Photon Factory Activity Report 2019 #37 (2020)

BL-11B/2019P003

Identification of the state of deposition inert gas
remaining in transparent conductive films deposited by magnetron sputtering
Junichi NOMOTO1,*
Advanced Coating Technology Research Center,
National Institute of Advanced Industrial Science and Technology (AIST),High Energy Research Organization,
Tsukuba Central 5-2, 1-1-1 Higashi, Tsukuba, 305-8565, Japan
12 Experiment
We deposited AZO films with systematic various Ar
contents by 10 different deposition conditions. Thesubstrate was alkali-free glass substrates (Corning, EagleXG). The target was a high-density sintered ceramic
circular AZO target (Toshima Manufacturing Corp.) withan Al2O3 content of 2.0 wt %. All of the deposition
processes were performed under a pure Ar atmosphere at apressure of 1.0 Pa. Prior to film deposition, the chamber
was evacuated until the base pressure reachedapproximately 2.0×10−5 Pa. The typical film thickness ofthe obtained AZO films was approximately 500 nm.

The XAS measurements were performed on the beamline BL-11B at Photon Factory. The synchrotron radiation
was monochromatized by a Si(111) double crystal
monochromator. All the XAS experiments were carried out
in a vacuum chamber at room temperature in thefluorescence yield mode using a Si drift detector. Incident
X-rays were perpendicular to the sample surface and thedetection angle was parallel to the sample surface to avoid
detecting the scattered X-rays.
3 Results and Discussion
Figure 1 shows the typical Ar K-edge X-ray absorption
near edge structure (XANES) spectrum for the AZO film.
Three peaks at the energies of 3.20, 3.205 and 3.212 keVwere clearly observed for all samples. The predominantpeak at the energy of 3.20 keV corresponds to the localized
transition of the 1s to 4p. [4] The peak at the photon energyof 3.212 keV is attributed to the cluster Ar Ka line. [4]These features are also observed from Ar K-edge XAS in
DC sputtered aluminum film, which reported by Takemura
et al., [5] On the other hand, the peak at the energy of 3.205
keV has never been reported.
Intensity [a.u.]

1 Introduction
Magnetron sputtering (MS) is most commonly
deposition technique for transparent conductive oxide
films. Magnetron-sputtered films, however, have an issue
to be resolved: electrical resistivity (ρ) strongly depends on
the substrate positions. ρ of the films grown at a positionin the area of the substrates opposite to the erosion zone of
the target is quite high compared with those of the films
deposited at a position in the regions located far away fromthe above area. To date, dominant factors determining theabove non-uniform of the spatial distribution of electricalproperties are not yet thoroughly understood. We havebeen investigating the effects of the erosion zone of MS
targets on the carrier transport of magnetron sputtered Aldoped ZnO (AZO) films prepared on a glass substrate togive a resolution to the issue described above. [1]A series of the experimental results yielded thefollowing. [1-3] For AZO films deposited by direct current(DC) MS, we found quite high amounts of residual argon(Ar) compared to AZO films deposited by radio frequency(RF) MS at any given substrate position; During film
growth, recoiling Ar-related species attacked the AZO
films grown at the substrate positions opposite to theerosion zone. Note that the impact of Ar atoms gives riseto the enhancement in the contribution of grain boundary
scattering to the carrier transport owing to the poor
crystallographic orientation between columnar grains. Inaddition, the residual Ar atoms present a significant
obstacle to free carriers in ingrains, causing a decrease in
intrinsic carrier mobility. [1-3] However, none of theprevious studies offers the detailed information on thelocal structure of Ar in ZnO crystal.
In this work, a combination of Ar K-edge X-ray
absorption spectroscopy (XAS) and first-principlescalculations ware used to investigate the local structure ofAr in ZnO crystal.

3.19 3.20

3.21 3.22

3.23

3.24 3.25

3.26

Energy [keV]
Fig. 1: Ar K-edge XANES spectrum for the AZO film
Acknowledgement
The authors express their sincere gratitude to Dr.
Yoshinori Kitajima of High Energy Accelerator Research
Organization for assistance with the XAS measurements.
References[1] J. Nomoto et al., J. Appl. Phys. 124, 065304 (2018).
[2] J. Nomoto et al., ACS-Omega 4, 14526 (2019).
[3] J. Nomoto et al., J. Vac. Sci. Technol. B 38, 022202(2020).
[4] E. Rühl et al., J. Chem. Phys. 98, 6820 (1993).
[5] M. Takemura et al., Spectrochim. Acta Part B, 54, 159(1999).
* nomoto.junichi@aist.go.jp