Tetrahydroxy-tetramethylcyclotetrasiloxane as an Inorganic Molecular Resist for Next-Generation Lithography: Understanding Chemical Contrast through Surface Science Analyses

Next-generation lithography techniques employ high-energy sources that generate secondary electrons, which subsequently induce chemical transformations in photoresist materials. To meet the demands of continued device scaling, the development of photoresists tailored for nanoscale patterning is essential. In this study, we investigate 1,3,5,7-tetrahydroxy-1,3,5,7-tetramethylcyclotetrasiloxane (TH-TMCTS), a silicon-oxide-based molecular resist designed for next-generation lithographic applications. The electron beam induced reactions of TH-TMCTS were comparatively characterized using imaging infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Heat treatment induced only the condensation of silanol groups, whereas electron beam exposure induced the further dissociation of the methyl groups and the cyclosiloxane core. To rationalize the observed bond cleavage patterns, we performed quantum chemical calculations and confirmed that the neutral dissociation cross sections of Si–CH3, Si–OH, SiO–H, SiCH2–H, and Si–O within the core are similar. These results suggest that all primary bonds in TH-TMCTS can be dissociated under electron–molecule collision conditions. In addition, TH-TMCTS thin films exhibit excellent dry etch resistance under O2/N2 plasma conditions, demonstrating an etch selectivity that is more than 65 times higher than that of standard spin-on-carbon (SOC) layers. Furthermore, they have a small molecular size of approximately 0.8 nm and exhibit unique structural transformation upon electron irradiation, generating a distinct chemical contrast. These complex properties, including excellent etch durability, nanoscale molecular size, and electron-induced reactivity, demonstrate the potential of TH-TMCTS as a promising photoresist material for nanoscale patterning in next-generation lithography.