Photolithographic properties of tin-oxo clusters using extreme ultraviolet light (13.5 nm)

• The photochemistry of tin clusters has been investigated for EUV lithography for the first time.
• Photosensitivity correlates with counter-ion (X) molecular weight, not bond energy.
• Resist sensitivity was also found to correlate directly with the organic ligand (R) bond energy.
• Results support a mechanism of organic ligand (R) photolysis followed by agglomeration.
• Utilizing this photochemical change, we have resolved dense-line patterns as small as 18 nm.

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 counter-anions and vs. the strength of the carbon–tin bonds. No correlation was observed between the strength of the carbon–carboxylate bonds in the counter-anions (X) and the EUV photosensitivity. However, the EUV sensitivity of the tin-oxide 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.

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