Effects of P on amorphous chemical vapor deposition Ru-P alloy films for Cu interconnect liner applications

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, Ru3 (CO) 12 and P (CH3) 3 or P (C6 H5) 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 Ru3 (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 μm 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× 10-17 cm2 /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.