The effect of implant species and doping level on cobalt silicide contact formation on ultra-shallow junctions

Cobalt silicide layer formation on ultra-shallow junctions (<100 nm deep) was studied as a function of junction doping species and concentration over the range from below the electrical activation limit to above it. The silicide thickness, as measured by XRF, was uniform to within 2-3% (1 sigma) and did not depend on the junction doping. XTEM measurements showed that the silicide microstructure was unaffected by doping. No discernable effect of doping or species could be observed on the silicide sheet resistance, where the standard deviation of the resistance variation across a 200 nm wafer was 3-4%. Silicides formed on substrates which were initially amorphized by the junction implant were slightly smoother that those formed on undoped wafers or B junctions. A large fraction (80-90%) of the junction dose was lost to the growing silicide.