Buried double-layered nitride structures in single-crystal (100) silicon have been produced by the implantation of doses of 0.75 × 1018 N+ cm-2 at 350 keV and 200 keV, respectively. Observations by RBS and channelling on the structure before and after high-temperature annealing and by TEM after annealing have shown two distinct buried nitride layers of different thicknesses. The mechanisms responsible for the formation of such a structure are discussed, together with possible routes for nitrogen migration. The processing conditions to form multilayer structures which are suitable for device applications are proposed.