Silicon was implanted with 2 MeV O + ions with doses covering the range from 2 10 1 7 cm - 2 to 1 10 1 8 cm - 2 at an implantation temperature of not less than 600 °C. Subsequently, samples were annealed at 1300°C for 6 h. Fourier transform infrared reflection spectroscopy has been used in order to characterise the as-implanted and annealed samples. The interference fringes observed in the transparent region (1500 cm - 1 to 7000 cm - 1 ), are very sensitive to changes in the structure of the examined sample. Cross-correlation with H + beam Rutherford backscattering spectroscopy (RBS)/channelling results, gives a good agreement within the depth resolution (100 nm) of the RBS technique. No anomalous diffusion was observed during annealing and a buried layer formed during annealing even for the lowest dose. IR spectroscopy constitutes the most suitable non-destructive method to investigate structures formed by MeV implantation.