Estimation of diffusion lengths of acid and quencher in chemically amplified resist on the basis of extreme ultraviolet exposure results J.Dependence of acid generation efficiency on the protection ratio of hydroxyl groups in chemically amplified electron beam, x-ray and EUV resists 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 energy͒, this sensitization mechanism generates a significant blur and an inhomogeneous acid distribution at the image boundary, which results in line edge roughness ͑LER͒ formation. The evaluation of resolution blur intrinsic to the reaction mechanisms is important in the optimization of resist processes for extreme ultraviolet ͑EUV͒ lithography, especially from the viewpoint of LER. In this study, the authors simulated acid generation induced by EUV photons in poly͑4-hydroxystyrene͒ with 10 wt % 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 blur͒ is 6.3 nm. 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 10 wt % acid generator loading.

For chemically amplified photoresists, the increase in the absorption of incident radiation by polymers leads to a decrease in the absorption by acid generators. Therefore, the absorption by polymers generally degrades resist sensitivities. However, this is not true for chemically amplified electron-beam (EB) resists because of the difference in the sensitization mechanisms of the acid generators. Whether the reaction mechanism of extreme-ultraviolet (EUV) resists is analogous to that of photoresists or EB resists is critical for material design. The difference in the reaction mechanisms characteristically appears in the polymer-structure dependence of the acid yield. In this study, we evaluated the relative dependence of the acid yield generated in polystyrene derivatives on the exposure to EUV. The dependence was similar to that of EB resists.

A series of high-performance polycarbonates have been prepared with glass-transition temperatures and decomposition temperatures that are tunable by varying the repeat-unit chemical structure. Patterning of the polymers with extreme UV lithography has been achieved by taking advantage of direct photoinduced chain scission of the polymer chains, which results in a molecular-weight based solubility switch. After selective development of the irradiated regions of the polymers, feature sizes as small as 28.6 nm have been printed and the importance of resist-developer interactions for maximizing image quality has been demonstrated.

No abstract