Encapsulated MEMS device and method to form the same

1. A method, comprising:

forming a silicon-germanium seal ring on a first substrate on which a MEMS device is disposed inside of a region enclosed by the silicon-germanium seal ring;

forming a vertical seal ring stack on a second substrate, the vertical seal ring stack including a metal seal ring;

forming a metal shielding layer on said second substrate including on a sidewall of the vertical seal ring stack;

bonding said metal seal ring to said silicon-germanium seal ring to provide a sealed cavity that houses the MEMS device, and to electrically couple the MEMS device and the metal shielding layer.

2. The method of claim 1 , wherein bonding said metal seal ring to said silicon-germanium seal ring comprises forming a eutectic bond between said metal seal ring and said silicon-germanium seal ring.

3. The method of claim 2 , wherein said metal seal ring comprises gold, and wherein said eutectic bond forms at a temperature less than approximately 400 degrees Celsius.

4. The method of claim 2 , wherein said metal seal ring comprises aluminum, and wherein said eutectic bond forms at a temperature less than approximately 450 degrees Celsius.

5. The method of claim 1 , wherein a width of the wall of said metal seal ring is smaller than a width of the wall of said silicon-germanium seal ring.

6. The method of claim 5 , wherein the width of the wall of said metal seal ring is approximately in the range of 20-40 microns, and wherein the width of the wall of said silicon-germanium seal ring is approximately in the range of 50-70 microns.

7. The method of claim 1 , wherein a combined height of a wall of said vertical seal ring stack and a wall of said silicon-germanium seal ring is approximately in the range of 60-100 microns.

8. The method of claim 1 , wherein a second MEMS device is housed in said sealed cavity, and wherein the second MEMS device is disposed on said second substrate, inside of a region enclosed by said metal seal ring.

9. The method of claim 1 , wherein said MEMS device is disposed on said second substrate, inside of the region enclosed by said metal seal ring.

10. The method of claim 1 , wherein said metal shielding layer comprises a material selected from the group consisting of titanium, tungsten, chromium and alloys thereof.

11. The method of claim 1 , wherein bonding said metal seal ring to said silicon-germanium seal ring comprises bonding in a reduced pressure atmosphere.

12. The method of claim 1 , wherein bonding said metal seal ring to said silicon-germanium seal ring comprises bonding in an ambient atmosphere.

13. The method of claim 1 , wherein bonding said metal seal ring to said silicon-germanium seal ring comprises bonding in an increased pressure atmosphere.

14. The method as recited in claim 1 wherein the metal seal ring has a width, prior to bonding, smaller than a seed layer.

15. The method as recited in claim 1 further comprising:

forming an interconnect in the first substrate to electrically couple the MEMS device through the interconnect, the silicon-germanium seal ring, and the metal seal ring, to the metal shielding layer.

16. The method as recited in claim 1 further comprising:

forming the metal shielding layer on the sidewall of the vertical seal ring stack inside of a region enclosed by said metal seal ring.

17. The method as recited in claim 1 further comprising:

forming the metal shielding layer on the sidewall of the vertical seal ring stack outside of a region enclosed by said metal seal ring.

18. The method as recited in claim 1 further comprising:

forming a grounding interconnect on the second substrate that is electrically connected through the metal shielding layer to the MEMS device after the bonding.

19. The method as recited in claim 1 comprising:

forming a set of trenches in a top surface of said second substrate, outside of the region enclosed by said metal seal ring;

thinning said second substrate, from a bottom surface of said second substrate, to expose said set of trenches and to provide a set of windows in said second substrate;

dicing said second substrate outside of the region enclosed by said metal seal ring, wherein said set of windows is used as a set of alignment marks for the dicing; and

dicing said first substrate outside of the region enclosed by said silicon-germanium seal ring.

20. The method of claim 19 , wherein each trench of said set of trenches is formed to a depth approximately in the range of 100-400 microns.

21. The method of claim 19 , wherein thinning said first substrate comprises grinding the bottom surface of said first substrate.

22. A method comprising:

forming a silicon-germanium seal ring on a first substrate;

forming a metal seal ring above a second substrate, wherein said metal seal ring is formed as part of a metal seal ring stack;

bonding said metal seal ring to said silicon-germanium seal ring to provide a sealed cavity that houses a MEMS device;

forming a metal shielding layer on said second substrate including on a sidewall of the metal seal ring stack, inside of a region enclosed by said metal seal ring, prior to bonding said metal seal ring to said silicon-germanium seal ring; and

forming an interconnect in the first substrate to electrically couple the MEMS device through the interconnect and the silicon-germanium seal ring to the metal shielding layer.

23. A method, comprising:

forming a silicon-germanium seal ring on a first substrate;

forming a metal seal ring on a second substrate;

forming inlets in the second substrate to provide an opening to a cavity, the inlets having a V-groove profile with a wider portion closer to the MEMS device, the inlets arranged to provide constructive interference of sound waves; and

bonding said metal seal ring to said silicon-germanium seal ring to provide the cavity that houses a MEMS device disposed on the first substrate.

24. A method, comprising:

forming a silicon-germanium seal ring on a first substrate;

forming a metal seal ring on a second substrate;

forming inlets in the second substrate to provide an opening to a cavity, the inlets having a V-groove profile with a wider portion closer to the MEMS device, the inlets arranged to provide constructive interference of optical waves; and

bonding said metal seal ring to said silicon-germanium seal ring to provide the cavity that houses a MEMS device disposed on the first substrate.