Direct Evaluation of Surface Roughness of Substrate and Interfacial Roughness in Molybdenum/Silicon Multilayers Using Extreme Ultraviolet Reflectometer

In this study, we developed a method of measuring the intensity of rays scattered from a molybdenum/silicon (Mo/Si) multilayer film using an extreme ultraviolet (EUV) reflectometer. We examined the correlations between the peak reflectance, the interfacial roughness of multilayer films, and the substrate roughness. We measured the intensity of scattered rays 13.5 nm from the substrate surface for normal smooth quartz (NSQz), supersmooth quartz (SSQz), and Si substrates using the EUV reflectometer. The intensity of rays scattered from the substrate surface was proportional to the atomic force microscopy (AFM) roughness of the surface. For NSQz, there was a particular strong correlation between the surface roughness determined by AFM and the intensity of scattering rays determined using the EUV reflectometer. However, a week correlation was observed for SSQz and Si. The precisions of the AFM and X-ray reflectivity (XRR) measurement were low for the quartz substrate. A direct measurement of the intensity of rays scattered from the substrate surface was used to estimate the relative surface roughness independent of the substrate material. The EUV reflectivity and intensity of rays scattered from the Mo/Si multilayer films with two deposition geometries were measured using the EUV reflectometer. The peak reflectivity was related to the substrate roughness for each deposition geometry. Moreover, the peak reflectivity was related to the intensity of rays scattered from the multilayer films and was not influenced by the deposition geometry. The results obtained using the EUV reflectometer showed an obvious relationship between the intensity of scattering rays and the interfacial roughness of multilayer films.