Traceable thickness determination of organic nanolayers by X-ray reflectometry

Reference-free x-ray fluorescence analysis with a micrometer-sized incident beam

Spatially resolved x-ray fluorescence (XRF) based analysis employing incident beam sizes in the low micrometer range (μXRF) is widely used to study lateral composition changes of various types of microstructured samples. However, up to now the quantitative analysis of such experimental datasets could only be realized employing adequate calibration or reference specimen. In this work, we extent the applicability of the so-called reference-free XRF approach to enable reference-freeμXRF analysis. Here, no calibration specimen are needed in order to derive a quantitative and position sensitive composition of the sample of interest. The necessary instrumental steps to realize reference-freeμXRF are explained and a validation of ref.-freeμXRF against ref.-free standard XRF is performed employing laterally homogeneous samples. Finally, an application example from semiconductor research is shown, where the lateral sample features require the usage of ref.-freeμXRF for quantitative analysis.

Nested Sampling aided determination of tantalum optical constants in the EUV spectral range

We report on determining the optical constants of Ta in the sub-extreme ultraviolet (EUV) spectral range 5.0-24.0 nm from the angle-dependent reflectance (ADR) measured using monochromatized synchrotron radiation. Two sputtered samples with differing thicknesses were investigated. Complementarily x-ray reflectance was measured at shorter wavelengths and evaluated by Fourier transform to facilitate an unambiguous selection of a model for the data evaluation based on an inverse solution of the Fresnel's equations for a layered system. Bayesian inferences coupled with a Nested Sampling (NS) algorithm were utilized to derive the optical constants with their corresponding uncertainties. This report further emphasizes the applicability of an acclaimed NS algorithm on a high-dimensional inverse problem. We explore the possibility of addressing the correlations between the optical constants of thin films and their structural parameters based on other established studies.

Development of x-ray reflectivity measurement system under N2 to prevent surface contamination

In this study, a method to prevent surface contamination on an SiO₂ film/Si substrate system was used to improve thickness determination by x-ray reflectometry (XRR). XRR profiles can be significantly affected by the growth of a surface contamination layer, originating from the organic matter present in the measurement environment. An N₂ spray method that enables XRR measurement under high-purity N₂ has been developed to keep the surface free of contaminants. The method was adopted due to its high applicability to an existing XRR instrument and the ease of system construction. The system mainly consists of an outlet for N₂ spray that is positioned in front of the sample and an N₂ gas purifier. The high-purity N₂ is sprayed on the sample until the measurements are complete. It was revealed that the measured XRR profiles were stable for 115 h, and the evaluated thicknesses were obtained with high reproducibility (±0.05 nm for 10 nm thickness) by adopting the analysis model for clean surfaces.

Grazing-incidence small-angle X-ray scattering (GISAXS) on small periodic targets using large beams

Grazing-incidence small-angle X-ray scattering (GISAXS) is often used as a versatile tool for the contactless and destruction-free investigation of nano-structured surfaces. However, due to the shallow incidence angles, the footprint of the X-ray beam is significantly elongated, limiting GISAXS to samples with typical target lengths of several millimetres. For many potential applications, the production of large target areas is impractical, and the targets are surrounded by structured areas. Because the beam footprint is larger than the targets, the surrounding structures contribute parasitic scattering, burying the target signal. In this paper, GISAXS measurements of isolated as well as surrounded grating targets in Si substrates with line lengths from 50 µm down to 4 µm are presented. For the isolated grating targets, the changes in the scattering patterns due to the reduced target length are explained. For the surrounded grating targets, the scattering signal of a 15 µm × 15 µm target grating structure is separated from the scattering signal of 100 µm × 100 µm nanostructured surroundings by producing the target with a different orientation with respect to the predominant direction of the surrounding structures. As virtually all litho-graphically produced nanostructures have a predominant direction, the described technique allows GISAXS to be applied in a range of applications, e.g. for characterization of metrology fields in the semiconductor industry, where up to now it has been considered impossible to use this method due to the large beam footprint.