The effect of thermal treatment on the stress state and evolving microstructure of Cu/W nano-multilayers

Abstract

The functionality and reliability of nano-multilayered devices and components are largely affected by the stress evolution during fabrication, processing, and operation. The impact of thermal treatment on the stress state and evolving microstructure of Cu/W nano-multilayers, as deposited on different substrates (i.e., Si(001), Al2O3-C, and Al2O3-R) by magnetron sputtering, was investigated by in-situ high temperature X-ray diffraction and high-resolution scanning electron microcopy. The as-deposited Cu and W nanolayers exhibit an out-of-plane orientation relationship according to Cu 〈111〉∥ W 〈110〉. On the Al2O3-C and Al2O3-R substrates, the Cu/W nanomultilayers also develop a pronounced in-plane texture given by Cu {111} 〈101〉∥ W {110} 〈001〉. The stress state of the Cu nanolayers in the as-deposited state and upon heating, investigated ex-situ, is largely imposed by the accumulated stresses in the much stiffer W nanolayers. In the as-deposited state, the W nanolayers exhibit a much larger in-plane compressive stress than the Cu nanolayers (i.e., −3.5 GPa versus −1.5 GPa), which both mainly originate from growth stresses generated during the deposition process. The growth stresses in the as-deposited Cu nanolayers are relaxed after annealing at 500 °C. Relief of compressive stresses in the W nanolayers is accompanied by grain coarsening which only occurs upon degradation of the nano-multilayered structure. The degradation of the periodic layer structure proceeds in the range of 750 − 900 °C and is independent of the substrate.