Tin doped indium oxide films have been deposited on PET substrates by an reactive magnetron sputtering method using a In-10at%Sn alloy target. Oxygen gas and argon gas were introduced near the substrates and the target in order to reduce target oxidation. The films ranged in thickness from 500 Å to 1500 Å. The films were deposited in the mixed gas of Ar and $O_2$ at a total pressure of 2 mTorr and 5 mTorr.
The effects of the oxygen partial pressure, working pressure and rf bias power applied to the substrates on the electrical and optical properties of ITO films were investigated. The substrates were not intentionally heated and the surface temperature of the substrates reached about 40℃ when the rf bias of 160W was applied to the substrates for 4 minutes. The films made by the above mentioned methods had amorphous structure.
As the oxygen flow rate increased, the resistivity of films decreased until the resistivity reached about $6×10^{-4}Ωcm$ which was the lowest value when the working pressure was 2 mTorr and the resistivity reached about $1×10^{-3}3Ωcm$ when working pressure was 5 mTorr. With further increase of oxygen flow rate, the resistivity of the ITO films increased again in the both cases. The visible light transmittance increased monotonously to about 80% as oxygen flow rate increased and saturated at this value.
Even at low oxygen flow rate which the target were kept metallic state and opaque ITO films were obtained, the ITO films with about 70∼80% transmission and about $1~2×10^{-3}Ωcm$ were produced by applying the rf substrate bias of between 20W and 160W during the deposition. The electrical and optical properties are strongly dependent on the applied rf power to the substrates. The resistivity of the ITO films that were deposited at the oxygen flow rate lower than 1.0 sccm decreased with rf bias power and reached a minimum value when working pressure was 2mTorr. With further increase of rf power the resistivity increased again. At the high oxygen flow rate higher than 1.1 sccm, the resistivity monotonously increased as increasing rf power.
Electron concentration measured by a Van der Pauw method increased with rf power and reached a maximum value when the oxygen flow rate was between 0.9 and 1.0 sccm. Electron concentration decreased again with further increase of rf power. From oxygen concentration in ITO films measured by X-ray photoelectron spectroscopy, it is concluded that the metal ion to oxygen ratio in films are a dominant factor for the resistivity of ITO films. Hall mobility decrease with increasing rf bias power. From Scanning electron microscope images, it is found that the decrease of Hall mobilities with rf bias was caused by the change of the surface morphology which may be associated with change of chemical properties of PET substrates by the positive ion bombardments. Mean transmission in the visible region increased with increasing rf bias power at the low oxygen flow rate.
