Grazing incidence X-ray fluorescence of periodic structures – a comparison between X-ray standing waves and geometrical optics calculations

Grazing incidence X-ray fluorescence spectra of nano-scaled periodic line structures were recorded at the four crystal monochromator beamline in the laboratory of the Physikalisch-Technische Bundesanstalt at the synchrotron radiation facility BESSY II. For different tilt angles between the lines and the plane of incidence of the monochromatic synchrotron radiation, spectral features are observed which can be understood and explained with calculations of the emerging X-ray standing wave (XSW) field. On the other hand, there are structures, i.e., pronounced modulations above the substrate's critical angle of external total reflection, which are not included in the XSW concept. Novel geometrical optics calculations can reproduce these structures taking the sample's specific geometric conditions into account

Characterization of ultra-shallow aluminum implants in silicon by grazing incidence and grazing emission X-ray fluorescence spectroscopy

In this work two synchrotron radiation-based depth-sensitive X-ray fluorescence techniques, grazing incidence X-ray fluorescence (GIXRF) and grazing emission X-ray fluorescence (GEXRF), are compared and their potential for non-destructive depth-profiling applications is investigated. The depth-profiling capabilities of the two methods are illustrated for five aluminum-implanted silicon wafers all having the same implantation dose of 1016 atoms per cm2 but with different implantation energies ranging from 1 keV up to 50 keV. The work was motivated by the ongoing downscaling effort of the microelectronics industry and the resulting need for more sensitive methods for the impurity and dopant depth-profile control. The principles of GIXRF and GEXRF, both based on the refraction of X-rays at the sample surface to enhance the surface-to-bulk ratio of the detected fluorescence signal, are explained. The complementary experimental setups employed at the Physikalisch-Technische Bundesanstalt (PTB) for GIXRF and the University of Fribourg for GEXRF are presented in detail. In particular, for each technique it is shown how the dopant depth profile can be derived from the angular intensity dependence of the Al Kα fluorescence line. The results are compared to theoretical predictions and, for two samples, crosschecked with values obtained from secondary ion mass spectroscopy (SIMS) measurements. A good agreement between the different approaches is found proving that the GIXRF and GEXRF methods can be efficiently employed to extract the dopant depth distribution of ion-implanted samples with good accuracy and over a wide range of implantation energies

Depth profiling of low energy ion implantations in Si and Ge by means of micro-focused grazing emission X-ray fluorescence and grazing incidence X-ray fluorescence

Depth-profiling measurements by means of synchrotron radiation based grazing XRF techniques, i.e., grazing emission X-ray fluorescence (GEXRF) and grazing incidence X-ray fluorescence (GIXRF), present a promising approach for the non-destructive, sub-nanometer scale precision characterization of ultra shallow ion-implantations. The nanometer resolution is of importance with respect to actual semiconductor applications where the down-scaling of the device dimensions requires the doping of shallower depth ranges. The depth distributions of implanted ions can be deduced from the intensity dependence of the detected X-ray fluorescence (XRF) signal from the dopant atoms on either the grazing emission angle of the emitted X-rays (GEXRF), or the grazing incidence angle of the incident X-rays (GIXRF). The investigated sample depth depends on the grazing angle and can be varied from a few to several hundred nanometers. The GEXRF setup was equipped with a focusing polycapillary half-lens to allow for laterally resolved studies. The dopant depth distribution of the investigated low-energy (energy range from 1 keV up to 8 keV) P, In and Sb ion-implantations in Si or Ge wafers were reconstructed from the GEXRF data by using two different approaches, one with and one without a priori knowledge about the bell-shaped dopant depth distribution function. The results were compared to simulations and the trends predicted by theory were found to be well reproduced. The experimental GEXRF findings were moreover verified for selected samples by GIXRF

Investigation of surface nanostructures with grazing angle x-ray fluorescence techniques

La présente thèse de doctorat a été réalisée au Département de Physique de l’Université de Fribourg dans le groupe de recherche « Atomic and X-Ray Physics » (AXP) du Prof. Jean-Claude Dousse. Elle est consacrée au développement de méthodes d’analyse basées sur la fluorescence X en haute-résolution et à angles rasants, plus spécifiquement la fluorescence X à émission rasante (GEXRF) et la fluorescence X à incidence rasante (GIXRF). Ces méthodes d’analyse à angles rasants permettent de sonder la surface d’échantillons ainsi que la région proche de la surface pour en extraire des informations comme la présence d’éléments-traces et la contamination de surface, la distribution en profondeur d’impuretés ou d’ions implantés, la structure de couches minces et d’interfaces et la caractérisation de particules déposées à la surface de substrats plats. Un objectif spécifique de cette étude était de déterminer comment l’intensité de fluorescence dépendait de la morphologie de la surface de l’échantillon pour les cas de l’émission rasante et de l’incidence rasante. La plupart des mesures présentées dans la thèse ont été effectuées auprès de sources de rayonnement synchrotronique comme l’Installation européenne de rayonnement synchrotron (ESRF) à Grenoble, France, la Source de lumière suisse (SLS) de l’Institut Paul Scherrer à Villigen, Suisse et l’Anneau de stockage d’électrons BESSY II à Berlin, Allemagne. Les mesures GEXRF ont été réalisées à l’aide du spectromètre à cristal courbé von Hamos de Fribourg tandis que les mesures GIXRF ont été effectuées en utilisant la chambre ultravide de spectroscopie X et le manipulateur ultravide à 6 axes du « Physikalish-Technische Bundesanstalt » (PTB) de Berlin. Le mémoire de thèse est articulé de la manière suivante : Dans le Chapitre I, les fondements des méthodes XRF à angles rasants ainsi que leur application pour la caractérisation de nanostructures sont présentés avec un passage en revue de la littérature existante. Dans le Chapitre II, les expériences réalisées sont décrites en détails avec, en particulier, une présentation complète des lignes de faisceau sur lesquelles les mesures ont été effectuées ainsi que des instruments utilisés pour ces mesures. Les échantillons analysés et les méthodes utilisées pour la préparation de ces derniers sont également discutés dans ce chapitre. Le Chapitre III concerne les méthodes utilisées pour l’analyse et le traitement des données. Pour pouvoir interpréter correctement les spectres GEXRF, de nouveaux logiciels ont dû être développés. Les programmes correspondants sont présentés dans ce chapitre, une description plus complète de ces derniers étant donnée dans les annexes. Tout d’abord un nouvel algorithme développé pour l’analyse d’événements correspondant à des impacts simple et multiple sur la caméra CCD est discuté. Ensuite sont abordés des problèmes concernant la correction des images CCD obtenues en géométrie von Hamos avec un accent principal sur le cas de l’émission rasante X. On trouvera également dans ce chapitre la présentation d’un nouveau modèle basé sur l’optique géométrique (GO) pour la simulation des spectres XRF angulaires de nanostructures et de distributions denses de nanoparticules déposées sur des substrats plats. Enfin, l’influence de la géométrie à incidence rasante sur le flux du faisceau de photons utilisé pour irradier l’échantillon est analysée pour le cas des matériaux granulaires. Le Chapitre IV présente les résultats obtenus pour des échantillons ayant des morphologies de surface correspondant à des distributions soit uniformes soit périodiques de structures de diverses formes et faites d’éléments différents. Les caractéristiques spectrales des profils angulaires GEXRF et GIXRF de ces échantillons sont présentées et commentées. Les résultats expérimentaux sont comparés aux valeurs théoriques obtenues à partir du nouveau modèle géométrique (GO) et du modèle des champs d’ondes stationnaires X (XSW). Le chapitre se termine avec un inventaire des principales difficultés expérimentales rencontrées durant la réalisation des différents projets. Les conclusions principales du travail sont énoncées dans le Chapitre V. Une discussion sur les possibilités d’application des techniques de spectroscopie X à angles rasants et des méthodes d’analyse développées dans la thèse clôt ce dernier chapitre.The present Ph.D. thesis was realized in the Atomic and X-Ray Physics (AXP) research group of Prof. Jean-Claude Dousse at the Physics Department of the University of Fribourg. It is devoted to the development of high-resolution X-Ray Fluorescence (XRF) methods at grazing angles, namely the Grazing Emission (GEXRF) and Grazing Incidence (GIXRF) X-Ray Fluorescence methods. These grazing angle techniques probe a sample in the near surface area and allow to perform trace-element analysis, surface contamination control, depth profiling of buried impurities or implanted ions, structure determination of layers and interfaces, and characterization of on-surface particles. A particular aim of this thesis was to establish the relations between the surface morphology and fluorescence intensity of a sample in the regimes of grazing emission and grazing incidence. Most measurements were performed at synchrotron radiation facilities, namely at the European Synchrotron Radiation Facility (ESRF), in Grenoble, France, at the Swiss Light Source (SLS), at PSI, in Villigen, Switzerland, and at the Electron Storage Ring BESSY II, in Berlin, Germany. The GEXRF projects were carried out using the von Hamos bent crystal spectrometer of Fribourg, whereas the GIXRF measurements were performed with the ultra-high vacuum x-ray spectrometry chamber and the 6-axis ultra-high vacuum manipulator of the Physikalish-Technische Bundesanstalt (PTB). The thesis is organized as follows: In Chapter I the basic concepts concerning the grazing angle XRF methods and their applications for nanostructures’ characterisation are presented together with an outlook of the related literature. In Chapter II the experiments carried out for this study are described in detail. In particular, the instruments used to perform the GEXRF and GIXRF measurements as well as the different synchrotron radiation beamlines where these measurements took place are presented. The investigated samples and the methods used to prepare them are also discussed in this part. Chapter III is devoted to the data analysis and data processing methods. In order to interpret correctly the measured GEXRF spectra, new software packages were developed. They are presented in this chapter while a more detailed description of them is given in the Appendices, at the end of the thesis. First, a new algorithm for the analysis of CCD single and multiple hit events is discussed. The problems related to the correction of the CCD images in the von Hamos geometry are then addressed with a special focus on the properties of images collected in the grazing emission arrangement. A novel analytical method based on Geometrical Optics (GO) for simulation of the XRF angular profiles of nanostructures and nanoparticles densely distributed on flat substrates is also presented. Finally the influence of the grazing incidence geometry on the effective flux of the exciting radiation for particulate media is described. Chapter IV presents the experimental results obtained for sample of various morphologies characterized by periodic and evenly distributed structures. The characteristic spectral features and trends of the measured GEXRF and GIXRF angular profiles are described and discussed. The experimental results are compared to the theoretical predictions from the GO model and to the values obtained from X-ray Standing Wave (XSW) simulations. At the end of this chapter, the experimental difficulties encountered during the different projects are discussed. In Chapter V conclusions about the most significant aspects of the thesis are drawn. Future perspectives concerning possible applications of the described x-ray grazing angle techniques and developed data analysis methods are outlined

Geometrical optics modelling of grazing incidence X-ray fluorescence of nanoscaled objects

X-ray Standing Wave (XSW) is a well established formalism for modelling Grazing Incidence X-ray Fluorescence (GIXRF) experiments. However, when probing nanostructured surfaces with complex morphology the effects of the interaction of the XSW with structure elements need to be investigated. This is not always easy and sometimes even not possible. In the present work a novel approach employing Geometrical Optics (GO) calculations is proposed. The model is employed for simulations of two different types of nano-particles distributed on a flat surface. It is shown that GO simulation yields results with good agreement when compared to absolute measurements even when XSW deteriorates

Electronic Structure of Third-Row Elements in Different Local Symmetries Studied by Valence-to-Core X‑ray Emission Spectroscopy

The electronic structure of phosphorus, sulfur, and chlorine in compounds with <i>T</i>_<i>d</i> and <i>C</i>_3<i>v</i> local symmetries was studied with high-resolution Kβ X-ray emission spectroscopy (XES) in the tender X-ray range. Measured spectra are compared to the results of <i>ab initio</i> quantum chemical calculations based on density functional theory (DFT). The spectral structure is reproduced by the model spectra of isolated XO₄^<i>n</i>– and XO₃^<i>n</i>– (X = P, S, or Cl) anions incorporating only the first coordination sphere around the central atom. The main spectral components can be explained by the molecular orbital theory. Finally, the potential of XES spectroscopy combined with DFT calculations to study the electronic structure of third-row elements in a slightly larger molecule is investigated