Interconnect structure for an integrated circuit and method of fabricating an interconnect structure

1. An integrated circuit, comprising:

a first metallization level including a first metal routing path; and

a second metallization level overlying the first metallization level, said second metallization level including:

a dielectric layer;

a via opening formed in said dielectric layer extending vertically through the dielectric layer to a top surface of the first metal routing path, wherein the via opening has a self-aligned direction and a non-self-aligned direction;

a metal plug at a bottom of the via opening in direct contact with the first metal routing path which leaves a remaining opening in the via opening, wherein a width of the metal plug in the self-aligned direction is less than a width of the metal plug in the non-self-aligned direction; and

a metal material which fills the remaining opening to define a second metal routing path;

wherein the metal plug is formed of cobalt or an alloy including cobalt.

2. The circuit of claim 1 , wherein the metal plug extends to a maximum height which is less than a height of the dielectric layer through which the via opening extends.

3. The circuit of claim 1 , wherein the metal material comprises a conformal liner and a metal fill.

4. The circuit of claim 2 , wherein the maximum height of the metal plug is between one-third and one-half of the height of the dielectric layer.

5. The circuit of claim 2 , wherein the maximum height is between 10 nm and 30 nm, where a width of the metal plug is between 15 nm and 40 nm.

6. The circuit of claim 5 , wherein the width of the metal plug is between 15 nm and 22 nm in the self-aligned direction and between 22 nm and 40 nm in the non-self-aligned direction.

7. The circuit of claim 3 , wherein the metal fill comprises copper.

8. The circuit of claim 3 , wherein the conformal liner provides a barrier layer.

9. The circuit of claim 3 , wherein the conformal liner provides a seed layer.

10. A circuit, comprising:

a metallization level which includes a first metal routing path;

a dielectric layer over said metallization level, the dielectric layer including a via opening extending vertically completely through the dielectric layer and aligned with a top surface of the first metal routing path, said via opening having a width and a first height and further having a self-aligned direction and a non-self-aligned direction;

a metal plug that is not a conformal liner disposed at a bottom of the via opening in direct contact with the top surface of the first metal routing path, said metal plug having a second height less than the first height, wherein a width of the metal plug in the self-aligned direction is less than a width of the metal plug in the non-self-aligned direction;

wherein the metal plug is formed of cobalt or an alloy including cobalt; and

a second metal routing path disposed within the via opening in contact with the metal plug;

wherein the second metal routing path is made of a material different than the metal plug.

11. The circuit of claim 10 , wherein the second metal routing path comprises:

a conformal liner in contact with the metal plug; and

a metal fill over the conformal liner.

12. The circuit of claim 11 , wherein the metal fill comprises copper.

13. The circuit of claim 11 , wherein the conformal liner is a barrier layer.

14. The circuit of claim 11 , wherein the conformal liner is a seed layer.

15. A circuit, comprising:

a metallization level which includes a first metal routing path;

an adhesion layer on said metallization level;

a dielectric layer on said adhesion layer;

a via opening extending vertically completely through the dielectric layer and the adhesion layer to a top surface of the first metal routing path, wherein the via opening has a self-aligned direction and a non-self-aligned direction;

a metal plug disposed at a bottom of the via opening in direct contact with the top surface of the first metal routing path, said metal plug having a height across its width that is greater than a thickness of the adhesion layer but less than a combined thickness of the adhesion layer and dielectric layer, wherein a width of the metal plug in the self-aligned direction is less than a width of the metal plug in the non-self-aligned direction;

wherein the metal plug is formed of cobalt or an alloy including cobalt; and

a second metal routing path disposed within the via opening in contact with the metal plug;

wherein the second metal routing path is made of a material different than the metal plug.

16. The circuit of claim 15 , wherein the thickness of the adhesion layer is 10-30 nm and a thickness of the dielectric layer greater than the thickness of the adhesion layer.

17. The circuit of claim 16 , wherein the thickness of the dielectric layer is 30-1000 nm.

18. The circuit of claim 16 , wherein the thickness of the dielectric layer is 60-200 nm.