Laser scanning tomography: direct evidence of precipitate-free zone at surface of silicon wafers

Silicon wafers are usually thermally processed to generate SiO_x microprecipitates which play a key role in the intrinsic gettering of the residual metallic atoms and control the device yield and performance. In the latter the authors report the direct imaging of the defect distributions obtained by laser scanning tomography. Typical Si materials were analysed with various levels of oxygen doping and annealing. It is shown that small nucleation sites give rise to a weak background of scattered light, whereas larger clusters appear as bright points. Densities are evaluated down to a level below the minimum etch pits detection limit.