22P024-O
Diagnosis of H2-N2 glow discharge plasma
H2-N2グロー放電プラズマの診断
Hideki Nakada, Kenichi Suda and Mitsuya Motohashi
仲田英起, 須田健一, 本橋光也
School of Engineering, Tokyo Denki University
2-2 Kanda-nishiki-cho, Chiyoda-ku, Tokyo 101-8457, Japan
東京電機大学工学部 〒101-8457 東京都千代田区神田錦町2-2
We evaluated the H2-N2 glow discharge plasma by using the optical emission spectroscopy. When γ
increased the emission intensity of the N2* and N2+ species increased, while the emission intensity of theH2* and H* species decreased. The emission intensity of almost all species increased with the rf power. In
this paper, we discuss the relationship between the emission intensities of all emission species. It wasinferred that while the intensity of emission is decided by the energy level, the intensity is related to theinternal reactions among species in the plasma discharge. Furthermore, it was found that the optical emission
characteristics of the species change when the energy of the species is high (above approximately 13 eV).

1. Introduction
Plasma generated using the H2-N2 gas is widelyused for the surface treatment of steel, resin andsemiconductor materials [1]. There have been
many studies on the surface modification ofsilicon-based materials, particularly because of thedevelopment of novel high-quality devices [2,3]. It
is well known that the radicals and ions in theplasma play an important role in the surface
treatment. Therefore, the analysis of these species(ions and radicals) is important. However, thediagnosis of the H2-N2 plasma is very difficult
because the mechanisms of the decomposition andexcited state reactions are very complicated. In
previous studies, the plasma has been evaluatedwith the probe method, optical emission
spectroscopy (OES), and mass spectroscopy. In
particular, OES is more convenient method.
Therefore, in this study, we evaluated the H2-N2 rf
glow discharge plasma by using the OES. In
addition, the decomposition and excited state
reactions were studied.
2. Experimental method
Diode-type CVD and source gas separated
plasma CVD (SSP-CVD) methods were used togenerate H2-N2 plasma. Fig.1 shows the structure of
the electrode in the reaction chamber, and the OESapparatus used in the SSP-CVD method [4].
Between the anode and cathode, the reaction
chamber was divided into three chambers—A, B,and C—by using an SS plate electrode with holes
and an SS mesh electrode. N 2 and H 2 wereintroduced into the chambers A and B. RF power(13.56 MHz) was supplied to the cathode and meshelectrode by using two power supplies. Table 1AnodeSS Mesh Electrode
SS PlateElectrodeCBA

H2 N2
RF Power
Supply, pCathode

Photomultiplier TubeSHIMADZU
Monochromator
SPG-120S

Quartz Fiber Motor Drive
SS Cylinder
Quartz Cylinder
Stepping
Motor Controller

Control
Amplifier

RF Power
Supply, q
ComputerFig.1 Electrode structure in the SSP-CVD reactor, and OES [4].
Table 1 Plasma conditions for SSP-CVD
Parameters
Source Gas
Gas Flow Rate
RF Power
Gas Pressure

Range
Chamber A
Chamber B
99.998% N2
99.99999% H22-10 sccm
60 sccmRFp = 5-25 W
RFq = 5 W
133 Pa (1 Torr)
1 sccm = 1 cm3/min at 760 Torr, 20 °C

shows the plasma generation conditions. The gas
flow rate ratio γ [N2/(H2+N2)] and the rf powers
RFp and RFq were varied. In the case of the diodemethod, the plasma condition was almost the sameas that in the SSP-CVD method. Fig.2 shows thepotential energy levels of N2, H2, and H [5]. Theemission species produced by the N2* 1st positivesystem, N2* 2nd positive system, N2+ 1st negativesystem, H2*, and H* (Hα and Hβ) were observed.
Then, the emission intensity of the species, I(N2*1st Pos.), I(N2* 2nd Pos.), I(N2+ 1st Neg.), I(H2*),
I(Hα), and I(Hβ), was measured by OES.

HFig.2 Energy levels [5].

I(N2* 2nd Pos.) [a.u.] I(N2+ 1st Neg.) [a.u.]

3. Results and discussion
When γ increased, I(N2* 1st Pos.), I(N2* 2ndPos.), and I(N2+ 1st Neg.) increased, while I(Hα),I(Hβ), and I(H2*) decreased in both methods. Theemission intensity of almost all species increased
with the rf power. From these results, we now
discuss the relationship between the emission
intensities of all species. Figs.3(a) and (b) show therelationship between I(N2+ 1st Neg.) and I(N2* 1stPos.) and between I(N2* 2nd Pos.) and I(N2* 1stPos.). I(N2* 2nd Pos.) and I(N2+ 1st Neg.) increased
with I(N2* 1st Pos.). I(N2+ 1st Neg.) in the diodeCVD was greater than that of the SSP-CVD(Fig.3(a)). The relationship between I(N2* 1st Pos.)and I(N2* 2nd Pos.) was the same in both SSP-CVD
and diode CVD (Fig.3(b)). Figs.4(a) and (b) show
the relationship between I(H 2*) and I(H α) andbetween I(Hβ) and I(Hα). I(Hβ) and I(H2*) increased
with I(Hα). I(H2*) in SSP-CVD was greater thanthat in diode CVD (Fig.4(a)). Furthermore, therelationship between I(Hα) and I(Hβ) was the same
in both methods (Fig.4(b)). From the energy levelsof the species in Fig.2, it was found that the energy
level of the N2* 2nd positive was closer to that of
1.5
(a)
1.0
Diode CVD
0.5
SSP-CVD0(b)0.8

Diode CVD

0.4
SSP-CVD
00

0.04
0.06
0.08
0.02
I(N2* 1st Pos.) [a.u.]
Fig.3 Relation between I(N2+ 1st Neg.) andI(N2* 1st Pos.) and between I(N2* 2ndPos.) and I(N2* 1st Pos.).

(a)0.04 SSP-CVD
0.02

Diode CVD0(b)I(Hβ) [a.u.]

H2N2H+Hβ13.60

12.712.09

X1∑g+0HαH+H
14.00

17.98

H2*8.87.3

5N2+, 1st Neg.
X2∑g＋
C3Πu
N2*, 2nd Pos. B3Πg
N2*, 1st Pos.
A3∑u+

24.3

15I(H2*) [a.u.]

B2∑u＋

20

100.06

N+N

10.9

Potential energy [eV]250.2
SSP-CVD

0.10Diode CVD
00.3 0.4
0.10.2I(Hα) [a.u.]
Fig.4 Relation between I(H2*) and I(Hα) andbetween I(Hβ) and I(Hα).

the N2* 1st positive than to the energy level of theN2+ 1st negative. It was also found that the energy
level of Hβ was closer to that of Hα than to theenergy level of H2*. Hence, I suspect that the ratioof I(N2* 2nd Pos.) to I(N2* 1st Pos.) and the ratio ofI(Hβ) to I(Hα) are constant regardless of the type ofCVD reactor. I(N2+ 1st Neg.) in diode CVD wasgreater than that in SSP-CVD (Fig.3(a)). I(H2*) inSSP-CVD was greater than that in diode CVD(Fig.4(a)). In other words, while the intensity ofemission is decided by the energy level, it is also
related to the internal reactions among species inthe plasma discharge. In addition, it was found thatthe optical emission characteristics of the specieschange when the energy of the species is high(above approximately 13 eV).
4. Conclusion
In the H2-N2 glow discharge plasma, the opticalemission intensities of N2+ and H2* depend on thetype of chamber used. It was found that it isimportant to make observations in the range overabout 13 eV for this plasma. Furthermore, it wasinferred that the decomposition and exited state
reactions of H2 differed from those of N2 gas. In afuture study, the reaction process of H2 and N2
gases will be discussed.
References[1] H. Nagai, et al.: Jpn. J. Appl. Phys., Part 2, 42 (2003)
L212.
[2] L. T. Canham: Appl. Phys. Lett., 57 (1990) 1046.
[3] V. Lehmann, et al.: Appl. Phys. Lett., 58 (1991) 856.
[4] M. Motohashi, et al.: Electron. Comm. Jpn., Part 2,90, 2 (2007) 9.
[5] R. W. B. Pearse, et al.: The Identification ofMolecular Spectra (Chapman and Hall, London,1976) 4th ed., p.217.