Combined evaluation of grazing incidence X-ray fluorescence and X-ray reflectivity data for improved profiling of ultra-shallow depth distributions

Abstract

The continuous downscaling of the process size for semiconductor devices pushes the junction depths and consequentially the implantation depths to the top few nanometers of the Si substrate. This motivates the need for sensitive methods capable of analyzing dopant distribution, total dose and possible impurities. X-ray techniques utilizing the external reflection of X-rays are very surface sensitive, hence providing a non-destructive tool for process analysis and control.X-ray reflectometry (XRR) is an established technique for the characterization of single- and multi-layered thin film structures with layer thicknesses in the nanometer range. XRR spectra are acquired by varying the incident angle in the grazing incidence regime while measuring the specular reflected X-ray beam. The shape of the resulting angle-dependent curve is correlated to changes of the electron density in the sample, but does not provide direct information on the presence or distribution of chemical elements in the sample.Grazing Incidence XRF (GIXRF) measures the X-ray fluorescence induced by an X-ray beam incident under grazing angles. The resulting angle dependent intensity curves are correlated to the depth distribution and mass density of the elements in the sample. GIXRF provides information on contaminations, total implanted dose and to some extent on the depth of the dopant distribution, but is ambiguous with regard to the exact distribution function.Both techniques use similar measurement procedures and data evaluation strategies, i.e. optimization of a sample model by fitting measured and calculated angle curves. Moreover, the applied sample models can be derived from the same physical properties, like atomic scattering/form factors and elemental concentrations; a simultaneous analysis is therefore a straightforward approach. This combined analysis in turn reduces the uncertainties of the individual techniques, allowing a determination of dose and depth profile of the implanted elements with drastically increased confidence level.Silicon wafers implanted with Arsenic at different implantation energies were measured by XRR and GIXRF using a combined, simultaneous measurement and data evaluation procedure. The data were processed using a self-developed software package (JGIXA), designed for simultaneous fitting of GIXRF and XRR data. The results were compared with depth profiles obtained by Secondary Ion Mass Spectrometry (SIMS).

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

“…The tunability of the probed depth region with the grazing angle in combination with the linearity in the intensity response of X-ray detectors was already applied to depth-proling measurements of ion-implanted samples (Al, As and B dopants in Si wafers were considered) by means of GEXRF and GIXRF. [46][47][48][49][50][51] It has to be pointed out that for the reported dopant-wafer combinations, the measurements could be performed either with excitation energies below the Si K-edge (1839 eV), thus avoiding a signicant background contribution from the wafer material or at energies above the As K-edge (11867 eV). In the latter situation the Si absorption cross-section is small and the As XRF signal can be well separated from the Si Ka line.…”

CASTOR, a new instrument for combined XRR‐GIXRF analysis at SOLEIL

“…First of all, we performed a preliminary analysis based only on the XRR data using the Leptos® software. Then, we performed a second analysis with the JGIXA software including the fluorescence spectra to derive the aluminum K α full‐energy peak area with respect to the incident angle. The results of both analyses are shown in Table .…”

2015 Atomic Spectrometry Update – a review of advances in X-ray fluorescence spectrometry and their applications

“…Nowak et al 77 performed GI-XRF and GE-XRF experiments to characterise periodic structures on silicon and silica surfaces. Ingerle et al 79 combined the evaluation of GI-XRF and XRR data for improved proling of ultra-shallow depth distributions. A novel theoretical approach based on simple geometrical optics considerations was used to explain the latter.…”