24G08
A nitriding treatment of aluminum films by atmospheric pressure discharge(1) Effects of substrate temperature for nitriding treatment of aluminum films
大気圧プラズマを用いたアルミニウム膜の窒化処理（１）表面窒化反応に対する温度の影響
Yusuke Ohtsuka, Akihiko Saikubo and Yoshio Ueda
大塚裕介, 西窪明彦，上田良夫
Graduate school of Engineering, Osaka University
2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学大学院工学研究科 〒565-0871 大阪府吹田市山田丘2-1
Nitride process for aluminum film was investigated under the atmospheric pressure condition with themixing of helium and nitrogen gases. At low temperature of 100 ºC, oxygen atoms were released from thesurface and nitrogen atoms were bounded to Al atoms. The small peak of XRD pattern corresponding toAlN crystalline was detected when the flow ratio of N2 gas to He gas is larger.

1. Introduction
The non-destructive inspection technique using
ultrasonicwaves,generatedbyanelectromagnetic acoustic transducer (EMAT), hasbeen introduced into the in-service inspection offast breeder reactors. The EMAT allows us toinspect the defect without any contact material
between the transducer [1-3]. However, theEMAT consists of permanent magnets andtransmission coil so that it is hard to apply to theinspection of the pipe at high temperature
condition of 550 ºC for the operating plant system.
In these circumstances, a proposal has been madeof a new EMAT driven by a pulse current method.
This EMAT allows us to make some multi-layers
piled alternately with insulation and conduction
materials, which works as a current circuit on asubstrate. The author has already studied thedeposition multi-layers of (AlN) by introducing
both an insulator with high thermal conductivity
and a copper conductor with high electricconductivity, but the bad adhesion on thesubstrate and the micro-cracks on the film wereobserved due to large residual stresses. This is aproblem to be solved for the current driven
EMAT. The present study aims to investigate thefundamental process for nitriding treatments ofaluminum films by atmospheric pressure plasma
in order to improve the deposition system.
2. Experimental setup
The experimental setup for depositing AlN films
is shown in Fig. 1. A cylindrical chamber has asubstrate holder and a large electrode at the top andbottom, respectively, operating at a frequency of
100 MHz. Evacuation was done at the base pressureof 1x10-5 Pa with a turbo molecular pump in orderto remove the influence of residual gases. After thisprocess, the chamber was filled with the mixture of
He and N2 gases up to a working pressure at 9 x 104
Pa. The gas mixing ratio was steadily adjusted by
the mass flow controllers (MFCs).
Cupper tungsten plates were used as a substrate.
Before the exposure of atmospheric pressureplasma, a aluminum film was deposited on thesubstrate using magnetron sputtering device which
generates Ar plasma at input power of 200 W. The
aluminum film on the substrate was heated up to400 ºC by a resistive heater mounted inside thesubstrate holder, which was kept at this temperature
within ± 10 ºC while making deposition. A disk ofpure aluminum (99.99 % in purity) with 3 inch indiameter and 2 mm in thickness was mounted on
the electrode. The substrate was moved in position
turbo molecular pumpvalve
substrate holder

substratepumptargetvacuum gauge
He and N2gas inlet

RF 100MHzFig.1. Schematic of experimental setup.

temp.：400 ˚C
N 2 ：50 sccm
Pressure：9×104 Pa

Intensity [arb. unit]

Intensity [arb. unit]

Mg Kα
Al 2p
0.9×105Pa
100 ˚C
Al-N

Al-O

77

76

75 74 73 72
Binding energy [eV]He:5 slm

He:1 slm

Al-Al
78

AlN 0002

He:10 slm

71

70

32

3436
38
2θ [deg.]

4042Fig.2 XPS spectrum for Al 2p.

Fig.3. XRD patterns for various He gas flow.

so that the deposition flux varied spatially from thetarget. The distance between the substrate holder
and the electrode was within 1mm. The two kindsof highly purified gases, helium (He) and nitrogen(N2), were supplied to the system as the reactivegases. The monitored gas flow of N2 was always set
at 50 sccm during operation.
X-ray
photoelectron spectroscopy (XPS,Shimazu AXIS-165), X-ray diffraction (XRD,Rigaku Rint2000), scanning electron microscopy(SEM: HITACHI HF-3000) were equipped to do
the measurements and analyses of the chemicalbonding states, surface morphology.

XRD patterns of the aluminum films wereinvestigated at atmospheric pressure condition,
when He gas flow was controlled from 1 slm to 10slm, and the N2 gas flow is constant flow of 50
sccm. Fig.3 shows the XRD patterns of thealuminum films for the different He gas flow. The
weak diffraction pattern corresponding to AlN 0002
was detected at He gas flow of 1 slm, while nopeaks related to AlN crystalline were observed at 5slm and 10 slm.

3. Results and discussion
Fig.2 shows an XPS spectrum for Al 2p corelevel of the aluminum film exposed by He/N2
mixture atmospheric plasma at 100 ºC. Mainspectrum was separated to three spectra
corresponding to Al-N, Al-O and Al-Al. The atomic
ratio of Al-N is about 30-50 % at the investigatedtemperature. It is noted that Al-O and Al-Al
components only exist before exposure. By theeffect of the atmospheric plasma, oxygen atoms
were released from the surface and nitrogen atoms
were bounded to Al atoms at low temperature of100 ºC.
The surface morphologies were not noticeably
different up to 400 ºC. On the other hand, AlN
crystalline was grown on the aluminum surface
when the total pressure was 2 x 104 Pa, and the flowrate of He and N2 gases was 50 sccm and 20 sccm,respectively. In this case, the flow ratio of N2 gas toHe gas was considerably high. It suggests that it
might be enough nitrogen atoms to form the AlN
crystalline.

4. Summary
Nitride process for aluminum films by He and N2
mixture plasma at 9 x 104 Pa were investigatedfrom 100 ºC to 400 ºC. At low temperature of 100ºC, nitrogen atoms were bounded to Al atoms on
the surface. AlN crystalline was found when theflow ratio of N2 gas to He gas is larger.
Acknowledgement
Present study is the result of “Core R&D
program for commercialization of the fast breeder
reactor by utilizing Monju” entrusted to Universityof Fukui by the Ministry of Education, Culture,Sports, Science and Technology of Japan (MEXT) ,and re-entrusted to Osaka University by Universityof Fukui at FY2011.
References[1] R.B. Thompson, IEEE Transactions on Sonic andUltrasonics, Vol. SU-20 (1973) 340[2] B.W .Maxfield, A. Kuramoto, J.K. Hulbert, Material
Evaluation 45 (1987) 1166
[3] Y. Kurozumi, M. Higashi, T. Satou, M. Nishikawa,
Material. Evaluation 59 (2001) 638