The effect of growth temperature (170–730 °C) on the properties of as-deposited 1000 Å thick Ta2O5 films has been studied. The layers were grown by evaporation of tantalum metal on silicon exposed to a flux of oxygen radicals. X-ray diffractometry (XRD) and high-resolution cross-sectional transmission electron microscopy (XTEM) revealed that films grown at or below 400 °C were deposited in an amorphous state. The layers grown at 520 °C were observed to be in a nanocrystalline state with no discernible grain boundaries whereas films grown at 650 °C demonstrated distinct grain boundary formation in the β-phase modification of Ta2O5 as evidenced by XTEM and XRD analyses. For the highest growth temperature of 730 °C, the XRD pattern indicated the presence of an impurity phase in the β-Ta2O5 film. XTEM revealed an abrupt 20–30 Å thick layer, presumably SiO2, between the Ta2O5 layer and the silicon substrate for all films. The measured relative static dielectric constant was found to increase with increasing growth temperature accompanied by an increase in film refractive index. For the amorphous layers, the leakage currents were lower for films grown at 380 °C than for films grown at 170 °C. This is proposed to be related to the reduction of annealable short-range defects in the amorphous Ta2O5 film with increasing growth temperature. For polycrystalline layers, the leakage currents were much higher compared to amorphous films, suggesting that crystal-induced defects play an important role in determining the leakage current even for the nanocrystalline film grown at 520 °C.

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