U- and W-shaped diffusion profiles of gold in silicon

Abstract

The diffusion of Au in dislocation-free Si was investigated at 1473K by means of neutron-activation analysis combined with mechanical sectioning. In most wafers the diffusion profiled were U-shaped, as known from previous studies of this kind performed at lower temperatures. In these wafers the Au concentration in the profile centres measured after 45 min diffusion anneals decrease inversely proportional to the wafer thicknesses in accordance with the so-called kick-out diffusion model. This model is confirmed further by the good agreement of the contribution by self-interstitials to the self-diffusion coefficient at 1473K calculated from the present Au-diffusion data with directly measured values of the Si self-diffusion coefficient. In some Au-diffused Si wafers W-shaped penetration profiles were found. From spreading-resistance, preferential-etching, and X-ray topography studies it is concluded that the Au-concentration peaks occurring in the interior of these specimens are located at faulted dislocation loops formed during the in-diffusion of Au. An electron-microscopy analysis showed that the stacking faults are of extrinsic nature. Presumably they were formed by agglomeration of self-interstitials produced in supersaturation via the kick-out diffusion mechanism.