A highly hydroxylated 6-tin oxide cluster serves as an efficient e-beam and EUV-photoresist to achieve...

A carboxylated-free cluster, formulated as (BuSn)₆O₄(OH)₁₀ (2) was synthesized from the reaction of (BuSn)₆O₄Cl₂(MeCO₂)₈ (1) with LiOH (aq.) in cold tetrahydrofuran (THF). This synthesis marks the first successful demonstration of complete decarboxylation of a metal carboxylate cluster using LiOH, resulting in the formation of a carboxylate-free metal oxide cluster. Comparative analysis of their ¹¹⁹Sn NMR, IR absorption spectra and ESI mass spectra suggests that cluster (2) possesses a ladder-type framework. Notably, cluster (2) exhibits superior surface smoothness and enhanced photosensitivity to both e-beams and EUV light compared to the well-known tin oxide cage, [(BuSn)₁₂O₁₄(OH)₆](OH)₂ (3). In e-beam lithography, cluster (2) facilitated the fabrication of high-resolution patterns with a half-pitch (HP) of 21 nm at a dose of J = 1760 μC cm^-2. Similarly, its EUV lithography achieved an impressive HP of 16 nm at J = 70 mJ cm^-2. In the etching resistance test, the tin carboxylate-free cluster (2) exhibited a low etching rate with a SiO₂-selectivity contrast of approximately 1.53, which is significantly higher than the 0.73 observed for the model tin carboxylate cluster (1'). Mechanistic studies by both FTIR and HRXPS revealed that the extent of Sn-butyl loss is less significant than that of Sn-OH loss. The photolytic aggregation of cluster (2) predominantly involves the dehydration of two Sn-OH groups. Additionally, FTIR identified a surface reaction between SiOH and Sn-OH, forming new Sn-O-Si absorption peaks.