wafers are each formed of single crystal silicon.

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

100>

.

40. A MEM tunneling sensor assembly as claimed in claim 37 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.

41. A MEM tunneling sensor assembly as claimed in claim 40 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.

42. A MEM tunneling sensor assembly as claimed in claim 40 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.

43. A MEM tunneling sensor assembly as claimed in claim 40 wherein the first and second ohmic contacts are formed of layers of Ti, Pt and Au.

44. A MEM tunneling sensor assembly as claimed in claim 42 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 or wafer and a second portion of the relatively thick layer of metal forming a pointed contact on said second ohmic contact.

45. A MEM tunneling sensor assembly as claimed in claim 44 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.

46. A MEM tunneling sensor assembly as claimed in claim 45 wherein the bonding layer is provided by a layer of Au—

Si eutectic disposed on the metal contact on said second substrate or wafer 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.

47. A MEM tunneling sensor assembly as claimed in claim 42 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.