Back-End-of-Line-Compatible Passivation of Sulfur Vacancies in MoS₂ Transistors Using Electron-Withdrawing Benzenethiol.

Abstract

Atomically thin two-dimensional semiconductor molybdenum disulfide (MoS₂) is considered an ideal n-type channel material for field-effect transistors (FETs) due to its immunity to short-channel effects by dangling bond-free surface. However, sulfur atom dissociation or nonideal film deposition can easily lead to sulfur vacancies (SVs) in the MoS₂ film. These crystal imperfections create defects in the electronic structure, thereby limiting the utility of this promising material. We introduce an electron-withdrawing benzenethiol (BT) to repair the vacancies with the exact missing atoms at 200°C─marking the lowest process temperature for complete SV repair. These thiol groups actively and selectively bond with the vacant sites due to their self-assembly nature. Notably, we found that the fluorination of BT weakens the S-C bond as the BT withdraws electrons from the sulfur side. This enables a low-temperature annealing process to detach the headgroups from the MoS₂ surface. The atomic ratio of MoS₂ was recovered from 1.68 to 1.98, leading to an ideal subthreshold swing of MoS₂ FETs 62.5 mV·dec^-1. The proposed SV repair process, repeatedly applicable between fabrication steps for its low process temperature, unveils the potential of the BEOL MoS₂ FETs with a nearly ideal atomic ratio adhering to their thermal budget.