| 摘要 |
PURPOSE:To use stably a titled device without causing a drop of intensity of illumination and unevenness of the intensity of illumination even against plural monochromatic lights by setting the thickness of a protecting film to a value of the least common multiple or a value of its integer hold of the value of a half-wavelength in a protecting film medium of each wavelength light. CONSTITUTION:A frame member 2 is provided on a reticle 1, and the pattern surface of the reticle 1 supported by this frame member 2 is protected by a protecting film 3 supported at a height (h). In that case, a film thickness of this protecting film 3 is set to the least common multiple of a value of a half-wavelength in a protecting film medium of the first wavelength light and a value of a half-wavelength in a protecting film medium of the second wavelength light, or a value almost equal to an integer fold or the least common multiple. That is to say, with respect to both wavelengths of the first wavelength lambda1 and the second wavelength lambda2 being different from said wavelength, lambda1' and lambda2' in the medium of the protecting film are shown by the expression I and an expression II when refractive indexes of the protecting film against each wavelength are denoted by n1 and n2, and when m1 and m2 are made natural numbers, the thickness (d) of the protecting film is selected so as to satisfy a condition of the expression III, by which it can be used in common for both the wavelengths. |
