Spectral artefacts post sputter-etching and how to cope with them – A case study of XPS on nitride-based coatings using monoatomic and cluster ion beams

Abstract

The issue of artefacts due to sputter-etching has been investigated for a group of AlN-based thin film materials with varying thermodynamical stability. Stability of the materials was controlled by alloying AlN with the group 14 elements Si, Ge or Sn in two different concentrations. The coatings were sputter-etched with monoatomic Ar + with energies between 0.2 and 4.0 keV to study the sensitivity of the materials for sputter damage. The use of Ar n+ clusters to remove an oxidised surface layer was also evaluated for a selected sample. The spectra were compared to pristine spectra obtained after in-vacuo sample transfer from the synthesis chamber to the analysis instrument. It was found that the all samples were affected by high energy (4 keV) Ar + ions to varying degrees. The determining factors for the amount of observed damage were found to be the materials’ enthalpy of formation, where a threshold value seems to exist at approximately −1.25 eV/atom (∼−120 kJ/mol atoms). For each sample, the observed amount of damage was found to have a linear dependence to the energy deposited by the ion beam per volume removed material. Despite the occurrence of sputter-damage in all samples, etching settings that result in almost artefact-free spectral data were found; using either very low energy (i.e. 200 eV) monoatomic ions, or an appropriate combination of ion cluster size and energy. The present study underlines that analysis post sputter-etching must be carried out with an awareness of possible sputter-induced artefacts.