Kikuo Tominaga

Influence of Energetic Oxygen Bombardment on Conductive ZnO Films

Conductive ZnO films were prepared by DC planar magnetron sputtering and DC diode sputtering, and the reason for the high resistivity shown by the films at the substrate positions facing the eroded area of the target was investigated. It was found that bombardment of the film by energetic O atoms or O- ions is responsible for the high film resistivity, since this results in a decrease in both the carrier mobility and the carrier concentration. The arrival of excess O atoms and O- ions with relatively lower energies also induces an increase in the film resistivity as a result of a decrease in carrier concentration. The positional dependence of the film resistivity is explained by considering the above two factors.

Radiation Effect due to Energetic Oxygen Atoms on Conductive Al-Doped ZnO Films

Al-doped ZnO films were prepared by both RF planar magnetron and RF diode sputterings. The dependence of the ZnO film resistivity on both substrate position and Ar gas pressure was investigated. Energetic oxygen atoms (O atoms) bombarding the film were also observed by time-of-flight apparatus, and the correlation between the film resistivity and the film bombardment by the energetic O atoms was examined. The following results were obtained: When the bombardment of energetic O atoms on Al-doped ZnO films became significant at the substrate positions facing the eroded area of the target, the film resistivity increased at the same positions. Then, both the carrier concentration and Hall mobility of the Al-doped ZnO films were decreased, which was thought to be due to the film bombardment by the energetic O atoms.

Energy Analysis of High-Energy Neutral Atoms in the Sputtering of ZnO and BaTiO3

The time-of-flight method has been employed to investigate the type and energy of high-energy neutral atoms bombarding the substrates in films of ZnO and BaTiO3 prepared by both DC planar magnetron sputtering and conventional DC diode sputtering. The high-energy neutral atoms are found to be oxygen atoms. The dependence of the flux of high-energy neutral oxygen atoms and negative oxygen ions on the pressure has also been measured for the planar magnetron sputtering of ZnO. It is shown that the high-energy particles bombarding the substrate are composed of neutral oxygen atoms at higher gas pressures ranging above 0.01 Torr, but negative oxygen ions are comparable with neutral oxygen atoms at pressures of the order of 10-3 Torr. The production mechanism of these energetic oxygen species is discussed.

Transparent conductive ZnO film preparation by alternating sputtering of ZnO:Al and Zn or Al targets

Abstract Multilayered ZnO:Al and ZnO:O v film was prepared by alternately sputtering ZnO:Al(2% wt.) and Zn targets. The films obtained were optically transparent and had lower resistivity than those prepared by ZnO:Al sputtering. Deposition from the Zn target gave a ZnO film containing native donors (a ZnO:O v film). The carrier concentration increased in the ZnO:Al/ZnO:O v multilayered film. Our results cannot be explained by the redistribution of the carrier between ZnO:Al and ZnO:O v . This result indicates an improvement in the doping efficiency. Multilayered films of ZnO:Al and Al oxide compounds were also prepared. In this case, with increasing thickness of the Al oxide film, a decrease was observed in the carrier mobility, due to the scattering at the interface.

Preparation of conductive ZnO:Al films by a facing target system with a strong magnetic field

Abstract Transparent conductive ZnO:Al films were prepared in Ar gas by a planar magnetron sputtering system with facing targets, where strong internal magnets were contained in target holders to confine the plasma between the targets. A film resistivity of 4 × 10 −4 Ω cm was attained at a substrate temperature of 200 dgC. However, the film resistivity increased with increasing substrate temperature, due to a decrease of the carrier concentration. The reason for this phenomenon was the decrease of Zn donors in the film as native donors or an increase of Zn defects. When excess Zn atoms were supplied during film growth, a low resistivity of 2 × 10 −4 Ω cm was obtained even at a substrate temperature of 250 °C.

High-Energy Neutral Atoms in the Sputtering of ZnO

Dips were observed in the distribution curves of the deposition rates of ZnO films prepared both by planar diode and by planar magnetron sputtering. These dips are ascribed to high-energy neutral atoms bombarding the films. The influence of high-energy neutral atoms on the mixed orientation of ZnO film is also investigated in planar diode sputtering. In planar magnetron sputtering, which gives highly [002] oriented ZnO films, the correlation between the degree of c-axis orientation and the flux of high-energy neutral atoms is examined. It is found that high-energy neutral atoms should be considered when trying to obtain highly-oriented ZnO films.

Transparent ZnO:Al films prepared by co-sputtering of ZnO:Al with either a Zn or an Al target

Abstract A ZnO:Al target was sputtered concurrently with additional Zn or Al, by co-sputtering it with either a Zn or an Al target. The influence of the deposition of these additional atoms on the ZnO:Al film properties was investigated. When co-sputtering the Zn target, the film resistivity shows a minimum for an adequate supply of Zn. With this supply of Zn, both the carrier concentration and the Hall mobility show maxima, and the optical transmittance and absorption edge are improved. When co-sputtering with the Al target, the carrier concentration alone is increased. These results indicate that there is a considerable Zn deficiency in the ZnO:Al films prepared in pure Ar gas, and additional Zn or Al atoms during film deposition can compensate for these Zn defects, in addition to the increased donor concentration in the film.

Film properties of ZnO:Al prepared by cosputtering of ZnO:Al and either Zn or Al targets

ZnO:Al and ZnO with oxygen vacancies (ZnO:OV) films were prepared by co-sputtering Zn and either ZnO:Al (Al2O3 2 wt %) or ZnO. The influence of the additional Zn supply on ZnO:Al film properties was investigated and compared with the data of ZnO:OV films. The additional Zn supply improved the film crystallinity and reduced the film resistivity. This was ascribed to the decrease of defects in ZnO:Al films due to the improvement of crystallinity, because the maximum carrier concentration in a ZnO:OV film was much smaller than that in a ZnO:Al film where the carrier concentration was created by Al donors. ZnO:Al films prepared by co-sputtering of ZnO:Al (2 wt %) and either ZnO:Al (6 wt %) or Al targets were also investigated. The doping of Al donors, in the first case, decreased the carrier mobility and increased the carrier concentration, in the second case, the carrier mobility increased with further doping.

Effects of nitrogen pressure and ion flux on the properties of direct current reactive magnetron sputtered Zr–N films

Zr–N films have been deposited by direct current reactive magnetron sputtering using a plasma emission monitoring (PEM) control system, where a signal proportional to the light emitted by the sputtered Zr in the plasma created by the electrical discharge was used to control the admission of the reactive nitrogen into the system. The Zr line set point for PEM control, φ, was used as a parameter; as the partial pressure of nitrogen rises the Zr line emission falls due to target poisoning. The influence of the nitrogen partial pressure on the Zr–N film structure, reflectivity, resistivity, and internal stress was investigated. The effect of ion flux during film deposition on the film properties was also investigated. The Zr–N films deposited at the Zr line set point φ=60%–70% revealed the minimum resistivity and goldlike reflectivity spectra. These films showed a ZrN single phase. The internal stress of the films showed a maximum at φ=60%–70%, which corresponds to the condition for depositing minimum resisti...

Energetic particles in the sputtering of an indium–tin oxide target

Energetic negative ions and neutral atoms were simultaneously observed using a time‐of‐flight apparatus during indium–tin oxide (ITO) film preparation by conventional planar magnetron sputtering of an ITO target. The sputtering was performed in pure Ar gas and compared with ZnO: Al sputtering. Energetic particles such as O− and O−2 ions and neutral O atoms were detected in the time‐of‐flight spectra, although the flux intensity of these particles was much less than that found in the ZnO sputtering. It was also found that other particles exist at the same time, which were thought to be reflected Ar atoms or O−3 ions from the target surface. However, the flux intensity of these particles was found to be less than that of the energetic O− ions and O atoms. The strong energetic particles, which primarily bombarded the substrate during the ITO sputtering were found to be energetic O− ions and O atoms.