Illumination system for a microlithographic projection exposure apparatus

1. An illumination system for a microlithographic projection exposure step-and-scan apparatus, comprising:

a light source,

a first optical raster element that extends in or in close proximity of a first pupil plane of the illumination system and includes a plurality of first substructures that increase the geometrical optical flux of the system in a first direction, said first direction being at least substantially perpendicular to a scan direction of the projection exposure apparatus, and

a second optical raster element that extends in or in close proximity of a second pupil plane of the illumination system, which is not necessarily different from the first pupil plane, and includes a plurality of second substructures that further increase the geometrical optical flux of the system in the first direction and increase the geometrical optical flux of the system in a second direction that is at least substantially parallel to the scan direction,

wherein the first optical raster element and the second optical raster element cause an intensity distribution in a reticle plane along the second direction that has a slope with smooth transitions between a zero intensity level and a top intensity level, and

wherein the slope has a Gaussian shape.

2. The illumination system of claim 1 , wherein the second optical raster element is a scattering element.

3. The illumination system of claim 2 , wherein the scattering element is a refractive scattering plate comprising a plurality of micro-lenses having a random shape.

4. The illumination system of claim 2 , wherein the scattering element is a computer generated hologram.

5. The illumination system of claim 1 , wherein the first optical raster element is a refractive optical element and the second optical raster element is a diffractive optical element.

6. The illumination system of claim 5 , wherein the second optical raster element is positioned, in the direction of light propagation, in front of the first optical raster element.

7. The illumination system of claim 5 , wherein the second optical raster element is positioned, in the direction of light propagation, behind the first optical raster element.

8. The illumination system of claim 5 , wherein the first optical raster element comprises an array of micro-lenses having a curved surface that is provided with diffractive structures forming the second optical raster element.

9. The illumination system of claim 5 , wherein the first optical raster element comprises a plurality of parallel prisms having a cross-section that has at least substantially the shape of a rectangular triangle.

10. The illumination system of claim 9 , wherein the cross-section of at least two prisms differ with respect to an angle formed between hypotenuses of the triangles and a reference plane.

11. The illumination system of claim 9 , wherein the second optical raster element comprises a plurality of zones that have different diffraction structures, wherein each of the zones corresponds to one prism of the first optical element.

12. A projection exposure apparatus comprising the illumination system of claim 1 .

13. A microlithographic method of fabricating a micro-structured device, comprising:

providing a substrate supporting a light sensitive layer;

providing a reticle containing structures to be imaged onto the light sensitive layer;

providing the illumination system of claim 1 ; and

projecting at least a part of the reticle onto the light sensitive layer by means of a projection lens.

14. An illumination system for a microlithographic projection exposure step-and-scan apparatus, comprising:

a light source.,

a first optical raster element that extends in or in close proximity of a first pupil plane of the illumination system and includes a plurality of first substructures that increase the geometrical optical flux of the system in a first direction, said first direction being at least substantially perpendicular to a scan direction of the projection exposure apparatus, and

a second optical raster element that extends in or in close proximity of a second pupil plane of the illumination system, which is not necessarily different from the first pupil plane, and includes a plurality of second substructures that further increase the geometrical optical flux of the system in the first direction and increase the geometrical optical flux of the system in a second direction that is at least substantially parallel to the scan direction,

wherein the second optical raster element alone causes an intensity distribution in a reticle plane along the second direction that has a slope with smooth transitions between a zero intensity level and a top intensity level, and

wherein the slope has a Gaussian shape.

15. The illumination system of claim 14 , wherein the first optical raster element alone produces an intensity distribution in the reticle plane that has at least substantially the shape of a line being parallel to the second direction.

16. The illumination system of claim 15 , wherein the first optical raster element comprises an array of parallel cylindrical micro-lenses extending along the second direction.

17. The illumination system of claim 14 , wherein the first optical raster element is a refractive optical element and the second optical raster element is a diffractive optical element.

18. A microlithographic method of fabricating a micro-structured device, comprising:

providing a substrate supporting a light sensitive layer;

providing a reticle containing structures to be imaged onto the light sensitive layer;

providing the illumination system of claim 14 ; and

projecting at least a part of the reticle onto the light sensitive layer by means of a projection lens.