US Patent 7388218 Subsurface imaging using an electron beam

A method of navigating or endpointing a microscopic structure by subsurface imaging using a beam of electrons having sufficient energy to penetrate the surface and produce a subsurface image. For endpointing, when the subsurface image become relatively clear at a known electron energy, a user knows that he is approaching the buried feature. For navigating, a subsurface image can be formed of fiducials or other features to determine the position of the beam on the device.