Transmission Electron Microscopy Unraveled Ionic Oxygen-Affinity Engineering of Metal Oxo Clusters with Extreme Ultraviolet Lithography Activity

Atomically precise tin oxo clusters (TOCs) with superior extreme ultraviolet (EUV) absorption and nanoscale homogeneity have been recognized as the most promising candidate resists for next-generation semiconductor manufacturing. However, the complex radiation reaction pathways of TOCs limit the full exploration of their high-resolution potential to meet advanced process requirements. Herein, using time-resolved transmission electron microscopy (TEM) as an accelerated and visualization method, we revealed that conventional Sn₁₂ TOCs underwent rapid radiation-induced crystallization into tin oxide nanocrystals under a high-energy electron beam. Interestingly, when larger-radius, lower-valence Eu³⁺ ions with stronger oxygen affinity than Sn⁴⁺ were further incorporated, the aggregation of tin-oxygen units was dramatically suppressed, and the bimetallic Sn₁₂Eu₈ cluster exhibited superior crystallization resistance. Density functional theory (DFT) calculations revealed that Eu³⁺ doping could significantly increase the formation energy of tin vacancies (VSn) and strengthen surrounding Sn-O bonds. Such high skeletal stability of Sn₁₂Eu₈ under higher-energy TEM irradiation promoted dense network formation ability in relatively mild lithography conditions, giving rise to an unprecedented small line width of 9.78 nm by EUV exposure. This work provides an efficient ionic oxygen-affinity engineering strategy for modulating radiation-induced structural evolution of atomically precise metal oxo cluster photoresists, which can benefit the development of high-resolution nanopatterning technology.