Interface-engineered EUV multilayer mirrors

Most applications of Mo/Si multilayer optics in EUV lithographic systems require a high normal-incidence reflectivity. Using dc-magnetron sputtering we achieved R = 68.8% at the wavelength of 13.5 nm. Different interface-engineered Mo/X/Si/X multilayers with a maximum reflectivity of 69.6% were developed. These new multilayer mirrors consist of molybdenum and silicon layers separated by different interdiffusion barriers (X = C and SiC). The Mo/C/Si/C interface-engineered mirrors were optimized in terms of high peak reflectivity at a wavelength near 13.5 nm (Rp {greater than or slanted equal to} 60.0%) and broad operating temperature range (T = 20-500 °C). The best results were obtained with 0.8 nm thicknesses of carbon interlayers on both interfaces. The combination of good optical properties and high thermal stability of interface-engineered Mo/C/Si/C multilayer mirrors underlines their potential for their use in EUV optics.