Large area Mo/Si multilayer (ML) mirrors with high reflectivity are fabricated using magnetron sputtering deposition system. Thin film growth is optimized for film roughness, density, and interface quality by changing process parameters through fabrication of thin films. Mo/Si MLs are fabricated with varying thickness ratio, number of layer pairs, and periodicity from 0.3 to 0.45, 5 to 65, and 40 to 100？？, respectively. The samples are characterized using hard X-ray reflectivity and transmission electron microscopy. Soft X-ray performance tests of MLs are done by soft X-ray reflectivity using Indus-1 synchrotron radiation. ML coating with thickness errors of ~0.03% per layer and interface roughness in the range of 2 to 5？？ has been realized. The lateral variation of the periodicity is controlled within 0.5？？ over the ？mm2 area of the plane substrate by using substrate motion and appropriate masking arrangement. Maximum variation of periodicity from run to run is less than 0.5？？. Peak reflectivity of ~63% at wavelength of ~127 ？ is achieved for incident angle of 71 degree. 1. Introduction X-ray multilayer (ML) mirror is a one dimensional artificial Bragg reflector [1]. It bridges between naturally occurring crystal optics and total reflection optics. The former gives excellent energy resolution however integrated reflectivity is small because of narrow rocking curve. The later gives high reflectivity at extremely small glancing incidence geometry and acts as energy cutoff reflector. X-ray ML mirror provides high integrated reflectivity with moderate spectral bandpass. ML mirror has reasonable high acceptance angle compared to total reflection optics in hard X-ray region, and also gives normal incidence optics in soft X-ray /extreme ultra violet spectral range. The main advantages of ML mirrors stem from the tunability of period thickness, composition, lateral and in-depth gradient of periodicity; these can be tailored according to the desired incidence geometry and wavelength regime. Furthermore, ML mirrors have the advantage of being used for focusing and imaging applications by depositing structures on figured surface. However, fabrication of these ML mirrors is a challenging task. It requires deposition system capable of fabricating uniform, ultrathin smooth layer (~8 to 50？？) with thickness control on atomic scale, and number of layer pairs ranging from ~50 to 500. This task becomes more stringent in case of large area ML for device applications. Large area MLs have different potential applications such as soft X-ray/extreme ultra violet (EUV)
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