Thickness and structure of thin films determined by background analysis in hard X-ray photoelectron spectroscopy

Abstract

We report on the analysis of inelastic backgrounds associated with photoelectron peaks from thin films of Ru on Si using hard X-ray photoelectron spectroscopy (HAXPES) with an X-ray energy of 7939 eV. To extract information on the thickness and morphology of the Ru films, the Tougaard-background-analysis method was used. Consistent results from the analysis of the Si 1s peaks as well as the Ru 2p, 2s peaks to the thicknesses determined with X-ray reflectivity were found. Good agreement was also found for surface topography (the Ru forms islands on the Si surface for film thicknesses <12 nm and covers the complete surface for larger thicknesses) determined by our fitting results and scanning electron microscopy. It is demonstrated that with this method it is possible to obtain information on films up to 150 nm thickness, which corresponds to ∼20 times the inelastic mean free paths (IMFPs). This is larger than the previously reported ∼10 times the IMFP for X-ray photoelectron spectroscopy with conventional X-ray sources owing to the fact that the spectrum can be followed over a larger range of energy-loss. The method can also be used to determine the IMFP if the film thickness is known by another technique and it was applied to determine the IMFP for Ru at 4900 eV (4.3 nm) and 6050 eV (5.3 nm). In addition, some possible applications of the methods are described.