Atomic layer deposition of high purity Ga2O3 films using liquid pentamethylcyclopentadienyl gallium and combinations of H2O and O2 plasma

The liquid compound pentamethylcyclopentadienyl gallium (GaCp*) exhibits several notable characteristics, including a relatively high vapor pressure and thermal stability up to 250 degrees C. Using it as a precursor, Ga2O3 thin films can be deposited by atomic layer deposition (ALD), with the combination of oxidants of H2O followed by O-2 plasma (WpO), where H2O is used to desorb the ligand, and O-2 plasma then oxidizes the surface Ga species. A self-limiting surface reaction during the ABC-type ALD process applying GaCp*, H2O, and O-2 plasma in order was observed with no delay in nucleation for pulse times for GaCp*, H2O, and O-2 plasma of 0.1, 3.0, and 50s, respectively, at a growth temperature of 200 degrees C. The growth rate was 0.06nm/cycle. ALD-Ga2O3 deposition was possible even if only O-2 plasma was used as an oxidant, though it takes a very long time for the oxidation by O-2 plasma to reach saturation. On the other hand, when no O-2 plasma was used, no film could be deposited using H2O and O-2 in any combination. Ga2O3 films deposited by ALD using the WpO oxidant exhibited a stoichiometric O/Ga ratio of 1.5, with negligible residual carbon and an amorphous structure. These results show that GaCp* is a promising candidate precursor for forming high quality Ga2O3 films.