Physical characterization and electrical properties of sol-gel-derived zirconia films

Article abstract of DOI:10.1149/1.2186182

We have developed a simple method for the preparation of ZrO2 ultrathin films; it involves a sequence of ZrCl4 precursor preparation in an ice bath, sol-gel spin-coating processing, baking, and annealing. The film thickness was controllable and tunable by altering the ZrCl4 hexanol ratio. High-resolution transmission electron microscopy (TEM) and thermal desorption spectrometry indicated that the fabricated ultrathin film was thermally stable at annealing temperatures as high as 900°C. Diffraction patterns of TEM indicated that the films obtained at various annealing temperatures were amorphous. Electron spectroscopy for chemical analysis (ESCA) demonstrated an increase in the intensity of the signal for the Zr-O bonds upon increasing the annealing temperature, whereas those for the signals of carbon and chlorine decreased. The ESCA and TEM analyses also suggested that the thickness of the silicon dioxide film increased upon increasing the annealing temperature. The electrical properties, such as the breakdown field (12.5 MVcm) and the gate current density (< 10-7 A cm2), of the sol-gel-derived ZrO2 ultrathin films obtained after annealing at 900°C suggested that they were good electrical insulators. These ZrO2 thin films are expected to behave as capacitors and as coatings for insulating films.

Full text of DOI:10.1149/1.2186182

F94
Journal of The Electrochemical Society, 153 ͑6͒ F94-F99 ͑2006͒
0
013-4651/2006/153͑6͒/F94/6/$20.00 © The Electrochemical Society
Physical Characterization and Electrical Properties
of Sol-Gel-Derived Zirconia Films
a
b, ,z
a
Hsin-Chiang You, Fu-Hsiang Ko, * and Tan-Fu Lei
a
Institute of Electronics Engineering, National Chiao Tung University, Taiwan
Institute of Nanotechnology, National Chiao Tung University, Taiwan
b
We have developed a simple method for the preparation of ZrO2 ultrathin films; it involves a sequence of ZrCl4 precursor
preparation in an ice bath, sol-gel spin-coating processing, baking, and annealing. The film thickness was controllable and tunable
by altering the ZrCl /hexanol ratio. High-resolution transmission electron microscopy ͑TEM͒ and thermal desorption spectrometry
4
indicated that the fabricated ultrathin film was thermally stable at annealing temperatures as high as 900°C. Diffraction patterns of
TEM indicated that the films obtained at various annealing temperatures were amorphous. Electron spectroscopy for chemical
analysis ͑ESCA͒ demonstrated an increase in the intensity of the signal for the Zr–O bonds upon increasing the annealing
temperature, whereas those for the signals of carbon and chlorine decreased. The ESCA and TEM analyses also suggested that the
thickness of the silicon dioxide film increased upon increasing the annealing temperature. The electrical properties, such as the
−
7
2
breakdown field ͑12.5 MV/cm͒ and the gate current density ͑Ͻ10 A/cm ͒, of the sol-gel-derived ZrO ultrathin films obtained
2
after annealing at 900°C suggested that they were good electrical insulators. These ZrO2 thin films are expected to behave as
capacitors and as coatings for insulating films.
©
2006 The Electrochemical Society. ͓DOI: 10.1149/1.2186182͔ All rights reserved.
Manuscript submitted June 14, 2005; revised manuscript received January 26, 2006. Available electronically April 11, 2006.
Silicon technology has formed the basis of microelectronics and
thermal stability, high hardness, a high melting point, chemical hard-
ness, and a high refractive index.
electronics systems for more than 30 years. In terms of productivity,
the density of devices on a silicon chip has followed Moore’s law,
doubling about every two or three years since about 1980. Many
researchers are interested in scaling down electronics devices so that
they may perform at higher speeds and be prepared at lower costs.
Recently, numerous technologies have been developed for the
1
0-13
preparation of various high-k films.
Atomic layer deposition
͑ALD͒, physical vapor deposition ͑PVD͒, and chemical vapor depo-
sition ͑CVD͒ methods have all been used to prepare insulating films
for new technologies. In the ALD process, ZrCl and H O are used
Conventional SiO gate dielectrics are reaching their physical thick-
2
4
2
ness limit ͑1.5 nm͒; they cannot be used as complementary meta-
loxide semiconductor devices because of the high direct-tunneling
current and poor reliability. For further scaling of devices, it has
to prepare the ZrO films. For the PVD process, a zirconium metal
target is used for sputtering under ambient oxygen to deposit the
2
ZrO films. In the CVD method, ZrCl is used as a precursor of the
2
4
been proposed that SiO be replaced by high-k dielectric constant
deposited ZrO films.
2
2
materials, such as ZrO , HfO , Ta O , Al O , TiO , and silicates
The sol-gel method is an interesting and simple technique for
2
2
2
5
2
3
2
1
-8
14-18
͑
ZrSi O and HfSi O ͒. . In fact, dielectric films having higher
preparing ceramic films.
This approach can provide colloidal
x
y
x
y
permittivity allow the use of thicker films of equivalent electrical
thickness as silicon dioxide; this situation reduces the leakage cur-
rent and improve the reliability of the dielectric films.
The most important properties of high-k dielectric materials that
are necessary to maintain continuous increases in device perfor-
mance and density are their low leakage current, low equivalent
oxide thickness ͑EOT͒, high breakdown strength, high thermal sta-
solvents or precursor compounds when metal halides are hydrolyzed
1
8
under controlled conditions. In the sol-gel process, hydrolysis,
condensation, and polymerization steps occur to form metal oxide
networks. These reactions play fateful roles in modifying the final
material’s properties. The most interesting feature of sol-gel process-
ing is its ability to synthesize new types of materials that are known
as “inorganic-organic hybrids.” Film formation through spin-coating
is a simpler method than using ALD, PVD, or CVD because it
requires the cheaper precursors and apparatus. In addition, the film
can be fabricated in a normal pressure system instead of under high
vacuum. Typically, ZrO2 is an excellent heat-resistant and chemi-
cally durable material that is used, for example, as a material for
bility, and gate electrode compatibility. The EOT, t , of an alterna-
eq
tive high-k dielectric can be obtained from the simple equation
teq = ͑K /Khigh-k͒thigh-k
ox
1
9
where Kox and Khigh-k are the dielectric constants of silicon oxide
and the high-k dielectric, respectively, and thigh-k is the physical
thickness of the high-k material. Future downscaling will require
furnaces. Although ZrO generally provides good electrical insu-
2
lation, no reports exist that describe the electrical insulation proper-
ties of sol-gel-derived ZrO ultrathin films.
2
9
high-k materials in which EOT values are reduced to nearly 0.7 nm.
In this paper, we applied different annealing conditions to sol-gel
ZrO2 ultrathin films on silicon and used various characterization
techniques to evaluate the properties and electrical performances of
these deposited films.
We must bear in mind that many of the characteristics of these high-
k dielectrics—such as their breakdown mechanism and hysteresis
phenomena—are quite different from those of conventional silicon
dioxide. When the gate dielectric materials experience high tempera-
tures ͑Ͼ800°C͒, the thermal stability of the high-k dielectric on
silicon is an important issue that must be addressed for future metal-
oxide-semiconductor field effect transistor devices. The most suit-
able range of dielectric constants is between 20 and 40. If the ma-
terial has an extremely high k-value ͑Ͼ80͒, it will induce a large
fringing effect. For the purposes of achieving a low leakage current,
it is desirable to choose a dielectric material that possesses a large
bandgap energy and a large band offset with respect to the Si sub-
Experimental
The materials were characterized using atomic force microscopy
͑AFM͒, electron spectroscopy for chemical analysis ͑ESCA͒, X-ray
diffractometry ͑XRD͒, thermal desorption spectrometry-atmosphere
ionization mass spectrometry ͑TDS-APIMS͒, and high-resolution
transmission electron microscopy ͑HRTEM͒. Capacitance–voltage
͑C–V͒ and current density–voltage ͑J–V͒ analyses were also per-
formed.
strate. ZrO has a dielectric constant of 25, a wide bandgap, good
Figure 1 displays the main procedures used for sample prepara-
2
tion. ZrO2 thin films were prepared using a sol-gel spin-coating
method. ZrCl ͑99.5%, Aldrich, USA͒ was used as the precursor for
4
the synthesis of zirconia. Prior to film fabrication, the purity of
*
Electrochemical Society Active Member.
E-mail: fhko@mail.nctu.edu.tw
z
ZrCl was monitored using inductivity coupled plasma optical emis-
4
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Journal of The Electrochemical Society, 153 ͑6͒ F94-F99 ͑2006͒
F95
Figure 1. The sol-gel process used for the preparation of ZrO films.
2
sion spectrometry; apart from the signal for Zr, all other impurities
were present at concentrations lower than 1000 ppm. The thin films
were prepared through polymerization in an organic solution. A
mother sol solution was first prepared by dissolving ZrCl in isopro-
4
panol ͑IPA; Fluka; water content Ͻ0.1%͒ and hexanol ͑Fluka; water
content Ͻ5%͒ under vigorous stirring in an ice bath. The sol solu-
tions were obtained after fully hydrolyzing ZrCl with a stoichio-
4
metric quantity of water in IPA and hexanol to yield Zr/IPA/hexanol
mixtures with molar ratios of 1:500:1000, 1:500:750, 1:500:500, and
1
:500:250. The metal halide solution was then subjected to ultra-
sonication at 0°C for 20 min to accelerate the gelling rate. The film
thickness was determined using the ellipsometer. Film analyses
͑
AFM, ESCA, XRD, TDS-APIMS, TEM, C–V, and J–V͒ were con-
ducted using the sample having a Zr IPA hexanol molar ratio of
1
:500:1000.
The n-type wafers ͑10–15 ⍀ cm, made in Japan͒, which were
used as substrates for the metal insulator semiconductor ͑MIS͒
structure, were RCA-cleaned to remove the native silicon oxide.
Figure 2. Cross-sectional TEM images of sol-gel-derived ͑Zr + IPA
+ hexanol͒ ZrO /Si structures annealed under an O atmosphere at ͑a͒ 200,
ZrO films were deposited by spin-coating at 3000 rpm for 60 s at
2
2
2
ambient temperature ͑25°C͒ to give a thickness of ca. 9.3 nm on the
͑b͒ 600, and ͑c͒ 900°C.
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Journal of The Electrochemical Society, 153 ͑6͒ F94-F99 ͑2006͒
a Zr-silicate. Very smooth interfaces exist in this sample. When we
increased the annealing temperature to 600 and 900°C ͑Fig. 2b and
c͒, the interfaces were also smooth and the ZrO films remained
2
amorphous in structure, as judged from the diffraction pattern.
We used AFM to evaluate the surface quality of these sol-gel-
derived zirconia films. The as-deposited ͑200°C͒ sample possessed
a whole-area-film root-mean-square ͑rms͒ roughness of 0.306 nm.
After annealing at 500, 600, and 900°C under ambient oxygen for
1
min, the rms roughnesses were 0.157, 0.165, and 0.189 nm, re-
spectively. The value of the surface roughness of the as-deposited
ultrathin film after spin-coating was very low, and these films be-
came even smoother after the annealing treatment. We determined
the roughness of each sample at five different regions and found that
the annealed samples remained smooth.
Next we investigated the ZrO crystallinity using 1.5° glancing-
2
angle XRD. High-k dielectric crystallinity is a concern because of
possible problems arising from leakage paths and dopant/impurity
diffusion along grain boundaries, as well as for the control of device
Figure 3. XRD data for ZrO2 films prepared under different conditions
͑
as-deposited and after annealing at the temperatures indicated͒.
uniformity. Figure 3 displays the XRD patterns of the ZrO films.
2
Broad features are present in the XRD pattern of the as-deposited
film; they did not change their appearance significantly after anneal-
ing at temperatures up to 900°C. These results suggest that the
samples have high thermal stability and that RTA treatment at
n-Si͑100͒ substrate. The spin-coater used was a TEL Clean Track
model-MK8 ͑Japan͒. These films were initially baked at 200°C for
9
00°C for 1 min under an oxygen atmosphere does not result in the
1
0 min. One of the samples was then maintained at 200°C for 1 min
crystallization of ZrO2.
for densification; the others were subjected to rapid thermal anneal-
To determine the bulk properties of the deposited films, we used
ing ͑RTA͒ at different temperatures ͑500, 600, or 900°C͒ for 1 min
ESCA to examine the nature of the chemical bonding structures of
these films. From the Zr 3d spectrum of the RTA samples in Fig. 4a,
we observed clearly two typical peaks, Zr 3d5/2 ͑183.2 eV͒ and Zr
under an oxygen atmosphere. ZrO /n-Si structures were used in our
2
experiments for the physical characterization of the zirconia.
Next, Al top electrodes having an area of 7.85 ϫ 10−5 cm were
2
3
d3/2 ͑185.6 eV͒, of ZrO . RTA annealing under O at 500, 600, and
deposited onto the top surface of the ZrO by using a shadow mask
2
2
2
and vaporizing a pure Al target. The thickness of the top electrode
was 400 nm. A buffered oxide etch ͑BOE͒ was performed to remove
the silicon back oxide and then the sample was thoroughly rinsed
with deionized water. Finally, bottom electrodes were attached on
the reverse side of the n-Si͑100͒ substrates by vaporizing a pure Al
target. The thickness of the bottom electrode was 100 nm. The di-
electric properties were then determined for the MIS capacitors hav-
900°C for 1 min led to remarkable changes in the ESCA spectra
͑Fig. 4a͒. The intensities of the signals at 183.2 eV after annealing
the as-deposited film at 500, 600, and 900°C were 1.24, 1.32, and
1.48 times higher, respectively, than that after baking at 200°C;
similarly, the peak intensities at185.6 eV were 1.25, 1.38, and 1.54
times higher, respectively. That is to say, increases in the signals of
the Zr–O bonds occur upon increasing the annealing temperature.
As-deposited zirconia films exist mainly in the form ZrO2−␦ ͑␦
ing an Al/ZrO /n-Si/Al structure. This deposition technique allows
2
the production of ultrathin gate dielectric films under excellent
thickness control.
Ͼ 0͒. Annealing under ambient oxygen can decrease the value of ␦,
8
leading to the formation of ZrO . The electron binding energy of
2
the C 1s orbital is 284 eV; this value increases to 286.5 eV when Cl
is bound to C, as in Fig. 4b. The C and Cl atoms both arise from
Results and Discussion
20
We studied the thicknesses of the smooth ZrO films as a func-
the precursor or the solvents used during the preparation procedure.
Annealing at 900°C in the oxygen-rich environment effectively re-
duces the intensity of the C–Cl signal ͑cf. Fig. 4b and c͒. This
observation suggests that annealing is beneficial for enhancing the
film’s quality and improving its electrical properties.
2
tion of the Zr/hexanol ratios. In this sol-gel process, the IPA solvent
was more hydrophilic than hexanol. For this reason, we fixed the
mole ratio of the IPA solvent with respect to the Zr ions at 1:500
͑
ZrCl /IPA͒. We varied the hexanol content to provide various
4
film thicknesses. The film thickness increased linearly upon decreas-
ing the Zr/hexanol ratio from 1:1000 to 1:750 to 1:500 to 1:250.
We obtained a smooth nanofilm ͑thickness 9.3 nm͒ at a Zr/hexanol
ratio of 0.001. Prior to annealing, the real thicknesses of the smooth
films obtained at Zr/hexanol ratios of 1:750, 1:500, and 1:250
were 10.7, 12.6, and 22.5 nm, respectively. The semi empirical
linear fit between the thickness and the Zr/hexanol ratio ͓thickness
T͑nm͒ = 4.55 + 4425.90ϫ ͑Zr/hexanol͒ ͑correlation coefficient:
For ESCA analysis, the surfaces of these samples were sputtered
away using a 2-kV argon beam ͑scanning X-ray microprobe,
Quantera SXM, ULVAC͒. Each sample was then eroded ϳ7 nm
from the surface. In the spectrum of each RTA sample ͑Fig. 5͒, Si 2p
peaks appears at 103.3 and 99.3 eV, corresponding to the binding
8
energies of SiO and Si–Si bonds, respectively. It is obvious that
2
the latter signal represents the silicon substrate. We found that the
intensity of the peak representing the Si–O bonds in the annealed
thin films increased upon increasing the annealing temperature ͑Fig.
5͒. This finding is consistent with our observations above regarding
the TEM images ͑Fig. 2͒. The color at the interface region ͑ZrO2/Si͒
lightened upon increasing the annealing temperature. This finding
suggests that the Zr silicate at the interface led to phase separation at
2
R = 0.9919͔͒ suggests that the film thickness is controllable and
tunable by altering the Zr/hexanol ratio.
Figure 2a-c displays cross-sectional TEM images of the inter-
faces of the ZrO /Si structures annealed at 200, 600, and 900°C,
2
respectively. The TEM image and its diffraction pattern in Fig. 2a
indicate that the sol-gel-deposited film consists of a ca. 0.82-nm
8
900°C to form amorphous SiO2.
interfacial layer and a 9.3-nm-thick bulk ZrO film, and the diffrac-
As we mentioned above, C–Cl bonds existed in the ZrO films;
2
2
tion pattern suggested that the ZrO exhibited an amorphous struc-
ture. Yamaguchi et al. observed the formation of an interfacial
annealing at 900°C in the oxygen-rich environment significantly
reduced their abundance. To verify this observation, we analyzed
these samples through TDS-APIMS measurements. We ramped the
desorption temperature of the TDS-APIMS system from room tem-
2
9
Zr-silicate layer after the pulsed-laser-ablation deposition of ZrO .
2
11
Wang and co-workers also proposed the presence of a Zr-silicate
layer after atomic layer chemical vapor deposition of ZrCl . We
perature to 800°C at 20°C/min under a N carrier gas. We analyzed
4
2
suggest that the interfacial layer in Fig. 2a may be attributed to such
the surface out-gasses at molecular weights of 16, 44, and 82 ͑Fig.
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Journal of The Electrochemical Society, 153 ͑6͒ F94-F99 ͑2006͒
F97
Figure 5. ESCA spectra ͑Si 2p͒ of ZrO films eroded by ca. 7 nm using an
2
argon sputter.
elements in the forms CH and CO , respectively. In addition, the
4
2
chlorine components of the film combined with C atoms to form
CCl . We find that the organic elements of all of the samples dissi-
2
pated violently at temperatures of ca. 400°C. As the annealing tem-
perature increased, the intensity of the TDS-APIMS desorption peak
gradually reduced. This result suggests that oxygen treatment at
higher temperatures is beneficial for the separation of unstable
carbon-containing compounds from the sol-gel-fabricated ultrathin
film.
Figure 7 illustrates the high-frequency ͑1-MHz͒ capacitance vs
gate voltage characteristics ͑C–V curves͒ for the MIS capacitors
prepared from sol-gel-derived ZrO dielectrics under various anneal-
2
ing conditions. For a high-k dielectric material, high-frequency C–V
characteristics are important for calculating the equivalent oxide
thickness ͑EOT͒. From Fig. 7a, we find that the shape of the C–V
curve of the sample annealed at 500°C is poor; several steps exist in
the curve, which is not very stable. In other words, the sample
annealed at 500°C does not appear to have excellent electrical prop-
erties because of the presence of unstable organic compounds re-
maining in the film. This observation is consistent with our finding
in Fig. 4b and 6a. When we raised the annealing temperature, the
ZrO films exhibited good electrical properties, i.e., lower current
2
densities and improved capacitance. Figure 7b provides detailed in-
formation regarding the sample annealed at 600°C. The value of the
capacitance of the RTA 600°C sample was 390 pF; this capacitor
appears to be very stable. Table I lists the C–V characteristics of the
RTA 600°C sample, which has an EOT value of 3.04 nm and a
dielectric constant of 13.9. In addition, Fig. 7b displays hysteresis in
the C–V characteristics of the samples in the absence of light. The
solid line represents the C–V characteristics after measuring the
curve by sweeping the voltage from accumulation to inversion and
sweeping back ͑from +2.0 to −2.0 to +2.0 V͒; we observe that the
shift is only 35 mV. We attribute this small shift to the reduction of
unstable carbon-containing compounds after annealing.
The capacitance of the film annealed at 900°C under an O at-
2
mosphere was 310 pF ͑Fig. 7c͒. Thus, the capacitance of the RTA
Figure 4. ͑a͒ ESCA spectra of as-deposited ZrO2 films and after RTA an-
9
00°C sample was lower than that of the RTA 600°C sample. From
nealing at 500, 600, and 900°C in O for 1 min ͑Zr 3d͒. ESCA spectra of ͑b͒
2
the ESCA signals of these samples, we find that the intensity of the
peak for the Si–O bonds in the annealed thin film increased upon
increasing the annealing temperature ͑see Fig. 5͒. The interfacial
Cl and ͑c͒ C atoms after annealing at different temperatures.
oxide ͑SiO ͒ influences the capacitance and the EOT, which is an
2
6
a-c͒. The film basically comprises Zr, Cl, C, H, and O elements
undesirable property. Nevertheless, the sol-gel-derived ZrO2 films
derived from the preparation solvents and the precursor. The out-
gassing molecular weights of 16 and 44 possibly represent carbon
annealed at 900°C display ͑Fig. 8͒ an improved breakdown field
͑Ͼ12 MV/cm ͒. Table I lists the C–V characteristics of the sample
2
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Journal of The Electrochemical Society, 153 ͑6͒ F94-F99 ͑2006͒
Figure 6. TDS-APIMS analyses of the ͑a͒ RTA 500°C, ͑b͒ RTA 600°C, and
c͒ RTA 900°C samples.
͑
Figure 7. High-frequency ͑1 MHz͒ C–V characteristics of the sol-gel-
derived ZrO2 dielectrics after RTA at ͑a͒ 500, ͑b͒ 600, and ͑c͒ 900°C under
an O2 atmosphere.
annealed at 900°C; the value of EOT was 3.91 nm and the dielectric
constant was 12.8. We observe that as the annealing temperature
increased, the EOT increased ͑from 3.07 to 3.91 nm͒ and the dielec-
tric constant decreased ͑from 13.9 to 12.8͒. The solid line in the
inset of Fig. 7c represents the C–V characteristics after measuring
the curve by sweeping the voltage from accumulation to inversion
and sweeping back ͑from +2.0 to −2.0 to +2.0 V͒. We observe a
shift of 20 mV for the hysteresis phenomenon for the sample an-
nealed at 900°C. Thus, the hysteresis phenomenon is lower than the
annealed at 200 and 500°C did not have sufficiently high thermal
budgets and thus, their breakdown electric fields were relatively low.
The breakdown electric fields increased upon increasing the anneal-
ing temperature. A high annealing temperature removed unstable
carbon-containing compounds from the ZrO film and stabilized the
2
dielectrics of the sol-gel-derived ZrO film annealed at 600°C.
thin film. The sol-gel-derived ZrO films displayed excellent electri-
2
2
We obtained the electric field ͑E͒ in the J–E curve of Fig. 8 by
cal performances because they did not crystallize during high-
temperature RTA, even after annealing at temperatures as high as
900°C. In addition, the samples subjected to RTA treatment at 600
using the equation E = V/t , where V is the applied voltage and t
ox
ox
is the EOT determined through C–V measurement. The samples
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Journal of The Electrochemical Society, 153 ͑6͒ F94-F99 ͑2006͒
F99
Figure 8. Gate current density vs electric field ͑J–E͒ characteristics of the
ultrathin film after RTA treatment.
Figure 9. TDDB lifetime projections for the Zr + IPA + hexanol samples
after RTA at 500, 600, and 900°C, respectively.
and 900°C displayed leakage current densities ͑Ͻ10−7 A/cm2͒
ZrO ultrathin films, which are readily produced, may behave as
suitable capacitors and coatings for insulating films.
2
lower than those reported in the literature for amorphous ZrO
2
8
,11
films.
Thin layers of zirconium dioxide that are used as dielectrics
for capacitors or as gate oxides for MIS devices are subject to a
mechanism known as time-dependent dielectric breakdown
Acknowledgment
This study was supported financially by the National Science
Council, Taiwan, ROC, through contract no. NSC 94-2113-M-009-
͑
TDDB͒. This mechanism causes the dielectric to break down and
0
20.
electrically short after a certain duration of operation. The expected
lifetime of a thin gate oxide under normal operating conditions
should be several million years. Figure 9 displays a projected life-
time operation of ca. 1.1 MV/cm for the Zr + IPA + hexanol RTA
National Chiao Tung University assisted in meeting the publication costs
of this article.
References
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00°C sample ͑five replicate measurements for each point͒. The
1
2
. Y. Ma, Y. Ono, L. Stecker, D. R. Evans, and S. T. Hsu, Tech. Dig. - Int. Electron
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sample is ca. 2.1 MV/cm, and that of the Zr + IPA + hexanol RTA
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00°C sample is ca. 10.4 MV/cm. In this figure, we observe a large
increment in the projection voltage for the 10-year lifetime when the
Zr + IPA + hexanol sample was annealed at 900°C. This result oc-
curs because the high annealing temperature stabilizes the ZrO2
film.
͑2003͒.
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In this paper, we propose a sol-gel method for preparing ultrathin
films that is attractive because of its low cost and because of the
improved thermal and electrical properties of the films. The sol-gel
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2
insulation ͑breakdown fields of up to 12.5 MV/cm͒ but also im-
proved thermal stability against crystallization ͑up to 900°C͒. These
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1
1
1
Table I. Properties of films annealed at 600 and 900°C.
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Heat-treatment
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Dielectric
constant ͑k͒
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EOT ͑nm͒
Zr + IPA + hexanol,
RTA 600°C, 1 min
Zr + IPA + hexanol,
RTA 900°C, 1 min
13.9
3.04
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2
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