Impurity segregation in thin films: effect of lateral interaction and site competition

A theoretical model describing both segregation kinetics and equilibrium, taking into account site competition and lateral interaction, for the cases of a semi-infinite medium and films of finite thickness has been developed. It has been shown that limiting the number of impurity atoms (i.e. film thickness) affects the segregation process similar to the effect of temperature increase. The level of equilibrium segregation decreases with film thinning for a given bulk concentration and temperature. A criterion for classification into “thick” and “thin” films, depending on impurity segregation activity and temperature, has been formulated. At low temperatures, the critical thickness is mainly determined by the d/c0δ ratio and does not show any pronounced temperature dependence. At high temperatures, the dimensional range widens with elevation of temperature due to the strong (exponential) temperature dependence of equilibrium segregation.