Mechanism and kinetics of the diffusion of gold in silicon

The diffusion of Au in Si is known to take place via the interchange of Au atoms between substitutional (Au _s ) and interstitial (Au _i ) sites. So far it has generally been believed that this interchange involves lattice vacancies (V) and that it occurs via the Frank-Turnbull mechanism V+Au _i ⇆Au _s . It is stated in the literature that this model explains the observation that the Au _s concentrationC _s ^m in the centre of Au-diffused Si wafers increases with timet according to . We show that this statement is incorrect, i.e., the Frank-Turnbull model cannot account for the law. Such a dependence is expected in the case of Si wafers with a sufficiently low density of internal sinks for self-interstitials if the Au _i −Au _s interchange is controlled by the so-called kick-out mechanism Au _i ⇆Au _s +1. Since this mechanism involves self-interstitials (I) the present result is in accordance with the fact that under high-temperature equilibrium conditions the dominating intrinsic point defects in Si are self-interstitials and not vacancies as in Ge or metals.