Atomic Layer Deposition of Ga2O3 Films Using Trimethylgallium and Ozone

Abstract

In this manuscript, we demonstrate a new process for the atomic layer deposition (ALD) of gallium oxide (Ga2O3) thin films using trimethylgallium (TMGa) and ozone. We evaluated a variety of oxygen sources for Ga2O3 ALD using TMGa but found that only ozone was effective. We explored the mechanism for Ga2O3 ALD using in situ quartz crystal microbalance, Fourier transform infrared spectroscopy, and quadrupole mass spectrometry studies. We found that TMGa dissociatively adsorbs onto the Ga2O3 surface to form Ga(CH3)2 surface species and liberate ∼20% of the methyl ligands as CH4. Next, the ozone reacts with these methyl species to form hydroxyl and formate surface groups and liberate CH2O. We prepared ALD Ga2O3 films on Si(100) and fused SiO2 substrates and analyzed the films using a variety of techniques. We found the Ga2O3 growth to be self-limiting with a growth rate of ∼0.52 Å/cycle between 200 and 375 °C. Moreover, the Ga2O3 films were stoichiometric, free of residual carbon, and exhibited properties similar to bulk Ga2O3. Scanning electron microscopy revealed smooth films with good step coverage over trench structures, and X-ray diffraction showed that the films were amorphous as-deposited but crystallized to β-Ga2O3 upon annealing at 900 °C.