Microscopic deprotection mechanisms and acid loss pathways of chemically amplified photoresists for deep/extreme ultraviolet photolithography

Chemically amplified resists are an important type of material to realize precise microscopic patterning in deep and extreme ultraviolet photolithography. Currently, their development relies heavily on trial-and-error, while achieving higher sensitivity and resolution requires rational molecular design. This task can benefit from an in-depth comprehension of the acid-catalyzed deprotection mechanisms and acid loss pathways at the atomic level. However, our current understanding is largely empirical and the diverse types of photoresists and protective groups pose a significant challenge in fully revealing the microscopic mechanisms. In this study, density functional theory calculations are employed to investigate three primary types of deprotection reactions: tert-butyloxycarbonyl, ester, and ring-opening. Representative polymer photoresist units and fully/half-protected molecular glasses are considered as model systems. The calculations reveal multiple reaction pathways, each characterized by distinct energy barriers. In particular, the rate-determining steps are identified, and potential photoacid loss pathways are uncovered. These findings establish a comprehensive molecular understanding of the deprotection mechanisms of chemically amplified resists for advanced photolithography, providing valuable theoretical insights for their systematic design to achieve higher performances.