Development of holistic measurement concepts for highly resolved measurement of micro structures based on scanning and imaging optical techniques

• Applicants: Professor Dr.-Ing. Peter Lehmann; Professor Dr.-Ing. Eberhard Manske
• Subject Area: Measurement Systems
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 401327404

Optical profilometers such as coherence scanning interferometers, confocal scanning microscopes as well as confocal, focal and interferometric point-sensors are restricted in their lateral resolution capabilities due to the diffraction limit. As a consequence, systematic deviations between optically measured and real surface topography data appear. In order to meet the continuously increasing demands on accuracy of optical measuring instruments, an improved physical understanding of the underlying effects considering all relevant influences is needed. With respect to the interaction of incident light with surface structures, accurate simulation models are essential. These must be included into holistic concepts for optical profilometry of micro- and nanostructures. With the present project, great progress has already been made, as it is documented in numerous publications.The resulting sensor models consider the optical interaction with the measurement object on the basis of rigorous simulations and achieve good agreement between simulated and measured topography data even for complex structures. In particular, the consideration of three-dimensional light propagation (conical illumination and diffraction) has proven to be crucial. The resulting new methodological approach, which consists of the investigation of model-based iterative inverse methods for exact profile reconstruction from the optical measurement data, has already been implemented exemplarily for individual edge structures. However, in order to enable an effective usage of the developed models for inverse profile reconstruction, the simulation models need to be extended to three-dimensional structures and, at the same time, the runtime of the simulation programs must be significantly reduced. Besides more efficient computation methods, the reduction of the parameter space by use of a data base needs to be examined. The cooperation of the two participating institutes provides an ideal complementation with respect to the investigated measurement techniques, the theoretical basics of the simulation models and the available measurement systems. Consequently, synergy effects arise and the models can be validated by direct comparison. The optical models will be adapted to the different measurement techniques mentioned above. The same applies to the methods developed for iterative inverse profile reconstruction from measurement data, which will be developed first for surface structures with a limited number of variable parameters due to computation time.Therefore, we expect that the investigations of the second project period will provide a substantial basis for the development of virtual measurement instruments, which can be used for the analysis of measurement uncertainty and for the determination of related instrumental properties such as profile or topography fidelity.

• DFG Programme: Research Grants