Mechanical reliability of CVD-copper thin films

Stress measurements on 0.5 mu m copper films (with optional SiO2/TiN passivation) on Si(100) have been performed during thermal cycling between 50 and 400 degrees C, During annealing the film stress follows the thermal stress as calculated from the thermomechanical properties of copper, silicon dioxide and silicon. A deviation from linear behaviour is found which is caused by plastic deformation (strengthening and relaxation). After the first anneal the stress temperature dependence is very similar in both sample types indicating that the deformation processes are alike. The actual stress values in the individual Cu, SiO2 and TiN/Ti layers at 50 degrees C are found: sigma(Cu) = 1.0 (+/- 0.2) GPa, sigma(SiO2) = - 0.35 (+/-0.05) GPa, and sigma(TiN/Ti) = 0.07 (+/-0.05) GPa. Annealing at constant temperature shows that in passivated and non-passivated Cu stacks stress relaxation occurs at any temperature (between 50 and 400 degrees C). From stress measurements on individual SiO2 and (SiO2 + Ti/TiN) layers it is shown that relaxation takes place primarily in the CVD-Cu layer.