Analysis of periodic Mo/Si multilayers: influence of the Mo thickness

TL;DR

This study investigates how varying Mo layer thickness in Mo/Si multilayers affects their optical properties and surface roughness, revealing a transition from amorphous to crystalline states influences the multilayers' structure and performance.

Contribution

It provides detailed analysis of the impact of Mo thickness on multilayer structure, composition, and roughness, highlighting the amorphous to crystalline transition effects.

Findings

Refractive index varies with Mo thickness due to phase transition.

Interfacial layer parameters remain stable across different Mo thicknesses.

Lateral roughness correlation length decreases as Mo becomes crystalline.

Abstract

A set of Mo/Si periodic multilayers is studied by non destructive analysis methods. The thickness of the Si layers is 5 nm while the thickness of the Mo layers changes from one multilayer to another, from 2 to 4 nm. This enables us to probe the effect of the transition between the amorphous to crystalline state of the Mo layers near the interfaces with Si on the optical performances of the multilayers. This transition results in the variation of the refractive index (density variation) of the Mo layers, as observed by x-ray reflectivity (XRR) at a wavelength of 0.154 nm. Combining x-ray emission spectroscopy and XRR, the parameters (composition, thickness and roughness) of the interfacial layers formed by the interaction between the Mo and Si layers are determined. However, these parameters do not evolve significantly as a function of the Mo thickness. It is observed by diffuse scattering at 1.33 nm that the lateral correlation length of the roughness strongly decreases when the Mo thickness goes from 2 to 3 nm. This is due to the development of Mo crystallites parallel to the multilayer surface.