RELIEF AND FUNCTIONAL PHOTOIMAGING WITH CHEMICALLY AMPLIFIED RESISTS BASED ON DI-TERT-BUTYL BUTENEDIOATE-CO-STYRENE

New photoimaging materials were formulated by dissolving photosensitive onium salts into the free-radical copolymer of di-tert-butyl trans-butenedioate (di-tert-butyl fumarate) and styrene. Exposure to mid- or deep-UV, followed by baking, drastically altered material solubility, absorbency, and other properties, through mass cleavage of the polymer's numerous ester groups by photogenerated strong acid catalyst (chemical amplification). With aqueous base or organic solvent as developer, respectively positive or negative relief images could be obtained with submicron resolution. The materials also showed other good qualities for their application as microlithographic resists, such as sensitivity (14-38 mJ/cm(2)), contrast (gamma = 4-7), transparency (0.17 mu m(-1) at 254 nm), and thermal stability against both flow-distortion (T-g of 139 degrees C for fresh copolymer; 199 degrees C after deprotection) and depolymerization (>300 degrees C). The transformation of carboxylic ester to acid or anhydride functional groups also facilitated an alternative method of development, in which various chemical species were selectively bound out of contacting solution to further alter the properties of photoselected areas of polymer film. Production of micron-scale functional images, including dual-tone developability with amphiphilic molecules, was demonstrated using fluorescent dyes.