In order to maximize Cu volume and reduce via resistance, barrier thickness reduction is a strong option. Alternative barriers for next-generation BEOL were evaluated in terms of barrier performance to O2 and Cu diffusion, and effects on reliability. A clear correlation of O2 barrier performance to electromigration was observed, suggesting that the key role of the barrier layer is to prevent oxidation of Cu or the Cu/barrier interface. Long-throw PVD-TaN showed superior O2 barrier performance to alternative metals such as PEALD-TaN, thermal ALD-TaN, -TaN(Mn) and - MnN and MnSiO3 self-forming barrier. © 2014 IEEE.