Optical element and manufacturing method thereof
An optical element and a manufacturing method therefor, an exposure apparatus, and a device manufacturing method that can reduce the effect of intrinsic birefringence under high NA conditions. According to an optical element as one aspect of the present invention, an angle between a [0 0 1] axis of an isometric crystal and an optical axis is less than 10°, and preferably 0°.
1. An exposure apparatus comprising:
an illumination optical system for illuminating a reticle using light from a light source; and
a projection optical system for projecting a repetitive pattern on the reticle onto an object to be exposed,
wherein said projection optical system includes an optical element comprising an isometric crystal,
wherein the angle between the [0 0 1] axis of the isometric crystal and the optical axis of said optical element is set lower than 10°, and
wherein the [0 1 0 ] axis perpendicular to the [0 0 1 ] axis in the isometric crystal is inclined to a direction of repetition of the pattern by 10° or greater.
2. An exposure apparatus according to claim 1 , wherein the direction of repetition the pattern forms an angle of 0°, 45° or 90° with a reference direction of the reticle.
3. An exposure apparatus according to claim 1 , wherein said angle between the [0 0 1]axis of the isometric cyrstal and the optical axis of said optical element is 0°.
4. An exposure apparatus according claim 1 , wherein the maximum angle between the light incident on the optical element and the optical axis of the optical element is 25° or greater.
5. An exposure apparatus according to claim 1 , wherein said projection optical system includes n optical elements, arranged around an optical axis so that the [0 1 0]axis of one of the optical elements and the [0 1 0]axis of another of the optical elements form an angle within 90°/n± 10° with each other.