Acid distribution in chemically amplified extreme ultraviolet resist

Abstract

Acid generators are sensitized by secondary electrons in chemically amplified resists for ionizing radiation. As acid generators react with low-energy electrons (as low as thermal energy), this sensitization mechanism generates a significant blur and an inhomogeneous acid distribution at the image boundary, which results in line edge roughness (LER) formation. The evaluation of resolution blur intrinsic to the reaction mechanisms is important in the optimization of resist processes for extreme ultraviolet (EUV) lithography, especially from the viewpoint of LER. In this study, the authors simulated acid generation induced by EUV photons in poly(4-hydroxystyrene) with 10wt% triphenylsulfonium triflate and clarified the extent of resolution blur in latent acid images and theoretical acid generation efficiency. The average distance between the EUV absorption point and the acid generation point (resolution blur) is 6.3nm. The theoretical acid generation efficiency through the ionization path is 2.6 per EUV photon in the model system. Considering the deprotonation efficiency of polymer radical cations and the contribution of electronic excited states, the acid generation efficiency including the excitation path is 2.0–2.8 in typical resist materials with 10wt% acid generator loading.