The deformation characteristics of continuous thin Cu films 0.3-1.0 μm thick on Si substrates with Si3N4 diffusion barriers and passivations have been investigated using substrate curvature and x-ray diffraction methods at room temperature and at temperatures up to 600°C. The stress levels at all temperatures were modelled on the basis of deformation mechanisms used to describe bulk Cu and using mechanisms and model modifications specific to thin films. The Cu films were found to support high stresses at room temperature which depended strongly on the film thickness and presence of a passivation. These stress levels could be adequately modelled by considering both dimensional and microstructural constraints on the glide motion of dislocations. At higher temperatures, the presence of a passivation was seen to change the stress levels reached in a film by one to two orders of magnitude. For unpassivated Cu films, a model based on power law creep could accurately describe stress-temperature data. For passivated films, the addition of a threshold stress to the power law model provides substantial agreement between model and measured data. Exposure of Cu films to small amounts of air or oxygen has a significant effect on thermomechanical behavior. The deformation behavior of differently oriented grains in the films were observed to be quite different from one another. Cu films behave neither like bulk Cu nor like Al thin films. A priori prediction of stress levels in Cu films or patterned structures for use in reliability calculations is not possible at this time.