A Study of Nonequilibrium Diffusion Modeling—Applications to Rapid Thermal Annealing and Advanced Bipolar Technologies

Bruno Baccus, Naoyuki Shigyo, Hiroomi Nakajima, Kazumi Inou, Toshihiko Iinuma, Hiroshi Iwai

Research output: Contribution to journalArticle

28 Scopus citations


A new nonequilibrium diffusion model has been developed aiming to study the influence of point defects on dopant redistribution, specially for transient enhanced diffusion. The coupled equations for point defects, substitutional impurities, and impurities/point defect pairs are solved under nonequilibrium condition. Charged species are included and Poisson equation is solved. The characteristics and domain of validity of this model have been investigated. From the numerical point of view, it is found that a decoupled scheme solves efficiently the system of equations, together with an automatic time step selection. Moreover, indications are suggested to predict the conditions under which a steady-state model can be used. In the case of high-concentration predeposition, enhanced diffusion is observed and concave or exponential profiles are obtained for very short-time diffusion. These effects are amplified by the nonequilibrium treatment. Applications are presented for oxide diffusion sources, in which insight is needed during the early steps of diffusion. Moreover, the generality of the model is confirmed by long-time diffusion behavior and by the influence of phosphorus diffusion on boron buried layer. Anomalous effects observed during RTA steps after ion implantation are also well reproduced by the model, in terms of duration of the transient diffusion and in terms of the amount of displacement, as a function of temperature. Successful comparisons with experiments are reported for boron and for actual bipolar structures, with coupled arsenic/boron diffusion in a 0.5-pm Bi-CMOS process. Furnace and RTA are also compared for these examples. The importance of the initial amount of point defects after ion implantation is discussed. Finally, the electrical influence of such problems is evaluated for a bipolar technology. The effects of damage on two-dimensional diffusion are also investigated. These results have been obtained using always the same values of the parameters, validating the generality of the model.

Original languageEnglish
Pages (from-to)648-661
Number of pages14
JournalIEEE Transactions on Electron Devices
Issue number3
StatePublished - Mar 1992

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