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Next: Danksagung Up: Dissertation Walter Bohmayr Previous: Kurzfassung


Simulation of Ion Implantation into Crystalline Silicon Structures

Ion implantation is the predominantly used method to introduce dopants into a semiconductor material of a modern device, because it ensures an exact and reproducible distribution of impurities. To meet the requirements of complex doping processes, physical phenomena which could be neglected a few years ago have to be taken into account by computer calculations.

However, only the simulation of process steps within a reasonable amount of time supports the work of a process engineer. The demand for accurate results is regarded as a matter of course, and even more importantly, the physical relations have to be expressed correctly. Furthermore, a very high degree of flexibility concerning the simulation structure and the orientation of the wafer relative to the ion beam is required.

A Monte Carlo strategy is selected to describe the physical processes of ion implantation. This approach enables a direct modeling of the energetic interactions of ions and target atoms. The details of the interactions are described in this work.

The integration of various software tools into a Technology CAD framework allows the simulation of complete process flows and their optimization. This facility leads to repeated calculations of the same process step. Therefore, special emphasis has to be put on the development of an algorithm which considerable reduces the computation time of one Monte Carlo run (trajectory-split method).

One drawback of ion implantation is the gradual destruction of the silicon crystal which requires a high-temperature treatment to restore the crystalline structure (annealing). The progress of the recrystallization crucially depends on the size and type of the damage. Therefore, a multi-dimensional amorphization model is introduced. It predicts the range of heavily damaged regions by taking into account the substrate temperature, the implantation dose, the implantation energy and the ion mass.

Several examples demonstrate the applicability of the new methods to a wide range of problems. Major issues are the comparison of simulation results with SIMS measurements and the processing of realistic three-dimensional geometries. Due to the trajectory-split method the time required to perform a simulation is considerable reduced and consequently a calculation of a complete device structure is feasible within a few hours on a today's workstation.


next up previous contents
Next: Danksagung Up: Dissertation Walter Bohmayr Previous: Kurzfassung

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