Research Progress on Diamond Plasma Etching Technology

In recent years, significant advancements have been made in diamond plasma etching technology, particularly in the processing of polycrystalline diamond (PCD) and single-crystal diamond. Here is a summary of the latest research progress:

A novel non-contact polishing technique known as Plasma Anisotropic Etching Polishing (Plasma-AEP) has been proposed to achieve efficient planarization of polycrystalline diamond (PCD) films. This technique utilizes a high-concentration reactive radical source from an inductively coupled plasma (ICP) to preferentially remove the top regions of pyramidal protrusions on the PCD surface, achieving a material removal rate of up to 127 μm/min. Studies have shown that Plasma-AEP is effective for PCD films of varying thicknesses (0.5, 1, and 2 mm) and represents a universal semi-finishing approach.

At the atomic level, the etching mechanism was revealed through NEB (Nudged Elastic Band) calculations and ReaxFF molecular dynamics simulations: carbon atoms with coordination numbers of 1 and 2 are preferentially removed during etching because their CO and CO₂ desorption barriers are significantly lower than those of carbon atoms with coordination numbers of 3 and 4. Furthermore, when combined with contact polishing techniques, Plasma-AEP can further achieve a nanoscale smooth surface with a surface roughness of 3.4 nm.

For single-crystal diamond, researchers have developed a new cyclic etching process to address the issue of micromasking caused by metal masks in traditional etching. This process employs a two-step cyclic etching of Ar/O₂-Ar/Cl₂/BCl₃. By optimizing the Cl₂/BCl₃ gas ratio, high-quality etching with nearly zero micromasking has been achieved. Studies have also shown that the use of chlorine-based gases helps eliminate micromasking and yields smooth etched surfaces.

In addition, an optimized Ar/O₂-Ar/Cl₂ ICP RIE (Inductively Coupled Plasma Reactive Ion Etching) process has been developed to address micromasking issues caused by aluminum masks. This process introduces a preferential "cleaning" step, achieving an etching depth of up to 10.6 μm, with an average surface roughness of 0.47 nm and an etching rate of 45 nm/min.

These research advancements demonstrate that plasma etching technology holds broad application prospects in the field of diamond processing. The Plasma-AEP technique provides a universal and efficient solution for the planarization of polycrystalline diamond films. Meanwhile, the cyclic etching process for single-crystal diamond offers a new technological approach for the fabrication of high-precision micro- and nanostructures. The development of these technologies will further promote the application of diamond in high-performance micro- and nanosystems.

In summary, plasma etching technology for diamond has made significant progress in improving processing efficiency, surface quality, and addressing micromasking issues. These advancements provide strong support for the future manufacturing of diamond-based devices.