THICKNESS DETERMINATION OF THIN OXIDE LAYERS ON METAL-SURFACES USING X-RAY PHOTOELECTRON-SPECTROSCOPY

Surface analysis of metals covered with thin oxide layers has been performed using X-ray photoelectron spectroscopy. Samples of Al2O3/Al, PbO/Pb, MgO/Mg and SiO2/Si were used. The spectra showing a double-peak structure due to metal and oxide components have been decomposed by a curve-fitting technique in order to obtain the intensities of each component. The thickness of the oxide layers obtained from these intensity ratios have been measured for various electron take-off angles. Two different X-rays of Mg K-alpha and Al K-alpha were employed to observe the effect due to the different inelastic mean-free paths. The experimental results concerning the thickness obtained for these X-rays were in excellent agreement with each other. It was confirmed that for flat samples, such as SiO2/Si, a measurement using only one take-off angle is required to obtain an overlayer thickness. On the contrary, measurements should be carried out for various take-off angles so as to deduce reliable values for such samples as lead for which the surface roughness cannot be neglected. As for aluminium and silicon oxide layers formed by exposure to air for a sufficiently long time, thicknesses of about 33 angstrom and 11 angstrom were obtained, respectively.