2.1.1 Unit Process Analysis

The traditional application of TCAD focuses on the analysis of unit fabrication processes used in VLSI manufacturing. All of the basic physical processes, including ion implantation, diffusion and oxidation, epitaxy, lithography, and etching and deposition, have been successfully modeled and implemented as numerical simulation modules, and form an indispensable basis for all further TCAD applications [Sel84] [Eng86] [Sze88] [DY93] [Mey95]. The objectives for unit process modeling are twofold:

1. Numerical simulation provides insight into the physical nature of fabrication processes that are not observable otherwise. A prominent example is given by the simulation of ion implantation, where the spatial distribution of dopants in the semiconductor material can only be measured with a spatial resolution far coarser than the typical feature size in modern devices. Therefore, a picture of the two-dimensional and three-dimensional dopant distribution can only be found by simulation.
2. The effects of variations of process settings for new or unfamiliar device geometries, for new materials or etchants can be most conveniently studied by process simulation. Unit processes can be tuned to a nominal target behavior before being grouped together with other process steps to form process modules for fabrication.