Technology CAD (TCAD) tools such as process/device simulators are expected to accelerate device development by starting from preoptimized transistor structures and process flows. To scale down device feature size, complex device structures such as trench memory cells are introduced using new process technologies. As a result of continuing efforts to verify the validity of TCAD software through intensive physical model developments and their model parameter calibrations the predictability of process/device simulators is being confirmed. Process simulation programs are designed to reproduce semiconductor device structures including dopant distributions by solving numerical models corresponding to each fabrication step such as ionimplantations, oxidation, diffusion, etching and deposition. Simulation of cross-sectional device structure is usually modeled by using a string model in which the cross section of each material layer is expressed by polygons. Compared with process simulation models, there are fewer variations of carrier transport models for standard device simulation.