24aP018
A Nitriding Treatment of Aluminum Films by Atmospheric Pressure Discharge(2) Effects of Gas Pressure for Helium/Nitrogen Mixture Gases
大気圧プラズマを用いたアルミニウム膜の窒化処理(2) ヘリウム／窒素混合ガスによるガス圧効果
Akihiko Saikubo, Yusuke Ohtsuka and Yoshio Ueda
西窪明彦、大塚裕介、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
Characteristic of aluminum films exposed to helium/nitrogen (He/N2) mixture plasma was investigatedusing an X-ray photoelectron spectroscopy (XPS) and a powder X-ray diffraction (XRD). The aluminum
films exposed to the He/N2 plasma was progressed nitridation and contained dominantly analuminum-nitrogen (Al-N) component. For the nitridation under relatively low nitrogen concentration,
microcrystalline aluminum nitride (AlN) would grow. On the other hand, for relatively high nitrogenconcentration, large AlN crystals started to grow.

1. Introduction
Nondestructive
inspectionwithanelectromagnetic acoustic transducer (EMAT)
employing electric drive system is promising tomonitor the crack and wastage caused at pipes ofthe fast-breeder reactor under the high temperatureof 550˚C during the operation. The EMAT isrequired to cover electronic circuits with aninsulating material in order to provide superior
performance. Aluminum nitride (AlN) is known as
one of good insulating coating materials because of
their excellent properties such as the resistivity andthe high thermal conductivity. In order to operate
the EMAT at 550˚C, it is necessary to coat theelectron circuits with the AlN film of the thickness
more than 10 m. Therefore, the AlN films were
fabricated by the nitridation of aluminum film using
atmospheric pressure plasma with a reaction rate
because of high plasma density. Characteristic of
their nitrided films was investigated using an X-ray
photoelectron spectroscopy (XPS) and a powder
X-ray diffraction (XRD).
2. Experimental
Aluminumfilms
deposited
ontoacopper-tungsten substrate with the rf wave
magnetron sputtering in the argon gas pressure of
6.7×10-1 Pa were nitrided by helium/nitrogen(He/N2) mixture plasma under atmospheric pressure.
Using gas mass flow meter, the He and N2 gaseswith flow rates of 10 slm and 50 sccm, respectively,
were accurately introduced into a reaction chamber
and the gas pressure in the chamber was kept at thepressure from 2.7×104 Pa to 9.3×104 Pa. The XPS

measurement of the nitrided aluminum films wasperformed using X-ray photoelectron spectrometer(Shimadzu Co. Ltd./Kratos Analytical Ltd.;
AXIS-165). The magnesium target as an X-ray
source was employed. An X-ray beam from amagnesium film was irradiated on the nitrided film.
The pass energy was employed the value of 40 eV.
In this system, the total resolution has been
estimated to be ~850 meV. The vacuum of ananalysis chamber was below 1.0×10-7 Pa.
Photoelectron spectra in an Al 2p region of thenitrided aluminum films were measured bydetecting the photoelectrons emitted from thesurface region. The XRD measurement of thenitrided aluminum films was performed using
powder X-ray diffractometer (Rigaku Co. Ltd.;RINT-2000). The copper target as an X-ray source
was employed. An X-ray beam from a cupper film
was monochromatized by means of a graphite
monochromator and was irradiated on the nitridedfilm. Diffracted X-ray beam intensity was recorded
using a NaI scintillation counter mounted on the 2
arm. Diffraction patterns were obtained by scanningthe 2 in the angular range from 31˚ to 42˚.
3. Results and discussion
Figure 1 shows a typical core-level photoelectron
spectrum in the Al 2p region for an aluminum film
exposed to He/N2 mixture plasma at the pressure of
8.0×104 Pa. The spectrum is divided into four
components with consideration of the chemicalshift. Peaks centered at 71.8 eV, 73.5 eV and 74.7
eV are assignable to Al-Al, Al-N and Al-O
bondings, respectively.[1,2] This spectrum isdominantly composed of the Al-N component. It isnoted that a typical spectrum for native aluminumoxide/aluminum is observed before nitridation. Thisphenomenon indicates that the Al-N component isgenerated in the aluminum film by expose of theHe/N2 plasma.

Intensity (arb. unit)

Mg K
Al 2p

Shirley background is subtracted.

Cu K

7876

Intensity (arb. unit)

Al-N

Al-O

Al-Al74

7270

Binding Energy (eV)Fig.1. A typical Al 2p photoelectron spectrum for an
aluminum film exposed to He/N2 mixture plasma

Gaussian width of the Al-N component derived
from the Al 2p spectra is plotted as a function ofgas pressure in Fig. 2. It is noted that red circle
indicates the Gaussian width estimated from a
photoelectron spectrum for a sample, where an
AlN0002 reflection peak is observed in an X-ray
diffraction pattern. (not shown) The Gaussian width
seems to be close to the value expressed by the redcircle over the pressure. This implies thatcrystalline structure of these samples would besimilar.

Gaussian Width (eV)

2.0

1.6Reference

1.2
1.0
2.0x104

He:10 slm

AlN 0002

He:5 slm

He:1 slm

3234

36

38

40

42

2 (degree)

Fig. 3 X-ray diffraction patterns for the nitrided films
with respect to different He flow rate.

4. Conclusion
The characteristic of the aluminum films exposedto the He/N2 mixture plasma was investigated using
XPS and XRD. The films exposed to the He/N2mixture plasma are composed of the Al-Al, Al-N
and Al-O components. It is found that themicrocrystalline AlN would grow for the relatively
low nitrogen concentration and the large AlN
crystal starts to grow.
Acknowledgments
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.

1.8

1.4Figure 3 shows X-ray diffraction patterns for thenitrided films with respect to different He flow rate
under the pressure of 9.3×104 Pa. It is noted that
nitrogen concentration increases with decrease of
the He flow rate. A weak AlN0002 reflection peakstarts to be observed when the He flow rate is
reduced and the nitrogen concentration is relativelyelevated. It is inferred that a large AlN crystal starts
to grow. For relatively low nitrogen concentration,
the reflection peak is not visible although theGaussian width would be close to that of the sample
for relatively high concentration. It is consideredthat collection of microcrystalline AlN would grow.

4.0x104

6.0x104

8.0x10

4

Pressure (Pa)Fig. 2 Gaussian width of the Al-N component.

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