Photoacid diffusion in chemically amplified photoresists and its detection methods: A review

Chemically amplified photoresists have been used in semiconductor lithography for more than four decades. These materials consist of an acid-sensitive polymer matrix and a small amount of photoacid generator, which decomposes upon exposure to radiation to produce strong acid, and other additives. During the subsequent post-exposure bake, the generated acid catalyzes the deprotection reaction of the polymer, resulting in a change in solubility that enables pattern formation. This patterning process is governed by a coupled reaction–diffusion mechanism, where the diffusion length of the acid catalyst directly affects the final feature dimensions. Photoacid diffusion affects the key performance parameters including sensitivity and resolution of chemically amplified photoresists. Accordingly, understanding and accurately characterizing the diffusion process is essential for analyzing and optimizing the performance of the photoresist. This review covers the acid diffusion mechanism in polymers and the application of various experimental techniques for probing photoacid diffusion in chemically amplified photoresists. It also discusses promising approaches for the control and detection of photoacid diffusion. • The mechanisms of photoacid diffusion and its influence on the performance of chemically amplified resists. • Various photoacid diffusion models compared to identify more accurate options for lithography simulation. • Strategies for controlling photoacid diffusion to guide the development of next-generation chemically amplified resists. • A systematic, side-by-side comparison of existing experimental techniques for photoacid diffusion characterization.