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D6.13.1

Indium in silicon: a study on diffusion and electrical activation. S. Scalese1, A. La Magna1, G. Mannino1, V. Privitera1, M. Bersani2, D. Giubertoni2, S. Solmi3, P. Pichler4 1 CNR-IMM Sezione Catania, Stradale Primosole 50, 95121 Catania, Italy 2 ITC-irst, via Sommarive 18, 38050 Povo (Trento), Italy 3 CNR-IMM Sezione Bologna, via Gobetti, 101, 40129 Bologna, Italy 4 Fraunhofer-Institute fuer Integrierte Schaltungen, Bauelementetechnologie, Schottkystrasse 10, 91058 Erlangen, Germany ABSTRACT In this work we investigate the diffusion and the electrical activation of In atoms implanted in silicon with different energies, in the range 80-360 keV, after rapid thermal processing. Our investigation shows a clear dependence of In out-diffusion and electrical activation on the implant depth, being the electrically active fraction higher with increasing the implant energy for a fixed dose. The data are explained considering the balance between the local In concentration and the C background inside the silicon substrate and the formation of C-In complexes, which play a role in the enhanced electrical activation due to the shallower level they introduce into the Si band gap (Ev+0.111 eV), with respect to the rather deep level (Ev+0.156 eV) of In alone. In and C co-implantation has also been studied within this work, in order to confirm the key role of C in the increase of the electrical activation. A large increase of the electrical activation has been detected in the co-implanted samples, up to a factor of about 8 after annealing at 900°C. However, C precipitation occurs at 1100°C, with dramatic effects on the carrier concentration. INTRODUCTION The study of indium as p-type dopant in silicon has recently gained an increasing interest due to the shallow and steep doping profile which can be obtained by implantation because of the heavy mass of In ions. Indium might potentially replace boron in many ultra large scale integration (ULSI) applications, for example channel doping and source-drain doping in sub100nm CMOS technologies. The studies on the diffusion mechanisms of In in Si are still controversial: Antoniadis and Moskowitz [1] estimated the fractional diffusivity via self-interstitials to be fi=0.35 at 1000°C, while a diffusion via self-interstitials was deduced by Griffin et al. [2] (fi=1) and by Kizilyalli et al. [3] because of the similarities found with the transient enhanced diffusion of B in Si. Concerning the electrical activation, the use of In as p-dopant could have some limitations due to incomplete ionisation because of its relatively deep-lying acceptor level and significant outdiffusion [4]. The low solubility of In, reported in previous studies [5-7] (the maximum value reported in literature by Solmi et al. is 1.8×1018 cm-3) is not a severe limitation in the case of MOSFET channel doping, where the concentration usually does not exceed 1018 cm-3, but would make it useless for source/drain applications. The poor electrical activation can be improved by C co-implantation, as observed by sheet resis