Effects of contact resistance and film thickness on current crowding and the critical product of electromigration in Blech structures

In using Blech structures to study electromigration, the current density has been assumed to be the same in similar sets of short strips deposited on an underlayer. But this is not true owing to the existence of contact resistance between the strips and the underlayer. The contact resistivity may change due to different methods of sample preparation. High contact resistivity reduces the maximum current in the strip. Also, it diffuses the currents at the strip/underlayer interface from a narrow crowding to a wide spreading. In this work, we simulate these phenomena of current reduction and spreading in terms of contact resistivity and film thickness. We explore their effects on back stress and incubation time of void formation in short strips. We demonstrate these effects by the discrepancy in the critical product measurements found in experiments using similar Blech structures. © 2001 American Institute of Physics.