Radiation Chemistry of Fluoronaphthalene as a Candidate for Absorption Enhancement Component of Chemically Amplified Extreme Ultraviolet Resists

Abstract

With the reduction of resist thickness accompanying the miniaturization of feature sizes, increasing the absorption coefficient of extreme ultraviolet (EUV) resists is becoming increasingly important from the viewpoint of the efficient use of incident radiation. The fluorination of the resist polymer is the most effective means of increasing the absorption coefficient. However, it has been pointed out that the dissociative electron attachment of the fluorinated polymer is a problem in the application of the fluorinated polymer to chemically amplified resists used for ionizing radiation. In this study, the electron flow in fluorinated resists was examined using fluoronaphthalene as a possible candidate for suppressing the dissociative electron attachment. The molecular structure dependence of the reactivity with tetrahydrofuran-solvated electrons, the electron transfer from fluoronaphthalene radical anions to triphenylsulfonium-triflate, the dissociation of fluoronaphthalene radical anions, and the charge recombination of fluoronaphthalene radical anions with protons were clarified by the comparison of octafluoronaphthalene, 1-fluoronaphthalene, and naphthalene. The dissociation of fluoronaphthalene radical anions was negligibly slow. Also, the recombination of octafluoronaphthalene radical anions with protons was significantly delayed compared with that of naphthalene radical anions. These results suggest that the molecular structure of fluoronaphthalene is suitable for the molecular design of chemically amplified EUV resists from the viewpoint of the control of electron flow in the acid generation processes.