Oliff & Berridge PLC
Optical element with multilayer thin film and exposure apparatus with the element
An optical element (1) of the present invention is provided with an optical substrate (10) and a multilayered optical thin film (11-16) formed on the optical substrate (10). An MgF2 layer (12, 16) of the multilayered optical thin film has a refractive index of 1.10 to 1.35, especially 1.15 to 1.25 with respect to a vacuum ultraviolet light beam having a wavelength of not more than 250 nm. Therefore, when the optical element (1) is used together with an excimer laser light beam having a wavelength of, for example, 248 nm (KrF), 193 nm (ArF), or 157 nm (F2), excellent optical characteristics are exhibited concerning, for example, the reflectance (anti-reflection), the polarization characteristics, and the dependency on the angle of incidence. The MgF2 layer (12, 16) can be produced in accordance with the sol-gel method. The optical element is preferably used for a projection lens of an exposure apparatus which uses the excimer laser light beam as a light source.
Nikon Corporation
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G03F G21K G21K G02B G02B B82Y G03F G02B
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Hitoshi Tsuyoshi
Ishizawa Murata