Effect of Free Radicals on Irradiation Chemistry of a Double-Coordination Organotin (Sn4) Photoresist by Adjusting Alkyl Ligands

Metal oxide cluster (MOC) photoresists are highly promising materials for the next generation of extreme ultraviolet lithography (EUVL). The consecutive exploration of novel MOC materials and their structural irradiation chemistry are the major concerns associated with EUVL. Herein, we report two bicoordinated tin-oxo clusters (TOCs), the organic ligands of which contain both adamantane carboxylic acids and alkyl groups (methyl: Sn4-Me-C10; butyl: Sn4-Bu-C10). We explore the correlation between the structures of the TOCs and their patterning properties by adjusting the alkyl groups coordinated to the Sn atom. The structural variation causes different irradiation chemistry, with Sn4-Me-C10 exhibiting improved resolution and Sn4-Bu-C10 demonstrating higher sensitivity. These differences are attributed to the bonding energies of the Sn-methyl and Sn-butyl groups, the size of the resulting alkyl radicals, and their reaction probabilities. Both clusters occur in the reactions of Sn-C bond cleavage and the decarboxylation of adamantane carboxylic acids upon irradiation. However, the entire process exhibits distinct characteristics. Based on the electron -beam lithography and other experiments, we proposed irradiationinduced reaction mechanisms for both clusters. The Sn4-Bu-C10 cluster predominantly undergoes alkane chain linkage, whereas the Sn4-Me-C10 cluster mainly follows the adamantanes linkage pathway.