Transmission Electron Microscopy Observation of CoSix Spikes in Si Substrates during Co-silicidation Process

Needle-like spikes penetrating into Si substrates have been detected by cross-sectional transmission electron microscopy (TEM) studies of Co silicide/Si interfaces. The spikes are crystalline CoSi x and form at annealing temperatures of 400–425° C, when the transformations of Co→Co 2 Si and Co 2 Si→CoSi are both taking place. They sometimes extend to the p/n junction depth of 100 nm. During annealing at above 500° C, they become spherical and their density decreases. The temperature range in which CoSi x spikes are formed and extend to near the junction depth corresponds well with that for the onset of junction leakage. Therefore, this supports the conclusion that Co silicide junction leakage is caused by such spike formation.