Thermodynamic Modeling of WCOHS System for Controlled Growth of WS2 Atomic Layers by True CVD

A detailed thermodynamic analysis of the solid and gas phases for the W-C-O-H-S system, used for large area chemical vapor deposition (CVD) of WS₂, is presented and compared with experimental results. Given the multivariable nature of the problem, good agreement is observed. CVD phase diagrams which predict parameter windows in which pure WS₂ can be synthesized have been provided for important gas phase chemistries. Pure H₂ as a carrier gas is shown to facilitate the largest contamination free process window. The ability to predict completely different outcomes on using Ar versus (Ar+H₂) mixture or pure H₂ as the carrier gas highlights the importance of such thermodynamic modelling. Comparison of these results with a similar system Mo-C-O-H-S has been performed, which indicates some differences in stability windows, but follows similar trends.