Plasma-enhanced atomic layer deposition of tungsten oxide thin films using (tBuN)2(Me2N)2W and O2 plasma

The growth of tungsten oxide (WO3) thin films by atomic layer deposition (ALD) offers numerous merits including atomic-scale thickness control at low deposition temperatures. In this work, we have developed and characterized a new plasma-enhanced ALD process for WO3 thin films using the metalorganic precursor (tBuN)2(Me2N)2W and O2 plasma as co-reactant over a wide temperature range of 100 °C-400 °C. The influence of deposition temperature on the growth behaviour and film properties is investigated in detail. The WO3 ALD process developed in this work yields a relatively high growth per cycle (GPC) which varies from ~0.7 Å at 100 °C to ~0.45 Å at 400 °C, as-determined by in-situ spectroscopic ellipsometry (SE). Rutherford backscattering spectrometry (RBS) measurements revealed a mass density of 5.9 g/cm3 and near stoichiometric film composition (O/W = 2.9). Both RBS and X-ray photoelectron spectroscopy (XPS) measurements confirmed no detectable C as well as N impurity incorporation. Grazing incidence X-ray diffraction (GI-XRD) measurements indicated that the films deposited at 400 °C were polycrystalline in nature.