CHEMICAL TITRATION OF CLEAN SILICON SURFACES WITH N2O AND O2 - ATOMIC NATURE OF 5X1 RECONSTRUCTED SI(110)

Using spectroscopic differential reflectometry (SDR), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) we have studied the room temperature adsorption behavior of N20 and 02at the clean low-Miller index Si surfaces. Decomposition of the nitrous oxide molecule, resulting in Si-0 bond formation, only occurs at the top layer Si atoms which have an unsaturated dangling bond. In this way it has been possible to determine the number of broken bonds at these clean reconstructed surfaces using AES. From a comparison of the site-specific adsorption of N20 with the non site-specific adsorption of 02we propose a model of the atomic nature of the Si(110) surface showing a prominent 5X1 reconstruction which is in agreement with previously published LEED results and recent scanning tunneling microscopy (STM) and ultraviolet photoemission spectroscopy (UPS) work. This model is based on a reduction of dangling bonds which is due to the formation of adatoms. The model also includes a kind of rest atoms and atoms in nearest-neighbor top layer chains along the [110] direction (A type). We have found that the ratio adatoms/rest atoms/A atoms per reconstructed unit cell determines the primary superstructure. This ratio also accounts for a more or less “apparent” coexistence of higher order reconstructions very often reported in LEED studies, their presence being in the form of streaks at various fractional order positions along the [TlO] direction. A real coexistence of various reconstructions with partial order at the Si(llG) surface cannot be excluded as evidenced by STM, a result which makes it the most complicated low-Miller index Si surface to study. Complementary information concerning the energy position of the unoccupied surface states has been obtained from SDR. Our clean Si( 110) surface shows partial order along the [TlO] direction, indicating the coexistence of 5X2 and 5x5 superstructures in addition to the observed prominent 5X1 LEED reconstruction. It has been derived that this surface has empty states at about 0.9 and 1.7 eV above the Fermi level (EF). The occupied states at about 0.8 and 2.4 eV below EFcould be identified with rest atoms and ^4-type atoms, respectively. © 1990, American Vacuum Society. All rights reserved.