The phase-shifting point-diffraction interferometer (PS/PDI) was recently developed and implemented at Lawrence Berkeley National Laboratory to characterize extreme-ultraviolet (EUV) projection optical systems for lithography. Here we quantitatively characterize the accuracy and precision of the PS/PDI. Experimental measurements are compared with theoretical results. Two major classes of errors affect the accuracy of the interferometer: systematic effects arising from measurement geometry and systematic and random errors due to an imperfect reference wave. To characterize these effects, and hence to calibrate the interferometer, a null test is used. This null test also serves as a measure of the accuracy of the interferometer. We show the EUV PS/PDI, as currently implemented, to have a systematic error-limited reference-wave accuracy of 0.0028 waves (λ/357 or 0.038 nm at λ = 13.5 nm) within a numerical aperture of 0.082.
© 1999 Optical Society of America
Original Manuscript: May 17, 1999
Revised Manuscript: August 16, 1999
Published: December 10, 1999
Patrick P. Naulleau, Kenneth A. Goldberg, Sang H. Lee, Chang Chang, David Attwood, and Jeffrey Bokor, "Extreme-ultraviolet phase-shifting point-diffraction interferometer: a wave-front metrology tool with subangstrom reference-wave accuracy," Appl. Opt. 38, 7252-7263 (1999)