Abstract: Using analytical high-resolution electron microscopy, the Si structure and the redistribution of Er and O recoil atoms embedded in thin (~10 nm) surface layers by Ar+ implantation with an energy of 250–290 keV and a dose of 1 × 1016 cm–2 through Er and SiO2 films, respectively, and subsequent annealing are studied. It is established that Si recrystallization fails at a distance of ~20 nm from the surface, where the erbium concentration of 5 × 1019 cm–3 critical for failure is achieved at T = 950°C. It disproves the generally accepted model of Er-atom transfer by the recrystallization front into SiO2 on the surface. Instead, it is shown that the redistribution of O recoil atoms to the initial oxide during annealing for immobile Er atoms provides the formation of surface-inhomogeneous erbium phases in such a way that the oxygen-enriched Er–Si–O phase turns out to be concentrated in the oxide, while the depleted Er–Si phase remains in Si. It explains the partial loss of implanted Er after removal of the oxide together with the Er–Si–O phase. It was shown that the formation of a high density of microtwins (locally up to 1013 cm–2) is associated with the formation of Ar bubbles and clusters, which is atypical for (100)–Si recrystallization.