23P020-O
Effect of Plasma Irradiation on Interfacial Nano Layers
in Organic/Inorganic Hybrid Structures
有機無機ハイブリッド構造におけるプラズマ照射によるナノ界面層への影響
Ken Cho, Kosuke Takenaka and Yuichi Setsuhara
趙 研，竹中 弘祐，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
Interactions of Ar-O2 mixture plasma and Zn/Alq3 interface have been investigated on the basis of depth
analyses of chemical bonding states via conventional x-ray photoelectron spectroscopy (XPS) and hard
x-ray photoelectron spectroscopy (HXPES). The HXPES analyses of Ar-O2 mixture plasma exposed
Zn/Alq3 samples indicated that the oxygen radicals and/or ions from the Ar-O2 mixture plasma formed
oxygen functionalities at the shallower region up to 10 nm from the interface. These results suggest that theAr-O2 plasma exposure make it possible to control molecular structures of organic semiconductors.

1. Introduction
For fabrication of electronics on polymers orflexible electronics which are expected as
next-generation
devices,developmentoflow-damage plasma processing technologies issignificant. It is of important to control thechemical bonding states in the vicinity of theorganic materials surface and at the interface
between the organic materials and the depositedfilms. However, bond-dissociation energies oforganic materials for thermal decomposition
range from 3.4 eV for the O-C(=O) bond, 3.6 eV
for the C-CH3 bond to 8.4 eV for C=O bond. Thus,in the plasma processes, it is considered that ions,radicals, photons and electrons from the plasma
may cause significant degradation of organic
materials beneath the surface and theinorganic/organic interface. In order to overcome
these problems, low-damage plasma processing
technologies with low-inductance antenna (LIA)
units [1] have been developed.
In this paper, interactions between plasma withorganic semiconductors have been investigated on
the basis of non-destructive depth analyses ofchemical bonding states at Zn/Alq3 interface. The
non-destructive depth analyses of chemical bonding
states were carried out using hard x-ray
photoelectron spectroscopy (HXPES)
2. Experimental
Schematic diagram of the process chamber isshown in Fig. 1. The LIA consists of a U-shapedantenna conductor (with a 80 mm height and a 70mm width), which was fully covered with dielectric
tubing for complete isolation from the plasma. The
chamber had a 500 mm inner diameter and a 200mm height, which was connected to a diffusion
chamber made of stainless-steel vessel with 500mm inner diameter and 400 mm height. Ar-O2
mixture plasma was generated via inductive
coupling of radio frequency (RF) power at 1000 W(13.56 MHz) with a set of eight LIA units at a gas
pressure of 2.6 Pa (oxygen partial pressure = 20%).
Alq3 film was formed on Si substrate usingvacuum evaporation. Zn thin film was deposited on
Alq3 substrate using magnetron sputtering.
Depth analysis of chemical bonding states wascarried out with conventional XPS and HXPES.
The HXPES analysis was performed with hard
x-ray from a synchrotron at a photon energy of7940 eV at the national synchrotron radiation
facility (SPring-8) of the Japan Synchrotron
Radiation Institute. The inelastic mean free path(IMFP) of 7940 eV electrons in organic materials isapproximately 18 nm. This feature with HXPES

Fig. 1. Schematic diagram of discharge chamber.

makes it possible to evaluate the chemical bonding
states at the Zn/Alq3 interface via variation of
take-off angle (TOA) for photoelectrons detection
from TOA of 88 deg for analysis of deeper region
up about 35 nm from the interface down to TOA of
9.6 deg for analysis of shallower region about a few
nm from the interface (Fig. 2).
3. Results
Fig. 3 shows HXPES C 1s spectra of Zn/Alq3
samples; (a) without plasma exposure and (b) withplasma exposure as a parameter of TOA. For
analysis of deeper region up about 35 nm from theinterface, TOA was set at 88 deg. And For analysisof shallower regions up about 8 nm and a few fromthe interface, TOA were set at 19.5 deg and 9.5 deg.
As shown in Fig. 2(a), after the deposition processof Zn thin film, O=C-O bond increased
significantly at shallower regions about a few nmfrom the interface. These results indicated that thesputter process cased degradation of molecule
structure at the interface. The HXPES C 1s spectra
measured at a TOA = 88 deg showed insignificant
change after the Ar-O2 mixture plasma exposure.
Whereas, the HXPES C1s spectra measured at TOA= 19.5 deg and TOA = 9.5 deg showed significant
increase in O=C–O bond after the Ar-O2 mixture
plasma exposure. These results indicated that new
oxygen functionalities are formed by the Ar-O2
mixture plasma exposure at the interface. Theseresults suggest that oxygen radicals and/or ions
make it possible to control molecular structures atthe interface.

Fig.2. Schematic diagram of HXPES measurement(a) Without plasma exposure

Binding energy (eV)(b) With plasma exposure

4. Conclusions
Interactions between plasma with organic
semiconductors have been investigated on the basisof non-destructive depth analyses of chemicalbonding states at Ar-O2 mixture plasma exposed
Zn/Alq3 interface. The HXPES analyses of Ar-O2
mixture plasma exposed Zn/Alq3 samples indicatedthat the oxygen radicals and/or ions from the Ar-O2
mixture plasma formed oxygen functionalities atthe interface.
Acknowledgments
This work was partly supported by The Global COE
Program "Center of Excellence for Advanced
Structural and Functional MaterialsDesign" throughthe Ministry of Education, Culture, Sports, Science.
References[1] Y. Setsuhara et al., Surf. Coat. Technol. 174 – 175(2003) 33.

Binding energy (eV)Fig.3. Variation of C1s HXPES spectrum ofZn/Alq3 films (a) without and (b) withAr-O2 mixture plasma exposure.