Triple-wavelength, narrowband Mg/SiC multilayers with corrosion barriers and high peak reflectance in the 25-80 nm wavelength region

Mónica Fernández-Perea,Juan I Larruquert,Jose A Méndez,Regina Soufli,Jeff C Robinson,Eric M Gullikson,Luis Rodríguez De Marcos

doi:10.1364/oe.20.024018

Abstract

We have developed new, Mg/SiC multilayer coatings with corrosion barriers which can be used to efficiently and simultaneously reflect extreme ultraviolet (EUV) radiation in single or multiple narrow bands centered at wavelengths in the spectral region from 25 to 80 nm. Corrosion mitigation was attempted through the use of Al-Mg or Al thin layers. Three different multilayer design concepts were developed and deposited by magnetron sputtering and the reflectance was measured at near-normal incidence in a broad spectral range. Standard Mg/SiC multilayers were also deposited and measured for comparison. They were shown to efficiently reflect radiation at a wavelength of 76.9 nm with a peak reflectance of 40.6% at near-normal incidence, the highest experimental reflectance reported at this wavelength for a narrowband coating. The demonstration of multilayer coatings with corrosion resistance and multiple-wavelength EUV performance is of great interest in the development of mirrors for space-borne solar physics telescopes and other applications requiring long-lasting coatings with narrowband response in multiple emission lines across the EUV range.

Highlights

In recent years, multilayer coatings with high near-normal-incidence reflectance in the extreme ultraviolet (EUV), defined here as the wavelength region from 10 to 100 nm, have enabled tremendous advances in the development of instrumentation for a wide range of applications and disciplines, from microchip production with EUV lithography to the observation of solar processes with space-borne telescopes
We have developed new, Mg/SiC multilayer coatings with corrosion barriers which can be used to efficiently and simultaneously reflect extreme ultraviolet (EUV) radiation in single or multiple narrow bands centered at wavelengths in the spectral region from 25 to 80 nm
All EUV reflectance measurements were performed within a period of 1 to 3 months after deposition of the samples, so the effects of hydrocarbons and native oxides on the top multilayer surface are likely to be present in these measurements

Summary

Introduction

Multilayer coatings with high near-normal-incidence reflectance in the extreme ultraviolet (EUV), defined here as the wavelength region from 10 to 100 nm, have enabled tremendous advances in the development of instrumentation for a wide range of applications and disciplines, from microchip production with EUV lithography to the observation of solar processes with space-borne telescopes. Mg/SiC is a remarkable material pair because (i) Mg absorption remains relatively low across a wide EUV wavelength range, beginning at 25 nm (the Mg 2p edge) and extending up to about 115 nm, (ii) there is good optical contrast between the Mg and SiC materials, and (iii) the Mg-SiC interfaces are sharp and stable This allows for efficient and simultaneous reflection of radiation in multiple narrow bands centered at wavelengths in the spectral region from 25 to 80 nm. The Al and Mg layers spontaneously intermix to form a partially amorphous Al-Mg layer which provides efficient corrosion protection while, due to the Al transparency below 83 nm, maintaining the favorable optical properties of the original, unprotected Mg/SiC multilayer The efficacy of this corrosion protection concept was verified experimentally on Mg/SiC films aged for 3 years. The same concepts used here to demonstrate triple-wavelength coatings can be adapted for singleand double-wavelength applications

Multilayer design

Experimental techniques

Results and discussion

Conclusions