Application of large scale binary optical elements to high resolution projection optics used for microlithography

Binary optical elements (BOEs) are very attractive because of their compactness and high aberration correction abilities. However, in their application to high resolution optics, some critical issues such as the influence of fabrication errors and the behavior of spurious order diffraction beams must be carefully examined. An eight-level BOE, ideally giving 95 % diffraction efficiency, is fabricated by lithographic techniques using a stepper for pattern delineation. A large element exceeding the size of stepper exposure area can be obtained by pattern stitching in the radial and the tangential directions. The performance of these BOEs confirm that it is fundamentally possible to apply BOEs fabricated with currently available techniques to high resolution projection optics used for microlithography.