Programmable structured DUV illumination by coherent harmonic generation at crystalline solids for nanometer-resolution inspection of periodic samples

Prof. Young-Jin Kim's group from the Department of Mechanical Engineering at KAIST in South Korea has developed a nanometer-scale displacement measurement technology enabled by active beam control in the deep-ultraviolet (DUV) laser regime.

As semiconductor manufacturing advances toward the 3-nm technology node, challenges related to detecting nanoscale defects and maintaining high yield have become increasingly critical. While short-wavelength light sources offer clear advantages in resolution, conventional beam-control components cannot be directly applied in the DUV and shorter-wavelength regions due to strong material absorption.

To overcome this limitation, the team generated a stable DUV beam (λ < 280 nm) through third-harmonic generation (THG) driven by an 800-nm near-infrared femtosecond laser. The key innovation lies in a new control strategy: instead of manipulating the beam directly in the DUV, the near-infrared driving beam is pre-modulated, and its modulation characteristics are transferred to the DUV beam through coherent harmonic generation.

Using this method, the researchers produced a high-visibility periodic beam and achieved real-time control of its pitch and angle. This enabled the implementation of a Moiré-based amplification mechanism with semiconductor micro-patterns, allowing the detection of nanometer-level displacements that were previously undetectable in conventional optical imaging.

This work marks the first demonstration of applying beam-modulation-based precision metrology techniques in the DUV and shorter-wavelength regimes. The technology provides a fundamental platform that can be extended to various measurement methodologies. Furthermore, its potential applications include extreme-ultraviolet (EUV) and X-ray regimes for next-generation precision metrology, such as linewidth measurements in 3 nm semiconductor processes, attosecond science, and real-time bio-imaging.