A method is presented to calculate two‐dimensional defect distributions induced by ion implantation through openings in a masking layer. It is shown that a realistic description of this model requires depth‐dependent lateral standard deviations to describe the dopant and the damage point response functions. Further refinements of the theory include arbitrary shapes for the mask edges and different materials in the masking layer and in the substrate. Cross‐sectional electron microscopy observations have been carried out to visualize the two‐dimensional extension of amorphous layers created by As implantation in silicon for different mask edge angles. It is shown that the theory fits well the cross‐sectional transmission electron microscopy observations. More generally, this study shows that for abrupt mask edges, the lateral extension of the two‐dimensional defect profile beneath the mask edge is directly governed by scattering of the ions and of the subsequent recoil atoms and, as a direct consequence, by the lateral standard deviation of the damage point response function. For tapered mask edges, however, the contribution of ions that pass through the mask edge region before damaging the substrate may be very high with respect to scattering effects.