Deposition of epitaxial silicon carbide films using high vacuum ...

Thin Solid Films 459 (2004) 7–12
Deposition of epitaxial silicon carbide films using high vacuum MOCVD
method for MEMS applications
a a a a a b a,
D.-C. Lim , H.-G. Jee , J.W. Kim , J.-S. Moon , S.-B. Lee , S.S. Choi , J.-H. Boo *
a
Department of Chemistry, Sungkyunkwan University, 300 Chunchun-Dong, Jangan-Gu, Suwon 440-746, South Korea
b
Department of Nanoscience, Sunmoon University, Ahsan 336-840, South Korea
Available Online April 2 2004
Abstract
Silicon carbide (SiC) thin film have been prepared on both Si(100) and SiO patterned Si(100) substrates by the high vacuum
2
metal-organic chemical vapor deposition (MOCVD) method using a single source precursor at various growth temperatures in
the range of 700–1000 8C. Diethylmethylsilane(DEMS) was used as precursor without carrier gas. The effects of substrate
temperature as well as deposition time on the crystal growth and hardness were mainly investigated in this study. The optimum
temperature for the formation of the epitaxial SiC thin films were found to 900 8C on the basis of XRD results. However, the
XPS result shows that the SiC film grown at 900 8C have carbon rich (Si:Cs1:1.2 composition) surface due to surface reaction
of the precursor itself. From the SEM images, substrate temperature has influence on the grain size and crystallinity of the SiC
films. Especially, the major crystal form of these deposited films was rectangular in shape on the substrates at 900 8C. We also
obtain a high hardness SiC thin film with 32 GPa.
2003 Elsevier B.V. All rights reserved.
Keywords: High vacuum metal-organic chemical vapor deposition (MOCVD); Epitxial SiC thin film; Diethylmethylsilane (DEMS); Selective
deposition of SiC
1. Introduction
The advances in silicon process technology over the
last 3 decades has led to the development of microcomponents
known as microelectromechanical system or
MEMS (Micro-Electro-Mechanical-Systems). Although
silicon based MEMS devices find such wide uses today,
they lack high temperature capabilities with respect to
both mechanical and electrical properties. Recently,
researchers have been pursuing SiC as material for hightemperature
microsensor and microactuator applications
w1–4x.
Silicon carbide become generally known as attractive
material for demanding mechanical and high-temperature
application, as well as for use in abrasive, erosive,
and corrosive media. Also, SiC is semiconductor of
great interest in high-power, high-temperature, and highradiation
applications w5–7x. Thus, the superior mechanical,
chemical, and electrical capabilities make SiC an
exceptionally attractive material in MEMS applications.
*Corresponding author. Tel.: q82-31-290-7072; fax: q82-31-290-
7075.
E-mail address: jhboo@chem.skku.ac.kr (J.-H. Boo).
Conventional silicon carbide chemical-vapor-deposition
(CVD) processes generally utilized multiple precursors
such as silane and hydrocarbons and required
elevated substrate temperatures in excess of 1000 8C.
High growth temperature sometimes results in high
tensile stress and lattice defects in the SiC films because
of the differences in lattice constants and thermal expansion
coefficients between silicon carbide and silicon w8x.
Therefore, low-temperature alternatives to the conventional
SiC CVD methods must be considered. To do
this, a simple CVD method utilizing a single precursor
is highly desirable for growing high-quality SiC films
at temperature below 1000 8C to enable SiC postprocessing
such etching w9x. In this study, therefore, we
have deposited epitaxial cubic-SiC thin films on Si
(001) and patterned SiO2
Si (100) substrates at temperatures
of 700–1000 8C utilizing diethylmethylsilane
(DEMS) as a single precursor for MEMS applications.
2. Experimental
Crystalline SiC thin films were fabricated in a parallel
low-pressure MOCVD reactor. Inside the reactor, the
0040-6090/04/$ - see front matter 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.tsf.2003.12.140

8 D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12
Fig. 1. X-Ray diffraction patterns of SiC thin films grown on Si(100) substrates using DEMD at various deposition temperatures and times given
in the figure.
substrate was mounted on a stainless holder that was
heated by DC power supply. The general CVD condition
y7
y5
was pressures between 2.0=10 Torr and 1.0=10
Torr and growth temperatures of 700–1000 8C, respectively.
The substrate temperature was measured with an
optical pyrometer. The deposition time was lasted to be
maximum 6 h and SiC films have been grown on both
Si (100) and SiO patterned Si (100) substrates.
2
The diethylmethylsilane (DEMS), (CH CH ) 3 2 2
–SiH–CH , used in this study as single precursor, is a
3
liquid at room temperature with boiling point of 78 8C.
This makes the handling aspects much more simplified
compared with conventional dual-source CVD. Also,
the use of single precursor insures stoichiometry, hence,
it eliminates the need for an elaborate gas handling
system.
After deposition, a number of analysis and characterization
techniques were employed to investigate the
deposited SiC films. These include X-ray Photoemission
Spectroscopy (XPS) to confirm chemical composition,
X-ray diffraction (XRD) to determine structural crystallinity,
and Atomic Force Microscope (AFM) to investigate
SiC film topology. Scanning electron microscopy
(SEM) was also used to investigate the SiC film
morphology and the quality of the SiCySi interface as
well as to estimate film thickness by cross-sectional
image.
3. Results and discussions
Fig. 1 shows the X-ray u–2u diffraction patterns of
cubic SiC thin films grown on Si (100) surface at
temperatures in the range 700–1000 8C and 1.0=10 y5
Torr for different deposition time. Fig. 1a shows the
XRD pattern of SiC thin film grown at 700 8C and 2 h.
From Fig. 1a b, we can see that SiC thin film (1a)
grown at 700 8C and 2 h has an amorphous structure.
However, with increasing the deposition time to 4 h at
the same temperature, the diffraction pattern shown in
the Fig. 1b shows a crystal structure with (200) 3C–
SiC plane (2us41.48) as well as the graphite carbon
structure (2us45.28). This indicates that with single
precursor MOCVD crystalline 3C–SiC film can be
deposited at much lower temperature than conventional
CVD. With increasing the deposition temperatures from
700 to 900 8C, moreover, a significant increase of the
intensity of 3C–SiC (002) diffraction peaks was
observed, showing an improvement of crystallinity. The
XRD pattern (see Fig. 2c) of 3C–SiC thin film grown
at 900 8C exhibits a very large and sharp peak at the
(200) reflection of 2us41.48. This indicates that this
thin film was grown epitaxially and may have a monocrystalline
nature with (200) preferred orientation. However,
in the Fig. 1d, small peaks attributed to the 3C–
SiC(111) diffraction also appeared in addition to major

D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12
9
Fig. 2. SEM images of SiC thin films grown on Si(100) substrates using DEMS at various deposition temperatures.
peaks of 3C–SiC (200) diffraction, indicating that
polycrystalline 3C–SiC thin film was obtained at deposition
temperatures of 1000 8C. From our XRD data,
with increasing the deposition temperature from 700 to
900 8C, high quality 3C–SiC layer was obtained under
the same deposition conditions. The XRD results also
show that the deposition time as well as deposition
temperature could be one of the important factors for
influencing the film crystallinity.
Fig. 2 shows surface morphology changes of the 3C–
SiC films grown at various temperatures (700–1000 8C)
for 2 h under the same deposition pressure of 1.0
y5
Torr=10 Torr, respectively. We can see that the film
grown at 700 8C has a smooth surface and nano size
SiC crystals as shown in the Fig. 2a. With increasing
the deposition temperature, 3C–SiC film with relatively
large crystals were deposited. The surface morphologies
of the films grown at 900 and 1000 8C show much
larger crystal size than those of the films grown at 700
and 800 8C. The SEM image of SiC film grown at 800
8C shown in the Fig. 2b exhibits a crystal shape of SiC
crystals with sub-micron size. Above 800 8C, the crystal
size and crystallinity of the 3C–SiC films are apparently
limited to the substrate temperature. Especially, from the
Fig. 2c, we can see that the major crystal form of a
deposited film grown on the substrate at 900 8C is
rectangular in shape. We also confirm the crystal form
of the SiC film deposited at 900 8C from a AFM result
(see Fig. 4a,c). However, a polycrystalline shape with
relatively larger crystal size can be seen in Fig. 2d,
when the growth temperature was at 1000 8C. This is
in good agreement with the XRD result shown in the
Fig. 1d.
Film stoichiometry of the 3C–SiC film with optimized
expitaxial crystal structure was determined utilizing
the XPS analysis. The survey spectrum of Fig. 3a
clearly shows the photoelectron peaks of Si 2s, Si 2p,
C1s and C (KLL) Auger signals indicating formation
of silicon carbide film. Oxygen (O 1s) can be attributed
to surface contamination by moisture during sample
transfer in the air condition. Also, we could see that the
carbon content decreased after the Ar ion sputtering as
shown in the Fig. 3c. As the sputtering depth is less
than 3 nm, the carbon is the adsorbed species on the
SiC surface. The reason for arising the carbon content
on the surface is mainly due to the air contamination
after deposition. In Fig. 3b, the Si 1s high-resolution
spectra obtained before and after Ar ion sputtering are
also shown. To compare the change of Si 1s binding
energies for the SiC film before and after Ar ion
sputtering, the Si 1s peak at 100.9 eV obtained without
Ar ion sputtering is shifted to lower binging energy at
100.3 eV after Ar ion sputtering. The reason for this
binding energy shift is due to increasing of carbidic
after removing of graphite carbon and surface SiO x
species by Ar ion sputtering. However, we also see
weak carbon shoulder peak in Fig. 5c but if we did
more Ar ion sputtering the graphite carbon can be

10 D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12
Fig. 3. X-Ray photoelectron spectra of a 3C–SiC thin film grown on Si (100) substrate at 900 8C obtained before and after Ar ion sputtering;
(a) Survey spectrum, (b) High-resolution XP spectra of Si 2p and (c) High-resolution XP spectra of C 1s.
removed completely. The stoichiometry of this film is
Si: Cs1: 1.2.
Fig. 4a,c show the atomic force microscopic (AFM)
images of 3C–SiC thin films grown on both the Si(100)
substrate (Fig. 4a) and SiO2
patterned Si(100) substrate
(Fig. 4c) at 900 8C. We can see the crystal size, the
crystal shape and surface roughness of the 3C–SiC thin
film clearly. The crystal size of the 3C–SiC is approximately
0.1 mm and RMS roughness value is ;32 nm
in the Fig. 4a. The 3C–SiC thin film also has rectangular
crystal shape. In the Fig. 4c, however, the 3C–SiC thin
film grown on SiO2
patterned Si(100) substrate has
more small crystal size and smooth surface with RMS
roughness value approximately 6 nm than that of the
3C–SiC thin film grown on Si(100) substrate. The
reason for this result can be explained by the fact that
a very thin SiO layer remained on the Si(100) substrate
2
since the substrate was transferred from air to vacuum
condition after the wet etching process. That’s why the
SiC film was grown in a different way compared with
clean Si(100) substrate. Fig. 4b shows the cross-sectional
TEM image and plane view TED pattern obtained
using the same film as Fig. 4a. The contrast seen in the
cross-sectional view TEM micrographs is believed to be
associated with mass contrast due to surface roughness
andyor misoriented or twinned regions surrounding the
epitaxial growth w10x. The thickness of the SiC film is
approximately 150 nm. Also, the SiC film has very
sharp interface and high dense crystal structure. In the
TED, besides the normal diffraction pattern due to the
cubic structure, extra pattern can be seen indicating the
existence of microtwins and stacking faults caused by
the lattice dismatch between the SiC film and the Si
(100) substrate.
Fig. 5a shows the optical microscopic image of a
3C–SiC thin film grown on a SiO2
patterned Si (100)
surface at 900 8C. With conventional high-temperature
CVD method, SiC films deposited on SiO2
patterned
Si(100) substrate have larger grain size and rougher
texture and become subsequently more porous than films
grown on Si(100). As a result, the SiC films on SiO 2
mask is more readily etched away in concentrated HF
solution w11–13x while the SiC film on the Si(100) side
is not clearly etched and etching takes a long time.
Therefore we have selectively deposited the 3C–SiC
thin film on SiO patterned Si (100) surface which
2

D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12
11
surface. To confirm this selectivity characteristic on
SiO2
patterned Si(100) substrate, we measure the EDX
(see Fig. 5c,d). Si and C species were detected in the
zone a while Si and O species were only detected in
zone b. Carbon species contributed to SiC was not
detected in zone b. From these results, we could derive
that the SiC film was deposited selectively on the SiO 2
patterned Si(100) substrate. Therefore, we could etch
away the SiO layer more easily and get the deposited
2
SiC film only by lifting off the SiO from the Si(100)
2
substrate, suggesting good MEMS applications. Fig. 5b
shows the SEM images of SiC thin film after SiO 2
pattern etched away using HF solution. Also, we measured
the hardness of SiC thin films using the micro
knoop hardness tester. Independently the deposition
temperature, the SiC thin films grown under the same
deposition conditions have high hardness approximately
32 GPa.
4. Conclusions
Fig. 4. AFM images SiC thin films grown on both Si(100) (a) and
SiO2
patterned Si(100) (b) substrates using DEMS at 900 8C. Fig.
4b shows TEM images of the same SiC thin film as Fig. 4a. The
insert of Fig. 4a shows TED pattern of the same film.
made by UV-dry etching of a mask shielded SiO layers 2
after a PR coating of the oxidized Si(100) substrate. In
Fig. 5a, we could clearly see the selective deposited SiC
film with more rough surface than that of the SiO 2
We have deposited the 3C–SiC thin films with high
hardness of 32 GPa on Si(100) surfaces by a diethylmethylsilane
(DEMS) single precursor at temperatures
y5
in the range 700–1000 8C and 1.0=10 Torr for
MEMS applications. With increasing the deposition
temperature to 900 8C, relatively well oriented 3C–SiC
layers were obtained. At this deposition condition, the
major crystal form of 3C–SiC thin film was rectangular
in shape on the substrate, and the average crystal size
and the value of RMS surface roughness are approximately
0.1 mm and ;32 nm, respectively. Otherwise,
the 3C–SiC thin film grown on SiO2
patterned Si(100)
substrate has more small crystal size and smooth surface
with RMS roughness value approximately 6 nm. With
increasing deposition time from 2 h to 4 h, the crystal
size as well as RMS roughness value also increased.
These results show that the deposition temperature and
time could be one of the important factors for influencing
the film crystallinity. The XPS result shows that the
SiC film grown at 900 8C has a slightly carbon rich.
We have also selectively deposited cubic silicon carbide
thin films on SiO2
patterned Si(100) substrates. In
conclusion, the low-temperature chemical vapor deposition
process using a single precursor for both eptixial
SiC growth on Si(100) and selective SiC deposition on
SiO patterned Si(100) substrates described in this study
2
will be readily adaptable to current MEMS applications.
Acknowledgments
Support of this research by the Ministry of Science
Technology in Korea (project No. M10214000278-
02B1500-04211) is gratefully acknowledged.

12 D.-C. Lim et al. / Thin Solid Films 459 (2004) 7–12
Fig. 5. Optical microscopic (a) and SEM (b) images before and after chemical etching of SiC thin films grown on SiO2
patterned Si(100)
substrate using DEMS at 900 8C. Fig. 5c,d show the EDX spectra of selectively deposited SiC thin film (zone a) on SiO2
patterned Si(100)
substrate (zone b) obtained from the same film as Fig. 5a.
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