Self- and Dopant Diffusion in Extrinsic Boron Doped Isotopically Controlled Silicon Multilayer Structures
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Self- and Dopant Diffusion in Extrinsic Boron Doped Isotopically Controlled Silicon Multilayer Structures Ian D. Sharp,a,b Hartmut A. Bracht,c Hughes H. Silvestri,a,b Samuel P. Nicols,a,b Jeffrey W. Beeman,b John L. Hansen,d Arne Nylandsted Larsen,d and Eugene E. Hallera,b a Department of Materials Science, University of California, Berkeley, CA 94720 b Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 c Institut für Materialphysik, Universität Münster, D 48149 Münster, Germany d Institute of Physics and Astronomy, University of Aarhus, DK 8000 Aarhus, Denmark ABSTRACT Isotopically controlled silicon multilayer structures were used to measure the enhancement of self- and dopant diffusion in extrinsic boron doped silicon. 30Si was used as a tracer through a multilayer structure of alternating natural Si and enriched 28Si layers. Low energy, high resolution secondary ion mass spectrometry (SIMS) allowed for simultaneous measurement of self- and dopant diffusion profiles of samples annealed at temperatures between 850oC and 1100°C. A specially designed ion-implanted amorphous Si surface layer was used as a dopant source to suppress excess defects in the multilayer structure, thereby eliminating transient enhanced diffusion (TED) behavior. Self- and dopant diffusion coefficients, diffusion mechanisms, and native defect charge states were determined from computer-aided modeling, based on differential equations describing the diffusion processes. We present a quantitative description of B diffusion enhanced self-diffusion in silicon and conclude that the diffusion of both B and Si is mainly mediated by neutral and singly positively charged self-interstitials under p-type doping. No significant contribution of vacancies to either B or Si diffusion is observed. INTRODUCTION The aim of this study is to reveal the mechanism of self- and dopant diffusion in boron doped extrinsic Si. Knowledge of the diffusion mechanism will allow for the development of a comprehensive and predictive diffusion model that is based upon physically justifiable parameters. This fundamental understanding of self- and dopant diffusion may help reduce diffusion-related problems associated with increasingly shallow and highly doped junctions. Simultaneous analysis of self- and dopant diffusion will also reveal information about the process of self-diffusion in intrinsic Si. Historically, Si self-diffusion experiments have been carried out using the radioactive isotope tracer 31Si [1-4]. Due to the short half-life of 31Si (t1/2 = 2.6 h), the usefulness of these experiments was limited to short diffusion anneals at high temperatures. In recent years, highly enriched and chemically pure stable isotopes have become available. Stable isotope tracers allow for annealing times of any length over much broader temperature ranges, thereby increasing the accuracy of experimental results. These stable isotopes have been successfully used for intrinsic Si self-diffusion experiments [5,6] and preliminary studies on self-diffusion
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