Metallurgical Techniques for More Reliable Integrated Circuits

One of the primary concerns in the manufacture of advanced microelectronic devices is to ensure that metallic contacts and interconnects do not fall by electromigration or stress-induced voiding. This article discusses the metallurgical techniques that can be used to improve resistance to these two failure modes. In the laboratory the microstructures of the thin-film interconnects can be controlled by simple heat treatments to improve reliability. In the manufacturing environment, however, beneficial heat treatments are difficult to implement since they must either be part of the normal fabrication process, or must fit within the "windows" it provides. Moreover, the various thermal cycles that are part of the chip manufacture and packaging processes also change the microstructure, in ways that may obliterate the beneficial effects of tailored heat treatments. In the following, we discuss the possibility of implementing two kinds of beneficial treatments within normal manufacturing processes: (1) treatments that modify grain structure to minimize failures through diffusional flux divergence, and (2) treatments that control solute and precipitate distributions to avoid undesirable "overaged" microstructures at the end of manufacturing.