The reflectivity of Al(1.0%wtSi)/Zr multilayer with 40 periods has been measured in the region of 17-19 nm. Experimental peak reflectivity is 41.2% at 5 degrees incidence angle. However, the corresponding theoretical value for an ideal Al(1.0%wtSi)/Zr multilayer is 70.9%. In order to explain the difference between theoretical and experimental reflectivity, the multilayer has been characterized by X-ray diffraction and X-ray photoelectron spectroscopy. Based on this analysis, the four impact factors responsible for the loss of reflectivity are inhomogeneous crystallization of aluminum, contamination of the multilayer, surface oxidized layer and interdiffusion between Al and Zr layers. The effects of different impact factors on the EUV reflectivity of the Al(1.0%wtSi)/Zr multilayer have been introduced independently by means of corresponding simulations. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.