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

Abstract

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.