We report on the growth of low defect density Mo/Si multilayer (ML) coatings. The coatings were grown in a deposition system specifically designed for extreme ultraviolet lithography mask blank fabrication. Complete, 81 layer, high reflectance Mo/Si ML coatings were deposited on 150 mm diam (100) oriented Si wafer substrates using ion beam sputter deposition. Process added defect densities correspond to 2x10(-2)/cm(-2) larger than 0.13 mu m as measured by optical scattering. This represents a reduction in defect density of Mo/Si ML coatings by a factor of 10(5).