Structural investigation of the initial interface region formed by thin zirconium films on silicon (111)

A structural study of the initial interface region formed by zirconium on silicon (111) was undertaken. Thin films (100 Å) of zirconium were deposited in ultrahigh-vacuum conditions onto atomically, clean silicon (111) wafers and annealed in situ at 25°C intervals between 300 and 425°C, over which range Auger spectroscopy indicated silicon diffusion to the surface. Structural characterization of the evolving interface was performed primarily via extended x-ray-absorption fine-structure (EXAFS) measurements. Results indicate that a major structural rearrangement takes place between 350 and 375°C. EXAFS fitting analysis reveals this transition to be from a disordered-intermixed phase to a more ordered state having interatomic distances closely resembling those of ZrSi, but lower coordination numbers. Ordering continues with progressively higher annealing temperatures until the interface region assumes the ZrSi structure at ∼425°C. The results are discussed in terms of the free energy and strain of the interface film.