Evaluation of electroless deposited Co(W,P) thin films as diffusion barriers for copper metallization

Electroless deposited Co(W,P) thin films were evaluated as diffusion barriers for copper metallization. Capacitance versus time measurements of MOS structures as well as SIMS depth profiles indicate that 30-nm-thick films can function as effective barriers against copper diffusion after thermal treatments up to 500 degreesC. The improved barrier properties relative to sputtered cobalt are explained by the incorporation of phosphorus (8-10 at.%) and tungsten (similar to2 at.%) which most probably enrich the grain boundaries of the nanocrystalline hcp cobalt grains, forming a 'stuffed' barrier. The phosphorus and tungsten additions stabilize the hcp crystalline structure of the cobalt grains, delaying the transition to the fee phase by more than 80 degreesC compared to bulk pure cobalt. An advantage of this material compared to alternative diffusion barriers for copper is its relatively low resistivity of 80 mu Omega cm. (C) 2001 Elsevier Science B.V. All rights reserved.