Structural Comparisons of SiO x and Si/SiO x Formed by Passivation of Single-Crystal Silicon by Atomic and Molecular Oxy
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Structural Comparisons of SiOx and Si/SiOx Formed by Passivation of Single-Crystal Silicon by Atomic and Molecular Oxygen Maja Kisa, Ray D. Twesten* and Judith C. Yang Materials Science and Engineering Department, 848 Benedum Hall, University of Pittsburgh, Pittsburgh, PA 15213 USA * Center for Microanalysis of Materials, Frederick Seitz Materials Research Laboratory 104 S. Goodwin Avenue, Urbana, IL 61801 USA ABSTRACT The structural characteristics of a silica layer and Si/SiO2 interface formed on Si singlecrystal by oxidation in hyperthermal atomic oxygen (AO) and molecular oxygen (MO) at 493K were compared by wide variety of experimental techniques. The hyperthermal AO with kinetic energy of 5.1eV was created by the pulsed laser detonation of oxygen gas. The oxide formed by AO and MO on Si single crystal is amorphous as observed by HRTEM and selected area electron diffraction (SAED). However, the oxide formed by AO has a less random distribution of silicon and oxygen atoms as compared to the oxide formed by MO, as evidenced by the SAED patterns and EELS spectra. In contrast to MO formed silica, initial EELS results across the Si/SiO2 interface revealed no region of suboxides exists near the interface in the AO formed silica. The Si/SiO2 interface formed by AO species was found to be very abrupt and the oxide homogeneous, as opposed to the broad interface and non-homogeneous oxide created by MO, as determined by HRTEM and EELS. INTRODUCTION Satellites and space vehicles residing in the low earth orbit (LEO) are subjected to a harsh environment that can increase their failure rate. LEO ranges from 200 to 700km in altitude, with average surface temperatures that vary between 200 and 400K [1]. The primary and the most hazardous factor causing materials corrosion and degradation is atomic oxygen (AO). AO concentration increases with decreasing altitude. As a direct consequence of high velocity of orbiting spacecrafts (8km/sec at 250km altitude), the AO flux is very high (1014 atoms cm-2sec-1) and has kinetic energy of about 5eV. There is also a distribution of AO impact energies as a result of the AO thermal velocity and orbital inclination. This study focuses on the passivation of semiconductors, particularly silicon, by hyperthermal AO. Silicon is chosen as a model material since 600-1300Ao thick SiOx (1.9 < x
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