Title: The Science of Inverse Lithography: Discovery vs. Recovery

Abstract: As feature sizes in semiconductor fabrication shrink far below the wavelength of light used to print them, mask patterns no longer resemble the circuits they yield — they must be discovered, not merely designed. This talk explores this discovery challenge and the inverse-problem methodology required to solve it.

In optical processing, image recovery estimates an unknown object distribution from a blurred measurement taken through a known imaging system. Image discovery, by contrast, synthesizes an object distribution capable of producing a desired target image at the output of a known, distorting optical system. While both inverse problems can achieve super-resolution, each presents a distinct theoretical hurdle: uniqueness for recovery, and existence for discovery.

This talk focuses on inverse image synthesis and its application to photolithography under diffraction-limited conditions and high-contrast, nonlinear photoresist responses, utilizing both coherent and partially coherent illumination. I will review my early foundational research that established the mathematical principles of Inverse Lithography Technology (ILT) — work that has propelled widespread industrial adoption and received recent recognition.

About the speaker: Bahaa Saleh is University Distinguished Professor Emeritus at CREOL, The College of Optics and Photonics, University of Central Florida, where he served as Dean from 2009 to 2019. He previously held faculty and research positions at a number of institutions including Boston University (1994–2008, serving as Chair of the Department of Electrical and Computer Engineering from 1994–2007 and becoming Professor Emeritus in 2009), the University of Wisconsin-Madison (1977–1994, serving as Chair of the ECE Department from 1990–1994), the University of Santa Catarina in Brazil, Kuwait University, the Max Planck Institute in Germany, the University of California-Berkeley, and Columbia University.

His research contributions cover a broad range of topics in optics and photonics, such as statistical optics, nonlinear optics, quantum optics, and image science. Saleh is a highly acclaimed author, having written Photoelectron Statistics (Springer, 1978), Fundamentals of Photonics (Wiley, Third Edition 2018, with M. C. Teich), Introduction to Subsurface Imaging (Cambridge University Press, 2011), and Quantum Photonics (Springer, 2025). He has published over 600 papers in journals and conference proceedings, and he holds 10 patents.

Saleh is a renowned figure in optics and photonics, having served as founding editor of Advances in Optics and Photonics (2008–2013) and editor of the Journal of the Optical Society of America A (1991–1997). He was also Vice President of the International Commission of Optics (2000–2002). He is Fellow of IEEE, Optica (formerly OSA), SPIE, APS, and the Guggenheim Foundation. He has received numerous awards and commendations, including OSA Beller Medal (1999), SPIE Photomask-Technology BACUS award (2004 and 2025), Kuwait Prize (2006), OSA Distinguished Service Award (2008 ), OSA Mees Medal (2013), and SPIE Photonics Education award (2026).