EFFECT OF GROWTH TEMPERATURE ON THE PROPERTIES OF EVAPORATED TANTALUMPENTOXIDE THIN-FILMS ON SILICON DEPOSITED USING OXYGEN RADICALS

The effect of growth temperature (170-730 degrees C) on the properties of as-deposited 1000 Angstrom 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-res olution cross-sectional transmission electron microscopy (XTEM) reveal ed that films grown at or below 400 degrees C were deposited in an amo rphous state. The layers grown at 520 degrees C were observed to be in a nanocrystalline state with no discernible grain boundaries whereas films grown at 650 degrees C demonstrated distinct grain boundary form ation in the beta-phase modification of Ta2O5 as evidenced by XTEM and XRD analyses. For the highest growth temperature of 730 degrees C, th e XRD pattern indicated the presence of an impurity phase in the beta- Ta2O5 film. XTEM revealed an abrupt 20-30 Angstrom thick layer, presum ably SiO2, between the Ta2O5 layer and the silicon substrate for all f ilms. The measured relative static dielectric constant was found to in crease with increasing growth temperature accompanied by an increase i n film refractive index. For the amorphous layers, the leakage current s were lower for films grown at 380 degrees C than for films grown at 170 degrees C. This is proposed to be related to the reduction of anne alable 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 curr ent even for the nanocrystalline film grown at 520 degrees C. (C) 1998 American Institute of Physics.