Technical problems in phase-shifting point diffraction interferometer

Extreme ultraviolet lithography (EUVL) technique is one of the most promising candidate next-Generation lithography technologies, in order to achieve diffraction-limited performance, the allowable wavefront error of the optical system must be less than one fourteenth of its work wavelength, viz. 1 nm RMS, which lies an unprecedented challenge on optical testing. The paper utilized the phase-shifting point diffraction interferometer, which was designed and constructed for the purpose of developing wavefront measurement technology with the exposure wavelength of the projection optics of EUV lithography systems. The paper discussed the key techniques and presented the solving methods in detail.