Extreme-ultraviolet multilayer mirrors deposited using radio-frequency-magnetron sputtering: the influence of self-bias voltage on reflectivity and roughness

Mirrors for the imaging optics of extreme-ultraviolet (EUV) lithography systems require optimal reflectivity. In this paper, results on Mo/Si multilayers for EUV radiation are reported. The multilayers were deposited using radiofrequency-magnetron sputtering; during deposition the self-bias voltages were measured, and the influence of their variation on the multilayer reflectivity and roughness was tested. The samples were characterized using small-grazing-angle x-ray reflectivity and their performance was evaluated by measuring the EUV reflectivity at near-normal incidence. The results show that high reflectivity (> 67%) and low roughness values (<2.5 Angstrom) can be obtained, depending on the stability of the self-bias voltage during deposition.