Thin film Ni-Cu diffusion couples (individual layer thicknesses: 50nm) have been prepared by DC-magnetron sputtering on silicon substrates coated with amorphous inter-layers (Si3N4). The microstructural development and the stress evolution during diffusion annealing have been investigated employing ex-situ and in-situ X-ray diffraction, transmission electron microscopy and Auger-electron spectroscopy (in combination with sputter-depth profiling).
Annealing at relatively low temperatures (175°C to 350°C) for durations up to about 100 hours results in considerable diffusional intermixing. The stress changes in the bilayer system during heating and isothermal annealing have been investigated employing ex-situ and, in particular, in-situ X-ray diffraction stress measurements and have been compared to corresponding results obtained for single layers of the components in the Ni-Cu bilayers system, produced under conditions identical to those employed for the sublayers of the diffusion couple. The specific residual stresses that develop due to diffusion between the (sub)layers in the bilayer could then be identified by comparing the stress evolutions upon annealing of the single layers with those recorded for the sublayers of the bilayer. The obtained stress data are discussed in terms of possible mechanisms of stress generation.