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Emulation and Simulation of
Microelectronic Fabrication Processes

3.3 Summary

Methods for finding the velocity field which describes the movement of a level set surface were discussed. Empirical modelling, or emulation, can be applied when the geometric effect of a process on the initial surface is known in advance and can simply be applied. Therefore, these types of processes can be modelled highly efficiently using the geometric advection algorithm presented in Section 2.4.3.

Chemical modelling is applied when intricate physical effects need to be included in the description. This includes the modelling of molecular transport through the feature scale region, which can be performed in a variety of ways. The most flexible and appropriate method for modelling complex fabrication processes was found to be top-down flux calculation employing Monte Carlo ray tracing. A highly efficient explicit data structure was presented in which discs tangential to the surface can be extracted directly from the level set. This allows for molecule-surface interactions to be recorded for all active grid points.

The modelling approach for molecular interactions with the surface, as used in the developed simulator, was presented. Using abstracted particle types for groups of molecules, this approach allows for a maximum of flexibility in the implementation of entirely different physical processes.

Finally, the modelling of chemical reactions on the surface, leading to the evolution of material interfaces, is discussed using the example of a modern ion-enhanced plasma etch process. For the appropriate modelling of this process, it is crucial to identify dominant physical mechanisms leading to material evolution. Therefore, if important physical behaviours are not encompassed by the model, process specific features cannot be generated, while the inclusion of unnecessary mechanisms will lead to computationally inefficient simulations of processes with only minor effects on the final structure.