Diffusion of Gold in Silicon

The spreading resistance technique has been used to measure the degree of resistivity compensation in NTD‐Si samples following Au diffusion under many different conditions. From the theoretical curves of Thurber and Bullis (1) these can be converted to substitutional Au concentration distributions, . Several new effects have been found, all of which can be interpreted using the "kick‐out" mechanism, whereby Au atoms enter substitutional sites by removing an Si atom that becomes a self‐interstitial, . The Au diffusion process is then controlled entirely by the local concentration,, and out‐diffusion of these self‐interstitials. Detailed analyses and numerical solutions of the diffusion equations are given, and the experimental results can all be fitted, for instance, at 845°C using an Si self‐interstitial diffusion constant . The time dependence of is also explained. For the first time, direct evidence for the very rapid diffusion of interstitial gold, , is presented. It is shown that and that the equilibrium concentration of is probably greater than or equal to the equilibrium concentration of substitutional atoms, . The effect of swirl defects on Au diffusion is also demonstrated and explained.