In-Situ Study of the Oxide Mediated Epitaxy of CoSi 2 on Si
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Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801 ** Institute of Materials Research and Engineering, Singapore 119260 and Department of Materials Science, University of Illinois at Urbana-Champaign, Urbana, IL 61801 *** Materials Research Division, Argonne National Laboratories, Argonne, IL 60439 and Departments of Physics and Materials Science, University of Illinois at UrbanaChampaign, Urbana, IL 61801 *
ABSTRACT Oxide Mediated Epitaxy (OME) shows promise as a method to form good quality, thin epitaxial CoSi 2 films on most Si surfaces. We have performed an in-situ study of the OME of CoSi, on the Si (001) surface. Our work was carried out with our specially modified ultra-high vacuum transmission electron microscope (UHV TEM) SHEBA (Surface High Energy Electron Beam Apparatus). With SHEBA we were able to monitor the diffraction pattern and therefore the phase formation throughout the anneal. Our results confirm the suppression of intermediate phases during CoSi 2 formation in the OME process. We also see a difference in the as deposited Co film when the oxide coated silicon surface is used rather than a clean substrate. From combined imaging and diffraction studies we will shed some light on the mechanism behind the success of OME. INTRODUCTION Uniform, thin epitaxial silicide films are sought after for their potential application in microelectronic structures. CoSi 2 is a particularly good candidate because of its good lattice match with Si (-1.2%) and low resistivity (14[tQ-cm). In addition, it does not suffer from the dimensional limitations of TiSi 2 . However, single crystal CoSi 2 fails to form by direct deposition and anneal on the most desirable silicon surface, Si (001) [1]. Several techniques have been proposed that facilitate single crystal growth on the Si (100) surface; TIME (Ti-interlayer mediated epitaxy) [2], HTS (high temperature sputtering) [3], and OME (oxide mediated epitaxy) [4] to name a few. Of these we have chosen to examine OME to gain some understanding of the underlying mechanism behind several of these techniques. In OME, a thin oxide layer is formed on the clean Si surface by the Shiraki process [5]. A thin layer of Co (1-3 nm ) is then deposited on top of the oxide. Upon annealing to 500-700' C an essentially uniform epitaxial single crystal CoSi 2 film is found in contact with the Si. It has been observed in OME that the traditional metal rich phases were not found in the process, but because of experimental difficulties the possibility could not be ruled out. It is therefore suspected that the absence of the phases Co2Si and CoSi in silicide growth play some role in the formation of single crystal CoSi 2. That is, the formation of the metal rich phases are responsible for the formation of polycrystalline CoSi 2 when no oxide layer is present. So there is still a question as to what aspect of the oxide layer aids in the silicide film development. The majority of the work performed in this study was carried out inside our modified UHV TEM, SHEBA,
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