Growth kinetics of amorphous interlayers by solid-state diffusion in polycrystalline Zr and Hf thin films on (111)Si

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Abstract
The growth kinetics of an amorphous (a-)interlayer in polycrystalline Zr and Hf thin films on (111)Si have been investigated by cross-sectional transmission electron microscopy. The growth of the a-interlayer in group-IVb metals and silicon systems was found to exhibit similar behaviors. The growth was found to follow a linear growth law initially. The growth rate then slows down and deviates from a linear growth law as a critical thickness of the a-interlayer was reached. Crystalline silicide (ZrSi or HfSi) was found to nucleate at the a-interlayer/Si interface in samples after prolonged and/or high-temperature annealing. Silicon atoms were found to be the dominant diffusing species during the formation of amorphous alloys. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be 1.4 eV, 17 nm and 1.2 eV, 27 nm in Zr/Si and Hf/Si systems, respectively. The correlations among the differences in atomic size between metal and Si atoms, growth rate and activation energy of the linear growth, critical and maximum a-interlayer thickness, the largest heat of formation energy for crystalline silicides, the calculated free-energy difference in forming amorphous phase, as well as the atomic mobility in Ti/Si, Zr/Si, and Hf/Si systems are discussed.