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Atomic force microscopy [Binnig etal, Phys. Rev. Lett. 56, 930 (1986)] and scanning capacitance microscopy [Williams etal, Appl. Phys. Lett. 55, 203 (1989)] (AFM/SCM) have been applied to study various implant structures of semiconductor devices. In this work, we present a unique application of AFM/SCM in two-dimensional-carrier profiling through a thick insulating layer. Therefore, AFM/SCM can be applied to delineate the lateral dopant diffusion and even to determine the lateral dopant diffusion length. In addition, an interesting phenomenon is observed when applying AFM/SCM to reveal the lateral dopant diffusion geometries on two different shapes of mask corners: one an obtuse corner and the other an acute corner. While it is reasonable and easily accepted that an obtuse corner in the mask would generally make the corresponding corner of the dopant-diffused region rounder, a shaper corner of the dopant-diffused region is observed on a corresponding acute corner in the mask. This demonstrates the utility of AFM/SCM in process control and failure analysis. Furthermore, three failed Si devices were studied by top-down AFM/SCM. These analyses show that the SCM images are clearly able to identify the nature and location of the three different types of defects. These random defects would be difficult to locate using more conventional cross-sectional analyses.