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

TL;DR

This study investigates the thermal stability of Mg/Co multilayers used in EUV applications, showing that reflectivity degrades above 300°C due to morphological and chemical changes in the multilayer structure.

Contribution

It provides a comprehensive analysis of the structural, chemical, and optical stability of Mg/Co multilayers under high-temperature annealing, highlighting the temperature threshold for reflectivity loss.

Findings

Reflectivity decreases above 300°C

Morphological changes occur at 305°C

Chemical state alterations are observed in Mg and Co

Abstract

We present the results of the characterization of Mg/Co periodic multilayers and their thermal stability for the EUV range. The annealing study is performed up to a temperature of 400\degree C. Images obtained by scanning transmission electron microscopy and electron energy loss spectroscopy clearly show the good quality of the multilayer structure. The measurements of the EUV reflectivity around 25 nm (~49 eV) indicate that the reflectivity decreases when the annealing temperature increases above 300\degreeC. X-ray emission spectroscopy is performed to determine the chemical state of the Mg atoms within the Mg/Co multilayer. Nuclear magnetic resonance used to determine the chemical state of the Co atoms and scanning electron microscopy images of cross sections of the Mg/Co multilayers reveal changes in the morphology of the stack from an annealing temperature of 305\degreee;C. This explains the observed reflectivity loss.