Microprobe technique for determining the thickness of thin metal films in multilayered structures

Abstract

The microprobe technique applies to metal or alloy film composites in which the chemical composition is uniform. Film thicknesses of such structures are determined on the basis of characteristic X-ray intensities detected for each layer. Composite standards with layers arranged in the same sequence as in the samples are required to minimize or eliminate backscattering and secondary fluorescence effects. The absorption correction, however, is built into the method. The technique was developed using Cu/Ni composites in which Cu was used as a tracer element at various depths in a Ni matrix. It was then applied to Al/SiO 2 structures with several thickness ratios ranging from 1.0 to 2.0. Routine analyses achieved an accuracy of ±5%. To determine thickness the ionization curves had to be expressed analytically as a function of depth and accelerating potential, and an expression was derived for the detected intensity. The X-ray intensity of each layer, from the surface down, was processed through a computer program so that thickness information determined for the first layer was input information for the second, and so on. The technique can also be used to determine a contaminant density in any of the layers.