Characterization of the Segregation of Arsenic at the Interface SiO 2 /Si
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0994-F08-02
Characterization of the Segregation of Arsenic at the Interface SiO2/Si Christian Steen1, Peter Pichler1,2, Heiner Ryssel1,2, Lirong Pei3, Gerd Duscher3,4, Matt Werner5, Jaap A. van den Berg5, and Wolfgang Windl6 1 University of Erlangen-Nuremberg, 91058 Erlangen, Germany 2 Fraunhofer Institute of Integrated Systems and Device Technology, 91058 Erlangen, Germany 3 North Carolina State University, Raleigh, NC, 27695-7907 4 Oak Ridge National Laboratory, Oak Ridge, TN, 37831 5 University of Salford, Salford, M5 4WT, United Kingdom 6 Ohio State University, Columbus, OH, 43210-1178
ABSTRACT The segregation of As atoms at the Si/SiO2 interface during annealing was investigated by grazing incidence X-ray fluorescence spectroscopy in combination with successive removal of silicon layers by etching with thicknesses on the order of a nanometer. With this method it is possible to clearly distinguish between the segregated atoms and the As atoms in the bulk over a large range of implantation doses from 3∑1012 cm-2 to 1∑1016 cm-2. The samples were annealed at 900 ∞C and 1000 ∞C, respectively, for times sufficiently long to ensure that the segregation reflects an equilibrium effect. The results were confirmed by medium energy ion scattering, Zcontrast measurements and electron energy loss spectroscopy. INTRODUCTION Due to the continuous shrinking of advanced semiconductor devices, dopant activation becomes one of the dominant problems to solve. One of its limiting factors is the segregation of dopants at the SiO2/Si interface. Previous work has established that the segregated dopants are immobile [1,2] and can be removed by a dip in hydrofluoric acid [3]. The most recent experiments strongly suggest that the dopants pile up in a thin layer on the silicon side of the interface [4,5] and that the dose loss is partially reversible [4]. To gain additional insight into the segregation process, a systematic study was made based on Gracing Incidence X-Ray Fluorescence spectroscopy (GI-XRF) in combination with the successive removal of thin silicon layers by etching. Selected samples were characterized by Medium Energy Ion Scattering (MEIS), Electron Energy Loss Spectroscopy (EELS), and Z-contrast measurements. EXPERIMENTAL DETAILS 150 mm Czochralski (100) Si wafers were used for all experiments. Prior to implanting arsenic with an energy of 32 keV and doses from 3∑1012 cm-2 to 1∑1016 cm-2, the native oxide was removed by HF. The tilting of the wafers was 7∞ to reduce channeling effects. After implantation, the wafers were cleaned in a 4:1 solution of H2SO4 and H2O2 at 140 ∞C for 20 min. The regrown thin surface oxide was then removed by another HF dip, followed by the growth of
a thin thermal oxide (about 5 ñ15 nm, dependent on the implantation dose) by wet oxidation at 700 ∞C for 10 minutes. Subsequently, samples were annealed in a nitrogen ambient for 2 and 6 h at 900 ∞C, and 10 and 30 min at 1000 ∞C. The annealing periods were chosen sufficiently long to ensure that the segregation at the interface found experimental
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