Metalorganic chemical vapor deposition of aluminum oxide on Si: Evidence of interface SiO2 formation

Article abstract of DOI:10.1063/1.1483903

Thin films of aluminum oxide were deposited on H-passivated Si(100) substrate using trimethylaluminum and oxygen at 0.5 Torr and 300°C. Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopic analyses of these films showed no aluminum silicate phase at the film-substrate interface. The O/Al ratio in the deposited film was found to be higher than that in stoichiometric Al₂O₃. On annealing the as-deposited samples in Ar at 900°C, an absorption peak due to the transverse optical phonon for the SiOSi stretching mode appeared in the FTIR spectra. A combination of Z-contrast imaging and electron energy-loss spectroscopy in the scanning transmission electron microscope confirmed that the annealed samples developed a layer of silicon dioxide at the aluminum oxide-Si interface. Our results suggest that excess oxygen present in the deposited film reacts with the underlying Si substrate and forms silicon oxide.

Full text of DOI:10.1063/1.1483903

Metalorganic chemical vapor deposition of aluminum oxide on Si: Evidence of interface
SiO 2 formation
A. Roy Chowdhuri, C. G. Takoudis, R. F. Klie, and N. D. Browning
Citation: Applied Physics Letters 80, 4241 (2002); doi: 10.1063/1.1483903
View online: http://dx.doi.org/10.1063/1.1483903
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APPLIED PHYSICS LETTERS
VOLUME 80, NUMBER 22
3 JUNE 2002
Metalorganic chemical vapor deposition of aluminum oxide on Si: Evidence
of interface SiO2 formation
A. Roy Chowdhuri and C. G. Takoudisa)
Department of Chemical Engineering (M/C 110), University of Illinois at Chicago, 810 S. Clinton Street,
Chicago, Illinois 60607-7000
R. F. Klie and N. D. Browning
Department of Physics (M/C 273), University of Illinois at Chicago, 845 West Taylor Street, Chicago,
Illinois 60607-7059
͑Received 7 February 2002; accepted for publication 10 April 2002͒
Thin films of aluminum oxide were deposited on H-passivated Si͑100͒ substrate using
trimethylaluminum and oxygen at 0.5 Torr and 300 °C. Fourier transform infrared ͑FTIR͒ and x-ray
photoelectron spectroscopic analyses of these films showed no aluminum silicate phase at the
film–substrate interface. The O/Al ratio in the deposited film was found to be higher than that in
stoichiometric Al2O3 . On annealing the as-deposited samples in Ar at 900 °C, an absorption peak
due to the transverse optical phonon for the SiuOuSi stretching mode appeared in the FTIR
spectra. A combination of Z-contrast imaging and electron energy-loss spectroscopy in the scanning
transmission electron microscope confirmed that the annealed samples developed a layer of silicon
dioxide at the aluminum oxide–Si interface. Our results suggest that excess oxygen present in the
deposited film reacts with the underlying Si substrate and forms silicon oxide. © 2002 American
Institute of Physics. ͓DOI: 10.1063/1.1483903͔
Aluminum oxide has emerged as one of the promising
substitutes for the SiO2 dielectric layer in complementary
metal–oxide–semiconductor device fabrication.1 It provides
many advantages over other potential candidates in several
aluminum oxide films on Si and characterize the deposited
films and their interfaces with the substrate using a combi-
nation of Fourier-transform infrared ͑FTIR͒ spectroscopy
and x-ray photoelectron spectroscopy ͑XPS͒. While the tra-
ditional method of investigating interfaces, transmission
electron microscopy ͑TEM͒, provides a high degree of spa-
tial resolution, it is not sensitive to small local changes in
composition and electronic structure. However a combina-
tion of Z-contrast imaging and electron energy-loss spectros-
copy ͑EELS͒, that has been used here, can provide an accu-
rate description of the structure and chemistry of the
interface with high spatial resolution.
Ultrathin aluminum oxide films were deposited using
TMA ͑Akzo Nobel͒ and oxygen in a custom-made low pres-
sure chemical vapor deposition chamber.8 The sample was
heated with a quartz halogen lamp and a proportional inte-
gral differential controller ͑Eurotherm Inc., Virginia͒ was
used to maintain the substrate temperature within Ϯ2 °C dur-
ing operation at 0.5 Torr. Bubbling Ar at 30 cm3 min ͑at 1
atm and 25 °C͒ delivered the organometallic precursor into
the chamber.
aspects. With a dielectric constant (␧
ϳ9) more than
Al O
2
3
twice that of SiO2 (␧
ϳ3.9), Al2O3 has a band gap of ϳ9
SiO
2
eV, a 2.8 eV conduction band offset to Si, and it is robust
enough to withstand high-temperature wafer processing
steps. Under normal processing conditions, Al2O3 is amor-
phous, although ␥-alumina ͑cubic͒ may form at high tem-
perature ͑Ͼ750 °C͒.2,3 Both amorphous Al2O3 ͑Ͻ350 °C͒
and cubic alumina ͑Ͼ750 °C͒ form a thermodynamically
stable interface2 on Si. One study,4 involving atomic layer
controlled deposition using trimethylaluminum ͑TMA͒ and
H2O, pointed out that Al2O3 was formed without any alumi-
num silicate phase at the interface when the Si substrate was
treated with HF prior to the deposition. However, another
study5 reported aluminum silicate phase formation at the ox-
ide substrate interface when triethyldialuminum tri-sec-
butoxide and O2 ͑at ϳ400 °C͒ was used.
TMA has been used in thermal as well as plasma en-
hanced chemical vapor deposition of alumina films,4,6 at
temperatures lower than 400 °C. The widespread use of TMA
is primarily due to its high vapor pressure at room tempera-
ture and high pyrolytic decomposition temperature
͑Ͼ350 °C͒, which allows its use over a wide temperature
range. In most studies involving TMA, H2O was used as the
oxygen source. Recently, reaction of TMA with oxygen has
been studied using a matrix isolation technique.7
Double polished 4 in. n-Si͑100͒ floating zone wafers,
diced into 15 mmϫ22 mm samples, were rinsed in deionized
water ͑NANO pure water system, Barnstead, Dubuque, IA͒,
followed by treatments in H2SO4 :H2O2 ͑1:2͒ to remove or-
ganic contamination and a 30 s dip in buffered HF ͑NH4F:
49% HF, 10:1͒ to remove the native oxide. In a typical op-
eration, after sample loading, the chamber was purged with
Ar at 0.1 Torr, while the sample temperature was ramped to
the desired setpoint. This was followed by alternate expo-
sures of TMA and O2, each for 30 s, with Ar purging in
between each reactant exposure.
In this work, we explore the use of TMA and oxygen for
low-temperature metalorganic chemical vapor deposition of
FTIR normal incidence transmission spectroscopy
͑Nicolet, Magna-IR 560͒ over the wavenumber range of
a͒
Electronic mail: takoudis@tigger.cc.uic.edu
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0003-6951/2002/80(22)/4241/3/$19.00 4241 © 2002 American Institute of Physics
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4242
Appl. Phys. Lett., Vol. 80, No. 22, 3 June 2002
Roy Chowdhuri et al.
FIG. 2. XPS spectra of as-deposited 5 nm aluminum-oxide film on
H-passivated Si deposited at 300 °C, showing the Si 2p, and Al 2p.
FIG. 1. FTIR spectra of 5 nm aluminum-oxide film on H-passivated Si
deposited at 300 °C; as-deposited ͑a͒; after 25 min annealing at 900 °C in Ar
͑b͒. The TO phonon associated with the asymmetric stretch of the O in
SiuOuSi bridging bond is present in the annealed sample.
optical ͑TO͒ phonon associated with the asymmetric stretch
of the O in SiuOuSi bridging bond. Also worth mention-
ing is the absence of any feature due to SiuOuAl mixed
4000 to 400 cmϪ1 was used. The sample thickness was mea-
sured with spectroscopic ellipsometry ͑J. A. Woollam Co.,
Inc., Model M-44͒. XPS ͑Kratos, AXIS Ultra XPS͒ analyses
of the samples were used to evaluate the bonding states and
atomic composition. The scanning tunneling electron micros-
copy ͑STEM͒ and EELS results presented in this letter were
obtained using a JEOL 2010F STEM/TEM, having a
Schottky field emission gain source and being operated at
200 kV.9,10 It is equipped with a standard UHR ‘‘ultrahigh
resolution’’ objective lens pole piece, a JEOL annular dark-
field detector and a postcolumn Gatan imaging filter.9,10 The
lens conditions in the microscope were defined for a probe
size of 0.2 nm, with a convergence angle of 13 mrad and a
collection angle of 52 mrad. With these settings, the probe
current is sufficient ͑40 pA͒ to obtain statistically significant
information and Z-contrast image is incoherent; i.e., a direct
image of the interface is acquired. The experimental setup
for this microscope allows us to use low-angle scattered elec-
trons that do not contribute to the Z-contrast image for
EELS.11 As the two techniques do not interfere, Z-contrast
images can be used to position the electron probe at the
desired spot in the sample to acquire spectra.12–14 The ex-
perimental conditions in the microscope mean that beam
damage is always a potential issue. However, for the results
obtained here, several spectra with acquisition times of ϳ0.5
s are acquired consecutively in each position and compared
to ensure that the beam damage is not contributing signifi-
cantly to the observed spectral changes.
vibrations, which appear18 above 1000 cmϪ1
.
XPS analysis of a 5 nm aluminum oxide film deposited
at 300 °C, on clean oxide-free Si ͑100͒ is presented in Fig. 2.
The Si 2p signal5,20 at 99.3 eV is due to Si0, however, no
signal from Sinϩ (nϾ0) states is present. A previous study
reporting aluminum silicate phase formation near the inter-
face during chemical vapor deposition of Al2O3 , assigned a
peak near 102 eV to Al in AluOuSi bonds.5 Beside such
bonds, presence of Si2ϩ in the Si 2p spectra of a 3.5 nm film
was reported. The position of the Al 2p peak at 75.43 ͑see
Fig. 2͒ indicates the presence of Al3ϩ state ͑corresponding to
anhydrous oxide͒.6,21,22 The absence of any other feature in
the Al 2p spectra shows that no Al0 is present. XPS analysis
of the same samples obtained at 30° gives identical binding
energies indicating homogeneous composition in the film.
The FTIR and XPS analyses of as-deposited films show that
neither any aluminum silicate phase nor any silicon oxide is
present at the film–substrate interface.
O/Al ratio in aluminum oxide depends on the process
conditions6,15 and values as high as 1.85 had been previously
reported.23 The O/Al ratio in the deposited film was calcu-
lated using the integrated intensities of the Al 2p and O 1s
peaks and atomic sensitivity factors for Al and O. The ratio
was found to be ϳ2.1, which is 40% higher than that for
stoichiometric Al2O3 . The slightly higher value of the bind-
ing energy of the Al3ϩ states can be explained by consider-
ing the presence of excess oxygen in the system.
Figure 1͑a͒ shows the FTIR absorbance spectra of a 5
nm aluminum oxide film deposited at 300 °C, on clean
oxide-free Si͑100͒. The broad features that appear in the
range of 500 to 1000 cmϪ1 are characteristic of aluminum
oxide. OuAluO bending mode appears in the range of 650
to 700 cmϪ1.6 The AluO stretching mode appears as a
Aluminum oxide films deposited at 300 °C were an-
nealed in Ar at 900 °C. A FTIR spectrum of a sample an-
nealed for 25 min is shown in Fig. 1͑b͒. The strong absorp-
tion band at 1058 cmϪ1 is identical to the TO mode arising
from the asymmetric stretching of O in SiuOuSi, in ther-
mally grown24,25 amorphous silicon dioxide (a-SiO2). The
intensity of this peak increased rapidly with annealing time
before reaching a constant value. This indicates that on an-
nealing an as-deposited sample, a SiO2 layer is formed be-
tween the deposited alumina film and the Si͑100͒ substrate.
Figure 3͑a͒ shows a high-resolution Z-contrast image of
a 5 nm deposited film annealed for 25 min in Ar at 900 °C.
The Si substrate is located at the bottom of the micrograph
broad band over 750 to 850 cmϪ1 6,15
The overlapping of
.
these two modes gives rise to the wide band with two distinct
peaks16 at ϳ690 and 745 cmϪ1. The absorption band at 610
cmϪ1 is due to AluO stretching in condensed AlO6
octahedral.17–19 No spectral feature is present at 1345 cmϪ1
indicating the absence of any AlvO in the film.15 The ab-
sence of any SiuO in the film is suggested by the absence of
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any feature near 1060 cmϪ1 corresponding to the transverse
and the individual atomic Si columns in the ͑110͒ direction
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Appl. Phys. Lett., Vol. 80, No. 22, 3 June 2002
Roy Chowdhuri et al.
4243
Diffusion of excess oxygen in the deposited
aluminum-oxide film is apparently responsible for the
formation of the interfacial SiO2 layer.
Experimental results were obtained on the JEOL 2010F,
operated by the Research Resources Center at UIC and
funded by the NSF under Grant No. DMR-9601796. This
research was supported in part by the NSF under Grant Nos.
DMR-9733895 and CTS 9813984. The XPS data were ob-
tained at the Center for Microanalysis of Materials, UIUC
supported by the U.S. Department of Energy under Grant
No. DEFG02-96-ER45439.
FIG. 3. Aluminum-oxide film, annealed at 900 °C in Ar for 25 min. ͑a͒
Z-contrast image ͑spatial resolution ϳ2 Å͒ with location of EELS analysis
indicated. ͑b͒ Background subtracted and multiple scattering corrected
EELS spectra ͑acquisition time 0.5 s; energy resolution 1.0 eV͒ showing Si
and Al edges.
1 G. D. Wilk, R. M. Wallace, and J. M. Anthony, J. Appl. Phys. 89, 5243
͑2001͒.
2 S. Guha, E. Cartier, N. A. Bojarczuk, J. Bruley, L. Gignac, and J. Kara-
sinski, J. Appl. Phys. 90, 512 ͑2001͒.
are visible. The dark region ͑5 nm͒ in between the Si and the
brighter Al2O3 film indicates the a-SiO2 . Figure 3͑b͒ dis-
plays EELS spectra taken from the position indicated in Fig.
3͑a͒. The spectrum from the Si substrate contains an edge
onset at (99.8Ϯ0.5) eV due to Si0 contribution26 but no dis-
tinct white line intensities that would indicate a native oxide.
The silicon-oxide layer shows a shift of the edge onset of
(6.2Ϯ0.5) eV and a distinct L3 , L2 splitting. This can be
interpreted as being caused by a change from predominantly
Si0 to predominantly Si4ϩ contributions to the spectrum. No
aluminum signal is detected, thus indicating a pure SiO2
layer. The deposited film spectrum contains a strong Al peak
characteristic27,28 of Al2O3 and no measurable intensities at
either the Si0 or the Si4ϩ core-loss onsets. The presence of
the oxide layer can be explained by considering diffusion of
the excess oxygen present in the film ͑as seen in the XPS
analysis͒ toward the Si substrate and reaction to form SiO2
upon annealing.
3 V. A. C. Haanappel, H. D. van Corbach, T. Fransen, and P. J. Gellings,
Surf. Coat. Technol. 72, 13 ͑1995͒.
4 E. P. Gusev, M. Copel, and E. Cartier, Appl. Phys. Lett. 76, 176 ͑2000͒.
5 T. M. Klein, D. Niu, W. S. Epling, W. Li, D. M. Maher, C. C. Hobbs, R.
I. Hegde, I. J. R. Baumvol, and G. N. Parsons, Appl. Phys. Lett. 75, 4001
͑1999͒.
6 Y.-C. Kim, H.-H. Park, J. S. Chun, and W.-J. Lee, Thin Solid Films 237,
57 ͑1994͒.
7 B. S. Ault, J. Organomet. Chem. 572, 169 ͑1999͒.
8 Z. Cui, J. Madsen, and C. G. Takoudis, J. Appl. Phys. 87, 8181 ͑2000͒.
9 E. M. James and N. D. Browning, Ultramicroscopy 78, 125 ͑1999͒.
10 E. M. James, N. D. Browning, A. W. Nicholls, M. Kawasaki, Y. Xin, and
S. Stemmer, J. Electron Microsc. 47, 561 ͑1998͒.
11 R. F. Egerton, Electron Energy-Loss Spectroscopy in the Electron Micro-
scope ͑Plenum, New York, 1986͒.
12 N. D. Browning, M. F. Chrisholm, and S. J. Pennycook, Nature ͑London͒
366, 143 ͑1993͒.
13 P. D. Nellist and S. J. Pennycook, Ultramicroscopy 78, 111 ͑1999͒.
14 D. E. Jesson and S. J. Pennycook, Proc. R. Soc. London, Ser. A 449, 273
͑1995͒.
15 Z. Katz-Tsameret and A. Raveh, J. Vac. Sci. Technol. A 13, 1121 ͑1995͒.
16 R. Cueff, G. Baud, M. Benmalek, J. P. Besse, J. R. Butruille, H. M.
Dunlop, and M. Jacquet, Thin Solid Films 270, 230 ͑1995͒.
17 P. Tarte, Spectrochim. Acta, Part A 23, 2127 ͑1967͒.
18 C. Morterra and G. Magnacca, Catal. Today 27, 497 ͑1996͒.
19 M. P. Kumar, C. Balasubramanian, N. D. Sali, S. V. Bhoraskar, V. K.
Rohatgi, and S. Badrinarayanan, Mater. Sci. Eng., B 63, 215 ͑1999͒.
20 W. R. Salenek, R. Bergman, J.-E. Sundgren, A. Rockett, T. Motooka, and
J. E. Green, Surf. Sci. 198, 461 ͑1988͒.
In this study, we addressed the interfacial chemistry of
aluminum-oxide films deposited on Si͑100͒. A combination
of FTIR, XPS, STEM, and EELS analyses was used to probe
as-deposited films and the effect of annealing in an inert
environment. The findings of this study are:
21 Q. Wang, W. Zhao, J. Lozano, Y.-M. Sun, C. G. Willson, and J. M. White,
Appl. Surf. Sci. 183, 182 ͑2001͒.
͑i͒
Low-temperature MOCVD of aluminum-oxide films
on Si using TMA and O2 does not give rise to any
aluminum-silicate layer. No detectable SiO2 layer is
formed during such a deposition process.
22 E. Paparazzo, Vacuum 62, 47 ͑2001͒.
23 B. G. Segda, M. Jacquet, and J. P. Besse, Vacuum 62, 27 ͑2001͒.
24 A. Pasquarello and R. Car, Phys. Rev. Lett. 79, 1766 ͑1997͒.
25 K. T. Queeney, M. K. Weldon, J. P. Chang, Y. J. Chabal, A. B. Gurevich,
J. Sapjeta, and R. L. Opila, J. Appl. Phys. 87, 1322 ͑2000͒.
26 P. E. Batson, Nature ͑London͒ 366, 727 ͑1993͒.
͑ii͒
The deposition carried out using O2 and TMA may
result in an O/Al ratio higher than that in stoichio-
metric Al2O3 ; and
27 M. Halvarsson, A. Larsson, and S. Ruppi, Micron 32, 807 ͑2001͒.
28 K. Suenaga, D. Bouchet, C. Colliex, A. Thorel, and D. G. Brandon, J. Eur.
Ceram. Soc. 18, 1453 ͑1998͒.
͑iii͒ Postdeposition annealing of the films at 900 °C gives
rise to an a-SiO2 layer at the film–substrate interface.
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