Single Layer Nanocrystalline Silicide Synthesis from Zr/Si Multilayers

概要

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Swift heavy ion (SHI) beam (120 MeV Au, 1013 ions/cm2) irradiation of Zr/Si multilayers, deposited on Si substrates at room temperature, resulted in complete mixing of the structure, transforming it directly into a single layer of purely crystalline ZrSi2 (C49 type structure) on the substrate. As-deposited and SHI irradiated samples were analyzed by specular x-ray reflectivity and grazing incidence x-ray diffraction. The generation of this refractory silicide, known to be vital to integrated device processing, directly on Si and without annealing is a technologically useful result. Dynamics of the process was attributed to electron-phonon energy transfer and interdiffusion at the interface during transient melt phase, through application of thermal spike model. Within the framework of this model, the present work establishes an experimentally observed threshold for electronic excitation (Se) of Zr (24.4 keV/nm), leading to mixing in the Zr/Si system. However, this value is lower than the reported threshold for defect/track creation by electronic energy loss in Zr (28 keV/nm). Since it is known that SHI induced mixing takes place across the interface when Se exceeds this threshold, the results obtained through this study signify in effect, the greater sensitivity of Zr to swift heavy ion induced radiation damage.
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