Interconnect structure and fabrication method thereof
An interconnect structure includes a dielectric layer and a conductor embedded in the dielectric layer. A top surface of the conductor is flush with a top surface of the dielectric layer. A cobalt cap layer is deposited on the top surface of the conductor. A nitrogen-doped cobalt layer is disposed on the cobalt cap layer.
1. An interconnect structure, comprising:
a dielectric layer;
a conductor embedded in the dielectric layer, wherein a top surface of the conductor is flush with a top surface of the dielectric layer;
a cobalt cap layer disposed on the top surface of the conductor; and
a nitrogen doped cobalt layer disposed on the cobalt cap layer, wherein the nitrogen doped cobalt layer has a gradient doping profile across a thickness of the nitrogen doped cobalt layer.
2. The interconnect structure according to claim 1 , wherein the nitrogen doped cobalt layer has a first nitrogen doping concentration adjacent a top surface of the nitrogen doped cobalt layer and a second nitrogen doping concentration adjacent the cobalt cap layer, wherein the first nitrogen doping concentration is greater than the second nitrogen doping concentration.
3. The interconnect structure according to claim 1 , wherein the thickness of the nitrogen doped cobalt layer ranges between 0-50 angstroms.
4. The interconnect structure according to claim 1 , wherein the conductor comprises copper.
5. The interconnect structure according to claim 1 , wherein the conductor is encased by a barrier layer.
6. The interconnect structure according to claim 5 , wherein the barrier layer comprises tantalum or tantalum nitride.
7. The interconnect structure according to claim 1 further comprising an etch stop layer in direct contact with the nitrogen doped cobalt layer.
8. The interconnect structure according to claim 7 , wherein the etch stop layer comprises SiCN, SiC, SiON, SiCON, or SiN.
9. The interconnect structure according to claim 1 , wherein the dielectric layer comprises low-k dielectric or ultra-low k dielectric.
10. A method of fabricating an interconnect structure, comprising:
providing a substrate having a dielectric layer thereon and a conductor embedded in the dielectric layer, wherein a top surface of the conductor is flush with a top surface of the dielectric layer;
depositing a cobalt cap layer on the top surface of the conductor; and
performing a surface treatment process to dope nitrogen into the cobalt cap layer thereby forming a nitrogen-doped cobalt layer along a sidewall and a top surface of the cobalt cap layer, wherein the nitrogen doped cobalt layer has a gradient doping profile across a thickness of the nitrogen doped cobalt layer.
11. The method of fabricating an interconnect structure according to claim 10 , further comprising:
depositing an etch stop layer on the dielectric layer and the nitrogen-doped cobalt layer.
12. The method of fabricating an interconnect structure according to claim 11 , wherein the etch stop layer comprises SiCN, SiC, SiON, SiCON, or SiN.
13. The method of fabricating an interconnect structure according to claim 10 , wherein the surface treatment process comprises:
subjecting the cobalt cap layer to a NH 3 plasma.
14. The method of fabricating an interconnect structure according to claim 10 , wherein the cobalt cap layer is deposited by using a chemical vapor deposition (CVD) process.