Failure mechanism study for high resistance contact in CMOS devices

In advanced CMOS manufacturing, when aspects including contacts with W plugs are being miniaturised, high resistance contacts causing low yield becomes a common issue. In failure analysis, contact failures such due to insufficient trench etching and particle blocking which can cause extremely high resistance or opens are relatively easy to isolate and identify. However, for those contacts with resistance marginally higher than normal, the root cause is very difficult to identify by traditional methods like passive voltage contrast (PVC) and scanning electron microscopy (SEM), or focused ion beam (FIB) technology, which is quite successful for the open contact cases. This contact resistance variation is normally due to the narrow process window or process parameters drifting and may lead to relatively low yield. Direct observation of these contacts by transmission electron microscopy (TEM) provides detailed microstructural and chemical information which correlates to the failure and are unobtainable by other material analysis techniques. In this paper, we report a novel failure mechanism of the high resistance contact revealed by TEM study. Direct evidence is provided to show the impact of process changes on the contact structure which may correlate to the high resistance.