Improving the Understanding of Ion-Beam-Induced Defect Formation and Evolution by Atomistic Computer Simulations
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Improving the Understanding of Ion-Beam-Induced Defect Formation and Evolution by Atomistic Computer Simulations
Matthias Posselt Forschungszentrum Rossendorf, Institute of Ion Beam Physics and Materials Research, P.O.Box 510119, D-01314 Dresden, Germany
ABSTRACT The morphology of the as-implanted damage in silicon is investigated using a recently developed combination of time-ordered computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations. The method is applied to determine the type and the amount of defects formed within the first nanosecond after ion impact. The depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) produced on average per incident ion are calculated for B+ (15 keV), P+ (5, 10, 20, 30 keV), and As+ (15 keV) implantations. It is shown that the asimplanted defect structure depends not only on the nuclear energy deposition per ion but also explicitly on the ion mass. Therefore for each ion species the damage morphology exhibits characteristic features. For heavy ions the percentage of extended defects is higher than for light ions. In all cases investigated the number of free or isolated interstitials exceeds the amount of free vacancies. The results obtained allow a microscopic interpretation of the phenomenological model for the as-implanted damage employed in conventional BCA simulations in order to describe the dose dependence of the shape of ion range profiles. They can be also applied to get more realistic initial conditions for the simulation of the defect kinetics during post-implantation annealing.
INTRODUCTION The explanation of many effects occurring during ion beam processing requires the understanding of damage formation and defect evolution. This is of particular importance in silicon technology where the control of the influence of implantation-induced defects plays a crucial role. The present work is focused on the morphology of the as-implanted damage in Si which is still not completely understood. However, its detailed knowledge is essential for a physically based description of technologically relevant effects. For instance, the defect accumulation during ion bombardment causes increasing dechanneling of the implanted dopants. With growing ion dose, this leads to the alteration of the shape of the ion range profiles: In channeled implants the channeling part of the range distribution shows a saturation, i.e. it does not further increase. In random implants the channeling tail behaves similarly. A second example is the defect-assisted diffusion of dopants during post-implantation annealing which can cause significant changes of the dopant profiles. Both effects are strongly dependent on the type and the amount of defects produced per incident ion. Due to a lack of microscopic information about the morphology of the as-implanted damage, the state-of-the-art computer simulations of these processes have to employ phenomenological models for the as-implanted
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