Highly hydroxylated hafnium clusters are accessible to high resolution EUV photoresists under small energy doses

This work reports the success in accessing high-resolution negative-tone EUV photoresists without radical chain growth in the aggregation mechanism. The synthesis of a highly hydroxylated Hf₆O₄(OH)₈(RCO₂)₈ cluster 3 (R = s-butyl or s-Bu) is described; its EUV performance enables high resolution patterns HP = 18 nm under only 30 mJ cm^-2. This photoresist also achieves high resolution patterns for e-beam lithography. Our new photoresist design to increase hydroxide substitutions of carboxylate ligands in the Hf₆O₄(OH)₄(RCO₂)₁₂ clusters improves the EUV resolution and also greatly reduces EUV doses. Mechanistic analysis indicates that EUV light not only enables photolytic decomposition of carboxylate ligands, but also enhances the Hf-OH dehydration. One additional advantage of cluster 3 is a very small loss of film thickness (ca. 13%) after the EUV pattern development.