Conductive structures with bottom-less barriers and liners

Abstract

A blocking material is selectively deposited on a bottom surface of a back end of line (BEOL) conductive structure such that a barrier layer is selectively deposited on sidewalls of the BEOL conductive structure but not the bottom surface. The blocking material is etched such that copper from a conductive structure underneath is exposed, and a ruthenium layer is deposited on the barrier layer but less ruthenium is deposited on the exposed copper. Accordingly, the barrier layer prevents diffusion of metal ions from the BEOL conductive structure and is substantially absent from the bottom surface as compared to the sidewalls in order to reduce contact resistance. Additionally, the ruthenium layer reduces surface roughness within the BEOL conductive structure and is thinner at the bottom surface as compared to the sidewalls in order to reduce contact resistance.