(Invited) Low Temperature Atomic Layer Deposition Processes for Large-Area Synthesis of 2D Transition Metal Dichalcogenides

2D materials have been the focus of intense research in the last decade due to their unique physical properties. This presentation will highlight our recent progress on the large-area synthesis of two-dimensional transition metal chalcogenides for nanoelectronics using advanced atomic layer deposition cycle schemes. First, how we can use advanced cycle schemes to deposit wafer-scale polycrystalline MoS 2 thin films at very low temperatures down to 100 °C. We have identified the critical role of hydrogen during the plasma step in controlling the composition and properties of molybdenum sulfide films. By increasing the H 2 /H 2 S ratio or adding an extra hydrogen plasma step to our ALD process, we are able to deposit pure polycrystalline MoS 2 films at temperatures as low as 100 °C. To the best of our knowledge, this represents the lowest temperature for crystalline MoS 2 films prepared by any chemical gas-phase method.[1] The most dominant methods for preparing MoS 2 via ALD is to alternately expose a substrate to a metalorganic precursor and a hydrogen sulfide (H 2 S) or a plasma containing H 2 S. H 2 S is a corrosive, toxic, and flammable gas that is heavier than air, which makes it hazardous and expensive to store, install, and transport. Alternative sulfur precursors in the solid or liquid phase would be beneficial in terms of cost and safety and would require the installation of no additional hardware for most ALD reactors. In the second half of this contribution, the widely researched ALD process using bis(tert-butylimido)bis(dimethylamino)molybdenum(IV) (( t BuN) 2 (NMe 2 ) 2 Mo) and H 2 S plasma is compared to a novel ALD process using ( t BuN) 2 (NMe 2 ) 2 Mo, hydrogen plasma, and di-tert-butyl disulfide (TBDS), which is an inexpensive, liquid-phase sulfur precursor. [1] M. Mattinen et al., Chem. Mater . (2022), 34 , 5104