Nondestructive and quantitative depth profiling analysis of ion bombarded Ta2O5 surfaces by medium energy ion scattering spectroscopy

Abstract

Ion beam sputtering has been widely used for sputter depth profiling with x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). However, the problem of surface compositional change due to ion bombardment remains to be understood and solved. So far sputtering processes have been usually studied by surface analysis tools such as XPS, AES, and secondary-ion mass spectrometry which use the sputtering process again. In this work, the altered surface layer of amorphous Ta2O5 thin films due to Ar+ ion bombardment was depth profiled nondestructively and quantitatively for the first time by medium energy ion spectroscopy (MEIS) as a function of the ion incidence angle and the ion dose with a depth resolution of better than 1.0 nm. The MEIS spectrum showed that the preferential sputtering of oxygen atoms developed with the ion dose and saturated in the ion dose of 3.1×1016 ions/cm2. The Ta mole fraction at the surface increased from 0.29 up to 0.42±0.03 at the saturation ion dose under normal incident 3 keV Ar+ ion bombardment, which corresponds to the stoichiometry of TaO1.4±0.2. The oxygen depletion depth was 2.6±0.8 nm at the saturation dose. The Ta concentration and the oxygen depleted depth decreased with the ion incidence angle. The MEIS experimental results were consistent with XPS results. These MEIS analysis results were compared with Monte Carlo simulation results and good agreement was obtained when both the sputtering and the ion beam induced diffusion were considered.