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 °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 O2 plasma (WpO), where H2O is used to desorb the ligand, and O2 plasma then oxidizes the surface Ga species. A self-limiting surface reaction during the ABC-type ALD process applying GaCp*, H2O, and O2 plasma in order was observed with no delay in nucleation for pulse times for GaCp*, H2O, and O2 plasma of 0.1, 3.0, and 50 s, respectively, at a growth temperature of 200 °C. The growth rate was 0.06 nm/cycle. ALD-Ga2O3 deposition was possible even if only O2 plasma was used as an oxidant, though it takes a very long time for the oxidation by O2 plasma to reach saturation. On the other hand, when no O2 plasma was used, no film could be deposited using H2O and O2 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.