Capping layer for liner-free conductive structures
The present disclosure describes a method for forming capping layers configured to prevent the migration of out-diffused cobalt atoms into upper metallization layers In some embodiments, the method includes depositing a cobalt diffusion barrier layer on a liner-free conductive structure that includes ruthenium, where depositing the cobalt diffusion barrier layer includes forming the cobalt diffusion barrier layer self-aligned to the liner-free conductive structure. The method also includes depositing, on the cobalt diffusion barrier layer, a stack with an etch stop layer and dielectric layer, and forming an opening in the stack to expose the cobalt diffusion barrier layer. Finally, the method includes forming a conductive structure on the cobalt diffusion barrier layer.
1. A structure, comprising:
a substrate;
a first metallization layer on the substrate, wherein the first metallization layer comprises a liner-free conductive structure and wherein a first portion of the liner-free conductive structure is surrounded by a dielectric and a second portion of the liner-free conductive structure is surrounded by a metal;
a capping layer on a top surface of the liner-free conductive structure; and
a second metallization layer on the first metallization layer and comprising a conductive structure on the liner-free conductive structure, wherein the capping layer is interposed between the top surface of the liner-free conductive structure and a bottom surface of the conductive structure.
2. The structure of claim 1 , wherein the top surface of the liner-free conductive structure is below a top surface of the dielectric, and wherein a top surface of the capping layer is coplanar with the top surface of the dielectric.
3. The structure of claim 2 , wherein the capping layer has a dome shape.
4. The structure of claim 3 , wherein a bottom surface of the capping layer is planar.
5. The structure of claim 1 , wherein the top surface of the liner-free conductive structure and a top surface of the capping layer are not coplanar with a top surface of the dielectric.
6. The structure of claim 1 , wherein the capping layer contacts bottom and sidewall surfaces of the conductive structure.
7. The structure of claim 1 , wherein the capping layer comprises tungsten, titanium nitride, or tantalum nitride.
8. The structure of claim 1 , wherein the liner-free conductive structure comprises ruthenium.
9. A structure, comprising:
a substrate;
a first metallization layer on the substrate and comprising a liner-free conductive structure surrounded by a dielectric;
a capping layer disposed on a top surface of the liner-free conductive structure, wherein the capping layer has a dome shape with a base larger than a width of the liner-free conductive structure; and
a second metallization layer on the first metallization layer and comprising a conductive structure on the liner-free conductive structure, wherein the liner-free conductive structure is separated from the conductive structure by the capping layer.
10. The structure of claim 9 , wherein the capping layer is embedded within a bottom portion of the conductive structure.
11. The structure of claim 9 , wherein top surfaces of the capping layer are not coplanar with the dielectric.
12. The structure of claim 9 , wherein a portion of a bottom surface of the capping layer is co-planar with the dielectric and wider than the liner-free conductive structure.
13. The structure of claim 9 , wherein the capping layer comprises tungsten.
14. The structure of claim 9 , wherein the capping layer covers a first portion of the dielectric and the conductive structure covers a second portion of the dielectric different from the first portion.
15. The structure of claim 9 , wherein a bottom surface of the conductive structure is not planar.
16. The structure of claim 9 , wherein the liner-free conductive structure comprises ruthenium metal, and wherein the capping layer comprises a metal selectively deposited on the ruthenium metal.
17. A method, comprising:
depositing a cobalt diffusion barrier layer on a liner-free conductive structure comprising ruthenium, wherein depositing the cobalt diffusion barrier layer comprises forming the cobalt diffusion barrier layer self-aligned to the liner-free conductive structure;
depositing, on the cobalt diffusion barrier layer, a stack comprising an etch stop layer and dielectric layer;
forming an opening in the stack to expose the cobalt diffusion barrier layer; and
forming a conductive structure on the cobalt diffusion barrier layer to surround the cobalt diffusion barrier layer.
18. The method of claim 17 , wherein forming the cobalt diffusion barrier layer comprises depositing a tungsten layer with a chemical vapor deposition process at a temperature range between about 300° C. and about 400° C. and at a process pressure between about 1 Torr and about 10 Torr.
19. The method of claim 18 , wherein the chemical vapor deposition process comprises tungsten hexafluoride and hydrogen.
20. The method of claim 17 , wherein depositing the cobalt diffusion barrier layer comprises depositing a metal with a melting point higher than about 600° C. and an electrical resistivity less than about 150 μΩ·cm.