Transition from amorphous to crystalline beta phase in co-sputtered FeSi2 films as a function of temperature

Abstract

A study of the stability of amorphous FeSi2 films and their transition to a crystalline phase as a function of deposition or annealing temperature is presented. Stoichiometric FeSi2 films, 300-400 nm thick, were deposited on (100) Si substrates by co-sputtering of Fe and Si. It was found that the films grow in an amorphous form for the substrate temperature ranging from room temperature to 200 degrees C, while from 300-700 degrees C, they grow in form of a crystalline beta-FeSi2 phase. In a postdeposition 30 min heat treatments, the layers retain the amorphous structure up to 400 degrees C, transforming to the crystalline beta phase at 500-700 degrees C. The results are discussed in the frame of the existing models, and compared to those found in the literature. It is shown that in as-deposited films, the growth is controlled by surface diffusion, the crystalline layers growing in a columnar structure strongly correlated to the Si substrate. Postdeposition treatments induce a random crystallization controlled by bulk diffusion, the resulting structure not being influenced by the substrate. The results of this work contribute to a better understanding of the processes involved in a transition of amorphous FeSi2 films to a crystalline phase, and provide a basis to determine the processing parameters in potential applications of this promising semiconducting material.

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