Mechanism and kinetics of the diffusion of gold in silicon

Abstract

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 $$C_s^m \propto \sqrt t $$ . We show that this statement is incorrect, i.e., the Frank-Turnbull model cannot account for the $$C_s^m \propto \sqrt t $$ 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.