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THE EFFECT OF CARBON/SELF-INTERSTITIAL CLUSTERS ON CARBON DIFFUSION IN SILICON MODELED BY KINETIC MONTE CARLO SIMULATIONS R. Pinacho a) b), M. Jaraízb), H. J. Gossmann, G. H. Gilmer, J. L. Benton, P. Werner1) Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974 1) Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany ABSTRACT A new model for carbon diffusion in silicon that explains carbon diffusion during annealing at 850ºC and 900ºC in superlattice carbon structures grown by MBE is implemented using the Monte Carlo atomistic simulator DADOS. Carbon concentrations in the delta layers are 2x1020 cm-3, exceeding by far the solid solubility. The simple kick-out mechanism which incorporates the well established values of the product of diffusivity and equilibrium concentrations of intrinsic point defects and in-diffusion experiments of carbon in silicon does not explain the observed C diffusion profiles. A more detailed analysis of the experiments shows that, in order to fit them, a more unstable Ci is required. Therefore, we include the formation of clusters in the simulations. The formation of carbon/Si self-interstitial clusters promotes the premature break-up of Ci and the increase of the Si self-interstitial concentration in the carbon rich regions and, consequently, provides a better fit to the experiments. The low solubility of carbon in silicon at the annealing temperatures explains why these clusters are formed, even under conditions where the self-interstitial concentration is below the equilibrium value. INTRODUCTION Carbon (C) is present in silicon (Si) as a substitutionally dissolved isovalent impurity, introduced during the crystal growth. It appears in high concentrations, ranging from 1016 cm-3 to 1018 cm-3 , well above its solubility at the usual annealing temperatures. Previous experiments have shown that C can reduce the implantation-induced supersaturation of Si self-interstitials (I) and thus prevent the so-called transient enhanced diffusion (TED) of interstitially diffusing dopants such as boron (B) [1]. Recently, it has been also shown that, even in the absence of I supersaturation, the presence of C in Si in concentrations • 1019 cm-3 leads to an undersaturation of I which, in turn, cause retarded boron diffusion [2]. The diffusion of C in Si occurs via the kick-out mechanism [3, 4]: Cs + I Ci

(1)

where Cs denotes a carbon in a substitutional position that can be considered immobile while Ci is the highly mobile specie that is either a carbon in a interstitial position or a pair composed of a carbon and a self-interstitial. In addition to being the mobile specie of carbon, Ci is believed to be the trap of self-interstitials that produces the reduction of boron diffusion even in conditions of thermal generation of point defects [2, 5] To reproduce carbon diffusion experiments in absence of I supersaturation, continuum simulations, based on standard partial differential equations for the concentrations of I, C i and Cs a) b)

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