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

Andrea Crovetto*, Patrick Rebsdorf Whelan, Ruizhi Wang, Miriam Galbiati, Stephan Hofmann, Luca Camilli

*Corresponding author for this work

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Abstract

The availability of an accurate, nondestructive method for measuring thickness and continuity of two-dimensional (2D) materials with monolayer sensitivity over large areas is of pivotal importance for the development of new applications based on these materials. While simple optical contrast methods and electrical measurements are sufficient for the case of metallic and semiconducting 2D materials, the low optical contrast and high electrical resistivity of wide band gap dielectric 2D materials such as hexagonal boron nitride (hBN) hamper their characterization. In this work, we demonstrate a nondestructive method to quantitatively map the thickness and continuity of hBN monolayers and bilayers overlarge areas. The proposed method is based on acquisition and subsequent fitting of ellipsometry spectra of hBN on Si/SiO2 substrates. Once a proper optical model is developed, it becomes possible to identify and map the commonly observed polymer residuals from the transfer process and obtain submonolayer thickness sensitivity for the hBNfilm. With some assumptions on the optical functions of hBN, the thickness of an as-transferred hBN monolayer on SiO2 is measured as 4.1 Å ± 0.1 Å, whereas the thickness of an air-annealedhBN monolayer on SiO2 is measured as 2.5 Å ±0.1 Å. We argue that the difference in the two measured values is due to the presence of a water layer trapped between the SiO2 surface and the hBN layer in the latter case. The procedure can be fully automated to wafer scale and extended to other 2D materials transferred onto any polished substrate, as long as their optical functions are approximately known.
Original languageEnglish
JournalA C S Applied Materials and Interfaces
Volume10
Pages (from-to)25804−25810
ISSN1944-8244
DOIs
Publication statusPublished - 2018

Keywords

  • Hexagonal boron nitride
  • 2D materials
  • Ellipsometry
  • Thickness
  • Chemical vapor deposition
  • Wafer-scale mapping

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