Green silicon carbide (SiC) is a high-purity abrasive material widely used in semiconductor substrate polishing due to its exceptional hardness (9.2–9.5 Mohs), thermal stability, and chemical inertness. Here’s a detailed breakdown of its role in semiconductor substrate polishing:
1. Key Properties of Green SiC for Polishing
High Hardness: Effective for precision grinding/polishing of hard materials like silicon (Si), gallium arsenide (GaAs), and sapphire.
Sharp Abrasive Grains: Provides efficient material removal while minimizing subsurface damage.
Thermal Stability: Maintains performance at high temperatures generated during polishing.
Chemical Inertness: Resists reactions with coolants or substrates, ensuring clean processing.
2. Applications in Semiconductor Substrate Polishing
Lapping & Rough Polishing: Used in early stages to achieve flatness and remove surface defects.
Fine Polishing: Combined with diamond slurries or colloidal silica for ultra-smooth finishes (Ra < 1 nm).
Edge Grinding: Shapes wafer edges to prevent chipping during handling.
3. Advantages Over Other Abrasives
Cost-Effective: Cheaper than diamond but harder than alumina or boron carbide.
Controlled Aggressiveness: Less likely to cause deep scratches compared to diamond, making it suitable for intermediate polishing steps.
4. Polishing Process Considerations
Grit Size:
Coarse grits (#600–#1200) for initial material removal.
Fine grits (#2000–#4000) for final smoothing.
Slurry Formulations: Often suspended in water or glycol-based fluids with pH stabilizers.
Equipment: Used in rotary polishers, CMP (Chemical Mechanical Planarization), or double-sided polishing machines.
5. Challenges & Mitigation
Surface Scratches: Can occur if grit size is mismatched; mitigated by multi-step polishing with progressively finer abrasives.
Contamination: High-purity (99.9%+) green SiC is essential to avoid introducing impurities.
6. Comparison with Alternatives
Diamond: Harder but more expensive; used for final polishing.
Alumina (Al₂O₃): Softer, cheaper, but less efficient for hard substrates.
Boron Carbide (B₄C): Harder than SiC but more expensive and brittle.
7. Industry Trends
Demand for Larger Wafers: SiC’s consistency is critical for 300mm+ wafer processing.
Green Manufacturing: Recycling SiC slurries to reduce waste.
Conclusion
Green silicon carbide is a versatile abrasive for semiconductor substrate polishing, balancing cost, hardness, and controllability. While diamond dominates final polishing, SiC remains indispensable for intermediate steps, especially for compound semiconductors (e.g., SiC, GaN) and traditional silicon wafers.