Impact of surface condition on Cobalt drift into LK3.0 films

Metal drift induced failure is a serious threat to the reliability of advanced back-end-of-line (BEOL) systems based on ultra-thin dielectric layers and metallization schemes with, at best, a very thin barrier. We evaluate the reliability of Cobalt (Co) and low-k dielectric (LK3.0) systems, with a focus on the impact of the metal/dielectric (m/d) interface and of barrier thickness and continuity. Our study confirms that metal drift is a surface driven phenomenon; in the case of low-k dielectrics, it is therefore crucial to preserve a hydrophobic m/d interface to minimize the occurrence of metal drift. Moreover, we find that, as the dielectric thickness is reduced, a thicker barrier is needed to prevent metal drift induced failure, regardless of the interface conditions. Nonetheless, we observed a sizeable increase of the intrinsic field acceleration factor, i.e. when no metal drift occurs, as dielectric thickness decreases, suggesting that scaled dielectrics are more resilient to intrinsic dielectric breakdown.