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The development of quantum technologies is one of the big challenges in modern research. A crucial component for many applications is an efficient, coherent spin–photon interface, and coupling single-color centers in thin diamond membranes to a microcavity is a promising approach. To structure such micrometer thin single-crystal diamond (SCD) membranes with a good quality, it is important to minimize defects originating from polishing or etching procedures. Here, we report on the fabrication of SCD membranes, with various diameters, exhibiting a low surface roughness down to 0.4 nm on a small area scale, by etching through a diamond bulk mask with angled holes. A significant reduction in pits induced by micromasking and polishing damages was accomplished by the application of alternating Ar/Cl2 + O2 dry etching steps. By a variation of etching parameters regarding the Ar/Cl2 step, an enhanced planarization of the surface was obtained, in particular, for surfaces with a higher initial surface roughness of several nanometers. Furthermore, we present the successful bonding of an SCD membrane via van der Waals forces on a cavity mirror and perform finesse measurements which yielded values between 500 and 5000, depending on the position and hence on the membrane thickness. Our results are promising for, e.g., an efficient spin–photon interface.

The use of an alkaline or acidic solution (the etchant) to chemically remove material from the surface of a sample is wet etching and this chapter explains the different types of wet etching. Although the etch rate anisotropy leads to faceting, the description of anisotropic etching as the propagation of a collection of crystallographic planes is an oversimplification. The important microscopic processes are briefly explained with relevant examples, which include pit nucleation and step flow, micromasking, diffusion, etc. The removal of the surface atoms during wet etching of silicon is a complex process that involves both chemical and electrochemical reactions. This chapter also provides an overview of the typical surface morphologies that can be observed during/after wet etching on different surface orientations, and an unified explanation of the mechanisms that may be responsible for it. The items used to characterize a silicon wafer like orientation issues, wafer dimensions, surface quality, and bulk features affect the etching result and thus silicon wafer plays a key role in wet chemical etching. This chapter gives detailed data on examples of wet etching, popular wet etchants, temperature dependence of the etch rate, concentration dependence of the etch rate and other variables affecting etch-rate values, etc. It also tries to give some data on the conversion between different measures of concentration.