Fluoroalkylated tin-oxo nano clusters as resist candidates for extreme UV lithography

Extreme UV (EUV) lithography is entering full-scale production of high-end IC chips. This transition gives researchers in academia and industry ample motivation to propose new chemistries that will contribute to alleviating the resolution-line edge roughness-sensitivity trade-off dilemma of EUV lithography. We also have a great interest in the radical chemistry of carbon-fluorine bonds working under EUV and have explored its applicability as a platform for implementing novel EUV resists. While it was checked that the chemical concept is viable by using fluorinated small molecules and polymers, it needed to be upgraded in terms of patterning resolution and sensitivity. Recently, we extended successfully the radical-based strategy to the tin-oxo nano cluster resist concept. Soluble fluorinated tin-oxo clusters could be prepared, and they were cast into thin films from a fluorous solution. When the thin film was exposed to EUV radiation, it lost solubility, resulting in the formation of negative-tone images. Under an EUV lithographic condition, the thin film could be tailored down to 10 nm or smaller sized features. In addition, their unique solubility in chemically orthogonal solvents also enabled the build-up of a bilayer structure composed of a non-fluorinated reactive polymer underlayer without curing. The stacked film structure was found to be helpful for the sensitivity improvement. These results propose another interesting EUV resist candidate possessing unique capabilities in thin film processing.