A N Danilewski, J Becker, T Baumbach, D Hänschke, A Kopmann, V Asadchikov, M Kovalchuk

Final report, BMBF Programme: “Development and Use of Accelerator-Based Photon Sources (2014)”

Project duration: 01.10.2014 – 30.09.2017

Executive summary

Within the STROBOS-CODE project, partners from two German (KIT, University Freiburg (UFREI)) and two Russian (Shubnikov Institute of Crystallography (SHUB), Kurchatov Institute (KUR)) institutions developed and optimized a novel methodology for correlative 2D, 3D, and 4D characterization of crystalline materials, based on X-ray diffraction imaging. In short, the joint work comprised the theoretical description of the measurement principles, the derivation of the measurement procedures, the specification, design, and construction of the corresponding instrumentation, the formulation and implementation of the data analysis algorithms, as well as the experimental demonstration of the methodology.

The driving application within the project is the in situ investigation of crystals and devices, aiming for a fundamental understanding of structure, nucleation, arrangement, propagation, and extension of defects like dislocations or cracks. In this context, the results of the STROBOS-CODE project will open new perspectives to improve prediction, control, and avoidance of critical defects during the industrial growth and processing of technologically relevant crystals, in particular semi-conductor wafers e.g. for microelectronic devices or solar cells. For several selected use cases, the methodology developed within the STROBOS-CODE project has already been demonstrated, successfully.

The core element of the methodical development is X-ray imaging based on Bragg diffraction contrast, which is highly sensitive to local elastic and plastic deformation of crystal lattices as typically associated with crystal defects. Based on the results of the preceding UFO project and on the prior development of the basic 3D X-ray diffraction laminography (XDL), within STROBOS-CODE an advanced methodology has been made available for correlative characterization and with in situ capabilities. The correlative analysis of data obtained by complementary techniques like X-ray white-beam topography or visible light microscopy now allows creating an unprecedented comprehensive picture of crystalline defects like dislocation networks.
The adaption and optimization of laminographic 3D reconstruction algorithms to the specific requirements of X-ray Bragg diffraction contrast imaging has been performed. Aiming for in situ ca-pabilities, particular interest was put on the reduction of the number of projections required for XDL reconstruction, which could be successfully reduced from about 700 to 50-100 by the appropriate utilization of DART-based algorithms. This progress in data processing resulted in a substantial reduction of the measurement time, for the first time enabling quasi in situ characterization of dislocation dynamics with 3D XDL scans interleaved with a step-wise thermal treatment of the investigated samples.

A concept for a mobile instrument suited for general purpose full-field X-ray diffraction imaging, referred to as the CODE station, has been worked out. A first prototype was successfully realized, served as a test instrument, and enabled first experiments. The results were used to further improve the methodology. Despite the constraints due to the compact and lightweight design, an angular precision and stability of all critical elements better than 1.5e-4 degree was successfully demonstrated. The components of the final instrumentation have been specified and ordered and the final assembly will be performed by UFREI during its extended project run-time until 2019. Afterwards, the highly flexible and mobile CODE-instrumentation will be available for routine experiments at all suitable synchrotron end stations, like e.g. at PETRA III or at the ESRF.

For the STROBOS-instrumentation in Moscow a modular camera system has been developed, constructed, implemented, and tested in cooperation with the Russian partners. It is designed to enable a continuous data streaming with up to 5GB/s. Depending on the application case, differ-ent image sensors can be installed: Sensors with 2, 4, and 20 megapixel are presently available, with a read-out speed of up to 330 frames/s. A sub-zero cooling system has been developed and the camera has been mechanically and electrically integrated for use within the STROBOS set-up.

Within the STROBOS-CODE project, several experiments demonstrated successfully the unique capabilities of the proposed concept for the instrumentation as well as of the developed methodology for correlative and quasi in situ characterization of crystal defects in technologically relevant samples like semiconductor wafers. An unprecedented, comprehensive picture of the onset of thermally driven plastic deformation of silicon wafers could be obtained and provided novel insight into the involved mechanisms. Moreover, for the first time the dynamics of dislocation nucleation and evolution could be monitored in 3D by interleaving XDL measurements and controlled step-wise annealing. Finally, also the applicability of the developed diffraction imaging methodology to higher absorbing materials could be demonstrated by the 3D visualization of dislocation cell structures in a GaAs wafer.
The results of the STROBOS-CODE project have been reported at several national and international workshops and conferences and in more than 10 peer-reviewed publications. In close collaboration, the German and Russian partners have advanced the development on the field of photon science and the methodological progress for large-scale facilities. The methodology and instrumentation developed (improve the research infrastructure at the Kurchatov Institute (STROBOS) and at KIT and other synchrotron infrastructures (CODE). The consortium created for the STROBOS-CODE project will exists beyond the project duration and will extend the cooperation and partnership of Russian and German institutions, in particular on the field of X-ray analytics, algorithms, image processing, and the characterization of crystalline materials and components. In Germany, STROBOS-CODE supports the research partnership of KIT and UFREI within the joint virtual institute “BIRD” and intensifies and strengthens their close collaboration on the field of materials science and microsystem technology.