High concentration diffusivity and clustering of arsenic and phosphorus in silicon

The As diffusion coefficient as a function of its concentration was determined by Boltzmann-Matano analysis of the profiles of the dopant diffusing out of its conjugate phase precipitates during furnace annealing at 900 and 1050 degrees C of samples heavily doped by ion implantation, This method allowed to assure a constant diffusion source of As and to investigate a doping range attaining 3 x 10(21) cm(-3). Along the same lines. the diffusivity versus concentration of specimens heavily implanted with P was determined at 900 and 1000 degrees C. Dopant profiles were determined by secondary neutral mass spectroscopy. The diffusivity of both As and P increases with dopant content, attaining a maximum at a concentration which closely corresponds to the saturation value of-the carrier density, n(e), which we previously determined by equilibration annealing of specimens with excess dopant. This finding demonstrates that n(e) represents the limiting value of the concentration of unclustered dopant at the diffusion temperature. On the contrary, a diffusivity monotonically increasing with dopant concentration up to its solubility limit, was observed in the case of B and Sb, which do not cluster. Finally, we report the results of a simulation model which can accurately describe the evolution of the As profile upon annealing, by using our diffusivity data and taking into account both the precipitation and clustering phenomena. (C) 1998 American Institute of Physics.