Methods for thermally forming a selective cobalt layer

1. A method of selectively depositing a cobalt layer, comprising:

(a) exposing a substrate to a first process gas to passivate an exposed dielectric surface, wherein the substrate comprises a dielectric layer having an exposed dielectric surface and a metal layer having an exposed metal surface, wherein the first process gas comprises a silane containing compound, a vinyl silane containing compound, or alcohols;

(b) selectively depositing a cobalt layer atop the exposed metal surface using a thermal deposition process; and

(c) exposing the substrate to the first process gas after selectively depositing the cobalt layer to reduce a dielectric constant of the dielectric layer, wherein the first process gas is a passivating gas.

2. The method of claim 1 , further comprising, prior to exposing the substrate to the first process gas, exposing the substrate to a reducing gas at a temperature of about 200 to about 800 degrees Celsius, exposing the substrate to a plasma formed from a reducing gas, or exposing the substrate to a UV light activated reducing gas, to remove contaminants from the exposed metal surface and exposed dielectric surface, wherein the first process gas is a passivating gas.

3. The method of claim 2 , wherein the reducing gas comprises nitrogen, ammonia, hydrogen, or alcohols.

4. The method of claim 1 , wherein the first process gas further comprises hydrogen gas (H 2 ) and an inert gas.

5. The method of claim 1 , wherein the substrate is exposed to the first process gas at a temperature of about 25 degrees Celsius to about 400 degrees Celsius.

6. The method of claim 1 , wherein exposing the substrate to the first process gas before selectively depositing the cobalt layer reduces the dielectric constant of the dielectric layer by about 1 percent to about 10 percent.

7. The method of claim 1 , wherein selectively depositing the cobalt layer further comprises exposing the substrate to a cobalt precursor gas.

8. The method of claim 7 , wherein the cobalt precursor gas is a cobalt carbonyl complex, a cobalt dienyl complex, or a cobalt nitrosyl complex.

9. The method of claim 1 , wherein the cobalt layer is selectively deposited at a temperature of about 200 degrees Celsius to about 400 degrees Celsius.

10. The method of claim 1 , wherein a ratio of a cobalt deposition rate on the exposed metal surface to a cobalt deposition rate on the exposed dielectric surface is about 200:1 to about 3000:1.

11. The method of claim 1 , wherein exposing the substrate to the first process gas after selectively depositing the cobalt layer reduces a dielectric constant of the dielectric layer by about 1 percent to about 10 percent.

12. The method of claim 1 , wherein the dielectric layer is a low-k dielectric layer having a dielectric constant of about 2.2 to about 3.

13. The method of claim 1 , wherein the metal layer is copper, tungsten, titanium nitride, or cobalt.

14. The method of claim 1 , further comprising repeating (a)-(b) to form the cobalt layer to a predetermined thickness.

15. A method of selectively depositing a cobalt layer, comprising:

exposing a substrate, comprising a dielectric layer having an exposed dielectric surface and a metal layer having an exposed metal surface, to a reducing gas at a temperature of about 200 to about 800 degrees Celsius, or to a plasma formed from a reducing gas, or to a UV light activated reducing gas to remove contaminants from the metal surface and from the dielectric surface;

exposing the substrate to a first process gas to passivate the exposed dielectric surface and reduce a dielectric constant of the dielectric layer by about 1percent to about 10 percent, wherein the first process gas comprises a silane containing compound, a vinyl silane containing compound, or alcohols;

selectively depositing a cobalt layer atop the metal surface using a thermal deposition process; and

exposing the substrate to the first process gas after selectively depositing the cobalt layer to reduce the dielectric constant of the dielectric layer by about 1percent to about 10 percent.

16. The method of claim 1 , wherein the silane containing compound is at least one of bis(dimethylamino)dimethylsilane, dimethlaminotrimethylsilane, 1-(trimethylsilyI)-1H-pyrrole, or chlorotrimethylsilane.

17. The method of claim 1 , further comprising depositing a barrier layer on the exposed dielectric surface prior to depositing the metal layer.

18. A method of selectively depositing a cobalt layer for forming a void-free feature, comprising:

(a) exposing a substrate having a metal layer disposed on the substrate to a first process gas;

(b) disposing a dielectric layer on the metal layer;

(c) etching a feature into the dielectric layer, the metal layer having an exposed surface;

(d) exposing the feature in the dielectric layer to a first process gas to passivate an exposed surface of the dielectric surface, the first process gas comprising a silane containing compound, a vinyl silane containing compound, or alcohols;

(e) exposing the substrate having the metal layer disposed thereon to a cobalt precursor gas, selectively depositing a cobalt layer atop the exposed metal surface using a thermal deposition process; and

(f) repeating (d)-(e) to deposit the cobalt layer to a pre-determined thickness or to fill the feature.

19. The method of claim 18 , further comprising, prior to exposing the substrate to the first process gas concurrent with exposing the substrate to a reducing gas at a temperature of about 200 to about 800 degrees Celsius to activate the reducing gas to remove contaminants from the exposed metal surface and the exposed dielectric surface.