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 (similar to 10 nm) and electrical resistivity (13.6-15.5 Omega<middle dot>cm for 3 nm thick films) compared to films made with H2S. Thus, the TBDS-based process is a suitable and safer alternative to the H2S-based process for large-area synthesis of layered MoS2.