Wafer-scale, conformal and direct growth of MoS ₂ thin films by atomic layer deposition

Molybdenum disulfide (MoS ₂ ) thin films were grown directly on SiO ₂ covered wafers by atomic layer deposition (ALD) at the deposition temperatures ranging from 175 to 225 °C using molybdenum hexacarbonyl [Mo(CO) ₆ ] and H ₂ S plasma as the precursor and reactant, respectively. Self-limited film growth on the thermally-grown SiO ₂ substrate was observed with both the precursor and reactant pulsing time. The growth rate was ∼0.05 nm/cycle and a short incubation cycle of around 13 was observed at a deposition temperature of 175 °C. The MoS ₂ films formed nanocrystalline microstructure with a hexagonal crystal system (2H-MoS ₂ ), which was confirmed by X-ray diffraction and transmission electron microscopy. Single crystal MoS ₂ nanosheets, ∼20 nm in size, were fabricated by controlling the number of ALD cycles. The ALD-MoS ₂ thin films exhibited good stoichiometry with negligible C impurities, approximately 0.1 at.% from Rutherford backscattering spectrometry (RBS). X-ray photoelectron spectroscopy confirmed the formation of chemical bonding from MoS ₂ . The step coverage of ALD-MoS ₂ was approximately 75% at a 100 nm sized trench. Overall, the ALD-MoS ₂ process made uniform deposition possible on the wafer-scale (4 in. in diameter).