Stress relaxation in CuNi thin films

Stress relaxation in sputtered and annealed Cu0.57Ni0.42Mn0.01 thin films has been studied at various temperatures. The microstructure of the films stabilized by a thermal cycle to 550 degrees C showed twinned grains of the dimension of the film thickness. Below 200 degrees C, a small low-temperature high-stress plasticity was observed, probably due to obstacle-controlled dislocation glide. Between 300 and 550 degrees C distinct plasticity was detected. This can be described by two relaxation processes with exponentially decreasing stress towards a final value. The activation energies for the two processes agree (0.4 eV/atom), the deformation rates differ by a factor of 10. We suppose that (i) the slower process is flow by grain-boundary diffusion limited as a result of the attachment of the film onto the substrate and (ii) the faster process is mechanical twinning with diffusional accommodation at the grain boundaries. (C) 1999 American Institute of Physics. [S0021-8979(99)06107-1].