Facile and Reconfigurable Opaque Droplet-based Photomask for Photolithography

Photolithography is a widely used technology in microfabrication, where photomasks are mostly indispensable. The fabrication of photomasks is generally costly, irreversible, and time-consuming, which limits the prompt delivery of photolithography especially in low-resource settings. Herein, we introduce a facile technique for green and reversible photomask fabrication with opaque droplets, termed as "droplet-based photomask." Paraffin oil, Span 80, and water are the only components needed (total volume ∼1 mL). Specifically, with a microchip, water droplets were generated and collected in paraffin oil dissolving Span 80 (1-10 wt %) as surfactant. Monodispersed droplets were obtained with adjustable diameters ranging from 128.7 ± 0.6 to 212.0 ± 3.4 μm. Subsequently, Span 80 reverse micelles adhered to the droplet surface, forming an opaque membrane. The mechanism was proposed. The equilibrium time of membrane formation varied from 8 to 20 h depending on the surfactant concentration. The lifespan of droplet-based photomasks was up to 339-398 h (∼14-17 days). Furthermore, the membrane could be removed and regenerated, permitting the reconfigurability of droplet-based photomasks. Finally, a proof-of-concept demonstration was conducted using a droplet-based photomask in photolithography. Concave circular molds were obtained with various patterns. Compared with traditional photomask manufacturing pipeline, the fabrication of droplet-based photomasks profoundly reduces the chemical use, environmental burden, time, and cost.