Design of three functionalities in hexameric tin oxide clusters to enhance e-beam lithographic quality and edge...

This work aims to enhance the edge resistance and e-beam lithographic performance of two tin oxide clusters (vinylSn)₆O₄(sec-butylCO₂)₈Cl₂ (1) and (vinylSn)₃(i-PrSn)₃O₄(sec-butylCO₂)₈Cl₂ (2) through chemical hydroxylation with aqueous LiOH, yielding two new hydroxylated tin oxide clusters, (vinylSn)₆O₄(sec-butylCO₂)₃(OH)₇ (3) and (vinylSn)₃(i-PrSn)₃O₄(sec-butylCO₂)_1.5(OH)_8.5 (4), respectively. Clusters (3) and (4) each contain three functional groups: vinyltin moieties that serve as radical propagation units, sec-butylCO₂ and i-Pr-Sn groups that act as radical sources, and additional Sn-OH groups serving as linkage units. Clusters (3) and (4) are better than initial carboxylate clusters (1) and (2), showing marked improvements in both edge resistance and e-beam lithographic performance, including pattern resolution and line edge roughness (LER), even at reduced energy doses. For cluster (4), a modest e-beam dose of J = 1280 μC cm^-2 can resolve a small HP = 19 nm pattern with a low LER of 2.8 nm, corresponding to a small Z-factor of 6.88 × 10^-7 nm³ μC. The etch selectivity, S = rate SiO₂/rate PR, was calculated to be S = 5.7 for cluster (3) and S = 9.2 for cluster (4), much higher than the values S = 1.4 and 5.4, respectively, for clusters (1) and (2). Such a small Z-factor and remarkable etch selectivity for cluster (4) highlight its commercial potential. Our mechanistic studies using FTIR and HRXPS reveal two aggregation processes that follow an initial light-induced decarboxylation step: (i) Sn-OH groups that promote molecular linkage and (ii) a radical chain propagation process.