On the Energetics of Extrinsic Defects in Si and their Role in Nonequilibrium Dopant Diffusion
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On the Energetics of Extrinsic Defects in Si and their Role in Nonequilibrium Dopant Diffusion Alain Claverie1, Filadelfo Cristiano1, Benjamin Colombeau1and Nicholas Cowern2 1 CEMES – CNRS, BP 4347, 31055 Toulouse Cedex 4, France 2 Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands
ABSTRACT In this paper, we discuss the mechanisms by which small clusters evolve through “magic” sizes into {113} defects and then, at sufficiently high dose levels, transform into dislocation loops of two types. This ripening process is mediated by the interchange of free Si(int)s between different extended defects, leading to a decrease of their formation energy. The calculation of the supersaturation of free Si-interstitials in dynamical equilibrium with these defects shows a hierarchy of levels of nonequilibrium diffusion, ranging from supersaturations S of about 106 in the presence of small clusters, through 103 in the presence of {113} defects, to S in the range 100 down to 1 as loops are formed, evolve and finally evaporate. A detailed analysis of defect energetics has been carried out and it is shown that Ostwald ripening is the key concept for understanding and modelling defect interactions during TED of dopants in silicon.
INTRODUCTION Transient Enhanced Diffusion (TED) of dopants is a major problem in advanced IC fabrication. It broadens dopant profiles and since the basic phenomena are not all well understood it is difficult to simulate in a predictive way. Under most process conditions, TED is observed in the presence of {113} defects and earlier works have ascribed the diffusion anomalies to the ripening and dissolution of these defects [1]. Recent experiments have shown that {113} defects are not a prerequisite for TED, i.e., TED is also observed when {113} defects are not formed [2] or have evolved further into dislocation loops during longer annealings [3]. The reasons why, depending on experimental conditions, these defects alternatively dissolve or transform into dislocation loops are not yet clear. Thus, a better knowledge of the energetics of the various extrinsic defects which form when annealing ion implanted Si is needed. It is a goal of this paper to review and discuss the mechanisms by which small clusters evolve into {113} defects and eventually transform into dislocation loops of different types. We will show that Ostwald ripening is the key concept for understanding and modelling defect interactions during TED of dopants in Si.
TYPE OF DEFECTS The possibility for extrinsic defects to evolve up to their most stable forms requires that the initial concentration of Si(int)s is sufficiently large and that the surface of the wafer is far
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Figure 1. Plan view (400) WBDF TEM micrographs from samples implanted with 150 keV Ge+ ions to a dose of 2x1015 ions/cm2 after RTA annealing in a N2 ambient. (a) T=800°C, t=10 sec. (b) T=800°C, t=100 sec. (c) T=900°C, t=10 sec. (d) T=900°C, t=400 sec. from the defect region. Such conditions are fulfilled after most
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