The Mechanism of Laser-Induced Vertical Links

Laser-induced vertical links between two metallization levels have provided the restructurable very large scale integrated approach to wafer-scale integration. In this process, interlevel insulation is reacted with molten metallic puddles formed by the application of suitable laser pulses. As a result, the insulating film is locally damaged, and the effected region becomes conductive, thus altering the signal path as desired. We discuss briefly the essential features of laser-beam application to a conductive film in contact with an insulating substrate. Of particular interest is the molten zone that forms at appropriate laser-beam and substrate conditions. We show how thermochemical effects result in low ohmic resistance connections in silicon nitride-based link structure. The understanding gained in this case led to a new possible link structure. Silicon dioxide-based links have been examined. In addition to electrical measurements, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy have been used to examine various properties of the vertical links.