Dynamic nonlinear light control and metrology with resonant metasurfaces

Humanity's pursuit of progress is etched into our innovative desire to make things faster, smaller and more efficient. Few fields embody this ambition as clearly as the advancement of microelectronic chips. Enabled by extreme ultraviolet lithography, progress in miniaturization underpin nearly all modern digital infrastructure, from smartphones to AI hardware and cloud data centers. A crucial step in chip fabrication is nanoscale inspection, or metrology. As device dimensions shrink, conventional optical metrology reaches its limits due to, for example, the Abbe’s diffraction limit, demanding new approaches with higher precision and sensitivity.

Nonlinear emission from resonant optical metasurfaces offers a highly promising alternative. Metasurfaces consist of arrays of subwavelength nanostructures that manipulate light with exceptional precision. Resonant effects, such as Fano resonances, enhance both linear and nonlinear optical responses. Nonlinear metrology provides two advantages: the generated harmonic wavelengths are shorter (and thus enable higher resolution), and the nonlinear polarization scales with a higher power of the local field, causing small structural variations to produce strongly amplified changes in the emission intensity and profile.

This thesis explores how nonlinear optics with resonant metasurfaces can advance semiconductor metrology through two scenarios. In the first, the metasurface itself acts as the metrology target, where geometric changes produce strong variations in harmonic emission. In the second, metasurfaces serve as compact (extreme) ultraviolet light sources with ultra-fast dynamically tailorable wavefronts for high-precision inspection.

Our goal is to bridge the fundamental rich physics of nonlinear diffractive metasurfaces with the practical demands of semiconductor metrology.