Composite contact plug structure and method of making same

1. A method for forming a contact plug, the method comprising:

forming a dielectric layer over a substrate;

patterning an opening in the dielectric layer, the opening exposing the substrate;

depositing a diffusion barrier layer in the opening;

depositing a conductive liner comprising cobalt or ruthenium over the diffusion barrier layer, wherein the conductive liner as deposited is thicker on a bottom surface of the opening than on sidewalls of the opening; and

filling remaining portions of the opening with a conductive core, wherein the conductive core and the conductive liner comprise different metallic materials, wherein a metallic material of the conductive core is in direct contact with a metallic material of the conductive liner, and wherein the conductive liner is disposed between the conductive core and the diffusion barrier layer.

2. The method of claim 1 , wherein depositing the diffusion barrier layer comprises depositing tantalum or tantalum nitride.

3. The method of claim 1 further comprising, before depositing the diffusion barrier layer, depositing a conductive film on the bottom surface of the opening, wherein the conductive film contacts the substrate.

4. The method of claim 3 further comprising, after filling the remaining portions of the opening with the conductive core, forming a silicide region in an upper portion of the substrate.

5. The method of claim 4 , wherein forming the silicide region comprises an annealing process, and wherein the annealing process diffuses at least a portion of the conductive film into the upper portion of the substrate.

6. The method of claim 4 , wherein filling the remaining portions of the opening with the conductive core comprises filling the remaining portions of the opening with a conductive material comprising tungsten, cobalt, or ruthenium.

7. The method of claim 4 further comprising, after filling the remaining portions of the opening with the conductive core, exposing a top surface of the dielectric layer.

8. A method for forming a contact plug, the method comprising:

forming a dielectric layer over a substrate;

etching the dielectric layer to form an opening in the dielectric layer, the opening exposing the substrate;

depositing a first metallic material on a bottom surface and sidewalls of the opening;

depositing a diffusion barrier layer over the first metallic material;

depositing a second metallic material over the diffusion barrier layer using a first deposition process, the second metallic material comprising cobalt or ruthenium, a first portion of the second metallic material extending along the sidewalls of the opening having a first thickness at the end of the first deposition process, a second portion of the second metallic material over the bottom surface of the opening having a second thickness at the end of the first deposition process, the first thickness being less than the second thickness; and

filling the opening with a third metallic material, the third metallic material being different from the second metallic material, the second metallic material extending along a bottom surface and sidewalls of the third metallic material, the second metallic material being in direct contact with the third metallic material.

9. The method of claim 8 further comprising forming a silicide region in the substrate, the silicide region being disposed below the bottom surface the opening, the silicide region comprising a silicide of the first metallic material.

10. The method of claim 9 , wherein the silicide region physically contacts the diffusion barrier layer.

11. The method of claim 9 , wherein forming the silicide region comprises an annealing process.

12. The method of claim 8 further comprising removing a portion of the third metallic material overfilling the opening.

13. The method of claim 8 , wherein in the diffusion barrier layer comprises tantalum or tantalum nitride.

14. The method of claim 8 , wherein the third metallic material comprises tungsten, cobalt, or ruthenium.

15. A method for forming a contact plug, the method comprising:

forming a dielectric layer over a substrate;

removing a portion of the dielectric layer to form an opening in the dielectric layer, the opening exposing an upper portion of the substrate;

forming a first conductive layer on a bottom surface and a sidewall of the opening, the first conductive layer comprising titanium, cobalt, nickel, or tungsten;

forming a diffusion barrier layer over the first conductive layer, the diffusion barrier layer comprising tantalum or tantalum nitride;

forming a second conductive layer over the diffusion barrier layer, the second conductive layer comprising cobalt or ruthenium;

forming a third conductive layer over the second conductive layer, the third conductive layer completely filling the opening, the third conductive layer comprising tungsten, cobalt, or ruthenium, the second conductive layer and third conductive layer being different mono-elemental metallic materials, the second conductive layer being in direct contact with the third conductive layer, an entirety of a first portion of the second conductive layer interposed between an entirety of the sidewall of the opening and an entirety of a sidewall of the third conductive layer having a first uniform thickness, a second portion of the second conductive layer interposed between the bottom surface of the opening and a bottom surface of the third conductive layer having a second thickness, the second thickness being greater than the first uniform thickness; and

after forming the third conductive layer, annealing the substrate.

16. The method of claim 15 , wherein annealing the substrate comprises forming a silicide region in the upper portion of the substrate, the silicide region comprising titanium silicide, cobalt silicide, nickel silicide, or tungsten silicide.

17. The method of claim 16 , wherein the silicide region physically contacts the diffusion barrier layer.

18. The method of claim 15 further comprising, after annealing the substrate, performing a planarization process to remove excess materials extending above a topmost surface of the dielectric layer.

19. The method of claim 15 , wherein the first conductive layer does not extend between the diffusion barrier layer and the substrate after annealing the substrate.

20. The method of claim 15 , wherein removing the portion of the dielectric layer comprises etching the dielectric layer.