Structures and properties of electron-beam-evaporated indium tin oxide films as studied by x-ray photoelectron spectroscopy and work-function measurements

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Abstract
Indium tin oxide (ITO) films deposited on single-crystal Si wafers by the electron-beam-(EB) evaporation method have been investigated by x-ray photoelectron spectroscopy (XPS) together with work-function and resistivity measurements. The XPS studies suggest that all the ITO films consist of crystalline and amorphous phases. The amount of the crystalline phase with respect to the amorphous phase for the ITO films, deposited with the incident angle of the ITO vapor to the Si substrate θi at 0°, is smaller than that for the ITO films deposited at θi=45°. The amount of the crystalline phase hardly depends on the conditions of postdeposition heat treatments, while that of the amorphous phase increases by raising the temperature of the heat treatments. Metal indium present in the films deposited at θi=0° is transformed into amorphous indium oxide by heating at 450 °C in air. Metal tin is also present near the ITO/Si interface for the ITO films deposited at θi=0°. The work function of the ITO films deposited at θi=0° is lower by 0.8 eV in maximum than that for the films deposited at θi=45°. It is concluded that the work function of the ITO films increases not only with a decrease in the amount of metal indium and metal tin in the films but also with an increase in the amount of the crystalline ITO phase with respect to that of the amorphous phase.