Thin layer composition profiling with angular resolved x-ray photoemission spectroscopy: Factors affecting quantitative results

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Composition profiling of thin films in the nanometer range is critical to the development of future electronic devices. However, the number of techniques with such depth resolution is limited. Among them, angle-resolved x-ray photoelectron spectroscopy (ARXPS) can be used for thin layers up to a few nanometers, but it is not yet a fully established method. In order to evaluate its capabilities for use as a routine and general method, the authors evaluate both its intrinsic capabilities in comparison with other methods and the factors affecting quantification by analyzing its variability when applied at various laboratory locations with different tools and data treatments. For this purpose, dedicated samples based on multilayers of HfO2 and SiON were produced with a well-determined layer structure. The results show that ARXPS, including depth profiling reconstruction, is very efficient and compares favorably with nuclear analysis techniques. It allows the separation of the surface contamination signal from the interfacial layer signal and allows determination of the coverage quantitatively. An accuracy of ±10% is achieved for most elements except for nitrogen, where strong peak interference with hafnium and a low intensity increase the inaccuracy up to 20%. This study also highlights several technique limitations. First, the quality of the retrieved profile is strongly dependent upon the exact determination of each photoemission peak intensity. Also it demonstrates that, while favorable for chemical identification, very high resolution spectra may lead to larger errors in profile reconstruction due to larger statistical errors in the intensities, though this is true mainly for deeper layers. Finally, it points out the importance of the physical parameters used in the final obtained results.