High resolution fluorocarbon based resist for 157-nm lithography

Lithography at 157 run represents the next evolutionary step in optical lithography and is clearly seen as the likely successor to 193-nm lithography. If successful, the photoresists used for this technology must be initially capable of 100-nm resolution and be extendable to less than 70 rim. As with the transition to shorter wavelengths in the past, the photoresist materials developed for longer wavelengths appear to be too absorbent for practical use as a traditional high resolution single layer resist imageable with 157-nm radiation. The high 157-nm absorbance of polyacrylate, polycyclic, and polyhydroxystyrene copolymer resists, will force the coated resist thickness to be under 100 nm. It has been shown that some fluorine-functionalized polymers are more transparent in this spectral region than pure hydrocarbon polymers. This has led us to investigate the use of fluorocarbon polymers in resists specially designed for 157-nm lithography. We have synthesized and evaluated a number of unique 4-hexafluoroisopropanol styrene based polymer systems that yield resists in which the 157-nm absorbance ranges from 3.0 to 4.0 mum(-1). Resists of this type are potentially capable of imaging at resist thickness of 150 rim. Examples of the high performance imaging capability of our resist design are shown to have imaging capability of 150 nm with a 0.50 NA microstepper and 40 rim employing interference lithography.