FIB lift-out STEM failure analysis technique

Abstract

Device fabrication with reduced linewidths makes it possible for smaller defects to affect device performance. The availability of 5-7 nm diameter focused ion beams has made it possible to expose most defects of interest for analysis using EDS or AES. However, device dimensions have become so small that even the site specific capability of the FIB can be challenged. The beam current at 7 nm resolution is not sufficient to perform significant material removal, therefore larger diameter beams are required. Failure analysis techniques are often unable to locate the region of interest better than within a few tenths of a micron. As this region is sputtered using the FIB, frequent checks are made to determine if the feature is visible. Unfortunately, it is quite possible in the case of small features to essentially remove most if not all of the material so that elemental identification is not possible. To resolve this problem, a method was developed to combine the features of the FIB to prepare a specimen for lift-out and the features of a scanning transmission electron microscope (STEM). This allows the gathering of information from a specimen of a thickness that would not be viewable in a conventional TEM, but is resolvable with the STEM due to its unique lens configuration.