Preparation and characterization of copolymers containing (+)-bornyl methacrylate and their racemate for positive-tone photoresist

This study investigated the chemical behavior of polymers bearing cycloaliphatic bornyl units along with the steric difference of the chiral (+)-bornyl methacrylate [(+)-BMA] and racemic (±)-BMA, expressed in the physical properties of the copolymers and the resist characteristics. To do this, a series of copolymers containing (+)-bornyl methacrylate [(+)-BMA] and [(±)-BMA] units was synthesized. Comonomers of tert-butyl methacrylate (TBMA), methyl methacrylate (MMA), and maleic anhydride (MA) were used. The thermogravimetric curves, glass-transition temperature (T_g), and molecular weight (MW) of the copolymers were evaluated. Exposure characteristics of chemical-amplified positive photoresists comprising various copolymers were investigated. It was found that copolymers bearing (±)-BMA have higher T_g and better thermostability than those of copolymers containing (+)-BMA units. The copolymers with (±)-BMA units, however, revealed an inert photochemical behavior on the positive-tone photoresist. The patterning properties of the positive photoresist, composed of copolymers bearing (+)-BMA and (±)-BMA, and the photoacid generator (PAG) were also investigated.