Technology Computer-Aided Design (TCAD) systems have become an indispensable
and integral part in modern technology design and fabrication. They contribute
significantly in the reduction of design and development time and in the
improvement of manufacturing yield. Whereas each system has its particular
characteristics [34][29], TCAD systems commonly provide
capabilities beyond those of individual process and device simulation tools.
Facilities for tool invocation, coupling, and for the definition and execution
of TCAD tasks are widely available
. By enabling the user to operate at the task rather than tool
level, TCAD fulfills the need for higher level analyses brought about by the
increase in design complexity and miniaturization. Typical TCAD high-level
task applications include optimization, characterization, and statistical
analysis. They offer a higher level, application oriented, conceptual means
for the representation of design and characterization methodologies.
In [1] the basic architecture of a TCAD Framework is described. Building on a unified representation and centralized software support, the framework was mainly divided in three layers:
Development work and the resulting implementations at the task level were less sophisticated and more unstructured. Early systems provided limited capabilities. The MASTIF system [11] focused on improving the ease of use of individual TCAD tools. EASE [66], a TCAD system with an application oriented user interface, supported the delivery of pre-defined task-oriented capabilities to users. In the MECCA system [83][62], command scripting was used to integrate and drive the underlying tools as well as higher level applications. The need for a programmable tool control language for the definition, management and execution of TCAD tasks was formulated in [51]. This is an instance of a command extension language with specialized TCAD syntax and semantics such as commands to run the simulation tools and extract the relevant values from the output files. Various implementations of such a task language exist. They range from a script and template driven approach [64] to the use of special interface programs [4].
A closely related task level concept is the Process Flow Representation (PFR) [75][13]. A PFR consists of the basic design, and/or manufacturing activities information. From a TCAD perspective, the PFR stores the sequence of simulation and analysis steps and their control data. This is the simulation flow controller role of the PFR [80]. By integrating the task language procedural aspects with the PFR and coupling it to the data representation layer, a uniform and homogenous interface layer to TCAD frameworks can be constructed [36]. This makes the task level the main contact point of the framework to the external world. This is a major feature of the Viennese Integrated System for Technology CAD Applications (VISTA) [35]. In the following section the VISTA system and its architecture are overviewed with particular emphasis placed on the task level features.