The influence of the passivation material on stress voiding in Al–Cu alloys

Abstract

Storage tests have been performed to obtain information on the influence of the passivation material and its geometry on the mechanical reliability of Al–Cu lines. During storage tests, the stress in the lines is tensile and depends on the passivation material and passivation geometry. The passivation was either a SiO 2 layer or a SiN x layer. In both cases the influence of a conformal and a planarised passivation geometry has been studied. Passivating the lines with a material with a higher stiffness such as SiN x will increase the stress void density in the lines. Moreover, a conformal passivation layer induces less stress voids in the metal than a planarised passivation, deposited by a Dep/Etch method. The number of stress voids saturates within 24 h at 200°C. However, the voids continue to grow during longer storage times. When the lines are passivated with the lower stiffness material SiO 2, stress voids have not been observed after storage testing.