Cobalt based interconnects and methods of fabrication thereof

1. A method of forming a metal interconnect structure, comprising:

forming an opening in a dielectric layer disposed on a substrate, wherein the opening exposes a conductive region of the substrate, wherein the conductive region is a semiconductor diffusion region;

forming a seed layer directly on the dielectric layer in the opening, over the conductive region of the substrate, and by a first method comprising a first set of parameters, the seed layer comprising at least 50 atomic % cobalt and having a first grain structure;

forming a fill material on a surface of the seed layer by a second method comprising a second set of parameters, wherein the first set of parameters is different than the second set of parameters, and wherein the fill material comprises 0.25-5 atomic % of a non-cobalt element with the remainder approximately 95+ atomic % cobalt, the fill material having a second grain structure larger than the first grain structure and having a composition different from the seed layer, wherein grain boundaries within the cobalt of the fill material are filled by the non-cobalt element; and

removing portions of the fill material and the seed layer disposed above an upper surface of the dielectric layer.

2. The method of claim 1 , where the first and second methods are the same methods.

3. The method of claim 1 , wherein the first and second methods are different methods.

4. The method of claim 1 , wherein the first method comprises a method selected from a group consisting of chemical vapor deposition (CVD), atomic layer deposition (ALD), and physical vapor deposition (PVD).

5. The method of claim 1 , wherein the second method comprises a method selected from a group consisting of CVD, ALD, PVD, Electroplating, and Electro-less plating.

6. The method of claim 1 , wherein the removing comprises chemical-mechanical polishing (CMP).

7. The method of claim 1 , wherein the seed layer further comprises at least one element selected from the group consisting of silicon and germanium.

8. The method of claim 1 , wherein the first method is conformal and the second method is non-conformal.

9. The method of claim 1 , wherein the first method is a slow deposition and the second method is a fast deposition.

10. The method of claim 1 , further comprising repeating a reflowing of the fill material and the forming the fill material until the opening is completely filled.

11. The method of claim 10 , wherein the repeating is performed at least three times.

12. A metal interconnect structure, comprising:

a dielectric layer disposed on a substrate;

an opening disposed in the dielectric layer and exposing a conductive region in the substrate, the opening having a lower portion and an upper portion, the upper portion wider than the lower portion;

a plug disposed in the lower portion of the opening the plug filling the lower portion of the opening, the plug comprising at least 50 atomic % cobalt and having a first grain structure; and

a fill material disposed on the plug and in the upper portion of the opening, the fill material comprising 0.25-5 atomic % of a non-cobalt element with the remainder approximately 95+ atomic % cobalt, and the fill material having a second grain structure larger than the first grain structure and having a composition different from the plug, wherein grain boundaries within the cobalt of the fill material are filled by the non-cobalt element.

13. The metal interconnect structure of claim 12 , wherein the plug further comprises at least one element selected from the group consisting of phosphorous and boron.

14. The metal interconnect structure of claim 12 , further comprising a seed layer comprising cobalt disposed over the plug and on a surface of at least the upper portion of the opening.

15. The metal interconnect structure of claim 14 , wherein the seed layer, the plug and the fill material have differing grain structure or composition.

16. A method of forming a metal interconnect structure, comprising:

forming an opening in a dielectric layer disposed on a substrate, exposing a conductive region in the substrate, the opening having an upper portion and a lower portion, the upper portion wider than the lower portion;

forming a plug over the conductive region of the substrate and within at least the lower portion of the opening by a first method comprising a first set of parameters, the plug material filling the lower portion of the opening, and the plug comprising at least 50 atomic % cobalt and having a first grain structure;

forming a fill material over the plug, the dielectric layer, and within at least the upper portion of the opening by a second method comprising a second set of parameters, wherein the first set of parameters is different than the second set of parameters, the fill material comprising 0.25-5 atomic % of a non-cobalt element with the remainder approximately 95+ atomic % cobalt, the fill material having a second grain structure larger than the first grain structure and having a composition different from the plug, wherein grain boundaries within the cobalt of the fill material are filled by the non-cobalt element; and

removing portions of the fill material disposed above an upper surface of the dielectric layer.

17. The method of claim 16 , wherein the first method comprises a method selected from a group consisting of chemical vapor deposition (CVD), atomic layer deposition (ALD), and physical vapor deposition (PVD), and the second method comprises a method selected from a group consisting of Electroplating and Electro-less plating.

18. The method of claim 16 , wherein the first and second methods are the same methods.

19. The method of claim 16 , wherein the first and second methods are different methods.