Interactions of Indium, Arsenic and Carbon in Silicon Using the Pseudopotential Technique
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Interactions of Indium, Arsenic and Carbon in Silicon Using the Pseudopotential Technique M. Shishkin, A. Yan, M. M. De Souza, Emerging Technologies Research Centre, De Montfort University, Leicester UK LE1 9BH. ABSTRACT Factors limiting the activation of indium in silicon are examined via the ab initio pseudopotential technique. The role of carbon in the enhancement/retardation of activation/diffusion respectively is clarified. It is found that (1) adjacent substitutional indium atoms are deactivated. Only second neighbour sites of indium are activated unlike the case of boron, where all substitutional sites remain activated. (2) Silicon self-interstitials deactivate indium by trapping them on substitutional sites. Carbon, on the other hand, traps such selfinterstitials with higher binding energy and prevents them from deactivating indium. (3) Since both indium and carbon diffusion is interstitial mediated, carbon reduces indium diffusion on account of its higher binding energy with the self-interstitial. Moreover, the release of the carbon interstitial is more favourable than the release of the indium interstitial from a carbon-indium pair. Therefore, carbon minimises indium interstitial diffusion. (4) Arsenic enhances deactivation of indium by neutralisation and by strong binding on adjacent substitutional sites. Furthermore since the release of the indium interstitial is more favourable in comparison to the release of the arsenic interstitial from the indium-arsenic pair, indium diffusion is enhanced in the presence of arsenic. INTRODUCTION Indium (In) is a promising option for achieving punch-through suppression and threshold voltage control in sub-100 nanometer MOSFET technologies. As an alternative p-type dopant to boron, it produces shallower and steeper as-implanted profiles due to its heavier mass. However, the activation of indium amounts to no more than 20%-40% of the implanted dose after RTA at temperatures 900ºC -1100ºC [1]. Carbon (C) co-implantation has been demonstrated to increase the electrical activation of indium by upto 50% [2]. In addition to the activation issue, indium also suffers from excessive diffusion due to Transient Enhanced Diffusion (TED) mediated by self-interstitials [3]. Since the diffusion of carbon occurs via the kickout interaction with the selfintersitial, there is an urgent requirement to understand and quantify the role of carbon in suppressing indium diffusion while simultaneously enhancing its activation. On the other hand, arsenic an n-type dopant required for source/drain implants diffuses via both vacancies and interstitials. When indium is used as a channel dopant for threshold control, its interactions with arsenic require clarification. Diffusion and activation can be affected by size/strain effects, Coulombic attraction and neutralisation. These issues require understanding from two major perspectives: (1) technological challenges in controlling TED and activation of indium and (2) accurate process modelling for sub-100 nanometer nodes. Our approach is to u
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