Acid distribution in chemically amplified extreme ultraviolet resist

Abstract

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.

PAG Study in EUV Lithography

“…One possible explanation for the phenomena observed here is difference in acid generation mechanism as discussed in the sensitivity part; it is known acid generation by the electron transfer from polymer matrix absorbing EUV irradiation is dominant in Copolymer A. [12] In such a case, the acid generation strongly depends on the absorption to PHS matrix. Thus the difference in exposure latitude among PAGs was small.…”

“…[10][11] It is widely proposed that the electrons generated from PHS polymer matrix of photoresists under EUV radiation are involved in the acid generation reaction from PAG. [12] However less information about the acid generation mechanism in poly(methacrylates) matrix is available. To investigate the possibility of direct excitation of PAG under EUV exposure, values of p-parameter with Copolymer A and Copolymer B were calculated and listed in Table 5.…”

Relationship between Absorption Coefficient and Line Edge Roughness of Chemically Amplified Resists Used for Extreme Ultraviolet Lithography

“…[28] Above the threshold energy, E th , we assumed that the electron energy is lost by either the ionization or electronic excitation of molecules. E th was set at 21 eV [29] so that the number of secondary electrons generated by a single EUV photon corresponds to the number predicted from the W-value (the average energy required for the generation of an ion pair) of a typical resist polymer, poly(4-hydroxystyrene) (PHS). [30] Below E th , the electrons were assumed to be thermalized through the excitation of intra-and intermolecular vibration.…”

Resist Materials and Processes for Extreme Ultraviolet Lithography

“…In chemically amplified resists, an aerial image of incident photons generated by an exposure tool is converted to an acid image. 29 Here, f LER , m, and dm=dx are a constant, the concentration of protected units normalized by the initial value, and the chemical gradient, respectively. 30) This relationship has been experimentally confirmed using high-performance resists including those shown in Fig.…”