Phase reactions at semiconductor metallization interfaces

During, or following, the fabrication of a microelectronic device, it is possible for the material phases at critical interfaces to react with one another, and so alter the elec-trical performance. This is particularly important for metallization contacts to semi-conductors and for multilevel interconnects. The present article shows that application of phase diagram principles can successfully predict the mutual stability or chemical reactivity in such circumstances. Since most relevant phase diagrams are not available, it is shown how they may be calculated from known thermochemical data, or deduced from observations on thin-film reactions. The article is illustrated by the behavior of titanium silicide with a diffusion barrier layer (TiN) and the surrounding dielectric SiO₂. In addition the Al-Si-O-N and W-N-Ga-As systems are described, and metastable amor-phous phase formation at the Ti-Si interface is discussed.