Effect of an epitaxial CoSi2 layer on diffusion of B and Sb in Si during annealing and oxidation

The diffusion of B and Sb in Si, with and without a 20-nm-thick epitaxial C oSi2 layer on top, is investigated, during annealing and oxidation, using d oping superlattices (DSLs). CoSi2 layers were grown on Si by molecular beam allotaxy. DSLs were grown by molecular beam epitaxy. They consisted of six spikes with peak concentrations of 10(18) cm(-3) (B) and about 10(19) cm(- 3)(Sb) with peak centers spaced 100 nm apart. The shallowest spike was capp ed with 100 nm of Si followed by 20 nm of CoSi2. Annealing in pure N-2 and oxidation in pure O-2 were performed at temperatures ranging from 800 to 12 00 degrees C. Concentration depth profiles were measured by secondary ion m ass spectrometry. The results showed that the dopant diffusion in Si was ma rkedly different with or without a CoSi2 layer. For specimens without CoSi2 layer, we observed oxidation enhanced diffusion of B and oxidation retarde d diffusion of Sb in accordance with the literature. However, 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 compare d to the thermal diffusivity and by a factor of 20-100 as compared to the c orresponding diffusivity for oxidation of Si without a CoSi2 layer. Sb diff usivity was enhanced by a factor of 2 with respect to thermal diffusivity a nd by about a factor of 5 as compared to the case without a CoSi2 layer. (C ) 1999 American Institute of Physics. [S0021-8979(99)07210-2].