Fundamental Studies of Fluoropolymer Photoresists for 157nm Lithography

A variety of fluorocarbinol containing polymers have been studied in an effort to identify transparent polymer platforms for use in 157nm VUV lithography. It was found that a single α-trifluoromethyl substituent renders poly(α-trifluoromethyl vinyl alcohol-co-vinyl alcohol), P(CF3VA-co-PVA), readily soluble in 0.262N TMAH. The THP-protected polymer can be spin-coated from PGMEA solutions and preliminary studies using 248nm exposure showed that it undergoes chemically amplified deprotection with a clearing dose of ∼-15mJ/cm2. Using a VUV spectrometer, absorption coefficients of ∼-3μm-1 were observed at 157nm with P(CF3VA-co-PVA) and THP protected P(CF3VA-co-PVA). On the basis of these results, we extended our investigation to a series of fluorocarbinol containing polydienes as aqueous base soluble polymer platforms synthesized by the ene reaction of hexafluoroacetone on the double bond. Fluorine content and glass transition temperature can be well controlled. We will discuss the scope and limitation of fluoropolymers for 157nm lithography.