Synthesis of pentameric chlorotin carboxylate clusters for high resolution EUV photoresists under small doses

Abstract

This work reports the synthesis and characterization of a novel pentameric tin chloro cluster, (vinylSn)₃Sn₂Cl₅O₂(OH)₂(t-BuCO₂)₆ (1), and explores its application as an efficient negative-tone photoresist in a 1 : 2 weight ratio blend with [(n-BuSn)₁₂O₁₄(OH)₆](BF₄)₂ (2). Through e-beam lithography, a small high-resolution pattern (HP = 20 nm) is achieved for the blend photoresist (3) at a dose of 2080 μC cm⁻². Additionally, EUV lithography demonstrates the development of a high-resolution pattern (HP = 16 nm) at an EUV dose of 70 mJ cm⁻². Mechanistic studies by reflective FTIR indicate a significant decomposition of Sn–carbon and SnO₂(t-Bu) moieties starting at J = 35 mJ cm⁻², which is accompanied by growth of the Sn–O absorption intensity. A collapse of the cluster frameworks of clusters (1) and (2) is observed at J > 70 mJ cm⁻². High-resolution X-ray photoelectron spectroscopy (HRXPS) reveals that low EUV light predominantly decomposes Sn–butyl and Sn–Cl bonds. As EUV doses increase, primary photolytic reactions involve cleavage of Sn–butyl, Sn–O₂CBu^t, and Sn–vinyl bonds. Notably, the photolytic decomposition of Sn–Cl bonds is distinctive, with only two out of five bonds being cleaved, even at high EUV doses, resulting in a break in film growth at J = 27–35 mJ cm⁻² in the EUV contrast curve. Moreover, HRXPS analysis suggests that radical propagation on the vinyltin end of the blend is unlikely, providing concise mechanistic insights into the photochemical processes governing the behavior of this advanced photoresist.