MoS2 was deposited on SiO2 substrate by RF sputtering. The substrate temperature was varied from 250°C to 600°C. Ar partial pressure was also varied from 0.09 to 1.0 Pa with RF power of 50 to 225 W. The sputtering duration was fixed to 600 s. In order to investigate the effect of the sputtering parameters, the sputter-deposited MoS2 flms were evaluated with X-ray electron spectroscopy (XPS) to confirm Mo-S bond formation. The S/Mo ratio of the film was calculated from the ratio of Mo 3d and S 2p spectra. The samples with elevated deposition temperature were evaluated with Raman spectroscopy and compared to the as-depo. sample and the PDS sample [4].
As a result of applying bias voltage, higher positive bias voltage yielded films with higher S/Mo. Stoichiometric S/Mo ratio of 2.0 was achieved by applying positive bias voltage even with high-temperature sputtering. This is considered to be the attracting effect of S2- to the substrate due to the positive bias. When the Ar partial pressure was increased, the S/Mo ratio decreased. This result shows that the mean free path of the sputtered particles have large effect on the amount of S2- reaching the substrate determining S/Mo ratio of the film. As the sputter RF power was increased S/Mo also increased, which may also provide larger Mo migration energy, therefore result in the better crystallinity. By optimizing each sputtering parameters, S/Mo of 2.0 was achieved at 400-600°C.
This work was partly supported by JST CREST Number JPMJCR16F4, Japan. This work was also partly supported by JSPS KAKENHI Grant Number 16J11377.
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