Reference-free X-ray spectrometry based on metrology using synchrotron radiation

Abstract

X-ray spectrometry is a wide spread technique for revealing reliable information concerning the elemental composition and binding state in various materials. Reference-free quantitation in X-ray spectrometry is based on the knowledge of both the instrumental and fundamental atomic parameters. Instrumental or experimental parameters involve the radiant power and spectral purity of the excitation radiation, the beam geometry, the solid angle of detection, and the response behavior and efficiency of the detector. The reliability of the quantitation equally depends on the relative uncertainty of the atomic fundamental parameters involved. Both the values and estimated uncertainty of atomic fundamental parameters given in the literature can be improved by dedicated experiments: By means of transmission and fluorescence experiments with tunable synchrotron radiation, the mass absorption coefficient and fluorescence yield of Al was determined. Furthermore, the transition probabilities of the fluorescence lines belonging to the Cu-L iii and L ii subshells were determined using a superconducting tunnel junction detector offering an energy resolution of about 10 eV in the soft X-ray range. Selected techniques and applications of reference-free X-ray spectrometry are presented. A particular advantage of reference-free quantitation modes is their capability to directly probe new materials without the need to wait for appropriate standard reference materials.

Comprehensive Comparison of Various Techniques for the Analysis of Elemental Distributions in Thin Films: Additional Techniques

“…Applying well-determined synchrotron radiation and calibrated instrumentation allows for a physically traceable quantification based on the knowledge of all relevant experimental and instrumental parameters as well as of the atomic fundamental parameters involved (Hönicke et al 2014), such as photoionization cross-sections, transition probabilities, and fluorescence yields. With this approach, no additional calibration samples or reference materials are needed for instrumental precalibration (Beckhoff, 2008). Varying the angle of incidence of the exciting radiation the matrix-dependent and energy-dependent information depth of the measured characteristic fluorescence lines can be equally tuned, and differential information about the compositional depth profiles obtained.…”

“…Reference-free grazing-incidence X-ray fluorescence (GIXRF) measurements were performed at the four-crystal monochromator (FCM) beamline in the PTB laboratory (Beckhoff et al, 2009) at the electron storage ring BESSY II. The angle of incidence was varied from 0 to 5°.…”

“…A photon energy of the incident radiation of 11 keV was chosen to excite the Cu-K, Ga-K, and In-L fluorescence lines which all were used for the GIXRF quantification. The incidence photon flux was determined by means of a calibrated photodiode (Beckhoff et al, 2009). The synchrotron beam profile exhibits an extension of approximately 300 µm x 200 µm.…”

“…Owing to the rotation of the sample in the incoming beam, one of the footprint dimensions on the excited sample surface varies up to a few mm. For the detection of fluorescence radiation, an energy-dispersive silicon drift-detector with known detection efficiency and response behavior was employed (Kumrey & Ulm, 2001;Scholze & Beckhoff, 2009). …”

Complementary methodologies for thin film characterization in one tool – a novel instrument for 450 mm wafers

“…This is a challenge when taking into account the fact that the selection of material parameters at different excitation energies has a considerable impact on the evaluated results. Databases from NIST, 9,10 PTB, 11,12 Panalytical, Atomica, Sopra, and Woollam were used. For thin-layer characterization, probably the most challenging issue is guring out the mass deposition, which is the product of thickness and density, also representing electron densities for scattering.…”