Effect of hydrogen on the chemical state, stoichiometry and density of amorphous Al₂O₃ films grown by thermal atomic layer deposition

Amorphous oxide thin films grown by thermal atomic layer deposition (ALD) typically contain high impurity concentrations of hydrogen, which affects both chemistry and structure and thereby the functional properties, such as the barrier properties in, for example, microelectronic and photovoltaic devices. This study discloses the effect of H incorporation in amorphous Al2O3 ALD oxide films on the local chemical binding states of Al, O and H, as well as the oxide density and stoichiometry, by a combined analytical approach using elastic recoil detection analysis, Rutherford backscattering spectroscopy and full chemical state analysis by dual-source X-ray photoelectron spectroscopy (XPS)/hard X-ray photoelectron spectroscopy (HAXPES). The experimental findings are compared with crystalline anhydrous alpha-Al2O3 and hydroxide alpha-Al (OH)(3) reference phases and further supported by molecular dynamic simulations. It is shown that H preferably forms covalent -OH hydroxyl bonds with O in the nearest-neighbour coordination spheres of interstitial Al cations, which affects both the ligand electronic polarizability and the bond length of the randomly interconnected [AlOn] polyhedral building blocks in the amorphous ALD oxide films.