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, 300–400nm 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°C, while from 300–700°C, they grow in form of a crystalline β-FeSi2 phase. In a postdeposition 30min heat treatments, the layers retain the amorphous structure up to 400°C, transforming to the crystalline β phase at 500–700°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.