2.2.2 Operations on the Wafer Data

In addition to the definition of the data representation there is also a set of required basic operations that are defined on that data. There is the need to interpolate data from one grid onto another. This interpolation must be explicitly invokable by the simulator, e.g. if a new grid is to be computed for the simulation run. This operation is necessary due to the fact that the grids stored on a Wafer need not be boundary conforming.

For topography simulations an operation to merge the input wafer and the result of the simulation is necessary. Consider a topography simulation that cuts off parts of a segment. After the cut operation the remaining pieces need to be identified, new grids need to be computed and finally the attributes need to be interpolated onto the new grids. Fig. 2.3 depicts a simplified two-dimensional example.

Figure 2.3: Two-dimensional merge operation after an etch-step.
\begin{figure}\centering\subfigure[Original Wafer]
...g{file=pics/merge-merged, angle=-90, width=0.3\linewidth}}

An etch simulation changes the hull of the Wafer, exposing parts of one or more segments. This introduces an inconsistency that must not be stored on a persistent Wafer. Storing a mixture of exposed segments and a new hull would not make any sense at all. Such data could never be fed to an, e.g., diffusion simulator. Therefore, after any topography simulation, such inconsistencies must be removed prior to storing the data. Since this procedure can be seen as a kind of repair operation, it will be referred to as repair step throughout this work. The repair step introduces design issues, where care must be taken that the simulator can control the grid generation process and take advantage of the repair automatism at the very same time. The simulator must thereby be able to chose the desired gridding algorithm, but must not be bothered with details as how this algorithm is applied and to which segments it must be applied.

Another operation is the creation of a single grid out of all grids on certain segments. This is used in e.g. device and diffusion simulations where interface conforming grids are a prerequisite to perform a simulation.

A whole class of operations is topology related. These operations are: