Today much of the development of semiconductor devices and processes is done by TCAD as it offers unique possibilities in visualisation of processing steps, description of the physical changes and understanding of the interrelation of the process variables. Modelling of processes provides a way to interactively explore the fabrication process, studying the effects of process choices, leading to a 'virtual wafer fabrication' (VWF) design environment. TCAD simulation tools provide a controlled and repeatable numerical experiment that can yield information that cannot be measured experimentally. The main aim of a TCAD simulator tool is to match the simulation methodology as close as possible to the fabrication technology and their integration into the actual fabrication. For TCAD tools to be useful in a practical environment, they must be physically accurate, computationally robust and usable by semiconductor process engineers.