Modeling of Effect of Stress on C Diffusion/Clustering in Si
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1070-E03-07
Modeling of Effect of Stress on C Diffusion/Clustering in Si Hsiu-Wu Guo1, Chihak Ahn2, and Scott T Dunham1 1 Electrical Engineering, University of Washington, Seattle, WA, 98195 2 Physics, University of Washington, Seattle, WA, 98195 ABSTRACT Extensive ab-initio calculations were performed to find formation energies of stable C complex configurations in silicon as function of stress. The results indicate that substitutional C is the lowest energy state, while the split interstitial is the dominant mobile species. Investigation of small carbon/interstitial clustering suggests that these clusters are only significant under a substantial interstitial supersaturation. We studied the diffusion path for neutral C including the impact of stress. Through KLMC analysis of stress effect on diffusivity, we found that tensile biaxial strain enhances the effective C diffusivity, with a stronger stress dependence for C diffusivity in the out-of-plane direction. INTRODUCTION The formation of very shallow and abrupt dopant profiles with high electrical activation is required for the exponential downscaling of metal-oxide-semiconductor field-effect transistors (MOSFETs). Carbon co-implantation can reduce B transient enhanced diffusion (TED) [1] and several experiments have shown that C provides a highly efficiency sink for excess interstitials during annealing [2-4]. Napolitani et al. [3] also found no detrimental effects on B electrical activation with the incorporation of C. Since strain engineering to enhance carrier mobility is widely used in CMOS technology, it is important for the behavior of impurity diffusion and activation under stress to be thorough understood. To that end, we perform ab-initio calculations for a range of carbon complex configurations and find the diffusion path of carbon interstitial in neutral charge statel. Using Kinetic Lattice Monte Carlo (KLMC) simulations, we predict the impact of stress on carbon diffusion. CARBON COMPEX FORMATION Carbon is most stable as a substitutional impurity Cs in the neutral charge state. Carbon interstitials (CI) can be generated through kick-out or Frank-Turnbull mechanisms [5-7]. (1) (2) Experimental results [5, 7] and theoretical study [8] suggest the split carbon interstitial as the ground-state CI configuration. Our DFT calculations of formation energies of carbon interstitials in different configurations (see TABLE I) confirmed the split as the most stable CI structure. In this configuration, the C and Si atoms are displaced along a direction sharing a single lattice site. For all the calculations in this work, the density function theory code VASP [9, 10] was used with 64-atom supercell, energy cutoff of 340eV, and 23 Monkhorst -point sampling method within generalized gradient approximation (GGA). A possible clustering reaction to reduce the silicon interstitial concentration is CI-Cs pairing (Eq.3), which forms a stable and immobile carbon complex [11]. (3) In equilibrium,
, where
(4)
is the free energy of formation for C2I, and is the density of
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