22P026-O
Numerical Analysis of Radio-Frequency Barrier Discharges in Xenon
for Excimer Lamps
エキシマランプ用高周波キセノンバリア放電の放電基礎特性の解析
Akinori Oda1 and Haruaki Akashi2
小田 昭紀1，明石 治朗2
1Chiba Institute of Technology
2-17-1, Tsudanuma, Narashino 275-0016, Japan
2
National Defense Academy
1-10-20, Hashirimizu, Yokosuka 239-8686, Japan1
千葉工業大学 〒275-0016 習志野市津田沼2-17-1
2
防衛大学校 〒239-8686 横須賀市走水1-10-20
Fundamental discharge properties in rf-excited dielectric-barrier discharges (RF-DBDs) in xenon havebeen analyzed using a one-dimensional fluid model, for the purpose of further performance optimization ofxenon excimer lamps (λ∼172 nm). This fluid model consists of the continuity equations for electrons,positive ions, excited atoms and molecules, the Poisson equation and the electron energy balance equation.
In lower input-power case (∼1Wcm-2), simulated discharge- current waveform is similar to sinusoidal one.
In xenon RF-DBDs, it is found that dominant positive ion species is found to be Xe3+ ions with the density
magnitude of 109 cm-3. Other fundamental discharge properties in xenon RF-DBDs are also analysed.

1. Introduction
Excimer lamps using dielectric barrierdischarges (DBDs) have been investigated anddeveloped [1-4] as a vacuum-ultraviolet lightsource for photo-chemical applications such as
photo-deposition of thin films, dry etching andsurface modification of plastics etc [5-7].
Until now, in order to examine a further
performance improvement of the lamps, we havereported the dependence of output power andefficiency of vacuum-ultraviolet light (λ∼172 nm)
on input-power for various driving frequencies
and gas-pressures [8], waveform of applied
voltage and gap lengths [9], from the aspect ofnumerical analysis in xenon DBDs.
In this paper, as one of the possibility toimprove the characteristics of the lamps, rfexcited dielectric-barrier discharges (RF-DBDs)
in xenon have been simulated using a onedimensional fluid model, and then analyzed thefundamental discharge properties, focused on thespatiotemporal behavior of the charged-species,
and the voltage and current waveforms.
2. Modeling of DBDs in Xenon
Figure 1 shows a schematic diagram of present
simulation model. The xenon gas with the totalpressure of 600 Torr and gas temperature of 300 K
is filled between two parallel-plate metallic
electrodes covered with dielectric-layer (width: 0.2
cm and relative permittivity: 3.8). The RF-DBDs

Grounded-side
Electrode

QuartzPowered-side
Electrode
Applied Voltage

εr Xe DBDs εrv(t)=V0 sin(2πft)

iDistance from
Grounded ElectrodezFig. 1. A schematic diagram of xenon RF-DBDs.

are generated and sustained by applying AC voltage
with driving frequency of 13.56 MHz. The
discharge-gap spacing and secondary emissioncoefficient due to ion bombardment are set to be 0.8
cm and 0.01, respectively. In this work, fourcharged-species (e−, Xe+, Xe2+, Xe3+) and six
excited-species (Xe∗(m), Xe∗(r), Xe∗∗, Xe2∗(Ou+),
Xe2∗(1Σu+), Xe2∗(3Σu+)) were considered as species
in the RF-DBDs in xenon.
3. Results and Discussion
In this section, as an example of simulation
results, fundamental discharge properties in xenon
RF-DBDs at low input-power (∼1Wcm-2) arediscussed below. Simulation conditions consideredhere are chosen to be similar to actual working
conditions of the excimer lamps.
Fig. 2 shows (a) the temporal variations ofvoltage-current waveforms, and the cyclic-averaged
spatial distributions of (b) the charged-species
density, (c) the excited-species density, and (d) theVoltage (kV)

-2

2.0

Current Desnity (mAcm ): Applied Voltage: Gap Voltage
2.0: DIscharge Current

1.0

1.0
0.0

0.0

-1.0

-1.0

-2.0
0.0

0.5

1.0

-2.0
2.0

1.5

4.0

Charged-species density (x109-3cm )RF Cycle

3.0:e+: Xe32.0

Acknowledgments
This work was partly supported by a Grant-inAid for Scientific Research (C) from the Japan
Society for the Promotion of Science.

1.00.0
0.0

0.2

0.4

0.6

0.8

1.5

*: Xe (m)*: Xe (r)Excited-species density (x1010-3cm )Distance from grounded electrode (cm)

* 1+

* 3+

: Xe2 ( Σu ): Xe2 ( Σu )

1.0

0.5

0.0
0.0

electron-temperature and electric field. As shown inFig 2(a), simulated discharge-current appears to bealmost the same as sinusoidal waveform. Theamplitude of the current is 1.5mAcm-2. The phaseangle between the current and the gap-voltage isalmost π/2. This result indicates that the electricalcharacteristics in xenon RF-DBDs may be the sameas those of capacitive discharge. In Fig 2(b) and2(c), the spatial density-profiles of charged- andexcited-species have like a cup-profile withdensity-peak at the middle of the whole dischargegap. In Fig. 2(b), the dominant positive-ion species
is found to be Xe3+ ions with the density-magnitudeof 109 cm-3. The density-magnitude of the excitedatoms (Xe∗(m) and Xe∗(r)) and excimers (Xe2∗(3Σu+)with long lifetime of about 100 ns) are on theorder of magnitude of 1010 cm-3 . The magnitude ofthe excited species is about three times higher thanthat of positive ions, as shown in Fig. 2(c). As aresult, xenon RF-DBDs at low input-power density(∼1 Wcm-2) is found to be almost pure capacitive
discharges. The other results on RF-DBDs in xenon
will be shown at the conference.

0.2

0.4

0.6

0.8

Distance from grounded electrode (cm)Fig. 2. Simulated fundamental discharge properties inxenon RF-DBDs at lower input-power (1 Wcm-2): (a) thevoltage-current waveforms; the cyclic-averaged spatial
distributions of (b) the charged-species density; (c) theexcited-species density.

References[1] B. Eliasson and U. Kogelschatz: Appl. Phys. B, 46(1988) 299.
[2] K. Stockwald and M. Neiger: Contrib. Plasma Phys.,
35 (1995) 15.
[3] H. Akashi et al., IEEE Trans. Plasma Sci., 33 (2005)
308.
[4] H. Akashi et al., IEEE Trans. Plasma Sci., 36 (2008)1336.
[5] J-Y.Zhang et al.: Appl. Surf. Sci., 96 (1996) 399.
[6] H. Esrom and U. Kogelschatz: Thin Solid Films, 218(1992) 231.
[7] S. Habibi et al., J. Vac. Sci. Technol., B13 (1995)
247.
[8] A. Oda et al., J. Phys. D: Appl. Phys., 32 (1999)
2726.
[9] A. Oda et al., J. Phys. D: Appl. Phys., 33 (2000)
1507.