Strengthening electroless Co-based barrier layers by minor refractory-metal doping

An electrochemical seeding process without involving sensitization-activation and displacement-activation is presented to grow catalytic particles of sizes only ~ 4 nm, subsequently initializing the deposition of Co–B and Co–W–B barrier layers which have controlled amounts of solutes, Co92B8 and Co90W3B7, on thermally oxidized SiO2 layer on Si using electroless plating. Analyzing the Si/SiO2/barrier layer samples before and after thermal annealing (450 °C/1 h) using depth-profiling secondary ion mass spectroscopy, transmission electron microscopy, and scanning electron microscopy reveals that the Co92B8 barrier layer is degraded by the mutual reactions between the barrier’s components, Co and B, and the outgoing Si, ultimately forming Co2Si and Co2B. However, doping a minor amount of tungsten not only strengthens the thermo-chemical and microstructure stability of the barrier layers, but also significantly reduces the self-diffusion of the matrix cobalt, and hence can prevent the intermixing of Co and Si. The strengthening behavior of the barrier layer by the doping of tungsten solute atoms will be clarified based on elemental depth-profiling and microstructure analyses.