Interdiffusion and stress development in Ni-Cu thin film diffusion couples

Thin film Ni-Cu diffusion couples (individual layer thicknesses: 50 mn) have been prepared by direct-current magnetron sputtering on silicon substrates. 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 degrees C to 350 degrees C) for durations up to about 100 hours results in considerable diffusional intermixing. In addition to thermal stresses due to mismatch of the coefficients of thermal expansion of layers and substrate, tensile stress contributions in the sublayers arise during diffusion anneals. The obtained stress data are discussed in terms of possible mechanisms of stress generation.