Fast, Non-Contact, Wafer-Scale, Atomic Layer Resolved Imaging of 2D Materials by Ellipsometric Contrast Micrography

Abstract

Adequate characterisation and quality control of atomically thin layered materials (2DM) has become a serious challenge particularly given the rapid advancements in their large area manufacturing and numerous emerging industrial applications with different substrate requirements. Here, we focus on ellipsometric contrast micrography (ECM), a fast intensity mode within spectroscopic imaging ellipsometry, and show that it can be effectively used for non-contact, large area characterisation of 2DM to map coverage, layer number, defects and contamination. We demonstrate atomic layer resolved, quantitative mapping of chemical vapour deposited graphene layers on Si/SiO2-wafers, but also on rough Cu catalyst foils, highlighting that ECM is applicable to all application relevant substrates. We discuss the optimisation of ECM parameters for high throughput characterisation. While the lateral resolution can be less than 1 µm, we particularly explore fast scanning and demonstrate imaging of a 4’’ graphene wafer in 47 min at 10 µm lateral resolution, i.e. an imaging speed of 1.7 cm2/min. Furthermore, we show ECM of mono-layer hexagonal BN (h-BN) and of h-BN/graphene bilayers, highlighting that ECM is applicable to a wide range of 2D layered structures that have previously been very challenging to characterise and thereby fills an important gap in 2DM metrology.