HIGH-CONCENTRATION DIFFUSIVITY AND CLUSTERING OF ARSENIC AND PHOSPHORUS IN SILICON

The As diffusion coefficient as a function of its concentration was de termined by Boltzmann-Matano analysis of the profiles of the dopant di ffusing out of its conjugate phase precipitates during furnace anneali ng at 900 and 1050 degrees C of samples heavily doped by ion implantat ion, This method allowed to assure a constant diffusion source of As a nd to investigate a doping range attaining 3 x 10(21) cm(-3). Along th e same lines. the diffusivity versus concentration of specimens heavil y implanted with P was determined at 900 and 1000 degrees C. Dopant pr ofiles were determined by secondary neutral mass spectroscopy. The dif fusivity of both As and P increases with dopant content, attaining a m aximum 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 concentrat ion of unclustered dopant at the diffusion temperature. On the contrar y, 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 w hich can accurately describe the evolution of the As profile upon anne aling, by using our diffusivity data and taking into account both the precipitation and clustering phenomena. (C) 1998 American Institute of Physics.