Stress migration related reliability concerns [IC interconnects]

Missing tungsten (W) was observed during the stress migration (SM) test. In this paper, we apply extensive experiments on via chain test structures to find the root cause, and successfully eliminate missing-W in vias by modifying the ash recipe, UV cure conditions, and ILD film thickness. In addition, adding EKC before W CMP increases W-missing failures, which verified the existence of galvanic effects. Failure analyses are conducted to identify the failure mechanism and to ensure the problem is solved. However, the cycle time for such improvement is far from acceptable. Therefore, a new test pattern - self-heated SM structure and its corresponding test methodology - wafer level SM temperature cycling are recommended for WLRC.