A New Local Electronic Stopping Model for the Monte Carlo Simulation of Arsenic Ion Implantation into (100) Single-Cryst
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ABSTRACT In this paper is reported the development and implementation of a new local electronic stopping model for arsenic ion implantation into single-crystal silicon. Monte Carlo binary collision (MCBC) models are appropriate for studying channeling effects since it is possible to include the crystal structure in the simulators. One major inadequacy of existing MCBC codes is that the electronic stopping of implanted ions is not accurately and physically accounted for, although it is absolutely necessary for predicting the channeling tails of the profiles. In order to address this need, we have developed a new electronic stopping power model using a directionally dependent electronic density (to account for valence bonding) and an electronic stopping power based on the density functional approach. This new model has been implemented in the MCBC code, UTMARLOWE. The predictions of UT-MARLOWE with this new model are in very good agreement with experimentally-measured secondary ion mass spectroscopy (SIMS) profiles for both on-axis and off-axis arsenic implants in the energy range of 15-180 keV.
INTRODUCTION Ion implantation has been the major technique for introducing dopants into semiconductor devices since the mid- 1970s. As the sizes of MOS devices continue to shrink to deep submicron dimensions, very shallow dopant profiles are required, and the thermal budget must be reduced. Due to this reduction of the thermal budget, the final dopant profile after annealing depends more and more on the as-implanted profile, which in turn depends on the key implant parameters such as energy, dose, and implant angles. Since as-implanted profile information is a necessary input for the simulation of subsequent dopant diffusion and device simulation, an accurate model which accounts for the profile dependence on the important implant parameters is required. Various techniques have been applied to this problem, and the Monte Carlo binary collision (MCBC) method is one of the most promising approaches. In this method, the entry point and the direction of an ion is used as the initial condition for the simulation. This ion is then followed as it travels through the target, and the energy losses, and hence the slowing down of the ion due to nuclear scattering and electronic stopping, are evaluated. The accuracy of the predicted implanted impurity distribution thus depends very strongly on the validity of the physical models implemented in the MCBC codes for these two energy loss mechanisms. For implants with energies higher than 1 keV, the MCBC method appears to handle the nuclear scattering mechanism quite adequately[l]. Inadequacies in electronic stopping models, however, are still a major obstacle for the development of an accurate Monte Carlo implant simulator, even though early work on electronic stopping power theory dates back to the 1950's[2-3]. In addition, it is well known that as-implanted impurity profiles in crystalline targets have a strong dependence on the implant tilt and rotation angles (i.e. crystal orientation e
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