Pseudo-breakdown phenomenon and barrier integrity in Cu/porous ultra low-k damascene interconnects

A pseudo-breakdown phenomenon in Cu/porous ultra low-k damascene interconnects, and its relation with Cu transport behavior in inter-metal dielectric (IMD), was investigated. It was found that the Cu penetration through the sidewall barrier into the porous dielectric was the dominating failure mechanism and resulted in the pseudo-breakdown phenomenon when a conventional physical vapor deposited (PVD) TaN/Ta barrier was used. Introducing a thin a-SiC:H modification layer prior to the deposition of the PVD Ta barrier improves the barrier integrity and considerably extends the lifetime of interconnects - but the dominating failure mechanism does not change. When a bilayer structure of thicker a-SiC:H and thinner Ta layers was used as sidewall barrier, the Cu penetration into IMD was inhibited. As a result, the pseudo-breakdown behavior was completely eliminated and a well-protected sidewall region was achieved. Simultaneously, the Cu mobility in the porous ultra low-k dielectric was calculated based on the pseudo-breakdown behavior.