Oxidation Of Si / nc-Ge / Si Heterostructures For Non Volatile Memory Applications
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Q11.34.1
Oxidation Of Si / nc-Ge / Si Heterostructures For Non Volatile Memory Applications M. Kanoun, A. Souifi, S. Decossas, C. Dubois, and G. Bremond. Laboratoire de Physique de La Matière, UMR-CNRS 5511, INSA De Lyon, Bât.502, 20 Av. Albert Einstein, 69621 Villeurbanne Cedex, France. F. Bassani, Y. Lim, A. Ronda, and I. Berbezier. Campus de Luminy, Case 913 13288 Marseille Cedex 9, France. O. Kermarrec, and D. Bensahel. STmicroelectronics, 850 Rue Jean Monnet, 38926 Crolles, France. ABSTRACT In this work, we present an extensive study of the oxidation process of Si/Ge nanocrystals (nc-Ge)/Si samples using SIMS (Second Ion Mass Spectroscopy), Transmission Electron Micrscopy (TEM), Atomic Force Microscopy (AFM) and electrical characterization of Metal/Oxide/Semiconductor capacitors (MOS). Various samples with different oxidation times have been studied and it is demonstrated that Silicon dry oxidation kinetics is not influenced by the presence of Ge. As shown by SIMS measurements, a pure SiO2 layer is formed on the top of the structure, while the Ge atoms are intermixed with the silicon substrate. The TEM and AFM analysis show that the nc-Ge height is drastically reduced during the oxidation process. The fabrication of MOS capacitors on the structures allowed to study electron and hole trapping in the Ge dots. From our analysis we have shown that the Ge nanostructures which covered by SiO2 are not isolated from the Si substrate. INTRODUCTION The use of nanocrystals has been proposed by Tiwari et al. [1] in order to develop highly integrated few electron memories. The use of a floating gate composed of isolated dots reduces the problems of charge loss encountered in conventional Flash memories, allowing for thinner injection oxides and, hence, smaller operating voltage, better endurance, and faster write/erase speeds [1,2]. The memory function of these devices has been attributed to the charge exchange between nanocrystals and inversion layer. After the first proposal of a memory transistor using silicon nanocrystals (nc-Si) as floating gates, other works have confirmed that non volatile memories (NVM) using PMOS or NMOS transistors can be achieved. In order to improve the data retention in NVM, it seems interesting to use Ge nanocrystals (nc-Ge) rather than nc-Si because of its smaller band gap. Indeed King et al [3] have recently demonstrate the superior properties of Ge based nanocrystals memories over those based on Si, in terms of the writing/erasing time. In spite of the fact that non volatile memories with implanted Genanocrystals have been demonstrated [4,5] it is also important to obtain well ordered nc-Ge for future NanoFlash memories with a few numbers of nanocrystals.
Q11.34.2
In this paper, we will describe the oxidation process of Si/nc-Ge/Si heterostructures grown by by Low Pressure chemical Vapor Deposition (LPCVD). For our study, we have combined AFM and TEM analysis for morphological characterization of the Ge dots. SIMS measurements have been also used in order to extract the Ge profiles and
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