The thermomechanical behavior of Cu thin films, 600–1125 nm thick and encapsulated between SiNx barrier and SiNx or AlNx passivation layers on silicon substrates, was studied during thermal cycling between room temperature and 400 or 500 °C using the substrate curvature method. Films were prepared with varying oxygen contents, and the distribution of oxygen through the thickness of selected films was studied before and after thermal cycling using secondary ion mass spectrometry. Large variations in the thermomechanical behavior with oxygen content were found and correlated with segregation of oxygen to the film/barrier and film/passivation interfaces. These variations are thought to be due to recovery of stored misfit dislocation energy, which is, in turn, controlled by oxygen in the film. Effects of oxygen on film deformation through variations in interfacial adhesion and diffusion-induced dislocation glide are considered.