24P014-O
Study on interaction between plasma fluctuation andnucleation of nanoparticles in plasma CVD
プラズマCVDにおけるプラズマ揺動とナノ粒子の核形成間の相互作用に関する研究
Kunihiro Kamataki1), Kazunori Koga2), Giichiro Uchida2), Hyunwoong Seo2),
Naho Itagaki2,3), Masaharu Shiratani2)
1)
鎌滝 晋礼 , 古閑 一憲2)，内田 儀一郎2)，徐 鉉雄2), 板垣 奈穂2,3), 白谷 正治2)
1)

Faculty of arts and science, Kyushu University
744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan2)
Graduate School of Information Science and Electrical Engineering, Kyushu University
744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan5)
PRESTO, Japan Science and Technology Agency,5, Sanban machi, chiyoda ku, Tokyo 102-0075, Japan1)
九州大学基幹教育院 〒819-0395 福岡県福岡市西区元岡744番地
2)
九州大学大学院システム情報科学府 〒819-0395 福岡県福岡市西区元岡744番地
3)
JST さきがけ 〒102-0075 東京都千代田区三番町5

We have investigated effects of plasma fluctuation on the growth of nanoparticles in capacitively-coupled
rf discharges with amplitude modulation. Nanoparticles grow more slowly for higher AM levels, that isthey have 7 times higher density and 23% smaller size. This AM method is useful for the production of alarge amount of nanoparticles with a small size.

1. Introduction
Studies focused on reducing the dimensions ofsemiconductor structures [1] to the nanometer
regime have led to a fascinating class of novel
materials that exhibit quantum confinement
characteristics. These materials are referred to as
nanoparticles or quantum dots. Although suchnano-composite materials with quantum dots allows
us to fabricate high-efficiency optoelectronic
devices [2-4], efficient methods for synthesizing
large numbers of small non-agglomerated
nanoparticles with a narrow size distribution arerequired. Plasma processing can be a goodcandidatemethodfor
synthesizing
such
nanoparticles in the gas phase of reactive plasmas[5-7]. For faster development of fabrication
methods for nano-materials, effects of plasma
fluctuations on the growth of nanoparticles inreactive plasmas must be taken into accountbecause plasma fluctuations affect nanoparticles indust plasmas [8]. Investigation of the effects leads
to control the growth of nanoparticles and toimprovethefabrication
technology
ofnano-materials. Moreover, effects of plasma
fluctuations on the growth of nanoparticles inreactive plasmas have not been reported yet. In
order to study the effects of plasma fluctuations on
the growth of nanoparticles, we use the amplitude
modulation (AM) method [9], which can control theFig.1 Experimental setup. In order to monitor the growthof nanoparticles, the nanoparticles are illuminated by
SHG of CW YAG laser light (λ = 532 nm, 2.0 W), and thescattering light is detected using an ICCD camera.

plasma fluctuation level in reactive plasmas [10].
In the present paper, we report observation
results of the effects of plasma fluctuations on thegrowth of nanoparticles in reactive plasmas using
an in-situ laser-light scattering (LLS) method.
Moreover, we succeed in the production of a higher
density of smaller nanoparticles than theconventional method without using AM [7], and wewill discuss the mechanism of the effects.
2. Experimental setup

Experiments were performed using a capacitively
coupled rf discharge reactor with an in-situ LLS
system, as shown in Fig. 1[10]. The inner diameterand height of this reactor were 260 mm and 230mm, respectively. In the reactor, a powered discelectrode with a diameter of 60 mm and a thicknessof 1 mm was placed 20 mm below an uppergrounded electrode with a diameter of 60 mm
located 20 mm above a lower grounded electrodewith a diameter of 60 mm. The reactor wasevacuated to a base pressure of less than 10-3 Pawith a rotary pump and a diffusion pump. The flow
rates of Si(CH3)2(OCH3)2 and Ar were 0.2 and 40
sccm, respectively. The total gas pressure in thereactor was 133 Pa. The temperature of the reactor
wall was maintained at 373 K in order to avoid
liquefaction of Si(CH3)2(OCH3)2. In order togenerate nanoparticles, we sustained a discharge byapplying 150 peak-to-peak voltage Vpp of 60 MHz
to the powered electrode for a discharge period of T= 8 s. The corresponding discharge power was 30 W.
The self-bias voltage Vdc was 0.4 V. The plasma
parameters of electron density ne and floating
potential Vf were measured using an rf-compensatedLangmuir probe. The typical electron density ne wasapproximately 1010 cm-3.
3. Experimental results and discussion
Plasma fluctuations can be synchronized with theAM of rf discharge voltage [19]. Figure 2 showsthat AM level dependence on LLS intensities at t =8s at plasma/sheath boundary region near the upper
grounded electrode. Here, a modulation frequency
fAM is 10 kHz. The LLS intensity with AM issmaller than ones without that. The LLS intensity
decreases by 60 % with increasing the AM level up
to 30%. This result shows AM of rf discharge
voltage suppresses the growth of nano-particles.
In order to clarify the growth suppression
mechanism, the size and density of nanoparticles
were determined based on the LLS intensity [11].
Figure 3 shows the dependence of the size anddensity of nanoparticles on the AM level. The
nanoparticle density increases by 7 times from
2.3×109 cm-3 for the 0% AM level to 1.6×1010 cm-3
for the 30% AM level, whereas the nanoparticle
size decreases by 23% from 12.5 nm for the 0%
AM level to 9.7 nm for the 30% AM level. In Ref.
[9], Y. Watanabe et al. controlled the size anddensity of nanoparticles by varying the rf discharge
power and/or discharge duration. Here, we showthat amplitude modulation of the rf discharge
voltage is another tuning knob for controlling
nanoparticle size and density.

Fig.2 AM level dependence on LLS intensities at t =8s at plasma/sheath boundary region near the upper
grounded electrode. AM was carried out with a sine
wave of 10 kHz.

Fig.3 Amplitude modulation level dependence of thedensity and size of nanoparticles.
Acknowledgements
This study is partly supported by MEXT.
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