Temperature-dependent impurity control and electronic structure optimization in ALD-deposited Al2O3 films for enhanced functional applications

Al₂O₃ thin films grown by atomic layer deposition (ALD) have been subject to great attention due to their application in electronic and energy devices. We present a new look at classical Al₂O₃ ALD growth with water vapour and Al(CH₃)₃ precursors by paying particular attention to the nature and concentration of contaminant atoms coming from residual precursor. Using a combination of Ion Beam Analysis (IBA), Monochromatized X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) we show that the band structure can be influenced by the residual hydrogen concentration which determines a balance between hydroxyl formation and the formation of oxygen vacancies, whereas the band structure is insensitive to residual carbon contamination. Use of deuterium enriched water vapour as precursor, combined with isotopically sensitive IBA analysis shows that the residual source of the hydrogen in the film, the TMA and water varies with the growth temperature. This finding is particularly relevant for applications where hydrogen state and oxygen stoichiometry is crucial, such as in battery, dielectrics, passivation layers, or gas-sensing applications.