Photoacid generator study for a chemically-amplified negative resist for high resolution lithography

The effect of photoacid generator and photogenerated acid molecular structures on a negative-tone chemically-amplified resist was tested using two different sets of acid generators, each set with one formulation creating a volatile acid (triflate derivative), and the other formulation creating a non-volatile acid (perfluoroalkane sulfonate derivative) when exposed to X-rays. The acids from one set were generated from a derivative of iodonium salt (ionic) and the acids from the other set were generated from a covalently bound (non-ionic) photoacid generator. Both sets were compared to Shipley SAL 605 resist. In this study of five formulations, normalized remaining thickness (NRT) curves, SEM images of printed lines, spectrophotometric titration of the photogenerated acid, real-time FTIR (RT-FTIR) for kinetics of the PEB reaction, dissolution rate measurements, and atomic force microscopy for surface roughness were employed. RT-FTIR suggested that both the proposed volatile and non-volatile acids were retained to approximately the same extent within the films cast from these formulations. A mechanism is suggested where the type of photogenerated acid has an effect on the kinetics of the reaction (general acid catalysis) and the photogenerated acid or photoacid generator has a large effect on the ability of the aqueous developer to penetrate or dissolve the film.