Silicon carbide (SiC), as a representative wide-bandgap semiconductor material, has become a cornerstone of next-generation power electronics due to its high breakdown field strength, excellent thermal conductivity, and capability to operate under extreme temperatures and voltages.
Among the various processes used to tailor the electrical properties of SiC, diffusion doping is one of the earliest and most fundamental techniques. Although significantly more challenging than in silicon, diffusion still plays a meaningful role in specific SiC device structures and research directions.

This article provides a systematic and rigorous overview of the principles, characteristics, applications, and current status of diffusion processes in SiC technology.

1. Core Applications of Diffusion in SiC Device Manufacturing

While ion implantation and epitaxial in-situ doping are the mainstream doping methods in modern SiC production, diffusion continues to serve several key purposes.

1.1 Formation of Junction Structures in Power Devices

Diffusion is used to introduce p-type or n-type dopants into SiC substrates to create essential junctions:

• PN junction formation in diodes, MOSFETs, and bipolar structures.

• Edge termination structures, such as Junction Termination Extension (JTE) and Field-Limiting Rings (FLR), designed to stabilize the electric field distribution and increase breakdown voltage.

• Formation of heavily doped ohmic contact regions to reduce contact resistance between metal electrodes and the semiconductor.

These functions are fundamental to enabling high-efficiency, high-voltage SiC device operation.

1.2 High-Temperature and High-Frequency Electronics

Due to its ability to retain crystal stability at temperatures exceeding 600 °C, SiC is used in aerospace electronics, deep-well drilling sensors, and high-frequency devices such as MESFETs.

Diffusion doping supports:

• Controlled adjustment of channel conductivity,

• Optimization of carrier concentration profiles,

• Enhancement of high-frequency performance metrics.

1.3 Optical and Photoelectronic Devices

Certain dopants introduced via diffusion—such as Al and N—may form luminescent centers or adjust optical absorption properties, enabling applications in:

• UV LEDs

• UV photodetectors

• Radiation-sensitive devices

2. Distinctive Characteristics of SiC Diffusion Compared with Silicon

The diffusion behavior in SiC differs dramatically from that in silicon due to its strong covalent bonding and crystalline rigidity.

2.1 Extremely High Processing Temperature

Typical diffusion temperatures:

• Si: 800–1200 °C

• SiC: 1600–2000 °C

The Si–C bond possesses a significantly higher binding energy than the Si–Si bond, requiring elevated temperatures to activate atomic motion. This necessitates specialized furnace designs and refractory materials capable of enduring prolonged exposure to extreme temperatures.

2.2 Low Dopant Diffusivity

Dopant atoms exhibit extremely slow diffusion rates in SiC due to limited vacancy migration and strong lattice integrity. As a result:

• Diffusion depths are shallow,

• Processing times are long,

• The process is highly sensitive to temperature fluctuations.

2.3 Masking and Patterning Challenges

Traditional SiO₂ masks degrade at high temperatures and cannot provide reliable dopant blocking. SiC diffusion commonly requires:

• Graphite masks,

• Metal films,

• Specialized high-temperature-resistant coatings.

2.4 Low Dopant Activation Efficiency

Even after diffusion, dopants tend to remain in interstitial sites and must be activated through subsequent high-temperature annealing. Activation rates are generally lower than in silicon, resulting in:

• Reduced free carrier concentration,

• Higher variability,

• Greater dependence on defect density.

3. Typical Dopant Species and Their Functions

The choice of dopant is determined by the desired electrical properties, diffusion behavior, and device structure requirements.

4. Engineering Challenges of SiC Diffusion

Despite its usefulness, diffusion in SiC presents several notable challenges:

4.1 Process Control and Crystal Integrity

Ultra-high temperatures may introduce lattice damage or surface roughening. Tight control of:

• Temperature profiles,

• Thermal gradients,

• Atmospheric purity

is required to maintain material quality.

4.2 Limited Capability for Fine Patterning

Due to the low diffusivity, achieving localized, highly precise doping profiles—commonly performed in silicon CMOS—is difficult in SiC. This limitation restricts diffusion to specific device architectures rather than general-purpose fabrication.

4.3 High Equipment and Operational Costs

Prolonged high-temperature processing leads to:

• Greater energy consumption,

• Increased equipment wear,

• Higher production costs compared to silicon diffusion.

5. Current Status and Future Trends in SiC Diffusion Technology

5.1 Industrial Adoption

In mass production, ion implantation combined with high-temperature annealing has become the dominant doping method due to its precision and scalability.
However, diffusion remains relevant in:

• Deep-junction devices,

• Certain bipolar structures,

• Experimental high-voltage components.

5.2 Research Directions

Current R&D focuses on overcoming diffusion limitations through:

• Laser-assisted or plasma-assisted low-temperature diffusion,

• Enhanced dopant activation techniques,

• Surface modification to increase vacancy concentration,

• Synergistic processes combining diffusion with epitaxial in-situ doping.

These developments aim to improve dopant incorporation efficiency while mitigating damage and reducing thermal requirements.

6. Conclusion

Diffusion doping in SiC represents a complex but essential technique in power semiconductor manufacturing. Although modern production increasingly relies on ion implantation and epitaxial doping, diffusion remains important in specific high-voltage and specialized device structures. Its unique challenges—high temperature, limited diffusivity, and activation difficulties—reflect the intrinsic physical characteristics of SiC as a highly robust material.

As SiC devices continue to advance toward higher power densities, improved reliability, and more demanding operating environments, diffusion processes will remain a valuable tool in both industrial and research settings, complementing other doping methodologies and contributing to the continual evolution of SiC semiconductor technology.