Deciphering EUV-Induced Chemistry in Photoresists Through in Situ and Ex Situ Characterization Techniques

Publication Date

4-10-2026

Document Type

Conference Proceeding

Publication Title

Proceedings of SPIE the International Society for Optical Engineering

Volume

13983

DOI

10.1117/12.3091210

Abstract

Chemically amplified resists (CARs) are widely used in extreme ultraviolet (EUV) lithography, where acid-catalyzed deprotection is conventionally assumed to occur predominantly during the post-exposure bake (PEB). In this work, we employ transmission-mode FTIR spectroscopy to quantitatively disentangle the contributions of EUV exposure and PEB to deprotection in a model CAR system. By monitoring the dose-dependent attenuation of the CH3 bending vibration feature, we independently quantify deprotection achieved by EUV irradiation alone and by the combined action of EUV exposure and PEB. Our results reveal that EUV exposure without any thermal treatment induces substantial deprotection increasing monotonically with dose. The additional PEB-driven deprotection becomes appreciable only above a threshold dose of ∼17 mJ/cm2 and remains smaller than the exposure-induced deprotection at all doses investigated. Contrast curve measurements confirm that EUV-induced deprotection alone is sufficient to switch resist solubility, yielding a dose-to-clear of ∼31 mJ/cm2 without PEB compared to ∼19 mJ/cm2 with PEB. The degree of deprotection at the dose-to-clear is approximately 40% for both conditions, indicating that the solubility threshold is governed by composition and is independent of the deprotection pathway. These findings challenge the conventional paradigm by demonstrating that direct, radiation-induced deprotection is the primary chemical conversion channel in this EUV CAR system. The feasibility of PEB-free processing suggests a potential route toward reduced line-edge roughness and improved resolution by eliminating acid diffusion blur inherent to the bake step.

Keywords

electron-induced chemistry, extreme ultraviolet (EUV), extreme ultraviolet lithography, lithography, photoresist, polymers, secondary electrons

Department

Chemical and Materials Engineering

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