In situ study of atomic layer epitaxy growth of tantalum oxide thin films from Ta(OC2H5)5 and H2O

Ta2O5 thin films have been deposited in atomic layer epitaxy process from Ta(OC2H5)5 and H2O. A quartz crystalline mass-sensor was exploited to detect the adsorption processes at the gas–solid interface during the film growth. It is suggested that Ta(OC2H5)5 reacts with surface hydroxyls producing intermediate surface species (-O)nTa(OC2H5)5−n where n varies with the reactor temperature. During the subsequent water pulse these species react further converting the surface back to the hydroxyl-terminated one. The uncontrolled deposition due to the temperature-induced decomposition of tantalum ethoxide with the activation energy of 100±6 kJ/mol contributes to the film growth above 275°C. The value of the diffusion coefficient D=0.0075 m2/s for gas-phase Ta(OC2H5)5 has been calculated at 250°C. Estimated sticking coefficient of Ta(OC2H5)5 is about one order of magnitude higher than that of H2O and nearly one order of magnitude lower than that of TaCl5.