CONTRAST ENHANCEMENT LITHOGRAPHY SYSTEM BASED ON PYRYLIUM DYE BLEACH CHEMISTRY

Contrast enhancement lithography (CEL) is a bilayer photolithographic process in which a photoresist film is overcoated with a thin, photobl eachable layer. On exposure, the CEL layer bleaches rapidly in areas o f highest light intensity, but it remains opaque to low-intensity flar e or scattered light. This enhanced contrast results in improved resol ution and a more vertical photoresist profile. In this study, bleach r ate data and preliminary microlithographic behavior of potential CEL f ormulations based on pyrylium dye bleach chemistry are described. The structure of the pyrylium dye was optimized to achieve maximum light a bsorption at both 405 and 436 nm, enabling the use of a single materia l at two common photolithographic exposure wave-lengths. An allylthiou rea coreactant provides a bleach quantum efficiency of 25%, the highes t obtained in pyrylium-based films to date. In addition, suitable poly meric binders enable spin-coating thin (ca. 0.5 mum), optically dense (2.0 O.D. or more), clear films that photobleach essentially as effici ently as commercial materials. Moreover, acidic groups incorporated in these polymers enable removal of the CEL layer simultaneously with de velopment of the photoresist layer, eliminating one of the extra proce ssing steps required by organic-based products. Finally, these formula tions exhibit good dark stability for a photobleachable system, underg oing only a modest loss in initial absorbance over a period of one-hal f year. No decrease in photobleach efficiency was noted during this ti me. Hence a contrast enhancement formulation based on pyrylium dye ble ach chemistry could offer several significant advantages for contrast enhancement.