Unlike the conventional silicon power device fabrication process,
silicon carbide power devices cannot be directly manufactured on
silicon carbide single crystal material. Instead, a layer of micron-scale new single crystal material must be grown on a carefully processed single crystal substrate through steps like cutting, grinding, and polishing. This new single crystal layer and the substrate can be made of the same material or different materials, a technique referred to as homoepitaxy or heteroepitaxy. The
epitaxial layer serves to eliminate surface or subsurface defects introduced during crystal growth and processing, resulting in a well-ordered crystal lattice and improved surface morphology. The quality of the
epitaxial layer significantly influences the final device performance.
2.The production method for SiC epitaxy
The production methods for
silicon carbide epitaxy include Chemical Vapor Deposition (CVD), Molecular Beam Epitaxy (MBE), Liquid Phase Epitaxy (LPE), Pulsed Laser Deposition (PLD), and others. Among these, the CVD method is the most widely used for
4H-SiC epitaxy. Its advantage lies in the effective control of gas source flow rates, reaction chamber temperature, and pressure during the growth process, enabling precise control over epitaxial layer thickness, doping concentration, and doping type, resulting in strong process controllability.
In the early stages, silicon carbide was epitaxially grown on non-misaligned substrates, yielding suboptimal results due to the influence of polytype mixing. Subsequently, a step-controlled epitaxy method was developed. By cutting
silicon carbide substrates at different angles, high-density epitaxial steps were formed. This technique achieved stable crystal growth while maintaining low-temperature growth conditions. Later, Trichlorosilane (TCS) was introduced, surpassing the limitations of the step-controlled epitaxy method and significantly increasing the growth rate to more than 10 times that of traditional methods. Currently, common precursor gases for the reaction include SiH4, CH4, and NH3 for silicon and nitrogen doping, while Trimethylaluminum (TMA) serves as the dopant source. Epitaxial growth is conducted on 4° off-cut
4H-SiC substrates at temperatures ranging from 1500 to 1650 degrees Celsius.
3.The key epitaxial parameters of SiC epitaxy
The epitaxial parameters primarily depend on the device design, with thickness and doping concentration being key factors for the
epitaxial wafers. As the device voltage increases, the requirements for
epitaxial thickness and doping concentration uniformity become more stringent, resulting in increased manufacturing complexity. For low-voltage applications at around 600V, the epitaxial thickness needs to be approximately 6 micrometers. In medium-voltage applications ranging from 1200V to 1700V, the epitaxial thickness should be around 10-15 micrometers. However, in high-voltage applications such as 10kV, the epitaxial thickness needs to exceed 100 micrometers.
In the field of medium and low-voltage applications, the technology for
silicon carbide epitaxy is relatively mature. The parameters such as epitaxial thickness and doping concentration of the wafers are more optimized, and they can generally meet the requirements for devices like Schottky Barrier Diodes (SBDs), Junction Barrier Schottky (JBS) diodes, Metal-Oxide-Semiconductor (MOS) devices, etc. at these voltage ranges. However, in the high-voltage domain, challenges need to be overcome regarding doping concentration uniformity and defect control for the
epitaxial wafers.
