Extreme ultraviolet (EUV) reflective multilayers were deposited and characterized. Since control of the d-spacing is critical for higher reflectivity, an effective and accurate d-spacing measurement technology is required. Even though cross-sectional transmission electron microscopy (TEM) and low-angle X-ray diffraction (XRD) are standard methods in evaluating multilayers, they provide different d-spacing values from each other. Cross-sectional TEM images can give a direct measurement of the individual layer, but cannot describe the optical behavior of the multilayer. On the contrary, low-angle XRD analysis can provide an effective d-spacing, which includes the non-ideal factors. As a result, low-angle XRD can predict the EUV peak position more precisely than TEM analysis. Additionally, Ru/Mo/Si multilayers were deposited and characterized. These exhibit interfacial layer structures and reflectivities superior to those of Mo/Si multilayers.