A Comprehensive Model for Carbon Suppression of Boron Transient Enhanced Diffusion
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A Comprehensive Model for Carbon Suppression of Boron Transient Enhanced Diffusion Julie L. Ngau, Peter B. Griffin, and James D. Plummer Center for Integrated Systems, Stanford University, Stanford, CA 94305, U.S.A. ABSTRACT In this work, the time evolution of B transient enhanced diffusion (TED) suppression due to the incorporation of 0.018% substitutional carbon in silicon was studied. The combination of having low C concentrations, which reduce B TED without completely eliminating it, and having diffused B profiles for several times at a single temperature provides much data upon which various models for the suppression of B TED can be tested. Recent work in the literature has indicated that the suppression of B TED in C-rich Si is caused by non-equilibrium Si point defect concentrations, specifically the undersaturation of Si self-interstitials, that result from the coupled out-diffusion of carbon interstitials via the kick-out and Frank-Turnbull reactions. Attempts to model our data with these two reactions revealed that the time evolved diffusion behavior of B was not accurately simulated and that an additional reaction that further reduces the Si self-interstitial concentration was necessary. In this work, we incorporate a carbon interstitial, carbon substitutional (CiCs) pairing mechanism into a comprehensive model that includes the C kick-out reaction, C Frank-Turnbull reaction, {311} defects, and boron interstitial clusters (BICs) and demonstrate that this model successfully simulates C suppression of B TED at 750 °C for anneal times ranging from 10 s to 60 min. INTRODUCTION Recently, research has shown that the incorporation of substitutional carbon in silicon suppresses boron transient enhanced diffusion (TED). Out-diffusion experiments of highly supersaturated C have indicated that the depletion of Si self-interstitials (I) in C-rich Si, which in turn leads to the reduction of B TED, is caused by the coupled out-diffusion of carbon interstitials via the kick-out [1] and Frank-Turnbull reactions [2]. We have previously investigated the suppression of boron TED through localized, substitutional incorporation of C into Si1-xGex for various times at 750 °C [3]. This work examines the phenomena of suppressed B TED for C-doped Si and eliminates any strain or chemical interactions between Ge and C. Simulating the time evolution of the B diffusion profiles has provided insight into the possible mechanisms through which C, B, and I interact to produce the observed experimental results. We have found that the kick-out and Frank-Turnbull reactions for C are insufficient for modeling the B and C profiles for all anneal times investigated. Therefore, we propose that an additional reaction that further reduces the Si I concentration is necessary. EXPERIMENTAL PROCEDURE The test structure used in these experiments consisted of 2 X 1018 cm-3 boron marker layers positioned above and below a pure Si or C-doped Si layer with [C]= 0.018% as illustrated in Fig. 1. The samples were grown by atmospheric pressure chemical vapo
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