Chemical and electrochemical staining for two-dimensional dopant concentration profiling on ULSI silicon devices

We discuss the sample preparation technique for the two-dimensional dopant concentration profiling in silicon based on chemical staining and transmission electron microscopy analysis. The capability of characterizing ULSI silicon devices is demonstrated by showing an example of failure analysis performed on a high speed bipolar transistor. The high spatial resolution of the technique allows to reveal many details which are not detectable by other techniques. The limitations of this method concern the impossibility to simultaneously delineate n and p-type regions on the same sample, and the need to have a p(+)n junction for delineating a boron profile with an acceptable sensitivity. We demonstrate that these limitations can be overcome by developing a novel electrochemical staining procedure based on anodic oxidation of silicon.