Gettering by Overpressurized Bubbles Induced by High-Energy-He-Implantation In Silicon
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Gettering by Overpressurized Bubbles Induced by High-Energy-He-Implantation In Silicon Gabrielle Regula, Rachid El Bouayadi, Bernard Pichaud, Sylvie Godey1, Romain Delamare1, Esidor Ntsoenzok1, Anton Van Veen2 Laboratoire TECSEN, Aix-Marseille III, Service 151, Marseille, F-13397 1 CERI-CNRS, 3A, rue de la Férollerie, Orléans cedex, F-45071 2 IRI, Delft University of Technology, Mekelweg 15, JB Delft, NL-2629 ABSTRACT Silicon samples were implanted with He ions at 1.6 MeV using doses ranging from 1×1016 cm-2 to 1×1017cm-2 with different fluxes (0.4µA/cm2 - 2.0µA/cm2) and annealed at high (1000°C) and low temperatures (800°C). The implantation induced-defect structure and their distribution in the depth of the sample were studied by cross section electron microscopy (XTEM). An unexpected consequence of the flux on the defect population and density was found solely for 2×1016 cm-2, which is the upper threshold to get nano-bubbles at such large implantation depth. Nuclear Reaction Analysis (NRA) were performed to measure the ratio of He remaining in the bubbles as a function of time and temperature anneal. Some samples were gold or nickel diffused at temperatures ranging from 870°C to 1050°C prior to He implantation. The gettering efficiency of the implantation-induced defects was measured by secondary ion mass spectroscopy (SIMS), after a high temperature getter annealing. SIMS profiles exhibit a shape and a width closely related to the presence of the defects (observed by XTEM) which are very efficient sinks for all kinds of metal impurities. The bubbles were found to be more efficient traps than the dislocation loops. INTRODUCTION Metal impurities can damage dramatically the performances of silicon-based devices even in very low concentration. Dissolved in the silicon bulk, these impurities can strongly reduce the minority carrier diffusion length. Actually, in a close future, with the size reduction of the device structure the contamination level in silicon will have not to exceed 1.25×1010 at cm-3 [1]. Thus, it is more and more interesting to create very localized gettering zones at (or just below) the active zone. If these zones are thermally stable, they can even be integrated in the device processes. The gettering area is a layer of nano-cavities/bubbles created currently by ion gas implantation (He, H, Ar) [2-5] at 1 µm (at the most) in the depth of the material. Since the minimum concentration of helium required to form bubbles in silicon is about 3.5×1020 He cm-3 [6], a high dose of He (≥1×1016 He cm-2), depending on the implantation energy, is needed to obtain He bubbles at the ion projection range Rp [7]. Simulations [8] and Rutherford Backscattering Spectrometry [9] showed that He atoms settle preferentially in an interstitial tetrahedral site (Ts) and that they are not stable in a vacancy (V). In adjacent Ts , He atoms can form complexes. There are three zones of point defects after implantation [10]: the closest to the surface has a high concentration of V decorated by few He atoms. The middle defect ba
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