Extreme ultraviolet alignment and testing of a four-mirror ring field extreme ultraviolet optical system

Extreme ultraviolet (EUV) interferometry has been used to characterize and align a recently fabricated, 4X reduction, four-minor, aspheric optical sys tem designed for EUV lithography. This system is called the Engineering Tes t Stand Set-1 Optic. An EUV phase-shifting point diffraction interferometer constructed on an undulator beamline at the Advanced Light Source was used to perform high-accuracy wavefront measurements during several alignment i terations. For each iteration, the alignment algorithm used 35 wavefront me asurements recorded across the 26-mm-wide image-side ring field. Adjustment s were made to systematically reduce the root mean square wavefront error m agnitude to approximately I nm, bringing the system to nearly diffraction-l imited performance. (C) 2000 American Vacuum Society. [q0734-211X(00)05106- 4].