Comparison of Damage Accumulation Models for Boron Implantation in Silicon
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A. SIMIONESCU and G. HOBLER Institut ffir Festkdrperelektronik, University of Technology Vienna GuBhausstrafle 25-29/362, A-1040 Vienna, Austria
ABSTRACT Two models of damage accumulation during boron implantation are compared: The first one analyzes the full collision cascades and lets vacancies and interstitials recombine, if they are located within some capture radius of each other. The second one uses a constant fraction of defects surviving damage annihilation within a recoil cascade and a damage saturation density to take into account recombination with defects generated in previous cascades. While the first model is more fundamental, the second one is computationally more efficient. By comparing model predictions with 20 keV boron implantations at various doses, performed into (100) and (110) silicon with 70 and 00, respectively, we conclude that different capture radii have to be used for damage annihilation within the recoil cascades and with defects generated in previous cascades. Moreover, we show that the two models are almost equivalent, if appropriate parameters are chosen. Recombination factors determined from simulations using a capture radius are almost independent of depth and implantation energy.
INTRODUCTION Modeling of damage accumulation during ion implantation in silicon has attracted considerable interest in recent years [1-7]. All models are based on the assumption that a vacancy is generated, if a target atom receives more energy in a collision than some displacement energy. When the target atom comes to rest, it is assumed to form an interstitial. The displacement energy is usually chosen 15 eV. It has been found that in the case of boron too much damage is predicted using this displacement energy. There have been proposed at least three models to describe this effect: (i) to increase the displacement energy [23, (ii) to let vacancies and interstitials recombine, if they are located within some capture radius [3, 4], and (iii) to reduce the number of defects by a constant "recombination" factor [6, 7]. The models using a capture radius for recombination result in a maximum damage concentration which may be achieved. By comparing simulations using a recombination factor with experimental data [7], it has also been found necessary to introduce a damage saturation density. Damage recombination is described by the capture radius model in a more fundamental way than by the recombination factor model. In contrast, the recombination factor model may be implemented more efficiently, leading to considerably lower computation times. The purpose of this paper is to investigate whether the capture radius model is more accurate than the recombination factor model. In the next section the two models will be described. Afterwards, results will be presented and conclusions will be drawn. 221 Mat. Res. Soc. Symp. Proc. Vol. 389 0 1995 Materials Research Society
MODELS Klein et al. [3] have proposed the following model for damage accumulation: Each collision cascade is simulated until all atoms come to
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