Analyzing a sidewall of a hole milled in a sample to determine thickness of a buried layer includes milling the hole in the sample using a charged particle beam of a focused ion beam (FIB) column to expose the buried layer along the sidewall of the hole. After milling, the sidewall of the hole has a known slope angle. From a perspective relative to a surface of the sample, a distance is measured between a first point on the sidewall corresponding to an upper surface of the buried layer and a second point on the sidewall corresponding to a lower surface of the buried layer. The thickness of the buried layer is determined using the known slope angle of the sidewall, the distance, and the angle relative to the surface of the sample.