Diamond Wafer Polishing
Polishing plays a crucial role in the preparation of high-quality single-crystal diamond substrates, mainly in two aspects:
(1) preparing seed crystals for homoepitaxial CVD growth, where surface flatness and defect density directly determine growth quality;
(2) planarizing CVD-grown single-crystal diamond by removing surface defects.
The main polishing techniques for diamond substrates include:
Mechanical Polishing (MP)
Mechanism: Friction between diamond and a high-speed rotating polishing plate (cast iron or grinding wheel), combining brittle fracture with temperature-induced graphitization to remove material.
Advantages: Simple process, high efficiency, scalable for mass production, applicable for coarse, medium, and fine polishing.
Disadvantages: Causes subsurface damage, scratches, and edge chipping; polishing plate wear affects surface quality.
Thermochemical Polishing (TCP)
Mechanism: Based on carbon diffusion into hot metals, diamond graphitization, and oxidation.
Advantages: Almost stress-free, produces flat surfaces with minimal damage.
Disadvantages: Requires high temperature and vacuum; equipment is complex and costly; difficult to achieve uniform heating.
Chemical Mechanical Polishing (CMP)
Mechanism: Incorporates oxidizers during mechanical polishing to accelerate carbon oxidation, enabling chemical–mechanical synergistic removal.
Advantages: Produces smooth, flat surfaces with low roughness and minimal damage; applicable to other hard materials.
Disadvantages: Time-consuming, requires multiple optimization cycles; high-grade slurries are expensive and often imported; slurry recycling remains a challenge.
Plasma-Assisted Polishing (PEP)
Mechanism: Ionized gases (e.g., Ar, O₂, N₂) interact with the surface to achieve atomic-level material removal.
Advantages: Non-contact, avoids mechanical damage, high precision and uniformity, suitable for fine polishing.
Disadvantages: High equipment cost, complex process control, risk of surface residues, limited by chamber size.
Laser Polishing (LP)
Mechanism: Laser irradiation heats the diamond surface, causing carbon atoms to gasify or graphitize, enabling material removal.
Advantages: High efficiency, adaptable to complex geometries, capable of localized polishing.
Disadvantages: Local overheating can cause thermal damage and graphite residues; requires precise control of laser parameters.
Conclusion:
Mechanical polishing is suitable for large-scale coarse processing, while TCP and CMP are more advantageous for achieving low-damage, ultra-smooth surfaces. PEP and LP represent advanced non-contact approaches with high precision and versatility, but their applications are limited by cost and process complexity. In practice, a combination of polishing techniques is often employed to obtain high-quality, low-damage single-crystal diamond substrates
