Silicon was implanted with 2 MeV O+ ions with doses covering the range from 2 x 10(17) cm(-2) to 1 x 10(18) cm(-2) at an implantation temperature of not less than 600 degrees C. Subsequently, samples were annealed at 1300 degrees 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 (RES)/channelling results, gives a good agreement within the depth resolution (100 nm) of the RES 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.