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 degrees 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.