The effect of the graded bilayer design on the strain depth profiles and microstructure of Cu/W nano-multilayers
A. V. Druzhinin, Giacomo Lorenzin, D. Ariosa, Sebastian Siol, Boris B. Straumal, Jolanta Janczak‐Rusch, Lars P. H. Jeurgens, Claudia Cancellieri
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.