It was noted that implanted B and P dopants exhibited a transient enhanced diffusion, during annealing, which was due to the excess interstitials which were generated by implantation. In order to study the mechanisms which were involved in such enhanced diffusion, transmission electron microscopic measurements of the implantation damage were combined with B diffusion experiments; using dopant marker structures that had been grown by molecular beam epitaxy. It was found that the damage which resulted from non-amorphizing Si implants, for doses that ranged from 5 x 1012 to 1014/cm2, evolved into a distribution of {311} interstitial agglomerates during initial annealing at 670 to 815C. The excess interstitial concentrations which were contained in these defects were roughly equal to the implanted ion doses. This was confirmed by atomistic Monte Carlo simulations of the implantation and annealing processes. The injection of interstitials from the damaged regions involved the dissolution of {311} defects, during Ostwald ripening, with an activation energy of 3.8eV. The excess interstitials drove substitutional B into electrically inactive metastable clusters of two or three B atoms, at concentrations below the solid solubility. This explained the immobile B peak which was usually observed during the transient enhanced diffusion of implanted B. Injected interstitials underwent retarded diffusion, in molecular beam epitaxially grown material, with an effective migration energy of about 3.5eV. This arose from trapping at substitutional C. It was suggested that the concept of trap-limited diffusion could help to explain the enormous observed disparity among published values of interstitial diffusivity. The population of excess interstitials was strongly reduced by incorporating substitutional C to levels of about 1019/cm3 before implantation. It was concluded that this offered a promising method for suppressing transient enhanced diffusion, and permitted shallow junctions to be formed by dopant implantation.

Physical Mechanisms of Transient Enhanced Dopant Diffusion in Ion-Implanted Silicon. P.A.Stolk, H.J.Gossmann, D.J.Eaglesham, D.C.Jacobson, C.S.Rafferty, G.H.Gilmer, M.Jaraíz, J.M.Poate, H.S.Luftman, T.E.Haynes: Journal of Applied Physics, 1997, 81[9], 6031-50