Experimental Investigation of the Impact of Implanted Phosphorus Dose and Anneal on Dopant Diffusion and Activation in G
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1070-E01-08
Experimental Investigation of the Impact of Implanted Phosphorus Dose and Anneal on Dopant Diffusion and Activation in Germanium Vincent Mazzocchi, Stéphane Koffel, Cyrille Le Royer, Pascal Scheiblin, Jean-Paul Barnes, and Marco Hopstaken CEA-LETI MINATEC, 17 rue des Martyrs, Grenoble, 38054, France ABSTRACT In this work, we have investigated the influence of low energy ions implantation, variations of dose implant and low temperature anneal on diffusion, exo-diffusion and activation of phosphorus into germanium. Experimental results show that we achieved a high electrical activation level, around 5×1019 at.cm-3. We tuned both dose implant and annealing temperature in order to limit the exo-diffusion with practically no in-diffusion of the dopant. We also showed that very abrupt profiles can be achieved with appropriate implant and thermal anneal conditions. To limit the leakage current in Ge MOS devices [1], the defects generation during the implantation has to be limited. For annealing temperature below 550°C, we have observed by cross-sectional Transmission Electron Microscopy (TEM) that the defects were totally removed by addition of a pre-annealing step of 1 hour at 400°C. INTRODUCTION Germanium has regained attention in the semiconductor industry for MOSFET application [2] because of its larger carrier mobility values – two times higher for electrons and four times for holes - as compared to silicon [3]. Two of the major issues with germanium are limiting the n-dopant diffusion [4] and increasing the electrical activation level. Because of its high chemical solubility limit, phosphorus seems to be the best choice for n-dopant in germanium [5]. However a large gap between the electrical activation and the equilibrium solid solubility of P in Ge has been observed. High level activation is still to be reached. Recent publications indicate that a high level of activation can not be obtained without the diffusion and exo-diffusion of the P into Ge [4]. In the present study, 2.5 µm germanium epitaxial layers on Si (001) [6] were subjected to several phosphorus implant conditions, and different activation anneals in order to determine the best conditions to obtain a high activation level without dopant diffusion. Furthermore cross-sectional TEM were performed to study conditions so as to obtain a crystalline germanium without any defects. EXPERIMENT In this study we used 2.5µm non-intentionally doped (NID) Ge layer epitaxially grown by Reduced Pressure-Chemical Vapor Deposition (RPCVD) onto 200mm Si (001) wafers [6]. No special surface preparation or cleaning was performed prior to implantation. Wafers were implanted with phosphorus at 7° tilt and 27° twist to avoid channelling effects. Implantations were performed at 0°C with energies from 15keV to 40keV and doses from 8×1013cm-2 up to 1×1015 cm-2. Selected implanted wafers were capped with 5 nm thick SiO2 deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) at a temperature of 380°C during 30s. Then wafers were annealed in nitrogen atmosphere
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