New materials for 157-nm photoresists: characterization and properties

The design of an organic material satisfying all of the requirements for a single layer photolithography resist at 157 nm is a formidable challenge. All known resists used for optical lithography at 193 nm or longer wavelengths are too highly absorbing at 157 nm to be used at film thicknesses greater than -90 nm. Our goal has been to identify potential, new photoresist platforms that have good transparency at 157 nm (thickness normalized absorbance of 2.5 pm-' or less), acceptable plasma etch resistance, high Ts, and compatibility with conventional 0.26 N tetramethylammonium hydroxide developers. We have been investigating partially fluorinated resins and copolymers containing transparent acidic groups as potential 157 nm photoresist binders; a variety of materials with promising initial sets of properties (transparency, etch resistance, solubility in aqueous TMAH) have been identified. Balancing these properties with imaging performance, however, remains a significant challenge.