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High-resolution fluorocarbon-based resist for 157-nm lithography

Lithography with 157 nm fluorine lasers is rapidly emerging as the next evolutionary step in optical lithography and is clearly seen as the likely successor to 193 nm lithography. In fact, it may become the technology of choice for the sub-100-nm node features. The photoresists used for this technology will be required to be extendable to less than 70 nm. As has been demonstrated with the transition to shorter wavelengths in the past, the photoresist materials that were developed for the longer wavelength applications are too absorbent for practical use as high-resolution single layer resist with 157 nm radiation. This high absorbency will force the coated resist thicknesses to be well under 100 nm. Fluorine containing polymers have been demonstrated to be more transparent in this spectral region than pure hydrocarbon polymers. We have developed and evaluated a number of unique 4-hexafluoroisopropanol styrene based polymer systems which we previously termed FESCAP resists and have developed new acetal partially blocked 4-hexafluoroisopropanol styrene based copolymers. These resists can have absorbencies of under 3 micrometers -1 at 157 nm which could allow imaging to thicknesses of 150 nm. Our recent resist designs are shown to have imaging capability down to 70 nm with a 0.60 NA microstepper.