Structural Evolution of Molybdenum Disulfide Prepared by Atomic Layer Deposition for Realization of Large Scale Films in Microelectronic Applications

Molybdenum disulfide (MoS₂) films are attractive materials for electronic and optoelectronic devices, but the temperatures used in the chemical vapor deposition (CVD) of these materials are too high for device integration. Recently, a low-temperature atomic layer deposition (ALD) process was demonstrated for growth of MoS₂ films at 200 °C using MoF₆ and H₂S. However, the as-deposited films were amorphous and required annealing to obtain the desired layered structure. The MoS₂ films were sulfur-deficient; however, after annealing the crystallinity improved. To study the structure of these films and the process by which they crystallize, we performed X-ray absorption spectroscopy and high-energy X-ray scattering experiments on both as-deposited and annealed MoS₂ films. Analysis indicated that molybdenum atoms in the as-deposited films were well coordinated with sulfur but not well coordinated with other molybdenum atoms when compared to a crystalline reference. Further analysis revealed clusters of the sulfur-rich phase [Mo₃S(S₆)₂]^2-, which decomposed after annealing in H₂ and H₂S at 400 and 600 °C. When compared to the sulfur-deficient films reported previously for this ALD process, the sulfur-rich phase found here indicates that nucleation on the substrate plays an important role in the resulting film stoichiometry, which could be tuned to produce higher quality films for microelectronic applications.