Illumination system design for a three-aspherical-mirror projection camera for extreme-ultraviolet lithography

A scanning critical illumination system is designed to couple a synchrotron radiation source to a thre-aspherical-mirror imaging system for extreme ultraviolet lithography. A static illumination area of H × V = 8 mm × 3 mm (where H is horizontal and V is vertical) can be obtained. Uniform intensity distribution and a large ring field of H × V = 150 mm × 3 mm can be achieved by scanning of the mirror of the condenser. The coherence factor (σ) of this illumination system is ∼0.6, with the same beam divergence in both the horizontal and the vertical directions. We describe the performance of the imaging optics at σ = 0.6 to confirm that the illumination optics can meet the requirements for threeaspherical- mirror imaging optics with a feature size of 0.06 μm.