Nanoscale IR imaging is an emerging tool for the characterization of micro- and nanostructures. However, their quantitative characterization requires hyperspectral imaging, where at each point in space a complete spectrum is recorded. As hyperspectral nano-IR imaging is based on the combination of the optical near-field with an AFM, it is inherently recorded serially. This severely limits its applicability due to the long acquisition times involved and accompanied stability issues. In addition, industrial applications are limited due to these issues. In this work we implement a subsampling strategy [1] using a commercial nano-FTIR system to significantly reduce the measurement time in hyperspectral imaging measurements by compressing the measurements combined with a low-rank matrix reconstruction. We apply this scheme to materials from the field of power electronics, where the ongoing development of wide-bandgap compound semiconductors is limited by material defects which IR imaging is sensitive to. [1] Metzner, S., Kästner, B., Marschall, M., Wübbeler, G., Wundrack, S., Bakin, A., Hoehl, A., Rühl, E., & Elster, C. (2022). Assessment of Subsampling Schemes for Compressive Nano-FTIR Imaging. IEEE Transactions on Instrumentation and Measurement, 71, 1–8. https://doi.org/10.1109/TIM.2022.3204072

Nanowire structures can be used for energy harvesting from renewable sources. These pillar structures with lateral dimensions in the nanometre range offer several advantages due to their small physical size and their large surface-to-volume ratio. The required nanodimensional characterization can be achieved efficiently by optical methods such as Mueller matrix ellipsometry. Here the measured Mueller matrices need to be analysed with numerical simulations to reconstruct the structural parameters of interest. We present the measurement method and measurement results on silicon nanowire test structures as well as the simulations on exemplary structures and a discussion of the results.

Parameter reconstruction problems appear frequently in optical metrology. Here, one attempts to explain a set of K experimental measurements by fitting to them a parameterized forward model of the measurement process. We present a Bayesian target vector optimization scheme that can be used to perform this fit. It has been shown to be capable of outperforming established methods such as Levenberg-Marquardt, and can after a successful fit enable very efficient and accurate determination of the distribution of the reconstructed model parameters using Markov chain Monte Carlo sampling.

In optical critical dimension metrology, experimental findings have shown that the line edge is systematically underestimated compared to SEM or AFM measurements. While these methods respond to the volume density, optical methods are sensitive to the permittivity. Due to line edge roughness there is a systematical deviation between these parameters. We discuss an analytic upper limit estimation for the contribution of LER. For low index gratings (resist, glass) the contribution is about 1 nm, for high index gratings the contribution may be as high as 5 nm rendering this crucial for sub-nanometer metrology.

Modelling the scattering of focused, coherent light by nano-scale structures is oftentimes used to reconstruct or infer geometrical or material properties of structures under investigation in optical scatterometry. This comprises both periodic and aperiodic nano-structures. Coherent Fourier scatterometry with focused light exploits the diffraction pattern formed by the nano-structures in Fourier plane. While the scattering of a focused beam by a spatially isolated scatterer is a standard modelling task for state-of-the art electromagnetic solvers based, e.g., on the finite element method, the case of periodically structured samples is more involved. In particular when the focused light covers several grating periods of as it is commonly the case. We will present a coherent illumination model for scattering of focused beams such as Gaussian- and Besselbeams by periodic structures such as line gratings. The model allows to take into account optical wavefront aberrations in optical systems used for both, the illumination and detection of the scattered fields. We compare the model with strategies implemented on large-scale super-cells and inverse Floquet-transform strategies to superimpose both near- and far fields coherently.

Plasmonic lenses are metastructures that use the excitation of surface plasmon polaritons in metallic nanoslits to focus light to particularly small focal spots at arbitrary distances. This facilitates possibilities for improving nano-optical methods, for example in ellipsometry. We developed two- and three-dimensional plasmonic lenses with a new inverted design that complies the fabrication process. However, plasmonic lenses show chromatic aberrations. In this contribution, we explore different approaches and limitations to expand the inverted plasmonic lens design to achromatic applications. We use numerical simulations based on the Finite Element Method to investigate in different lens geometries.

In this contribution, we present a technique for the determination of optical aberrations, which is based on measurements of the point spread function and a Bayesian optimization of rigorous simulations. The measuring system is a UV-microscope in a reflected light configuration with a 200x magnification, unpolarized light, and an illumination and imaging NA of 0.44 and 0.55, respectively. The PSF is measured by imaging a small quadratic chrome dot (side length ≈ 180 nm) on a glass substrate. We investigate the impact of different adjustment states, different dot locations and different optical microscopes.

Dimensional optical microscopy allows for the rapid inspection of devices at the cost of limited accuracy. Introducing a model-based approach that includes diffraction effects allows for increased accuracies. The model needs to be efficient and accurate to evaluate the measurements in an acceptable time frame. We present an overview of the illumination model and different incidence-pupil sampling techniques. Furthermore, we will demonstrate strategies for efficiently calculating the near-field scattering response from structures using the finite element method. Using these aspects, we demonstrate a significant increase in the accuracy of dimensional estimates for a range of structures.