Investigation of electromigration in micrometer-scale metal wires by in-situ optical microscopy

Electromigration-induced gap formation of μm-scale Au wires was investigated by in-situ optical microscopy. The crack growth and gap formation occurred rapidly with increasing the average power dissipated in the wires during electromigration (EM). We visualized the thermal distribution of passivated Au wires during EM. Heating process of the wires was clearly observed through the color variation of the passivation film due to Joule heating. In particular, slow gap formation and gradual color transition were clearly observed under feedback-controlled EM (FCE) procedure. The color transition area was proportional to the average power during EM. Moreover, in-situ imaging of heating in 300-μm-scale graphite and 30-μm-scale W wires was also studied using near-infrared (NIR) microscopy with a low-cost, standard charge coupled device (CCD) detector. In-situ observations based on optical microscopy are useful methods for the investigation of EM in μm-scale metal wires.