Introduction

Silicon carbide (SiC), gallium nitride (GaN), and sapphire (Al₂O₃) are essential materials in semiconductor, optoelectronic, and high-power electronic devices due to their exceptional physical and chemical properties. However, their high hardness and chemical stability make processing challenging. Traditional mechanical polishing (MP) and chemical mechanical polishing (CMP) have limitations in surface quality and damage layer control. Therefore, exploring advanced polishing technologies to enhance surface quality and minimize damage layers is crucial for improving device performance.

1. Ion Beam Polishing (IBP)

Principle

Ion Beam Polishing (IBP) utilizes high-energy ion beams to bombard the wafer surface, removing microscopic surface irregularities for ultra-precise finishing. By controlling ion beam energy and angle, it effectively reduces damage layers while improving surface smoothness.

Advantages

1. Non-contact processing, avoiding microcracks and stress from traditional grinding.

   
   

2. Suitable for ultra-hard materials, such as 4H-SiC, 6H-SiC, and GaN.

   
   

3. Achieves atomic-level smooth surfaces (Ra < 0.1 nm).

Applications

1. Final polishing before SiC and GaN epitaxy, reducing dislocation density and improving epitaxial layer quality.

   
   

2. Ultra-precision polishing for high-end optical components.

2. Gas Cluster Ion Beam Polishing (GCIB)

Principle

GCIB uses high-density gas clusters (e.g., argon or nitrogen) to bombard the surface, enabling damage-free material removal. Compared to single-ion beams, gas cluster ion beams distribute energy more uniformly, allowing finer surface finishing.

Advantages

1. Completely damage-free, ideal for high-precision semiconductor and optical components.

   
   

2. Achieves atomic-level smoothness (Ra < 0.1 nm).

   
   

3. Suitable for final polishing of sapphire, SiC, and GaN.

Applications

1. Ultra-precision polishing before SiC and GaN epitaxy.

   
   

2. Surface treatment of high-end optical materials for EUV lithography.

3. Thermochemical Polishing (TCP)

Principle

Under high temperatures (typically > 1000°C), specific atmospheric conditions (such as oxygen, chlorine, or hydrogen) selectively etch the material surface while airflow or plasma smooths the surface.

Advantages

1. Effectively removes deep damage layers that conventional CMP struggles with.

   
   

2. Suitable for ultra-hard materials (SiC), particularly for power electronic substrates.

   
   

3. Eliminates scratches and microcracks by avoiding mechanical pressure.

Applications

1. Final processing of high-power SiC device substrates to enhance thermal conductivity and surface quality.

   
   

2. Ultra-fine polishing of high-end GaN laser substrates.

4. Ultrasonic Assisted Polishing (UAP)

Principle

During traditional CMP, ultrasonic vibrations are applied to distribute abrasive particles evenly in the polishing slurry and accelerate chemical reactions.

Advantages

1. Increases material removal rate (MRR), reducing polishing time and improving efficiency.

   
   

2. Suitable for large-diameter SiC/GaN wafer polishing.

   
   

3. Achieves surface roughness below 0.2 nm.

Applications

1. High-yield polishing of 6-8 inch SiC/GaN wafers.

   
   

2. Enhancing interface quality of GaN-on-SiC epitaxial wafers.

5. Magnetorheological Finishing (MRF)

Principle

MRF controls abrasive particles in a magnetic fluid using a magnetic field, enabling highly precise material removal, ideal for precision machining.

Advantages

1. Precisely controls material removal rate, achieving sub-nanometer flatness.

   
   

2. Suitable for curved or complex geometries (e.g., specialized optical lenses).

   
   

3. Ideal for ultra-precise optical and semiconductor components.

Applications

1. Ultimate polishing of high-end sapphire windows and GaN optoelectronic devices.

   
   

2. Sapphire substrate processing for high-power laser applications.

6. Plasma-Assisted Polishing (PAP)

Principle

Low-temperature plasma activates the wafer surface, making chemical polishing reactions more uniform and gentle, resulting in high-quality surface treatment.

Advantages

1. Suitable for hard materials like GaN and SiC without mechanical damage.

   
   

2. Can be combined with CMP for final surface correction, further enhancing smoothness.

   
   

3. Applicable to ultra-precision microelectronics and optical applications.

Applications

1. Pre-epitaxial treatment of high-end SiC/GaN devices.

   
   

2. Surface refinement of high-precision optical components.

Conclusion: Which Polishing Technology is Most Suitable?

For large-scale production, CMP remains the mainstream choice. However, for high-end SiC/GaN epitaxial substrates, IBP, GCIB, and PAP technologies hold significant potential to improve surface quality and minimize damage layers, ultimately enhancing semiconductor device performance.