The growth of pinhole-free epitaxial Yb and Er silicide thin films on (111)Si has been achieved by capping appropriate amorphous Si(a-Si) layer at room temperature followed by annealing at 700°C in an ultrahigh vacuum chamber. The thickness of the a-Si capping layer was selected to be such that the consumption of Si atoms from the substrate is minimized. The design and reimplementation of the scheme involving appropriate thickness of a-Si capping layer was based on an understanding of the formation mechanism of the pinholes with epitaxial rare-earth islands as diffusion barriers for Si diffusion at the silicide∕Si interfaces.
A number of nanosize Ti silicides, Ti5Si3,Ti5Si4, and TiSi, were found to form simultaneously in the amorphous intermixing layer of annealed ultrahigh-vacuum-deposited Ti thin films on (001)Si. Autocorrelation function analysis has been applied to the high-resolution transmission electron microscope images to identify the phases formed in the initial stages of reaction. The intermediate silicide phases were detected to form earlier than that of the previous study owing to the superior sensitivity in detecting nanocrystals in an amorphous layer. The phase formation can be explained from the constructed metastable free-energy diagram.
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