Formation of Epitaxial CoSi2 Films on Si(111) a Low Temperature (≤400°C)

Abstract

The growth of thin (≤100A) epitaxial CoSi2 layers on Si(111) is studied by angle resolved photoemission and low energy electron diffraction experiments. Various preparation methods at low temperature (≤400°) are investigated. First it is demonstrated that layer growth can be achieved by a series of sequential Co(1ML) and Si(2ML) evaporations and subsequent low temperature annealing. Ending the deposition series with either Co or Si results in a Co or Si rich CoSi2 surface labeled CoSi2(111)-Co and CoSi2(111)-Si respectively with characteristics photoemission signature. According to photoemission, a minimum annealing temperature of 360°C is found to be necessary to produce epitaxial CoSi2 films with a good crystallinity. CoSi2 layers were also grown by coevaporation of Co and Si in their stoichiometric ratio onto Si(111) subjected to thermal processing at 360°C either during or after deposition. The CoSi2, prepared in this way, invariably exhibits a bulk and surface excess of Si. In particular the film surface is systematically of the silicon rich CoSi2(111)-Si type. In contrast a different preparation method which consists in deposition of Co only onto the Si(111) substrate held at −360°C produces CoSi2 films exposing a Co rich CoSi2(111)-Co surfaces without any Si excess in bulk. It is concluded from these experiments that at 360°C diffusion of Si from substrate through the CoSi2 layer is much easier than usually expected and quite sufficient to sustain further CoSi2 growth without any extra Si supply.