Method of manufacturing a dual wafer tunneling gyroscope

• US 6,555,404 B1
• Filed: 08/01/2000
• Issued: 04/29/2003
• Est. Priority Date: 08/01/2000
• Status: Expired due to Fees

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Kubena, Randall L., Chang, David T.
• Primary Examiner(s): Nelms, David
• Assistant Examiner(s): Le, Dung Anh
• Application Number:
  US09/629,679
• Time in Patent Office: 1,001 Days
• Field of Search: 438/48, 438/51, 438/52, 438/53, 257/414-420
• US Class Current: 438/22
• CPC Class Codes: B81B 2201/0242 Gyroscopes
• 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 2201/014 by depositing an etch stop layer, e.g. silicon nitride, silicon oxide, metal
• CPC Class Codes: B81C 2201/0191 Transfer of a layer from a carrier wafer to a device wafer
• CPC Class Codes: B81C 2203/036 Fusion bonding
• 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

Abstract

A method of making a micro electromechanical gyroscope. A cantilevered beam structure, first portions of side drive electrodes and a mating structure are defined on a first substrate or wafer; and at least one contact structure, second portions of the side drive electrodes 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 and the first and second portions of the side drive electrodes being of a complementary shape to each other. A bonding layer, preferably a eutectic bonding layer, is provided on at least one of the mating structures and one or the first and second portions of the side drive electrodes. 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 and also between the first and second portions of the side drive electrodes to cause a bond to occur therebetween. Then the first substrate or wafer is removed to free the cantilevered beam structure for movement relative to the second substrate or wafer. The bonds are preferably eutectic bonds.

Claims

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

(a) defining a cantilevered beam structure, first portions of at least two side drive electrodes and a mating structure on a first substrate or wafer;

(b) forming at least one contact structure, second portions of said at least two side drive electrodes 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 and the second portions of the side drive electrodes being of a complementary shape to the first portions of the side drive electrodes 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;

(e) bonding layers associated with said first portions of at least two side drive electrodes on the first substrate or wafer with layers associated with said second portions of at least two side drive electrodes on the second substrate or wafer;

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

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

7. A method of making a MEM tunneling gyroscope 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 gyroscope 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 gyroscope 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 gyroscope 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 and between the first and second portions of the side drive electrodes.

11. A method of making a MEM tunneling gyroscope 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 gyroscope 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 gyroscope 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.

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

15. A method of making a MEM tunneling gyroscope as claimed in claim 13 wherein a layer of metal, preferably formed of individual layers of Ti, Pt and 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 or wafer.

16. A method of making a MEM tunneling gyroscope as claimed in claim 15 wherein a relatively thick layer of metal is deposited and then sintered on a relatively thin metal layer, a first portion of the relatively thick layer of metal 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.

17. A method of making a MEM tunneling gyroscope as claimed in claim 16 wherein the relatively thick layer of metal is Ti/Pt/Au.

18. A method of making a MEM tunneling gyroscope 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 gyroscope 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 method of making a MEM tunneling gyroscope as claimed in claim 1 wherein said first substrate includes an etch stop layer and wherein the cantilevered beam structure, the first portions of at least two side drive electrodes and the mating structure thereof are disposed adjacent said etch stop layer and wherein the cantilevered beam structure is released by first etching away the first substrate and then by etching away the etch stop layer.

21. A method of making a MEM tunneling gyroscope as claimed in claim 20 wherein the second substrate or wafer is formed of silicon.

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

23. A method of making a MEM tunneling gyroscope as claimed in claim 22 wherein the crystalline structure of the silicon is <

100>

.

24. A method of making a MEM tunneling gyroscope as claimed in claim 23 wherein the silicon is n-type.

25. A method of making a MEM tunneling gyroscope as claimed in claim 20 wherein the first substrate or wafer is formed of silicon.

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

27. A method of making a MEM tunneling gyroscope as claimed in claim 26 wherein the crystalline structure of the silicon in the first substrate or wafer is <

100>

.

28. A method of making a MEM tunneling gyroscope as claimed in claim 27 wherein the silicon of the first substrate or wafer is n-type.

29. A method of making a MEM tunneling gyroscope as claimed in claim 20 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 and between the first and second portions of the side drive electrodes.

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

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

100>

.

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