Antimony &dgr;‐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 &dgr; 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 &dgr; 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 &dgr; plane, with subsequent diffusion‐controlled growth, and (ii) slow, continuous generation of a larger number of nuclei at random sites in the &dgr; 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.