We have studied microstructure Mo/Si multilayers grown by RF and DC sputtering at different deposition parameters by cross-sectional transmission electron microscopy and X-ray reflectivity for the wavelength 13.4 nm and 0.154 nm. It is shown experimentally that reflection properties of mirrors are determined by the crystalline state of molybdenum layers. The results are compared for the different samples and discussed in view of the choice an optimal deposition parameters to produce multilayers with a high X-ray reflectivity for the lambda = 13.4 nm.