The disclosure is directed to multilayer Mo/Si coatings for reflective mirrors used in extreme ultraviolet lithographic systems and to a method of making such mirrors using plasma ion assisted deposition (PIAD) techniques. The coating are deposited on a substrate suitable for EUV lithography, and are Mo/Si coating consisting of 40-100 Mo/Si periods, each period consisting on a Mo layer followed by a Si layer. Each of the individual Mo and Si layers is deposited to a specified or target thickness in the range of 2 nm to 5 nm, and the thicknesses are controlled to ±0.1 nm. A plasma from a plasma source is used to densify and smooth the substrate prior to deposition of the coating, and each layer of the coating is plasma densified and smoothed.