Enhancement of seeding for electroless Cu plating of metallic barrier layers by using alkyl self-assembled monolayers

Abstract Tethering a self-assembled monolayer (SAM) on ultralow-k (porous) dielectric materials as a seed-trapping layer for electroless Cu plating has been extensively studied. By contrast, literature on direct electroless Cu plating of metallic barrier layers assisted by SAMs is scarce. Therefore, Ta, a crucial component of barrier materials for Cu interconnect metallization, was investigated as a model substrate for a new seeding (Ni catalyst formation) process of electroless Cu plating. Transmission and scanning electron microscopies indicated that catalytic particles formed on Ta films through Ta OH groups tend to become aggregates with an average size of 14 nm and density of 2 × 1015 m−2. By contrast, Ta films with a plasma-functionalized SAM tightly bound catalytic particles without agglomeration, thus yielding a markedly smaller size (3 nm) and higher density (3 × 1016 m−2; one order greater than those formed by other novel methods). X-ray photoelectron spectroscopy clearly identified the types of material species and functional groups induced at each step of the seeding process. Moreover, the phase of the catalytic particles, either nickel alkoxide, Ni(OH)2, or metallic Ni, along with the seed-bonding mechanism, was also unambiguously distinguished. The enhancement of film-formation quality of Cu by the new seeding process was thus demonstrated.