A highly efficient semi-finishing approach for polycrystalline diamond film via plasma-based anisotropic etching

Plasma anisotropic etching polishing (plasma-AEP), a non-contact polishing method, is proposed to achieve highly efficient planarization of polycrystalline diamond (PCD) films. Inductively coupled plasma, with a high concentration of reactive radicals, serves as the source of plasma-AEP. In-situ observation confirms that the planarization effect of plasma-AEP is realized through the preferential removal of the top areas of the pyramid-shaped protrusions, despite the entire surface being uniformly irradiated by the plasma. The material removal rate in plasma-AEP for PCD achieves 127 μm/min. Plasma-AEP is proven effective for PCD films with thicknesses of 0.5, 1, and 2 mm, demonstrating a generic semi-finishing approach for PCD regardless of thickness. Atomic-scale nudged elastic band calculations revealed that the energy barriers for CO and CO₂ desorption from 1- and 2-coordinated C atoms are significantly lower than those for 3- and 4-coordinated ones. ReaxFF molecular dynamics simulations showed that at the top areas of the pyramid-shaped protrusions, 1- and 2-coordinated C atoms with a higher etching priority remained dominant during plasma-AEP, leading to the preferential removal of C atoms forming these protrusions. Furthermore, contact polishing was added to complete the finishing of the PCD film, followed by plasma-AEP, resulting in a nanoscale smooth surface with a roughness of 3.4 nm. Transmission electron microscopy confirmed that the crystal structures on the surface and subsurface of the PCD film were well ordered. Overall, this paper displays that plasma-AEP is a promising approach for highly efficient semi-finishing of PCD films.