Alignment of a multilayer‐coated imaging system using extreme ultraviolet Foucault and Ronchi interferometric testing

Multilayer‐coated imaging systems for extreme ultraviolet (EUV) lithography at 13 nm represent a significant challenge for alignment and characterization. The standard practice of utilizing visible light interferometry fundamentally provides an incomplete picture since this technique fails to account for phase effects induced by the multilayer coating. Thus the development of optical techniques at the functional EUV wavelength is required. We present the development of two EUV optical tests based on Foucault and Ronchi techniques. These relatively simple techniques are extremely sensitive due to the factor of 50 reduction in wavelength. Both techniques were utilized to align a Mo–Si multilayer‐coated Schwarzschild camera. By varying the illumination wavelength, phase shift effects due to the interplay of multilayer coating and incident angle were uniquely detected.