PD-07
Very Fast Silicon Deposition with High Speed Jet in SiH4/ H2 PE-CVD
Satoshi NISHIDA1,2, Hiroshi MUTA1,2, Shizuma Kuribayashi1,2
1 Environmental and Energy System Division, Graduate School of Engineering, Gifu University
2 Center of Innovative Photovoltaic Systems, Gifu University
Email: snishida@gifu-u.ac.jp
Previous Researches

Background・Silicon thin film (micro crystalline silicon (μ-Si) andhydrogenated amorphous silicon (a-Si:H)) is major material insemiconductors, e.g. thin film solar cells.
・Plasma Enhanced Chemical Vapor Deposition (PE-CVD) inSiH4/H2 is utilized to obtain silicon thin film.
・In standard PE-CVD, deposition rate is several nm/s, and highdeposition rate is desired for short deposition time.

Methodology

Typical experimental conditions･Both the nozzle and the heater are
electrodes.
Gap distance ･Sample gas is injected through a holeat the vertex of the nozzle.
･The gas flow becomes underexpanded
supersonic jet.

Substrate

Substrate
PlasmaPump

HeaterGas

Fig. Setup of our system

Fig. Standard PE-CVD setup (for comparison)

5 mm

Maximum deposition rate （μｍ/s）

2 mm

800 PaInlet pressure

6.6×104 Pa

M.F.R. of H2

100～1000 sccm

M.F.R. of SiH4

1～10 sccm

Temperature

200 ℃

Gap distanceh= 1～20 mm

Nozzle diamete

0.3 mmVHF Frequency

60 MHzInput power

45 W

Deposition time

30 min

7 mm

5Outlet
4Inlet(Φ0.3 mm)2

Electrode distance(1–20 mm)

1Diameter 20 mm

0510152020 mm

・CFD calculations based on
FLUENT 14.0 (ANSYS Inc.) wereused to simulate the impinging jets
・These calculations were
performed using 2-D axis
symmetry, and shear stresstransport (SST) k–ω as a turbulent
model. Double-precision andupwind-difference schemes using
primary accuracy were also used.

Number of cells : 41,000
Inlet pressure : mesured value in each experiment
Outlet pressure : 800 Pa

Fig. Plot of deposition rate and gap distanceFig. Deposited film at several gap distancesFig. Picture during deposition

25Gap distance （ｍｍ）

15 mm

Outlet3010 mm

Back groud pressure

CFD calculation

Results (gap distance dependence)

1 mm

・To investigate the mechanism behind such high-rate
deposition, We investigate how deposition rate and shapeof the deposited hydrogenated silicon depend on gap
distance and mass-flow rate on the deposition rate.
・We also use computational fluid dynamics (CFD)
calculations to analyze how gas flow affects high ratehydrogenated silicon deposition.
・We try combination of the jet CVD and dynamic
deposition proposed by Sugai.

NozzleHeaterShower Head nozzle

Objective

・Sobajima et al. (2008) obtained a deposition rate of 8 nm/s
at 2700 Pa with a RF power of 2.2 W/cm2. Such methods
have been hypothesized to be mass-transfer limited because
the diffusion constants decrease at higher pressures.
・Kuribayashi et al. (our group, 2013) developed a process
for high-rate hydrogenated silicon deposition that iscontrolled by the conditions of gas flow. The experimental
results showed that localized Si:H deposition occurs at over
1 μm/s when using an underexpanded supersonic jet at abackground pressure of 800 Pa without a capillary, andexcited at 60 MHz, 0.8 W/cm2.

・Deposited silicon structure changed depending on the gap distance.
・Very thin deposition under the nozzle, when the gap distance was < 2 mm.
・Local deposition was observed, when the gap distance was >5 mm .

100 sccm

12121010Deposited mass [mg]80 sccm

Deposition rate [μm/s]

Results (mass flow rate dependence)

8642880 sccm

60500

1000

1500

0500

Flow rate [sccm]

1000 sccm
Fig. Deposited film at several
mass flow rate

1000

1000 sccm･The results of these CFD calculations indicate that the jet velocity near thesubstrate increases with the inlet mass-flow rate. This can be explained byturbulence that is generated by an increase in the jet-gas velocity in lowvacuum, which in turn promotes convection and increases mass transfer.
･Although the jet shapes at 80 sccm and 100 sccm are similar to each other, theshapes of the localized deposits are far more different. Although the reason forthis discrepancy is not clear, it may be caused by a collaborative effect between
chemical reactions and gas flow inside the chamber.

Fig. Mass of silicon deposited as afunction of mass flow rate

･The deposition rate is very low with a mass-flow rate ≤ 90 sccm, but rapidly increases
to a maximum for mass-flow rates of 110 and 120 sccm. Beyond this point, thedeposition rate decreases slightly, and remains almost constant between 250 and 1000
sccm, though the deposited mass monotonically increases as a function of the massflow rate.

Dynamic deposition

Conclusion

To obtain uniform deposition, combination of Jet CVD anddynamic deposition, proposed by Sugai (2010), wastested.

A slit type nozzle (0.3×12 mm) was made.
Z12mm

0Y
MFC
MFC

X-Z
plane

X

2500
Y-Z
plane

1300

Calculated velocity at slit type nozzle experiment
SiH4 + H20Velocity (m/s)

Matching box
VHF

Pressure gauge

12Jet nozzle
Substrate

IRHeaterGas supply system

0.3mm

Drypump

Thickness (μm）

10mm

Standard
Dynamic deposition(statistic)
Fig. Schematic diagram of dynamic deposition fromSugai (2010)
The substrate moves relative to the fixed plasma source,
whereas in the standard deposition process, the positions of
the plasma source and substrate are fixed. Dynamicdeposition has been considered to be an effective method
for fabricating flexible solar cells.

500 sccm

Discussion

1500

Flow rate [sccm]

Fig. Deposition rate as a function ofmass-flow rate

250 sccmFig. Calculated velocity

200100 sccm

4840048Position （ｍｍ）

12・A high-rate silicon-deposition process was developed based on ahigh speed jet, in which the mass-flow rate was found tosignificantly influence the deposition process.
･This proposed high-rate deposition process requires only ~1W/cm2 of VHF power to achieve deposition rates of 1 μm/s, which
is much less power than is required by thermal-plasma-jet
processes.
･This process is quite similar to conventional PE-CVD processes,
and therefore requires little additional investment to implement. A
better understanding and control of the proposed process will
require further experimentation and analysis into its unique jetflows, plasma conditions, and chemical reactions.
･Combination of dynamic deposition and the developed CVD
process can be effective for uniform deposition with highdeposition rate, but more improvement of nozzle design isnecessary.

･Uniformity was improved.
･Peaks was observed at the center and edges of the deposition.
･Nozzle design is important for better uniformity

Reference
・Kuribayashi, S., Y. Tsunekawa, S. Akahori, D. Ando, J. Nakamura, S. Nishida, H. Muta, Y. Takeuchi, Y. Yamauchi, and H. Takatsuka; “Effect of VHF Excitation Frequency on Localized Deposition of Hydrogenated Siliconin Non-equilibrium-plasma-enhanced CVD by an Under-expanded Supersonic Jet,” Surf. Coat. Technol. 225, 75-78 (2013)
・Nishida, S., H. Muta, and S. Kuribayashi; “Effect of Gas Flow Rate on the High-Rate, Localized Jet-Deposition of Silicon in SiH4/H2 PE-CVD,” J. Chem. Eng. Jpn, 47, 478-482 (2014)
・Sobajima, Y., S.Nakano, M. Nishino, Y. Tanaka, T. Toyama, and H. Okamoto; “Microstructures of High-Growth-Rate (up to 8.3 nm/s) Microcrystalline Silicon Photovoltaic Layers and Their Influence on thePhotovoltaic Performance of Thin-Film Solar Cells,” J. Non-Cryst. Solids, 354, 2407-2410 (2008)
・Sugai, H.; “Frontier of Development of Large-Area Plasma CVD Processing” (in Japanese), J. Plasma Fusion Res., 86, 28-32 (2010)