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Abstract

Thermal fatigue failure of metallization interconnect lines subjected to alternating currents (AC) is becoming a severe threat to the long-term reliability of micro/nanodevices with increasing electrical current density/power. Here, thermal fatigue failure behaviors and damage mechanisms of nanocrystalline Au interconnect lines on the silicon glass substrate have been investigated by applying general alternating currents (the pure alternating current coupled with a direct current (DC) component) with different frequencies ranging from 0.05 Hz to 5 kHz. We observed both thermal fatigue damages caused by Joule heating-induced cyclic strain/stress and electromigration (EM) damages caused by the DC component. Besides, the damage formation showed a strong electrically-thermally-mechanically coupled effect and frequency dependence. At lower frequencies, thermal fatigue damages were dominant and the main damage forms were grain coarsening with grain boundary (GB) cracking/voiding and grain thinning. At higher frequencies, EM damages took over and the main damage forms were GB cracking/voiding of smaller grains and hillocks. Furthermore, the healing effect of the reversing current was considered to elucidate damage mechanisms of the nanocrystalline Au lines generated by the general AC. Lastly, a modified model was proposed to predict the lifetime of the nanocrystalline metal interconnect lines, i.e., that was a competing drift velocity-based approach based on the threshold time required for reverse diffusion/healing to occur.

Cu/Ni laminated composites with a thickness ratio of the Cu layer to the nanocrystalline Ni layer of 1:20 are prepared by the dual-bath electrodeposition technique. Tensile and fatigue tests are performed at room temperature. The results show that the laminated composites not only have a better synergy of the tensile strength and ductility, but also the higher fatigue strength than the pure Ni counterpart sheets. The introduction of the ultrathin Cu layer into the composite may play a key role in enhancing the ductility and the fatigue cracking resistance. The basic mechanisms for the blunting at the crack tip in the laminated composites are discussed.