TRANSIENT ENHANCED DIFFUSION OF BORON IN PRESENCE OF END-OF-RANGE DEFECTS

The presence of a supersaturation of Si self-interstitials in ion impl anted silicon has been shown to be the origin of several physical phen omena such as transient enhanced diffusion (TED) of boron, the formati on of extended defects at the projected range of implanted atoms at do ses below the amorphization threshold, and the formation of end-of-ran ge (EOR) defects in the case of a preamorphization stage, In this arti cle, we discuss the relation between boron anomalous diffusion and end -of-range defects. Modeling of the behavior of these defects upon anne aling allows one to understand why and how they affect dopant diffusio n, This is possible through the development of the Ostwald ripening th eory applied to extrinsic dislocation loops. This theory is shown to g ive access to the variations of the mean supersaturation of Si self-in terstitial atoms between the loops and also to be responsible for anom alous diffusion. This initial supersaturation is, before annealing, at least five decades larger than the equilibrium value and exponentiall y decays with time upon annealing with activation energies that are th e 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 diffu sivity through the interstitial component of boron diffusion. Side exp eriments shed light on the effect of the proximity of a free surface o n the thermal behavior of EOR defects and allow us to quantitatively d escribe the space and time evolutions of boron diffusivity upon anneal ing of preamorphized Si layers. (C) 1997 American Institute of Physics .