Competing Sn-O and Sn-C Bond Cleavage Pathways Control Cross-Linking in Tin-Oxo Clusters

Tin-oxo clusters, owing to their exceptionally high extreme ultraviolet (EUV) absorption cross sections, have emerged as promising photoresist materials for EUV lithography, yet their atomic-scale photochemical mechanisms remain poorly understood. Here, by combining density functional theory (DFT) and large-scale molecular dynamics enabled by machine-learning interatomic potentials (MLIPs), we reveal a previously underexplored atomistic pathway for cross-linking in tin-oxo clusters. Beyond conventional Sn-C bond cleavage, cross-linking is strongly influenced by ligand-controlled destabilization of the Sn-O cage framework. Cleavage of Sn-O bonds disrupts cage structural integrity and generates coordinatively unsaturated tin centers that actively facilitate intercluster linkage formation. Notably, the free-energy cost associated with Sn-O bond cleavage is comparable to that of Sn-C dissociation under the same simulation protocol, which identifies framework instability as a driving factor in the structural evolution and cross-linking of tin-oxo photoresists. We further demonstrate that ligand identity critically governs cross-linking behavior by modulating both Sn-C stability and cage resilience: vinyl-functionalized clusters form extensive cross-linked networks containing aggregates up to Sn160 during MLIP molecular dynamics simulation, whereas phenyl ligands largely suppress cross-linking due to stronger Sn-C bonding and steric stabilization. These findings expand the mechanistic picture of tin-oxo photoresist cross-linking and provide atomistic insight for the molecular design of tin-oxo photoresist materials.