Failure mechanism study for high resistance gate contact in dram devices for 2008 IRPS

Resistive contacts and, in particular, resistive gate contacts in multilayer interconnects have been an ongoing challenge for semiconductor industries. The failing mechanisms behind them were difficult to uncover, which made it necessary to initiate deeper research into each issue that we managed to isolate. The traditional approach of using passive voltage contrast (PVC), scanning electron microscope (SEM), or focused ion beam (FIB) to identify resistance gate contacts is getting more difficult, especially for those contacts with resistance that is only marginally higher than normal contacts. In this paper, we discuss a resistive gate contact issue arising from reliability tests. Finding the root cause for the resistive gate contacts is vital to solving reliability and yield losses. Specifically, we focused on the physical failure analysis to characterize and to uncover the abnormal material behind the resistive gate contacts so we could explain the underdetermined failure mechanism. We established a novel approach to electrical characterization using conductive atomic force microscopy (CAFM). Using transmission electron microscope (TEM), we were able to directly observe the details and to identify the chemical composition of the abnormal, subtle resistive material between the contact and the gate. With these findings, we were able to fully understand the root cause of the failure mechanism and to resolve this issue.