Trapping of Oxygen at Homoepitaxial Si-Si Interfaces Grown by Molecular Beam Epitaxy
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TRAPPING OF OXYGEN AT HOMOEPITAXIAL Si-Si INTERFACES GROWN BY MOLECULAR BEAM EPITAXY
R. HULL*, M.E. TWIGG, J.C. BEAN, J.M. GIBSON, and D.C.JOY AT&T Bell Laboratories, 600 Mountain Av., Murray Hill, NJ 07974 *Now at: Hewlett Packard Laboratories, 3500 Deer Creek Road, Palo Alto, CA 94304
ABSTRACT Interfaces between Si substrates and epitaxial Si buffer layers grown are shown to contain a high density of by Molecular Beam Epitaxy (MBE) It is also SiOx pockets for certain sustrate preparation conditions. shown that post-deposition thermal annealing of these structures grown upon Czochralski wafers can lead to a greatly increased defect density at the interface. The primary model proposed for this increase is trapping of background oxygen diffusing from the bulk of the Czochralski substrate wafers.
INTRODUCTION AND SUBSTRATE PREPARATION and electron beam-stimulated Transmission electron microscopy (TEM) X-ray microanalysis are used to study the interface structure between substrates. epitaxial Si buffer layers grown by MBE and Si (100) and (111) Buffer layers are commonly employed in MBE growth to ensure high For quality crystal surfaces for subsequent growth of epitaxial layers. optimum results, careful attention has to be paid both to the buffer layer growth and to preparation of the original substrate surface (see reference In this work we adopted Wi for a review of these topics in Si MBE). the following procedure: (1) Chemical cleaning of Si substrates is performed using the method outlined by Henderson [2]. The substrates most commonly used in this 10 ohm-cm boron-doped Czochralski-grown, although study were Wacker (100) Czochralski (111) and Float Zone (100) wafers were also utilized. (2) Following chemical cleaning, room temperature argon ion sputtering was performed in vacuo to remove surface oxide and any other contaminants. Standard conditions were a beam energy of 1 keV and current density of 2 lmA/cm . Earlier work has shown these to be the optimum conditions for substrate preparation by argon ion sputtering [3]. 0
(3) The substrate is annealed at 800 C for about 5 minutes to remove sputtering damage. LEED patterns, Rutherford Backscattering and TEM show that this is sufficient to remove sputtering damage and restore the relevant surface reconstruction [3]. (4) Following radiative cooling, 0 temperatures between 550 and 750 C. 1000A at a growth rate of 5 k/sec.
the buffer layer is The thickness grown
Mat. Res. Soc. Symp. Proc. Vol. 59. 91986 Materials Research Society
deposited at is generally
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STRUCTURE OF INTERFACIAL DEFECTS Cross-sectional transmission electron microscopy (i.e. with the electron beam parallel to the Si-Si interface) shows a high density of ellipsoidal defects at the (100) homoepitaxial interface for certain sputter cleaning conditions, as shown in Fig. 1. These defects are typically 30A along the major axis and are separated by about 200 A. As seen in Fig. 1(A), there is no lattice disturbance across the interface, indicating that these defects are not associated with isolat
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