DESIGN OF ASPHERIC MIRROR FOR SYNCHROTRON-RADIATION X-RAY-LITHOGRAPHYBEAMLINE

The illumination system for synchrotron radiation X-ray lithography co nsists of a storage ring to produce the X-rays, and a beamline to tran sport the X-rays to the exposure stage. Because the wavelengths are sh ort, only grazing incident mirrors are used in the beamlines. The beam line optics need to deliver a beam with high transmission in the X-ray region. A condenser is a key component in the X-ray lithography beaml ine. For a scanning X-ray lithography system, the condenser is used to focus X-rays vertically while collimating horizontally. The lack of s ymmetry in grazing incident optics results in large aberrations if sim ple conical mirrors are used. In the past, we have used two toroidal m irrors to compensate each other's aberrations. Here we present the des ign for a novel aspherical mirror. It is calculated using numerical me thods and described by polynomials. Ray-tracing with a finite synchrot ron radiation source shows that the novel mirror shape gives superior performance in the synchrotron radiation collecting angle, and beam un iformity at the exposure stage. The design method is useful in designi ng aspheric surfaces in other beamlines.