Hybrid alkyl-ligand tin-oxo clusters for enhanced lithographic patterning performance via intramolecular interactions†

Tin-oxo clusters (TOCs) are promising candidates for next-generation extreme ultraviolet (EUV) photoresist materials due to their strong EUV absorption properties and small molecular sizes. The surface ligands are critical to the photolithographic patterning process; however, the precise regulatory mechanisms governing their functionality require further investigation. Building upon our previously reported Sn4-oxo clusters, Sn4–Me–C10 and Sn4–Bu–C10, which incorporate butyl and methyl groups, respectively, this study presents the synthesis of a novel cluster, Sn4-MB, which integrates both butyl and methyl groups within the same Sn4-oxo core. This new compound demonstrates superior patterning performance compared to both Sn4–Me–C10 and Sn4–Bu–C10, as well as their mixed formulations. The enhanced performance is attributed to the intramolecular hybridization between Sn–methyl and Sn–butyl moieties in Sn4-MB, which facilitates radical feedback regulation, thereby minimizing energy dissipation and suppressing the extent of reaction diffusion during pattern formation. In electron beam lithography (EBL) exposure experiments, optimization of the developer and reduction of film thickness allowed Sn4-MB to achieve lines with a critical dimension (CD) of 17 nm. Furthermore, during EUV exposure, Sn4-MB produced 75 nm pitch lines at a dose of 150 mJ cm⁻², with a line CD of 33 nm. This study provides an effective molecular design strategy for enhancing the lithographic performance of TOC photoresists, highlighting their substantial potential for next-generation EUV lithography applications.

Keywords: Tin-oxo clusters; Intramolecular radical regulation; Photoresist; Electron beam lithography; Extreme ultraviolet lithography.