F + implants in crystalline Si: the Si interstitial contribution
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1070-E06-07
F+ implants in crystalline Si: the Si interstitial contribution Pedro Lopez1, Lourdes Pelaz1, Ray Duffy2, P. Meunier-Beillard2, F. Roozeboom3, K. van der Tak4, P. Breimer4, J. G. M. van Berkum4, M. A. Verheijen4, and M. Kaiser4 1 Electricidad y Electronica, Universidad de Valladolid, E.T.S.I. Telecomunicacion. Campus Miguel Delibes s/n, Valladolid, 47011, Spain 2 NXP semiconductors, Leuven, 3001, Belgium 3 NXP semiconductors, Eindhoven, 5656, Netherlands 4 Philips Research Laboratories Eindhoven, Eindhoven, 5656, Netherlands ABSTRACT In this work the Si interstitial contribution of F+ implants in crystalline Si is quantified by the analysis of extended defects and B diffusion in samples implanted with 25 keV F+ and/or 40 keV Si+. We estimate that approximately 0.4 to 0.5 Si interstitials are generated per implanted F+ ion, which is in good agreement with the value resulting from the net separation of Frenkel pairs obtained from MARLOWE simulations. The damage created by F+ implants in crystalline Si may explain the presence of extended defects in F-enriched samples and the evolution of B profiles during annealing. For short anneals, B diffusion is reduced when F+ is co-implanted with Si+ compared to the sample only implanted with Si+, due to the formation of more stable defects that set a lower Si interstitial supersaturation. For longer anneals, when defects have dissolved and TED is complete, B diffusion is higher because the additional damage created by the F+ implant has contributed to enhance B diffusion. INTRODUCTION The co-implantation of F+ and B+ in pre-amorphized Si, followed by solid phase epitaxial regrowth, has been proved to be beneficial for ultrashallow junction formation since a remarkable reduction of B diffusion can be achieved [1]. The beneficial effect of F has been attributed to the formation of fluorine-vacancy complexes (FnVm) during recrystallization. This results in a regrown layer rich in vacancies (V´s) which act as annihilation centers for Si interstitials (I´s) injected from the end of range (EOR) damage. This hypothesis is supported by the high affinity of F with vacancies, as indicated by theoretical calculations [2], and by the direct observation by transmission electron microscopy (TEM) of bubbles in the high concentration region of a F profile [3]. The case of F+ implantation in crystalline Si (c-Si) has been less studied and the available information is sometimes contradictory. There is not even agreement about the possible beneficial effect of F. Both B diffusion enhancement [4] and reduction [5, 6] by the presence of F have been reported. The clarification of the role of F in c-Si is gaining relevance since in some cases amorphization is not advisable due to the high leakage currents caused by residual EOR defects [7] or to the poor crystal quality after regrowth as observed in FinFET structures [8].
An important difference between F+ implantation in amorphous and crystalline Si is related to the defect balance. In amorphizing conditions, the introduction of F in
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