1.1 What is a TCAD System?

TCAD systems try to provide generic services and a stable environment for all of the TCAD tools to integrate and make them work together, thus gaining synergetic effects from this union - ``the whole is more than the sum of its parts''. The ultimate goal of a TCAD framework is to provide not only this virtual factory to the process and device engineer, where he finds manufacturing equipment (process simulators) as well as measurement equipment (device simulators) to combine at will, but also to provide automated high-level tasks which simply cannot be performed in a real-world factory due to physical and time constraints.

Two different types of TCAD frameworks can be distinguished [Hala94]:

Integration Framework
This type of framework integrates tools into a common environment, but does not provide any services or support for extending the environment. It is targeted at end users who usually do not integrate additional tools into the framework, or want to extend the framework with additional functionality.

Application Framework
This type of framework provides elaborate means for integrating existing applications into and developing new applications inside the framework. It is not designed to have a static ``cast-in-concrete'' architecture, but rather implements a number of basic but generic concepts which make up a basis for extension of the framework in general.

  
Figure 1.1: The Viennese Integrated System for Technology CAD Applications

The Viennese Integrated System for Technology CAD Applications (VISTA) [Selb91] framework developed at the Institute for Microelectronics of the Technical University of Vienna is such an application framework whose major design principles are targeted at overall conceptual integrity of the framework architecture and flexibility and openness for all future concepts that we do not know of today and that are going to be used in TCAD tools to come.

Fig. 1.1 shows the basic VISTA architecture. The task level provides an extension language (also called TCAD shell) with high-level programs solving engineering tasks and aiding tool integration and development. The tool level integrates various tools and provides generic services usable by all other tools inside the framework. The data level copes with the manifold types of information and data flowing inside the framework, and the additional burden which existing simulators impose on the framework by employing their own data formats.