Inelastic background modelling applied to hard X-ray photoelectron spectroscopy of deeply buried layers: A comparison of synchrotron and lab-based (9.25 keV) measurements

Hard X-ray Photoelectron Spectroscopy (HAXPES) provides minimally destructive depth profiling into the bulk, extending the photoelectron sampling depth. Detection of deeply buried layers beyond the elastic limit is enabled through inelastic background analysis. To test the robustness of this technique, we present results on a thin (18 nm) layer of metal-organic complex buried up to 200 nm beneath organic material. Overlayers with thicknesses 25-140 nm were measured using photon energies ranging 6-10 keV at the 109 end station at Diamond Light Source, and a new fixed energy Ga K alpha (9.25 keV) laboratory-based HAXPES spectrometer was also used to measure samples with overlayers up to 200 nm thick. The sampling depth was varied: at Diamond Light Source by changing the photon energy, and in the lab system by performing angle-resolved measurements. For all the different overlayers and sampling depths, inelastic background modelling consistently provided thicknesses which agreed, within reasonable error, with the ellipsometric thickness. Relative sensitivity factors were calculated, and these factors consistently provided reasonable agreement with the expected nominal stoichiometry, suggesting the calculation method can be extended to any element. These results demonstrate the potential for the characterisation of deeply buried layers using synchrotron and laboratory-based HAXPES.

Automated summary

Hard X-ray Photoelectron Spectroscopy (HAXPES) allows minimally destructive depth profiling into deeply buried layers, with inelastic background analysis enabling detection beyond the elastic limit. Results from both synchrotron and laboratory-based HAXPES measurements consistently showed reliable thickness measurements and relative sensitivity factors. This method demonstrates potential for characterizing deeply buried layers with reasonable agreement in stoichiometry calculations.