Development of an Atomic Layer Etching process for diamond substrates

An Atomic Layer Etching process for (100)-oriented diamond substrates has been developed using a standard Inductively-Coupled Plasma Reactive Ion Etching (ICP-RIE) reactor. The process relies on a cyclic sequence comprising a surface modification step in a CF4/Ar plasma followed by selective removal through low energy argon sputtering. A well-defined ALE window is identified, yielding a stable and reproducible etch rate corresponding to two (100) diamond unit cells (7.1 Å) per cycle. Surface characterization of the diamond etched surface reveals a significant reduction in surface roughness across a wide range of sputtering energies, although further optimization remains possible, given the initially high surface roughness of the diamond substrates. To demonstrate the relevance of this process, a so-called bull's eye photonic structures have been fabricated in diamond substrates using a conventional electron beam lithography and RIE etching process, ending up by multiple ALE cycles. This combined approach enabled the formation of smooth etched surfaces and side walls, with minimal micro-masking. The resulting structures provide a benchmark for resonant nonlinear spectroscopy and coherent control of color centers in diamond.