Design and properties of new deep-UV positive photoresist

A new class of photodefinable polymer based on di-tert-butyl malonate protecting group was developed. A novel alkyl malonated copolymer was synthesized by copolymerization of di-tert-butyl malonylmethyl styrene (DBMST) with 4-acetoxystyrene (AST), and the subsequent deprotection of acetoxy group. Exposure of the material to deep-UV light followed by postbaking results in significant changes in solubility and polarity due to the formation of carboxylic functions which were produced on the polymer chain through the photogenerated acid catalyst (chemical amplification). This resist resolved 0.24 mu m line-and-space patterns, formulated from di-tert-butyl malonate-protected polyhydroxystyrene (PHS) and triphenylsulfonium (TPS) triflate, wit the aqueous base development using a KrF excimer laser stepper (NA 0.45) with a dose of 44 mJ/cm(2).