Extended seal ring structure on wafer-stacking

1. A method comprising:

bonding first connectors of a first wafer to second connectors of a second wafer, the first wafer comprising a first seal ring, the second wafer comprising a second seal ring;

forming a third seal ring surrounding the first connectors and the second connectors, the third seal ring spanning an interface between the first wafer and the second wafer, the third seal ring comprising a first seal ring extension extending from the first seal ring and a second seal ring extension extending from the second seal ring;

forming a trench through the second wafer, the trench penetrating the first wafer, the trench surrounding the first connectors and the second connectors;

filling the trench with a seal ring material to form a fourth seal ring; and

singulating the first wafer and the second wafer to singulate a first package therefrom.

2. The method of claim 1 , wherein forming the third seal ring comprises:

forming a first trench opening in a first dielectric layer over the first seal ring, the first trench opening and exposing an upper surface of the first seal ring;

depositing a conductive material in the first trench opening to form the first seal ring extension;

forming a second trench opening in a second dielectric layer over the second seal ring, the second trench opening exposing an upper surface of the second seal ring;

depositing the conductive material in the second trench opening to form the second seal ring extension; and

at the same time as bonding the first connectors of the first wafer to the second connectors of the second wafer, bonding the first seal ring extension to the second seal ring extension.

3. The method of claim 2 , wherein the first seal ring extension and the second seal ring extension comprise a eutectic material.

4. The method of claim 2 , wherein the first seal ring extension and the second seal ring extension are bonded together using a direct metal-to-metal bond.

5. The method of claim 1 , further comprising prior to forming the trench,

thinning the second wafer.

6. The method of claim 1 , wherein the seal ring material is a conductive material.

7. The method of claim 1 , further comprising:

forming a bond pad over the fourth seal ring.

8. The method of claim 1 , wherein the trench exposes the first seal ring and the second seal ring, the seal ring material electrically and physically coupling the first seal ring and the second seal ring.

9. A method comprising:

forming a first trench in an upper surface of a first workpiece, the first trench exposing a first seal ring of the first workpiece;

depositing a first conductive material in the first trench to form a first seal ring extension, the first seal ring extension extending continuously from a first interface with the first seal ring to an upper surface of the first workpiece;

forming a second trench in an upper surface of a second workpiece, the second trench exposing a second seal ring of the second workpiece;

depositing a second conductive material in the second trench to form a second seal ring extension, the second seal ring extension extending continuously from a second interface with the first seal ring to an upper surface of the second workpiece;

bonding the first workpiece to the second workpiece and the first seal ring extension to the second seal ring extension to form a third interface between the first seal ring extension and the second seal ring extension and to form an air gap between the first workpiece and the second workpiece, the air gap extending horizontally between an upper surface of the first workpiece and an upper surface of the second workpiece, the air gap sealed by the third interface; and

singulating a first package from the first workpiece and the second workpiece.

10. The method of claim 9 , further comprising bonding the first seal ring extension to the second seal ring extension by a direct metal-to-metal bond without a eutectic material formed therebetween.

11. The method of claim 9 , wherein the first seal ring extension and the second seal ring extension are offset by a lateral distance.

12. The method of claim 11 , wherein bonding the upper surface of the first workpiece to the upper surface of the second workpiece includes bonding a first contact of the first workpiece to a second contact of the second workpiece, the first contact being offset from the second contact by the lateral distance, the lateral distance being a larger percentage of a footprint of the first seal ring extension than a footprint of the first contact.

13. The method of claim 9 , further comprising:

after bonding the first workpiece to the second workpiece, forming a third trench surrounding the first seal ring and the second seal ring, the third trench extending completely through the second workpiece and into the first workpiece; and

depositing a third conductive material in the third trench to form a third seal ring extension.

14. The method of claim 13 , wherein the third trench exposes a side portion of the first seal ring and a side portion of the second seal ring, the third seal ring extension contacting the first seal ring and the second seal ring.

15. The method of claim 13 , wherein the third seal ring extension expands laterally in a space between the first workpiece and the second workpiece.

16. A method comprising:

bonding a front side of a second wafer to a front side of a first wafer to form a wafer-on-wafer structure;

forming a trench through the second wafer into the first wafer;

filling the trench to form an extended seal ring; and

singulating a first package from the wafer-on-wafer structure, the first package comprising:

a first die and a second die, the a first die comprising a first seal ring surrounding a periphery thereof, the second die comprising a second seal ring surrounding a periphery thereof;

the extended seal ring spanning between the first die and the second die, the extended seal ring surrounding a contact area of the wafer-on-wafer structure and sealing the contact area within the extended seal ring; and

a contact pad disposed at an upper surface of the first package, the contact pad electrically coupled to the extended seal ring.

17. The method of claim 16 , wherein the extended seal ring contacts the first seal ring and the second seal ring.

18. The method of claim 16 , further comprising:

bonding second contacts and a second seal ring extension of a second wafer of the wafer-on-wafer structure to corresponding first contacts and a first seal ring extension of a first wafer of the wafer-on-wafer structure, the first seal ring extension and second seal ring extension together forming a third seal ring.

19. The method of claim 16 , wherein the extended seal ring expands laterally into a gap between the first wafer and the second wafer.

20. The method of claim 16 , wherein the extended seal ring seals an air gap which extends between the first die and the second die, surrounding contacts of the contact area.