The PS/PDI: A high accuracy development tool for diffraction limited short-wavelength optics

The extreme ultraviolet (EUV) phase-shifting point diffraction interferometer (PS/PDI) was developed and implemented at Lawrence Berkeley National Laboratory to meet the significant measurement challenge of characterizing EUV projection lithography optics. The PS/PDI has been in continuous use and under ongoing development since 1996. This unique and flexible tool is applicable to any imaging system with real conjugate points, including Schwarschild objectives, Fresnel zone plates, and Kirkpatrick-Baez systems. Here we describe recent improvements made to the interferometer, and we summarize metrology results from state-of-the-art 10×-reduction EUV Schwarschild objective.