Variation of the electron inelastic mean free path during depth profiling of the Fe/Si interface as determined by quantitative REELS

Abstract

The aim of this work is to determine the dependence of the electron inelastic mean free path (IMFP) at the Fe/Si interface during depth profiling by sputtering with 3 keV Ar + ions. In order to estimate the variation of the IMFP at the interface, reflection electron energy-loss spectroscopy (REELS) measurements were performed after different sputtering times at the Fe/Si interface with three different primary electron energies (i.e. 0.5, 1 and 1.5 keV). Even though it is highly likely that a compound (i.e. Fe x Si) is formed at the interface, all the experimental REELS spectra could be analysed as a linear combination of those corresponding to pure Si and Fe. Using the model developed by Yubero and Tougaard for quantitative analysis of these REELS spectra we could estimate the IMFP values along the depth profile at the interface. The resulting IMFPs are observed to vary linearly with the average composition (as determined by REELS) at the Fe/Si interface as it is sputter depth profiled. The energy dependence of the IMFP for different compositions is presented and discussed. For completeness, we have determined the energy-loss functions as well as the IMFPs of the pure elements (i.e. Fe and Si).

Validity of Yubero-Tougaard theory to quantitatively determine the dielectric properties of surface nanofilms

“…10,11 However, even for Al and Si the agreement between theory and experiment is good for energy loss less than the sum of surface and bulk plasmon energies. 7,17,22 Most materials have wider energy-loss structures, and the effect is expected to be small. However, we want to test how important this possible problem is.…”

Electron Backscattering in Sputter Depth Profiling Using AES, EPES, and REELS

“…When sputtering through an A/B interface, it is obvious that the IMFP and the AL will gradually change from the value in A to that of the value in B. It is possible to directly follow this change by evaluation of REELS spectra taken during sputtering, as shown by Prieto et al [24] for sputtering through the interface of a thin film of Fe on a Si substrate. At first, a quantitative analysis of REELS spectra after Yubero et al [5] was used to calculate the electron loss function of pure Si and Fe, and then these results were used to determine the IMFPs in the electron energy range 250-2000 eV.…”

“…The above method for pure Fe and Si was used to determine the variation of the IMFP at the Fe/Si interface when it is sputter depth profiled with 3 keV Ar + ions. Figure 2(a) shows the variation of REELS spectra when sputtering through the Fe/Si interface [24]. In Fig.…”

“…The sample consists of a 150 nm thick Fe film deposited on a Si substrate which was carefully sputter cleaned before deposition. From Ref [24]…”

“…Left side lower picture shows REELS spectra of pure Fe (B1) and pure Si (B2), upper picture shows profile of these two components for E p = 1500 eV and right picture for both E p = 500 and 1500 eV. From Ref [24]…”