A study of nonequilibrium diffusion modeling-applications to rapid thermal annealing and advanced bipolar technologies

A nonequilibrium diffusion model has been developed to study the influence of point defects on dopant redistribution, especially for transient enhanced diffusion. The coupled equations for point defects, substitutional impurities, and impurities/point defect pairs are solved under nonequilibriums condition. Charged species are included and the Poisson equation is solved. The characteristics and domain of validity of this model have been investigated. Indications are suggested to predict the conditions under which a steady-state model can be used. In the case of high-concentration predisposition, enhanced diffusion is observed and concave or exponential profiles are obtained for very short-time diffusion. Applications are presented for oxide diffusion sources. The generality of the model is confirmed by long-time diffusion behavior and by the influence of phosphorus diffusion on the boron buried layer. Anomalous effects observed during RTA steps after ion implantation are also well reproduced by the model. Successful comparisons with experiments are reported for boron and for actual bipolar structures, with coupled arsenic/boron diffusion in a 0.5- mu m BiCMOS process.<
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