Aluminum Based Bonding of Semiconductor Wafers

• US 20080237823A1
• Filed: 01/11/2008
• Published: 10/02/2008
• Est. Priority Date: 01/11/2007
• Status: Abandoned Application

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Martin, John R.
• Application Number:
  US12/013,310
• Publication Number:
  US 20080237823A1
• Time in Patent Office: Days
• US Class Current: 257/685
• CPC Class Codes: B81B 2203/053 Translation according to an axis perpendicular to the substrate
• CPC Class Codes: B81B 7/0077 Other packages not provided for in groups B81B7/0035 - B81B7/0074
• CPC Class Codes: B81C 1/00269 Bonding of solid lids or wafers to the substrate
• CPC Class Codes: B81C 99/0045 End test of the packaged device
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

Aluminum or aluminum alloy on each of a pair of semiconductor wafers is thermocompression bonded. Aluminum-based seal rings or electrical interconnects between layers may be thus formed. On a MEMS device, the aluminum-based seal ring surrounds an area occupied by a movably attached microelectromechanical structure. According to a manufacturing method, wafers have an aluminum or aluminum alloy deposited thereon are etched to form an array of aluminum-based rings. The wafers are placed so as to bring the arrays of aluminum-based rings into alignment. Heat and compression bonds the rings. The wafers are singulated to separate out the individual semiconductor devices each with a bonded aluminum-based ring.

Claims

1. Bonded wafers comprising:

a first wafer including an array of microelectronic dies;

a second wafer; and

a plurality of seal rings each associated with one of the microelectronic dies and forming a seal between the first wafer and the second wafer wherein each seal ring consists essentially of aluminum and/or aluminum alloy.

2. The bonded wafers of claim 1 wherein the seal rings each hermetically seal the volume within the seal rings from the outside environment.

3. The bonded wafers of claim 1 wherein the plurality of seal rings hold the first wafer and second wafer at least 2 microns apart.

4. The bonded wafers of claim 1 wherein each of the seal rings has a wall width of between 3 and 90 microns.

5. The bonded wafers of claim 4 wherein each of the seal rings has a wall width of between 5 and 30 microns.

6. The bonded wafers of claim 1 wherein each of the microelectronic dies comprises a movable microelectromechanical structure.

7. A MEMS device comprising:

a semiconductor die;

a microelectromechanical structure movably attached to the semiconductor die;

a cap; and

a conductive seal ring formed entirely of at least one from the group of aluminum and aluminum alloy, the seal ring being bonded between the semiconductor die and the cap and surrounding an area occupied by the microelectromechanical structure.

8. The MEMS device of claim 7 wherein the micromechanical structure is an inertial sensor.

9. The MEMS device of claim 7 wherein the microelectromechanical structure is formed in an SOI wafer.

10. The MEMS device of claim 7 wherein the microelectromechanical structure is formed in a standard silicon wafer.

11. The method of claim 10 wherein thin film depositions are used in the formation of the microelectromechanical structure.

12. The method of claim 10 wherein the microelectromechanical structure is substantially formed by etching into the surface of the wafer.

13. The MEMS device of claim 7 wherein the conductive seal ring hermetically seals the volume within the seal ring from the outside environment.

14. The MEMS device of claim 7 wherein the seal ring holds the semiconductor die and the cap at least 2 microns apart.

15. The MEMS device of claim 7 wherein the seal ring has a wall width of between 3 and 90 microns.

16. The MEMS device of claim 15 wherein the seal ring has a wall width of between 5 and 30 microns.

17. A method of making semiconductor devices comprising:

depositing aluminum or aluminum alloy to form an aluminum-based layer on a first semiconductor wafer;

patterning the aluminum-based layer to form an array of aluminum-based rings;

depositing aluminum or aluminum alloy to form an aluminum-based layer on a second semiconductor wafer;

patterning the aluminum-based layer to form an array of aluminum-based rings;

placing the second wafer on the first wafer so that the array of aluminum-based rings on the first wafer aligns with the array of aluminum-based rings on the second wafer;

heating the first and second wafers;

compressing the first and second wafers against each other to form a bond between aluminum-based rings on the first wafer with their respective aluminum-based rings on the second wafer; and

singulating the first and second wafers into individual semiconductor devices each having a bonded aluminum-based ring.

18. The method of claim 17 wherein patterning comprises etching.

19. The method of claim 17 wherein heating is performed up to less than 500°

C.

20. The method of claim 19 wherein compressing applies over about 30 MPa.

21. The method of claim 19 further comprising performing an anti-stiction treatment on at least one of the wafers.

22. The method of claim 21 wherein compressing applies over about 90 MPa.

23. The method of claim 19 further comprising annealing the bonded aluminum-based rings.

24. The method of claim 23 wherein annealing is conducted at about 450°

C.

25. The method of claim 19 further comprising planarizing the aluminum-based layer on each of the first and second wafers.

26. The method of claim 17 wherein the aluminum-based rings each have a wall width between 3 and 90 microns.

27. The method of claim 26 wherein the aluminum-based rings each have a wall width between 5 and 30 microns.

28. A semiconductor device, said device made by a process comprising:

thermocompressing an aluminum-based deposit on a first semiconductor wafer against an aluminum-based deposit on a second semiconductor wafer; and

singulating the wafers to separate the semiconductor device.

29. The semiconductor device of claim 28 further comprising a microelectromechanical structure movably attached to a semiconductor die singulated from one of the first or second semiconductor wafers.

30. The semiconductor device of claim 28 wherein the aluminum-based deposits on the first semiconductor wafer and on the second semiconductor wafer are in the form of rings, such that conductive seal rings are formed upon thermocompressing.

31. The semiconductor device of claim 30 wherein thermocompressing forms a conductive seal ring having a wall width of between 3 and 90 microns.

32. The semiconductor device of claim 31 wherein the conductive seal ring has a wall width between 5 and 30 microns.

33. The semiconductor device of claim 28 wherein the aluminum-based deposits form an electrical connection between a layer from the first semiconductor wafer and a layer from the second semiconductor wafer upon thermocompressing.

34. A method of determining the quality of thermocompression bonds formed between aluminum and/or aluminum alloy surfaces comprising:

inspecting an interface between the aluminum-based surfaces with an IR microscope for presence and amount of re-crystallization of aluminum-based material.