Multilevel metallization of very large-scale integrated (VLSI) circuits has become an area of intense research interest as devices are scaled down in order to increase circuit density. As device dimensions approach the submicron regime, reliability becomes more of an issue. Metallization generally requires good conductivity, electromigration resistance, controllable contact performance, corrosion resistance, adherence, thermal stability, bondability, ability to be patterned into a desirable geometry, and economic feasibility.

Aluminum and its alloys have been commonly used as the main metallization materials because they meet most of the metallization requirements for microelectronic devices. Aluminum, however, suffers from major limitations, such as elec-tromigration and stress-voiding induced open-circuit failure. For the development of ultralarge-scale integration (ULSI) for fast-switching-speed devices, the electrical resistivities of aluminum and its alloys are not low enough. As the minimum geometry is scaled down to one-quarter micron, aluminum and its alloys potentially will be replaced by other materials such as Cu, Au, or superconductors for on-chip interconnection.