Naphthalimide-based nonionic sulfonate photoacid generators: structure–property relationship and sub-30 nm resolution lithography

Abstract

This study reports the design and synthesis of five novel nonionic photoacid generators (PAGs) based on a naphthalimide–benzenesulfonate backbone. Comprehensive evaluations were conducted to assess their solubility, thermal stability, photophysical properties, acid generation quantum yields (Φ_a), and lithographic performance. Ultraviolet-visible (UV-vis) spectroscopy revealed that the optical properties of the PAGs could be finely tuned through structural modifications, with all compounds exhibiting strong absorption at key lithographic wavelengths (248, 254, and 365 nm). Measurements of Φ_a ranged from 6.2% to 17.6%, establishing clear structure–property relationships. Notably, PAG 1d exhibited the highest Φ_a (17.6%) due to its optimal donor–π–acceptor (D–π–A) configuration, where the synergistic combination of electron-donating and electron-withdrawing groups enhanced photosensitivity and facilitated efficient acid release. Density functional theory (DFT) calculations corroborated these findings, confirming that the established structure–property relationships provide a robust foundation for the molecular engineering of PAGs with high Φ_a. When formulated into photoresists, all PAGs produced high-quality patterning across multiple lithographic platforms, including i-line (365 nm), deep-UV (254 nm), and electron-beam lithography (EBL), with their sensitivity directly correlating to the Φ_a of the PAGs. Remarkably, the PR-1d formulation exhibited exceptional performance in EBL, attaining the highest sensitivity (E₀ = 54.4 μC cm⁻²) and a high resolution of 28 nm, thereby establishing its potential for sub-30 nm lithography applications. This work provides fundamental insights into the structure–property relationships of nonionic sulfonate PAGs and advances resist technology for next-generation lithography.

Keywords: Nonionic photoacid generators; Naphthalimide-benzenesulfonate; Acid generation quantum yield; Structure–property relationship; Sub-30 nm lithography.