Fabrication and Characterization of SiC Thin Films - IEEE Xplore

Proceedings of the 2011 6th IEEE International
Conference on Nano/Micro Engineered and Molecular Systems
February 20-23, 2011, Kaohsiung, Taiwan
Fabrication and Characterization of SiC Thin Films
Lei Liu, Wei Tang, Bai-xiang Zheng and Hai-xia Zhang*, Senior Member, IEEE
National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Institute of Microelectronics,
Peking University, Beijing, 100871, China
*Contacting Author: Haixia Zhang, zhang-alice@pku.edu.cn
Abstract Silicon carbide (SiC) is a material with excellent
properties for micro systems applications. In this paper, three
chemical vapor deposition methods, low pressure chemical vapor
deposition (LPCVD), plasma enhance chemical vapor deposition
(PECVD) at two different temperatures have been utilized to
fabricate the silicon carbide thin films. The roughness, the crystal
structure, the Young modulus, the hardness and the intrinsic
stress of the silicon carbide films were studied in order to obtain
the discriminating applications for MEMS fabrication.
Keywords- LPCVD; PECVD; SiC; MEMS
I. INTRODUCTION
Silicon carbide has long been known for its outstanding
mechanical, electrical and chemical properties, making it a
valuable material for MEMS sensors and actuators designed for
harsh environments including locations of high temperature,
intense vibrations, erosive surroundings [1, 2]. So far, it has
been utilized to fabricate RF MEMS devices [3], implanted
biomedical devices [4], pressure sensors [5], accelerometers [6]
and resonators [7], etc.
There have been developed several ways to grow silicon
carbide including atmospheric pressure chemical vapor
deposition (APCVD) [8], LPCVD [9], PECVD [5, 10] and so
on. APCVD and LPCVD are usually used to deposit poly-SiC
at high temperature, above 800 [8, 9], whereas Sputtering
and PECVD are employed to form amorphous SiC at low
temperature, below 700 [11, 5, 10]. The former takes the
advantages of material properties, however the high deposition
temperature makes it not compatible with POST-CMOS
process; the latter is attractive for its low deposition
temperature. But films made by Sputtering always have the
"hollow voids" to affect the material properties [12]. PECVD
SiC films have been used as coating films [13], pressure
sensors [5] and resonators [14], etc. However, this film has a
compressive stress, due to the hydrogen inside, which might
also affect the stability of devices.
In this work, three growth methods of SiC including
PECVD at 300, PECVD at 900 and LPCVD have been
investigated. In session II, the growth process of SiC thin film
preparation including the advance-phase preparation was
introduced. In session III, the characteristics of SiC thin film
was researched, and the growth conditions for the optional
films, the thickness, roughness, hardness, Young modulus and
the intrinsic stress of the SiC films deposited were measured in
order to obtain the applications for MEMS fabrications.
II. SIC THIN FILM PREPARATION
PECVD has been one important method for SiC
preparation because of its low formation temperature which
makes it compatible with IC processes, but normally
amorphous SiC was fabricated by PECVD process. To get the
poly-SiC films, LPCVD was utilized. Both amorphous SiC and
poly-SiC can be used in MEMS devices and packaging. Two
types of SiC, poly-SiC and amorphous were fabricated, Table 1
shows the three methods which were utilized, PECVD at 300
and 900, LPCVD at 1200. In the LPCVD process the RF
power was not loaded, and the data of pressure in vacuum
chamber was not recorded.
TABLE I.
THREE METHODS FOR GROWING SIC THIN FILM
Method Temperature Pressure RF power Source gas
PECVD 300 1Torr 300W SiH 4 ,CH 4
PECVD 900 414mTorr 60W SiH 4 , CH 4
LPCVD 1200 NULL NULL SiH 4 ,C 2 H 4
A. PECVD at 300
The STS PECVD equipment was utilized to deposit SiC
films. The Si (100) substrate was isolated with a layer of
thermally grown SiO2, with an approximate thickness of
0.3m. The deposition parameters were as follows: 300
deposition temperature, 1000mTorr pressure, 300W RF power
(high frequency for 10s and low frequency for 30s), 20sccm
SiH 4 flow and 400sccm CH 4 flow. The thicknesses of SiC
films were decided by the deposition time and deposition rate.
B. PECVD at 900
The PECVD equipment was from SKY Technology
Development Co. Ltd. Chinese Academy of Sciences.
Similarly the substrates were Si (100) with the 0.3m
thermally grown SiO 2 . The deposition temperature was 900 ,
the RF power was 60W, the frequency was 13.56MHz, the
pressure was 414mTorr, the gas sources included 20sccm SiH 4
flow (to 5% diluted by He) and 40sccm CH 4 flow. The time of
growing 1um SiC film was about 45minutes.
C. LPCVD at 1200
The LPCVD equipment was developed by Semiconductor
Institute of Chinese Academy of Sciences and employed for
978-1-61284-777-1/11/$26.00 ©2011 IEEE
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the growth of 3C-SiC on SiO 2 /Si (100) and Si(100) substrates.
The temperature of growth was 1200 . SiH4 and C 2 H 4 were
used as the reactive gases and H 2 as the carrier gas, NH 3 as the
dopant gas. The flow rates of SiH 4 , C 2 H 4 and NH 3 were 3sccm,
4.5sccm and 0.36sccm, respectively. In the vacuum chamber,
the wafer was placed on a graphite table which rotated in a
high speed throughout the growth process. The duration of
growing 1um SiC film was also about 45minutes.
The surface morphology was characterized by SEM
measurement, just as shown in Fig.1. Sample (a) has the
smoothest surface in the three, without pits and cracks. Sample
(c) shows the crystalline grains with randomly-oriented
growth and bigger size than sample (b). Sample (d) is the side
view of SiC film which grows on the oxidation silicon
substrate. The thicknesses of SiC and SiO 2 film are 606nm,
272nm respectively.
The surfaces of the three SiC films are shown in Fig.1. The
thicknesses of SiC films were measured with K-MAC coating
thickness tester. The roughness, hardness, and Young modulus
were obtained by TriboIndenter, moreover SiC samples were
characterized by means of X-ray diffraction (XRD), scanning
electron microscopy (SEM), stress meter, and X-ray
photoelectron spectroscopy (XPS).
The film thickness was listed in Table 2. This was
controlled by time. In comparison below, we chose three
different growth samples which are near the 1um X-ray
diffraction measurement was used to investigate the crystalline
of SiC thin films grown on SiO 2 /Si (100). Fig.2 shows the
XRD spectrum of SiC films grown by LPCVD at 1200 and
PECVD at 900 . In (a) the second high SiC (111) peak
observed at 2=35.7° and the third at 2=60.16° indicate the
partial oriented crystallization; in (b) no obvious peak shows
no crystallization of SiC. This is also revealed from the
crystalline grains in Fig.1. These films are either amorphous,
as in the case of low temperature PECVD, or polycrystalline
with a low degree of texture and a temperature dependence to
the distribution of grain orientations [1].
Figure 1. SEM images of the SiC film, (a)PECVD at 300; (b) PECVD at
900 ; (c) LPCVD at 1200; (d) LPCVD at 1200.
Intensity(a.u.)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
-200
SiC(111)
35.70
(a)
SiC(220)
60.16
20 30 40 50 60 70
2theta(deg.)
III. CHARACTERISTICS OF SIC THIN FILM
The different growth techniques of SiC decide the different
characteristics and thus decide the discriminating functions.
For studying the characteristics of SiC thin film, the thickness,
the roughness, the hardness, the Young modulus and the
intrinsic stress of the SiC films deposited were measured.
Detailed data was listed in Table 2.
TABLE II. THE CHARACTERISTICS OF 6 SIC SAMPLES INCLUDING THICKNESS,
YOUNG MODULUS, HARDNESS AND STRESS.
Method Temp.
()
Thickness
(nm)
Young modulus
(GPa)
Hardness
(GPa)
Stress
(MPa)
PECVD 300 986.2 126.83 15.44 -420.2
PECVD 300 1013.5 135.17 17.19 -465.7
PECVD 900 295.3 123.42 10.29 104.4
PECVD 900 887.9 157.52 12.89 63.6
LPCVD 1200 670.8 212.40 23.00 234.3
LPCVD 1200 1025.3 205.66 18.21 263.8
Intensity(a.u.)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
-200
(b)
20 30 40 50 60 70
2theta(deg.)
Figure 2. X-ray diffraction spectrum of the SiC film, (a) doped SiC film
grown by LPCVD at 1200 ; (b) undoped SiC film grown by PECVD at
900 .
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In Fig.3 the images of three growth conditions are shown,
which were measured by the TriboIndenter. The average
roughness of the film deposited in the 300 PECVD is
44.8nm smaller than that of the film deposited in the 900
PECVD which is 63.8nm. The maximal one is 82.4nm
deposited by LPCVD. From (c) the crystal particles are
obviously seen, which is in agreement with the X-ray
diffraction and SEM result shown in Fig.1.
In Fig.4, we find that the Young modulus of the films
deposited by LPCVD is around 200GPa, and it rises as the
growth temperature increases. By different growth conditions
the three groups of hardness data are significantly different
from Fig.5. The hardness of SiC deposited by PECVD at
900 was the lowest and that by LPCVD was the highest.
Because of the crystal structure, the SiC film deposited by
LPCVD has the high mechanical strength.
Fig.6 shows the stress of SiC deposited by PECVD at
300PECVD at 900 and LPCVD. The residual stress
of thin films can vary significantly under different deposition
conditions. The tensile stress of SiC films deposited by
LPCVD is 234.3MPa and 263.8MPa, higher than that of films
deposited by PECVD at 900 . The 300 SiC film has a
compression stress. The PECVD SiC film at 900 has the
closest data to 0 which is expected in most cases. It is known
that intrinsic stress of a film is affected by chemical
composition variations and the structure modes.
Young Modulus(GPa)
200
150
100
50
0
1 2 3
Figure 4. The Young modulus of~1m thin SiC films, number 1, 2, 3
represent SiC film deposited by PECVD at 300, SiC film deposited by
PECVD at 900, SiC film deposited by LPCVD respectively.
Hardness(GPa)
18
16
14
12
10
8
6
4
2
0
1 2 3
Figure 3. The TriboIndenter images(5×5um 2 ) of~1m thin SiC films,(a) SiC
film deposited by PECVD at 300(b) SiC film deposited by PECVD at
900(c) SiC film deposited by LPCVD.
Figure 5. The hardness of~1m thin SiC films, number 1, 2, 3 represent SiC
film deposited by PECVD at 300, SiC film deposited by PECVD at 900,
SiC film deposited by LPCVD respectively.
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Stress(MPa)
300
200
100
0
-100
-200
-300
-400
-500
1 2 3
Figure 6. The stress of~1m thin SiC films, number 1, 2, 3 represent SiC film
deposited by PECVD at 300, SiC film deposited by PECVD at 900, SiC
film deposited by LPCVD respectively.
From these properties, we find that the 1200 growth
condition of LPCVD makes the SiC film a potential material
for high-temperature MEMS applications which need further
research. Because of the great mechanical strength, the LPCVD
SiC is also the ideal structure material for MEMS, such as the
micro cantilever, suspended film, shadow mask and so on. The
PECVD SiC film at 300 has a smoother surface to get a
better line in the lithography process, at the same time the low
growth temperature makes the MEMS process compatible with
the IC process. The SiC films deposited by PECVD at 900
which have the intrinsic stress closest to 0 is fit for maintaining
the shape in the MEMS structure fabrication. Because of not
need annealing the SiC film deposited by 900 PECVD
reduces the likelihood of rupture.
IV. CONCLUSIONS
In this paper, three kinds of SiC films were studied. From
the testing results of the crystal structure, roughness, Young
modulus, hardness and stress, it can be found that LPCVD SiC
exhibits exceptional mechanical properties, due to the
crystalline grains inside, which makes it a very large intrinsic
tensile stress owing to the different lattice constants of SiC
and Si [16]. High temperature PECVD SiC solves stress
problem for its amorphous lattice structure. However, it has a
low mechanical properties compared to the former. Because of
their high forming temperature, these two materials are
suitable for harsh temperature applications, including locations
of high temperature, intense vibrations, and erosive. Moreover,
low temperature PECVD SiC takes the advantage of low
forming temperature, making its deivce able to be integrated
with read-out circuit in one single chip. And thanks to its
chemical inertness, its device can be applied in some erosive
surroundings.
Sciences and National Key Laboratory of Nano/Micro
Fabrication Technology, Peking University. The authors wish
to thank all the students and staff of the MEMS group for their
help on this paper.
REFERENCES
[1] M. Mehregany, C. A. Zorman, N. Rajan, C. H. Wu, “Silicon Carbide
MEMS for Harsh Environments,” Proceeding of the IEEE, Vol. 86, No.
8, pp. 1594-1610,1998.
[2] M. Mehregany, C.A. Zorman, A.J. Fleischman, C.H. Wu, and N. Rajan,
"Silicon carbide for microelectromechanical systems," International
Materials Review, Vol,45,pp. 85-108,2000.
[3] Jeffrey M. Melzak, "Silicon Carbide for RF MEMS," Microwave
Symposium Digest, Vol. 3, pp. 1629-1632, 2003.
[4] A.J. Rosenbloom, D.M. Sipe, Y. Shishkin, Y. Ke, R.P. Devaty, and W.J.
Chyke, "Nanoporous SiC: A Candidate Semi-Permeable material for
Biomedical Applications," Biomedical Microdevices, Vol. 6,No.4, pp.
261-267,2004.
[5] Haixia Zhang, Hui Guo, Yu Wang, Guobing Zhang and Zhihong Li,
"Study on a PECVD SiC-coated pressure sensor," Journal of
Micromechanics and Microengineering, Vol.17, pp. 426-431,2007.
[6] L.S. Pakula, H. Yang and P.J. French, "A CMOS compatible SiC
accelerometer," Sensors, Proceedings of IEEE, Vol.2, pp. 761-764,2003.
[7] Liudi Jiang, R. Cheung, J. Hedley, M. Hassan, A.J. Harris, J.S. Burdess,
M. Mehregany, C.A. Zorman, "SiC cantilever resonators with
electrothermal actuation, " Sensors and Actuators A: Physical, Vol.128,
Issue 2, pp.376-386, 2006.
[8] Yin-tang Yang, Hu-jun Jia, Chang-chun Chai, Yue-jin Li," Growth and
characterization of Si/SiN/SiC structures by APCVD process,"
Solid-State and Integrated-Circuit Technology ICSICT,
pp.730-733,2008.
[9] C.A. Zorman, S. Rajgopal, X.A. Fu, R. Jezeski, J. Melzak and M.
Mehregany," Deposition of Polycrystalline 3C-SiC Films on 100 nm
Diameter Si(100) Wafers in a Large-Volume LPCVD Furnace,"
Electrochem. Solid-State Lett., Vol. 5, Issue 10, pp.G99-G101, 2002.
[10] Zhe Chen, Dayu Tian, Guobing Zhang, and Haixia Zhang,"
Investigation of PECVD SiC Nano Film," Proceedings of the 7th IEEE
International Conference on Nanotechnology, 2007, Hong Kong.
[11] A. Valentini, A. Convertino, R. Cingolani, T. Ligonzo, R. Lanendola
and L. Tapfer," Synthesis of silicon carbide thin films by ion beam
sputtering," Thin Solid Films, Vol.335, Issues 1-2, pp.80-84, 1998.
[12] Sun, Yong Miyasato, Tatsuro Wigmore, J. Keith Sonoda, Nobuo Watari,
Yoshihiko, "Characterization of 3C-SiC films grown on monocrystalline
Si by reactive hydrogen plasma sputtering," Journal of Applied Physics,
Vol.82, Issue.5, pp.2334-2341, 1997.
[13] Hui Guo, Yu Wang, Sheng Chen, Guobing Zhang, Haixia Zhang,
Zhihong Li," PECVD SiC as a Chemical Resistant Material in MEMS,"
Proceedings of the 1st IEEE International Conference on Nano/Micro
Engineered and Molecular Systems,2006.
[14] Yu Wang, Hui Guo, Haixia Zhang and Zhihong Li,"Fabrication and Test
of PECVD SiC Resonator," First International Conference on
Integration and Commercialization of Micro and Nanosystems, Parts A
and B, 2007.
[15] L.S. Pakula, H. Yang, etc. "Fabrication of a CMOS compatible pressure
sensor for harsh environment," MEMS'2003,pp.502-505,2003.
[16] Fang Liu, Carlo Carraro, Albert P Pisano, and Roya Maboudian,"
Growth and characterization of nitrogen-doped polycrystalline 3C-SiC
thin films for harsh environment MEMS applications," Journal of
Micromechanics and Microengineering, Vol.20, No. 3, 2010.
ACKNOWLEDGMENT
This work was supported by the Beijing Natural Science
Fund, fabrications and tests were done in Chinese Academy of
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