Fabrication of zirconium oxide films by reactive HiPIMS combined with multi pulse magnetron sputtering

抄録

1. Introduction

Reactive magnetron sputtering, which is one of physical vapor deposition techniques, has been widely used to fabricate metal oxides such as titanium oxides, vanadium oxides, and tungsten oxides, due to its versatility and possibility of large-scale fabrication. In reactive magnetron sputtering with a metal target, Ar gas is generally employed as an ambient gas, whereas oxygen gas is used as the reactive gas. Both the deposition rate and the film properties significantly are sensitive to the mixing ratio of the reactive gas such as oxygen gas in reactive magnetron sputtering including reactive high-power impulse magnetron sputtering (HiPIMS). Reactive HiPIMS system with a pulsed oxygen gas flow control has been proposed to deposit metal oxide films [1,2], indicating the usefulness for the deposition in a transition region close to the metallic mode. However, there seems to be a room to research the growth of metal oxide thin films with a high degree of control and good reproducibility. In this study, we propose a HiPIMS combined with reactive multi pulse magnetron sputtering (mPMS) with a low target current and fabricate zirconium oxide film, which is characterized by wear resistance, large band gap and wide spectral transparency range.

2. Experiment

The magnetron sputtering system with a zirconium target with 76 mm diameter was set in a cylindrical vacuum chamber with 150 mm inner diameter and 280 mm height. The distance between the substrates (Si and glass) and the target was 70 mm. The flow rate of Ar gas was about 15 sccm, whereas the oxygen gas flow rate was 0.23 sccm. Then, the total gas pressure was 0.7 Pa. Figure 1 shows the typical waveform of the target current in HiPIMS combined with mPMS, where the pulse number N of mPMS is 7. The maximum of instantaneous power reached about 17 kW in HiPIMS and 1 kW in mPMS, respectively. The repetition rate was 400 cycle/s.

3. Results and Discussion

Figure 2 shows the deposition rate as a function of N. The deposition rate linearly increased from 0.9 nm/min at N=0 to 1.6 nm at N=6 with the increase in the pulse number N, and then it abruptly increased. This may be caused by the change in the rate of the oxide cover on the target surface (target poisoning). In other words, this result may indicate that the deposition process, which is classified into three regions such as metallic region, transition region and metal oxide region, can be controlled by changing the pulse number of mPMS. In the XRD patterns for the films fabricated at various N, a weak peak at about 28°, which is attributed to (11-1) preferred orientation of ZrO₂, was observed. The weak XRD peak observed for the films fabricated at N≦6 suggested that films were nano-crystallized.

4. Conclusion

Reactive HiPIMS combined with multi pulse magnetron sputtering can be expected to be suitable for fabricating metal oxide films such as zirconia and to achieve the control of film property depending on the pulse number of pulse magnetron sputtering.

Acknowledgements

This work is partially supported by JSPS KAKENHI Grant Number JP23K03817.

References

[1] N-W Pi, M. Zhang, J. Jiang, A. Belosludtsev, J. Vlček, J. Houška and E. I. Meletis, Thin Solid Films, 619 ,239 (2016).

[2] J. Houška, D. Kolenatý J. Vlček, and R. Čerstvý, Thin Solid Films, 660, 463 (2018).