Patent ID: 6472087
Filing Date: 2002-10-29
Classification: G02B

Abstract:
An antireflection film consisting of:an alternately multilayered film having a designed center wavelength &lgr;0 in a range of wavelengths 190 nm to 250 nm and comprising high-index layers of a refractive index nh and low-index layers of a refractive index nl in order from the side of a substrate to the side of air, said alternately multilayered film having a four layered structure, wherein when a refractive index of the substrate is n, the refractive indices satisfy the following conditions: 1.35&lE;nl&lE;1.45 1.60&lE;nh&lE;1.85 nl&lE;n&lE;nh; and wherein when optical thicknesses (refractive index x geometrical thickness) of the respective layers are represented by d1, d2, d3, and d4 in order from the first layer to the fourth layer when counted from the substrate side, the first layer and the third layer are the high-index layers, the second layer and the fourth layer are the low-index layers, and the optical thicknesses satisfy the following conditions: 0.38 &lgr;0&lE;d1&lE;0.43 &lgr;0 0.38 &lgr;0&lE;d2&lE;0.43 &lgr;0 0.20 &lgr;0&lE;d3&lE;0.25 &lgr;0 0.20 &lgr;0&lE;d4&lE;0.25 &lgr;0.