Defects in Ni and Co silicide: Si interfaces

Abstract

Silicide formation has been studied by deposition of Ni and Co on (001) and (111) Si substrates, followed by annealing. NiSi2 and CoSi2, exhibiting both the A (parallel lattices) and B (twin related lattices) type epitaxial relationships, and also CoSi (lattices rotated by 30° about a coincident [111] direction), have been investigated. Observations, using transmission electron microscopy, have been interpreted in the framework of a topological theory of interfacial discontinuities, and extensive agreement has been found between theory and experiment. In NiSi2Si A-type specimens, crystal dislocations were observed to accomodate misfit, although this was not completely relieved in general. In addition, irregular arrangements of dislocations with b=1/4<111> were observed on (001) interfaces and at the intersection of obtuse pairs of {111} facets. (001) interfaces were frequently found to facet on {111} planes, sometimes on a fine scale with facet spacings as small as 6 nm. NiSi2Si and CoSi2Si (111) type B specimens exhibit arrays of interfacial dislocations with b=1/6<211>, partially accommodating misfit. On theoretical grounds, these dislocations are thought to exhibit interfacial steps at their cores. Direct confirmation of this was obtained in plan view ultra-thin specimens by using a contrast technique based on a method for revealing steps on crystal surfaces. Arrays of interfacial dislocations were also observed in CoSiSi (111) specimens. The components of their Burgers vector parallel to the interface were determined to be close to 1/3<110>, in agreement with theory. Possible evidence of disclination formation was also found in these samples.