The VISTA/SFC simulation environment is based on the VISTA framework [1] and its extension language VLISP [2], an enhanced version of XLISP [3]. VISTA is designed in a highly portable way and runs on all UNIX and VMS platforms. To facilitate the integration of heterogeneous simulation tools, the Profile Interchange Format (PIF) [4] in the VISTA implementation [5] is used as the primary data format for the exchange of wafer data (e.g., geometry and dopant distribution data) as well as device data (e.g., carrier density and potential distribution data). Nevertheless, native tool data formats are supported as well, ensuring maximum flexibility in the choice of simulation tools for a particular task or at a particular site, while minimizing computation overhead and numerical errors due to excess data conversion; if all tools being used understand the same data format, no conversion is necessary at all during simulation. For example, if all tools understand the TIF format, a conversion from TIF to PIF is only necessary if the built-in post-processors, which operate on PIF, should be used; a robust wrapper from TIF to PIF and vice versa is provided with VISTA.
To capture large fabrication process flows and simulation sequences, a process flow representation has been defined [6]. It offers simulator-dependent and simulator-independent statements with a vocabulary that can be easily extended. Using a visual flow editor, process flows can defined in a hierarchical manner from arbitrarily nested, parameterized process modules. The automatic generation of split points both for sequentially and simultaneously initiated runs and the parallel and distributed execution of independent split tree branches allow the fast computation of large-scale experiments on heterogeneous work station clusters. A persistent run data base keeps the results (output files and extracted data) of each completed step and prevents unnecessary re-computations.
To support more complex analysis tasks based on process and device simulation, e.g., process tuning, device optimization, and calibration, an additional level of framework services has been added to the environment that establishes standardized interfaces between simulation tasks, response surface models, optimizers, and other TCAD applications. Evaluable Entity objects are used to encapsulate all kinds of model evaluation tasks; they will be treated in more detail in the remainder of this text.