A study of via depletion electromigration with very long failure times

Liner coverage in the via plays a critical role on via depletion EM for dual damascene Cu interconnects. Poor liner coverage at the via bottom often results in early EM fails. On the other hand, if the liner at via bottom is permeable to Cu diffusion, thanks to the constant Cu supply into the via from the line below, a very long or even “immortal” EM failure mode can be observed. This paper discusses how to modulate the Cu diffusion through the via bottom liner and its impact on product reliability.