Interfacial properties of Hf-silicate/Si and Hf-silicate/Al 2O3/Si deposited by atomic layer chemical vapor deposition

Article abstract of DOI:10.1149/1.2007127

Ultrathin Hf_xSi_yO_z and Hf _xSi_yO_z/Al₂O₃, grown on Si surfaces by atomic layer chemical vapor deposition, were characterized in terms of their interface properties using

Full text of DOI:10.1149/1.2007127

Journal of The Electrochemical Society, 152 ͑10͒ F153-F155 ͑2005͒
F153
0
013-4651/2005/152͑10͒/F153/3/$7.00 © The Electrochemical Society, Inc.
Interfacial Properties of Hf-silicate/Si and Hf-silicate/Al O /Si
2
3
Deposited by Atomic Layer Chemical Vapor Deposition
Jaehyun Kim and Kijung Yong
z
Electrical and Computer Engineering Division, Department of Chemical Engineering,
Pohang University of Science and Technology, San 31, Hyoja-dong, Nam-gu, Pohang,
Kyunbuk 790-784, Korea
Ultrathin Hf Si O and Hf Si O /Al O , grown on Si surfaces by atomic layer chemical vapor deposition, were characterized in
x
y
z
x
y
z
2
3
terms of their interface properties using X-ray photoelectron spectroscopy ͑XPS͒ and high-resolution transmission electron mi-
croscopy. The formation of Hf-silicide at Hf Si O /Si interfaces was induced by the reaction of metallic Hf atoms with Si substrate
x
y
z
atoms; this formation was suppressed by the presence of Al O interlayers between Hf Si O and Si. As the Al O interlayer
2
3
x
y
z
2
3
thickness increased, the Hf 4f XPS peak intensity from Hf-silicide decreased and completely disappeared for Al O thickness
2
3
greater than 10 nm. Effects of Al O interlayers on the atomic structure of the films were also discussed.
2
3
©
2005 The Electrochemical Society. ͓DOI: 10.1149/1.2007127͔ All rights reserved.
Manuscript submitted March 9, 2005; revised manuscript received May 11, 2005. Available electronically August 12, 2005.
As the gate oxide thickness of a complementary metal-oxide-
transport source vapors into the reactor. The Ar flow rates of
semiconductor ͑CMOS͒ device is decreased to less than 1.5 nm, a
Hf͓N͑C H ͒ ͔ and Si͑OC H ͒ were 20 sccm, respectively. The Ar
2
5 2 4
4
9 4
conventional SiO is no longer applicable due to the exponentially
buffer flow or purge flow rate was 300 sccm.
2
1
increasing leakage current and boron penetration. Hafnium silicates
Figure 1b shows a schematic representation of the structure of
n
͑
Hf Si O ͒ have been widely studied as a promising candidate to
Hf͓N͑C2H5͒2͔4 and Si͑OC4H9͒4, where NEt2 and O Bu signify
x
y
z
replace SiO since Hf Si O has a high dielectric constant ͑k͒ and an
N͑C2H5͒2 and OC4H9, respectively. The vapor pressures of
Hf͓N͑C2H5͒2͔4 and Si͑OC4H9͒4 were 0.7-0.86 Torr at 70°C and
1.71 Torr at 85°C, respectively.
The composition and chemical states of the films were analyzed
by X-ray photoelectron spectroscopy ͑XPS͒ and Auger electron
spectroscopy ͑AES͒. The cross-sectional atomic structure of the
films was investigated though use of high-resolution transmission
electron microscopy ͑HRTEM͒.
2
x
y
z
1
excellent thermal stability with silicon. As a gate oxide becomes
thinner, the interfaces between the high-k material and the Si sub-
1
,2
strate have been shown to play a key role in device performance.
The formation of silicide ͑HfSi ͒ at the silicate/Si interfaces has
x
been reported during the Hf-silicate film deposition, or during the
3-6
subsequent rapid thermal annealing ͑RTA͒. In addition, the diffu-
7
sion of Hf atoms through silicate/Si interfaces has been found. Any
interfacial silicide formation is partly responsible for the high inter-
5
4
face trap density and also for the roughness of the intersurface.
Results and Discussion
These effects result in a decrease of the channel mobility and low
reliability of device performance.
In this study, the focus was on investigating the physical and
chemical characteristics of Hf Si O and Hf Si O /Al O films
grown on Si by atomic layer chemical vapor deposition ͑ALCVD͒,
as well as on their interfacial reactions. Another candidate for the
high-k gate oxide, Al O , is thermodynamically stable on Si against
metal-silicide formation. Additionally, Al O is expected to serve
as interlayers that block reactions between Hf-silicates and Si sub-
strates.
3
XPS depth profile analysis was performed in order to investigate
the chemical binding states through the film thickness and at the
interfaces. Figure 2 shows the Hf 4f, Si 2p, and O 1s core-level
photoelectron spectra of the Hf Si O ͑ϳ12 nm͒/Si ͑100͒ sample.
x
y
z
x
y
z
2
3
1
4
25 61
The binding energy of the Hf 4f5/2,7/2 doublet peak, 20.2 and 18.6
eV, at the film surface was shifted slightly toward a lower binding
energy as the film thickness decreased. Furthermore, an additional
doublet, 16.1 and 14.4 eV, appeared at the interface. Similar shifts of
2
3
8
2
3
+
binding energies were also observed for Si 2p and O 1s during Ar
sputtering, as shown in Fig. 2b and c, respectively. These results
indicated that the Hf/͑Hf + Si͒ composition ratio increased as the
film thickness decreased. In other words, the Hf Si O films that
were grown have a compositional gradation; this was discussed in
our previous reports of zirconium silicate studies. According to
x
y
z
Experimental
1
Hf Si O films were deposited by ALCVD at 300°C using an
x
y
z
model calculations that are based on the relative atomic electrone-
alternating
supply
of
tetrakis-diethylamido-hafnium
gativities, higher Hf contents in silicate films result in lower binding
n
͑
Hf͓N͑C H ͒ ͔ ͒ and tetra-n-butyl-orthosilicate ͓Si͑O Bu͒ ͔ on ei-
ther Si ͑100͒ or Al O /Si ͑100͒. In order to deposit Al O films on
Si, trimethylaluminum ͓Al͑CH ͒ ͔ and H O were used as source
materials at the growth temperature of 200°C. Immediately prior to
deposition, p-type Si͑100͒ wafers ͑8-10 ⍀ cm͒ were precleaned
with a HF:H O solution of ratio 1:10 for 30 s; they were then rinsed
9,10
2
5 2 4
4
energies of Hf, Si, and O.
The composition of Hf Si O is a
14 25 61
2
3
2
3
weighted average value over the XPS sample depth at the film sur-
face. Another Hf 4f doublet peak at the interface, 16.1 and 14.4 eV,
is shown in Fig. 2a and corresponds to the hafnium silicide bonding.
It is believed that the formation of Hf-silicide is the result of the
3
3
2
2
reaction at Hf-silicate/silicon interfaces between the metallic Hf and
n
with deionized ͑DI͒ water to remove any native oxide layers.
During deposition, the pressure in the reactor as shown in Fig. 1a
was maintained at 0.1 Torr. The substrate holder was heated using a
resistance heater with ±2°C temperature stability. The temperatures
of Hf͓N͑C H ͒ ͔ and Si͑OC H ͒ bubblers were fixed at 70 and
Si atoms. In this study, Si͑O Bu͒ was used as a single source for
4
both O and Si since Si-O bonds are strong in alkoxides. Due to the
n
different reactivity of Hf͓N͑C H ͒ ͔ and Si͑O Bu͒ , the Hf-amido
2
5 2 4
4
molecule will decompose more easily on a silicon surface than Si-
alkoxide. According to the experimental results found in this study,
2
5 2 4
4
9 4
1
1
n
8
5°C, respectively. The transport lines were kept at 100°C to avoid
the condensation of precursors. Argon ͑99.9995%͒ was used as a
buffer flow to keep the flow uniform, and carrier gas was used to
Hf͓N͑C H ͒ ͔ readily decomposes on Si at 450°C, but Si͑O Bu͒
2 5 2 4 4
12
does not decompose even at temperatures as high as 700°C. How-
n
ever, Si͑O Bu͒ reacts to grow silicate films in the presence of
4
Hf͓N͑C H ͒ ͔ . Thus, during initial growth stages, more Hf atoms
2
5 2 4
are incorporated into films. Furthermore, this Hf metal-rich and
O-deficient atmosphere allows direct Hf-Six bonding to be
z
E-mail: kyong@postech.ac.kr
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F154
Journal of The Electrochemical Society, 152 ͑10͒ F153-F155 ͑2005͒
Figure 2. XPS depth profile of the 12 nm Hf Si O film on silicon. ͑a͒ Hf
1
4
25 61
4
f core-level spectra, ͑b͒ Si 2p core-level spectra, and ͑c͒ O 1s core-level
spectra.
1
4.3 eV, corresponding to Hf-Si was significantly decreased due to
x
the Al O interlayers. The presence of Al O interlayers between
2
3
2
3
the Hf Si O film and the Si substrate was confirmed by XPS pro-
x
y
z
files of Al 2p, as shown in Fig. 3c. The Al 2p peak had a maximum
intensity at the middle of the Al O interlayers, and the binding
2
3
energies, 75.5-75.7 eV, of most intense Al 2p peaks corresponded to
8
,13
a stoichiometric Al O .
According to the XPS depth profiles, a
2
3
metallic Hf 4f doublet peak began to appear at the Al O /Si inter-
2
3
faces; this indicates that the Hf-Six phase was located at the
Al O /Si interfaces. The results of our Auger depth profiles also
2
3
support the presence of Hf-silicide at the Al O /Si interface. Ac-
2
3
cording to our Auger depth profiles, the metallic Hf intensity was
continuously decreased through Al O but it showed an ϳ4 atom %
2
3
higher value at the Al O /Si interface. One possible mechanism for
2
3
Figure 1. ͑a͒ Schematic diagram of the ALCVD system for Hf-silicate depo-
sition. ͑b͒ Schematic representations of the structures and vapor pressures of
Hf͓N͑C H ͒ ͔ and Si͑OC H ͒ .
2
5
2
4
4
9 4
3
,6
formed. In Fig. 2b, the Si 2p peak position of 99.2-99.4 eV was
not changed at the Hf-silicate/Si ͑100͒ interface and the Si substrate.
This was due to the Si 2p binding-energy difference of Hf-Si and Si
x
substrate being too small to be resolved.
Figure
3
displays XPS depth profiles of an
8
nm
Hf Si O /5 nm Al O /Si͑100͒ sample. When compared to
1
3
25 62
2
3
Figure 3. XPS depth profile of the 8 nm Hf Si O /5 nm Al O film on
13 25 62 2 3
silicon. ͑a͒ Hf 4f core-level spectra, ͑b͒ Si 2p core-level spectra, ͑c͒ Al 2p
core-level spectra, and ͑d͒ O 1s core-level spectra.
Hf Si O /Si, one remarkable change in the Hf 4f depth profile ͑Fig.
x
y
z
3a͒ is that the intensity of the metallic Hf 4f doublet peak, 16.0 and
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Journal of The Electrochemical Society, 152 ͑10͒ F153-F155 ͑2005͒
F155
Figure 4. Hf 4f core-level XPS spectra of Hf-silicate/Si and
Hf-silicate/Al O /Si with different thicknesses of Al O interlayers: ͑a͒ 12
2
3
2
3
nm Hf-silicate/Si, ͑b͒ 8 nm Hf-silicate/5 nm Al O /Si, and ͑c͒ 8 nm
2
3
Hf-silicate/10 nm Al O /Si. The key regions of the nearby spectra interface
2
3
Figure 5. HRTEM images of ͑a͒ 12 nm Hf-silicate film on silicon, ͑b͒ 8 nm
Hf-silicate/5 nm Al O /Si, and ͑c͒ scanning EDX image for the sample of
were enclosed to highlight the Hf-Si bonding.
x
2
3
͑
b͒. Note: Peak positions corresponding to the maximum concentrations of
Hf and Al elements have about 6 nm differences.
this phenomenon is that unoxidized, metallic Hf atoms diffused
through the Al O interlayers and reacted with the Si substrate, thus
2
3
forming Hf-silicide. In this case, thicker Al O layers may effec-
tively block the direct reaction of the Hf atoms with Si substrate
atoms.
2
3
Hf Si O /Si and Hf Si O /Al O /Si, fabricated by ALCVD. A Hf-
x
y
z
x
y
z
2
3
silicide layer was formed at the Hf Si O /Si interfaces because the
x
y
z
The effects of the interlayer ͑Al O ͒ thickness on the Hf-silicide
conditions of ALCVD, which combined Hf-amide and Si-alkoxide,
involved an oxygen-deficient atmosphere during the initial growth.
The formation of Hf-silicide was dynamically suppressed according
to the thickness of the Al2O3 interlayer between Hf-silicate and Si.
In addition, Al2O3 interlayers enhanced the amorphous characteris-
tics of HfxSiyOz/Al2O3/Si.
2
3
formation were investigated using several Hf Si O /Al O /Si
x
y
z
2
3
samples having various Al O layers with thickness ranging from 0
2
3
to 22 nm. Figure 4a-c shows Hf 4f depth profiles of samples A, B,
and C, which have Al O interlayer thicknesses of 0, 5, and 10 nm,
2
3
respectively. The key regions of the nearby spectra interface were
enclosed to highlight the Hf-Si bonding. As the Al O interlayer
x
2
3
thickness increased, the metallic Hf doublet peak intensity decreased
significantly. Interlayers of Al O that were over 10 nm thick re-
Acknowledgments
2
3
This work was supported by Grant No. R01-2002-000-00279-
0͑2002͒ from the Korea Science and Engineering Foundation, San-
hakfund, and Grant No. RTI04-01-04 from the Regional Technology
Innovation Program of the Ministry of Commerce, Industry and En-
ergy ͑MOCIE͒.
sulted in complete suppression of the Hf-Si formation ͑Fig. 4c͒.
x
These results indicate that there is a critical thickness of Al O
2
3
interlayers required to prevent the hafnium silicide formation. Simi-
lar phenomena have been observed for Hf diffusion into SiO
layers. According to Renault et al., the incorporation concentration
2
7
Pohang University of Science and Technology assisted in meeting the
publication costs of this article.
of Hf into Si through the SiO interlayers decreased as the interlayer
2
14
thickness was increased.
The cross-sectional atomic structures of Hf-silicate/Si and
Hf-silicate/Al O /Si are shown in Fig. 5a and b, respectively. The
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