Wafer-Level Fabrication and Characterization of Amorphous Thin Films MoS2 Prepared by RF Magnetron Sputtering Technique
Authors: Gustavsen Kim R , Nygård Ken A , Honerød-Bentsen Preben , Du Kang , Liu Guohua , Tayyib Muhammad , Breiby Dag W , Weibye Kristian , Nilsen Ola , Aasmundeveit Knut E , Wang Kaiying 
Published: February 2020

Thin film molybdenum disulfide (MoS2) is an important semiconducting material, with unique physical and chemical properties. It is a promising candidate for potential applications in energy conversion, optoelectronics and field-effect transistors [1,2]. A proper fabrication technique capable of mass-producing large-area thin film MoS2 is vital. In this paper, we present a study of wafer-level process for deposition of thin films MoS2 by radio frequency (RF) magnetron sputtering technique, which is a typical method for large-scale thin film production. The deposition parameters vs film stoichiometry, morphology, optical and electrical properties have been investigated on glass, silicon and quartz substrates respectively.
Thin film deposition was performed in Argon atmosphere with pressure around 10-3 to 10-4 Torr, RF power between100-250 W and temperature from room temperature up to 250°C. The thin films with thickness from 5 to 100 nm were prepared under 150°C and 150 W. Figure 1a shows a digital camera photograph of the thin films MoS2 on quartz substrate and patterned silicon chips. From top-left to right, the color of thin films MoS2 are changed gradually from highly transparent to slightly grey color that progressively turns opaque and finally shows a dark brown color for the thickest film. The absorbance spectra (200 - 850 nm) confirm that thicker films result in higher absorption (Figure 1b). X-ray diffraction indicates that the thin film is amorphous, as shown in Figure 1c and their ratio of element molybdenum to Sulphur is close to chemical formula MoS2 (figure 1c inset). Surface morphology of the thin films MoS2was continuous with low roughness (± 3 nm, atomic force microscopy) [3,4]. The electric properties of the amorphous thin films are to be recorded on the patterned substrates from 5 K to room temperature.
In conclusion, we have demonstrated a wafer-scale fabrication for amorphous MoS2 films by RF magnetron sputtering technique. Morphology, optical and electrical properties of amorphous thin film with thickness from 5 to 100 nm have been studied on glass, silicon, and quartz substrates respectively. The thin films are continuous at the thickness 5-100 nm with low roughness, which might be a potential candidate of large-scale production for advanced electronics or sensor applications.

Note: The students KAN, KRG and PHB have equal contributions to this paper.

References

[1] Butler, S., Hollen, S., Cao, L., Cui, Y., Gupta, J., Gutiérrez, H., Heinz, T., Hong, S., Huang, J., Ismach, A., Johnston-Halperin, E., Kuno, M., Plashnitsa, V., Robinson, R., Ruoff, R., Salahuddin, S., Shan, J., Shi, L., Spencer, M., Terrones, M., Windl, W. and Goldberger, J. (2013). Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano, 7(4), pp.2898-2926.
[2] Zhang, G., Liu, H., Qu, J. and Li, J. (2016). Two-dimensional layered MoS2: rational design, properties and electrochemical applications. Energy Environ. Sci.DOI: 10.1039/C5EE03761A
[3] Tao, J., Chai, J., Lu, X., Wong, L., Wong, T., Pan, J., Xiong, Q., Chi, D. and Wang, S. (2015). Growth of wafer-scale MoS2 monolayer by magnetron sputtering. Nanoscale, 7(6), pp.2497-2503.
[4] Ling, Z., Yang, R., Chai, J., Wang, S., Leong, W., Tong, Y., Lei, D., Zhou, Q., Gong, X., Chi, D. and Ang, K. (2015). Large-scale two-dimensional MoS2 photodetectors by magnetron sputtering. Opt. Express, 23(10), p.13580.

Figure 1