| 摘要 |
PURPOSE: To reduce instability in wafer positioning by comprising such transparent 4-mirror type optical system as a relatively wide and flat image field, telecentric in the image space, in other words, on short conjugate axis side. CONSTITUTION: The wavelength of radiation for work incident on a mask 14 is generally shorter than 30nm. A first mirror 21 reflects an incoming radiation, and it is sent to, as a form of this divergent light, the secondary mirror 22 which is a concave spherical mirror. The radiation is further reflected on the secondary mirror 22, and reaches a tertiary mirror 23 which is a concave mirror, as a form of focused light. The radiation is reflected on the tertiary mirror 23 and reaches a quaternary mirror 24 which is convex off-axis, and aspherical mirror, as a form of a divergent light. The curvature and position of the quaternary mirror 24 is transported so that the radiation reflected on the quaternary mirror 24 is telecentric in an image space. An image field is two-dimensional, with each side in the two-dimensional size being a and b, respectively, and the axis of the image field is selected so that a is equal to or larger than b. The image field size can be of a relation such that b>=0.1a, and b>=1mm. The resolution in the image field is better than 0.25μm.
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