Positive‐Tone Nanolithography of Antimony Trisulfide with Femtosecond Laser Wet‐Etching

ABSTRACT Antimony trisulfide (Sb 2 S 3 ), 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 Sb 2 S 3 challenging. Here, we demonstrate that positive‐tone fabrication of Sb 2 S 3 nanostructures using femtosecond laser wet‐etch processing, a straightforward technique for the engraving of micro‐ and nanoscale structures, can address major fabrication challenges. The patterning mechanism and factors influencing the resolution of Sb 2 S 3 thin film structures deposited on quartz (transmissive) and gold (reflective) substrates are experimentally investigated and supported by theoretical modelling. Linewidths down to 178 nm are achieved, along with depth‐controlled (2.5D) structuring. 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 Sb 2 S 3 ‐based integrated photonic devices.