REFRACTIVE-INDEX PROFILES AND RANGE DISTRIBUTIONS OF SILICON IMPLANTED WITH HIGH-ENERGY NITROGEN

Single-crystal silicon has been implanted with nitrogen ions at MeV energies, to fluences between 0.25×1018 and 1.65×10 18 ions/cm2 at a substrate temperature of 700 °C. Infrared transmission and reflection spectra in the range of 1.25-40 μm were measured and interference fringes were observed which are produced by the interference of light which has been multiply reflected between the front surface and the buried layers. By detailed theoretical analyses of the interference fringes we obtain refractive-index profiles, which, under suitable interpretation, provide accurate measurements of the range and straggling of the implanted ions. Rutherford backscattering measurements on the same samples confirm this interpretation. Between the energies of 0.67 and 3.17 MeV, the measured values of the projected range agree with theory after adjusting the electronic stopping power, but the straggling measurements are lower by ∼30%. It is demonstrated that the asymmetry of the range distribution can be measured with this technique as well.