Method of measuring a deviation of an optical surface from a target shape
View Patent ↗A method of aligning at least two wave shaping elements, a method of measuring a deviation of an optical surface from a target shape and a measuring apparatus for interferometrically measuring a deviation of an optical surface from a target shape. The method of aligning at least two wave shaping elements, each of which wave shaping elements has a diffractive measurement structure for adapting part of a wave front of incoming light to a respective portion of the target shape, includes: providing a first one of the wave shaping elements with a diffractive alignment structure, arranging the wave shaping elements relative to each other such that each of the diffractive measurement structures is traversed by a separate subset of rays of the incoming light during operation of the measuring apparatus, and aligning the first wave shaping element and a second one of the wave shaping elements relative to each other by evaluating alignment light having consecutively interacted with the diffractive alignment structure and with the second wave shaping element.
1. An asphere having an aspherical optical surface extending over a diameter D of said asphere, wherein a best fitting spherical surface of said aspherical optical surface has a radius of curvature R, and the parameters D and R are related as follows:
D
>
2
R
·
sin
(
arctan
500
mm
2
R
)
.
2. An asphere having an aspherical optical surface extending over a diameter D of said asphere, wherein a best fitting spherical surface of said aspherical optical surface has a radius of curvature R of at least 130 mm, and the ratio D/R is larger than 1.3.
3. The asphere according to claim 1 ,
wherein said best fitting aspherical optical surface is convex.
4. The asphere according to claim 1 ,
wherein said best fitting aspherical optical surface is concave.
5. The asphere according to claim 1 ,
wherein said diameter D is larger than 500 mm.
6. The asphere according to claim 1 ,
wherein said optical surface is rotationally non-symmetric and said diameter D is larger than 300 mm.
7. The asphere according to claim 1 ,
wherein said optical surface has a deviation from said best fitting spherical surface of at least 50 μm.
8. The asphere according to claim 1 ,
wherein said asphere is manufactured to a tolerance sufficient for microlithographic application.
9. The asphere according to claim 8 ,
wherein the actual shape of said optical surface deviates from a target shape of said optical surface by a maximum of 5 μm.
10. The asphere according to claim 1 ,
wherein said asphere has two convex optical surfaces, each being shaped aspherically.
11. An arrangement of a multitude of aspheres according to claim 1 , wherein the actual shape of said optical surfaces of the respective aspheres deviate from each other by a maximum of 5 μm.
12. A projection objective of a projection exposure tool for microlithography comprising at least one asphere according to claim 1 .
13. A projection objective of a projection exposure tool for microlithography comprising at least one asphere according to claim 2 .