Fabrication of High‐Quality Thin Single‐Crystal Diamond Membranes with Low Surface Roughness

Certain aspects before and during the fabrication of single-crystal diamond (SCD) membranes are highlighted, which are decisive to obtain high-quality membranes with low surface roughness values around 0.2 nm on a small area scale. In addition to the requirements for the starting material, including a high planarity and a moderate surface roughness, the importance of cleaning processes to minimize particles and impurities before and during the structuring is emphasized. With the help of a planarization procedure, consisting of a combination of different Ar/Cl$_2$ recipes with low etch rates, surface defects like grooves due to polishing are minimized and smooth surfaces are acquired. Severe micromasking can be prevented by the application of a cyclic Ar/Cl$_2$ + O$_2$ recipe, allowing finally the fabrication of defect-minimized and planarized SCD membranes in the thickness range between few microns and a few hundred nanometers. The high quality of the structured SCD membranes is evidenced with a morphological as well as an optical characterization via fiber-based microcavity measurements.