MEMS ring shutter for high-aperture sub-microscale interferometry with dynamic selective aperture illumination

• Applicants: Dr.-Ing. Mustaqim Siddi Que Iskhandar; Professor Dr.-Ing. Peter Lehmann
• Subject Area: Measurement Systems ; Microsystems
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564674145

The project aims to optimize the simulation, design, and fabrication of a MEMS ring shutter as well as its integration and application in a high-aperture (0.95 NA) Linnik interferometer to enable frequency-selective illumination. By imaging of the ring shutter, the pupil plane of the microscope objectives can be partially illuminated, allowing light to reach the sample only at selected incidence angles in specified sectors, thereby altering the spectral composition of the measurable interferograms. Different spatial frequencies are crucial for the reconstruction of topography depending on the surface structure, and thus, the signal-to-noise ratio can be significantly improved through this method. This is particularly relevant for challenging structural features with steep surface slopes and small grating periods. In this setup, the ring shutter serves as a light manipulator and will be optimized for its optical properties, specifically transmission and contrast, through modifications in design, manufacturing process, and material choice. The project aims to find ideally suited parameters, particularly the number and width of ring sectors, to advantageously affect spatial frequency distributions of interference signals when analyzing selected reference samples. With switching speeds in the microsecond range, it allows for rapid dynamic control and thus, measurements with different illumination apertures can be performed in a single depth scan. To develop the methodology and ensure optimal results, the ring shutter must be integrated and adjusted with high accuracy in the optical path of the interferometer. The electronic control must be synchronized with the measurement process, and the signal processing algorithms must be adjusted to the alterable signal spectra.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Hartmut Hillmer