Bonding structure and method thereof

1. A method, comprising:

providing a device substrate comprising a plurality of semiconductor devices, wherein each of the semiconductor devices comprises a first bonding layer;

providing a cap substrate comprising a plurality of cap structures, wherein each of the cap structures comprises a second bonding layer, the second bonding layer having a planar surface and a first protrusion protruding from the planar surface, wherein the first protrusion has an outer sidewall flushed with an outer sidewall of the second bonding layer and an inner sidewall having a stepped profile; and

bonding the device substrate to the cap substrate by engaging the first protrusion of the second bonding layer of each of the cap structures with the corresponding first bonding layer of each of the semiconductor devices in the device substrate.

2. The method of claim 1 , wherein the bonding of the device substrate to the cap substrate comprises forming a cavity between each of the cap structures and the corresponding semiconductor devices.

3. The method of claim 1 , wherein the second bonding layer further comprises a second protrusion adjacent to the first protrusion and protruding from the planar surface.

4. The method of claim 3 , wherein the first protrusion has a first height greater than a second height of the second protrusion.

5. The method of claim 1 , wherein the providing of the device substrate comprises causing an oxide layer to be formed on the first bonding layer.

6. The method of claim 5 , wherein the bonding of the device substrate to the cap substrate comprises causing the first protrusion to penetrate through the oxide layer and bond to the first bonding layer.

7. The method of claim 5 , wherein through the bonding the oxide layer has a first thickness at the first protrusion and a second thickness, greater than the first thickness, at the planar surface.

8. The method of claim 1 , wherein the engaging of the first protrusion with the first bonding layer comprises performing eutectic bonding to form a eutectic bond between the first protrusion and the first bonding layer.

9. The method of claim 8 , wherein the eutectic bond has a first thickness at the planar surface less than a second thickness at the first protrusion.

10. The method of claim 1 , wherein the first protrusion includes a ring shape from a top-view perspective.

11. A method, comprising:

forming a semiconductor device in a first substrate, wherein the semiconductor device comprises a first bonding layer including a first planar surface;

forming a cap structure in a second substrate, wherein the cap structure comprises a second bonding layer, and the second bonding layer includes a second planar surface and a first protrusion protruding from the second planar surface, wherein the first protrusion has an outer sidewall flushed with an outer sidewall of the second bonding layer and an inner sidewall having a stepped profile; and

bonding the semiconductor device to the second substrate by engaging the first planar surface with the second planar surface such that the first protrusion penetrates into the first bonding layer.

12. The method of claim 11 , wherein the forming of the semiconductor device comprises forming an oxide layer on the first bonding layer, wherein the bonding of the semiconductor device to the second substrate comprises causing the first protrusion to penetrate through the oxide layer and bond to the first bonding layer.

13. The method of claim 11 , wherein the forming of the semiconductor device comprises forming an oxide layer on the first bonding layer, wherein the bonding of the semiconductor device to the second substrate comprises causing the second bonding layer to bond to the first bonding layer with the oxide layer therebetween.

14. The method of claim 11 , wherein the second bonding layer further includes a second protrusion adjacent to the first protrusion and protruding from the second planar surface, wherein the first protrusion and the second protrusion form concentric rings.

15. The method of claim 14 , wherein the engaging of the first planar surface with the second planar surface forms a eutectic bond between the first bonding layer and the second bonding layer, wherein the eutectic bond includes different thicknesses at the first protrusion, the second protrusion and the second planar surface.

16. The method of claim 15 , wherein the eutectic bond is non-contiguous across the second planar surface.

17. The method of claim 11 , wherein the first protrusion includes tapered sidewalls.

18. A method, comprising:

providing a cap substrate comprising a first cap structure and a second cap structure, wherein the first cap structure comprises a first bonding layer having a first planar surface, the second cap structure comprises a second bonding layer having a second planar surface and a first protrusion protruding from the second planar surface;

providing a device substrate comprising a plurality of semiconductor devices, wherein each of the semiconductor devices comprises a third bonding layer having a third planar surface; and

bonding the device substrate to the cap substrate by engaging the first planar surface with one of the third planar surfaces and engaging the second planar surface with another third planar surface.

19. The method of claim 18 , wherein the first bonding layer has a first width less than a second width of the second bonding layer.

20. The method of claim 18 , wherein the device substrate further comprising a trench adjacent to the third bonding layer and configured to contain squeezed bonding materials generated during the bonding of the device substrate to the cap substrate.