Non-Destructive Thickness Mapping of Wafer-Scale Hexagonal Boron Nitride Down to a Monolayer

Characterization of the thickness and continuity of wide band gap 2D materials with monolayer sensitivity over large areas has proven to be very challenging. A prime example is 2D hexagonal boron nitride (hBN). Optical contrast methods suffer from the lack of visible absorption in the material; Raman spectral signatures are weak and often not conclusive; and electrical measurements are not possible due to a high electrical resistivity. In this contribution, we will demonstrate an experimental method based on the ellipsometry technique, which makes it possible to map the thickness and continuity of large-area hBN monolayers and bilayers transferred to Si/SiO₂ substrates. The method has sub-monolayer thickness sensitivity, is relatively fast, non-destructive, and can be easily automated. The hBN thicknesses measured in this study have been confirmed by Raman spectroscopy, x-ray photoemission spectroscopy, and by a series of ellipsometry control experiments. We will present a workflow of our experimental procedure, so that other researchers can extend this characterization method to other 2D materials and hopefully accelerate their development.