Architectural Effects on Acid Reaction-Diffusion Kinetics in Molecular Glass Photoresists

Understanding acid reaction-diffusion kinetics is crucial for controlling the lithographic performance of chemically amplified photoresists. In this work, we study how the molecular architectures of positive-tone chemically amplified molecular glass resists affect the acid reaction-diffusion kinetics during the post-expose bake (PEB) or annealing step. We compare the acid reaction-diffusion kinetics of a common photoacid generator in molecular glass resists with chemical similarity to poly(4-hydroxystyrene), and that are designed with branched and ring architectures. In situ Fourier transform infrared (FTIR) spectroscopy methods are used to measure reaction rate, acid trapping behavior, and acid diffusivity as a function of PEB temperature. We find that the acid reaction-diffusion kinetics in molecular glass resists is correlated to the film molar density that in turn depends on the architecture of the molecular glass molecules. These results allow modeling of the latent image formation in molecular glass resists that is critical for pattern feature resolution and line edge roughness. A comparison between experimentally measured and theoretically predicted diffusion lengths in one molecular glass resist system was made. Because little is understood of the fundamentals of acid diffusion in this class of molecular glass resists, this paper provides critical insight into the molecular design of next-generation photoresists for high-resolution lithography.