Atomic layer deposition of lanthanum oxide with heteroleptic cyclopentadienyl-amidinate lanthanum precursor - Effect of the oxygen source on the film growth and properties

La2O3 thin films were deposited by atomic layer deposition from a liquid heteroleptic La precursor, La ((PrCp)-Pr-i)(2)(Pr-i-amd), with either water, ozone, ethanol, or both water and ozone (separated by a purge) as the oxygen source. The effect of the oxygen source on the film growth rate and properties such as crystallinity and impurities was studied. Saturation of the growth rate was achieved at 225 degrees C with O-3 as the oxygen source. With water, very long purge times were used due to the hygroscopicity of La2O3 but saturation of the growth rate was not achieved. Interestingly, when an O-3 pulse was added after the water pulse with a purge in between, the growth rate decreased and the growth saturated at 200 degrees C. With ethanol lanthanum hydroxide was formed instead of La2O3 at 200-275 degrees C whereas hexagonal La2O3 films were obtained at 300 degrees C but the growth was not saturative. Using the separate pulses of water and ozone in the same deposition provided the best results from the four studied deposition processes. After annealing the films deposited with the La((PrCp)-Pr-i)(2)((i)PrAMD)/H2O/O-3 process showed pure hexagonal phase in all the films regardless of the deposition temperature, whereas mixtures of cubic and hexagonal La2O3 were seen with the other processes.