Indium Oxide Atomic Layer Deposition Facilitated by the Synergy between Oxygen and Water

This paper explores the atomic layer deposition (ALD) of indium oxide (In2O3) films using cyclopentadienyl indium (InCp) and combinations of both molecular oxygen and water as the co-reactants. When either O2 or H2O were used individually as the oxygen source the In2O3 growth was negligible over the temperature range 100−250 °C. However, when oxygen and water were used in combination either as a simultaneous exposure or supplied sequentially, In2O3 films were deposited at growth rates of 1.0−1.6 Å/cycle over the full range of deposition temperatures. In situ quadrupole mass spectrometry and quartz crystal microbalance measurements revealed that water serves the function of releasing ligands from the surface while oxygen performs the role of oxidizing the indium. Since both processes are necessary for sustained growth, both O2 and H2O are required for the In2O3 ALD. The electrical resistivity, mobility, and carrier concentration of the In2O3 films varied dramatically with both the deposition temperature and co-reactant sequence and correlated to a crystallization occurring at ∼140 °C observed by X-ray diffraction and scanning electron microscopy. Using this new process we successfully deposited ALD In2O3 films over large area substrates (12 in. × 18 in.) with very high uniformity in thickness and resistivity.