1.2 The Role of Technology CAD

Historically, most of the TCAD development has been at the unit process level in developing models and simulators for a single fabrication step. These ``point solution simulators'' are used to identify phenomena dominating a particular process step, to determine optimum process conditions, and to explore hypothetical impacts of improvements in materials and equipment. All of the basic unit process steps described in Section 1.1.1 have successfully been modeled and implemented as numerical simulation modules. The analysis and characterization of the fabricated semiconductor device is the second classical task of TCAD point tools. Both, fabrication process and device design are thereby evaluated. As the physical quantities inside a device are not observable in nature due to the limited resolution of measurement techniques simulation provides the only means for looking inside a device.

For industrial TCAD applications such stand-alone-tools have to be combined together with other services like tool control, experiment generation, and data handling tasks to form an overall TCAD framework. During the past years heavy efforts have been undertaken to implement integrated TCAD frameworks. They are nowadays widely used in the semiconductor industry, although their role and application differ from company to company, ranging from the characterization of critical process sequences to fully integrated modeling and simulation of actual factory floor processes.

Challenges of further TCAD development include the possibility of optimizing entire simulation flows. First objectives have already been approached by the use of Design of Experiment (DOE) and Response Surface Models (RSM) methods. The ultimate solution to the optimization task would be a rigorous inverse modeling. Efficient optimization and the possibility of statistical analysis are two fundamental requirements of a ``Virtual Wafer Fab.''

On the other side it is extremely difficult to keep up the physical models and numerical algorithms of point tools with the very rapid technology evolution in IC manufacturing. Physical effects that had second order influence in older technologies are nowadays of crucial importance. Often a three-dimensional simulation becomes necessary to model the process and device in an appropriate manner. The requirements on computer resources is thus steadily increasing. Under these circumstances it is even harder to make TCAD tools predictive as is necessary for technology development, when unexplored territory has to be probed at the early development stage.