Relay lens used in an illumination system of a lithography system
View Patent ↗A relay lens is provided in an illumination system for use in microlithography. The relay lens can be used to uniformly illuminate a field at a reticle by telecentric light beams with variable aperture size. The relay lens can include first, second, and third lens groups. At least one of the second and third lens groups can include a single lens. This can reduce costs and increase transmission by requiring less CaF 2 because fewer optical elements are used compared to prior systems.
1. A relay lens system positioned between a delimiter plane and a pattern generator plane of a lithography system, comprising:
a first lens group comprising three lenses that decrease numerical aperture of a received beam of radiation;
a second lens group having at least one lens that receives the beam of radiation from the first lens group and controls characteristics of the beam of radiation at a pupil plane;
a third lens group consisting of a single lens element made from a single material having a single index of refraction that receives the beam of radiation from the second lens group and controls field characteristics of the beam of radiation at a patterning device plane;
an aperture stop positioned between the first and second lens groups; and
a fold mirror positioned between the second and third lens groups.
2. The system of claim 1 , wherein the second lens group consists of two lenses.
3. The system of claim 1 , wherein the second lens group consists of three lenses.
4. The system of claim 1 , wherein one of the three lenses in the first lens group is a meniscus lens.
5. The system of claim 1 , wherein two of the three lenses in the first lens group are biconvex lenses.
6. The system of claim 5 , wherein one of the two biconvex lenses has an aspherical surface.
7. The system of claim 1 , wherein the at least one lens in the second lens group has at least one aspherical surface.
8. The system of claim 1 , wherein the at least one lens in the second lens group has at least one convex surface.
9. The system of claim 1 , wherein the single lens in the third lens group comprises two spherical surfaces.
10. The system of claim 1 , further comprising:
a light source positioned before the first lens group; and
a pattern generator positioned after the third lens group in the pattern generator plane.
11. The system of claim 1 , wherein the characteristics controlled by the second lens group comprise at least one of pupil aberration correction, pupil shape correction, elipticity correction, and telecentricity correction.
12. The system of claim 1 , wherein the field characteristics controlled by the third lens group comprises at least one of creating a desired field size at the pattern generator plane and correcting telecentricity.