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 MoS 2, which have varied applications in low-dimensional electronics and electrocatalysts. Hydrogen sulfide (H 2 S) has been used in many sulfide ALD processes; however, H 2 S 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 MoS 2 without H 2 S. 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 H 2 S. It was found that the TBDS-based PEALD process results in layered, stoichiometric MoS 2 with limited contamination. The TBDS-based PEALD process was also analyzed via mass spectrometry to determine the mechanistic roles of each reactant. Apparently, H 2 plasma removes ligands from the chemisorbed Mo precursor, which allows TBDS to sulfurize the top layer, producing H 2 S and isobutene as byproducts. MoS 2 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 H 2 S. Thus, the TBDS-based process is a suitable and safer alternative to the H 2 S-based process for large-area synthesis of layered MoS 2 .