Mechanistic insights in Zr- and Hf-based molecular hybrid EUV photoresists

Abstract

<bold>Background:</bold> Inorganic resists show promising performances in extreme ultraviolet (EUV) lithography. Yet, there is a need for understanding the exact chemical mechanisms induced by EUV light on these materials. <bold>Aim:</bold> To gain knowledge on the EUV chemistry of inorganic resists, we investigate hybrid inorganic–organic molecular compounds, metal oxoclusters (MOCs). Their molecular nature allows for the monitoring of specific structural changes by means of spectroscopy and thus for the elucidation of the mechanisms behind pattern formation. <bold>Approach:</bold> We compare the sensitivity of MOCs based on Zr and Hf, and methacrylate ligands as EUV resists. The chemical and structural changes causing the solubility switch were investigated by <italic>ex situ</italic> x-ray spectroscopy, infrared spectroscopy, ultraviolet–visible spectroscopy, and grazing incidence x-ray scattering. <bold>Results:</bold> Higher sensitivity was detected for the Hf-based material, in line with its higher absorptivity. A small fraction of the carboxylate ligands is lost at doses that yield solubility contrast, whereas aggregation of the inorganic clusters was not observed. <bold>Conclusions:</bold> These results provide evidence that, although the mechanism of solubility switch in these materials starts with decarboxylation reactions, it mainly proceeds through cross linking of the organic shells instead of aggregation of the inorganic clusters.