Plastic packaging stress induced failures in TiW/Al-Si metal to silicide contacts

The effects of long-term temperature/humidity stress on a TiW/Al-Si-TiSi₂ metal contact system were investigated. Plastic packaged DRAM test sites were subjected to conventional unbiased humidity testing procedures which induced electrical opens. Failure analysis showed these opens to occur in the contact region. The nature of this phenomenon was studied. It was found that plastic-package-induced shear stress causes plastic deformation of Al-Si and forces it into the contact hole. The mass built up inside the contact hole increases, causing an alloy formation, and can eventually lift the metal from the diffusion surface, causing the electrical open circuit to occur. One proposed solution is to enhance the protective overcoat´s ability to absorb this stress and thus minimize its transmittal to the metallization system