High resolution inspection and metrology is an important part of current semiconductor technology and has an increasingly active role as miniaturization is pushed beyond 200 nm. Current and future semiconductor design rules require not only high resolution CD control and inspection but also the ability to image high aspect ratio structures patterned on complex layers. This goal is usually achieved by using e-beam based tools that exploit voltage contrast to form images of deep structures; although useful, such images are not obviously and uniquely determined by their topographical counterpart since other parameters may significantly affect image appearance. In this paper we present a simulation approach that explains the imaging properties of charged surfaces under different conditions. This approach shows that in order to get a physical description of an e-beam image formation process, the surface must be considered as an electrostatic optical element with its own properties.