SYNTHESIS AND EVALUATION OF COPOLYMERS OF (TERT-BUTOXYCARBONYLOXY)STYRENE AND (2-NITROBENZYL)STYRENE SULFONATES - SINGLE-COMPONENT CHEMICALLY AMPLIFIED DEEP-UV IMAGING MATERIALS

Copolymers of (tert-butoxycarbonyloxy)styrene (t-BOC-styrene) and (2-nitrobenzyl)styrene sulfonates were prepared to give hydrophobic, photosensitive materials. Exposure to ultraviolet light converted the pendant 2-nitrobenzyl sulfonate esters to sulfonic acid moieties, and this photogenerated acid catalyzed the removal of the t-BOC groups on subsequent heating. The resulting material was a copolymer of 4-hydroxystyrene and styrenesulfonic acid, which was hydrophilic and soluble in aqueous base. Copolymers with different compositions (monomer ratios) and molecular weights were synthesized, and the resulting materials were analyzed by thermal and spectroscopic methods and evaluated for lithographic performance as positive tone resists. As the percentage of the photosensitive 2-nitrobenzylstyrene sulfonate monomer was increased, the lithographic sensitivity improved but the thermal stability of the copolymers decreased. The photoresponse of some of the materials was inhomogeneous, apparently the result of inhomogeneous distribution of acid-generating monomers in the polymers.