Sims Characterization of Thin Thermal Oxide Layers on Polycrystalline Aluminium

Abstract

ABSTRACTThermal oxide layers of different thickness (T = 3.5–18 am) covering polycrystalline aluminium sheets were investigated by dynamic SIMS in an ion microscope. Depth profiles of major elements (Al, O), segregated impurities in the oxide layer (Li, Na, Be, Mg) and implanted 18O were recorded for different operating conditions : energy, incident angle, chemical (Ar+ or O2+) and isotopic (16O2+ or 18O2+) nature of the primary beam and oxygen jet to saturate the surface.The main results are:- the shape of the depth profiles is very sensitive to operating conditions : the best depth resolution is obtained at low energy (2.5 keV) and the minimal distorsion with an O2 jet, even under O2+ bombardment. Deconvolution would be necessary to deduce the true depth profiles.- a tremendous enrichment (103 – 104) of the oxide to the Al bulk is observed for Li, Na, Be and Mg via an efficient diffusion mechanism during heat 425°C. Their depth distribution within the oxide layer is heterogenous with surface enrichment for Li and Na and sub-layer (towards the oxide/metal interface) for Be lateral distribution below the interface is also heterogeneous e.g. at the grain boundaries for Be and Na.- the depth profile of implanted 18O+ versus operating conditions and oxide thickness gives direct information on the dynamic oxidation of Al induced by O2+ sputtering in the first 20 nm.