HIGH-RESOLUTION AND INSITU TEM STUDIES OF ANNEALING OF TI-SI MULTILAYERS

The solid state amorphization reaction in sputtered amorphous-silicon-polycrystalline-titanium multilayers has been studied in cross-section by high-resolution transmission electron microscopy (TEM). Heat treatments included rapid thermal annealing and in situ heating in the microscope. The bilayer spacing of the sample is 25.0 nm and the composition is 50at.%Ti-50at.%Si. Growth of the alloy is strictly planar. The amorphization does not occur preferentially along titanium grain boundaries. The reaction is diffusion controlled with an activation energy of about 2.0 ev atom-1. When the layers are partially reacted, the amorphous alloy composition is silicon rich, with an estimated Ti:Si atomic ratio of 1:2. Once all of the elemental silicon is consumed the alloy incorporates more titanium, reaching a composition of about Ti45Si55. In situ studies reveal that Kirkendall voids from at this point in place of the silicon layers. In situ annealing studies duplicate the microstructure observed in the bulk-annealed samples; from this we conclude that bulk diffusion dominated in the thin TEM foil.