Mechanisms of forming damascene interconnect structures

1. An interconnect structure, comprising:

a first trench; and

a second trench, wherein the second trench is wider than the first trench, and wherein both trenches are lined with a diffusion barrier layer having a substantially uniform thickness, and wherein a first conductive layer is deposited over the diffusion barrier layer, and wherein a metal cap layer is over the first conductive layer, and wherein a second conductive layer is deposited over the metal cap layer in the second trench, and the diffusion barrier layer is between the second conductive layer and a sidewall of the second trench, and the metal cap layer inside the second trench is in direct contact with the diffusion barrier layer,

wherein a first maximum thickness of the first conductive layer in the second trench is less than a second maximum thickness of the first conductive layer in the first trench.

2. The interconnect structure of claim 1 , wherein the second conductive layer is over the metal cap layer in the first trench.

3. The interconnect structure of claim 1 , wherein the first conductive layer is thicker in the first trench than the second trench.

4. The interconnect structure of claim 1 , wherein the first conductive layer and the second conductive layer both comprise copper.

5. The interconnect structure of claim 1 , wherein the metal cap layer comprises at least one of cobalt, nickel, tungsten, molybdenum, silicon, zinc, chrome, boron, phosphorus, nitrogen, or combinations thereof.

6. The interconnect structure of claim 1 , wherein the metal cap layer has a thickness in a range from 0.5 nm to 20 nm.

7. The interconnect structure of claim 1 , wherein the width of the first trench is in a range from 10 nm to 100 nm.

8. The interconnect structure of claim 1 , wherein first and second trenches are part of at least one dual damascene structure.

9. The interconnect structure of claim 1 , wherein a distance from a top surface of the second trench to the first conductive layer is in a range from 1 nm to 50 nm.

10. An interconnect structure, comprising:

a first trench; and

a second trench, wherein the second trench is wider than the first trench, and wherein both trenches are lined with a diffusion barrier layer having a substantially uniform thickness, and wherein a conductive layer is over the diffusion barrier layer, and a metal cap layer in both trenches is over an entirety of the conductive layer, and a second conductive layer is over the metal cap layer in the second trench, and the diffusion barrier layer is between the second conductive layer and a sidewall of the second trench,

wherein a first maximum thickness of the first conductive layer in the second trench is different from a second maximum thickness of the first conductive layer in the first trench, and a bottom surface of the first conductive layer in the second trench is substantially co-planar with a bottom surface of the first conductive layer in the first trench.

11. An interconnect structure comprising:

a substrate;

a dielectric layer over the substrate, the dielectric layer having a first opening therein;

a diffusion barrier layer lining the first opening, wherein a top surface of the diffusion barrier layer is planar with a top surface of the dielectric layer, and the diffusion barrier layer has a substantially uniform thickness;

a first conductive layer in the first opening, wherein an entirety of the first conductive layer is below the top surface of the dielectric layer;

a first process layer over the first conductive layer, wherein a top surface of a central portion of the first process layer is below the top surface of the dielectric layer; and

a second conductive layer in the first opening, wherein the first process layer is between the second conductive layer in the first opening and the dielectric layer, wherein a maximum thickness of the second conductive layer in the first opening is greater than a maximum thickness of the second conductive layer in a neighboring trench.

12. The interconnect structure of claim 11 , wherein the second conductive layer in the first opening is over the first process layer, wherein the first process layer is a metal cap layer.

13. The interconnect structure of claim 12 , wherein a top surface of the second conductive layer in the first opening is planar with the top surface of the dielectric layer.

14. The interconnect structure of claim 11 , further comprising:

a second conductive layer in a second opening in the dielectric layer, wherein a top surface of the second conductive layer in the second opening is below the top surface of the dielectric layer; and

a second process layer over the second conductive layer in the second opening.

15. The interconnect structure of claim 14 , wherein a first distance between the top surface of the first conductive layer and the top surface of the dielectric layer is greater than a second distance between the top surface of the second conductive layer in the second opening and the top surface of the dielectric layer.

16. The interconnect structure of claim 14 , wherein the second process layer is a metal cap layer and a top surface of the metal cap layer is planar with the top surface of the dielectric layer.

17. The interconnect structure of claim 14 , wherein the second process layer is a metal cap layer.

18. The interconnect structure of claim 14 , further comprising a third conductive layer over the second process layer, wherein the second process layer is a metal cap layer.

19. The interconnect structure of claim 18 , wherein a top surface of the third conductive layer is planar with the top surface of the dielectric layer.

20. The interconnect structure of claim 11 , wherein the diffusion barrier layer is between a sidewall of the first process layer and the dielectric layer.