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Influence of Carbon on the Diffusion of Interstitials and Boron in Silicon Mark E. Law, Michelle D. Griglione, and Misty Northridge Department of Electrical and Computer Engineering, University of Florida Gainesville, FL 32611-6130, U.S.A ABSTRACT Carbon is a native impurity in Si which is known to trap self-interstitials and decrease their diffusivity. Carbon has also been observed to decrease B transient enhanced diffusion (TED) in Si through these interstitial interactions. Recently it has been proposed that vacancies must also be considered when accounting for the reduction of B TED. We have incorporated both the kick-out mechanism and the Frank-Turnbull (F-T) mechanism in simulations of interstitial diffusion and carbon diffusion, as well as experiments involving B diffusion in B doped superlattices (DSLs) with varying C concentration regions. We have used the binding energy between a carbon atom and a self-interstitial as a basis for the reaction rates for both mechanisms, and have found that an single energy of 2.25 eV best reproduces the results from several experiments, assuming equilibrium initial conditions for both mechanisms and ab-initio equilibrium values for all point defects. INTRODUCTION Carbon is a common elemental impurity in silicon and its diffusion behavior is well known [1,2]. It is believed to act as a Si interstitial trap [3] which can reduce interstitial diffusivity (DI) values to effective values (DIeff). There has also been significant experimental evidence that high concentrations of carbon reduce transient enhanced diffusion (TED) of B in Si [4,5]. Boron is known to diffuse predominantly via interstitials (fI~0.80 to 1.00) [6]. It is believed that interactions between the carbon and interstitials atoms reduce the number of interstitials available to aid in boron diffusion. Scholz et al. have recently proposed that carbon interaction with vacancies, specifically the Frank-Turnbull (F-T) mechanism, should also be considered when explaining this reduction in B TED [7]. The goal of our investigations is to corroborate this theory by incorporating both the kick-out and F-T mechanisms in the Florida Object Oriented Process Simulator (FLOOPS) and using these combined reactions to fit a variety of experimental conditions. THEORY The carbon interaction with Si interstitials is described by the kick-out reaction C sub + I ←→ C i

(1)

in which Csub denotes a carbon substitutional atom, I denotes a Si interstitial, and Ci denotes a carbon interstitial. The occurrence of a carbon atom combining with a vacant lattice site is described by the F-T reaction C i + V←→ Csub B7.4.1

(2)

where V denotes a lattice vacancy. The forward reaction rate is given simply by 4πrlDI for equation 1 and 4πrlDV for equation 2, with rl being the distance between the lattice atoms. The reverse reaction rate for equation 1 is a function of the binding energy and entropy of a substitutional carbon atom and a Si interstitial. It is important to note that we have assumed these reaction equations to be in equilibrium at