Atomic Layer Deposition of Molybdenum Disulfide Films Using MoF₆ and H₂S

Molybdenum sulfide films were grown by atomic layer deposition on silicon and fused silica substrates using molybdenum hexafluoride (MoF₆) and hydrogen sulfide at 200 °C. In situ quartz crystal microbalance (QCM) measurements confirmed linear growth at 0.46 Å/cycle and self-limiting chemistry for both precursors. Analysis of the QCM step shapes indicated that MoS₂ is the reaction product, and this finding is supported by x-ray photoelectron spectroscopy measurements showing that Mo is predominantly in the Mo(IV) state. However, Raman spectroscopy and x-ray diffraction measurements failed to identify crystalline MoS₂ in the as-deposited films, and this might result from unreacted MoF_x residues in the films. Annealing the films at 350 °C in a hydrogen rich environment yielded crystalline MoS₂ and reduced the F concentration in the films. Optical transmission measurements yielded a bandgap of 1.3 eV. Finally, the authors observed that the MoS₂ growth per cycle was accelerated when a fraction of the MoF₆ pulses were substituted with diethyl zinc.