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 barrie rs for copper metallization. Capacitance versus time measurements of MOS st ructures as well as SIMS depth profiles indicate that 30-nm-thick films can function as effective barriers against copper diffusion after thermal trea tments up to 500 degreesC. The improved barrier properties relative to sput tered cobalt are explained by the incorporation of phosphorus (8-10 at.%) a nd tungsten (similar to2 at.%) which most probably enrich the grain boundar ies of the nanocrystalline hcp cobalt grains, forming a 'stuffed' barrier. The phosphorus and tungsten additions stabilize the hcp crystalline structu re of the cobalt grains, delaying the transition to the fee phase by more t han 80 degreesC compared to bulk pure cobalt. An advantage of this material compared to alternative diffusion barriers for copper is its relatively lo w resistivity of 80 mu Omega cm. (C) 2001 Elsevier Science B.V. All rights reserved.