Interfacial Adhesion Energies of Uniformly Self-Formed Cr2O3 Barriers for Advanced Co Interconnects

The effects of Cr doping and postannealing on the interfacial adhesion energies between a Co interconnect and a SiO2 dielectric layer prepared by physical vapor deposition were systematically evaluated using a four-point bending test. Co, as a promising interconnect due to its scalability, is vulnerable to electromigration on its interface because the poor adhesion energy between Co and a barrier metal provides a diffusion path for atoms. To solve this problem, we suggest doping of Cr, which easily diffuses from the Co metal to the Co/SiO2 interface during postannealing, to form a uniformly distributed layer on the Co interface. Atomic force microscopy analysis clearly showed uniformly segregated Cr at the Co-Cr/SiO2 interface without hillocks or voids. The roughness root mean square values of annealed Co/TiN/Ti, annealed Co-4.7 at% Cr, and annealed Co-7.5 at% Cr were 0.72, 0.18, and 0.21 nm, respectively. In the four-point bending test, Co-4.7 at% Cr/SiO2 and Co-7.5 at% Cr/SiO2 were not delaminated at their interface, unlike pure Co and Co with the conventional barrier metal, which were delaminated at the interface with SiO2. In the X-ray photoelectron spectroscopy analysis of the Co-Cr/SiO2 interface, an increase in Cr-O bonding was clearly detected after annealing. Therefore, a properly annealed Cr2O3 self-forming barrier with strong interfacial reliability appears to be a promising diffusion barrier for Co interconnects.