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 MoFx 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.