Double Etch Method for the Fabrication of Nanophotonic Devices from Hexagonal Boron Nitride
Otto Cranwell Schaeper
University of Technology – Sydney, Australia
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Integrated quantum photonics could be the building blocks of tomorrow’s quantum world. Integrated quantum photonics rely on photons as qubits. Photons are innately robust against decoherence, and by utilising fabricated structures—including waveguides, cavities, and resonators—the fidelity can be further increased. Additionally, these structures can be designed to manipulate photons for a variety of purposes, including entanglement or two-photon interference.
In recent years, hBN has emerged as a promising platform for quantum photonic devices, due to properties such as nonlinear effects and a high refractive index. The most enticing property of hBN is the material’s ability to host on-demand engineered single photon emitters (the B centre) as well as the spin active boron vacancy (VB-), both with reproducible emission wavelengths, both defects could be critical to integrated quantum photonics. The key roadblock to the further development of these defects is in the fabrication of practical on-chip devices, which would allow for high-efficiency generation, manipulation and collection of the emitted photons.
The most common fabrication protocol in current literature is the lift-off method, where metal is deposited onto a pre-defined mask on the sample. Agitation via sonication is a necessary step to produce a high-quality mask, this is incompatible with the Van der Waals nature of hBN, in the current work, we present a fabrication method tailored for hBN. Here we employ a double etch approach for mask transfer, where a continuous metal layer is deposited over the entire substrate, and a mask is defined in a layer of electron beam resist (e-beam resist) on top of the metal layer. Using an ion beam etcher the e-beam resist functions as the hard mask while the pattern is etched into the metal layer. Following an inductively coupled plasma reactive ion etcher is used to transfer the pattern from the metal layer in the hBN below. This method unlocks key avenues to the further development of hBN as a quantum platform, through its ability to bring metal masking to 2D materials. Allowing for the fabrication of devices from thicker hBN, its potential for large-scale fabrication, ease of suspended structures engineering, and potentially easier mask removal address significant scalability issues.