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

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 ∼0.05nm/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, ∼20nm in size, were fabricated by controlling the number of ALD cycles. The ALD-MoS2 thin films exhibited good stoichiometry with negligible C impurities, approximately 0.1at.% 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 100nm sized trench. Overall, the ALD-MoS2 process made uniform deposition possible on the wafer-scale (4in. in diameter).