Single-Source Chemical Vapor Deposition of 3C-SiC Films
in a LPCVD Reactor
I. Growth, Structure, and Chemical Characterization
Muthu B. J. Wijesundara,
a,z
Gianluca Valente,
b
William R. Ashurst,
a
Roger T. Howe,
c,d
Albert P. Pisano,
d,c
Carlo Carraro,
a
and Roya Maboudian
a
a
Berkeley Sensor and Actuator Center, Department of Chemical Engineering,
c
Department of Electrical
Engineering and Computer Science, and
d
Department of Mechanical Engineering, University of California,
Berkeley, California, USA
b
Dipartimento di Chimica, Ingegniria Chimica Materiali—G. Natta, Politecnico di Milano,
I-20131 Milan, Italy
We report the deposition of 3C-SiC films on an Si100 substrate from 1,3-disilabutane precursor molecule utilizing a conventional
low-pressure chemical vapor deposition CVD system. The chemical, structural, and growth properties of the resulting films are
investigated as functions of deposition temperature and flow rates. Based on X-ray photoelectron spectroscopy, the films deposited
at temperatures as low as 650°C are indeed carbidic. X-ray diffraction analysis indicates the films to be amorphous up to 750°C,
above which they become polycrystalline. The effect of process parameters on film uniformity is also reported. Highly uniform
films are achieved at 800°C and lower, essentially independent of the flow rate.
© 2004 The Electrochemical Society. DOI: 10.1149/1.1646141 All rights reserved.
Manuscript received December 16, 2002. Available electronically February 9, 2004.
The wide energy bandgap, high thermal conductivity, large
breakdown field, and high saturation velocity of silicon carbide
makes this material an ideal choice for high-temperature, high-
power, and high-voltage electronic devices.
1-3
In addition, its chemi-
cal inertness, high melting point, extreme hardness, and high wear
resistance make it possible to fabricate sensors and actuators capable
of performing in harsh environments,
4,5
which has motivated the
increasing interest in SiC in microelectromechanical systems
MEMS technology. Furthermore, SiC is an attractive material for
micro- and nanomechanical resonators due to the large ratio of it’s
Young’s modulus to density, as compared to silicon.
6
The practical implementation of SiC for device fabrication re-
quires high quality material processing with carefully defined and
reproducible material properties. Furthermore, for the realization of
SiC in MEMS technology, low-temperature processing methods are
preferred. Low growth temperatures are important to reduce the
strain produced by the thermal expansion mismatch and to minimize
the formation of crystal defects. In particular for MEMS devices,
high residual stresses in SiC films deposited on Si substrates tend to
result in deformed and nonviable microstructures after release.
7
In chemical vapor deposition CVD, poly- and single-crystalline
SiC are typically grown at temperatures above 1000°C using dual
source precursors such as silane and propane.
8,9
Up to now, signifi-
cant progress has been made in the growth of single-crystalline SiC
bulk films, with special emphasis on the 6H- and 4H-hexagonal
polytypes, and 3C-cubic polytype. More recent efforts have focused
on the growth of cubic SiC thin films utilizing single precursors that
contain both silicon and carbon atoms with a reduced activation
barrier for SiC formation.
10
Several single-source precursor mol-
ecules have been successfully utilized to grow SiC at lower tempera-
tures 750-900°C.
10-12
Recently, our group has utilized a 1,3-
disilabutane, SiH
3
-CH
2
-SiH
2
-CH
3
, 1,3-DSB precursor to deposit
polycrystalline SiC thin films
13,14
for MEMS applications at lower
deposition temperatures.
To date, the SiC deposition using 1,3-DSB has been limited to
high vacuum and home-built systems capable of processing samples
less than 1 1 cm in size.
10,13,14
For this deposition methodology
to find widespread use, it is essential to determine the feasibility of
using a conventional chemical vapor deposition CVD system for
this process. In this paper, we report on the processing parameters in
a commercial low-pressure CVD LPCVD reactor for the deposi-
tion of SiC films on Si100 wafers from 1,3-DSB.
Experimental
Figure 1 shows the schematic diagram of the conventional hori-
zontal hot-wall tubular reactor TekVac CVD-300-M. Briefly, the
reactor consists of a quartz tube 75 mm inner diameter, 600 mm
long with a hot-wall zone of 450 mm in length with temperature
uniformity of 1°C. The reactor base pressure is less than 10
-7
Torr
using 80 L/s turbomolecular pump. The precursor molecule, 1,3-
DSB Gelest Inc., 95% purity is further purified by freeze-pump-
thaw cycles using liquid N
2
before introduction into the reactor via
a mass flow controller MKS SDS-1640.
All experiments reported here are performed on 30 80 mm
rectangular samples of Si100 substrate. Prior to deposition, the
n-type Si100 substrate is dipped in concentrated HF to remove the
native oxide, then rinsed with deionized water, and dried under N
2
.
The substrate is placed horizontally, parallel to the gas flow in the
center of the hot-wall zone of the reactor tube as shown in Fig. 1.
Most of the experiments reported here are carried out at 1,3-DSB
flow of 5.5 sccm with the reactor pressure of approximately 50
mTorr. The substrate temperature is varied from 650 to 850°C to
investigate the effect of temperature on the deposition process. Due
to the changes in growth rate with the temperature, the deposition
times are varied 1 to 4 h in order to achieve films with nearly the
same thickness of 2 m.
Various analysis and characterization techniques are employed to
investigate the effect of deposition temperature on the film compo-
sition, structure, and growth rate and uniformity. Ex situ X-ray pho-
toelectron spectroscopy XPS is used to determine the chemical
nature and elemental composition of the deposited films. The XPS
analysis is performed using an Omicron Dar400 achromatic Mg-K
X-ray source 15 keV, 20 mA emission current and an Omicron EA
125 hemispherical analyzer. The analyzer is operated in the constant
energy mode with 50 eV pass energy. The elemental percentages of
the films are determined based on the high-resolution photoemission
peak areas, photoionization cross sections, and the electron energy
analyzer transmission function.
15
X-ray diffraction XRD patterns
are recorded using a Siemens D5000 automated diffractometer op-
erated in -2 geometry to determine the crystal structure of the
deposited SiC films. The film morphology is examined by Digital
Instrument Nano Scope III atomic force microscope AFM in con-
tact mode. Both optical reflectometry NanoSpec model 3000 and
cross-sectional scanning electron microscope SEM, JEOL 6400 are
z
E-mail: mwijes1@uclink.berkeley.edu
Journal of The Electrochemical Society, 151 3 C210-C214 2004
0013-4651/2004/1513/C210/5/$7.00 © The Electrochemical Society, Inc.
C210
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