EPITAXIAL-GROWTH OF BETA-FESI2 ON SILICON (111) - A REAL-TIME RHEED ANALYSIS

We present a detailed analysis of the solid phase epitaxy (SPE) of beta-FeSi2 on the silicon (111) face. The initial thickness of the iron film epitaxially deposited on the (111) silicon face has been varied from 2 to 1000 angstrom. Using a well-defined procedure of annealing (a fixed heating rate dT/dt = 1-4-degrees-C), we show that this initial iron thickness is a key parameter which controls the kinetic behaviour of Fe-Si intermixing at the interface. Indeed at the same temperature after the same thermal treatment, completely different chemical and crystalline states have been observed at the surface depending essentially upon the original iron film thickness. This kinetic behaviour at the Fe-Si interface is experimentally analysed through a quantitative analysis of RHEED patterns. Major facts are: (i) all the low-temperature equilibrium Fe-Si phases (bcc Fe(+ Si), simple cubic FeSi, beta-FeSi2) have been grown epitaxially on the silicon (111) face, (ii) an epitaxial FeSi2 strained phase has been clearly identified by the RHEED technique. This result is suggested to be an intrinsic consequence of the silicon stress field applied to the distorted fluorite structure of beta-FeSi2; (iii) a transient amorphous phase is most probably formed at 300 < T < 450-degrees-C for e(Fe) almost-equal-to 30-50 angstrom, preceding the formation of the epitaxial beta-FeSi2 phase. The appearance of such an amorphous phase at a definite iron thickness adds new experimental insights into solid state amorphisation which is a typical process occurring at interfaces of transition-metal systems.