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Nanostructure Characterisation by Electron Beam Techniques
Signal Intensity Distribution in PAR-XPS from Rough Surfaces
Josef Brenner, 1,* Davide Bianchi, 1 László Katona, 1 András Vernes, 1 and Wolfgang Werner 2
1 AC2T research GmbH, Viktor Kaplan-Straße 2, 2700 Wr. Neustadt, Austria
2 IAP, Wiedner Hauptstraße 8-10/134, 1040 Wien , Austria
*brenner@ac2t.at
One limiting factor in quantitative Angle Resolved X-Ray Photoelectron Spectroscopy (AR-XPS) is
the difficulty of interpreting measured data in case of inhomogeneous chemical composition, morphology and
topography. The determination of layer thicknesses and the underlying understanding of signal generation, for
example, are prone to large uncertainties.
This contribution deals with the impact of surface roughness in parallel AR-XPS (PAR-XPS)
measurements. In order to study this, a layered structure, laterally uniform in both chemical composition and
layer thickness, covering the overall topography was chosen.
For sake of simplicity, a well-defined periodic roof-like surface was considered and compared with a
flat one, which allows one to validate the computational results by an analytical closed form. In particular,
PAR-XPS measurements and the corresponding numerical investigations were performed on a silicon sample
covered by a native oxide layer, containing both a parallel roof-like topography and a flat surface area. The
sample topography was measured by Atomic Force Microscopy (AFM) and parameterized using
Non-Uniform Rational B-Splines (NURBS) [1]. This parameterization is general enough giving the possibility
to be extended to arbitrary rough surfaces as characterized by well-known metrological methods. Another
advantage of NURBS is the intrinsic availability of arbitrary small surface facets and the fact that it directly
provides the angular orientation of these facts with respect to a fixed global coordinate system.
For each NURBS-facet the contribution to the total PAR-XPS intensity was calculated using a
generalized Beer-Lambert law in straight line approximation by also taking into account the shadowing due to
roughness of the surface. The computational results were cross-checked for a nominally flat surface using the
SESSA [2] simulation toolkit.
References
[1] L. Katona, D. Bianchi, J. Brenner, G. Vorlaufer, A. Vernes, G. Betz, and W.S.M. Werner, “Effect of surface
roughness on angle-resolved XPS”, Surf. Interface Anal. 44, 1119 (2012).
[2] W. S. M. Werner, W. Smekal, and C. J. Powell, “NIST Database for the Simulation of Electron Spectra for
Surface Analysis (SESSA)”, National Institute of Standards and Technology, Gaithersburg, MD, 2005.
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