Development and Interfacial Characterization of Co/Mg Periodic Multilayers for the EUV Range

Abstract

Reprinted with permission from (J. Phys. Chem. C, 2010, 114 (14), pp 6484-6490). Copyright (2010) American Chemical Society.International audienceWe propose a new system, namely the periodic Co/Mg multilayer system, for optics applications in the EUV range. Close to the Mg L edge, i.e., around a wavelength of 25 nm or a photon energy of 50 eV, a reflectivity of about 43% is measured at 45° for s-polarized radiation. Moreover, it appears that this system is stable over a period of time of three months. The introduction of thin boron carbide interfacial layers proves disastrous contrary to simulations that show this could be beneficial. We combine X-ray reflectivity in the hard X-ray range, X-ray emission spectroscopy, and nuclear magnetic resonance to determine the thickness and roughness of the Co and Mg layers as well as the chemical state of the Co and Mg atoms at the interfaces. This reveals that in the Co/Mg system the interfaces are abrupt and there is no interdiffusion between the Co and Mg layers. Then the difference between the experimental and simulated reflectivities is ascribed to the interfacial roughness of the order of 0.4 nm. In the Co/Mg/B4C system, evidence of a large mixing of the Co and B4C layers is presented and explains the poor reflectance of this system

Investigation of the thermal stability of Mg/Co periodic multilayers for EUV applications

“…An additional line is observed at 156 MHz for the multilayer without annealing and for the sample annealed at 280°C in Figure 7(b). This line has been identified in our previous work with the Co atoms situated at perfect interfaces between Co and Mg atoms [1]. The overall shape of the spectrum after annealing at 280°C is very similar to that observed for the as deposited sample.…”

Introduction of Zr in nanometric periodic Mg/Co multilayers

“…Then, the discrepancy could be due to the different penetration depth or to the different power spectral densities of the interface roughness of the layer surface; the presence of highly reactive materials, as for example Mg, could induce the formation of interface compounds whose optical properties are also not well known. Concerning this latter argument, we have recently demonstrated that in Co/Mg the interfaces are abrupt [3].…”

“…Nevertheless, in our recent study on Co/Mg/B 4 C multilayers, nuclear magnetic resonance (NMR) spectroscopy has allow us to evidence a strong intermixing between Co atoms and B and/or C atoms from B 4 C layers leading to a reflectivity of 0.7% at 25.1 nm [3].…”

“…We are interested in the design, the development and the characterization of multilayered mirrors exhibiting high reflectance values in the extreme ultraviolet (EUV) range [1][2][3][4]. To that purpose, we explore different ways as for instance the introduction of a third material within a bilayered structure and the effect of annealing.…”

“…We have recently shown that Co/Mg multilayers exhibit a reflectance value equal to 42.6% at 25.1 nm [3]. To enhance the performance of this system, in the following we present the comparative analysis of the optical performances in the EUV spectral range of bi-, tri-and quadri-layered structures based on Mg, Co and Zr.…”