Cross-section SEM images a cleaved or FIB-cut wafer edge to reveal layer structures, film thicknesses, feature profiles, and subsurface defects. Preparation: Cleave: Break wafer through region of interest. Quick but imprecise location. FIB (Focused Ion Beam): Mill precise cross-section at exact location of interest using Ga+ beam. Much more precise. Imaging: SEM images the exposed cross-section face. Shows all layers in profile view. Information: Film thicknesses, sidewall angles, undercut, notching, voids, grain structure, interface quality, defect morphology. Resolution: Nanometer-scale features visible. Modern FIB-SEM achieves <1nm resolution. 3D profile: Shows feature shape that top-down SEM cannot - sidewall angle, footing, bowing, retrograde profiles. Failure analysis: Primary technique for investigating process defects, yield issues, and reliability failures. TEM prep: FIB used to prepare thin lamellae (<100nm thick) for transmission electron microscopy. Destructive: Cleaving or FIB milling destroys the measured area. Cannot be done inline on production wafers. Site-specific: FIB enables targeting exact features or defects. Navigate to coordinates from defect inspection tools. Dual-beam FIB-SEM: Combined FIB and SEM in one tool. Mill with ion beam, image with electron beam simultaneously. Artifacts: FIB milling can introduce artifacts (curtaining, redeposition, Ga implantation). Careful technique minimizes these.