The influence of an epitaxial CoSi2 layer on diffusion of B and Sb in underlying Si during oxidation

The effect of an epitaxial 20 nm thick CoSi2 layer on the diffusion of B and Sb in Si is investigated during oxidation and is compared to thermal diffusion in Si. B and Sb doping superlattices (DSLs) were grown by molecular beam epitaxy (MBE). They consisted of six spikes with peak concentrations of about 1018 cm–3 (B) and about 1019 cm–3 (Sb) and peak centres spaced 100 nm apart. The shallowest spike was capped with 100 nm of Si followed by 20 nm of CoSi2 grown by molecular beam allotaxy (MBA). Oxidation in dry O2 and annealing in pure N2 were performed at temperatures of 800 °C to 1200 °C. Concentration depth profiles were measured by secondary ion mass spectrometry (SIMS). The results showed that the diffusion of B and Sb in Si was markedly different for specimens with or without a CoSi2 layer. Oxidation enhanced diffusion (OED) of B and oxidation retarded diffusion (ORD) of Sb was observed for specimens without a CoSi2 layer. The effect of CoSi2 layer was a strong retardation of B diffusion and an enhancement of Sb diffusion. The B diffusivity was retarded by a factor of 2–10 as compared to the thermal diffusivity and by a factor of 20–100 as compared to the corresponding diffusivity for oxidation of Si without a CoSi2 layer. Sb diffusivity was enhanced by a factor of 2 with respect to thermal diffusivity and by about a factor of 5 as compared to the case without a CoSi2 layer.