The chemical composition profile of a nitride layer obtained by 20 keV N+2 ion implantation through an oxide layer was determined by x‐ray photoelectron spectroscopy at two different analysis angles. The nitrogen concentration shows a plateau followed by a slow decrease. Oxygen, presumably due to a recoil implantation, is always present in the nitride layer in exponentially decreasing amounts. The film is composed of elemental silicon, silicon oxynitride, and diffused oxygen. The respective concentrations of the two silicon components are nearly constant and the diffused oxygen decreases. In the interface region, the oxynitride loses its oxygen progressively; at the very end of the interface, nitrogen seems to be partially chemisorbed. In a sample which has undergone a double annealing, the oxygen diffuses deeper in the bulk of the substrate.