Illumination system of a microlithographic projection exposure apparatus
View Patent ↗An illumination system of a microlithographic projection exposure apparatus includes a beam deflection array including a number beam deflection elements, for example mirrors. Each beam deflection element is adapted to deflect an impinging light beam by a deflection angle that is variable in response to control signals. The light beams reflected from the beam deflection elements produce spots in a system pupil surface. The number of spots illuminated in the system pupil surface during an exposure process, during which a mask is imaged on a light sensitive surface, is greater than the number of beam deflection elements. This may be accomplished with the help of a beam multiplier unit that multiplies the light beams reflected from the beam deflection elements. In another embodiment the beam deflecting elements are controlled such that the irradiance distribution produced in the system pupil surface changes between two consecutive light pulses of an exposure process.
1. An illumination system of a microlithographic projection exposure apparatus, comprising:
a) a beam deflection array of reflective or transparent beam deflection elements, wherein each beam deflection element is adapted to deflect an impinging light beam by a deflection angle,
b) a system pupil surface,
c) a beam multiplier unit which is arranged between the beam deflection array and the system pupil surface such that the number of light beams in the system pupil surface is greater than the number of light beams emerging from the beam deflection array.
2. The illumination system of claim 1 , wherein the beam multiplier unit comprises a beam splitter.
3. The illumination system of claim 2 , wherein the beam splitter comprises a beam splitting surface.
4. The illumination system of claim 3 , wherein the beam splitting surface has a transmittance/reflectance ratio of about 1.
5. The illumination system of claim 3 , wherein the beam splitting surface is formed by a beam splitting coating applied on a support.
6. The illumination system of claim 3 , wherein the beam splitting surface is plane and extends parallel to an optical axis of the illumination system.
7. The illumination system of claim 6 , wherein the beam splitting surface has a transmittance versus reflectance ratio that varies along the optical axis.
8. The illumination system of claim 3 , comprising an actuator for moving the beam splitting surface.
9. The illumination system of claim 8 , wherein the actuator is configured to rotate the beam splitting surface.
10. The illumination system of claim 8 , wherein the actuator is capable of completely removing the beam splitting surface from a light propagation path.
11. The illumination system of claim 3 , wherein the beam multiplier unit comprises at least two plane beam splitting surfaces arranged at an angle which at least substantially equals 90°.
12. The illumination system of claim 11 , wherein the at least two plane beam splitting surfaces are arranged in planes intersecting at the optical axis of the illumination system.
13. The illumination system of claim 3 , wherein the beam multiplier unit comprises a plane mirror which is arranged with respect to the beam splitting surface at an angle which at least substantially equals 90°.
14. The illumination system of claim 13 , wherein the beam splitting surface and the mirror are arranged in planes intersecting at the optical axis of the illumination system.
15. The illumination system of claim 14 , wherein the beam deflection array is cen tered with respect to the optical axis.