Metallorganic chemical vapor deposition of Ru films using cyclopentadienyl-propylcyclopentadienylruthenium(II) and oxygen

Article abstract of DOI:10.1149/1.1471547

Ru thin films were prepared by metallorganic chemical vapor deposition using a cyclopentadienyl-propylcyclopentadienylruthenium(II) precursor and O₂. The nucleation and deposition behavior, thermal stability of the film surface, reaction at the Ru/TiN interface, and the stresses of the Ru thin films were investigated. The films consisted of single phase metallic Ru under all deposition conditions and showed an electrical resistivity as low as 12 μΩ cm. The Ru thin films had a negligible oxygen content. Therefore, the interface between Ru and TiN was not changed after annealing at 600°C under a N₂ atmosphere. However, the poor nucleation property especially on a SiO₂ surface resulted in a rough surface morphology. It was found that the stress of the Ru thin film decreased as the deposition temperature and growth rate increased. The deposition behavior and physical properties of the films were investigated for use as an electrode in a metal-insulator-metal capacitor in future generation dynamic random access memory devices.

Full text of DOI:10.1149/1.1471547

Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
C317
0013-4651/2002/149͑6͒/C317/7/$7.00 © The Electrochemical Society, Inc.
Metallorganic Chemical Vapor Deposition of Ru Films Using
Cyclopentadienyl-Propylcyclopentadienylruthenium„II…
and Oxygen
,z
*
*
Sang Yeol Kang, Ha Jin Lim, Cheol Seong Hwang, and Hyeong Joon Kim
School of Materials Science and Engineering and Interuniversity Semiconductor Research Center,
Seoul National University, Kwanak-ku, Seoul 151-742, Korea
Ru thin films were prepared by metallorganic chemical vapor deposition using
a
cyclopentadienyl-propyl-
cyclopentadienylruthenium͑II͒ precursor and O2 . The nucleation and deposition behavior, thermal stability of the film surface,
reaction at the Ru/TiN interface, and the stresses of the Ru thin films were investigated. The films consisted of single phase
metallic Ru under all deposition conditions and showed an electrical resistivity as low as 12 ␮⍀ cm. The Ru thin films had a
negligible oxygen content. Therefore, the interface between Ru and TiN was not changed after annealing at 600°C under a N2
atmosphere. However, the poor nucleation property especially on a SiO2 surface resulted in a rough surface morphology. It was
found that the stress of the Ru thin film decreased as the deposition temperature and growth rate increased. The deposition
behavior and physical properties of the films were investigated for use as an electrode in a metal-insulator-metal capacitor in future
generation dynamic random access memory devices.
© 2002 The Electrochemical Society. ͓DOI: 10.1149/1.1471547͔ All rights reserved.
Manuscript submitted August 23, 2001; revised manuscript received December 21, 2001. Available electronically April 12, 2002.
because the stress should be a critical factor for determining the
thermal stability of the electrode films when the film thickness is as
low as 10 nm owing to the integration purposes of DRAMs.
Metal-insulator-metal ͑MIM͒ capacitors using Ta2O5 and
(Ba,Sr)TiO3 ͑BST͒ dielectric films have been studied for use as
storage capacitors to shrink the storage capacitor area in dynamic
random access memories ͑DRAMs͒ having a minimum feature size
Ͻ0.12 ␮m. Due to the extremely small size of the capacitor, a three-
dimensional structure, such as hole-type, is required for Gbit-scale
DRAMs to obtain sufficient storage capacitance even though dielec-
trics with a high permittivity are used. Therefore, a chemical vapor
deposition ͑CVD͒ technique providing excellent conformality is re-
quired in order to fabricate the top and bottom electrodes as well as
the dielectric films.1
Experimental
The MOCVD apparatus consisted of a vertical warm wall reactor
and a resistive substrate heater that could handle Si wafers of up to
a 6 in. diam. A more detailed geometry of the deposition system was
reported earlier.10 The experimental conditions are summarized in
Table I. RuCp͑i-PrCp͒ was vaporized at 85°C via a standard subli-
mation technique, where a vapor pressure of approximately 0.2 Torr
was obtained. Figure 1 shows the molecular structure of RuCp͑i-
PrCp͒. Ar was used as both a carrier gas and diluent gas. O2 gas was
introduced into the reactor in order to enhance metallorganic precur-
sor decomposition and to reduce carbon incorporation into the films.
Ru thin films were deposited on Si͑100͒ and TiN ͑500 Å,
sputtered͒/TiO2 ͑200 Å, sputtered͒/SiO2 ͑1000 Å͒/Si substrates at
temperatures ranging from 300 to 400°C. Some of the deposited
films were annealed in an atmosphere-controlled furnace under N2
or H2 /Ar ambient.
Film phase analysis and the resistivity measurements were per-
formed by X-ray diffraction ͑XRD͒ and a four-point probe, respec-
tively. The film thickness and surface morphology were observed by
scanning electron microscopy ͑SEM͒ and atomic force microscopy
͑AFM͒. The Ru/TiN interface was investigated by both Auger elec-
tron spectroscopy ͑AES͒ and transmission electron microscopy
͑TEM͒. Stresses in the thin films were characterized from the mea-
sured curvature of the samples ͑films and the Si substrate͒ using a
laser scanning technique in a commercial apparatus ͑Tencor FLX-
2320͒ and Stoney’s equation.11 The average thickness of the Ru thin
films used in the stress measurements was 1000 Å.
The Ru thin film is one of the promising materials for capacitor
electrodes due to its excellent characteristics, such as low resistivity
and good dry etching property. In addition, it forms conducting
RuO2 even when it oxidizes preventing the formation of a low di-
electric interfacial layer at the interface with a high dielectric layer.
Previous studies of the metallorganic CVD ͑MOCVD͒ of Ru
metal films have utilized several precursors such as Ru(C5H5)2
(RuCp2)2-4 where Cp is cyclopentadienyl, Ru3(CO)12
,
2,5
Ru(C11H19O2)3 Ru(dpm)
where dpm is dipivaloylmetha-
͓
͔
͓
3
6,7
nate, Ru(octanedionate)3 Ru(OD)
,
and Ru(C5H4C2H5)2
͔
3
1,8,9
Ru(EtCp)
where Et is ethyl. Ru(EtCp)2 appears to be the
͓
͔
2
precursor of choice for Ru CVD these days due to its high vapor
pressure and good thermal stability. Furthermore, it exists as a liquid
at room temperature, making supply of the precursor stable either by
liquid delivery or a standard bubbling technique. CVD Ru thin films
grown using Ru(EtCp)2 showed good properties such as low
electrical resistivity, high deposition rates, and low impurity
concentrations.
However, Ru(EtCp)2 is too expensive to be used as a precursor
for Ru CVD in a mass production stage. Therefore, a new precursor
that has a comparable performance is required for Ru CVD. In
this study, cyclopentadienyl-propylcyclopentadienylruthenium͑II͒
͓RuCp͑i-PrCp͔͒, developed by Tanaka Kikinzoku Co., Japan, was
used to deposit the Ru films. This new precursor is potentially
cheaper than Ru(EtCp)2 although it possesses comparable thermal
properties. The growth behavior, structural, and electrical properties
of the Ru films are reported in comparison with the results using the
Ru(EtCp)2 precursor. In particular, variations in the stresses of Ru
thin films with the deposition conditions were investigated. This is
Results and Discussion
Figure 2a and b shows the variations in XRD patterns of the thin
films deposited on Si with the substrate temperatures when the O2
flow rate was 50 standard cubic centimeters per minute ͑sccm͒, and
with the O2 flow rate when the substrate temperature was 325°C,
respectively. Below 300°C, no film was deposited under the given
deposition conditions. Here, the range of deposition conditions were
determined from the experimental conditions for Ru CVD using the
Ru(EtCp)2 which produced the phase-pure Ru films. Figure 2 shows
that all the deposited films are Ru metal layers without RuO2 found
in the experimental results from the Ru(EtCp)2 precursor.8 It was
estimated that the detection limit for XRD of the oxide phase, such
* Electrochemical Society Active Member.
z E-mail: cheolsh@plaza.snu.ac.kr
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Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
Table I. Experimental conditions for Ru MOCVD.
Precursor
RuCp͑i-PrCp͒
Source temperature
Carrier gas flow rate
Deposition temperature
Reaction gas flow rate
Total flow rate
85°C
100 sccm
300-375°C
O2 0-100 sccm
1000 sccm
3 Torr
Deposition pressure
as RuO2 , was approximately 1-2%. It has been observed that the
RuO2 phase was obtained from deposition under the conditions of a
higher deposition temperature or a higher oxygen concentration.8
Therefore, it was expected that deposition at temperatures higher
than 400°C and an O2 flow rate higher than 200 sccm would result
in a slight incorporation of the oxide phase in the grown films. The
variations in the crystallographic orientation of the grown films are
also similar to the films grown using the Ru(EtCp)2 precursor.
Therefore, the thermal decomposition property of the RuCp͑i-PrCp͒
precursor and oxidation behavior of the grown Ru film using this
precursor are similar to those when using Ru(EtCp)2 precursor.
Figure 3a and b shows the variations in resistivity of the Ru films
as functions of the deposition temperature and oxygen flow rate,
respectively. In Fig. 3a, the O2 flow rate was 50 sccm. The resistiv-
ities of the Ru thin films were from approximately 12 to 13 ␮⍀ cm,
almost irrespective of temperature. In Fig. 3b, the growth tempera-
ture was 325°C. The resistivity of the Ru thin film deposited with
the addition of 25 sccm was slightly larger than those of films de-
posited under other conditions. This might be due to the incomplete
removal of carbon in the film when the oxygen flow rate was
small, which corresponds to the case of the experiments using
Ru(EtCp)2 .8 This also corresponds to thermodynamic consider-
Figure 2. The XRD patterns of Ru thin films deposited on Si ͑a͒ at various
substrate temperature with the addition of 50 sccm of oxygen and ͑b͒ at
325°C with various oxygen flow rates.
ations that the removal of carbon, which is included in the precursor,
occurs through the reaction with added oxygen to form primarily to
CO2 and CO.8 In fact, this was the reason why metallic Ru films
were obtained under the oxidizing atmosphere; almost all the oxy-
gen was consumed to oxidize the carbon due to the larger oxidation
potential of C compared to that of Ru. Therefore, it can be reason-
ably assumed that the phase-pure Ru film growth window in terms
of the oxygen flow rate at a given temperature is dependent on the
precursor delivery technique. For example, the liquid delivery tech-
nique, where an excessive amount of solvent ͑C source͒ is intro-
duced to the chamber, may require a much larger O2 flow rate to
obtain metallic Ru films. The required amount of oxygen to com-
pletely oxidize and remove all the carbon in the system was larger
than that expected from the thermodynamic calculation8 due to the
relatively small adsorption of oxygen onto the growing surface.
However, it is apparent that the addition of a sufficient amount of
Figure 3. The electrical resistivites of Ru thin films deposited ͑a͒ at various
substrate temperatures with the addition of 50 sccm of oxygen, and ͑b͒ at
325°C with various oxygen flow rates.
Figure 1. The structure of RuCp͑i-PrCp͒.
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Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
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Figure 5. Cross-sectional TEM images of the Ru films deposited ͑a͒ at
375°C with 50 sccm of oxygen flow rate on TiN/TiO2 /SiO2 /Si substrate and
͑b͒ annealed under H2 atmosphere at 400°C and then N2 atmosphere at
600°C.
oxygen, not enough to induce oxidation of the deposited Ru film, is
essential to obtain high quality Ru films. This also corresponds to
the experimental results when using Ru(EtCp)2 .
Another potential contaminant in the Ru film is oxygen. Oxygen
largely degrades the electrical conductivity compared to carbon.8
Furthermore, oxygen in the Ru layer can oxidize the surface of the
underlying barrier layer, such as TiN or TiAlN, when it is used as a
bottom electrode. This results in a serious increase in the contact
resistance of the integrated capacitors, even under the conditions
where no further oxygen is introduced during dielectric deposition
and postannealing. To investigate this potential problem, Ru films
were deposited on the barrier TiN layer and the interfacial reaction
between the Ru and TiN layers was investigated by both AES and
TEM.
It was a concern that oxygen in the Ru film could diffuse to the
Ru/TiN interface during dielectric deposition and postannealing, and
form a TiOx thin layer at the interface even when the amount of the
oxygen is not very large. This concern is due to the much larger
thermodynamic stability of TiO2 compared to that of RuO2 ͑⌬Gf of
TiO2 and RuO2 at 900 K are Ϫ780.233 and Ϫ153.312 kJ/mol,
respectively.12͒ The TiOx layer can increase the contact resistance of
the Ru/TiN interface.
Figure 4 shows the AES depth profile of a typical Ru film,
deposited at 375°C with 50 sccm of oxygen flow rate, on
TiN/TiO2 /SiO2 /Si substrate and annealed under various conditions.
It can be clearly observed that the Ru film contains a negligible
amount of oxygen (Ͻ1%) even in the as-deposited state. The rela-
tively high oxygen concentration on the TiN surface is due to the
exposure of the TiN film to air prior to Ru film growth. 15 to 20% of
the oxygen concentration on the TiN surface after exposure to air is
a well-known phenomenon.13 It can be clearly seen that all anneal-
ing conditions do not induce change in the concentration distribution
Figure 4. The AES depth profiles of the Ru films deposited at 375°C with
50 sccm of oxygen flow rate on TiN/TiO2 /SiO2 /Si substrate and annealed
under various conditions; ͑a͒ as-deposited, ͑b͒ postannealed under N2 atmo-
sphere at 600°C, ͑c͒ under H2 atmosphere at 400°C, and ͑d͒ under H2 atmo-
sphere at 400°C and N2 atmosphere at 600°C.
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Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
Figure 7. The variation of the growth rates of Ru films deposited at 350°C
with varying O2 flow rate.
Figure 6. The Arrehnius plot of the growth rate of Ru film deposited at
various substrate temperatures with 100 sccm of oxygen addition.
increases with increasing O2 flow rate, and then saturates to approxi-
mately 250 Å/min. This behavior corresponds to the oxygen assisted
decomposition behavior of the precursor. The growth rate has a very
strong relationship with the stress behavior of the film as discussed
later.
The rough surface morphology of CVD Ru films has been known
as one of the potential problems for its use as the bottom electrode.14
Therefore, variations in surface morphology and roughness with the
various deposition and postannealing conditions and types of sub-
strate were investigated by SEM and AFM.
Figure 8 shows the surface morphologies of 750 Å thick Ru thin
films deposited at 325°C with various oxygen flow rates. The sur-
face morphologies are almost independent of the oxygen flow rates
and the root-mean-squared ͑RMS͒ roughness of the films are ap-
proximately 40 Å. However, the surface morphology was dependent
on the deposition temperature. Figure 9 shows the surface mor-
phologies of 1000 Å thick Ru films deposited at 325, 350, 375, and
400°C, respectively. The grain size increases with increasing growth
temperature, as might be expected.
The surface roughness of the Ru film depends on the types of
substrate on which the films were grown. The surface dependent
roughness might originate from the different nucleation properties of
the Ru film on different surfaces. Figure 10a, b, c, and d shows the
SEM micrographs of the films grown only for 1 min under a depo-
sition temperature of 350°C and an O2 flow rate 100 sccm on Si,
SiO2 , TiN, and Ta2O5 surfaces, respectively. The SiO2 , TiN, and
Ta2O5 films were prepared by thermal oxidation, reactive sputtering,
of the constituent elements, except a slight decrease in the C con-
centration after the high temperature annealing. This implies that the
initial oxygen concentration of the grown Ru film was small enough
not to cause any interfacial oxidation or intermixing problem with
the TiN barrier layer.
Figure 5a and b shows cross-sectional TEM images of the as-
deposited and postannealed films under H2 atmosphere at 400°C
followed by a N2 atmosphere at 600°C, respectively. The slightly
light contrast effect on the TiN surface is due to the initially high
oxygen concentration. It can be confirmed that postannealing does
not induce any structural change at the interface.
Figure 6 shows the Arrehnius plot of the Ru film growth ratewith
the deposition temperature when the O2 flow rate was 100 sccm.
The diffusion-limited-growth region was determined to be approxi-
mately Ͼ370°C because the growth rate at 375°C is almost the
same as that at 400°C. Therefore, the growth rates at 325 and 350°C
belong to the surface-chemical-reaction controlled region and the
apparent activation energy for the surface-chemical-reaction was es-
timated from the slope of the straight line connecting the two points.
The growth behavior changes from the surface chemical reaction
controlled region to diffusion limited region at around 365°C, and
the activation energy is approximately 0.8 eV, which is comparable
to that from the experiment using Ru(EtCp)2 .
Figure 7 shows the variation of the Ru film growth rate with O2
flow rate at a deposition temperature of 350°C. The growth rate
Figure 8. The surface morphologies of Ru thin films deposited at 350°C with various O2 flow rates ͑in sccm͒; ͑a͒ 25, ͑b͒ 50, and ͑c͒ 100.
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Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
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Figure 9. The surface morphologies of Ru thin films deposited at ͑a͒ 325°C, ͑b͒ 350°C, ͑c͒ 375°C, and ͑d͒ 400°C with 100 sccm of oxygen addition.
and low pressure CVD, respectively. The Si surface actually had a
very thin SiO2 ͑native oxide͒ due to the air exposure of the substrate
before the film deposition. The RMS roughnesses of the four
samples measured by AFM were 82.7, 99.8, 43.7, and 34.8°C, re-
spectively. It can be understood that the Ru film grown on the SiO2
surface has a small nucleation probability, due probably to the high
SiO2 /Ru interface energy. The low nucleation probability, thereby
large surface roughness, of the Ru film on the SiO2 surface may
induce a leakage current problem in the MIM capacitor structure of
the integrated DRAM device. A certain nucleation layer or buffer
layer, such as TiN, may be required to improve the nucleation prop-
erty of the Ru film on a SiO2 layer. However, this will make the
integration process more complicated with the extremely small fea-
ture size (ϳ0.1 ␮m). The poor nucleation of the Ru film on SiO2
results in a Volmer-Weber type growth behavior, which greatly in-
fluences the stress behavior of the film. This sort of poor nucleation
behavior of Ru is also observed on the Ta2O5 film surface even
though it is less severe compared to the Si or SiO2 case.
Figure 11 shows the AFM surface morphologies of the Ru film
grown on the Ta2O5 film surface. When the film is very thin, as in
Fig. 11a, the connectivity between each nucleus is poor. Therefore,
coalescence during the postannealing results in the island-like grains
on the surface and the rougher surface ͑Fig. 11c͒. However, as the
film thickness increases, the surface is fully covered with the Ru
film resulting in a more stable surface against postannealing, as in
the case of Fig. 11d. This implies that there is a certain critical
thickness under which the electrode is unstable to postannealing as
the top electrode of the Ta2O5 MIM capacitor. This critical value
appeared to be approximately 600 Å in this study.
concern in integrated circuit ͑IC͒ technology. This is especially the
case as the feature size becomes smaller and smaller. High stress
values in the thin films can cause a film to migrate, crack and even
peel off.15 Therefore, it is important to investigate the stress gener-
ated in Ru thin films for their use as the top as well as the bottom
electrode of the DRAM capacitor.
The stress of the thin films is generally classified into either
thermal or intrinsic stresses. In general, for high melting point ma-
terials such as Ru and Pt, intrinsic tensile stress is mainly observed16
and this type of stress is associated with island impingement and
coalescence.17
Figure 12a shows the variations in stresses in Ru thin films de-
posited on Si as a function of various substrate temperatures when
the oxygen flow rate was 100 sccm. As the deposition temperature
increases, the tensile stress decreases. Therefore, the generated stress
in the film originates mainly from the intrinsic component and not
from the thermal component of the stress. Figure 12b shows the
stresses in the Ru thin films deposited at 350°C with various oxygen
flow rates. The stress decreases with oxygen flow rates up to 200
sccm and then slightly increases. From the comparison between the
variations in stress of the films ͑Fig. 12a and b͒ and the variations in
the film growth rate ͑Fig. 6 and 7͒ according to the various deposi-
tion conditions, it can be understood that the higher the growth rate,
the smaller the stress.
It is generally accepted that the tensile stress observed during the
island coalescence stage of Volmer-Weber film growth is associated
with the formation of grain boundaries. When two growing islands
first touch, some portion of the adjacent surfaces of the islands
‘‘zip’’ together to form a grain boundary. Zipping, which is driven
by the reduction in the overall surface energy, is accomplished
through elastic deformation of the islands, thereby imposing a cost
of increased strain energy. In contrast, the tensile stresses generated
by grain boundary formation can be relieved by diffusion of ada-
toms on the free surface of a film into the grain boundary.15
Therefore, the intrinsic stress generated in the film can be viewed
as a by-product from competition between the zipping of adjacent
The stress affects the thermal stabilities of the Ru films as the
bottom and top electrodes. As the design rule of memory devices
decreases, the residual stress in the films became increasingly cru-
cial for the fabrication of memory devices and their reliability. Al-
though the precise influence of stress on device production and re-
liability is still not clearly understood, residual stresses in the thin
films on silicon substrates are generally considered to be of major
Figure 10. The SEM micrographs of the Ru films grown on ͑a͒ Si, ͑b͒ SiO2 , ͑c͒ TiN, and ͑d͒ Ta2O5 for 1 min under the conditions of 350°C deposition
temperature and 100 sccm of O2 flow rate.
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Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
Figure 12. Stresses in Ru thin films deposited on Si ͑a͒ at various substrate
temperature with 100 sccm of oxygen addition and ͑b͒ at 350°C with various
oxygen addition.
Most of the grain boundaries were formed by zipping when the
film growth rate was low, whereas the zipping is suppressed by the
fast accumulation of constituent atoms in the grain boundary area
when the growth rate is high. This is a diffusive stress relaxation
mechanism.
In addition, for the case of Ru film deposition at high tempera-
ture, the surface diffusion of adatoms is more active compared to
film deposition at low temperature resulting in a more effective re-
lease of thin film stress. Therefore, the tensile stress decreases very
fast as the deposition temperature increases ͑Fig. 12a͒.
The high stress at 325°C is a serious concern since the typical Ru
film growth temperature should be approximately 300°C consider-
ing the conformal deposition property at this low temperature. Fur-
ther research will certainly be required to reduce the stress at low
deposition temperatures.
Conclusion
Ru thin films were deposited using a RuCp͑i-PrCp͒ precursor
and O2 on Si wafers. The films consisted of a metallic Ru single
phase under all deposition conditions and exhibited good electrical
resistivities as low as 12 ␮⍀ cm. Almost all the deposition behavior
and physical characteristics of the Ru films are quite similar to the
Ru films produced using the Ru(EtCp)2 precursor, which is the most
widely used precursor for Ru CVD. The deposited films had a neg-
ligible amount of residual oxygen which meant oxidation of the
underlying barrier layer, TiN, after the postannealing at 600°C was
negligible.
However, the films showed a poor nucleation behavior especially
on SiO2 surface due to the nonwetting behavior of Ru on SiO2
resulting in a rough surface morphology. The poor nucleation prop-
erty also occurred on Ta2O5 surface resulting in a increased rough-
ness after postannealing at 600°C when the film thickness is very
small. No increase in roughness after annealing was observed when
the film thickness was larger than a critical thickness of approxi-
mately 600 Å. This nucleation behavior of the Ru film also affected
the stress property of the grown film. The stress greatly increased
with the decreasing growth rate almost irrespective of the deposition
conditions. This behavior was explained in terms of intrinsic stress
generation by zipping of the nuclei when the film growth rate was
low. The decrease in stress with increasing growth rate and tempera-
ture was explained by a diffusive stress relaxation mechanism.
Figure 11. The AFM surface morphologies of the Ru film grown on the
Ta2O5 film surface for ͑a͒, ͑c͒ 1 min and ͑b͒, ͑d͒ 3 min at 350°C, respec-
tively. And in ͑c͒ and ͑d͒, the films were annealed at 600°C under N2 atmo-
sphere for 30 min.
Acknowledgments
The authors acknowledge the financial support of Samsung elec-
tronics, and the Korean government through A Collaborative Project
for Excellence in Basic System IC Technology ͑System IC 2010͒
and National Research Laboratory ͑NRL͒ program. The authors also
acknowledge Tanaka Kikinzoku Co. Japan for their supply of
RuCp͑i-PrCp͒.
nuclei or grains, which increases the stress, and surface diffusion of
adatoms into the grain boundary area, which reduces the stress when
the film grows via the Volmer-Weber mechanism. The Volmer-
Weber type growth behavior of the Ru films was confirmed by
AFM.
Seoul National University assisted in meeting the publication costs of this
article.
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Journal of The Electrochemical Society, 149 ͑6͒ C317-C323 ͑2002͒
C323
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