1. An apparatus for detecting defects in a two-sided sample including three-dimensional transistor circuitry, comprising: an electron microscope operative to produce an image of one or more structures in the sample and produce a voltage contrast in the image in an area of a faulty structure; a focused ion beam operative to mill material from the sample; and a processor configured to: control the electron microscope to image a first transistor structure on a first side of the sample to determine through voltage contrast whether the first transistor structure is defective, control the electron microscope to image a second transistor structure on a second side of the sample responsive to a determination that the first transistor structure is not defective, and control the focused ion beam to mill the sample to include only the first structure responsive to a determination that the first transistor structure is defective.