Title: Optical Metrology for Resolving Topological Information of Nanoscale Structures via Modified Mueller Matrix Ellipsometry
Authors: Käseberg, Tim, Physikalisch-Technische Bundesanstalt (PTB), Fachbereich 4.2, Bild- und Wellenoptik
Contributors: HostingInstitution: Physikalisch-Technische Bundesanstalt (PTB), ISNI: 0000 0001 2186 1887
Resource Type: Text / Dissertation
Publisher: Physikalisch-Technische Bundesanstalt (PTB)
Rights: Download for personal/private use only, if your national copyright law allows this kind of use.
Relationships: IsPartOf: ISSN 2941-1297
IsIdenticalTo: ISBN 978-3-944659-33-6
Dates: Available: 2024-05-30
Created: 2024-03
File: Download File (application/pdf) 78.56 MB (82378943 Bytes)
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Keywords ellipsometry ; Mueller matrix ; plasmonic lenses ; optical nanometrology ; machine learning
Abstract: With the on-going progress in nanotechnology, the necessary metrology to characterize fabricated structures struggles to keep pace. Indirect optical methods like ellipsometry are promising for this task, being highly accurate and at the same time non-invasive, fast, and flexible. In conventional ellipsometry, results are integrated over the whole illumination spot, making it applicable only on larger measurement fields and periodic structures. While imaging ellipsometry enables a more local evaluation of polarizing properties, it is not widely used in metrology yet. Measured images are usually evaluated like conventional measurements, neglecting useful information from inhomogeneous areas. These are only fully accessible using 3D simulations, which are computationally highly expensive. In this thesis, I investigate approaches to enhance the performance of imaging Mueller matrix ellipsometry to establish it for nanometrology. Using specially designed nanostructures, I examine the influence of subwavelength scale structure form and size on Mueller matrix images, observable in both, measurements and simulations. With these samples, I explore possibilities to advance Mueller matrix ellipsometry. This includes ways to evaluate Mueller matrix images without the need for 3D simulations, using techniques inspired by machine learning that provide information exceeding microscopy images alone. In addition, this thesis covers the problem of usually disregarded thermal drifts, proving that they are a potential source of uncertainty in imaging ellipsometry by performing experiments on moving samples. I also offer an algorithmic solution for handling drifts to improve even already existing setups. Apart from that, I explore the applicability of plasmonic lenses for the advancement of ellipsometric methods. Conventional plasmonic lenses are challenging to fabricate with common lithographic methods. Therefore, I developed a new design scheme, so-called inverted plasmonic lenses. They keep the same functionality while complying with fabrication conditions, enabling higher fabrication rates for possible future applications. Plasmonic lenses were designed, optimized, and their parameters systematically examined with numerical simulations. Then, lenses were fabricated with varying parameters and examined using microscopy and imaging ellipsometry. Fabricated lenses produced expected focal spots and showed dispersion. Design schemes to enhance the performance of plasmonic lenses in terms of throughput maximization and dispersion reduction are compared and discussed. I present an approach to merge plasmonic lens designs for different wavelengths, which successfully reduces dispersion, albeit at the cost of focal spot intensity. Numerical simulations showed that plasmonic lenses focusing the illumination on a sample enhances the sensitivity of ellipsometric measurements to subwavelength sized structures significantly. The contributions from this thesis will help to establish imaging ellipsometry as a tool in optical nanometrology, pushing it further beyond its limits to ultimately help bridging the gap towards nanotechnology.
Series Information: PTB-Bericht Diss-4
Citation: Käseberg, T., 2024. Optical Metrology for Resolving Topological Information of Nanoscale Structures via Modified Mueller Matrix Ellipsometry. Dissertation, Technische Universität Carolo-Wilhelmina zu Braunschweig. Braunschweig: Physikalisch-Technische Bundesanstalt. PTB-Bericht Diss-4. ISBN 978-3-944659-33-6. Verfügbar unter: https://doi.org/10.7795/110.20240308