Ion implantation and ion-beam-induced defect formation in Si and SiC studied by atomistic computer simulations
Forschungszentrum Rossendorf, Institute of Ion Beam Physics and Materials Research, P.O.Box 510113 D-01314 Dresden, Germany
Ion implantation is one of the major techniques to introduce dopants into Si and SiC in a controlled manner. However, ion irradiation produces defects which prevent their electrical activation. Therefore, subsequent annealing is necessary in order to restore the crystallinity and to obtain dopant activation. The precise knowledge of the spatial distribution of the implanted ions and the radiation damage as well as the understanding of the nature of ion-beam-induced defects are important prerequisites for further improvements in the technology of ion implantation doping. Besides experimental investigations, atomistic computer simulations play an important role to achieve progress in this field. Simulations based on the binary collision approximation (BCA) are employed to determine the depth profile of implanted ions and atomic displacements. The influence of various implantation parameters like energy, direction of ion incidence, dose, dose rate and temperature is considered. A phenomenological model is used to treat the dependence of channeling effects on damage buildup and dynamic annealing during ion bombardment. The implantation profiles determined by the simulations show a good agreement with available experimental data. On the other hand, BCA simulations are limited to the treatment of ballistic processes. They do not yield details of the (meta)stable defect structure formed in subsequent fast relaxation processes. In order to obtain such information, a combined simulation method is employed. Processes in the collision cascade with energy transfers above 100 eV are treated by BCA simulations. Classical molecular dynamics (MD) calculations are applied to consider processes in certain parts of the cascade which start with energy transfers less than 100 eV. Detailed investigations are performed to study the temporal evolution of the defect structure, and to determine the damage morphology obtained after the fast relaxation is finished. The influence of nuclear energy deposition and target temperature is discussed. The combination of BCA and MD methods allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion. The results obtained allow a microscopic interpretation of the phenomenological model employed in conventional BCA simulations to describe the enhanced dechanneling of implanted ions due to damage buildup during implantation. In particular the explicit dependence on the ion mass can be explained. Furthermore, the procedure yields more realistic initial conditions for the simulation of post-implantation annealing than hitherto used.