Resist material design to improve sensitivity in EUV lithography

Polymer ionization and reductive sensitization of PAG play an important role for acid generation in EUV lithography. We have systematically investigated effects of PAG structure, polymer structure and their loadings on sensitivity of EUV resists. With an increase in PAG loading, both sensitivity and acid generation yield were successfully improved, however, these were saturated at higher PAG loadings. Least-square fitting of sensitivity as a function of PAG loading, polymer loading and quencher loading indicates that both PAG and polymer have a positive effect on sensitivity improvement, and contribution ratio of polymer to PAG on sensitivity is estimated as 1 to 2. This indicates that decrease of polymer loading in place of increasing PAG loading reduce ionization frequency of polymer. To further improve sensitivity, we have synthesized a series of PAGs to clarify how large the electron affinity of PAG affects acid generation yield. A linear relationship between the reduction potential of PAG and EB sensitivity clearly revealed that the strong electron affinity of PAG causes both high acid yield and sensitivity. To further increase acid generation yield, we have synthesized a series of polymers to clarify how polymer structure affects sensitivity. Actually, acid generation yield and sensitivity were both improved by using a newly developed polymer in EUV lithography.