Large-field unit-magnification projection system
View Patent ↗An optical system for projection photolithography is disclosed. The optical system is a modified Dyson system capable of imaging a large field over a broad spectral range. The optical system includes a positive lens group having three elements: a plano-convex element and two negative meniscus elements. The lens group is arranged adjacent to but spaced apart from a concave mirror along the mirror axis. A projection photolithography system that employs the optical system is also disclosed.
1. An optical system comprising along an optical axis:
a concave spherical mirror;
a lens group with positive refracting power arranged adjacent the mirror with an airspace therebetween, the lens group comprising in order farthest from, to closest to, the mirror:
a plano-convex lens element having a convex surface facing the mirror and a flat surface facing away from the mirror;
a first negative meniscus lens element adjacent the plano-convex lens and having a convex surface facing the mirror; and
a second negative meniscus lens element adjacent the first negative meniscus lens and having a convex surface facing the mirror; and
first and second prisms each having respective first and second flat surfaces, wherein the second flat surfaces are arranged adjacent the fiat surface of the plano-convex lens element on opposite sides of the optical axis, and wherein the first flat surfaces are arranged adjacent object and image planes, respectively;
wherein each lens element in the lens group is formed from a different glass type such that the lens group and first and second prisms provide chromatic aberration correction in a spectral region that contains at least g, h and i-line wavelengths.
2. The optical system of claim 1 , having:
at least one of a square field having a size of at least 61.5 mm×61.5 mm, and a rectangular field having a size of at least 50 mm×100 mm; and
a numerical aperture of 0.15 or greater.
3. The optical system of claim 1 , having a field size of between 50 mm×100 mm and 52.5 mm×100 mm, inclusive.
4. The optical system of claim 1 , having a numerical aperture of between 0.16 and 0.20, inclusive.
5. The optical system of claim 1 , wherein the lens elements in the lens group are spherical.
6. The optical system of claim 1 , in which at least one lens element in the lens group includes an aspherical surface.
7. The optical system of claim 1 , in which adjacent surfaces of lens elements in the lens group are in contact one with the other.
8. The optical system of claim 1 , in which at least one surface of the lens elements in the lens group is closely air-spaced apart from an adjacent surface of an adjacent lens element.
9. The optical system of claim 1 , wherein said first and second prisms are formed with glass type 603606.
10. The optical system of claim 6 , wherein the plano-convex lens is formed from one of fused silica and silica glass.
11. The optical system of claim 8 , wherein the plano-convex lens is formed from glass type 458678.
12. The optical system of claim 8 , wherein the first and second meniscus lens elements are respectively formed from glass type 581408 and glass type 532490.
13. The optical system of claim 1 , wherein the first and second prisms are formed with glass type 603606, the plano-convex lens is formed with glass type 458678, and the first and second meniscus lens elements are respectively formed with glass types 581408 and 532490.
14. The optical system of claim 1 , wherein the convex surface of the second meniscus lens element is aspherical.
15. The optical system of claim 1 , wherein the convex surface of the first meniscus lens element is aspherical.
16. The optical system of claim 1 , wherein the first meniscus lens has an aspherical concave surface.
17. The optical system of claim 1 , wherein the mirror includes an aperture formed along the optical axis.
18. A projection lithography system comprising: an optical system comprising:
a concave spherical mirror;
a lens group with positive refracting power arranged adjacent the mirror with an airspace therebetween, the lens group comprising in order farthest from to closest to the mirror:
a plano-convex lens element having a convex surface facing the mirror and a flat surface facing away from the mirror; and
a first negative meniscus lens element adjacent the plano-convex lens and having a convex surface facing the mirror; and
a second negative meniscus lens element adjacent the first negative meniscus lens and having a convex surface facing the mirror; and
first and second prisms each having respective first and second flat surfaces, wherein the second flat surfaces are arranged adjacent the flat surface of the plano-convex lens element on opposite sides of the optical axis, and wherein the first flat surfaces are arranged adjacent object and image planes, respectively;
wherein each lens element in the lens group is formed from a different glass type such that the lens group and first and second prisms provide chromatic aberration correction in a spectral region that contains at least g, h and i-line wavelengths;
a mask stage capable of supporting a mask at the object plane;
an illuminator adapted to illuminate the mask with at least one wavelength in a spectral region that contains at least the g-line, h-line and i-line wavelengths; and
a wafer stage capable of movably supporting a wafer at the image plane.
19. The system of claim 18 , having:
at least one of a square field having a size of 61.5 mm×61.5 mm or greater, and a rectangular field having a size of 50 mm×100 mm or greater; and
a numerical aperture 0.15 or greater.
20. The system of claim 18 , having a field having a size of between 50 mm×100 mm and 52.5 mm×100 mm, inclusive.
21. The system of claim 18 , further including a numerical aperture of between 0.16 and 0.20, inclusive.