S3-4

Atmospheric Pressure Microwave Plasma System and Applications
大気圧マイクロ波プラズマシステムと応用
Ramasamy Raju, Kazunari Fujioka, Takuya Urayama and Shuitsu Fujii
ラマサミー ラズ､藤岡 万也､ 浦山 卓也､ 藤井 修逸

Adtec Plasma technology Co. Ltd., 5-6-10 Hikinocho, Fukuyama-shi, Hiroshima, 721-0942, JAPAN
アドテックプラズマテクノロジー、721-0942, 広島県福山市引野町 5-6-10.
A new type of atmospheric low temperature plasma source was developed utilizing a coaxial cable formicrowave transmission rather than conventionally used waveguides. We have developed two kinds ofplasma sources, one is resonator type cavity and another one is called non-resonance pen-style torch.
Two-dimensional gas-temperature and gas-velocity distributions of the plasma are measured using theE-type thermocouple and the Pitot tube respectively and results are presented. The applications of theatmospheric pressure plasma in various fields such as surface modification, cleaning and sterilization arediscussed.

1.Introduction
Microwave induced plasma sources have alreadybeen used for more than two decades [1-3] inspectrochemical analysis. Early types of plasma
sources utilize waveguides for the microwavetransmission. The bigger size, higher cost and fixed
positioning is the drawback of the system. Anotherproblem associated with the wave-guide fed systemis the generation of thermal plasma and the need foran igniter for plasma ignition. The new type of
microwave plasma system described in this paper
utilizes co-axial cable for the microwave
transmission and has several advantages such ascompact, low cost, flexible for positioning and self
ignition of plasma.

Quartz Plasma

2. System description
The basic set-up is shown in figure.1. The system
basically consists of a microwave power source,
stub-tuners for impedance matching, the co-axial
cable for the microwave transmission and theplasma generator. The microwave source is astandard industrial microwave oven magnetron
operating at 2.45 GHz with power rating up to600W. The Impedance matcher is a two-stub tuner.
The co-axial cable is a standard RG-393 cable.
There are two types of plasma generators one is a
CavityCoaxial cable
Tuner

resonator cavity and another one is a non-resonancepen-style torch.

Antenna
Antenna
400 W
Quartz Plasma(b).Ar-20 SLM(a).Ar-20 SLM(c). Ar(10)+N2(0.1) SLM- 200 W

Fig.2.Plasma generation

3. Results and discussion
3.1. Plasma characteristics
In a resonator cavity the plasma is generated
inside the discharge tube along the inner surface(Fig.2.a). In a non-resonator pen-style torch, plasma
400 W

400 W

Measuring region
(K)

(K)

zr

13mm

PlasmaGas cylinder

Stub-tuner

Ar 20 (SLM)

Power supply

Test surface
Fig.1.Schematic of the set-up

Ar 18/He1/O20.5 (SLM)

Fig.3.Temperature distribution

is generated between the gap of the antenna and the14.2. Plasma cleaning
Figure 6 shows the cleaning of the Si-wafer edge
using Ar(10)+O2(1) L/min plasma at input powerof 400 W, exposure time of 30 s. The result showsthat the plasma can be used to remove the organic
contaminants. Experimental results show that ourplasma torches can be used for the cleaning of thewafer backside and the ashing of photo-resist.

discharge tube (Fig.2.b). In both cases plasma looks
like a surface wave discharge. The plasma jet below
the discharge tube is cold plasma and can betouched by human fingers (Fig.2.c).
Figure 3 shows two dimensional temperature
distributions of the plasma under conditions ofargon with 20 L/min, Ar(18)+He(1)+O2(0.5) L/min
at input power of 400 W for resonator cavity.
The peak value of temperature is 863 K for Ar 20
SLM and the same is about 600 K forAr(18)+He(1)+O2(0.5) is observed in the vicinity ofthe wall at the nozzle exit ( z = 0 mm, y = 5 mm).

Ink mark

Quartz tube
Z=0 mm
Z=5 mm
Z=10 mm
Z=15 mm
Z=20 mm
Z=25 mm
Z=30 mm
Z=35 mm
Z=40 mm
Z=45 mm
Z=50 mm
Z=55 mm
Z=65 mm
Z=75.4 mm

1614Velocity (M/s)

1210864Ar-20 SLM
Microwave power-400 W

2BeforeAfter
Fig.6.Si wafer edge cleaning

4.3.Sterilization
Figure 7 shows the sterilization rate in relation tothe temperature for various sterilization methods.
Plasma sterilization of bacteria using our torches at
input power of 400 W with Ar and Ar+O2 as plasma
gas is superior to other conventional methods UV,ozone, steam and hot Ar gas. The sterilization rate
is higher for plasma sterilization methods and thesterilization temperature also lower compared toother methods.

02224262830

32343638

Radial distance (mm)Fig.4.Velocity distribution

001Figure 4 shows velocity distributions of theplasma under the condition of Ar(20 L/min ). The
maximum velocity is observed around 15 m/s in thevicinity of the wall. The peak velocity does notchange much with the mixture of N2 and O2 withAr.

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Aluminum/after0

Aluminum/before

02

Plastic/after04

Plastic/before

064.Applications
4.1. Surface modification
Figure 5 shows the results of the improvement ofwettability and contact change of the plastic,aluminum, Kapton after the treatment ofAr(10)+N2(0.5) L/min plasma at input power of 400
W. The exposure time is 45 s. The improvement ofwettability on the plastic surfaces after plasma
exposure is clearly seen by the change in thecontact angle of the water droplets.

08)%(etarnoitaziliret
S

Fig.7.Sterilization rate Vs temperature

5.Conclusion
Atmospheric plasma has been generated using Ar,
Ar+He, Ar+N2, Ar+O2, Ar+He+N2, and Ar+He+O2
feed gases. The torches can be used for surface
modification of Kapton sheet, plastics and metal,
cleaning of Si-wafer edge, reverse side and ashingof photo-resist and sterilization of bacillus subtilis
and E-coli bacteria.
References[1].C.I.M.Bennakker: Spectrochim.Acta, part B 31
(1976) 483-486.
[2].Y.Okamoto,M.Yasuda,S.Murayama,: Jap.J.Appl.Phys.
29(4) (1990) L670-672.
[3].M.Moisan,R.Grenier,: Spectrochim.Acta, part B 50
(1995) 781-789.

After
BeforeFig.5.Improvement of wettability of surfaces

2