Structural characteristics and performances of rf-sputtered Mo/Si and Co/Si multilayers for soft x-ray optics

Precise structural analysis of Mo/Si multilayers deposited by a diode rf-sputtering system has been made using in-situ kinetic ellipsometry, grazing x-ray reflection, x-ray diffraction, Auger profile analysis, Rutherford backscattering, and high-resolution electron microscopy. The main structural imperfections (interface roughness and interdiffusion) have been related to the Mo crystallization and to the molybdenum silicide formation at the interfaces. The comparison to Co/Si multilayers deposited in the same conditions was useful to deduce the influence of the intrinsic properties of these systems on their structural behavior. Silicide layers are formed in real-time during the growth of the samples. They are completely amorphous and their composition is not far from defined compounds (MoSi2 and CoSi2). In Mo/Si multilayers the Mo on Si interface is always thicker than the other interface (approximately equals 15 angstrom compared to 8 angstrom). It is not due to the deposition conditions but to the crystallization of the molybdenum layers which reduces the silicon diffusion at the Si on Mo interface. The higher reactivity of cobalt with silicon produces thicker quasi-symmetric silicide layers (approximately equals 25 angstrom). The thermal behavior of the two systems is also controlled by the interdiffusion and the crystallization of the silicide layers. Absolute soft x-ray reflection was measured on different Mo/Si x-ray mirrors by synchrotron radiation at various wavelengths above the Si L-(alpha) line and related to the structural characteristics. In spite of the occurrence of thin silicide layers at each interface, reflectivities as high as 55% in normal incidence have been obtained at 130 angstrom.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.