Deep ultraviolet unit-magnification projection optical system and projection exposure apparatus
View Patent ↗A 1X projection optical system for deep ultra-violet (DUV) photolithography is disclosed. The optical system is a modified Dyson system capable of imaging a relatively large field at high numerical apertures at DUV wavelengths. The optical system includes a lens group having first and second prisms and four lenses having a positive-negative-positive negative arrangement as arranged in order from the prisms toward the mirror. A projection photolithography system that employs the projection optical system of the invention is also disclosed.
1. A projection Optical system comprising along an optical axis:
a mirror having a concave surface;
an aperture stop located at the mirror that determines a numerical aperture (NA) of the system; and
a lens group with positive refracting power arranged adjacent the mirror and spaced apart therefrom, the lens group comprising in order towards the mirror:
first and second prisms arranged on opposite sides of the optical axis and each having a planar surface, wherein the planar surfaces are arranged adjacent object and image planes, respectively, and
a first positive lens, a second negative lens, a third positive lens and a fourth negative lens, wherein the lenses of the lens group have surfaces that are non-concentric with respect to the mirror surface.
2. The optical systems of claim 1 , wherein the first lens is a piano convex lens, the second lens is a negative meniscus lens, the third lens is a positive meniscus lens and the fourth lens is a negative meniscus lens, wherein the first through fourth lenses each have a convex surface facing the mirror.
3. The optical system of claim 1 , wherein the mirror has an aspherical surface.
4. The optical system of claim 1 , wherein prisms and first through fourth lenses are formed from fused silica.
5. The optical system of claim 1 , wherein the prisms and first through fourth lenses are formed from calcium fluoride.
6. The optical system of claim 1 , wherein the prisms, the second lens and the fourth lens are formed from calcium fluoride and the remaining elements from fused silica.
7. The optical system of claim 1 , wherein the system is corrected for a wavelength selected from the group of wavelengths comprising: 248 nm, 193 nm and 157 nm.
8. The optical system of claim 1 , wherein the system includes a working distance of 3.5 mm or greater.
9. The optical system of claim 1 , wherein 0.3=NA=0.5.
10. A projection lithography system comprising:
an optical system comprising:
a mirror having a concave surface;
an aperture stop located at the mirror that determines a numerical aperture (NA) of the system; and
a lens group with positive refracting power arranged adjacent the mirror and spaced apart therefrom, the lens group comprising in order towards the mirror:
first and second prisms arranged on opposite sides of the optical axis and each having a planar surface, wherein the planar surfaces are arranged adjacent object and image planes, respectively; and
a first positive lens, a second negative lens, a third positive lens and a fourth negative lens, wherein the lenses of the lens group have surfaces that are non-concentric with respect to the mirror surface;
a mask stage capable of supporting a mask at the object plane;
an illuminator adapted to illuminate the mask with at least one of 248 nm, 193 nm and 157 nm radiation; and
a wafer stage capable of movably supporting a wafer at the image plane.