Di-tert-butyl Disulfide as a Replacement for Hydrogen Sulfide in the Atomic Layer Deposition of Two-Dimensional Molybdenum Disulfide

Atomic layer deposition (ALD), with its precise process control and conformality, has recently gained interest for synthesizing transition metal sulfides like MoS₂, which have varied applications in low-dimensional electronics and electrocatalysts. Hydrogen sulfide (H₂S) has been used in many sulfide ALD processes; however, H₂S is a toxic gas that requires expensive containment and abatement measures for shipping, installation, and storage. Herein, we report a PEALD process capable of synthesizing MoS₂ without H₂S. This process utilizes a Mo precursor commonly used in ALD, hydrogen plasma, and di-tert-butyl disulfide (TBDS), which is a liquid that is significantly less hazardous and expensive than H₂S. It was found that the TBDS-based PEALD process results in layered, stoichiometric MoS₂ with limited contamination. The TBDS-based PEALD process was also analyzed via mass spectrometry to determine the mechanistic roles of each reactant. Apparently, H₂ plasma removes ligands from the chemisorbed Mo precursor, which allows TBDS to sulfurize the top layer, producing H₂S and isobutene as byproducts. MoS₂ films deposited via the TBDS-based process possessed fewer yet taller out-of-plane growths and similar crystal grain diameter (∼10 nm) and electrical resistivity (13.6-15.5 Ω·cm for 3 nm thick films) compared to films made with H₂S.