Low-resistivity metallic interconnect structures

1. A method, comprising:

forming a sacrificial dielectric layer on a substrate;

patterning the sacrificial dielectric layer to form an opening in the sacrificial dielectric layer;

filling the opening with metallic material to form a metallic interconnect structure;

removing the sacrificial dielectric layer to expose the metallic interconnect structure;

applying a heat treatment process to heat the exposed metallic interconnect structure to (i) modulate a microstructure of the metallic material of the metallic interconnect structure from a first microstructure to a second microstructure, and to (ii) cause surface rounding of an upper surface of the metallic interconnect structure;

performing a selective deposition process to selectively deposit a conformal liner layer on exposed surfaces of the metallic interconnect structure, subsequent to the heat treatment process, wherein the selective deposition is performed so that material forming the liner layer is deposited only on the exposed sidewall and upper surfaces of the metallic interconnect structure; and

forming a dielectric layer to encapsulate the metallic interconnect structure in dielectric material,

wherein the conformal liner layer comprises a diffusion barrier layer between the metallic interconnect structure and the dielectric layer.

2. The method of claim 1 , wherein the metallic interconnect structure comprises one of a metallic via and a metallic line.

3. The method of claim 1 , wherein the metallic material of the metallic interconnect structure comprises copper.

4. The method of claim 1 , wherein the metallic material of the metallic interconnect structure comprises one of aluminum, tungsten, iridium, cobalt, and ruthenium.

5. The method of claim 1 , wherein applying the heat treatment comprises thermally annealing the metallic interconnect structure in a furnace.

6. The method of claim 1 , wherein applying the heat treatment comprises applying laser radiation to the metallic interconnect structure to heat the metallic interconnect structure.

7. The method of claim 1 , wherein applying the heat treatment process to cause the surface rounding of the upper surface of the metallic interconnect structure comprises rounding upper corners of the metallic interconnect structure.

8. The method of claim 1 , wherein the first microstructure comprises a polycrystalline microstructure and wherein the second microstructure comprises an average grain size which is greater than an average grain size of the polycrystalline microstructure.

9. The method of claim 1 , wherein an average grain size of the second microstructure of the metallic interconnect structure is greater than a critical dimension of the metallic interconnect structure.

10. The method of claim 1 , wherein end portions of grain boundaries of the second microstructure of the metallic interconnect structure extend from an upper surface to a bottom surface of the metallic interconnect structure.

11. The method of claim 1 , wherein the dielectric layer comprises an interlayer dielectric (ILD) layer of a back-end-of-line (BEOL) structure.

12. The method of claim 1 , wherein the conformal liner layer comprises one of cobalt, ruthenium, tungsten, aluminum, iridium, rhodium, tantalum, and alloys thereof.

13. The method of claim 1 , wherein forming the dielectric layer to encapsulate the metallic interconnect structure in dielectric material, comprises depositing a non-conformal layer of dielectric material to form an air gap in the dielectric layer adjacent to the metallic interconnect structure.

14. A device, comprising:

a dielectric layer disposed on a substrate;

a metallic interconnect structure encapsulated in the dielectric layer;

wherein the metallic interconnect structure comprises a conformal liner layer formed on an upper surface and sidewall surfaces of the metallic interconnect structure, wherein the conformal liner layer comprises a diffusion barrier layer between the metallic interconnect structure and the dielectric layer;

wherein the metallic interconnect structure comprises metallic material having an average grain size which is greater than a critical dimension of metallic interconnect structure;

wherein the metallic interconnect structure comprises a rounded upper surface; and

wherein the conformal liner layer comprises a conformal rounded portion which is disposed on the rounded upper surface of the metallic interconnect structure.

15. The device of claim 14 , wherein the metallic interconnect structure comprises one of a metallic via, a metallic line, and both a metallic via and a metallic line.

16. The device of claim 14 , wherein end portions of grain boundaries of the metallic material of the metallic interconnect structure extend from an upper surface to a bottom surface of the metallic interconnect structure.

17. The device of claim 14 , wherein the dielectric layer comprises an interlayer dielectric (ILD) layer of a back-end-of-line (BEOL) structure.

18. The device of claim 14 , wherein the metallic interconnect structure comprises copper.

19. The device of claim 14 , wherein the conformal liner layer comprises one of cobalt, ruthenium, tungsten, aluminum, iridium, rhodium, tantalum, and alloys thereof.

20. The device of claim 14 , wherein the conformal liner layer is formed with a thickness in a range of about 0.5 nm to about 20 nm.