Strength of micro-bump joints

1. A method of forming a device, the method comprising:

forming a metal bump on a first work piece;

forming a dielectric layer over and contacting the metal bump;

forming an opening in the dielectric layer to expose a portion of the metal bump;

etching the portion of the metal bump exposed through the opening to form a recess, a portion of the recess extending to directly under the dielectric layer; and

forming a metal finish on the metal bump, with at least a portion of the metal finish formed in the recess.

2. The method of claim 1 further comprising providing a second work piece comprising an additional metal bump, and bonding the additional metal bump of the second work piece to the metal bump of the first work piece.

3. The method of claim 1 , wherein the step of etching the portion of the metal bump is performed using the dielectric layer as a self-aligned mask, with no additional mask formed over the dielectric layer.

4. The method of claim 1 further comprising:

after the step of forming the opening, forming a patterned mask over the dielectric layer, the metal bump comprising portions exposed through the patterned mask; and

performing the step of etching the portion of the metal bump through openings in the patterned mask.

5. The method of claim 1 , wherein the recess comprises a plurality of isolated portions isolated from each other by un-etched portions of the metal bump.

6. The method of claim 1 , wherein the step of etching comprises an isotropic etching process.

7. The method of claim 1 , wherein the step of forming the metal finish comprises electroless plating.

8. The method of claim 1 , wherein the metal bump comprises copper, and wherein the metal finish comprises nickel.

9. A method of forming a device, the method comprising:

forming a metal bump protruding above a top surface of a substrate, the metal bump comprising sidewalls and a top surface;

forming a dielectric layer comprising a first portion directly over the top surface of the metal bump, and a second portion on the sidewalls of the metal bump, the metal bump and the first portion of the dielectric layer forming an interface;

etching the first portion of the dielectric layer to form an opening, a portion of the metal bump being exposed through the opening;

etching the portion of the metal bump to form a recess in the metal bump, the recess extending to directly under the dielectric layer to form an undercut; and

performing a selective plating to form a metal finish in the recess, a portion of the metal finish extending into the undercut.

10. The method of claim 9 , wherein the metal finish comprises a portion extending to directly over the first portion of the dielectric layer.

11. The method of claim 9 , wherein the recess comprises a plurality of isolated portions isolated from each other by un-etched portions of the metal bump.

12. The method of claim 9 , wherein the step of etching the portion of the metal bump is performed with no additional mask formed over the dielectric layer.

13. The method of claim 9 , wherein the step of etching the portion of the metal bump is performed with a patterned mask over the dielectric layer, and wherein the portion of the metal bump is etched through openings in the patterned mask.

14. The method of claim 9 , wherein the metal finish comprises electroless nickel electroless palladium immersion gold (ENEPIG).

15. A method of forming a device, the method comprising:

forming a metal bump on a first work piece, the metal bump comprising a top surface comprising a center portion and an edge portion surrounding the center portion;

forming a dielectric layer to cover the edge portion of the metal bump;

recessing the center portion of the metal bump to form a recess in the metal bump; and

plating a metal finish on the metal bump, the metal finish comprising a portion extending down into the recess and directly under a portion of the dielectric layer.

16. The method of claim 15 further comprising providing a second work piece comprising an additional metal bump, and bonding the additional metal bump of the second work piece to the metal finish.

17. The method of claim 15 , wherein the metal finish comprises another portion extending to directly over the dielectric layer.

18. The method of claim 15 , wherein the step of etching the center portion of the metal bump is performed using the dielectric layer as a self-aligned mask.

19. The method of claim 15 further comprising:

forming a patterned mask over the metal bump, a portion of the metal bump being exposed through the patterned mask; and

performing the step of recessing through the patterned mask.

20. The method of claim 15 , wherein the metal bump comprises copper.