Zinc diffusion under laser annealing of implanted silicon layers

Using the method of He+ back scattering, studied was the redistribution of zinc implanted in silicon under the action of nanosecond laser pulses. In laser annealing, a large part of impurity atoms move out of the implantation layer into the depths of the crystal distances of no less than 1 μm. The estimated diffusion coefficient of the zinc atoms exceeds by several orders of magnitude the value found from experiments with prolonged annealing. The effect of radiation defects on the displacement of implanted atoms has been examined. It is shown that the deep damaged layer produced by preliminary N+ bombardment (65 keV, 1015 cm-2), limits the migration of zinc into the crystal. The limiting degree depends on the crystallographic orientation of a sample, and decreases in the series of <111>, <110>, <100>. Annealing does not make the zinc atoms move out of the subsurfaces layer, but does facilitate their diffusion into the volume in subsequent laser irradiation. The results of the experiments are explained on the base of fast diffusion of zinc atoms through interstitials, and their capture on defects