Formation of SiGe Nanoparticles by Dry and Steam Thermal Oxidation of Thin Polycrystalline Layers
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Formation of SiGe Nanoparticles by Dry and Steam Thermal Oxidation of Thin Polycrystalline Layers M. I. Ortiz 1, C. Ballesteros 1, A. Rodríguez 2, J. Sangrador 2, T. Rodríguez 2, M. Avella 3, P. Martín 3, J. Jiménez 3 1 Dpto. Física, E.P.S., Universidad Carlos III, 28015 Leganés (Madrid), Spain. 2 Dpto. Tecnología Electrónica, E.T.S.I.T., Universidad Politécnica de Madrid, Madrid, Spain 3 Dpto. Física de la Materia Condensada, E.T.S.I.I., U. de Valladolid, Valladolid, Spain.
ABSTRACT Nanoparticles embedded in a dielectric medium have been formed by dry and steam thermal oxidation at specific temperatures and process times of polycrystalline Si0.7Ge0.3 layers deposited on thermally oxidized Si substrates. We present a study of the influence of the oxidation process parameters: oxidation atmosphere, temperature and time on: a) the composition of the grown oxide, b) the Ge segregation, c) the formation of nanoparticles, their composition and size, and d) the properties of the cathodoluminescence emission of the oxidized films. Oxidation in a dry O2 atmosphere results in a full Ge segregation. The formation of Ge islands embedded in an oxide matrix is demonstrated. Ge segregation is slower in steam thermal oxidation than in dry O2. In this case Ge-rich SiGe particles are formed. In both processes, an important increase in the cathodoluminescence emission associated with the presence of Ge rich nanoparticles is obtained.
INTRODUCTION The formation of a high density of nanocrystals with uniform size, less than 5 nm, embedded in a high quality oxide matrix is an essential process for the fabrication of the single electronic devices proposed for the next generation of nanoscale electronic devices. The formation of the upper control oxide and the nanocrystals by simultaneous dry oxidation and solid phase crystallization of amorphous SiGe films has been reported [1]. We present results about the formation of the upper oxide and the nanocrystals by dry O2 and steam thermal oxidation of thin polycrystalline Si0.7Ge0.3 layers. The use of polycrystalline films makes possible to study the oxidation process isolated, not competing with crystallization. Moreover, a more accurate control of the particle composition is expected using steam oxidation, since Ge segregation is less important than in dry O2 oxidation. The characteristics of the grown oxides and the nanocrystals formed were studied by FTIR, Raman spectroscopy, cathodoluminiscence and TEM.
EXPERIMENT Amorphous SiGe 35 nm thick layers with Ge fraction x=0.3 were deposited using a hot wall LPCVD reactor. Pure disilane (Si2H6) and germane (GeH4) were used as precursor gases. The GeH4 to Si2H6 gas flow ratio was 0.82, while keeping the total flow constant at 10 sccm. No carrier gas was used. During the deposition, both temperature and pressure were kept constant at
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425 ºC and 300 mTorr respectively. Thermally oxidized silicon wafers were used as substrates. The details of the deposition process are described elsewhere [2]. After the deposition, the films
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