Development of hard masks for reactive ion beam angled etching of diamond

TL;DR

This paper develops and evaluates different mask materials for reactive ion beam angled etching of diamond, enabling better fabrication of large, high-quality photonic devices for quantum applications.

Contribution

It introduces a new mask material combination that improves etch profiles and optical performance in diamond RIBAE, facilitating larger device fabrication.

Findings

Hydrogen silesquioxane (HSQ) with alumina provides optimal etch profiles.

Thick HSQ masks improve mask erosion resistance for larger devices.

Techniques can be adapted to other bulk materials.

Abstract

Diamond offers good optical properties and hosts bright color centers with long spin coherence times. Recent advances in angled-etching of diamond, specifically with reactive ion beam angled etching (RIBAE), have led to successful demonstration of quantum photonic devices operating at visible wavelengths. However, larger devices operating at telecommunication wavelengths have been difficult to fabricate due to the increased mask erosion, arising from the increased size of devices requiring longer etch times. We evaluated different mask materials for RIBAE of diamond photonic crystal nanobeams and waveguides, and how their thickness, selectivity, aspect ratio and sidewall smoothness affected the resultant etch profiles and optical performance. We found that a thick hydrogen silesquioxane (HSQ) layer on a thin alumina adhesion layer provided the best etch profile and optical performance. The techniques explored in this work can also be adapted to other bulk materials that are not available heteroepitaxially or as thin films-on-insulator.