Abstract

To achieve the image performance necessary for soft x-ray projection lithography, interferometric testing at the design wavelength is required to accurately characterize the wavefront of the imaging system. The wavefront depends not only on the surface figure of the individual optics and on their relative alignment, but also on aperture dependent phase shifts induced by the resonant multilayer coatings on the optical surfaces. This paper describes the design and lithographic fabrication of an array of point diffraction interferometers on a Si₃N₄ membrane that has been over-coated with a spatially graded absorbing film to provide fringe contrast control. Experimental results using a visible light analogue (larger pinholes and different absorption gradient) will be presented.

© 1993 Optical Society of America