NiSi2/Si interface chemistry and epitaxial growth mode

Epitaxial NiSi2 thin films are formed by annealing of Ni on sulfur-implanted silicon (1 0 0). The atomic structure and chemistry of the NiSi2/Si interface are investigated by aberration-corrected transmission electron microscopy. The interface is atomically sharp and runs mainly along the (1 0 0) plane. {1 1 1} segments of interface are also observed as minor facets. The atomic structure of the (1 0 0) and (1 1 1) interface has been determined. Interfacial dislocations with Burgers vectors a/4<1 1 1> and a/2<1 1 0> are observed near {1 1 1} facets. In particular, these dislocations have extra half atomic planes in the Si substrate. This configuration of dislocation does not agree with the sign of the lattice mismatch between bulk NiSi2 and Si. This novel phenomenon is understood by the fact that a high concentration of sulfur in the interface area leads to an expansion of the NiSi2 lattice and thus inverts the sign of the lattice mismatch. It is suggested that the change of the strain status, in addition to the doping effect of S, also plays a role in the tunable Schottky barrier height in this system.