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 (Ga 2 O 3 ) thin films using trimethylgallium (TMGa) and ozone. We evaluated a variety of oxygen sources for Ga 2 O 3 ALD using TMGa but found that only ozone was effective. We explored the mechanism for Ga 2 O 3 ALD using in situ quartz crystal microbalance, Fourier transform infrared spectroscopy, and quadrupole mass spectrometry studies. We found that TMGa dissociatively adsorbs onto the Ga 2 O 3 surface to form Ga(CH 3 ) 2 surface species and liberate ∼20% of the methyl ligands as CH 4 . Next, the ozone reacts with these methyl species to form hydroxyl and formate surface groups and liberate CH 2 O. We prepared ALD Ga 2 O 3 films on Si(100) and fused SiO 2 substrates and analyzed the films using a variety of techniques. We found the Ga 2 O 3 growth to be self-limiting with a growth rate of ∼0.52 Å/cycle between 200 and 375 °C. Moreover, the Ga 2 O 3 films were stoichiometric, free of residual carbon, and exhibited properties similar to bulk Ga 2 O 3 . 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-Ga 2 O 3 upon annealing at 900 °C.