In-line characterization of ultrathin transition metal dichalcogenides using X-ray fluorescence and X-ray photoelectron spectroscopy

Abstract Industry-scalable fabrication methods of sulfur-based transition metal dichalcogenides are being developed, which puts strong requirements on the characterization of these mono- and few-layer materials in a cleanroom environment. In this paper, we show that the stoichiometry of ultrathin molydbenum disulfide layers can be determined by inline X-ray photoemission spectroscopy and wavelength-dispersive X-ray fluorescence, within the uncertainty provided by reference-free X-ray fluorescence in grazing incidence performed at the Physikalisch-Technische Bundesanstalt. In addition, we demonstrate that automated inline wavelength-dispersive X-ray fluorescence analysis can accurately determine the mass deposition of molybdenum and sulfur. Such information is crucial to support and accelerate the development of multi-parametric sulfur-based transition metal dichalcogenides processes, for instance by careful adjustment of the mass deposition per deposition cycle, both on samples and full wafers.