Microstructure local effect for electromigration reliability improvement and Cu damascene lines design rules relaxation

Implication of microstructure during electromigration void formation process is studied in this paper. Dual damascene Cu lines with cathode end width variations are characterized. The idea of these variations being to force different microstructure profiles within the same test structure. The narrow-to-wide (NTW) width transition structure shows better electromigration performances than usual structure with a constant width (CW) along the line length. Bamboo Cu grains in the NTW structure wider segment are evidenced to slow down Cu atoms migration, inducing a local Blech´s-like effect. This results in delayed void nucleation time and reduced void growth rate leading to increased lifetime. By this study, we show how great advantage can be taken on lifetime with this new design.