Evaluation of the initial growth of electroless deposited Co(W,P) diffusion barrier thin film for Cu metallization

The formation mechanism of electroless deposited Co(W,P) films is investigated. Co(W,P) films, containing 88–90 at% of Co and 10–12 at% of W and P, are deposited directly onto p-type Si(100) substrate via Pd wet activation. Co(W,P) initially nucleates around Pd activation sites and this is followed by a strong lateral growth. Uniform Co(W,P) thin films can be obtained after 2 min deposition. Fast immersion measurement shows that the mixed potential of Co(W,P) is −0.78 V versus Ag/AgCl electrode. XRD examination shows that the Pd layer has a domination of (111) texture and the principle microstructure of the as-deposited Co(W,P) film is the hcp phase of nano-sized ε-Co. The inelastic mean free path of diffused Cu in Co(W,P) is determined to be 7.37 Å which is significantly smaller than that (9.9 Å) in pure Co, indicating that Co(W,P) is a very effective barrier layer.