Apparatus and Method of Wafer Bonding Using Compatible Alloy

• US 20100059835A1
• Filed: 05/04/2009
• Published: 03/11/2010
• Est. Priority Date: 09/10/2008
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Tsau, Christine H., Frey, Timothy J., Martin, John R.
• Granted Patent: US 7,943,411 B2
• Time in Patent Office: Days
• US Class Current: 257/417
• CPC Class Codes: B81C 1/00269 Bonding of solid lids or wafers to the substrate
• CPC Class Codes: B81C 2203/0118 Bonding a wafer on the substrate, i.e. where the cap consists of another wafer
• CPC Class Codes: H01L 23/10 characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/01079 Gold [Au]

Abstract

A method of forming an inertial sensor provides 1) a device wafer with a two-dimensional array of inertial sensors and 2) a second wafer, and deposits an alloy of aluminum/germanium onto one or both of the wafers. The alloy is deposited and patterned to form a plurality of closed loops. The method then aligns the device wafer and the second wafer, and then positions the alloy between the wafers. Next, the method melts the alloy, and then solidifies the alloy to form a plurality of conductive hermetic seal rings about the plurality of the inertial sensors. The seal rings bond the device wafer to the second wafer. Finally, the method dices the wafers to form a plurality of individual, hermetically sealed inertial sensors.

Claims

1. A method of bonding a MEMS device wafer to a second wafer, the method comprising:

forming an aluminum layer on the MEMS device wafer;

forming a germanium layer on the second wafer;

bringing the aluminum layer on the device wafer into contact with the germanium layer on the second wafer;

heating the aluminum layer and the germanium layer,

heating at least in part causing the aluminum layer and germanium layer to form a eutectic material, heating being initiated either before or after the aluminum layer is in contact with the germanium layer; and

cooling the wafers to form a plurality of hermetic seal rings between the wafers.

2. The method as defined by claim 1 wherein forming an aluminum layer comprises using sputter deposition processes to form the aluminum layer on the device wafer.

3. The method as defined by claim 1 wherein forming a germanium layer comprises using sputter deposition processes to form the germanium layer on the second wafer.

4. The method as defined by claim 1 wherein at least one of the seal rings has varying concentrations of aluminum, germanium, or aluminum/germanium eutectic, the region of the seal ring adjacent to the device wafer having a higher concentration of aluminum than the region of the seal ring adjacent to the second wafer, the region of the seal ring adjacent to the second wafer having a higher concentration of germanium than the region of the seal ring adjacent to the device wafer.

5. The apparatus formed by the process of claim 4.

6. The method as defined by claim 1 wherein the device wafer comprises a two dimensional array of MEMS inertial sensors, the second wafer comprising a corresponding two-dimensional array of caps.

7. The method as defined by claim 1 wherein heating comprises heating to between about 349 and 424 degrees C.

8. The method as defined by claim 1 wherein heating comprises heating to between about 424 and 499 degrees C.

9. A method of forming an inertial sensor, the method comprising:

providing a device wafer with a two-dimensional array of MEMS inertial sensors;

providing a second wafer;

depositing an alloy comprising aluminum/germanium onto one or both the device wafer and the second wafer;

position the alloy between the device wafer and the second wafer;

heating the alloy before, after, or substantially simultaneously with positioning the alloy;

cooling the alloy after melting to form a plurality of conductive hermetic seal rings about the plurality of the inertial sensors, the seal rings bonding the device wafer to the second wafer; and

dicing the wafers to form a plurality of individual, hermetically sealed inertial sensors.

10. The method as defined by claim 9 wherein depositing comprises sputtering the alloy onto one or both the device wafer and the second wafer.

11. The method as defined by claim 9 further comprising adding a rare earth element to the alloy.

12. The apparatus formed by the process defined by claim 9.

13. A method of bonding a device wafer to a second wafer, the method comprising:

providing the device wafer with a two-dimensional array of MEMS devices; and

providing the second wafer;

depositing a metal alloy onto one or both the device wafer and the second wafer, the metal alloy being substantially CMOS fabrication compatible;

aligning the device wafer and the second wafer;

forming an intermediate apparatus having the metal alloy between the device wafer and the second wafer;

heating the intermediate apparatus to within about 75 degrees C. of the metal alloy eutectic temperature between the device wafer and the second wafer; and

cooling the wafers to form a plurality of conductive hermetic seal rings about the plurality of the MEMS devices on the device wafer, the seal rings bonding the device wafer to the second wafer.

14. The method as defined by claim 13 wherein the metal alloy comprises aluminum/germanium or silicon-germanium.

15. The method as defined by claim 13 further comprising forming coupling material on the wafer that did not receive the deposited metal alloy, the metal alloy adhering with the coupling material to form the seal rings, the coupling material comprising a material that is at least a part of the metal alloy.

16. The method as defined by claim 13 further comprising adding a rare earth element to the metal alloy.

17. The method as defined by claim 13 further comprising forming a barrier layer on the wafer receiving the metal alloy, the barrier layer being between the wafer and the metal alloy.

18. The method as defined by claim 13 further comprising forming pedestal rings on one of the wafers.

19. The method as defined by claim 13 further comprising dicing the wafers to form a plurality of individual, hermetically sealed MEMS devices.

20. The hermetically sealed MEMS devices formed by the process defined by claim 19.

21. The method as defined by claim 13 further comprising forming a conductive pathway electrically connecting the device wafer and the second wafer, the conductive pathway comprising a substantially uniform metal alloy with a melting point of less than about 500 degrees C. and being substantially CMOS fabrication compatible.

22. A method of bonding a first wafer to a second wafer, the method comprising:

forming a first metal layer on the first wafer, the first metal layer including one of aluminum-germanium or silicon-germanium;

forming a second metal layer on the second wafer, the second metal layer including one of aluminum, germanium, or aluminum-germanium;

bringing the first metal layer on the first wafer into contact with the second metal layer on the second wafer;

heating the first and second metal layers to diffuse together the first and second metal layers to form a mechanical bond, heating being initiated either before or after bringing the first metal layer into contact with the second metal layer; and

cooling the wafers to form a plurality of hermetic seal rings between the wafers.

23. The method as defined by claim 22 wherein the first wafer comprises MEMS devices.

24. The method as defined by claim 22 wherein the second wafer comprises MEMS devices.

25. The method as defined by claim 22 wherein at least one of the first and second wafers comprise non-hermetic structures.