Structure, thermal stability and extreme ultraviolet performance of Mo/Y multilayers

• We studied Mo/Y multilayers that were fabricated at non-ultrahigh vacuum system.
• EUV reflectance of Mo/Y increases with lower base pressure, up to a maximum of 36%.
• Mo/Y multilayer period is almost constant during annealing up to 500 °C.
• Mo/Y interface is broadened with interfacial amorphization after annealing.
• Different vacuums in fabrication change the thermal dynamic properties of Mo/Y.

The extreme ultraviolet (EUV) performance of Mo/Y multilayer mirrors is known to be dependent on the base pressure before deposition. In this work, Mo/Y multilayers were fabricated at non-ultrahigh vacuum system with a base pressure of 8.0 × 10− 4 Pa to 2.0 × 10− 5 Pa. The multilayer structure and corresponding EUV reflectance were measured while a maximum value of 36% was achieved at λ = 11.3 nm (E = 110 eV). Thermal stability of the fabricated multilayer was studied by annealing the sample at different temperatures from 100 °C to 500 °C. Grazing incidence X-ray reflectance measurements and high resolution transmission electron microscopy revealed that the layered structure and its hard X-ray reflectivity were preserved although the interface area was increased at elevated temperatures. The broadened interfaces can be explained by a solid state amorphization effect. Unlike the reported results before, the multilayer period was almost constant during annealing up to 500 °C, indicating a better thermal stability.