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Advanced Optical Technologies

Editor-in-Chief: Pfeffer, Michael

CiteScore 2018: 1.42

SCImago Journal Rank (SJR) 2018: 0.499
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Volume 4, Issue 1


Micro-optics and lithography simulation are key enabling technologies for shadow printing lithography in mask aligners

Reinhard Voelkel / Uwe Vogler / Arianna Bramati / Wilfried Noell
Published Online: 2015-02-06 | DOI: https://doi.org/10.1515/aot-2014-0065


Mask aligners are lithographic tools used to transfer a pattern of microstructures by shadow printing lithography onto a planar wafer. Contact lithography allows us to print large mask fields with sub-micron resolution, but requires frequent mask cleaning. Thus, contact lithography is used for small series of wafer production. Proximity lithography, where the mask is located at a distance of typically 30–100 μm above the wafer, provides a resolution of approximately 3–5 μm, limited by diffraction effects. Proximity lithography in mask aligners is a very cost-efficient method widely used in semiconductor, packaging and MEMS manufacturing industry for high-volume production. Micro-optics plays a key role in improving the performance of shadow printing lithography in mask aligners. Refractive or diffractive micro-optics allows us to efficiently collect the light from the light source and to precisely shape the illumination light (customized illumination). Optical proximity correction and phase shift mask technology allow us to influence the diffraction effects in the aerial image and to enhance resolution and critical dimension. The paper describes the status and future trends of shadow printing lithography in mask aligners and the decisive role of micro-optics as key enabling technology.

Keywords: Köhler integrator; lithography simulation; mask aligner; microlens array; micro-optics; proximity lithography; shadow printing lithography


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About the article

Reinhard Voelkel

Reinhard Voelkel received his Diploma in Physics in 1989 and his PhD in 1994 from the University of Erlangen-Nuernberg, Germany, where he worked at the Applied Optics Institute (Prof. Adolf W. Lohmann and Prof. Johannes Schwider) on holographic optical elements for optical interconnects and backplanes. After his PhD he joined the Institute of Microtechnology (Prof. René Dandliker and Prof. Hans Peter Herzig) at the University of Neuchatel, Switzerland, working on micro-optics for biosensors, optical interconnects, photolithography systems, miniaturized imaging and camera systems. Reinhard Voelkel is the co-founder and CEO of SUSS MicroOptics SA, a leading supplier of micro-optical components and systems located in Neuchâtel, Switzerland. He is a member of the German Optical Society (DGaO), the Swiss Optical Society (SSOM), the European Optical Society (EOS), SPIE and the Optical Society of America (OSA).

Uwe Vogler

After studying Mechanical Engineering, Optics and Illumination at the Technical University Ilmenau, Germany, he joined SUSS MicroOptics in 2009 as optical engineer. His current position is Group Leader for Lithography and Illumination Systems. He is responsible for MO Exposure Optics and Advanced Mask Aligner Lithography (AMALITH) at SUSS MicroOptics.

Arianna Bramati

Bachelor (2008) and Master of Science (2010) in Physics Engineering at Politecnico of Milan in Italy with specialization in Micro-Nano Optics and Photonics Technologies. After a brief experience in Industrial LASER applications and Optoelectronics for Biomedicine, she joined SUSS MicroOptics as Optical Engineer in 2010. Here she is mainly working on optical simulation of Proximity Lithography for Mask Aligner, MO Exposure Optics and AMALITH.

Wilfried Noell

Wilfried Noell joined Suss MicroOptics SA in May 2014 as a Chief Scientist. He is responsible for scientific and optical design projects. For the preceding two years, Wilfried Noell was Physicist and Process Engineer in the industrial x-rays business unit of the COMET AG, Flamatt, Switzerland. His tasks were focused on process development, material characterization and extended analyses of high-voltage components and x-ray sources. From 1998 through 2012 he worked as Senior Scientist and Team Leader in the IMT-SAMLAB of the University of Neuchâtel and later at the EPFL, Neuchâtel, Switzerland. From 1994 through 1998, he was a PhD student at the Institut für Mikrotechnik Mainz GmbH (IMM), Germany, and at the University of Ulm, where he developed optical near-field sensors (AFM-SNOM) based on microfabrication technology. Wilfried Noell holds a Diploma (equiv. MSc) in Physics from the Technical University of Darmstadt, Germany. The majority of the thesis was carried out at R&D center of the Deutsche Telekom (FTZ) on InP-based integrated optical waveguides and resonators.

Corresponding author: Reinhard Voelkel, SUSS MicroOptics SA, Rouges-Terres 61, CH-2068 Hauterive, Switzerland, e-mail:

Received: 2014-11-28

Accepted: 2015-01-05

Published Online: 2015-02-06

Published in Print: 2015-02-01

Citation Information: Advanced Optical Technologies, Volume 4, Issue 1, Pages 63–69, ISSN (Online) 2192-8584, ISSN (Print) 2192-8576, DOI: https://doi.org/10.1515/aot-2014-0065.

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