The fast growing market for semiconductor devices and the high costs for fabricating the devices give rise to ongoing miniaturization. Advances in process technology and increasing demands on the electrical and thermal characteristics of the devices lead to complex structures.

Device simulation turned out to be mandatory to predict the behavior of semiconductor devices and to be able to influence the process line in the very first steps. Today, mostly two-dimensional simulations are performed assuming uniform extension of the geometries into the third dimension. The resulting inaccuracies limit their application to wide devices.

As the feature sizes become smaller and smaller, three-dimensional effects become more pronounced, and three-dimensional device geometries noticeably influence the electrical characteristics of the devices. Moreover, three-dimensional simulations are mandatory to gain additional insight in the operation of real three-dimensional structures.

Three-dimensional simulation poses several difficulties. One of the main issues is the computational effort which increases dramatically. The use of appropriate numerical solvers is mandatory to obtain accurate results within affordable simulation time. Even the definition of geometries is difficult due to the lack of adequate software tools. The numerical results strongly depend on the quality of the grid. For three-dimensional simulations high quality grid generation is even more important than in the two-dimensional case, because adjustment by hand becomes rather tedious. Several criterions and strategies are depicted.

In this work an existing two-dimensional device simulator has been extended to three dimensions. Thus, all physical models, the discretization, and the handling of physical quantities have been extended to perform both two- and three-dimensional simulations. Complex TCAD applications require powerful, flexible, but easy to use control systems. Therefore, a new kind of object-oriented database is presented in this work which has been designed with respect to the specific requirements of TCAD applications. The database is used to manage hierarchically structured data, such as material and model parameters or the definition of complex circuits. It has been applied to control the simulator in each phase of the simulation flow. Particularly for three-dimensional simulation with hardly predictable simulation times, an interactive mode has been implemented, which enables to adjust simulation parameters during runtime.

Three-dimensional investigations have been performed for several state-of-the-art semiconductor devices which demonstrate the necessity of three-dimensional device simulation.

Robert Klima 2003-02-06