Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

19B/2002G194

Electronic Structure of Mn/4H-SiC Interface by SXFS
Masaaki HIRAI*1, Sergei AZATYAN2, CHUNFENG2, CHAGANBALA2,Tomoya FUJISAWA2, Masahiko KUSAKA1 and Motohiro IWAMI1
1
Research Laboratory for Surface Science, Faculty of Science,2
Graduate School of Natural Science and Technology,
Okayama University, Okayama 700-8530, Japan
Introduction
Silicon carbide (SiC) is one of candidate materials in
hard electronics such as high-power, high-frequency,
high-temperature and high-radiation field because of highsaturation electron velocity and high breakdown electricfield compared with silicon (Si). For the application ofelectronic devices it is necessary that the physicalproperties of metal-SiC contact system are clarified. In
this report the partial density of states for Mn/4HSiC(0001) Si-face contact system is studied by soft X-ray
florescence spectroscopy (SXFS).
Experimental
The samples were prepared as follows.
(i) A wafer of 4H-SiC(0001) Si-face was cleaned bybeing rinsed in ethyl alcohol, dipped in 5% HF solutionand flashed under ultra-high vacuum (UHV) condition.
(ii) Mn metal was evaporated on the surface of thissubstrate by heating of tungsten boat with Mn chunks.
(iii)The sample of Mn/4H-SiC(0001) contact system wasthermally treated with direct Joule heating at 400-800°C
for 30 minuets. The film thickness of evaporated Mn was
about 50nm. X-ray emission spectra were obtained in an
SXFS apparatus, which is installed to a beamline BL-19B
at synchrotron radiation facility of Photon Factory in
KEK [1]. Si L2,3 and C K emissions were induced by 135
and 350eV photons, respectively. Photon energies werecalibrated against 4f signals and Fermi edge of Au. ThisSXFS is characterized considering partial density of statesin the total energy states due to dipole selection rule ofelectron transitions.
Results and Discussion
A shape and peak energies of the Si L2,3 florescence
spectra obtained from (a) thermal-treated specimens in
400-800°C for Mn/4H-SiC(0001) Si-face contact systemwere compared with reference ones obtained from
specimens of (b) a pressed powder of MnSi2 and (c) a 4HSiC(0001) Si-face. The spectrum of (c) is characterized
by a hump of 86.5eV, a main peak of 91.7eV and plateau
region from 93eV to 99eV including a small peak at 97eV.
The spectrum of (b) has two peaks at ~91.3 and ~96.2eV
with the similar intensity. The spectra of (a) have thesimilar characteristics as (c), but are entirely different
from one of (b) for spectrum shape and peak energies,
where incident photon beam angle to the specimen
surface normal is 45°.

Next, we have performed the depth profiling analysis
by varying the angle of incident photons. For thespecimen annealed at 500°C, the Si L2,3 florescence
spectrum obtained at the incident angle of 80° to thespecimen surface normal indicates the results that thehump of 86.5eV disappears and the other have the similar
characteristics as 4H-SiC spectrum. Therefore, surface
layer may be covered by very thin reacted materials. But
a component of reacted products cannot be specified due
to be buried under major substrate signal. Also the Si L2,3SXF spectrum obtained from the incident angle of 75° tothe specimen surface normal for specimen annealed at800°C has the same characteristics as 4H-SiC(0001) Siface. Therefore it is considered in this case that Mn metalhas been evaporated from the substrate surface and/or
diffused under the surface region due to high annealing
temperature.
A spectrum shape and peak energies of the C K
florescence spectra obtained from (a) thermal-treatedspecimens in 400-800°C for Mn/4H-SiC(0001) Si-facecontact system were compared with reference ones
obtained from specimens of (b) a 4H-SiC(0001) Si-faceand (c) a graphite plate. The spectrum of (a) ischaracterized by a main peak at 280.7eV, a small peak at
270.7eV and a shoulder at 275.7eV. The spectrum of (b)has a main peak at about 281eV and a shoulder around
276eV. The spectrum of (c) has a single peak at 278eV
and a shoulder around 282eV. The spectra (a) have thesimilar characteristics to one of (b) in respect of spectrum
shape and peak energies. Therefore, it is concluded froma comparison with characteristics of these spectra that CK SXF signals does not indicate possible formation ofcarbides and/or graphite.
Summary
These results are summarized as follows. The Si L2,3
SXF spectra obtained from specimens of thermal-treated
Mn/4H-SiC(0001) Si-fase contact system are the same
one as 4H-SiC to the exclusion of 500°C. It is concluded
that the C K spectra obtained from thermal-treatedsamples are the same one as a carbon signal of thesubstrate and different from a graphite spectrum.
References[1] Y. Harada, et al., J. Sync. Rad. 5, 1013 (1998).
* hirai@science.okayama-u.ac.jp

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