Highly efficient and atomic-scale smoothing of single crystal diamond through plasma-based atom-selective etching

Single crystal diamond (SCD) presents promising and extensive applications in electronics, thermal management, and optical windows for its excellent physical and chemical properties. However, its difficult-to-machine features, such as high hardness, processing brittleness, and chemical inertness make it challenging to smooth SCD, greatly inhibiting its further applications. Herein, a highly efficient and atomic-scale smoothing method for SCD based on the mechanism of plasma-based atom-selective etching (PASE) is proposed. During the smoothing process, oxygen active radicals in high temperature atmospheric inductively coupled plasma (ICP) would preferentially remove carbon atoms with more dangling bonds on SCD surface. By tuning the key parameters of oxygen plasma of radio frequency power, flow rate of oxygen, and torch-wafer distance, sufficient energy input and oxygen radicals concentration were obtained to generate PASE for SCD smoothing. The key parameters for PASE were investigated and the highest material removal rate reached up to 56.533 μm/min, which was thousands of times higher than conventional chemical mechanical polishing. After smoothing for 5 min, the Sa roughness began to stabilize at around 0.5 nm and an atomic-scale smooth surface was acquired. X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy characterization results demonstrate that the smoothed SCD surface is crystallographically perfect without any non-diamond composition introduced. PASE of SCD with different initial surfaces, sizes, and crystal planes is proved to be feasible, showing the powerful applicability of PASE for SCD. In conclusion, PASE presents huge potential to achieve high-efficiency and atomic-scale smoothing of SCD to fulfill its industrial application demand.