Unravelling chemical etchant influences during assisted wet-transfer to obtain high quality MoS2 atomic layers

Two-dimensional (2D) MoS2 is an emerging alternative to traditional semiconductors, overcoming scaling limits in device fabrication. Ongoing efforts to realize the full potential of 2D MoS2 in CMOS back-end-of-line integration encounters notable challenges due to synthesis of such 2D materials requiring high temperature growth substrates and a transfer step. Consequently, lattice preservation of MoS2 atomic layers during transfer from growth substrate to a target substrate is crucial for fabrication and system integration. This work, investigates the impact of commonly used chemical etchant potassium hydroxide (KOH) on MoS2 during the poly(methylmethacrylate) (PMMA) assisted wet-transfer process from sapphire substrates. A systematic experimental framework involving Raman spectroscopy, Atomic Force Microscopy (AFM), Optical Microscopy, and X-ray Photoelectron Spectroscopy (XPS) was employed for comparative evaluation of MoS2 upon transfer. While the investigations highlight the relation of etchant concentration and exposure time to be the deterministic factors, topographic and spectroscopic evidence corroborate the role of K+ ions in etching and oxidation of MoS2 at higher concentrations affecting the MoS2 quality. Thorough characterizations of transfer process, while following the MoS2 quality in this work, provides crucial information on etchant concentration selection to achieve shorter substrate transfer time with minimal impact on material quality.