Stress evaluation in thin films: Micro-focus synchrotron X-ray diffraction combined with focused ion beam patterning for do evaluation

•In situ deformation study of laminate polycrystalline W–Cu thin films•Focused ion beam (FIB) patterning of an array of “islands” on thin films surface•X-ray diffraction on island-patterned region•Constant strain on “islands” independently of the deformation of the substrate

Nanocrystalline metallic coatings of sub-micron thickness are widely used in modern microelectronic applications. In X-ray diffraction experiments to determine both the residual and applied stresses in nanocrystalline coatings, one difficult challenge that comes up invariably is the determination of the strain-free lattice spacing do. The present study addresses this challenge by using the focused ion beam (FIB) to generate a built-in strain-free reference by patterning (milling) a 50 × 50 μm2 region of the coating to produce an array of small stress-relieved “islands” ~ 0.8 × 0.8 μm2 each. Transmission X-ray diffraction setup was used for data collection at DIFFABS beamline (Synchrotron SOLEIL, France). A 150 nm-thick multi-layered W–Cu nano-composite thin film on polyimide (Kapton®) substrate was studied. The samples were loaded incrementally using a compact uniaxial loading device, and micro-beam diffraction data were collected on and away from the reference array. It was shown experimentally that the “island” array remained approximately strain free throughout the experiment, providing an on-board do lattice spacing reference. The changing lattice spacing d in the coating was also monitored away from the array, to deduce the elastic strain evolution during deformation. The results and their implications are presented and discussed.