A general framework is presented for the quantitative analysis of surfaces by X-ray photoelectron spectroscopy (XPS or ESCA). The approach starts by considering analysis using reference data recorded on the same instrument and under identical conditions as the analysed sample. Matrix factors are evaluated and the quantification for adsorbed layers and sputter profiles discussed. More popularly reference data are not recorded each time but are taken from the published literature. In this case the angular anisotropy term and analyser transmission functions need to be known. These are discussed and the analyser transfer functions of commercial spectrometers are presented in detail. Nine published reference data sets are assessed to test their correlation with the theoretical predictions. Theree sets are found to give moderate agreement but agree more closely with each other in their divergence from the theory for particular elements. This divergence enables a peak intensity factor to be defined which quantifies the intensity lost from a peak due to shake-up events, etc. With this factor and the analyser transfer functions quantification can be made to an accuracy of 10% in all instruments from a single reference data set.

The quantitative analysis of surfaces by XPS: A review

Improved depth resolution by sample rotation during Auger electron spectroscopy depth profiling

Beginning with some introductory remarks about aims and scope, historical background and present state of the art, a brief survey of the technique of sputter depth profiling is given. The fundamental principles of ion/solid interactions during sputtering and the resulting changes in surface composition and surface topography as well as their influence on the conversion of sputtering time to sputtered depth are illustrated by some examples. Together with the specific analysis method employed, such as secondary ion mass spectrometry or Auger electron spectroscopy, these effects determine the shape of the depth profile of interfaces and of thin layers. Recent developments in evaluation and quantification of depth profiles are reviewed with emphasis on the role of the depth resolution function in profile reconstruction, including experimental determination and theoretical modelling of the depth resolution function by the three fundamental parameters: atomic mixing, surface roughness and information depth (MRI model). A summary of optimized experimental conditions for high-resolution depth profiles highlights the use of sample rotation and of low-energy primary ions. Practical application of depth profiling at interfaces is further elucidated by typical examples in the fields of surface and grain boundary segregation, corrosion, oxidation and interdiffusion controlled reactions at thin-film interfaces in electronic materials. An outlook on future trends focuses on theoretical profile simulation methods and on instrumental developments.

https://iopscience.iop.org/article/10.1088/0034-4885/61/7/002/pdf

Sputter depth profile analysis of interfaces

A major use of surface analysis instruments concerns composition depth profiling. In many instances poor depth resolution is obtained, one cause of which is poor ion beam alignment and uniformity. To enable instrument users to optimise instrument settings and know (1) the instrument contribution to depth resolution and (2) the ion etch rate, tantalum pentoxide reference materials have been developed with thicknesses of 30 nm and 100 nm and interface widths, measured by AES, of 1.5 and 1.7 nm respectively. The effects of argon ion beam energy, electron beam current density, sputtering geometry and gas purity effects on etch rate and interface width are measured and interpreted in terms of basic parameters, showing that the material is a well-behaved model system that is robust and easily used. The precise shape of the interface and preferential sputtering effects are also analysed.

C. Lea

Papers

Depth resolution in composition profiles by ion sputtering and surface analysis for single-layer and multilayer structures on real substrates

Optimized depth resolution in ion-sputtered and lapped compositional profiles with Auger electron spectroscopy