Wafer-scale, conformal and direct growth of MoS₂ thin films by atomic layer deposition

Graphical abstract: - Highlights: • The formation of pure and stoichiometric MoS₂ thin film by atomic layer deposition (ALD). • ALD of MoS₂ using Mo(CO)₆ and H₂S plasma. • Large-area (4 in. in diameter) and direct growth of MoS₂ thin films and nanosheets by ALD. • Remarkable step coverage at 100 nm trench. - Abstract: Molybdenum disulfide (MoS₂) thin films were grown directly on SiO₂ covered wafers by atomic layer deposition (ALD) at the deposition temperatures ranging from 175 to 225 °C using molybdenum hexacarbonyl [Mo(CO)₆] and H₂S plasma as the precursor and reactant, respectively. Self-limited film growth on the thermally-grown SiO₂ 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 MoS₂ films formed nanocrystalline microstructure with a hexagonal crystal system (2H-MoS₂), which was confirmed by X-ray diffraction and transmission electron microscopy. Single crystal MoS₂ nanosheets, ∼20 nm in size, were fabricated by controlling the number of ALD cycles. The ALD-MoS₂ 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 MoS₂. The step coverage of ALD-MoS₂ was approximately 75% at a 100 nm sized trench. Overall, the ALD-MoS₂ process made uniform deposition possible on the wafer-scale (4 in. in diameter).