Formation of amorphous interlayers by a solid-state diffusion in Zr and Hf thin films on silicon

The formation of amorphous interlayers (a interlayers) in polycrystalline Zr and Hf thin films on single-crystal (111)Si has been observed by cross-sectional transmission electron microscopy. The growth of a interlayers in group IVa metal thin films on silicon was found to exhibit similar behavior but was fundamentally different from those of metal-metal diffusion couples. The growth of a interlayers was found to follow a linear growth law initially then slowed down until a critical thickness was reached. Si was found to be the dominant diffusing species. Good correlation was found among the maximum thickness of the a interlayer, the difference in atomic size between metal and Si, the activation energy of the linear growth, and the largest heats of formation of the respective silicides.