Quantitative ARXPS investigation of systems with ultrathin aluminium oxide layers

Abstract

Angle-resolved x-ray photoelectron spectroscopy (ARXPS) is a non-destructive method to investigate the near-surface structure of specimens with a flat surface. For interpretation of the electron intensities emitted from different depth regions, model calculations are necessary. Based on an earlier algorithm we have developed a program for ARXPS studies of thin multilayers.In our model calculation the sample structure is treated as consisting of several layers (one to three) on the substrate, whereas the top layer can be incomplete. Emitted electrons are assumed to be attenuated exponentially in the layers. Different atomic volumes, electron attenuation lengths (including consideration of elastic scattering) and assumptions on stoichiometry are taken into account for the particular layers.As an application of our model calculations we present a study of a set of Al samples that were oxidized by different methods, i.e. natural and plasma oxidation (plasma obtained by electron cyclotron resonance). The oxide layers produced by plasma oxidation were protected by a 2 nm thick Co film, before exposing the samples to the air. Additionally, in order to check our results of the ARXPS model calculation, x-ray reflectometry (XRR) analysis was used.

Modeling of complex surface structures for ARXPS

“…In a first step (I) (shortly called 'simulation') atomic concentrations are simulated for a given near-surface model structure and are assumed to be experimental ARXPS results from a specific sample. Afterwards (II) the ARXPS data are approximated with a standard 'layer-by-layer' ARXPS quantification procedure [1,5] using the same model surface structure for the definition of the starting conditions. The comparison of both results leads to a 'RMS starting value' (1), which is a measure for the differences occurring due to real-structure effects that are not considered in the 'layer-by-layer' approach.…”

“…Simple models with smooth layers (at most with islands on top) mostly are used for the ARXPS quantification up to now (e.g. Refs [3][4][5]). This is in agreement with the conclusions of Cumpson, [1] who stated, in general, a very restricted information content in ARXPS.…”

Initial growth of W‐based films deposited on Si studied with ARXPS

“…Details on the used calculation procedure can be found in previous papers. [12,13] One of the major steps in ARXPS investigation is the selection of an appropriate model and suitable starting conditions for the optimization calculations. Both information on the sample preparation process (e.g.…”

“…As explained in our previous work. [12] we used as approximation the formula CS2 (Cumpson-Seah-2. [24] )…”

“…[8 -11] We used XPS for analysis because it can characterize the interface chemistry by analysis of chemical shifts of the photoelectron peaks. With angle-resolved XPS (ARXPS), additional nondestructive depth information can be derived and may be used to reconstruct element depth profiles at the nanometer thickness level [12,13] in the interface regions. For the mentioned Ta-and Ti-based systems, we found various phase formation such as silicide, nitride, and oxide formation.…”