Scaling effects on microstructure and electromigration reliability for Cu and Cu(Mn) interconnects

EM reliability of Cu and Cu(Mn) interconnects was investigated, focusing on the scaling effect on grain structure and mass transport. The microstructure of Cu and Cu(Mn) interconnects was characterized up to the 22 nm node using a high-resolution TEM diffraction technique. Compared to Cu interconnects of the 45 nm node, the 28 nm Cu(Mn) structures were found to have a strong {111} texture along the line length direction and a low fraction of coherent twin boundaries (~2%). Inclusion of Mn was found to be important for microstructure evolution. The effect of Mn alloying on EM reliability was examined by comparing the lifetime statistics to Cu interconnects with standard SiCN cap and CoWP metal cap. The interfacial and GB diffusivities together with activation energies were extracted from resistance traces in EM tests. Mn was found to effectively reduce EM-induced mass transport, particularly for interfacial diffusion. These results were combined to project the Mn alloying effect for future technology.