High-TG base-soluble copolymers as novolac replacements for positive photoresists

Several high-T_g, phenolic copolymers based on N-(p-hy-droxyphenyl)maleimide with various comonomers were prepared, and the properties of a number of these copolymers were studied. The copolymers were 1:1 in composition and were predominantly alternating. The thermal properties of these copolymers were investigated by differential scanning calorimetry and thermal gravimetric analyses. The chain-stiffening effect of the maleimide group was responsible for T_g's of 200°C and above. T_g was a function of composition and molecular weight. Dissolution rates of thin films of these copolymers were investigated by laser interferometry. The dissolution rates were sensitive to copolymer molecular weight and to the functionality, i. e., the type of phenolic ? OH groups and the concentration of ? OH groups present. When these copolymers were used as binders for NDS (diazonaphthoquinone sulfonate) photochemistry, high-resolution positive images were obtained that were resistant to thermal deformation at 200°C and above.