Arsenic profiles in plasma doped silicon wafers were traced by scattering of H+ and H-2(+) ions at medium energies. Two wafers were doped with the same bias, gas pressure, total implanted dose and AsH3 concentration. After implantation, the wafers were submitted to industrial cleaning processes, resulting in the formation of a surface SiO2 layer, and one wafer was subjected to an additional thermal treatment. Scattering spectra of single and molecular ion beams with the same energy per nucleon and charge state differed only by the energy broadening due to the break-up of the molecule, allowing depth profiling by calculation of the dwell time before the backscattering collision. For the SiO2 layers of these samples a density reduction of, on average, 13% was observed, compared to thermally grown SiO2. In addition, the arsenic depth-profile determined were in close agreement with independent findings obtained by electron techniques.