EUV resists based on tin-oxo clusters

Abstract

We have studied the photolysis of tin clusters of the type [(RSn)₁₂O₁₄(OH)₆] X₂ using extreme ultraviolet (EUV, 13.5 nm) light, and developed these clusters into novel high-resolution photoresists. A thin film of [(BuSn)₁₂O₁₄(OH)₆][p-toluenesulfonate]₂ (1) was prepared by spin coating a solution of (1) in 2-butanone onto a silicon wafer. Exposure to EUV light caused the compound (1) to be converted into a substance that was markedly less soluble in aqueous isopropanol. To optimize the EUV lithographic performance of resists using tin-oxo clusters, and to gain insight into the mechanism of their photochemical reactions, we prepared several compounds based on [(RSn)₁₂O₁₄(OH)₆] X₂. The sensitivity of tin-oxide films to EUV light were studied as a function of variations in the structure of the counter-anions (X, primarily carboxylates) and organic ligands bound to tin (R). Correlations were sought between the EUV sensitivity of these complexes vs. the strength of the carbon-carboxylate bonds in the counteranions and vs. the strength of the carbon-tin bonds. No correlation was observed between the strength of the carboncarboxylate bonds in the counter-anions (X) and the EUV photosensitivity. However, the EUV sensitivity of the tinoxide films appears to be well-correlated with the strength of the carbon-tin bonds. We hypothesize this correlation indicates a mechanism of carbon-tin bond homolysis during exposure. Using these tin clusters, 18-nm lines were printed showcasing the high resolution capabilities of these materials as photoresists for EUV lithography.