Electromigration instability: Transgranular slits in interconnects

Evidence has recently accumulated that an interconnect under intense electric current can fail by a transgranular slit. A rounded void first forms, enlarges, and drifts. When the void becomes sufficiently large, a narrow slit emerges at the expense of the void, running across the linewidth. In this letter we describe a physical mechanism that explains this instability. Both electric current and surface energy drive atoms to diffuse on the void surface, but in the opposite directions. The slit emerges if the electric current prevails. An approximate analysis shows how the slit selects its width and velocity.