Wavelength despersive spectroscopy analysis at high spectral resolution:: application to the study of Mo/Si multilayers

We show that x-ray emission spectroscopy (XES) induced by electrons, analyzed at high spectral resolution by a WDS Johann-type spectrometer, is a powerful technique to characterize in a nondestructive way the interlayers in Mo/Si multilayers. The analysis is performed using the IRIS (Instrument de Recherche sur les Interfaces et Surfaces) apparatus equipped with a curved crystal. Within those experimental conditions the spectral resolution E/Delta E is about 2000 in the 1800-1900 eV photon energy range. Because of the high resolution of the spectrometer, the evolution of the shape of the Si K beta emission band (3p-1s transition) as a function of the chemical environment of the Si atoms is easily evidenced. We study a series of Mo/Si multilayers, where the thickness of the Si layers is 2 nm and that of the Mo layers is 1, 2, 3 or 4 nm. It clearly appears that the emission band from the Si atoms within the multilayers is different from that of amorphous Si (a-Si), which should be observed if no diffusion process takes place at the interfaces. By comparing the observed emission band to that of a-Si and molybdenum silicides and using a simple diffusion model, we deduce the composition of the interlayers. Their thickness is deduced and estimated to be 0.4 +/- 0.1 nm or 0.8 +/- 0.2 nm depending on the samples. Copyright (C) 2007 John Wiley & Sons, Ltd.