A model for the diffusion and precipitation of antimony in highly doped δ layers in silicon

Antimony δ-doping layers were made by deposition of Sb on monocrystalline Si, followed by the deposition of amorphous Si and a final solid-phase-epitaxy treatment at 620 °C. After post-annealing at temperatures between 625 and 725 °C, Sb precipitates with a diameter of several nm are observed in the δ plane with the aid of transmission electron microscopy. Using channeling Rutherford Backscattering Spectrometry the increase of the precipitated fraction with time was determined from the minimum-yield signal. The results are interpreted using a model for the generation of Sb nuclei which grow subsequently due to lateral diffusion of Sb atoms in the δ plane, followed by incorporation into the nucleus. The generation of the nuclei appears to take place by way of two parallel processes: (i) fast, simultaneous generation of a limited number of nuclei at low-energetic sites in the δ plane, with subsequent diffusion-controlled growth, and (ii) slow, continuous generation of a larger number of nuclei at random sites in the δ plane, with subsequent incorporation-controlled growth. The Sb diffusion at the extremely high concentrations under consideration is very fast and concentration dependent, which can be explained by the model of vacancy-percolation diffusion of Mathiot and Pfister [J. Appl. Phys. 66, 970 (1989)]. The activation energy for incorporation of Sb atoms into liquid precipitates appears to be considerably lower than for incorporation into solid ones

Precipitation of antimony delta-doping layers in Si studied with channeling Rutherford backscattering spectrometry

Antimony 5-doping layers in Si have been prepared using molecular beam epitaxy. First of all, a crystalline buffer layer was deposited at 700°C, followed by Sb deposition from a Knudsen cell. After cooling down to room temperature, amorphous Si was deposited on top and subsequently crystallized using solid phase epitaxy (SPE). The thermal stability of the 8-doping layers was studied in the temperature range of 625-725°C which is only slightly above the SPE temperature. Lateral Sb redistribution was followed by measurement of the Sb minimum yield in channeling Rutherford backscattering spectrometry. An increase in minimum yield was found and was correlated with the formation of precipitates as measured with transmission electron microscopy. The high diffusion coefficients required to explain the observed precipitation are qualitatively in agreement with a diffusion model, based on percolation theory, proposed before for Sb diffusion in heavily doped Si