Mirror for the EUV wavelength range, projection objective for microlithography comprising such a mirror, and projection exposure apparatus for microlithography comprising such a projection objective
View Patent ↗A mirror for the EUV wavelength range ( 1 ) having a layer arrangement (P) applied on a substrate (S), the layer arrangement having a periodic sequence of individual layers, where the periodic sequence has at least two individual layers—forming a period—composed respectively of silicon (Si) and ruthenium (Ru). Also disclosed are a projection objective for microlithography ( 2 ) including such a mirror, and a projection exposure apparatus for microlithography having such a projection objective ( 2 ).
1. A mirror comprising:
a layer arrangement applied on a substrate and configured for an extreme-ultraviolet wavelength range of light, said layer arrangement comprising:
at least two periods of a periodic sequence, wherein each period of the periodic sequence consists of a silicon layer, a ruthenium layer, and at least one barrier layer composed of B 4 C having a thickness of greater than 0.35 nm and situated between the silicon layer and the ruthenium layer; and
at least one barrier layer composed of B 4 C having a thickness of greater than 0.35 nm and situated between the at least two periods.
2. The mirror as claimed in claim 1 , wherein the barrier layer situated between the silicion layer and the ruthenium layer has a thickness of less than 1 nm.
3. The mirror as claimed in claim 1 , wherein the barrier layer situated between the silicon later and the ruthenium layer has a thickness of between 0.4 nm and 0.6 nm.
4. The mirror as claimed in claim 1 , wherein each of the silicon layers has a thickness of between 4 nm and 7 nm and each of the ruthenium layers has a thickness of between 2.5 nm and 4.5 nm, and further comprising a covering layer system that terminates the layer arrangement of the mirror and comprises at least one layer composed of a chemically inert material.
5. The mirror as claimed in claim 1 , having a reflectivity of more than 30% of the light at an angle of incidence of 24° and a wavelength of between 13.3 nm and 13.7 nm.
6. The mirror as claimed in claim 1 , having a reflectivity of more than 30% of the light at an angle of incidence of between 0° and 24° and a wavelength of between 13.3 nm and 13.7 nm.
7. The mirror as claimed in claim 1 , having a reflectivity of more than 30% of the light at an angle-of-incidence interval having an interval length of between 0° and 11° and a wavelength of between 13.3 nm and 13.7 nm.
8. A projection objective for microlithography comprising a mirror as claimed in claim 1 .
9. The projection objective for microlithography as claimed in claim 8 , further comprising an exit pupil and defining an image plane, wherein the mirror has a reflectivity of more than 30% over the exit pupil of the central image point in the image plane of the projection objective.
10. The mirror as claimed in claim 1 , further comprising a covering layer applied on the layer arrangement on a side of the mirror most distant from the substrate.
11. The mirror as claimed in claim 10 , wherein the covering layer consists of:
two further layers composed respectively of silicon and ruthenium, and
one barrier layer composed of B 4 C having a thickness of between 0.4 nm and 0.6 nm, and situated between the further layers.