Reference-Free X-Ray Spectrometry

Well-characterized monochromatic synchrotron radiation of BESSY is used for the investigation of wafer surface contamination and nanolayered materials by X-ray spectrometry, allowing for the non-destructive determination of elemental mass depositions or elemental concentrations. For this purpose the fluorescence spectra can be recorded in different geometries: varying the incident angle from close to zero degrees, i. e. total-reflection geometry (T), over grazing incidence (GI) to conventional X-ray fluorescence (XRF). In TXRF geometry only the surface is analyzed, whereas GIXRF and XRF provide information from subsurface layers (incl. depth profiling) respectively the bulk of a sample [1,2].
Reference-free quantification in X-ray fluorescence analysis requires the accurate knowledge of all experimental values both in the excitation and detection channels as well as of the atomic fundamental parameters involved. The experimental data are accessible through calibrated devices such as photodiodes, diaphragms and energy-dispersive detectors. Nanolayer thicknesses [3] obtained for transition metals as well as for silicon dioxide layers by XRF are well in line with the results of X-ray reflectometry (XRR).
For the speciation of contaminants on wafer surfaces or the constituents of nanolayers TXRF, GIXRF [4] and XRF can be combined with near-edge X-ray absorption fine structure (NEXAFS or XANES) taking advantage of the excellent tunability of monochromatized synchrotron radiation.