Ni-Ti Shape Memory Alloy thin films are suitable materials for microelectromechanical
devices. During the deposition of Ni-Ti thin films on Si substrates, there exist interfacial diffusion
and chemical interactions at the interface due to the high temperature processing necessary to
crystallize the film. For the present study, Ni-Ti thin films were prepared by magnetron cosputtering
from Ni-Ti and Ti targets in a specially designed chamber mounted on the 6-circle
goniometer of the ROssendorf BeamLine (ROBL-CRG) at ESRF, Grenoble (France). The objective
of this study has been to investigate the interfacial structure resulting from depositions (at a
temperature of ≈ 470°C) on different substrates: naturally oxidized Si(100), Si(111) and poly-Si
substrates. A detailed High-Resolution TEM analysis of the interfacial structure has been
performed. When Ni-Ti is deposited on Si(100) substrate, a considerable diffusion of Ni into the
substrate takes place, resulting in the growth of semi-octaeder A-NiSi2 silicide. In the case of Ni-Ti
deposited on Si(111), there appears an uniform thickness plate, due to the alignment between
substrate orientation and the [111]-growth front. For Ni-Ti deposited on poly-Si, the diffusion is
inhomogeneous. Preferential diffusion is found along the columnar grains of poly-Si, which are
favourably aligned for Ni diffusion. These results show that for the Ni-Ti/Si system, the morphology
of the diffusion interface is strongly dependent on the type of substrates.
