Angle Dependent XRF for the Analysis of Thin Al(x)Ga(1-x)As Layers on GaAs and Thin Zn Layers on Steel

Abstract

Depth profiling is performed by monochromatic primary excitation using variable incidence and take-off angles, A proper choice of the photon energy and the angular range of incident radiation allows depth profiling of layered structures without comparison to reference samples. The method has been verified for two different systems. Thin Al(x)Ga(1-x)As-layers on GaAs substrates are characterized by thickness D and atomic ratio x. For an excitation of AlKα-radiation by SiKα-radiation from a secondary target, the lower limit of measurement is layer thicknesses of 40 to 80 nm at x=0.6 to 0.4. Zn-coatings on steel have been investigated with CuKα radiation for selective excitation of FeKα-radiation from the substrate and with GeKα radiation for the excitation of ZnKα radiation from the layer. The scatter of the results required a measurement of the lateral homogeneity of the coating thickness. These experiments have been performed by step scanning in steps of 1 mm under fixed incidence and take-off geometry over an area of 30mm*30mm and excitation with unfiltered radiation from a Cu target diffraction tube with a beam cross section of less than 1 mm². The obtained thickness distribution of ±20% has been confirmed by electron micrographs.