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The unique structures of metal nitrides and silicides allow these materials to exhibit highly attractive physical and chemical properties, some of which include high hardness, low electrical resistivity, high-temperature stability, and chemical compatibility. Although common deposition methods for metal nitride films include vacuum arc evaporation, direct (DC) or radio frequent (RF) magnetron reactive sputtering, a 2019 Coatings paper discussed how an expanding plasma process proved to be superior.
Improving Thin Metal Film Properties
The chemical reactions that occur in thin metal films during their production allow for specific properties to be attained when these films are incorporated into final products, such as supercapacitors or solar cells.
Production techniques that allow for the development of multilayer films of transition metals, such as Ti-Mo systems, have been shown to exhibit greater electron transportation capability, capacitance, and high cycling stability; each of which are crucial properties for supercapacitor electrode materials.
The study discussed here demonstrated that thermochemical treatment of both nitrides and silicides in Mo-Ti bilayer films in expanding plasma gas mixtures supported the crystallization and growth of various phases, including Ti nitrides and Mo silicides.
The Expanding Plasma Process
In this work, the researchers deposited both Mo and Ti films on Si(100) wafers in an electron beam evaporator that was filled with argon (Ar) gas. With a total thickness equivalent to 250 nanometers (nm) each, the Mo-Ti bilayer films were then placed onto a heating substrate holder to allow the plasma nitriding process to occur. As the heat increased to as high as 800 °C, the Ar gas mixture was introduced into the vacuum chamber for three different time points: 1 hour, 1 hour and 30 minutes and 3 hours.
To evaluate the phase compositions and crystallization of the Mo-Ti bilayer films following completion of the expanding plasma process, the researchers utilized both X-ray diffraction (XRD) and Raman spectroscopy techniques. The XRD investigations demonstrated that TiN began to crystallize at 600°C, during which small crystallites were formed within the Mo-Ti layers. This phenomenon was hypothesized to occur as a result of the presence of Mo films between the Ti and Si layers.
When the substrate temperatures reached 800 °C, MoSi2 layers appears to crystallize at 1 hour and 30 minutes. Overall, the more considerable amount of time that the films were exposed to the plasma process resulted in a more significant amount of growth of both the TiN and MoSi2 layers. The obtained Raman spectra provided similar results which indicated a well-structured signal of the Mo-Ti bilayer film when processed at 600 °C for 1 hour and 30 minutes.
Conclusion
Overall, the results of this study demonstrated that the Mo-Ti bilayer film components, when coated on a Si wafer, exhibited a strong ability to diffuse across various interfaces when heated to both 600 °C and 800 °C and exposed to an Ar gas mixture.
Although the researchers anticipate that more studies will need to be performed to fully evaluate how the growth of both nitrides and silicides can be improved, the work presented here supports the use of an expanding plasma process for this purpose.
References
- Jauberteau, I., Mayet, R., Cornette, J., Carles, P., Manging, D., Bessaudou, A., et al. (2019). Expanding Plasma Process for Nitriding Mo-Ti Bilayer Thin Films. Coatings 9(96). DOI: 10.3390/coatings9020096.
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