PROJECTION OBJECTIVE AND PROJECTION EXPOSURE APPARATUS FOR MICROLITHOGRAPHY
A projection objective of a projection exposure apparatus for microlithography serves for imaging an object arranged in an object plane onto a light-sensitive wafer in an image plane. The projection objective has a plurality of optical elements which have at least one reflective element and at least one refractive element. The plurality of optical elements lie, in the light propagation direction of the useful light, downstream of the reflective element on a common straight optical axis. The at least one reflective element has a substrate having at least one opening through which light beams can pass. The at least one reflective element is at least partly made from a material which suppresses stray light impinging on the reflective element rearward.
1 . A projection objective configured to image an object in an object plane onto an image field in an image plane, the projection objective comprising:
a plurality of optical elements comprising at least one reflective element and at least one refractive element, the at least one refractive element lying, in a light propagation direction of useful light, downstream of the at least one reflective element on a common straight optical axis,
wherein the at least one reflective element has a substrate having at least one opening through which light beams can pass, the at least one reflective element is at least partly made from a material which suppresses stray light impinging on the reflective element in a rearward direction, and the projection objective is configured to be used in microlithography.
2 . The projection objective of claim 1 , wherein the substrate of the reflective element at least partly comprises the stray-light-suppressing material.
3 . The projection objective of claim 1 , wherein the substrate of the reflective element at least partly comprises a layer comprising the stray-light-suppressing material.
4 . The projection objective of claim 3 , wherein the layer is under a reflective surface of the substrate.
5 . The projection objective of claim 4 , wherein the layer is arranged directly under the reflective surface of the substrate.
6 . The projection objective of claim 4 , wherein the layer is arranged along an entire extent of the reflective surface of the substrate.
7 . The projection objective of claim 3 , wherein the layer is at least partly arranged along the opening of the substrate.
8 . The projection objective of claim 1 , wherein the reflective element has a mount arranged at least partly at a rear side of the substrate, and the mount at least partly comprises the stray-light-suppressing material.
9 . The projection objective of claim 8 , wherein the mount at least partly comprises a coating made from the stray-light-suppressing material.
10 . The projection objective of claim 1 , wherein the stray-light-suppressing material is light-absorbing.
11 . The projection objective of claim 10 , wherein the light-absorbing material is Zerodur.
12 . The projection objective of claim 1 , wherein the stray-light-suppressing material is non-directionally light-scattering.
13 . The projection objective of claim 1 , wherein the stray-light-suppressing material is metal.
14 . The projection objective of claim 1 , wherein the at least one reflective element is a mirror.
15 . The projection objective of claim 1 , wherein the optical elements form a non-obscured imaging system.
16 . The projection objective of claim 15 , wherein the object field is off-axis in the object plane and does not contain the common straight optical axis, and the image field in the image plane is off-axis.
17 . The projection objective of claim 1 , wherein only refractive elements are arranged downstream of the reflective element and upstream of the image plane as seen in the light propagation of the useful light, and wherein the stray light is produced by at least one reflection at at least one surface of the at least one of the refractive element.
18 . The projection objective of claim 17 , wherein the at least one surface of the last refractive element is upstream of the image plane.
19 . The projection objective of claim 18 , wherein the at least one surface of the at least one reflective element is a front surface of the last reflective element as seen in the light propagation direction.
20 . An apparatus, comprising:
an illumination system; and
a projection objective according to anyone of claim 1 ,
wherein the apparatus is a microlithography projection exposure apparatus.