We propose visualizing techniques of a diffusion layer using an electron beam induced current (EBIC) for a site-specific cross-section formed by focused ion beam (FIB) treatment. Moreover, we present a three-dimensional (3-D) EBIC technique using a double beam (FIB & EB) system to understand the diffusion structure. This 3-D application of the EBIC technique is very useful for delineating PN junctions and pointing out implant defects in ULSI devices. Furthermore, we applied the EBIC technique to backside circuit editing with FIB. The end-point of the silicon trench etching can be easily decided by observing the plane EBIC images. Highly reliable backside circuit editing becomes possible together with a DUV laser marking technique using an IR-optical microscope system.