PNNL

Abstract

Because of the increasing technological importance of oxide films for a variety of applications, there is a growing interest in knowing the sputter rates for a wide variety of oxides. To support needs of users of the Environmental Molecular Sciences Laboratory (EMSL) User facility as well as our research programs, we have made a series of measurements of the sputter rates for oxide films that have been grown by oxygen plasma assisted molecular beam epitaxy (OPA-MBE), pulsed laser deposition (PLD), Atomic Layer Deposition (ALD), electrochemical oxidation, or sputter deposition. The sputter rates for these oxide films were determined in comparison to the sputter rates for thermally grown SiO2, a common sputter rate reference material. The film thicknesses and densities of these films were usually measured using x-ray reflectivity (XRR). These samples were mounted in an x-ray photoelectron spectroscopy (XPS) system or an Auger electron spectrometer for sputtering measurements using argon ion sputtering. Although the primary objective was to determine relative sputter rates at a fixed angle, the measurements were also used to determine: i) the angle dependence of the relative sputter rates; ii) the energy dependence of the relative sputter rates; and iii) the extent of ion beam reduction for the various oxides. Materials examined include: SiO2 (reference films), Al2O3, CeO2, Cr2O3, Fe2O3, HfO2, ITO (In-Sn-oxide) Ta2O5, TiO2 (anatase and rutile) and ZnO. We find that the sputter rates for the oxides can vary up to a factor of two (usually slower) from that observed for SiO2. The ratios of sputter rates to SiO2 appear to be relatively independent of ion beam energy for the range of 1kV to 4 kV and for incident angles of less than 50º. As expected, the ion beam reduction of the oxides varies with the sputter angle. These studies demonstrate that we can usually obtain sputter rate reproducibility better than 5% for similar oxide films.