With the rapid development of power electronics and RF technologies, Silicon Carbide (SiC), as a representative of third-generation wide bandgap semiconductors, is entering a golden era of industrialization. Among them, the 4-inch SiC substrate is currently the most mature and widely adopted specification, serving as the critical bridge between laboratory research and mass production.

Why Silicon Carbide? — Advantages

Compared with conventional silicon (Si), SiC offers several outstanding advantages:

Wide bandgap: ~3.26 eV, nearly three times that of Si, enabling higher breakdown voltages and superior high-temperature operation.

High thermal conductivity: About three times higher than Si, significantly improving heat dissipation.

High critical electric field: Over 10 times that of Si, allowing devices to maintain compact size and high efficiency under high voltage.

High electron saturation drift velocity: Facilitates high-frequency applications.

Thanks to these properties, SiC is particularly well-suited for electric vehicles, power electronics, 5G communications, and aerospace, where efficiency and reliability are crucial.

Fabrication Process of 4-Inch SiC Substrates

The production of 4-inch SiC substrates is highly complex and involves multiple key steps:

Raw Material Synthesis
High-purity carbon and silicon sources are reacted at elevated temperatures to synthesize high-purity SiC powder.

Crystal Growth
The most widely adopted method is Physical Vapor Transport (PVT), also known as the modified Lely method. In this process, SiC powder sublimates above 2000 °C and recrystallizes on a seed crystal to form a bulk single crystal.

Ingot Processing
The grown SiC boule is sliced into wafers, followed by grinding and polishing to obtain smooth and defect-free substrates.

Epitaxial Growth (Optional)
A high-quality SiC epitaxial layer may be deposited on the substrate surface, enabling advanced device fabrication.

This entire process is energy-intensive, time-consuming, and requires stringent environmental and equipment control, which is why SiC substrates remain relatively costly.

Key Parameters

The quality of 4-inch SiC substrates is typically evaluated by the following parameters:

Diameter & Thickness: 100 mm (4 inches) diameter, thickness usually 350–500 μm.

Polytype: Predominantly 4H-SiC, offering a balance between high carrier mobility and mature manufacturing technology.

Defect Density: Includes threading screw dislocations (TSD), threading edge dislocations (TED), and micropipes (MPD). Lower densities lead to higher device performance.

Conductivity Type: n-type and semi-insulating types are available, suited for power devices and RF devices, respectively.

Surface Roughness: Typically <0.1 nm, ensuring reliability of downstream device processes.

Application Fields

Currently, 4-inch SiC substrates are mainly used in:

Power Devices: SiC MOSFETs and Schottky Barrier Diodes (SBDs), widely applied in EV inverters, high-voltage power supplies, and industrial motor drives.

RF Devices: Often combined with GaN epitaxy to produce GaN-on-SiC devices, enabling 5G base stations and radar systems.

Optoelectronic Devices: Blue LEDs, UV photodetectors, and more.

High-Temperature Sensors: Suitable for harsh environments such as oil exploration and aerospace engines.

Future Development Trends

Although 4-inch substrates have achieved relatively mature mass production, challenges remain in reducing cost and defect density. Key future directions include:

Larger Diameter Substrates: 6-inch wafers are becoming mainstream, and 8-inch R&D is accelerating to meet large-scale industrial demand.

Defect Reduction: Improvements in PVT technology and seed crystal quality will further decrease dislocation density and improve device yields.

Cost Reduction: Scaling production and optimizing slicing, grinding, and polishing processes will lower cost per unit area.

Application Expansion: With automotive-grade SiC devices maturing, broader adoption is expected in solar energy, smart grids, and high-speed rail.

Conclusion

The 4-inch SiC substrate is a cornerstone of the wide bandgap semiconductor industry. It not only represents the transition of SiC technology from research to industrial-scale production but also paves the way for larger-diameter, higher-performance substrates. With the accelerating adoption of electric vehicles, 5G, and renewable energy, demand for SiC will continue to grow — and 4-inch substrates will remain a crucial driver of this technological evolution.