Residual stress and thermal stress observation in thin copper films

Abstract

Internal stresses in thin copper films with or without passivation were investigated by the diffraction method using an in-lab X-ray apparatus and a synchrotron radiation system. The in-lab X-ray stress equipment primarily measures the stresses m films thicker than 100 nm, whereas the synchrotron radiation system can measure stresses in films as thin as 8 nm. The residual stresses in the copper films were tensile in all cases. Thermal stress development was investigated in the heating and cooling processes. In the case of thick films, the internal stress decreased to the compressive side in an early stage of the heating process followed by non-linear behavior. In the cooling stage, the stresses in the film changed to tensile and increased to the final state at room temperature. The stress difference between the heating and cooling cycle was shown as a hysteresis loop in thick films. A thin film exhibits neither hysteresis loop nor a non-linear relation in a thermal stress change during a thermal cycle.