Bis(fluoroalcohol) Monomers and Polymers:  Improved Transparency Fluoropolymer Photoresists for Semiconductor Photolithography at 157 nm

Novel norbornene and [4.2.1.02,5]tricyclononene monomers bearing two hexafluoro-2-propanol substituents are polymerized with tetrafluoroethylene in solution, giving amorphous, largely alternating copolymers. The norbornene copolymer shows excellent transparency at 157 nm and a dissolution rate in aqueous tetramethylammonium hydroxide that is 100 000 times faster than the corresponding polymer with a single hexafluoro-2-propanol substituent on the norbornene ring. Intermediate dissolution rates are readily obtained using mixtures of the mono- and disubstituted norbornenes. The tricyclononene copolymer is obtained in higher conversion and molecular weight but has a higher absorbance at 157 nm and a slower dissolution rate. Partial protection of the fluoroalcohol groups as their methoxymethyl derivatives gives photoresist polymers with absorbance of 1.0 μm-1 or less which can be imaged at 157 nm using a photoacid generator.