To investigate the cause of the lower electromigration (EM) resistance in Al/Al3Ti lines compared to that in Al/TiN lines, we studied the Al microstructure and the EM characteristics. Even after fine-grained Al3Ti formation through a reaction of the Al and Ti, the Al microstructure of the unreacted Al on the AI3Ti remained a bamboo grain structure with a high 111 orientation. Thus, the Al grain structure and texture did not affect the EM resistance. The critical current density for voiding was 0.64 MA/cm2. The Al drift velocity in the Al/Al3Ti bamboo lines was two orders of magnitude higher than that for Al/TiN bamboo lines from 180°C to 280°C. This higher Al drift velocity decreased the EM resistance in the lines. The activation energy of Al drift in the AI/AI3Ti lines was 0.6 to 0.7 eV, which is lower than that for Al lattice diffusion. Thus, the Al lattice is not the dominant transport path in Al/Al3Ti lines. The dependence of the Al drift velocity on the line size showed that the Al/Al3Ti interface was the dominant path in the Al/Al3Ti bamboo lines. Thus, we concluded that the rapid Al transport through the Al/Al3Ti interface decreases EM resistance in Al/Al3Ti lines.