High Current Effects in Silicide Films for Sub - 0 . 25 pm VLSI Technologies

Characterization and modeling of high current conduction in Ti& and COSz films formed on n+ Si and n+ polySi under DC and pulsed stress conditions is reported for the first time. High current conductance of silicides is shown to be strongly affected by the technology and process conditions. The non-linear I-V characteristics of silicide films under DC and pulsed high current stress has been modeled and the nonlinearity has been shown to be due to self-heating. Two physical parameters, B and h, associated with DC and pulsed current stress, have been shown to be able to describe the sensitivity of the films to high current conduction. At high currents, an abrupt lowering of the resistance of the silicided structures is observed. Detailed analysis of the evolution of this resistance drop has been made. It is shown that the cause is related to the melting of the structures, which also causes degradation in the post-stress silicide film resistance. The critical current for these failures have been shown to be strongly influenced by the silicide film width and the time duration of the pulse. CoSi, films and films on poly-Si are shown to be more sensitive to high current conduction and degradation.