23G02
Formation of ZnO Films by Plasma-Assisted Mist-CVD Using Zn(CH3COO)2
酢酸亜鉛を用いたプラズマ支援ミストCVDによる酸化亜鉛薄膜の形成
Kosuke Takenaka, Yusuke Okumura and Yuichi Setsuhara
竹中 弘祐, 奥村 祐介，節原 裕一
Joining and Welding Research Institute, Osaka University,
11-1 Mihogaoka,Ibaraki-shi, Osaka, 567-0047, Japan
大阪大学接合科学研究所 〒567-0047 大阪府茨木市美穂ヶ丘11-1
Mist-included high-density RF plasma source has been developed for low temperature and high rate
deposition process of zinc oxide films. For the deposition of a zinc oxide, the inductively coupled RFdischarge was generated with injection of mists including metallic salt of zinc. Zinc oxide (ZnO) film byplasma-assisted mist-CVD using Zn(CH3COO)2 have been reported and effects of the plasma exposure on
film properties. Zinc oxidize films deposited by mist CVD assisted with argon/oxygen mixture plasma
have showed existence of the crystallized zinc oxide films.

1. Introduction
Zinc oxide (ZnO) which has a wide- direct band
gap of 3.37 eV, is a very attractive material for
optical and electrical devices, such as ultraviolet
emitters and detectors, transparent conducting
electrodes, heterojunction transistors, thin filmtransistors and sensors[1-3]. ZnO films have beengrown by various techniques including magnetron
sputtering [4], chemical vapour deposition [5], pulsed
laser deposition [6] and molecular beam epitaxy [7].
However, deposition of zinc oxide via conventional
methods involves problems associated with low
deposition rate.
To overcome this problem,
plasma-assisted mist CVD method has beendeveloped for low temperature and high rate
deposition process of ZnO films.
In thispresentation, the experimental results regarding
zinc oxide film deposition with plasma-assisted
mist-CVD using Zn(CH3COO)2 deposition method
have been reported and effects of the plasma
exposure on film properties.
2. Experimental
Schematic diagram of experimental
setup for the plasma-assisted mist-CVD isshown in Fig.1. A water-cooled copper
coil antenna (three turns) was looped
around alumina discharge tube of 50 mm
in outer diameter and 42 mm in innerdiameter. The antenna is coupled to a1000 W RF power generator at 13.56
MHz via a matching network. Air andargon gas were supplied from upstreamof the stainless tube of 18 mm in outer
diameter and 15 mm in inner diameter.
In this study, the Zn(CH3COO)2 solution
was used for zinc oxide source. The

supply of the Zn(CH3COO)2 solution wasperformed by ejection of droplets of Zn(CH3COO)2solution from a nozzle in the vacuum chamber.
The total pressure was kept constant at 50-100 Pa.
The Si and glass substrates were located in thedownstream region at 250 mm from the copper coilantenna.
Plasma density was measured with a cylindricalLangmuir probe. Crystalline structure of zincoxide films was analyzed with X-ray diffraction.
Surface properties of zinc oxide films were studied
with a scanning electron microscope (SEM).
3. Results
To investigate characteristics of plasmas forplasma-assisted mist-CVD of zinc oxide films,
plasma density for argon gas (Ar 100%) at a
distance of 195 mm from the antenna was measured.
Figure 2 shows RF power dependence of the argon
plasma density with total pressure as a parameter.

Fig.1. Schematic diagram of experimental setup for theplasma-assisted mist-CVD

840 Pa
20 Pa

610 Pa4ZnO(1012)

60 Pa

ZnO(0002)

10ZnO(1011)

80 Pa

ZnO(1010)
Si10Plasma density (1012Intensity (a.u.)

100 Pa-3cm )14Ar + O2 10%2Ar

00200

400

600

800

RF power (W)Fig. 2 Variation of plasma density on RF power asa parameter of pressure.

With increasing RF power, the argon plasma
density linearly increased at all the conditions oftotal pressure. The results also show that theincreasing in plasma density depended on theincreasing in total pressure. The argon plasma
density became as high as 1.2 x 1011 cm-3 at 700 W
at 1000 Pa. From the viewpoint of an efficientdeposition, it is desirable that the plasmas fordeposition of ZnO films are high-density. The
result indicates that high-density plasmas as high as
1010-1011 cm-3 can be obtained using plasmaassisted mist-CVD.
Surface properties of zinc oxide films werestudied with an X-ray diffraction (XRD). Figure 3shows XRD patterns of zinc oxide films using pureargon and argon/oxygen mixture plasmas (oxygenflow ratio 10%) exposure to droplets ofZn(CH3COO)2 solution. As shown in Fig. 3, XRD
patterns of zinc oxidize films with argon/oxygen
mixture plasma exposure have showed the XRD
results showed the XRD results showed evident
peaks of ZnO(0002), indicating that highly c-axis
oriented films were grown, and small peak ofZnO(101̄ 0), ZnO(101̄1) and ZnO(101̄ 2). These
results suggest that the ZnO deposited withargon/oxygen mixture plasma assisted mist CVD
method shows the highly c-axis-orientation.
Figure 4 shows SEM images of surface morphologiesof ZnO films deposited by plasma-assisted mist-CVDas a parameter of oxygen flow ratio. The ZnO films
for argon/oxygen mixture plasma exhibited columnar
growth on the round gains.
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30

3540

45

50

55

60

Diffraction angle 2(degree)
Fig. 3. XRD patterns of films deposited with
irradiating Ar plasma and Ar+O2 (10%)
mixture plasma.

Fig. 4. SEM images of ZnO films deposited with
irradiating Ar plasma and Ar+O2 (10%)
mixture plasma.
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