Electromigration-induced compressive stresses in encapsulated thin-film conductors

Electromigration-induced compressive stresses in encapsulated thin-film conductors were studied by using NPN transistors as pressure sensors. The time-dependent behavior of the common-emitter current gain (beta) was monitored on shallow-junction NPN transistors operated in the conduction mode. In a long conductor, the compressive stress decreased exponentially within a distance much shorter than the conductor. In a short conductor, there was an improvement in electromigration resistance and a suppression of extrusions as a consequence of the higher compressive stress gradient. The primary failure mode observed for an encapsulated conductor is an intralevel extrusion along the silicon nitride to sputtered quartz interface.<>