Characterization of the accuracy of EUV phase-shifting point diffraction interferometry

The phase-shifting point diffraction interferometer (PS/PDI) has recently been developed and implement at Lawrence Berkeley National Laboratory to meet the significant measurement challenge of characterizing extreme UV (EUV) projection lithography systems. Here progress on the characterization of the PS/PDI accuracy is presented. Two major classes of errors affect the accuracy of the interferometer: the first being systematic effects arising from the measurement geometry, and the second being random and systematic errors caused by an imperfect reference wave. In order to characterize these contribution and calibrate the interferometer. Experimental results demonstrating a systematic-error-limited accuracy of 0.004 waves is reported.