A method for observing a buried defect on a substrate using a charged particle beam, comprising: (a) directing an ion beam toward a substrate to mill a trench in the substrate, the substrate comprising a first material and a second material, the trench exposing a vertical wall including at least a portion of the first material and the second material, the interface between the first material and the second material not being initially visible in an electron beam image of the exposed vertical wall; (b) directing an electron beam toward the vertical wall in the presence of an etchant to etch material from the vertical wall, the first material being etched at a greater rate than the second material, the difference in the etch rates between the first material and the second material being sufficient to make visible in an electron beam image the interface between the first material and the second material; (c) directing an electron beam toward the vertical wall to form an electron beam image of the vertical wall, the image showing the interface between the first and second materials; and further comprising: (d) directing an ion beam toward the substrate to remove material from the vertical wall to expose a subsequent vertical wall including at least the first material and the second material, the interface between the first material and the second material not being initially visible in an electron beam image of the newly exposed vertical wall, the distance between the vertical wall and the subsequent vertical wall being between 30 nm and 60 nm of material; (e) repeating steps (b) through (d) such that the vertical wall advances to expose a buried feature for imaging. (a) directing an ion beam toward a substrate to mill a trench in the substrate, the substrate comprising a first material and a second material, the trench exposing a vertical wall including at least a portion of the first material and the second material, the interface between the first material and the second material not being initially visible in an electron beam image of the exposed vertical wall; (b) directing an electron beam toward the vertical wall in the presence of an etchant to etch material from the vertical wall, the first material being etched at a greater rate than the second material, the difference in the etch rates between the first material and the second material being sufficient to make visible in an electron beam image the interface between the first material and the second material; (c) directing an electron beam toward the vertical wall to form an electron beam image of the vertical wall, the image showing the interface between the first and second materials; and further comprising: (d) directing an ion beam toward the substrate to remove material from the vertical wall to expose a subsequent vertical wall including at least the first material and the second material, the interface between the first material and the second material not being initially visible in an electron beam image of the newly exposed vertical wall, the distance between the vertical wall and the subsequent vertical wall being between 30 nm and 60 nm of material; (e) repeating steps (b) through (d) such that the vertical wall advances to expose a buried feature for imaging.