Multi-layered MoS2 film formed by high-temperature sputtering for enhancement-mode nMOSFETs

A multi-layered MoS2 film was formed on a SiO2 film by high-temperature sputtering, which is one of the alternative methods of Si LSI technology. It was found that the carrier density of a sputter-deposited MoS2 film is 1000 times smaller than that of an exfoliated one. By sputtering, two different orientations, namely a layer lateral to a SiO2/Si substrate and a layer perpendicular to the substrate, were formed. The lateral layer showed a lower carrier density than the perpendicular layer because of the decrease in the number of sulfur vacancies, as commonly discussed in several research studies. However, the vacancies are not sufficient for describing this significant reduction in carrier density. It is considered that a sodium ion functioning as an interface trapped charge is one of the main origins of carriers. Sputtering, which enables us to determine the sodium contamination level, can be seen as appropriate for reducing the carrier density; hence, this method is considered to be efficient in realizing enhancement-mode MoS2 MOSFETs. In addition, sputtering also enable us to form large-scale MoS2 films up to a wafer size. Therefore, a sputter-deposited MoS2 film is a promising material for post-silicon devices.