Stress-induced Void Formation in Passivated Cu Films

摘要

In this paper, we investigated void formation in passivated Cu films focusing on the kinetics of void formation under isothermal annealing as a function of temperature. Interestingly, we found that the kinetics of void formation in Cu films is consistent with that observed in Cu lines, which is driven by the combined effect of thermal stress and mass transport resulting in a peak growth rate at about 250℃. To analyze the observed results, we have calculated the stress state at the < 111 > / < 200 > Cu grain boundary to demonstrate the existence of a localized triaxial stress state as a result of elastic anisotropy. To account for void density, x-ray analysis was performed to measure the grain texture using inverse pole figure plot and the result can account for the void density observed. A kinetic model was used to analyze void growth under isothermal annealing. A threshold stress of about 40MPa was deduced for void growth in passivated Cu films with an activation energy of 0.75 eV.