Fabrication of extreme-ultraviolet point-diffraction interferometer aperture arrays.

Interferometric testing at the design wavelength is required for accurately characterizing the wave front of an imaging system operating in the extreme ultraviolet. The fabrication of point-diffraction interferometer apertures for extreme ultraviolet wave-front aberration analysis is described. The apertures are formed in a 200-nm-thick low-pressure chemical-vapor-deposited Si(3)N(4) film and vary in size from approximately 0.