If the ion implantation simulation is performed directly on the structure provided on input a boundary effect arises. The region in the vicinity of the boundary can only be reached from ions coming from inside the simulation domain the doping concentration is smaller in a boundary region than in a region in the middle of the simulation domain, which can be reached from ions coming from all spatial direction. This boundary effect obviously does not represent the simulated process, because the structure that is provided on input is not the real structure which is applied to the production process, but a rectangular or planar cut through the real structure. Therefore the ions coming from outside the simulation domain have to be considered somehow in the simulation.
In MCIMPL this is done by expanding the simulation domain as indicated in Fig. 4.1, Thereby it is assumed that the structure outside the simulation domain looks like the structure at the front, back, left and right boundaries of the input structure. If the original geometry is expanded more than the lateral range of the implanted ions the boundary effect vanishes inside the original simulation domain, because all remarkable contribution from outside are considered then.
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