The effect of end group modification on the transparency of vinyl addition norbornene polymers at 193 nm

Homopolymers of a bis-trifluorocarbinol substituted norbornene (1) (alpha,alpha-bis(trifluoromethyl)bicyclo[2.2.1]hept-5-ene-2-ethanol or HFANB) and copolymers of 1 with t-butyl ester of 5-carboxylic acid (2, t-BuEsNB) were produced using palladium catalysts and olefinic chain transfer agents such as 1-hexene and ethylene to control molecular weight. However, these low-molecular-weight polymers exhibited relatively low optical transparencies at 193 nm. In fact, the opacity (measured as optical densities in absorbance units per micron) of thin films of these homo- and copolymers was inversely proportional to their molecular weight. This relationship is consistent with an end group contribution to the film opacity. Spectroscopic analysis of these polymers by H-1 NMR and MALDI-TOF MS confirmed that 1-hexene and ethylene chain transfer agents generated olefin-terminated vinyl addition polymers. The olefinic end group contribution to optical density can be eliminated by appropriate chemical modification. Both epoxidation and hydrogenation of the polymer olefinic end groups generated very low optical density materials, independent of molecular weight, that are suitable as 193-nm photoresist binder resins.