Total reflection X-ray fluorescence spectrometry for quantitative surface and layer analysis

Abstract

Abstract. Measurements of X-ray fluorescence spectra versus grazing incident angles provide information on elemental composition as well as density and thickness of near surface layers. Calculations of fluorescence intensities are presented, which are used for the evaluation of data obtained by total reflection X-ray fluorescence (TXRF) spectrometry. The calculation is based on a matrix formalism to account for standing wave phenomena due to transmission and reflection in layered material. For the determination of concentrations the model makes additional use of the fundamental parameter technique in order to include absorption and enhancement effects of the fluorescence radiation. On the basis of experimental data some capabilities of this nondestructive and contactless probing technique are presented. PACS: 0%85, 68.35The production and application of thin films, single layers and layer systems on diverse substrates have reached a high degree of economic importance. It is widely appreciated that this technology will require further analytical techniques, especially those which can be employed in a production environment to support the increased requirements for contamination control and layer specification. In this paper we describe total reflection X-ray fluorescence (TXRF) spectrometry as a nondestructive and contactless probing technique for quantitative surface and layer analysis in the nanometer range.For X-rays striking a surface at grazing incidence, a critical angle exists below which total reflection occurs. Under total reflection conditions, the incident X-ray beam interacts, in contrast to conventional XRF, only with the near surface layers. Depending mainly on the density of the reflecting interface, the penetration depth of the primary X-ray beam is approximately 2-8 nm. In this mode of operation, the TXRF is an intrinsically surface sensitive as well as a proven method of trace element analysis [1]. Detection limits better than 10 l° atoms/cm 2 are obtained for metal impurities in the oxide layer of silicon wafers [2]. Moreover, it is possible to distinguish quantitatively between impurities which are embedded in a surface and those on a surface as particles or residues [3].* Author to whom correspondence should be addressed On exceeding a critical angle, the reflectivity decreases rapidly and the primary beam illuminates deeper parts of the material according to the angle of incidence. Therefore, X-ray fluorescence spectrometry in the critical angle regime offers the advantage of combining surface sensitivity with the analysis of stratified heterostructures [4,5]. We outline a procedure for the quantitative determination of elemental composition, density and thickness of layers: a calibrated instrument is used for measuring fluorescence intensities as a function of the incident angle. In order to deduce the layer parameters from the experimental data modelling calculations of the fluorescence intensities are compared with the measured data. By means of an iterative process that set of parameters ...

Synchrotron radiation-induced total reflection X-ray fluorescence analysis

“…The resulting values are plotted versus angle to give the intensity profiles. From these profiles, the respective sample parameters (particle size, layer thickness) can be evaluated by an iterative fitting procedure on the basis of modeling calculations using the modulated intensity distribution above the reflector as an extremely fine dynamic ruler [11,21,[39][40][41].…”

Grazing Incidence-X-ray Fluorescence Spectrometry for the Compositional Analysis of Nanometer-Thin High-κDielectric HfO2 Layers

“…The angle-dependent fluorescence intensities were interpreted using calculations or fittings obtained with the dedicated software developed by the GKSS research center (Geesthacht, Germany). 17,19 TOF-SIMS depth profiles were obtained using a commercial instrument (Iontof-IV). The HfO2 layer was sputtered using a Xe + beam at an energy of 500 eV and a flux of 7 × 10 13 at/cm 2 (current of 20 mA over a raster of 400 × 400 µm 2 ).…”

“…If the layer is sufficiently thick, the density and thickness can also be determined. The method is based on calculating the angle dependent fluorescence intensities from layered samples, as developed simultaneously by Weisbrod et al and de Boer et al 17,18 The Fresnel relations are used to account for standing-wave phenomena due to transmission and reflection in these samples. For quantification, the model makes additional use of the fundamental parameter technique to account for absorption and enhancement effects of the fluorescent radiation.…”

Effect of Energy Dependence of Primary Beam Divergence on the X-ray Standing Wave Characterization of Layered Materials

“…11,12 The various advantages of GI-XRF technique over the other commonly used techniques of thin film analysis, such as X-ray reflectivity or secondary ion mass spectrometry, have been described by several workers. [13][14][15] Apart from analysis of thin layer and adsorbed particulate matter on a substrate, Barbee and Warburton 16 applied the GI-XRF technique to investigate periodic multilayer structures. They showed that X-ray standing wave (XSW) effects occur in multilayer Bragg peak regions as in perfect crystals.…”