Cu Diffusion Barrier Properties of Various CoWB Electroless Plated Films on SiO2/Si Substrate for Via-last TSV Application

There is a serious problem of poor sidewall coverage for the sputtered barrier metals in high aspect ratio TSVs, and it is becoming difficult for complete filling of Cu. We have proposed electroless plated Co-alloy barrier metals for replacing conventional sputtered barrier metals. In this study, we evaluated Cu diffusion barrier properties of various electroless CoWB films with different atomic compositions. CoWB and CoB films were electroless plated on Pd nanoparticle catalyst. A typical structure for evaluation of interdiffusion is stacked layers of TiN/Cu/CoWB barrier layer/thin SiCh/Si substrate. We evaluated Cu interdiffusion characteristics after annealing by SIMS depth profiling. The ratio of the atomic composition of CoWB were varied by tuning plating bath conditions. It was shown that an electroless CoWB film with W content larger than 15% had a good Cu diffusion barrier property against 350 °C annealing.