A method for forming a silicon alloy based barrier layer comprises providing a substrate having a dielectric layer including a trench, placing the substrate in a reactor, and carrying out a process cycle, wherein the process cycle comprises introducing a silicon containing precursor into the reactor, introducing a metal containing precursor into the reactor, and introducing a co-reactant into the reactor, wherein the silicon, metal, and co-reactant react to form a silicon alloy layer that is conformally deposited on a bottom and a sidewall of the trench.