Lithographic Damage to Two Dimensional Materials Probed by Photoluminescence and Raman Spectroscopy

To probe the electronic and optical properties of two-dimensional (2D) materials, electron beam (e-beam) lithography is often employed to pattern gates or contacts, which requires high energy particle bombardment during the exposure process. In this work, we present evidence of dose-dependent defect creation in monolayer MoS₂ and WSe₂ using photoluminescence (PL) and Raman spectroscopy. These defects introduce states within the band gap which cause sub-bandgap energy signatures in the PL spectra at T = 5 K. Additionally, we compare three accelerating e-beam voltages (10 kV, 50 kV, 100 kV) to show that this damage occurs regardless of the incident electron energy and in both monolayer MoS₂ and WSe₂. Defect creation is shown to be mitigated at or below doses of 25 μC/cm²; however, this is a lithographic dose far lower than those typically required to clear conventional resists such as PMMA during development. To mitigate this trade-off between defect creation and resist residue from insufficient dosing, we demonstrate a new low-damage lithographic process whereby we utilize multi-pass e-beam patterning. Raman spectroscopy confirms that this process mitigates damage of 2D materials compared to conventional processing. Our work employs spectroscopic techniques to demonstrate the importance of optimizing lithography for higher performance optical and electronic devices in 2D materials.