Transient enhanced diffusion of boron in presence of end-of-range defects

Abstract

The presence of a supersaturation of Si self-interstitials in ion implanted silicon has been shown to be the origin of several physical phenomena such as transient enhanced diffusion (TED) of boron, the formation of extended defects at the projected range of implanted atoms at doses below the amorphization threshold, and the formation of end-of-range (EOR) defects in the case of a preamorphization stage. In this article, we discuss the relation between boron anomalous diffusion and end-of-range defects. Modeling of the behavior of these defects upon annealing allows one to understand why and how they affect dopant diffusion. This is possible through the development of the Ostwald ripening theory applied to extrinsic dislocation loops. This theory is shown to give access to the variations of the mean supersaturation of Si self-interstitial atoms between the loops and also to be responsible for anomalous diffusion. This initial supersaturation is, before annealing, at least five decades larger than the equilibrium value and exponentially decays with time upon annealing with activation energies that are the same as the ones observed for TED. It is shown that this time decay is precisely at the origin of the transient enhancement of boron diffusivity through the interstitial component of boron diffusion. Side experiments shed light on the effect of the proximity of a free surface on the thermal behavior of EOR defects and allow us to quantitatively describe the space and time evolutions of boron diffusivity upon annealing of preamorphized Si layers.