Ligand Modulation and Bismuth Incorporation for Enhanced Sensitivity and Resolution in Sn-Based Metal-Oxo Cluster Photoresist for E-Beam Lithography

Abstract

As artificial intelligence technologies have advanced and become increasingly widespread, the importance of semiconductor chip development has grown correspondingly. The core of this advancement lies in achieving higher integration, which fundamentally depends on scaling. Higher integration requires reducing critical dimensions and implementing high aspect ratio three-dimensional structures to accommodate more circuitry within a limited area. According to the Rayleigh criterion, achieving smaller feature sizes demands exposure sources with shorter wavelengths, and current lithography systems have therefore progressed to extreme ultraviolet (EUV) radiation at 13.5 nm. However, conventional chemically amplified organic photoresists suffer from limited photon budgets and excessive secondary-electron scattering under EUV irradiation, making it difficult to simultaneously achieve high sensitivity, high resolution, and low line-width roughness (LWR). As key materials in semiconductor lithography, next-generation photoresists must provide strong absorption, etch resistance, stability during deposition and etching, and robust patterning performance. Sn-based metal-oxo clusters have recently emerged as promising candidates for next-generation EUV and electron-beam (e-beam) photoresist due to their strong EUV absorption and high etching selectivity. However, the roles of the organic ligands and metal centers during exposure have yet to be fully clarified. To explore the mechanism and improve the performance of the photoresist, the ligand was modulated and high EUV absorption of bismuth metal was added. in this study, two cluster systems were synthesized and evaluated using e-beam lithography: (i) 3Sn DPP, prepared with Sn oxo core diphenyl phosphonate ligands, and (ii) Sn-Bi PP, incorporating a Sn-Bi metal core and phenyl phosphonic acid ligands. 3Sn DPP resist was designed to form rigid patterns with low roughness by introducing diphenyl phosphonate and synthesizing small oxo-clusters with a low number of Sn metal sites and ligands. The aim was to maximize the reduction of roughness. For Sn-Bi PP resist, the incorporation of phenyl ligands and Bi significantly improved solubility, dispersibility, and sensitivity. Upon exposure, Sn–C bond cleavage generated butyl-derived radicals that facilitated network formation and solubility switching. In the Sn-Bi PP system, phenyl phosphonate ligands additionally participated in crosslinking network formation, opening multiple reaction pathways. Combined with the inherently strong EUV absorption of Bi metal, these effects contributed to the enhanced sensitivity observed in the Sn-Bi PP resist. Overall, ligand modulation and Bi incorporation effectively enhanced sensitivity, high-aspect- ratio patterning capability, and resolution in Sn-based metal-oxo cluster photoresists, supporting a viable design strategy for future high-performance EUV and e-beam lithography materials.