CAFM detection of resistive tungsten contacts in DRAM devices

Resistive 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) [1] 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 the use of CAFM current scanning mode to detect a failing resistive gate contact as well as a failing resistive substrate contact. Finding the root cause for these resistive contacts is vital to solving reliability and yield losses, and that cannot be achieved unless we first find the resistive contacts with great accuracy. This novel approach to electrical fault isolation using conductive atomic force microscopy (CAFM) will enhance the advanced failure analysis techniques which has so far failed to achieve the accurate detection of resistive tungsten contacts.