Efficacy of Boron Nitride Encapsulation against Plasma-Processing in van der Waals Heterostructures

TL;DR

This study investigates how hexagonal boron nitride (h-BN) can protect MoS2 monolayers from plasma-induced damage during semiconductor processing, showing effectiveness for short exposures but failure for longer ones.

Contribution

It provides detailed analysis of h-BN's protective capabilities against plasma damage in TMDCs, using advanced microscopy and spectroscopy techniques.

Findings

h-BN effectively shields MoS2 from short plasma exposures

Protection diminishes with plasma exposure longer than 30 seconds

Extended plasma exposure causes damage and amorphization in MoS2

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are the subject of intense investigation for applications in optics, electronics, catalysis, and energy storage. Their optical and electronic properties can be significantly enhanced when encapsulated in an environment that is free of charge disorder. Because hexagonal boron nitride (h-BN) is atomically thin, highly-crystalline, and is a strong insulator, it is one of the most commonly used 2D materials to encapsulate and passivate TMDCs. In this report, we examine how ultrathin h-BN shields an underlying MoS2 TMDC layer from the energetic argon plasmas that are routinely used during semiconductor device fabrication and post-processing. Aberration-corrected Scanning Transmission Electron Microscopy is used to analyze defect formation in both the h-BN and MoS2 layers, and these observations are correlated with Raman and photoluminescence spectroscopy. Our results highlight that h-BN is an effective barrier for short plasma exposures (< 30 secs) but is ineffective for longer exposures, which result in extensive knock-on damage and amorphization in the underlying MoS2.