Stress relaxation of passivated aluminum line metallizations on silicon substrates

In the present study, the Eshelby theory of inclusions is applied to model the stresses arising after heat treatment at 400 °C in aluminum line metallizations, embedded in silicon/passivation matrix. The stresses obtained are about 200 MPa higher than the ones previously reported. Moreover, the stresses in the axial and width directions of the lines are shown to be on the same order, while the normal stress is smaller, especially in the lines of low thickness-to-width ratio. A modification of the familiar sin2 ψ method of x-ray stress measurement is presented to deal more accurately with the [111]-fiber texture present in the aluminum lines studied. The lateral and normal stresses in the aluminum metallizations after a heat treatment at 400 °C are measured in room temperature by x-ray diffraction from 4 h after the heat treatment at 400 °C up to 3 months. The experimental results are well in accord with predictions obtained from the Eshelby model. Particularly, the lateral stresses are found to be about equal, while the initial normal stress is smaller, but eventually becomes the largest stress component. Dislocation mechanisms to rationalize the present observations are discussed: at longer times, diffusion-controlled dislocation climb and void growth connected to it appear to be the most important mechanisms to relieve the stress, while during cooling dislocation glide is also significant.