Selective Etching of Hexagonal Boron Nitride by High-Pressure CF4 Plasma for Individual One-dimensional Ohmic Contacts to Graphene Layers

TL;DR

This paper presents a plasma-based technique for creating precise one-dimensional ohmic contacts to individual graphene layers encapsulated in hexagonal boron nitride, enabling advanced device fabrication and experimental access.

Contribution

It introduces a high-pressure CF4 plasma etching method that selectively etches h-BN while protecting graphene, facilitating the fabrication of complex graphene-based devices.

Findings

Achieved >1000 etch selectivity of h-BN over graphene.

Enabled patterning of metal electrodes on h-BN over graphene.

Demonstrated fabrication of graphene Hall bar devices with cryogenic functionality.

Abstract

We describe a technique for making one-dimensional ohmic contacts to individual graphene layers encapsulated in hexagonal boron nitride (h-BN) using CF4 and O2 plasmas. The high etch selectivity of h-BN against graphene (>1000) is achieved by increasing the plasma pressure, which enables etching of h-BN, while graphene acts as an etch stop to protect underlying h-BN. A low-pressure O2 plasma anisotropically etches graphene in the vertical direction, which exposes graphene edges at h-BN sidewalls. Despite the O2 plasma bombardment, the lower h-BN layer functions as an insulating layer. Thus, this method allows us to pattern metal electrodes on h-BN over a second graphene layer. Subsequent electron-beam lithography and evaporation fabricate metal contacts at the graphene edges that are active down to cryogenic temperatures. This fabrication method is demonstrated by the preparation of a graphene Hall bar with a graphite back-gate and double bilayer-graphene Hall bar devices. The high flexibility of the device geometries enabled by this method creates access to a variety of experiments on electrostatically coupled graphene layers.