J. Eur. Opt. Society-Rapid Publ. 2026, 22, 9 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2026002 Available online at: https:// jeos. edpsciences. org
Journal of the European Optical Society-Rapid Publications
RESEARCH ARTICLE
Polarization camera based fringe locking system for scanning beam interference lithography
Kevin Treptow 1,*
, Josias Rühle 2, Hansen Wu 1, Christof Pruß 1, Ingo Ortlepp 3, Christian Schober 1, Tobias Haist 1, Oliver Sawodny 2, Eberhard Manske 3, Thomas Kissinger 3, and Stephan Reichelt 1
1 Institute of Applied Optics( ITO), University of Stuttgart, Pfaffenwaldring 9, 70569 Stuttgart, Germany 2 Institute for System Dynamics, University of Stuttgart, Waldburgstraße 19, 70563 Stuttgart, Germany 3 Institute of Process Measurement and Sensor Technology, Technische Universität Ilmenau,
Gustav-Kirchhoff-Str. 5, 98693 Ilmenau, Germany
Received 31 October 2025 / Accepted 9 January 2026
1 Introduction
Abstract. A fringe displacement during the exposure process in scanning beam interference lithography( SBIL) systems leads to wavefront errors in linear gratings. The exact orientation of the fringe pattern along the scan direction is also essential for the production of high-quality gratings. In this paper, we report on the development of a fringe stabilization system with a separate measuring beam, which can precisely determine the fringe movement during the exposure of the photoresist and simultaneously record the orientation of the fringe pattern. This is specifically designed to minimize low-frequency phase errors originating in the lithography writing head itself, which can be a dominant source of instability independent of the stage positioning. Using polarization camera based phase-shifting interferometry, we determine the phase offset between the two interfering beams in real time, and thus reduce the fringe movement to single-digit nanometers by moving a piezo-actuated mirror. In addition, we can use the area-based phase measurement to align the setup and track the rotation of the fringe spot during exposure. In combination with a nano positioning and measuring machine, a fringe observation system was implemented that can precisely record the fringe displacement in the substrate plane. This allows the performance of the fringe stabilization system to be quantified.
Keywords: Laser lithography, Gratings, Diffractive elements.
Diffractive gratings are used in various areas of optics. They are often integrated in optical metrology setups such as spectrometers [ 1 ] and interferometers [ 2 ], used in beam sources like monochromators, optical pulse compressing devices [ 3 ] and are used to shape the polarization [ 4 ]. The requirements for the precise fabrication of the gratings are constantly increasing. There are various approaches to producing these diffractive elements, depending on the size of the elements and the geometry of the substrate. A highly precise manufacturing technique for large substrate areas is mask lithography, especially EUV lithopgraphy [ 5 ]. However, the lithography mask is expensive and the setup is not flexible in manufacturing different elements. Direct laser writing [ 6, 7 ] offers a flexible process, but the structure size is limited by the spot width and the exposure times are long. Interference lithography [ 8 ] offers high-precision manufacturing for sub-wavelength structures on different substrate geometries and flexible grating periods. Due to
* Corrresponding author: kevin. treptow @ ito. uni-stuttgart. de the curved profile of the exposure beams, periodic chirping errors occur, which increases the wavefront error of the diffractive element [ 9 ]. Accordingly, the next approach is the scanning beam interference lithography. A small exposure spot is used to scan along the surface of the substrate. After every line, the position is shifted perpendicular to the scan direction and the next area will be scanned. Scanning beam interference lithography( SBIL) was first introduced by the Massachusetts Institute of Technology( MIT) in context of the“ Nanoruler” [ 10 ]. The problem of phase errors between the two interference beams is well known. The environment disturbances such as vibrations, pressure changes, air turbulence and refractive index fluctuations are critical factors while fabricating linear gratings with sub-micron structures. There are different approaches for optical metrology systems and mechanical compensations to minimize these errors. In general, the two writing beams are directed by beam splitters and subsequently interfere on CCDs, PSDs and standard photodetectors [ 11 – 13 ]. Using the phase-shifting method of interferometry, the phase
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