22P050-P
Measurement of Plasma and Electron Beamof a Pseudo-spark Discharge Plasma Jet by Hydrogen-diluted Methane
水素希釈メタンを用いた擬火花放電プラズマジェットのプラズマおよび電子ビーム計測
Takaharu Kamada1, Masayuki Watanabe2 and Tamiya Fujiwara
鎌田貴晴1, 渡部政行2, 藤原民也3
1

Hachinohe National College of Technology
16-1, Uwanodaira, Tamonoki, Hachinohe, Aomori 039-1192, Japan
八戸工業高等専門学校 〒039-1192 青森県八戸市田面木上野平16-1
2
College of Science and Technology, Nihon University
1-8-14, Kandasurugadai, Chiyoda-ku, Tokyo 101-8308, Japan
日本大学量子科学研究所 〒101-8308 東京都千代田区神田駿河台 1-8-14
3
Faculty of Engineering, Iwate University
4-3-5, Ueda, Morioka, Iwate 020-8551, Japan
岩手大学工学部 〒020-8551 岩手県盛岡市上田 4-3-5
A pseudo-spark discharge (PSD) is a high current glow-like discharge, which is formed on the left side of
the minimum of the Paschen curve. Even if the discharge current exceeds several tens of kiloamperes,discharge craters are less than the arc discharge on electrodes. And the PSD can generate high density
plasma. For the reasons mentioned above, it is expected the plasma chemical vapor deposition method withhigh deposition rate and quality by using the PSD to plasma source of the DLC. In this study, the PSD
plasma is generated with hydrogen dilution methane, and plasma parameters are investigated by triple
probe and faraday cup to check whether there is any electron beam.

1. Introduction
In the semiconductor manufacturing process,the material process technology using plasma is
gaining importance. It’s a diamond-like carbon(DLC) [1] thin film to one of material processes.
This is a metastable form of amorphous carbon
containing a significant fraction of sp3 bonds. It
can have a high infrared transparency, hardness,chemical inertness, insulation and low dielectric
constant. The DLC thin films have electron
emission devices for plasma display panels,
insulator film for LSIs and coatings treatments
for forming dies for industrial applications. In
generally, the DLC thin films are deposited under
low pressure. A microwave plasma chemical
vapor deposition (CVD) method is mentioned to atypical technique of deposition. This method canmake a film with very stable growth andsufficient reproducibility. But this have a problem
with low deposition rate because of low pressure
discharge.
In this study, a pseudo-spark discharge (PSD)[2, 3] is applied to the plasma source of DLC film.
The PSD is a large current discharge at
low-pressure, but discharge craters are less than
the arc discharge on electrodes. Consequently, theplasma density increase and it is less that

Hollow
CathodeAnodeHollow
Cathode

Anode

jj’e

Equipotential Line

(a)

(b)

Fig.1 Schematic diagrams of the PSD electrodes.
(a) Discharge path j’ in the case of the PSD.
(b) Activation of ionization in the hollow cathode bythe γ-effect.

impurities are ejected from the melted electrodeto the plasma. If the PSD with these features isapplied to plasma source of the DLC, highdeposition rate will be obtained in a low pressure.
PSD is a large current discharge with anespecially geometrical shape of a pair of parallel
disk electrodes at low pressure region on the left
hand side of the minimum point of the Paschencurve. The PSD’s electrodes consist of a small
circular hole on the axis are adopted instead of apair of single plane and the cathode has acylindrical cavity behind the circular hole asshown in Fig.1. In the case of the PSD, thedischarge path can be formed into or throughcircular holes so that its length becomes longcompared with the distance between theelectrodes by using at low pressure region.
Because pulse voltage is applied, electric fieldchanges in time between electrodes. Furthermore,
electric field is formed into the cathode cavity
and the ionization is enhanced by the gamma
effect [3]. Many electrons are supplied from thecathode cavity to the bulk of the discharge. As aresult, the discharge retains the glow mode andthe discharge current density can be small. Ourstudies revealed that high density plasma(~ 10-20 m－ 3) was spouted out from the anodehole in experiment with hydrogen gas [4].
However, the applied voltage is approximately
2.3 kV between electrodes when it is generated
the PSD discharge. Therefore it is possible thathigh density plasma is generated by high energy
electron beam. In this study, the PSD plasma isgenerated with hydrogen dilution methane, andplasma parameters are investigated by triple
probe and faraday cup to check whether there isany electron beam. It’s described theexperimental equipment in this paper.
2. Experimental setup
The experimental device is shown in Fig. 2. Thevacuum chamber is made of stainless steel, it is26.7 cm in diameter and 51.8 cm in height. The
chamber was evacuated to about 10－4 Pa using anoil diffusion pump. After the evacuation, thevacuum valve to the oil diffusion pump was closed
and the chamber was flushed with material gas(CH4+H2) up to a desired pressure using needle andstop valves. A gas flow can be added, maintaining
the pressure by slight pumping. The 24 μ F
condenser bank is slowly charged up to negative
high voltage. When the potential of the cathodereaches the breakdown voltage, the discharge isgenerated spontaneously. The discharge current ismeasured with a Rogowskii coil and the breakdown
voltage is measured with a high-voltage meter. The
ion density of the plasma is determined with a triple
probe, time evolutions of the electron beam ismeasured by a faraday cup. Most of the cathode ismade stainless, the central part of cathode is madetungsten, and anode is made of molybdam. The
diameter of the cathode hole is 5mm and that of theFig.2 Schematic diagrams of experimental setup.

anode hole is a 10mm. The distance between theanode and cathode is 5 mm. Initially the discharge
path of the PSD is formed into or through thecircular holes. Then, it moves between the anodeand cathode with time. To prevent this motion ofthe discharge path between the anode and cathode,an intermediate insulator was inserted between
them. The intermediate insulator is made ofalumina and has a hole diameter of 10 mm. Thecapacitance (C in Fig.2) is 24 μ F, and thebreakdown voltage for the discharge current of 10kA is approximately 2 kV.
References[1] J.Rovertson : “Diamond-like amorphous carbon”,
Mater. Sci. Eng. R, Vol.37, pp.129-281 (2002)[2] J.Christiansen and C.Schultheiss : “Production ofhigh current particle beams by low pressure sparkdischarge”, Z. Phys., Vol.A290, pp.35-41 (1979)[3] M.Stetter, P.Felsner, J.Christiansen, K.Frank,
A.Gortler, G.Hintz, T.Mehr, R.Stark and R.Tkotz :“Investigation of the different discharge mechanisms
in pseudospark discharges”, IEEE Trans. Plasma Sci.,
Vol.23, No3, pp.283-293 (1995)[4] T.Kamada, T.Fujiwara, M.Itagaki, T.Ishikawa andM.Watanabe : “Production of plasma jet based onhigh-current pseudo-spark discharge”, Jpn. J. Appl.
Phys., Vol.44, No.9A, p.6747-6751 (2005)