Spatial ALD of Al2O3 and ZnO using heavy water

Al2O3 and ZnO thin films were deposited from trimethylaluminium (TMA) and diethylzinc (DEZ) in combination with water using cylindrical rotating substrate spatial atomic layer deposition (SALD). The depositions were done between 67 and 140 °C. The growth per cycle for Al2O3 varied between 0.75 and 2.0 × 1015 at./cm2 per cycle and for ZnO between 0.52 and 1.07 × 1015 at./cm2 per cycle. The hydrogen incorporation was studied by varying the deposition temperature and substrate rotation speed. The rotation speed affects the precursor exposure time (46–458 ms) and inert gas purging time (111–1120 ms). The results show that Al2O3 films can contain up to 25 at.% of hydrogen when the deposition temperature is 67 °C or the deposition exposure/purging times are short. The deposition of ZnO in similar conditions produces films with hydrogen concentrations up to 15 at.%. The source of impurity hydrogen was investigated by using heavy water, 2H2O, as an oxygen source. The main hydrogen isotope in the Al2O3 films at low temperatures and fast deposition speed was found to be 1H, while at higher temperatures and lower deposition speeds 2H isotope was dominant. For ZnO, 1H was the majority hydrogen isotope in the films in all the studied deposition conditions except at the lowest rotation speed.