Fabrication of poly-Si films by continuous local thermal chemical vapor deposition on flexible quartz glass substrate

Article abstract of DOI:10.1063/1.3013839

The continuous deposition of polycrystalline silicon film on quartz fiber by local thermal chemical deposition was investigated. High-speed deposition owing to high temperature and locality was examined using fixed and moving substrates. We confirmed the high-speed deposition of polycrystalline silicon and achieved a maximum speed of over 1 μms. Furthermore, we succeeded in a continuous deposition of polycrystalline thin silicon with a thickness of 50-100 nm on a quartz fiber with low roughness and low impurity content. Thin film transistor with a mobility more than 3.7 cm² V s was achieved by using this film.

Full text of DOI:10.1063/1.3013839

Fabrication of poly-Si films by continuous local thermal chemical vapor deposition
on flexible quartz glass substrate
T. Nakamura, H. Kuraseko, K. Hanazawa, H. Koaizawa, Y. Uraoka, T. Fuyuki, and A. Mimura
Citation: Applied Physics Letters 93, 241503 (2008); doi: 10.1063/1.3013839
View online: http://dx.doi.org/10.1063/1.3013839
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APPLIED PHYSICS LETTERS 93, 241503 ͑2008͒
Fabrication of poly-Si films by continuous local thermal chemical vapor
deposition on flexible quartz glass substrate
T. Nakamura,1 H. Kuraseko,1 K. Hanazawa,1 H. Koaizawa,1 Y. Uraoka,2,a͒ T. Fuyuki,2 and
A. Mimura3
1Furukawa Electric Corp., 6 Yawata-Kaigandori, Ichihara, Chiba 290-8555, Japan
2NAIST, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan
3AIST, Tsukuba Central 5, Tsukuba, Ibaraki 305-8565, Japan
͑Received 13 June 2008; accepted 19 September 2008; published online 18 December 2008͒
The continuous deposition of polycrystalline silicon film on quartz fiber by local thermal chemical
deposition was investigated. High-speed deposition owing to high temperature and locality was
examined using fixed and moving substrates. We confirmed the high-speed deposition of
polycrystalline silicon and achieved a maximum speed of over 1 ␮m/s. Furthermore, we succeeded
in a continuous deposition of polycrystalline thin silicon with a thickness of 50–100 nm on a quartz
fiber with low roughness and low impurity content. Thin film transistor with a mobility more than
3.7 cm2/V s was achieved by using this film. © 2008 American Institute of Physics.
͓DOI: 10.1063/1.3013839͔
Low temperature polycrystalline silicon thin film transis-
tors ͑TFTs͒ are regarded as promising for use in next genera-
tion displays.1,2 For this purpose, low temperature fabrication
of silicon films on large glass substrates with a maximum
temperature of 450 °C are being widely studied.3–6 These
studies are very important for the fabrication of high-
performance displays. However, if high-performance TFTs
can be fabricated on quartz fibers, the applicability of the
TFT will be widely extended, such as to integrated circuit
tags or flexible displays. In our previous studies, we reported
that polycrystalline silicon TFT can be fabricated on quartz
fiber and that a deposition technique for silicon film was
required.7,8
In this study, a novel technique for depositing silicon
thin film on quartz fiber, continuous local thermal chemical
deposition ͑CoLT-CVD͒, was studied. Features of the fiber
are as follows. Control of the surface roughness becomes
simple, low production cost is realized, and flexibility is
increased owing to the thickness of substrates, as shown in
Fig. 1. High endurance against high temperature process im-
proves the reliability of the device fabricated on the fibers.9
In order to compete the productivity by the conventional
process on a wide glass substrate, a high-speed deposition
technique is necessary. In our experiments, silicon film was
deposited by thermal CVD at more than 1000 °C by utilizing
their high thermal stability, and the film was analyzed to
discuss the effectiveness of CoLT CVD.
Source gas was introduced from the left-hand side and
evacuated from the right-hand side. In the center area, a car-
bon susceptor was placed within a reaction tube set together
with an infrared gold furnace heats the susceptor area by
infrared radiation. The moving axis of substrate was set at
the right-hand side of the system to move them from left to
right at high speed. The moving direction was the same as
the gas flow. The width and thickness of the fiber used in this
experiment were 1 mm and 100 ␮m, respectively.
The maximum deposition speed was investigated by
controlling the ratio of DCS to hydrogen. With a DCS gas
concentration of over 7%, a maximum speed of 1 ␮m/s was
obtained. By increasing the flow rate of the source gas at a
fixed ratio of DCS/H2, the maximum deposition speed was
measured. With increasing flow rate, maximum speed further
increased, and 1400 nm/s was obtained. When the maximum
temperature in the reaction tube, flow rates of DCS and hy-
drogen were 1250 °C, 300 SCCM, and 3 slm, respectively,
the maximum deposition speed and average deposition speed
were 1330 nm/min and 761 nm/s, respectively. These con-
ditions were employed for the deposition on the moving sub-
strates.
For the moving substrates passing though the deposition
area, the deposited film thickness was calculated using the
length of the deposition area and the average deposition
speed. Figure 3 shows the relationship between the moving
In order to establish a high-speed deposition method,
deposition speed was investigated using the system shown in
Fig. 2. In a thin quartz tube with a diameter of 6 mm, silicon
film was deposited onto the quartz substrate set on a carbon
susceptor. Dichlorosilane ͑DCS͒ and hydrogen were used as
source gases, where the concentration ratio of the two gases
was varied. Range of the flow rate of DCS and H2 were
100–250 SCCM ͑SCCM denotes standard cubic centimeter
per minute at STP͒ and 2–3.5 slm, respectively. Deposition
was performed in atomic pressure.
a͒
Electronic mail: uraoka@ms.naist.jp.
FIG. 1. ͑Color online͒ Quarts fiber used in this study.
0003-6951/2008/93͑24͒/241503/3/$23.00
93, 241503-1
© 2008 American Institute of Physics
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241503-2
Nakamura et al.
Appl. Phys. Lett. 93, 241503 ͑2008͒
FIG. 2. ͑Color online͒ CoLT-CVD system for depositing silicon thin film on
quartz fiber.
speed and film thickness obtained in the experiment and by
calculation using the deposition rate. These curves suggest
that the deposited film thickness can be controlled by adjust-
ing the moving speed. Any small discrepancy will be due to
the parameter obtained under the static condition. When the
moving speed was high, the rates of substrate and gas flow
became closer and the nominal gas flow rate decreased,
therefore the deposition rate decreased.
Figure 4 shows the cross-sectional transmission electron
microscopy ͑TEM͒ image of silicon thin film deposited on
the moving substrate at 400 mm/s. Polycrystalline silicon
film with a film thickness of approximately 50 nm was de-
posited on quartz fiber. The surface of the polycrystalline
film was very smooth with an rms value of 2.4 nm. Raman
spectrum of the silicon film was examined. Steep peak at
520 cm−1 clearly indicated that the deposited silicon was
crystallized.
The impurity profile of this film was examined by sec-
ondary ion mass spectroscopy and compared the film depos-
ited by conventional plasma CVD. As this system is operated
under atmospheric pressure, deterioration of the purity was a
cause of concern. However, concentrations of oxygen and
nitrogen were under 1020 atom/cc, therefore, this film was
found to be comparable with that deposited under the
vacuum condition.
FIG. 4. ͑Color online͒ Cross-sectional TEM image of silicon thin film de-
posited on the moving substrate at 400 mm/s.
wafer and from batch to batch, is a serious problem, particu-
larly for thin film deposition. These problems were resolved
by thinning, narrowing, and elongating substrates and mov-
ing them at high speed. When the thin glass substrate moves
though a high-temperature area, thermal capacitance be-
comes small. Furthermore, surface area increases, and con-
sequently, markedly high heating and cooling rates were re-
alized. Therefore, migration of silicon atom species on the
substrate was suppressed and surface roughness was im-
proved. The reaction time was as short as within 0.7 s and
contamination could be minimized.
Finally, we fabricated TFT. It was fabricated as shown
in Fig. 5. Gate oxide with a thickness of 100 nm was depos-
ited by CVD method. Field effect mobility more than
3.7 cm2/V s was achieved. Electronic properties indicated
that the deposited film was sufficiently crystallized and that
this method is useful for the fabrication of TFT on flexible
quartz glass substrate.
In conclusion, we investigated continuous silicon
deposition using a band formed of thin quartz fiber and
obtained polycrystalline silicon film with high crystallinity
and low impurity content comparable to those obtained by
Through these experiments, we achieved a continuous
high deposition rate that could not be obtained by the con-
ventional method. With a conventional thermal CVD system,
variation of the film thickness within a wafer, from wafer to
FIG. 3. ͑Color online͒ Relationship between the moving speed and film
FIG. 5. Transfer curve of the thin film transistor fabricated using silicon thin
thickness obtained in the experiment and by calculation using the deposition
film on quartz fiber. Field effect mobility more than 3.7 cm2 /V s was
rate.
achieved.
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