Furnace and Rta Injection of Point Defects into CVD-Grown B Doped Si and SiGe
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FURNACE AND RTA INJECTION OF POINT DEFECTS INTO CVD-GROWN B DOPED Si AND SiGe Janet M. BONAR, Barry M. McGREGOR***, Nick E. B. Cowern**, Aihua DAN*, Graham A. COOKE****, and Arthur F. W. WILLOUGHBY*, Department of Electronics and Computer Science, and *Materials Research Group, School of Engineering, University of Southampton, Southampton, UK; **Philips, Eindhoven, The Netherlands; ***Department of Engineering, University of Cambridge, Cambridge, UK; ****ASP Group, University of Warwick, Coventry, UK; ABSTRACT The diffusion of B in Si and SiGe under the influence of point defect injection by Rapid Thermal Anneal (RTA) and conventional furnace anneal is studied in this work. B-doped regions in SiGe and Si were grown by LPCVD, and point defects were injected by RTA or furnace annealing bare, Si3N4 or SiO2 + Si3N4 covered samples in an oxygen atmosphere. Self-interstitial defects will be injected into bare Si while vacancy defects will be injected into Si3N4 covered samples, and inert annealing will occur in SiO2 + Si3N4 covered samples. The annealed and asgrown profiles were determined using SIMS analysis, and the diffusivities extracted by direct comparison of the profiles. Both interstitials and vacancies were injected during furnace annealing of SiGe, as demonstrated by the respective enhancement and retardation of the B diffusion. Enhanced B diffusion in SiGe was observed even for 5 s RTA at 10000C, with an enhancement factor of ~2.5. The B in Si diffusivity enhancement for interstitial injection by RTA oxidation was found to be a factor of ~3 compared to inert anneals, close to the factor for SiGe. INTRODUCTION Boron is generally accepted to diffuse by an interstitial-mediated mechanism in Si, and recently published results suggest a primarily interstitial-mediated mechanism is responsible in SiGe alloy concentrations of 20% Ge1. Kuo et al2 showed that injection of interstitials by 800oC furnace anneals under oxidizing conditions enhanced B diffusivity up to a factor of 10 for B in Si and 13 for B in SiGe compared to inert anneals, independent of Ge content. Fang et al1 showed that injection of vacancies by annealing in ammonia retarded the diffusion of B in 20% SiGe compared with inert annealing by a factor of 0.2. Given that RTA is often utilized in the Si device fabrication process, and that B is the dominant p-type doping species in Si devices, the study of B diffusion by defect injection by RTA, in comparison to furnace annealing, seems relevant. Therefore, this work attempts to inject both interstitials and vacancies in the same run, by furnace annealing and by RTA, to compare the effects of defect injection by the different anneal processes. Samples consisting of both Si and 10% SiGe will allow confirmation of the models developed from the separate injection experiments, as well as comparison of defect injection by the different annealing methods. EXPERIMENT Epitaxial layers were grown by Low Pressure Chemical Vapour Deposition (LPCVD) using SiH4, GeH4, B2 H6 and H2. Substrates were p+ CZ (100), and were R
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