Positive-tone Nanolithography of Antimony Trisulfide with Femtosecond Laser Wet-etching

: Antimony trisulfide (Sb₂S₃), as an emerging material for integrated photonic devices, has attracted significant attention due to its high index, low loss, and phase-changing property in the optical regime. However, conventional lithography-based fabrication methods involve complex, time-consuming, multistep processes, rendering the photonic application of Sb₂S₃ challenging. Here, we demonstrate that positive-tone fabrication of Sb₂S₃ nanostructures using wetetch femtosecond laser processing, a straightforward technique for the engraving of micro- and nanoscale structures, can address major fabrication challenges. The patterning mechanism and factors influencing resolution of Sb₂S₃ thin film structures deposited on quartz (transmissive) and gold (reflective) substrates are experimentally investigated and supported by theoretical modelling. Using this approach, the smallest linewidth fabricated is measured at 178 nm. Consequently, multiple test patterns are demonstrated showing versatile functionalities. Functional Fresnel Zone Plates (FZPs) with varying focal length are fabricated and characterized. This study provides a significantly simplified approach for realizing Sb₂S₃ based integrated photonic devices.