Photogenerated amines and their use in the design of a positive-tone resist material based on electrophilic aromatic substitution

Abstract

The photogeneration of an active amine within a cationically curable polymer coating can be used to design a novel positive-tone resist material. The resist is based on a copolymer containing 4-hydroxystyrene as well as 4-acetoxymethylstyrene units; when heated in the presence of an acid, this copolymer crosslinks through an electrophilic aromatic substitution process. Therefore, a small amount of 2-nitrobenzyl toluene-p-sulphonate, that decomposes upon heating to produce toluene sulphonic acid, is added to the resist along with a thermally stable but photoactive carbamate that liberates an amine upon irradiation. Exposure of a film of the resist to 254 nm UV radiation results in the formation of a latent image consisting of amine molecules dispersed within the polymer film. The latent image is ‘fixed’ by heating; this liberates acid, which is neutralized where amine has been formed, but causes crosslinking of the polymer by a cationic process in those areas of the film where no amine has been produced. This resist, based on an image-reversal concept applicable to numerous cationically activated resists, can be developed in aqueous base and shows a good sensitivity of ca. 19 mJ cm^–2.