Mechanistic Insights into Acid Generation from Nonionic Photoacid Generators for Extreme Ultraviolet and Electron...

Area of Science:

• Materials Science
• Computational Chemistry
• Chemical Engineering

Background:

• Nonionic photoacid generators (PAGs) are vital in advanced lithography (EUV/EB) for photoresist formulations.
• Current limitations in understanding PAG acid generation mechanisms impede rational design, relying on empirical methods.
• Key advantages of nonionic PAGs include low dark loss, reduced outgassing, and suppressed phase separation.

Purpose of the Study:

• To elucidate the postexposure reaction pathways of nonionic PAGs at a molecular level using computational methods.
• To establish a structure-mechanism-function relationship for nonionic PAGs to guide rational design.
• To develop a predictive framework for designing next-generation high-sensitivity PAGs for advanced lithography.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to investigate 22 representative nonionic PAGs.
• Analysis focused on electron-triggered dissociation modes, byproduct formation, and proton transfer mechanisms.
• Energy barriers for various reaction pathways were quantified to assess efficiency and selectivity.

Main Results:

• Four distinct electron-triggered dissociation modes were identified, including productive N-O/C-O and nonproductive S-O bond cleavage.
• The relative energy barrier between productive and unproductive pathways was found to be a critical descriptor for photoacid generation efficiency and photoresist sensitivity.
• Molecular conformation and substituents significantly influence bond dissociation selectivity, impacting acid generation efficiency.

Conclusions:

• A clear structure-mechanism-function relationship for nonionic PAGs has been established.
• The study provides critical insights into the factors governing acid generation efficiency, including dissociation modes and proton transfer pathways.
• The findings offer a predictive framework for the rational design of high-performance nonionic PAGs for advanced lithographic applications.