| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Film Poster Session |
| Presenter: | Yuki Yokoiwa, Kitami Institute of Technology, Japan |
| Authors: | Y. Yokoiwa, Kitami Institute of Technology, Japan Y. Abe, Kitami Institute of Technology, Japan M. Kawamura, Kitami Institute of Technology, Japan K.H. Kim, Kitami Institute of Technology, Japan T. Kiba, Kitami Institute of Technology, Japan |
| Correspondent: | Click to Email |
Reactive sputtering is one of the most commonly used techniques for obtaining compound thin films. It is well known that target mode change is very important in reactive sputtering, because the change in the target surface state induces drastic changes in the deposition rate. In the previous study, we reported that the reactive sputtering with substrate cooling and water vapor injection was promising technique to obtain Ni oxide thin films with high-rate deposition. We speculated that the high deposition rate was realized by metallic target state. In the present study, we investigated the target state in more detail using plasma emission spectroscopy and target voltage measurements.
Ni oxide thin films were formed by a RF magnetron sputtering system. Substrate temperature was varied from room temperature (RT) to -80 °C. Ni metal target was sputtered in Ar and H2O sputtering gas atmosphere, and the flow ratio (H2O/(H2O+Ar)=RH2O) was varied from 0 to 100%. H2O was injected onto the target surface. Target voltage and plasma emission spectrum were measured to investigate the target surface state during sputter deposition. Film thickness was measured using a stylus profiler. The deposition rate was calculated from the film thickness and sputtering time. The optical and electrical properties of the films were studied by UV-Vis spectroscopy and four-point prove method.
At RT, deposition rate decreased from 15-20 nm/min to 4 nm/min above RH2O=20%. On the contrary, at -80 °C, deposition rate increased monotonously with increasing RH2O, and a maximum deposition rate of 35 nm/min was obtained at RH2O=50%, which was approximately 8 times larger than that at RT. Corresponding to the change of the deposition rate, target voltage decreased abruptly from 330 V to 190 V above RH2O=20% at RT when RH2O was increased gradually. In contrast, target voltage maintained a high value of 290-330 V at -80 °C. Plasma emission spectra indicated that emission peaks due to Ni atoms disappeared at RT above RH2O=20%, however, the peaks were clearly observed regardless of the change of RH2O at -80 °C. These results indicate that the Ni target changed from metallic mode to oxide mode above RH2O=20% at RT, however, metallic target mode was maintained at -80 °C.
The optical and electrical properties of the films were studied. The films deposited at substrate temperatures of RT and -80 °C below RH2O=10% have metallic character. And transparent and insulating Ni oxide films were obtained above RH2O=20% at both the substrate temperatures.
In summary, reactive sputtering of Ni oxide thin films in metallic target mode was realized using substrate cooling and water vapor injection.