OPTICAL ELEMENT AND EXPOSURE APPARATUS

摘要

PROBLEM TO BE SOLVED: To provide: an optical element which uses as a glass material an LuAG substrate of 2.10 to 2.20 in refractive index used for light of about 193 nm in wavelength, the optical element being used in a liquid E of 1.64±0.01 in refractive index and having an antireflection film having superior characteristics; an optical system; and an exposure apparatus.

SOLUTION: The optical element 10 is configured to have a base 12 composed of the LuAG substrate having a refractive index of 2.14±0.01 and an antireflection film (20) formed on the base, the optical element being configured to contact a liquid E having a refractive index of 1.6±0.01 for light B having a design center wavelength of 193 nm. The antireflection film 20 includes: a high refractive index layer 22 that is formed on the base 12, contains Al2O3having a refractive index of 1.87 to 1.92, and has an optical film thickness of 0.21λ to 0.34λ and a low refractive index layer 24 that is closer to the liquid E than the high refractive index layer 22, contains Al2O3having a refractive index equal to or smaller than 1.78 but larger than the refractive index of the liquid E, and has an optical film thickness of 0.29λ to 0.52λ.

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