Growth kinetics of amorphous interlayers by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Nb and Ta thin films on (111)Si

Abstract

The growth kinetics of amorphous interlayer (a-interlayer) formed by solid-state diffusion in ultrahigh vacuum deposited polycrystalline Nb and Ta thin films on (111)Si have been investigated by cross-sectional transmission electron microscopy. The growth of a-interlayers in Nb/Si and Ta/Si systems was found to exhibit similar behaviors. The growth was found to follow a linear growth law initially in sample annealed at 450–500 °C and 550–625 °C for Nb/Si and Ta/Si, respectively. The growth then slows down and deviates from a linear growth law as a critical thickness of a-interlayer was reached. The activation energy for the linear growth of a-interlayer was found to be 0.8±0.3 and 0.9±0.3 eV for Nb/Si and Ta/Si, respectively. The correlations among difference 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 atomic mobility in Ti/Si, Zr/Si, Hf/Si, Ta/Si, and Nb/Si systems are discussed.