Amorphous Ru(P) films grown by chemical vapor deposition at 575 K using a single source precursor, cis-RuH2(P(CH3)(3))(4), or dual sources, Ru-3(CO)(12) and P(CH3)(3) or P(C6H5)(3), are studied. The phosphorus percentage affects the film microstructure, and incorporating > 13 % P resulted in amorphous Ru(P) films. While codosing P(CH3)(3) with Ru-3(CO)(12) improves film step coverage, the most conformal Ru(P) film is obtained with cis-RuH2(P(CH3)(3))(4). A fully continuous 5 nm Ru(P) film is formed within 1 mu m deep, 8:1 aspect ratio trenches. The barrier performance is tested using Cu/Ru/Si(100) stacks annealed at 575 K, and sheet resistance was used as a measure of barrier failure. Cu diffusivity in physical vapor deposition (PVD) Ru is approximated to be 6.6 x 10(-17) cm(2)/s at 575 K, which indicates fast Cu diffusion along the grain boundaries. While 26 nm polycrystalline PVD Ru. failed after 6 h annealing by Cu penetration, 28 nm amorphous Ru(P) survived after 67 h annealing. First principles density functional calculations suggest 16.7% P degraded the adhesion strength by 12% when compared to crystalline Cu/Ru, by the presence of P at the interface. However, due to the strong Ru-Cu bonds, amorphous Ru(P) still forms a stronger interface with Cu than do Ta and TaN to Cu, as observed when annealing 10 nm Cu films on these surfaces at 675 K. (C) 2008 American Vacuum Society.