TRBS modelling of LEIS spectra – fundamentals and applications

(1) ION-TOF GmbH, Heisenbergstr. 15, 48149 Münster, Germany
(2) Johannes Kepler University Linz, Inst. of Exp. Physics, Altenberger Str. 69, 4040 Linz, Austria

Due to its monolayer sensitivity, straight-forward quantification and good detection limits, low energy ion scattering (LEIS) is routinely used in the characterization of ultra-thin films to address analytical questions like layer closure, surface composition, diffusion processes, or growth modes.  For these applications, LEIS delivers essential information about the surface composition, especially in the early phases of film growth, before a full monolayer is formed. Nevertheless, the additional in-depth information contains valuable extra information about the thickness of the film and the thickness distribution or interface quality. In the past, this in-depth information has mainly been exploited semi-empirically [1].   In order to get a more accurate description of the spectra and ultimately deduce a better analytical result for the samples, a physical modelling of the spectra is required. One possible approach is the application of TRBS [2] to simulate the scattering spectra. As this software was developed for much higher energies than those used in LEIS (1-10 keV), the application requires some modifications and corrections to the parameters used in the program.   Another complication arises from the fact that LEIS electrostatic energy analysers only detect scattered ions, not neutrals, while TRBS only handles the particle kinematics. Consequently, the ion fraction has to be handled independently. We found a way to measure the ion fraction and apply it to the simulated spectra from TRBS to fit the measured data.  In addition to presenting the progress in our methodology [3] to model the in-depth signal of LEIS spectra in general, we will also show results from several applications. These applications include HfO2/Al2O3 films manufactured by atomic layer deposition (ALD) as well as other thin film system, e.g. Ru liners for advanced interconnects on Ta- and Mn-based barriers.  

[1] R. ter Veen et al., J. Vac. Sci. Technol. A 31, 01A113 (2013).
[2] J. P. Biersack et al., Nucl. Inst. and Meth. in Phys. Res., B61, 1991, 77-82.
[3] P. Brüner et al., J. Vac. Sci. Technol. A 33, 01A122 (2015).