Transient diffusion of ion-implanted phosphorus under nonoxidizing conditions is studied for P doses of 7 x 10(13) and 1 X 10(15) cm-2 at 20 keV The annealing steps [rapid thermal anneal (RTA) or furnace anneal (FA)] are carried out in an N2 ambient at 950 or 1050-degrees-C. A "kink" is observed in secondary ion mass spectroscopy (SIMS) profiles for both RTA and FA runs. A significant enhanced diffusion is observed in the concentration regime below the kink. In addition, from the SIMS profiles it appears that phosphorus atoms in the surf ace region tend to pile up at the SiO2/Si interface. Phosphorus diffusion is modeled using a previously reported empirical model for boron and arsenic diffusion.1 Activation energies and other model coefficients have been fit based on the RTA data only, and then applied to both RTA and FA diffusions. The long preannealing cycle in FA runs has been accounted for in simulations. A comparison of simulations, SIMS, SRP, and electrical measurements shows that phosphorus concentration above the kink (i.e., phosphorus pileup) is immobile. Further, phosphorus pileup appears to be active in the high dose samples, but inactive in the low dose ones. This deactivation is believed to be due to the formation of some type of phosphorus-vacancy complex in the vacancy-rich region at the surface.