A tracking ellipsometer of picometer sensitivity enabling 0.1% sputtering-rate monitoring of EUV nanometer multilayer fabrication

An automatic ellipsometer of picometer sensitivity has been developed for sputtering rate monitoring of extreme ultraviolet multilayer fabrication. With the automatic ellipsometer, the relative amplitude attenuation ρ were measured at every 0.2 s during fabrication of a periodic multilayer composed of a 2.9-nm Mo layer and a 4.0-nm Si layer. The recorded data plotted with calibrated thickness by X-ray diffractometry proved the picometer sensitivity needed for 0.1% reflection wavelength matching of the mirror multilayers of nanometer periods