An Operando Spectroscopic Imaging Ellipsometry Study of HfS2 Oxidation

The advancement of 2D technologies and the application potential of 2D heterostructures relies on controlled, clean interfacing. The interest in HfS2 as a 2D semiconductor is tied to its native oxide, and the potential of a well-defined interface with a stable high k dielectric. However, the understanding of the underpinning oxidation kinetics remains in its infancy, as reactions at buried interfaces are challenging to resolve across scales and at relevant conditions.

In this study, we investigate the oxidation of few-layer HfS2 by spectroscopic imaging ellipsometry (SIE) - a fast, non-destructive, large-area characterisation tool for mapping and analysis of multi-layer heterostructures. Given the 1um lateral resolution and atomic layer precision, we can resolve three-dimensional images of the oxidation process and the formation of a HfS2/HfO2 interface in operando. Through optical modelling, we quantify the oxide thickness, uniformity and quality for different oxidation methods. This leads to a finer control of the oxidation process, while the rapid, high-throughput wafer-scale acquisition capabilities of SIE allow for statically relevant data sets and open up data-driven approaches.