Articles you may be interested inThe effects of the stress dependence of atomic diffusivity on stress evolution due to electromigration Stress evolution during stress migration and electromigration in passivated interconnect lines AIP Conf. Proc. 305, 231 (1994); 10.1063/1.45694
Microstructure based statistical model of electromigration damage in confined line metallizations in the presence of thermally induced stressesElectromigration is an important concern in very large scale integrated circuits. In narrow, conilned metal interconnects used at the chip level, the electromigration flux is resisted by the evolution of mechanical stresses in the interconnects. Solutions for the differential equation governing the evolution of back stresses are presented for several representative cases, and the solutions are discussed in the light of experimental as well as theoretical developments from the literature.
During the solidification of solder joints composed of near-eutectic Sn–Ag–Cu alloys, the Sn phase grows rapidly with a dendritic growth morphology, characterized by copious branching. Notwithstanding the complicated Sn growth topology, the Sn phase demonstrates single crystallographic orientations over large regions. Typical solder ball grid array joints, 900 μm in diameter, are composed of 1 to perhaps 12 different Sn crystallographic domains (Sn grains). When such solder joints are submitted to cyclic thermomechanical strains, the solder joint fatigue process is characterized by the recrystallization of the Sn phase in the higher deformation regions with the production of a much smaller grain size. Grain boundary sliding and diffusion in these recrystallized regions then leads to extensive grain boundary damage and results in fatigue crack initiation and growth along the recrystallized Sn grain boundaries.
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.
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