The effect of the graded bilayer design on the strain depth profiles and microstructure of Cu/W nano-multilayers

A.V Druzhinin,G Lorenzin,D Ariosa,S Siol,B.B Straumal,J Janczak-Rusch,L.P.H Jeurgens,C Cancellieri

doi:10.1016/j.matdes.2021.110002

Abstract

The properties and thermal stability of thin films and nano-multilayers (NMLs) are generally governed by the in-depth stress (strain) gradients rather than the average stress state. The effect of strain gradient variation in Cu/W NMLs on the thermal stability between 400 and 800 °C was investigated. The strain distribution in the NML stacks was varied by combining Cu/W bilayers with different Cu and W thicknesses of either 3 or 10 nm. A recently developed method based on in-plane grazing X-ray diffraction was adopted to extract the strain depth profiles. In addition, the evolution of the average stress in the Cu/W NMLs during growth was monitored by an in-situ wafer curvature technique. The mean residual stresses in Cu and W were found to be independent of the disposition of the different Cu/W bilayer substacks. On the contrary, the strain depth profile of the W nanolayers was found to strongly depend on the disposition of Cu/W bilayer substacks in the Cu/W NML, which resulted in different Cu outflow characteristics upon annealing. Moreover, application of different Cu/W bilayer units within the NML stack also provides an innovative pathway for producing Cu/W nanocomposites with graded thermal and mechanical properties.

Highlights

Nano-multilayers (NMLs) are functional architectures which combine nanometer size layers, whose physical properties can be tailored by smart microstructural and interfacial design [1]
For comparison the scanning electron microscopy (SEM) image of the surface of Sub + {10Cu/3W} NML with OTB annealed at 600 °C is presented, where it can be seen that the amount of Cu particles is sufficiently smaller
The strain depth profiles in NMLs were for the first time experimentally accessed by an innovative experimental-modelling approach and compared to the stress measured by the substrate curvature measured during the different nanolayer deposition steps

Summary

Introduction

Nano-multilayers (NMLs) are functional architectures which combine nanometer size layers, whose physical properties can be tailored by smart microstructural and interfacial design [1]. These nanomaterials are of great scientific and technological interest, since their nanolaminated architecture offers very flexible design criteria to achieve a unique combination of optical [2,3], magnetic [4,5], mechanical properties [6,7,8], thermal and electronic conductivity for microelectronic devices [9] and radiation tolerance [10]. Adjusting the initial NML microstructure in order to control the stress depth distribution is one of the key challenges for achieving a stable microstructure with the desired functional properties

Methods

Results

Conclusion