First-Principles Calculation Guided High-Purity Layer Control of 4 in. MoS₂ by Plasma RIE

Abstract

Two-dimensional molybdenum disulfide (MoS2) is one of the most promising candidates for next-generation semiconductors. Among the advantages offered by MoS2, a tunable bandgap that depends on the thickness is essential for the on-demand manufacturing of nanoelectronics. For this reason, elaborate layer control of MoS2 has been a long-standing research objective. However, prior efforts had several critical issues including surface roughness, poor uniformity/scalability, and impurities. Through this study, we aimed to achieve both ultrahigh precision and purity in large-scale (4 in.) layer control of MoS2 by two consecutive plasma processes: plasma-enhanced chemical vapor deposition (PECVD) and reactive ion etching (RIE). The 4 in. wafer-scale MoS2 was synthesized by PECVD, and the as-grown bulk layers were etched using RIE with a computationally screened gas mixture in the cyclic step. For every RIE cycle, the 4 in. MoS2 wafer was evenly etched to a thickness of 0.3–0.4 nm while there was no damage to the atomic structure and chemical impurities. For the computational screening of candidate gases, first-principles calculations explored the energetics of surface reaction and offered physical insights into the associated electronic interaction. The combination of computational screening and experimentation accelerates optimal process design and provides an in-depth understanding of the plasma–surface interactions.

Machine Learning-Based Prediction of Atomic Layer Control for MoS2 via Reactive Ion Etcher

“…The etching of MoS 2 films was carried out using an Ar + CF 4 + O 2 gas mixture, with the gas mixing ratio and chamber conditions precisely controlled to establish optimal etching conditions. Specific details about MoS 2 etching can be found in previous studies [7,17].…”

“…Moreover, numerical analysis offers the ability to evaluate the impact of different process conditions on the final device performance, aiding in the design and development of advanced semiconductor devices. As a result, the integration of numerical analysis and simulation techniques into the investigation of etching processes facilitates process control and accelerates technology innovation [6,7].…”

Plasma Processing and Treatment of 2D Transition Metal Dichalcogenides: Tuning Properties and Defect Engineering

“…274,620 Recent studies have revealed that a combination of Ar + CF 4 + O 2 plasma gases in an ICP-RIE process can effectively minimize the presence of F residue and maintain the original conductivity of MoS 2 while enhancing the etching peel-off ability. 640 Such a method is capable of achieving a remarkable thickness reduction from bulk (4L) down to a monolayer with high uniformity and a precise layer-by-layer control on a 4-in. 640 Atomic layer etching (ALE) is an alternative process that can be used to precisely control the number of TMD layers without introducing damages or contaminations.…”

“…640 Such a method is capable of achieving a remarkable thickness reduction from bulk (4L) down to a monolayer with high uniformity and a precise layer-by-layer control on a 4-in. 640 Atomic layer etching (ALE) is an alternative process that can be used to precisely control the number of TMD layers without introducing damages or contaminations. The process consists of two steps including (i) radical-adsorption (e.g., •Cl) and (ii) reacted-compound desorption by employing a lowenergy Ar plasma.…”

“…Moreover, while the presence of ·Cl radicals on the MoS 2 surface triggers fluorine adsorption, O radicals in a MoS 2 structure significantly suppress it, preventing any possible electrical degradation caused by remaining F species after etching. It has been demonstrated that the accurate and clean MoS 2 thinning process by using an Ar + CF 4 + O 2 combinational environment originates from (i) superior etching selectivity of ·F and ·O radicals; (ii) adsorption inhibition activity of ·O radicals which minimizes the formation of F residues; (iii) Ar + ion bombardment that can effectively eliminate undesired impurities …”