Yes, SEM is usefeul for analyzing circuits, but STM (http://en.wikipedia.org/wiki/Scanning_tunneling_microscope http://en.wikipedia.org/wiki/Scanning_tunneling_

Yes, SEM is usefeul for analyzing circuits, but STM (http://en.wikipedia.org/wiki/Scanning_tunneling_microscope http://en.wikipedia.org/wiki/Scanning_tunneling_microscope) is a completely different technique, which works at a scale about two orders of magnitude smaller. In a nutshell, SEM scans the sample with an electron beam and senses the reflected electrons to produce an image, while in STM, a metal probe is scanned across the surface at a very close distance, and variations in the tunneling current between the probe and the sample produce a topological map of the sample (because tunneling current depends strongly on distance). I don't see how you could use the same machine for both techniques, nor why you would need an STM in a semiconductor fab.