Valence Band Discontinuity at and Near The SiO 2 /Si(111) Interface
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First, 200-nm-thick-oxide film
421 Mat. Res. Soc. Symp. Proc. Vol. 477 01997 Materials Research Society
was formed on 10 - 20 Q "cm n-type Si(11) surface. Second, this oxide was removed, followed by the treatment in 40% NH 4F solution.[7] The Si surfaces thus prepared were terminated with hydrogen atoms and are atomically flat. By heating hydrogen-terminated Si surfaces (abbreviated as the H-Si surfaces hereafter) thus prepared in 4 Torr dry oxygen at 3000C for nearly 360 min, preoxide with the thickness of nearly 0.5 nm was formed. Through this preoxide, oxidation was performed in the same oxidation atmosphere at 6009C up to the thickness of nearly 0.95 nm. Further oxidation was performed at 8009G up to the thickness of nearly 1.6 nm and at 8509C up to the thickness of nearly 1.8 nm. A part of the Si surface, whose area is 20 mm in diameter and the central part of which was used for valence band study, was heated by light. The dew point of oxygen gas used for the oxidation are below -959C. The valence band spectra and Si 2p photoelectron spectra excited by monochromatic AlKa radiation were measured at photoelectron take-off angle of 15 and 90 degrees with an acceptance angle of 3.3 degrees, using ESCA-300 manufactured by Scienta Instruments AB. [8] Other experimental details and the analytical procedure of Si 2p photoelectron spectra were described elsewhere.[9] EXPERIMENTAL RESULTS AND DISCUSSION Figure 1 shows the changes in valence band spectra with the progress of oxidation in 1 Torr dry oxygen at 600-8501C for oxide film thickness up to 1.8 nm measured at photoelectron takeoff angle of 15 and 90 degrees. The valence band of H-Si surface before the oxidation and that of Si surface after the oxidation of H-Si surface in 1 Torr dry oxygen at 3001C are strongly affected by the termination with Because the hydrogen atoms. e=15" C desorption of hydrogen occurs above Si02 9i(111) 2 5009C , the valence band spectra of Dry 02 .TonW silicon oxide formed in 1 Torr dry .9o oxygen at 600 - 850 °C can be 5 consideringin Si-H analyzedandwithout C-Oxide Film bond are discussed the
/2
following. Figures 2(a) and 2(b) indicate examples of two kinds of analytical procedures. The first procedure is to take difference between valence band spectra measured for two thicknesses, which are close enough to each other, so as to eliminate the valence band spectrum of silicon substrate. From this analysis the valence band
spectrum of oxide surface can be
If we assume that the obtained. valence band discontinuity does not depend on the interface structure, but depend on the distance from the interface, the change in valence band spectrum produced as a result of
1.0 Thickness (nm)
Q
"/0 Z
0 15 10 5 Binding Energy (eV)
Cn
2 1a) Z' C.0 M_. " D
e =go,
Si02 S011) lTon" Dry 02 Si 1.5 O eFc 1.0 Thickness (nm)
0.2 0 5 15 10 Binding Energy (eV) Fig. 1 Changes in valence band spectra of silicon oxide with the progress of oxidation. E z
422
small increase in oxide film thickness corresponds to the valence band spectrum of the oxide
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