Water-Processable PVA-SbQ as an Eco-Friendly Photoreversible Dual-Tone Photoresist for Advanced Lithography

Conventional photoresists often rely on organic solvents and photoinitiators, raising environmental and processing concerns in advanced lithography. In this study, we report an eco-friendly, water-processable photoresist based on poly(vinyl alcohol) modified with N-methyl-4-formylstyrylpyridinium methosulfate (PVA-SbQ), which functions as a photoreversible dual-tone photoresist without requiring photoinitiators and organic solvents. PVA-SbQ copolymers with varying compositions were synthesized via the acetalization reaction between the hydroxyl groups of PVA and the aldehyde functionality of SbQ. Structural characterization using nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy confirmed the successful incorporation of SbQ moieties into the PVA backbone. The photoreversible behavior of the SbQ groups was systematically investigated using UV-vis and FT-IR analyses, revealing efficient [2 + 2] cycloaddition-driven photodimerization under 365 nm UV irradiation, followed by photocleavage of the cyclobutane ring under deep UV (DUV, 220-260 nm) exposure. Quantitative evaluation indicated a photodimerization degree (PDD) of ∼91.3%, while the photocleavage degree (PCD) reached ∼51.3%, enabling partial recovery of the original state. Optimized as a 10 wt% aqueous formulation, PVA-SbQ demonstrated excellent film-forming ability and photopatternability, achieving well-resolved negative-type, positive-type patterns, and complex square-type patterns, by simply modulating UV exposure conditions. This work presents the potential of PVA-SbQ as a sustainable, functional alternative to conventional photoresists.