A new type of dislocation mechanism in ultrathin copper films

In this study of thin film plasticity, the relationship between thermomechanical behavior and dislocation motion has been investigated in copper constrained by a silicon substrate. The stress-temperature behavior as determined from wafer curvature experiments has been directly compared to deformation microstructures observed during in situ thermal cycling of plan-view specimens in the transmission electron microscope. The flow stress of copper films with thicknesses ranging from 100 nm to 400 nm was found to be constant, indicating that strengthening mechanisms may be saturated in this thickness regime. Moreover, unexpected dislocation glide on a plane parallel to the film surface, which should experience no resolved shear stress, provides potential evidence for the occurrence of constrained diffusional creep in a 270 nm film.