Electromigration in strapped metal layers with large dimensions for lateral power device applications

摘要

Interconnects for lateral power devices generally have multiple metal layers that are wide and thick to carry large current. Often times, these metal layers are also strapped together. In order to investigate the electromigration (EM) reliability for such metal systems, we stress an interconnect that straps three metal layers (ohmic contact metal (M0), M1, and M2) at 500 mA, 225°C; 400 mA, 225°C; and 500 mA 210°C. It shows three distinctive failure modes of early and late failures, and immortality. Massive voiding at M1 takes place with overhang effect, and voiding at M2 step turns out as the fatal failure mode. The temperature gradient over the M2 step is simulated and identified as a root cause of this failure. For the late fails, metal layer thickening and PO layer lift-up are newly observed, which are attributed to the massive force from the thickening of large dimensional M1 layer. These results provide new insights on the EM reliability of lateral power devices, contrasting to the Cu (or Al) voiding failure completely confined in the interconnect for CMOS circuits.