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Development of 157 nm Resist Using Highly Exact Theoretical Calculation of Absorption Spectra

Vacuum ultraviolet (VUV) absorption spectra of organic materials were calculated theoretically by the symmetry-adapted cluster-configuration interaction (SAC-CI) method [rf1,rf2,rf3,rf4] to establish a molecular design for high-transparency resist materials to be used in 157 nm lithography. We investigated several saturated hydrocarbons and fluorinated compounds, and obtained low prediction error of absorption peaks (< 0.25 eV, in the case of formaldehyde). High-precision prediction enables exact assignment of an absorption spectrum. The theoretical SAC-CI spectra obtained were very close to the experimentally measured spectra. In addition, we investigated the reasons for changes occurring in VUV-absorption spectra when C–H bonds of alkane are substituted with C–F bonds, and found that major changes in electronic structure occur with fluorination.