S5-7
Analysis of coupling between nanoparticles and radicals
using perturbation of radical density in reactive plasmas
ラジカル密度摂動によるナノ粒子とラジカルのカップリング解析
Kazunori Koga, Teppei Ito, Hyunwoong Seo, Naho Itagaki, and Masaharu Shiratani
古閑一憲, 伊東鉄平，徐鉉雄，板垣奈穂、白谷正治
KYUSHU UNIVERSITY
744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan
九州大学 〒819-0395 福岡市西区元岡744
Coupling between nanoparticles and radicals in short and long time scale was analyzed by applying
perturbation of radical density in reactive plasmas. Non-linear coupling between nanoparticles and radicals
is suggested by spectrum analysis of time evolution of nanoparticle amount measured by two dimensionallaser light scattering method. Optical emission intensity measurements show spatial profiles of radical
density in the device scale is coupled with the time evolution of nanoparticle amount.

1. Introduction
Understanding linear and non-linear interactions
between plasmas and surface of nano-materials is
important in fabrication of semiconductor devices
and nanostructures. For instance, device
performance often depends on perturbations ofinteractions in nanometer scale. To study suchinteractions, we have employed nanoparticles inreactive plasmas as a model of nano-inteface
between plasmas and nanostructure and studied
growth of nanoparticles with amplitude modulation(AM) to perturb radical density in the plasmas.
Recently, we have revealed that applying AM
suppresses growth of nanoparticles [1-5]. We haveanalyzed dynamics of radical density andnanoparticle amount to understand the interaction
between plasmas and nanoparticles by measuring
spatiotemporal profiles of particle amount andradicals. Here we report the experimental results.
2. ExperimentalWe employed a capacitively-coupled discharge
reactor equipped with a two-dimensional laser lightscattering (LLS) system as shown in Fig. 1 [4].
Si(CH3)2(OCH3)2 (DM-DMOS) diluted with Ar gas
was supplied to the reactor as precursor molecules.
The flow rate of Ar and DM-DMOS were 40 sccm
and 0.2 sccm, respectively. The total gas pressure
was 1.25 Torr. We applied high frequency voltageof 60 MHz for 8 seconds between the powered andgrounded electrodes to generate discharges. Thedischarge voltage was 120 V, which corresponds tothe power of 30 W. For the amplitude modulation
experiments, AM frequency fAM was 100 Hz and theAM level was 30 %. A sheet beam of YAG laserlight (= 532 nm and 2 W) was irradiated between
the powered electrode and the upper groundedelectrode from side of the reactor. We havemeasured90oRayleighscattering
fromnanoparticles using a high speed camera (PhotoronFASTCAM SA4) equipped with an interference
filter of 532 nm with 1 nm FWHM at a frame rateof 1000 fps. Optical emission intensities from Ar I
lines of 750.4nm and 811.5nm were measured using
the same camera with interference filters of a center
wavelength of 750 nm and 810 nm with 10 nm
FWHM.

Fig. 1. Experimental setup.

3. Results and Discussion
Optical emission intensities of Ar I 750.4 nm and811.5 nm give information of generation rate ofradicals. The 750.4 nm emission takes place due tothe direct excitation:
Ar + e → Ar(4p´[1/2]0) + e (ε ≧ 13.48eV) ,Ar(4p´[1/2]0) → Ar(4s´[1/2]1) + hν (750.4nm).
Ar I 811.5 nm is emitted by the two step
excitation:

Ar + e → Arm(4s[3/2]2) + e (ε ≧ 11.55eV),
Arm + e → Ar(4p[5/2]3) + e (ε ≧ 1.53eV), andAr(4p[5/2]3) → Arm(4s[3/2]2) + hν (811.5nm).
The ratio intensity of 811.5nm to 750.4nm gives
information on Ar metastable density [6-7]. We
have employed the ratio as an indicator of radicaldensity.
Figure 2(a) shows spatial profiles of power
spectrum of the optical emission intensity ratio. The
peaks of fluctuation of the optical emission
intensity ratio are observed at the fundamental
frequency and higher harmonics of fAM. It indicates
perturbation of radical density is directly coupledwith amplitude modulation of the discharge voltage.
Figure 2(b) shows that of LLS intensity whichindicates particle amount. The LLS intensity is also
perturbed at the fundamental frequency and higher
harmonics of fAM. In addition, perturbation at
sub-harmonics such as f = 3/5fAM = 60Hz are
observed in Fig. 2(b). It suggests that the amount of
nanoparticle is non-linearly coupled with the radicaldensity in the short time scale.
We also studied such coupling from a longer
time scale. Figure 3(a) shows time evolution ofratio of 811.5nm emission intensity to 750.4 nm
one at the center of the discharges. The solidsquares shows results for discharges without
nanoparticles (pure Ar discharges), and the solid
circles shows those for discharges withnanoparticles. For the discharges without
nanoparticles, the intensity ratio rapidly increases
just after discharge initiation, and keeps almost
constant value. For the discharge withnanoparticles, the intensity ratio is almost zero fromGND 20
18161412108642RF 0normalized power(a. u.)

laser beamz (mm)

Iratio1.0E+05
4.0E+04
1.6E+04
6.3E+03
2.5E+03
1.0E+03
4.0E+02
1.6E+02632510(a)0100

GND 20200f (Hz)18ILLS

normalized power(a. u.)

laser beamz (mm)

16
14

1.0E+05
4.0E+04
1.6E+04
6.3E+03
2.5E+03
1.0E+03
4.0E+02
1.6E+026325
1012
1086(b)42RF0050

100

150200250Frequency (Hz)Fig. 2. Spatial profile of power spectrum of (a)optical emission intensity ratio and (b) LLS intensity.

(a)

(b)

Fig. 3. Time evolution of (a) optical emission intensity
ratio and (b) LLS intensity.

t= 0 s to t= 3 s then increases gradually with t.
Figure 3(b) shows time evolution of the LLS
intensity ILLS at the center of the discharges. The
ILLS monotonically increases with increasing t fromt = 1 s, then is saturated around t= 5 s. The
characteristic rise time of LLS intensity is almost
the same as that of the emission intensity ratio. This
long time scale coupling is caused by the fact thatthe rather slow growth of nanorpaticles modifies
radical density.
4. Conclusion
We have measured the ratio of optical emission
intensities of 811.5nm to 750.4nm and LLS
intensity. The optical emission ratio hows theperturbation of radical density by amplitude
modulation of discharge voltage. The characteristic
time of increase of the ratio is similar to that of theamount of nanoparticles. There are two kinds ofcoupling: the short time scale of several ms iscaused by the fact that perturbation of radical
density modify the nanoparticle growth, and thelong time scale coupling is caused by the fact thatthe rather slow growth of nanorpaticles modifies
radical density.
Acknowledgments
This work was partly supported by JSPS
KAKENHI grant number 26246036.
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