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/Cl₂ recipes with low etch rates, surface defects like grooves due to polishing are minimized and smooth surfaces are acquired. Severe micro-masking can be prevented by the application of a cyclic Ar/Cl₂ + O₂ recipe, allowing finally the fabrication of defect-minimized and planarized SCD membranes in the thickness range between a few microns and a few hundred nanometers. The high quality of the structured SCD membranes is evidenced with a morphological as well as optical characterization via fiber-based microcavity measurements.