Reactive plasma cleaning and restoration of transition metal dichalcogenide monolayers

Daniil Marinov,Pieter-Jan Wyndaele,Patrick C With,Inge Asselberghs,Jianran Zhang,Stefan De Gendt,Dennis Lin,Quentin Smets,Yuri Mankelevich,Tatyana Rakhimova,Ankit Nalin Mehta,Salim El Kazzi,Kristof M Bal,Erik C Neyts,Ekaterina Voronina,Sreetama Banerjee,Markus Hartmut Heyne,Jean-François De Marneffe,Goutham Arutchelvan

doi:10.1038/s41699-020-00197-7

Abstract

The cleaning of two-dimensional (2D) materials is an essential step in the fabrication of future devices, leveraging their unique physical, optical, and chemical properties. Part of these emerging 2D materials are transition metal dichalcogenides (TMDs). So far there is limited understanding of the cleaning of “monolayer” TMD materials. In this study, we report on the use of downstream H2 plasma to clean the surface of monolayer WS2 grown by MOCVD. We demonstrate that high-temperature processing is essential, allowing to maximize the removal rate of polymers and to mitigate damage caused to the WS2 in the form of sulfur vacancies. We show that low temperature in situ carbonyl sulfide (OCS) soak is an efficient way to resulfurize the material, besides high-temperature H2S annealing. The cleaning processes and mechanisms elucidated in this work are tested on back-gated field-effect transistors, confirming that transport properties of WS2 devices can be maintained by the combination of H2 plasma cleaning and OCS restoration. The low-damage plasma cleaning based on H2 and OCS is very reproducible, fast (completed in a few minutes) and uses a 300 mm industrial plasma etch system qualified for standard semiconductor pilot production. This process is, therefore, expected to enable the industrial scale-up of 2D-based devices, co-integrated with silicon technology.

Highlights

Two-dimensional transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have attracted significant interest due to their unique properties and the relevance to numerous applications, as synergistic combination with silicon-based nanosystems[1]
The first part of this study investigates the nature of PMMA residues and their removal using plasma-based methods
After spin-coating the adhesive layer on the 2D layer and applying the rest of the transfer stack, the 2D layer is delaminated from the growth substrate, the entire stack is transferred to the target wafer and the transfer stack is removed

Summary

INTRODUCTION

Two-dimensional transition metal dichalcogenides (TMDs) such as MoS2 and WS2 have attracted significant interest due to their unique properties and the relevance to numerous applications, as synergistic combination with silicon-based nanosystems[1]. The thickness grow first following a linear law (full lines), becomes logarithmic (dashed lines), eventually reaching a saturation “equilibrium” thickness Γ∞ (reached after ~ 7.5 h at 160 ∘C) This fully corresponds to the description available in literature[27,28]: first, a linear regime with a large number of free sites available on the silicon surface for the attachment of new PMMA chains. This layer, in the immediate vicinity of the interface, has a higher density than in the bulk polymer, and is difficult to

RESULTS AND DISCUSSION

Marinov et al 4

METHODS

CODE AVAILABILITY